"""
Session management for the gateway.

Handles:
- Session context tracking (where messages come from)
- Session storage (conversations persisted to disk)
- Reset policy evaluation (when to start fresh)
- Dynamic system prompt injection (agent knows its context)
"""

import hashlib
import logging
import os
import json
import threading
import uuid
from pathlib import Path
from datetime import datetime, timedelta
from dataclasses import dataclass
from typing import Dict, List, Optional, Any

logger = logging.getLogger(__name__)


def _now() -> datetime:
    """Return the current local time."""
    return datetime.now()


# ---------------------------------------------------------------------------
# PII redaction helpers
# ---------------------------------------------------------------------------

def _hash_id(value: str) -> str:
    """Deterministic 12-char hex hash of an identifier."""
    return hashlib.sha256(value.encode("utf-8")).hexdigest()[:12]


def _hash_sender_id(value: str) -> str:
    """Hash a sender ID to ``user_<12hex>``."""
    return f"user_{_hash_id(value)}"


def _hash_chat_id(value: str) -> str:
    """Hash the numeric portion of a chat ID, preserving platform prefix.

    ``telegram:12345`` → ``telegram:<hash>``
    ``12345``          → ``<hash>``
    """
    colon = value.find(":")
    if colon > 0:
        prefix = value[:colon]
        return f"{prefix}:{_hash_id(value[colon + 1:])}"
    return _hash_id(value)


from .config import (
    Platform,
    GatewayConfig,
    SessionResetPolicy,  # noqa: F401 — re-exported via gateway/__init__.py
    HomeChannel,
)
from .whatsapp_identity import (
    canonical_whatsapp_identifier,
    normalize_whatsapp_identifier,  # noqa: F401 - re-exported for gateway.session callers
)
from utils import atomic_replace


@dataclass
class SessionSource:
    """
    Describes where a message originated from.
    
    This information is used to:
    1. Route responses back to the right place
    2. Inject context into the system prompt
    3. Track origin for cron job delivery
    """
    platform: Platform
    chat_id: str
    chat_name: Optional[str] = None
    chat_type: str = "dm"  # "dm", "group", "channel", "thread"
    user_id: Optional[str] = None
    user_name: Optional[str] = None
    thread_id: Optional[str] = None  # For forum topics, Discord threads, etc.
    chat_topic: Optional[str] = None  # Channel topic/description (Discord, Slack)
    user_id_alt: Optional[str] = None  # Platform-specific stable alt ID (Signal UUID, Feishu union_id)
    chat_id_alt: Optional[str] = None  # Signal group internal ID
    is_bot: bool = False  # True when the message author is a bot/webhook (Discord)
    guild_id: Optional[str] = None  # Discord guild / Slack workspace / Matrix server scope
    parent_chat_id: Optional[str] = None  # Parent channel when chat_id refers to a thread
    message_id: Optional[str] = None  # ID of the triggering message (for pin/reply/react)
    
    @property
    def description(self) -> str:
        """Human-readable description of the source."""
        if self.platform == Platform.LOCAL:
            return "CLI terminal"
        
        parts = []
        if self.chat_type == "dm":
            parts.append(f"DM with {self.user_name or self.user_id or 'user'}")
        elif self.chat_type == "group":
            parts.append(f"group: {self.chat_name or self.chat_id}")
        elif self.chat_type == "channel":
            parts.append(f"channel: {self.chat_name or self.chat_id}")
        else:
            parts.append(self.chat_name or self.chat_id)
        
        if self.thread_id:
            parts.append(f"thread: {self.thread_id}")
        
        return ", ".join(parts)
    
    def to_dict(self) -> Dict[str, Any]:
        d = {
            "platform": self.platform.value,
            "chat_id": self.chat_id,
            "chat_name": self.chat_name,
            "chat_type": self.chat_type,
            "user_id": self.user_id,
            "user_name": self.user_name,
            "thread_id": self.thread_id,
            "chat_topic": self.chat_topic,
        }
        if self.user_id_alt:
            d["user_id_alt"] = self.user_id_alt
        if self.chat_id_alt:
            d["chat_id_alt"] = self.chat_id_alt
        if self.guild_id:
            d["guild_id"] = self.guild_id
        if self.parent_chat_id:
            d["parent_chat_id"] = self.parent_chat_id
        if self.message_id:
            d["message_id"] = self.message_id
        return d

    @classmethod
    def from_dict(cls, data: Dict[str, Any]) -> "SessionSource":
        return cls(
            platform=Platform(data["platform"]),
            chat_id=str(data["chat_id"]),
            chat_name=data.get("chat_name"),
            chat_type=data.get("chat_type", "dm"),
            user_id=data.get("user_id"),
            user_name=data.get("user_name"),
            thread_id=data.get("thread_id"),
            chat_topic=data.get("chat_topic"),
            user_id_alt=data.get("user_id_alt"),
            chat_id_alt=data.get("chat_id_alt"),
            guild_id=data.get("guild_id"),
            parent_chat_id=data.get("parent_chat_id"),
            message_id=data.get("message_id"),
        )
    


@dataclass
class SessionContext:
    """
    Full context for a session, used for dynamic system prompt injection.
    
    The agent receives this information to understand:
    - Where messages are coming from
    - What platforms are available
    - Where it can deliver scheduled task outputs
    """
    source: SessionSource
    connected_platforms: List[Platform]
    home_channels: Dict[Platform, HomeChannel]
    shared_multi_user_session: bool = False
    
    # Session metadata
    session_key: str = ""
    session_id: str = ""
    created_at: Optional[datetime] = None
    updated_at: Optional[datetime] = None
    
    def to_dict(self) -> Dict[str, Any]:
        return {
            "source": self.source.to_dict(),
            "connected_platforms": [p.value for p in self.connected_platforms],
            "home_channels": {
                p.value: hc.to_dict() for p, hc in self.home_channels.items()
            },
            "shared_multi_user_session": self.shared_multi_user_session,
            "session_key": self.session_key,
            "session_id": self.session_id,
            "created_at": self.created_at.isoformat() if self.created_at else None,
            "updated_at": self.updated_at.isoformat() if self.updated_at else None,
        }


_PII_SAFE_PLATFORMS = frozenset({
    Platform.WHATSAPP,
    Platform.SIGNAL,
    Platform.TELEGRAM,
    Platform.BLUEBUBBLES,
})
"""Platforms where user IDs can be safely redacted (no in-message mention system
that requires raw IDs).  Discord is excluded because mentions use ``<@user_id>``
and the LLM needs the real ID to tag users."""


def _discord_tools_loaded() -> bool:
    """True iff the agent will actually have Discord tools this session.

    Two conditions must hold:
      1. The `discord` or `discord_admin` toolset is enabled for the
         Discord platform via `hermes tools` (opt-in, default OFF).
      2. `DISCORD_BOT_TOKEN` is set — the tool's `check_fn` gates on it
         at registry time, so the toolset being enabled in config is not
         enough if the token isn't configured.

    Returns False (safe default — keeps the stale-API disclaimer) on any
    error so a bad config can't silently promise tools the agent lacks.
    """
    if not (os.environ.get("DISCORD_BOT_TOKEN") or "").strip():
        return False
    try:
        from hermes_cli.config import load_config
        from hermes_cli.tools_config import _get_platform_tools
        cfg = load_config()
        enabled = _get_platform_tools(cfg, "discord", include_default_mcp_servers=False)
        return "discord" in enabled or "discord_admin" in enabled
    except Exception:
        return False


def build_session_context_prompt(
    context: SessionContext,
    *,
    redact_pii: bool = False,
) -> str:
    """
    Build the dynamic system prompt section that tells the agent about its context.

    This is injected into the system prompt so the agent knows:
    - Where messages are coming from
    - What platforms are connected
    - Where it can deliver scheduled task outputs

    When *redact_pii* is True **and** the source platform is in
    ``_PII_SAFE_PLATFORMS``, phone numbers are stripped and user/chat IDs
    are replaced with deterministic hashes before being sent to the LLM.
    Platforms like Discord are excluded because mentions need real IDs.
    Routing still uses the original values (they stay in SessionSource).
    """
    # Only apply redaction on platforms where IDs aren't needed for mentions.
    # Check both the hardcoded set (builtins) and the plugin registry.
    _is_pii_safe = context.source.platform in _PII_SAFE_PLATFORMS
    if not _is_pii_safe:
        try:
            from gateway.platform_registry import platform_registry
            entry = platform_registry.get(context.source.platform.value)
            if entry and entry.pii_safe:
                _is_pii_safe = True
        except Exception:
            pass
    redact_pii = redact_pii and _is_pii_safe
    lines = [
        "## Current Session Context",
        "",
    ]

    # Source info
    platform_name = context.source.platform.value.title()
    if context.source.platform == Platform.LOCAL:
        lines.append(f"**Source:** {platform_name} (the machine running this agent)")
    else:
        # Build a description that respects PII redaction
        src = context.source
        if redact_pii:
            # Build a safe description without raw IDs
            _uname = src.user_name or (
                _hash_sender_id(src.user_id) if src.user_id else "user"
            )
            _cname = src.chat_name or _hash_chat_id(src.chat_id)
            if src.chat_type == "dm":
                desc = f"DM with {_uname}"
            elif src.chat_type == "group":
                desc = f"group: {_cname}"
            elif src.chat_type == "channel":
                desc = f"channel: {_cname}"
            else:
                desc = _cname
        else:
            desc = src.description
        lines.append(f"**Source:** {platform_name} ({desc})")

    # Channel topic (if available - provides context about the channel's purpose)
    if context.source.chat_topic:
        lines.append(f"**Channel Topic:** {context.source.chat_topic}")

    # User identity.
    # In shared multi-user sessions (shared threads OR shared non-thread groups
    # when group_sessions_per_user=False), multiple users contribute to the same
    # conversation.  Don't pin a single user name in the system prompt — it
    # changes per-turn and would bust the prompt cache.  Instead, note that
    # this is a multi-user session; individual sender names are prefixed on
    # each user message by the gateway.
    if context.shared_multi_user_session:
        session_label = "Multi-user thread" if context.source.thread_id else "Multi-user session"
        lines.append(
            f"**Session type:** {session_label} — messages are prefixed "
            "with [sender name]. Multiple users may participate."
        )
    elif context.source.user_name:
        lines.append(f"**User:** {context.source.user_name}")
    elif context.source.user_id:
        uid = context.source.user_id
        if redact_pii:
            uid = _hash_sender_id(uid)
        lines.append(f"**User ID:** {uid}")

    # Platform-specific behavioral notes
    if context.source.platform == Platform.SLACK:
        lines.append("")
        lines.append(
            "**Platform notes:** You are running inside Slack. "
            "You do NOT have access to Slack-specific APIs — you cannot search "
            "channel history, pin/unpin messages, manage channels, or list users. "
            "Do not promise to perform these actions. The gateway may inline the "
            "current message's Slack block/attachment payload when available, but "
            "you still cannot call Slack APIs yourself."
        )
    elif context.source.platform == Platform.DISCORD:
        # Inject the Discord IDs block only when the agent actually has
        # Discord tools loaded this session — i.e. the user opted into
        # `discord` / `discord_admin` via `hermes tools` AND the bot
        # token is configured.  Otherwise keep the stale-API disclaimer
        # honest so we never promise tools the agent lacks.
        if _discord_tools_loaded():
            src = context.source
            id_lines = ["", "**Discord IDs (for the `discord` / `discord_admin` tools):**"]
            if src.guild_id:
                id_lines.append(f"  - Guild: `{src.guild_id}`")
            if src.thread_id and src.parent_chat_id:
                id_lines.append(f"  - Parent channel: `{src.parent_chat_id}`")
                id_lines.append(f"  - Thread: `{src.thread_id}` (use as `channel_id` for fetch_messages etc.)")
            else:
                id_lines.append(f"  - Channel: `{src.chat_id}`")
            if src.message_id:
                id_lines.append(f"  - Triggering message: `{src.message_id}`")
            lines.extend(id_lines)
        else:
            lines.append("")
            lines.append(
                "**Platform notes:** You are running inside Discord. "
                "You do NOT have access to Discord-specific APIs — you cannot search "
                "channel history, pin messages, manage roles, or list server members. "
                "Do not promise to perform these actions. If the user asks, explain "
                "that you can only read messages sent directly to you and respond."
            )
    elif context.source.platform == Platform.BLUEBUBBLES:
        lines.append("")
        lines.append(
            "**Platform notes:** You are responding via iMessage. "
            "Keep responses short and conversational — think texts, not essays. "
            "Structure longer replies as separate short thoughts, each separated "
            "by a blank line (double newline). Each block between blank lines "
            "will be delivered as its own iMessage bubble, so write accordingly: "
            "one idea per bubble, 1–3 sentences each. "
            "If the user needs a detailed answer, give the short version first "
            "and offer to elaborate."
        )
    elif context.source.platform == Platform.YUANBAO:
        lines.append("")
        lines.append(
            "**Platform notes:** You are running inside Yuanbao. "
            "You CAN send private (DM) messages via the send_message tool. "
            "Use target='yuanbao:direct:<account_id>' for DM "
            "and target='yuanbao:group:<group_code>' for group chat."
        )

    # Connected platforms
    platforms_list = ["local (files on this machine)"]
    for p in context.connected_platforms:
        if p != Platform.LOCAL:
            platforms_list.append(f"{p.value}: Connected ✓")

    lines.append(f"**Connected Platforms:** {', '.join(platforms_list)}")

    # Home channels
    if context.home_channels:
        lines.append("")
        lines.append("**Home Channels (default destinations):**")
        for platform, home in context.home_channels.items():
            hc_id = _hash_chat_id(home.chat_id) if redact_pii else home.chat_id
            lines.append(f"  - {platform.value}: {home.name} (ID: {hc_id})")

    # Delivery options for scheduled tasks
    lines.append("")
    lines.append("**Delivery options for scheduled tasks:**")

    from hermes_constants import display_hermes_home

    # Origin delivery
    if context.source.platform == Platform.LOCAL:
        lines.append("- `\"origin\"` → Local output (saved to files)")
    else:
        _origin_label = context.source.chat_name or (
            _hash_chat_id(context.source.chat_id) if redact_pii else context.source.chat_id
        )
        lines.append(f"- `\"origin\"` → Back to this chat ({_origin_label})")

    # Local always available
    lines.append(
        f"- `\"local\"` → Save to local files only ({display_hermes_home()}/cron/output/)"
    )

    # Platform home channels
    for platform, home in context.home_channels.items():
        lines.append(f"- `\"{platform.value}\"` → Home channel ({home.name})")

    # Note about explicit targeting
    lines.append("")
    lines.append("*For explicit targeting, use `\"platform:chat_id\"` format if the user provides a specific chat ID.*")

    return "\n".join(lines)


@dataclass
class SessionEntry:
    """
    Entry in the session store.
    
    Maps a session key to its current session ID and metadata.
    """
    session_key: str
    session_id: str
    created_at: datetime
    updated_at: datetime
    
    # Origin metadata for delivery routing
    origin: Optional[SessionSource] = None
    
    # Display metadata
    display_name: Optional[str] = None
    platform: Optional[Platform] = None
    chat_type: str = "dm"
    
    # Token tracking
    input_tokens: int = 0
    output_tokens: int = 0
    cache_read_tokens: int = 0
    cache_write_tokens: int = 0
    total_tokens: int = 0
    estimated_cost_usd: float = 0.0
    cost_status: str = "unknown"
    
    # Last API-reported prompt tokens (for accurate compression pre-check)
    last_prompt_tokens: int = 0
    
    # Set when a session was created because the previous one expired;
    # consumed once by the message handler to inject a notice into context
    was_auto_reset: bool = False
    auto_reset_reason: Optional[str] = None  # "idle" or "daily"
    reset_had_activity: bool = False  # whether the expired session had any messages

    # Set by reset_session() when the user explicitly sends /new or /reset.
    # Consumed once by _handle_message_with_agent to trigger topic/channel
    # skill re-injection on the first message of the new session.  We can't
    # reuse was_auto_reset for this because that flag fires the "session
    # expired due to inactivity" user-facing notice and a misleading
    # context-note prepend — both wrong for an explicit manual reset.
    # See issue #6508.
    is_fresh_reset: bool = False
    
    # Set by the background expiry watcher after it finalizes an expired
    # session (invoking on_session_finalize hooks and evicting the cached
    # agent).  Persisted to sessions.json so the flag survives gateway
    # restarts — prevents redundant finalization runs.
    expiry_finalized: bool = False

    # When True the next call to get_or_create_session() will auto-reset
    # this session (create a new session_id) so the user starts fresh.
    # Set by /stop to break stuck-resume loops (#7536).
    suspended: bool = False

    # When True the session was interrupted by a gateway restart/shutdown
    # drain timeout, but recovery is still expected.  Unlike ``suspended``,
    # ``resume_pending`` preserves the existing session_id on next access —
    # the user stays on the same transcript and the agent auto-continues
    # from where it left off.  Cleared after the next successful turn.
    # Escalation to ``suspended`` is handled by the existing
    # ``.restart_failure_counts`` stuck-loop counter (#7536), not by a
    # parallel counter on this entry.
    resume_pending: bool = False
    resume_reason: Optional[str] = None  # e.g. "restart_timeout"
    last_resume_marked_at: Optional[datetime] = None

    def to_dict(self) -> Dict[str, Any]:
        result = {
            "session_key": self.session_key,
            "session_id": self.session_id,
            "created_at": self.created_at.isoformat(),
            "updated_at": self.updated_at.isoformat(),
            "display_name": self.display_name,
            "platform": self.platform.value if self.platform else None,
            "chat_type": self.chat_type,
            "input_tokens": self.input_tokens,
            "output_tokens": self.output_tokens,
            "cache_read_tokens": self.cache_read_tokens,
            "cache_write_tokens": self.cache_write_tokens,
            "total_tokens": self.total_tokens,
            "last_prompt_tokens": self.last_prompt_tokens,
            "estimated_cost_usd": self.estimated_cost_usd,
            "cost_status": self.cost_status,
            "expiry_finalized": self.expiry_finalized,
            "suspended": self.suspended,
            "resume_pending": self.resume_pending,
            "resume_reason": self.resume_reason,
            "last_resume_marked_at": (
                self.last_resume_marked_at.isoformat()
                if self.last_resume_marked_at
                else None
            ),
            "is_fresh_reset": self.is_fresh_reset,
            "was_auto_reset": self.was_auto_reset,
            "auto_reset_reason": self.auto_reset_reason,
            "reset_had_activity": self.reset_had_activity,
        }
        if self.origin:
            result["origin"] = self.origin.to_dict()
        return result
    
    @classmethod
    def from_dict(cls, data: Dict[str, Any]) -> "SessionEntry":
        origin = None
        if "origin" in data and data["origin"]:
            origin = SessionSource.from_dict(data["origin"])
        
        platform = None
        if data.get("platform"):
            try:
                platform = Platform(data["platform"])
            except ValueError as e:
                logger.debug("Unknown platform value %r: %s", data["platform"], e)

        last_resume_marked_at = None
        _lrma = data.get("last_resume_marked_at")
        if _lrma:
            try:
                last_resume_marked_at = datetime.fromisoformat(_lrma)
            except (TypeError, ValueError):
                last_resume_marked_at = None

        return cls(
            session_key=data["session_key"],
            session_id=data["session_id"],
            created_at=datetime.fromisoformat(data["created_at"]),
            updated_at=datetime.fromisoformat(data["updated_at"]),
            origin=origin,
            display_name=data.get("display_name"),
            platform=platform,
            chat_type=data.get("chat_type", "dm"),
            input_tokens=data.get("input_tokens", 0),
            output_tokens=data.get("output_tokens", 0),
            cache_read_tokens=data.get("cache_read_tokens", 0),
            cache_write_tokens=data.get("cache_write_tokens", 0),
            total_tokens=data.get("total_tokens", 0),
            last_prompt_tokens=data.get("last_prompt_tokens", 0),
            estimated_cost_usd=data.get("estimated_cost_usd", 0.0),
            cost_status=data.get("cost_status", "unknown"),
            expiry_finalized=data.get("expiry_finalized", data.get("memory_flushed", False)),
            suspended=data.get("suspended", False),
            resume_pending=data.get("resume_pending", False),
            resume_reason=data.get("resume_reason"),
            last_resume_marked_at=last_resume_marked_at,
            is_fresh_reset=data.get("is_fresh_reset", False),
            was_auto_reset=data.get("was_auto_reset", False),
            auto_reset_reason=data.get("auto_reset_reason"),
            reset_had_activity=data.get("reset_had_activity", False),
        )


def is_shared_multi_user_session(
    source: SessionSource,
    *,
    group_sessions_per_user: bool = True,
    thread_sessions_per_user: bool = False,
) -> bool:
    """Return True when a non-DM session is shared across participants.

    Mirrors the isolation rules in :func:`build_session_key`:
      - DMs are never shared.
      - Threads are shared unless ``thread_sessions_per_user`` is True.
      - Non-thread group/channel sessions are shared unless
        ``group_sessions_per_user`` is True (default: True = isolated).
    """
    if source.chat_type == "dm":
        return False
    if source.thread_id:
        return not thread_sessions_per_user
    return not group_sessions_per_user


def build_session_key(
    source: SessionSource,
    group_sessions_per_user: bool = True,
    thread_sessions_per_user: bool = False,
) -> str:
    """Build a deterministic session key from a message source.

    This is the single source of truth for session key construction.

    DM rules:
      - DMs include chat_id when present, so each private conversation is isolated.
      - thread_id further differentiates threaded DMs within the same DM chat.
      - Without chat_id, thread_id is used as a best-effort fallback.
      - Without thread_id or chat_id, DMs share a single session.

    Group/channel rules:
      - chat_id identifies the parent group/channel.
      - user_id/user_id_alt isolates participants within that parent chat when available when
        ``group_sessions_per_user`` is enabled.
      - thread_id differentiates threads within that parent chat.  When
        ``thread_sessions_per_user`` is False (default), threads are *shared* across all
        participants — user_id is NOT appended, so every user in the thread
        shares a single session.  This is the expected UX for threaded
        conversations (Telegram forum topics, Discord threads, Slack threads).
      - Without participant identifiers, or when isolation is disabled, messages fall back to one
        shared session per chat.
      - Without identifiers, messages fall back to one session per platform/chat_type.
    """
    platform = source.platform.value
    if source.chat_type == "dm":
        dm_chat_id = source.chat_id
        if source.platform == Platform.WHATSAPP:
            dm_chat_id = canonical_whatsapp_identifier(source.chat_id)

        if dm_chat_id:
            if source.thread_id:
                return f"agent:main:{platform}:dm:{dm_chat_id}:{source.thread_id}"
            return f"agent:main:{platform}:dm:{dm_chat_id}"
        if source.thread_id:
            return f"agent:main:{platform}:dm:{source.thread_id}"
        return f"agent:main:{platform}:dm"

    participant_id = source.user_id_alt or source.user_id
    if participant_id and source.platform == Platform.WHATSAPP:
        # Same JID/LID-flip bug as the DM case: without canonicalisation, a
        # single group member gets two isolated per-user sessions when the
        # bridge reshuffles alias forms.
        participant_id = canonical_whatsapp_identifier(str(participant_id)) or participant_id
    key_parts = ["agent:main", platform, source.chat_type]

    if source.chat_id:
        key_parts.append(source.chat_id)
    if source.thread_id:
        key_parts.append(source.thread_id)

    # In threads, default to shared sessions (all participants see the same
    # conversation).  Per-user isolation only applies when explicitly enabled
    # via thread_sessions_per_user, or when there is no thread (regular group).
    isolate_user = group_sessions_per_user
    if source.thread_id and not thread_sessions_per_user:
        isolate_user = False

    if isolate_user and participant_id:
        key_parts.append(str(participant_id))

    return ":".join(key_parts)


class SessionStore:
    """
    Manages session storage and retrieval.
    
    Uses SQLite (via SessionDB) for session metadata and message transcripts.
    Falls back to legacy JSONL files if SQLite is unavailable.
    """
    
    def __init__(self, sessions_dir: Path, config: GatewayConfig,
                 has_active_processes_fn=None):
        self.sessions_dir = sessions_dir
        self.config = config
        self._entries: Dict[str, SessionEntry] = {}
        self._loaded = False
        self._lock = threading.Lock()
        self._has_active_processes_fn = has_active_processes_fn
        
        # Initialize SQLite session database
        self._db = None
        try:
            from hermes_state import SessionDB
            self._db = SessionDB()
        except Exception as e:
            print(f"[gateway] Warning: SQLite session store unavailable, falling back to JSONL: {e}")
    
    def _ensure_loaded(self) -> None:
        """Load sessions index from disk if not already loaded."""
        with self._lock:
            self._ensure_loaded_locked()

    def _ensure_loaded_locked(self) -> None:
        """Load sessions index from disk. Must be called with self._lock held."""
        if self._loaded:
            return

        self.sessions_dir.mkdir(parents=True, exist_ok=True)
        sessions_file = self.sessions_dir / "sessions.json"

        if sessions_file.exists():
            try:
                with open(sessions_file, "r", encoding="utf-8") as f:
                    data = json.load(f)
                    for key, entry_data in data.items():
                        try:
                            self._entries[key] = SessionEntry.from_dict(entry_data)
                        except (ValueError, KeyError):
                            # Skip entries with unknown/removed platform values
                            continue
            except Exception as e:
                print(f"[gateway] Warning: Failed to load sessions: {e}")

        self._loaded = True
    
    def _save(self) -> None:
        """Save sessions index to disk (kept for session key -> ID mapping)."""
        import tempfile
        self.sessions_dir.mkdir(parents=True, exist_ok=True)
        sessions_file = self.sessions_dir / "sessions.json"

        data = {key: entry.to_dict() for key, entry in self._entries.items()}
        fd, tmp_path = tempfile.mkstemp(
            dir=str(self.sessions_dir), suffix=".tmp", prefix=".sessions_"
        )
        try:
            with os.fdopen(fd, "w", encoding="utf-8") as f:
                json.dump(data, f, indent=2)
                f.flush()
                os.fsync(f.fileno())
            atomic_replace(tmp_path, sessions_file)
        except BaseException:
            try:
                os.unlink(tmp_path)
            except OSError as e:
                logger.debug("Could not remove temp file %s: %s", tmp_path, e)
            raise
    
    def _generate_session_key(self, source: SessionSource) -> str:
        """Generate a session key from a source."""
        return build_session_key(
            source,
            group_sessions_per_user=getattr(self.config, "group_sessions_per_user", True),
            thread_sessions_per_user=getattr(self.config, "thread_sessions_per_user", False),
        )
    
    def _is_session_expired(self, entry: SessionEntry) -> bool:
        """Check if a session has expired based on its reset policy.
        
        Works from the entry alone — no SessionSource needed.
        Used by the background expiry watcher to proactively flush memories.
        Sessions with active background processes are never considered expired.
        """
        if self._has_active_processes_fn:
            if self._has_active_processes_fn(entry.session_key):
                return False

        policy = self.config.get_reset_policy(
            platform=entry.platform,
            session_type=entry.chat_type,
        )

        if policy.mode == "none":
            return False

        now = _now()

        if policy.mode in {"idle", "both"}:
            idle_deadline = entry.updated_at + timedelta(minutes=policy.idle_minutes)
            if now > idle_deadline:
                return True

        if policy.mode in {"daily", "both"}:
            today_reset = now.replace(
                hour=policy.at_hour,
                minute=0, second=0, microsecond=0,
            )
            if now.hour < policy.at_hour:
                today_reset -= timedelta(days=1)
            if entry.updated_at < today_reset:
                return True

        return False

    def _should_reset(self, entry: SessionEntry, source: SessionSource) -> Optional[str]:
        """
        Check if a session should be reset based on policy.
        
        Returns the reset reason ("idle" or "daily") if a reset is needed,
        or None if the session is still valid.
        
        Sessions with active background processes are never reset.
        """
        if self._has_active_processes_fn:
            session_key = self._generate_session_key(source)
            if self._has_active_processes_fn(session_key):
                return None

        policy = self.config.get_reset_policy(
            platform=source.platform,
            session_type=source.chat_type
        )
        
        if policy.mode == "none":
            return None
        
        now = _now()
        
        if policy.mode in {"idle", "both"}:
            idle_deadline = entry.updated_at + timedelta(minutes=policy.idle_minutes)
            if now > idle_deadline:
                return "idle"
        
        if policy.mode in {"daily", "both"}:
            today_reset = now.replace(
                hour=policy.at_hour, 
                minute=0, 
                second=0, 
                microsecond=0
            )
            if now.hour < policy.at_hour:
                today_reset -= timedelta(days=1)
            
            if entry.updated_at < today_reset:
                return "daily"
        
        return None
    
    def has_any_sessions(self) -> bool:
        """Check if any sessions have ever been created (across all platforms).

        Uses the SQLite database as the source of truth because it preserves
        historical session records (ended sessions still count).  The in-memory
        ``_entries`` dict replaces entries on reset, so ``len(_entries)`` would
        stay at 1 for single-platform users — which is the bug this fixes.

        The current session is already in the DB by the time this is called
        (get_or_create_session runs first), so we check ``> 1``.
        """
        if self._db:
            try:
                return self._db.session_count() > 1
            except Exception:
                pass  # fall through to heuristic
        # Fallback: check if sessions.json was loaded with existing data.
        # This covers the rare case where the DB is unavailable.
        with self._lock:
            self._ensure_loaded_locked()
            return len(self._entries) > 1

    def get_or_create_session(
        self,
        source: SessionSource,
        force_new: bool = False
    ) -> SessionEntry:
        """
        Get an existing session or create a new one.

        Evaluates reset policy to determine if the existing session is stale.
        Creates a session record in SQLite when a new session starts.
        """
        session_key = self._generate_session_key(source)
        now = _now()

        # SQLite calls are made outside the lock to avoid holding it during I/O.
        # All _entries / _loaded mutations are protected by self._lock.
        db_end_session_id = None
        db_create_kwargs = None

        with self._lock:
            self._ensure_loaded_locked()

            if session_key in self._entries and not force_new:
                entry = self._entries[session_key]

                # Auto-reset sessions marked as suspended (e.g. after /stop
                # broke a stuck loop — #7536).  ``suspended`` is the hard
                # forced-wipe signal and always wins over ``resume_pending``,
                # so repeated interrupted restarts that escalate via the
                # existing ``.restart_failure_counts`` stuck-loop counter
                # still converge to a clean slate.
                if entry.suspended:
                    reset_reason = "suspended"
                elif entry.resume_pending:
                    # Restart-interrupted session: preserve the session_id
                    # and return the existing entry so the transcript
                    # reloads intact.  ``resume_pending`` is cleared after
                    # the NEXT successful turn completes (not here), which
                    # means a re-interrupted retry keeps trying — the
                    # stuck-loop counter handles terminal escalation.
                    entry.updated_at = now
                    self._save()
                    return entry
                else:
                    reset_reason = self._should_reset(entry, source)
                if not reset_reason:
                    entry.updated_at = now
                    self._save()
                    return entry
                else:
                    # Session is being auto-reset.
                    was_auto_reset = True
                    auto_reset_reason = reset_reason
                    # Track whether the expired session had any real conversation
                    reset_had_activity = entry.total_tokens > 0
                    db_end_session_id = entry.session_id
            else:
                was_auto_reset = False
                auto_reset_reason = None
                reset_had_activity = False

            # Create new session
            session_id = f"{now.strftime('%Y%m%d_%H%M%S')}_{uuid.uuid4().hex[:8]}"

            entry = SessionEntry(
                session_key=session_key,
                session_id=session_id,
                created_at=now,
                updated_at=now,
                origin=source,
                display_name=source.chat_name,
                platform=source.platform,
                chat_type=source.chat_type,
                was_auto_reset=was_auto_reset,
                auto_reset_reason=auto_reset_reason,
                reset_had_activity=reset_had_activity,
            )

            self._entries[session_key] = entry
            self._save()
            db_create_kwargs = {
                "session_id": session_id,
                "source": source.platform.value,
                "user_id": source.user_id,
            }

        # SQLite operations outside the lock
        if self._db and db_end_session_id:
            try:
                self._db.end_session(db_end_session_id, "session_reset")
            except Exception as e:
                logger.debug("Session DB operation failed: %s", e)

        if self._db and db_create_kwargs:
            try:
                self._db.create_session(**db_create_kwargs)
            except Exception as e:
                print(f"[gateway] Warning: Failed to create SQLite session: {e}")

        return entry

    def update_session(
        self,
        session_key: str,
        last_prompt_tokens: int = None,
    ) -> None:
        """Update lightweight session metadata after an interaction."""
        with self._lock:
            self._ensure_loaded_locked()

            if session_key in self._entries:
                entry = self._entries[session_key]
                entry.updated_at = _now()
                if last_prompt_tokens is not None:
                    entry.last_prompt_tokens = last_prompt_tokens
                self._save()

    def suspend_session(self, session_key: str) -> bool:
        """Mark a session as suspended so it auto-resets on next access.

        Used by ``/stop`` to prevent stuck sessions from being resumed
        after a gateway restart (#7536).  Returns True if the session
        existed and was marked.
        """
        with self._lock:
            self._ensure_loaded_locked()
            if session_key in self._entries:
                self._entries[session_key].suspended = True
                self._save()
                return True
        return False

    def mark_resume_pending(
        self,
        session_key: str,
        reason: str = "restart_timeout",
    ) -> bool:
        """Mark a session as resumable after a restart interruption.

        Unlike ``suspend_session()``, this preserves the existing
        ``session_id`` and the transcript.  The next call to
        ``get_or_create_session()`` for this key returns the same entry
        so the user auto-resumes on the same conversation lane.

        Returns True if the session existed and was marked.
        """
        with self._lock:
            self._ensure_loaded_locked()
            if session_key in self._entries:
                entry = self._entries[session_key]
                # Never override an explicit ``suspended`` — that is a hard
                # forced-wipe signal (from /stop or stuck-loop escalation).
                if entry.suspended:
                    return False
                entry.resume_pending = True
                entry.resume_reason = reason
                entry.last_resume_marked_at = _now()
                self._save()
                return True
        return False

    def clear_resume_pending(self, session_key: str) -> bool:
        """Clear the resume-pending flag after a successful resumed turn.

        Called from the gateway after ``run_conversation()`` returns a
        final response for a session that had ``resume_pending=True``,
        signalling that recovery succeeded.

        Returns True if a flag was cleared.
        """
        with self._lock:
            self._ensure_loaded_locked()
            entry = self._entries.get(session_key)
            if entry is None or not entry.resume_pending:
                return False
            entry.resume_pending = False
            entry.resume_reason = None
            entry.last_resume_marked_at = None
            self._save()
            return True

    def prune_old_entries(self, max_age_days: int) -> int:
        """Drop SessionEntry records older than max_age_days.

        Pruning is based on ``updated_at`` (last activity), not ``created_at``.
        A session that's been active within the window is kept regardless of
        how old it is.  Entries marked ``suspended`` are kept — the user
        explicitly paused them for later resume.  Entries held by an active
        process (via has_active_processes_fn) are also kept so long-running
        background work isn't orphaned.

        Pruning is functionally identical to a natural reset-policy expiry:
        the transcript in SQLite stays, but the session_key → session_id
        mapping is dropped and the user starts a fresh session on return.

        ``max_age_days <= 0`` disables pruning; returns 0 immediately.
        Returns the number of entries removed.
        """
        if max_age_days is None or max_age_days <= 0:
            return 0
        from datetime import timedelta

        cutoff = _now() - timedelta(days=max_age_days)
        removed_keys: list[str] = []

        with self._lock:
            self._ensure_loaded_locked()
            for key, entry in list(self._entries.items()):
                if entry.suspended:
                    continue
                # Never prune sessions with an active background process
                # attached — the user may still be waiting on output.
                # The callback is keyed by session_key (see process_registry.
                # has_active_for_session); passing session_id here used to
                # never match, so active sessions got pruned anyway.
                if self._has_active_processes_fn is not None:
                    try:
                        if self._has_active_processes_fn(entry.session_key):
                            continue
                    except Exception as exc:
                        logger.debug(
                            "has_active_processes_fn raised during prune for %s: %s",
                            entry.session_key, exc,
                        )
                if entry.updated_at < cutoff:
                    removed_keys.append(key)
            for key in removed_keys:
                self._entries.pop(key, None)
            if removed_keys:
                self._save()

        if removed_keys:
            logger.info(
                "SessionStore pruned %d entries older than %d days",
                len(removed_keys), max_age_days,
            )
        return len(removed_keys)

    def suspend_recently_active(self, max_age_seconds: int = 120) -> int:
        """Mark recently-active sessions as resumable after an unexpected exit.

        Called on gateway startup after a crash or fast restart to preserve
        in-flight sessions instead of destroying their conversation history
        (#7536).  Only marks sessions updated within *max_age_seconds* to
        avoid touching long-idle sessions.  Sets ``resume_pending=True`` so
        the next incoming message on the same session_key auto-resumes from
        the existing transcript.

        Entries already flagged ``resume_pending=True`` are skipped.  Entries
        explicitly ``suspended=True`` (from /stop or stuck-loop escalation)
        are also skipped.  Terminal escalation for genuinely stuck sessions
        is still handled by the existing ``.restart_failure_counts`` counter
        (threshold 3), which runs after this method and sets ``suspended=True``.

        Returns the number of sessions marked resumable.
        """
        from datetime import timedelta

        cutoff = _now() - timedelta(seconds=max_age_seconds)
        count = 0
        with self._lock:
            self._ensure_loaded_locked()
            for entry in self._entries.values():
                if entry.resume_pending:
                    continue
                if not entry.suspended and entry.updated_at >= cutoff:
                    entry.resume_pending = True
                    entry.resume_reason = "restart_interrupted"
                    entry.last_resume_marked_at = _now()
                    count += 1
            if count:
                self._save()
        return count

    def reset_session(self, session_key: str, display_name: Optional[str] = None) -> Optional[SessionEntry]:
        """Force reset a session, creating a new session ID."""
        db_end_session_id = None
        db_create_kwargs = None
        new_entry = None

        with self._lock:
            self._ensure_loaded_locked()

            if session_key not in self._entries:
                return None

            old_entry = self._entries[session_key]
            db_end_session_id = old_entry.session_id

            now = _now()
            session_id = f"{now.strftime('%Y%m%d_%H%M%S')}_{uuid.uuid4().hex[:8]}"

            new_entry = SessionEntry(
                session_key=session_key,
                session_id=session_id,
                created_at=now,
                updated_at=now,
                origin=old_entry.origin,
                display_name=display_name if display_name is not None else old_entry.display_name,
                platform=old_entry.platform,
                chat_type=old_entry.chat_type,
                is_fresh_reset=True,
            )

            self._entries[session_key] = new_entry
            self._save()
            db_create_kwargs = {
                "session_id": session_id,
                "source": old_entry.platform.value if old_entry.platform else "unknown",
                "user_id": old_entry.origin.user_id if old_entry.origin else None,
            }

        if self._db and db_end_session_id:
            try:
                self._db.end_session(db_end_session_id, "session_reset")
            except Exception as e:
                logger.debug("Session DB operation failed: %s", e)

        if self._db and db_create_kwargs:
            try:
                self._db.create_session(**db_create_kwargs)
            except Exception as e:
                logger.debug("Session DB operation failed: %s", e)

        return new_entry

    def switch_session(self, session_key: str, target_session_id: str) -> Optional[SessionEntry]:
        """Switch a session key to point at an existing session ID.

        Used by ``/resume`` to restore a previously-named session.
        Ends the current session in SQLite (like reset), but instead of
        generating a fresh session ID, re-uses ``target_session_id`` so the
        old transcript is loaded on the next message. If the target session was
        previously ended, re-open it so gateway resume semantics match the CLI.
        """
        db_end_session_id = None
        new_entry = None

        with self._lock:
            self._ensure_loaded_locked()

            if session_key not in self._entries:
                return None

            old_entry = self._entries[session_key]

            # Don't switch if already on that session
            if old_entry.session_id == target_session_id:
                return old_entry

            db_end_session_id = old_entry.session_id

            now = _now()
            new_entry = SessionEntry(
                session_key=session_key,
                session_id=target_session_id,
                created_at=now,
                updated_at=now,
                origin=old_entry.origin,
                display_name=old_entry.display_name,
                platform=old_entry.platform,
                chat_type=old_entry.chat_type,
            )

            self._entries[session_key] = new_entry
            self._save()

        if self._db and db_end_session_id:
            try:
                self._db.end_session(db_end_session_id, "session_switch")
            except Exception as e:
                logger.debug("Session DB end_session failed: %s", e)

        if self._db:
            try:
                self._db.reopen_session(target_session_id)
            except Exception as e:
                logger.debug("Session DB reopen_session failed: %s", e)

        return new_entry

    def list_sessions(self, active_minutes: Optional[int] = None) -> List[SessionEntry]:
        """List all sessions, optionally filtered by activity."""
        with self._lock:
            self._ensure_loaded_locked()
            entries = list(self._entries.values())

        if active_minutes is not None:
            cutoff = _now() - timedelta(minutes=active_minutes)
            entries = [e for e in entries if e.updated_at >= cutoff]

        entries.sort(key=lambda e: e.updated_at, reverse=True)

        return entries
    
    def append_to_transcript(self, session_id: str, message: Dict[str, Any], skip_db: bool = False) -> None:
        """Append a message to a session's transcript (SQLite).

        Args:
            skip_db: When True, skip the SQLite write. Used when the agent
                     already persisted messages to SQLite via its own
                     _flush_messages_to_session_db(), preventing the
                     duplicate-write bug (#860).
        """
        if self._db and not skip_db:
            try:
                self._db.append_message(
                    session_id=session_id,
                    role=message.get("role", "unknown"),
                    content=message.get("content"),
                    tool_name=message.get("tool_name"),
                    tool_calls=message.get("tool_calls"),
                    tool_call_id=message.get("tool_call_id"),
                    reasoning=message.get("reasoning") if message.get("role") == "assistant" else None,
                    reasoning_content=message.get("reasoning_content") if message.get("role") == "assistant" else None,
                    reasoning_details=message.get("reasoning_details") if message.get("role") == "assistant" else None,
                    codex_reasoning_items=message.get("codex_reasoning_items") if message.get("role") == "assistant" else None,
                    codex_message_items=message.get("codex_message_items") if message.get("role") == "assistant" else None,
                    # Platform-side message id (yuanbao msg_id, telegram update_id, …).
                    # Accept either explicit ``platform_message_id`` or the legacy
                    # ``message_id`` key the JSONL transcript used.
                    platform_message_id=(
                        message.get("platform_message_id") or message.get("message_id")
                    ),
                    observed=bool(message.get("observed")),
                )
            except Exception as e:
                logger.debug("Session DB operation failed: %s", e)
    
    def rewrite_transcript(self, session_id: str, messages: List[Dict[str, Any]]) -> None:
        """Replace the entire transcript for a session with new messages.

        Used by /retry, /undo, and /compress to persist modified conversation
        history. state.db is the canonical store.
        """
        if self._db:
            try:
                self._db.replace_messages(session_id, messages)
            except Exception as e:
                logger.debug("Failed to rewrite transcript in DB: %s", e)

    def load_transcript(self, session_id: str) -> List[Dict[str, Any]]:
        """Load all messages from a session's transcript.

        state.db is the canonical store. The legacy JSONL fallback was removed
        in spec 002 — pre-DB sessions on existing disks have already been
        migrated (their DB row holds the full message history).
        """
        if not self._db:
            return []
        try:
            return self._db.get_messages_as_conversation(session_id)
        except Exception as e:
            logger.debug("Could not load messages from DB: %s", e)
            return []

    def rewind_session(self, session_id: str, n: int = 1) -> Optional[Dict[str, Any]]:
        """Back up ``n`` user turns via soft-delete, keeping rows for audit.

        Unlike :meth:`rewrite_transcript` (a hard replace used by /retry),
        this flips the truncated rows to ``active=0`` in state.db so they
        survive for audit and stay hidden from re-prompts and search. Mirrors
        the CLI/TUI ``/undo [N]`` behavior via ``SessionDB.rewind_to_message``.

        Returns a dict ``{"rewound_count", "turns_undone", "target_text"}`` on
        success, or ``None`` if there's no DB or no user message to back up to.
        ``n`` clamps to the oldest user turn when it exceeds the turn count.
        """
        if not self._db:
            return None
        if n < 1:
            n = 1
        try:
            recents = self._db.list_recent_user_messages(session_id, limit=max(n, 10))
        except Exception as e:
            logger.debug("rewind_session: failed to list user messages: %s", e)
            return None
        if not recents:
            return None
        target_idx = min(n - 1, len(recents) - 1)
        target_id = recents[target_idx]["id"]
        try:
            result = self._db.rewind_to_message(session_id, target_id)
        except ValueError as e:
            logger.debug("rewind_session: %s", e)
            return None
        except Exception as e:
            logger.debug("rewind_session: rewind_to_message failed: %s", e)
            return None
        target_msg = result.get("target_message") or {}
        content = target_msg.get("content") or ""
        if isinstance(content, list):
            parts = [
                p.get("text", "")
                for p in content
                if isinstance(p, dict) and p.get("type") == "text"
            ]
            target_text = "\n".join(t for t in parts if t)
        elif isinstance(content, str):
            target_text = content
        else:
            target_text = ""
        return {
            "rewound_count": result.get("rewound_count", 0),
            "turns_undone": target_idx + 1,
            "target_text": target_text,
        }


def build_session_context(
    source: SessionSource,
    config: GatewayConfig,
    session_entry: Optional[SessionEntry] = None
) -> SessionContext:
    """
    Build a full session context from a source and config.
    
    This is used to inject context into the agent's system prompt.
    """
    connected = config.get_connected_platforms()
    
    home_channels = {}
    for platform in connected:
        home = config.get_home_channel(platform)
        if home:
            home_channels[platform] = home
    
    context = SessionContext(
        source=source,
        connected_platforms=connected,
        home_channels=home_channels,
        shared_multi_user_session=is_shared_multi_user_session(
            source,
            group_sessions_per_user=getattr(config, "group_sessions_per_user", True),
            thread_sessions_per_user=getattr(config, "thread_sessions_per_user", False),
        ),
    )
    
    if session_entry:
        context.session_key = session_entry.session_key
        context.session_id = session_entry.session_id
        context.created_at = session_entry.created_at
        context.updated_at = session_entry.updated_at
    
    return context
