"""
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,
)


@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  # Signal UUID (alternative to phone number)
    chat_id_alt: Optional[str] = None  # Signal group internal ID
    is_bot: bool = False  # True when the message author is a bot/webhook (Discord)
    
    @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
        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"),
        )
    


@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]
    
    # 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()
            },
            "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 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
    redact_pii = redact_pii and context.source.platform in _PII_SAFE_PLATFORMS
    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 thread sessions (non-DM with thread_id), 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 thread; individual
    # sender names are prefixed on each user message by the gateway.
    _is_shared_thread = (
        context.source.chat_type != "dm"
        and context.source.thread_id
    )
    if _is_shared_thread:
        lines.append(
            "**Session type:** Multi-user thread — 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. If the user asks, explain "
            "that you can only read messages sent directly to you and respond."
        )
    elif context.source.platform == Platform.DISCORD:
        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."
        )

    # 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 the background expiry watcher after it successfully flushes
    # memories for this session.  Persisted to sessions.json so the flag
    # survives gateway restarts (the old in-memory _pre_flushed_sessions
    # set was lost on restart, causing redundant re-flushes).
    memory_flushed: 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
    
    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,
            "memory_flushed": self.memory_flushed,
            "suspended": self.suspended,
        }
        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)
        
        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"),
            memory_flushed=data.get("memory_flushed", False),
            suspended=data.get("suspended", False),
        )


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":
        if source.chat_id:
            if source.thread_id:
                return f"agent:main:{platform}:dm:{source.chat_id}:{source.thread_id}"
            return f"agent:main:{platform}:dm:{source.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
    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())
            os.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).
                if entry.suspended:
                    reset_reason = "suspended"
                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 suspend_recently_active(self, max_age_seconds: int = 120) -> int:
        """Mark recently-active sessions as suspended.

        Called on gateway startup to prevent sessions that were likely
        in-flight when the gateway last exited from being blindly resumed
        (#7536).  Only suspends sessions updated within *max_age_seconds*
        to avoid resetting long-idle sessions that are harmless to resume.
        Returns the number of sessions that were suspended.
        """
        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 not entry.suspended and entry.updated_at >= cutoff:
                    entry.suspended = True
                    count += 1
            if count:
                self._save()
        return count

    def reset_session(self, session_key: str) -> 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=old_entry.display_name,
                platform=old_entry.platform,
                chat_type=old_entry.chat_type,
            )

            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 get_transcript_path(self, session_id: str) -> Path:
        """Get the path to a session's legacy transcript file."""
        return self.sessions_dir / f"{session_id}.jsonl"
    
    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 + legacy JSONL).

        Args:
            skip_db: When True, only write to JSONL and 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).
        """
        # Write to SQLite (unless the agent already handled it)
        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"),
                )
            except Exception as e:
                logger.debug("Session DB operation failed: %s", e)
        
        # Also write legacy JSONL (keeps existing tooling working during transition)
        transcript_path = self.get_transcript_path(session_id)
        with open(transcript_path, "a", encoding="utf-8") as f:
            f.write(json.dumps(message, ensure_ascii=False) + "\n")
    
    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.
        Rewrites both SQLite and legacy JSONL storage.
        """
        # SQLite: clear old messages and re-insert
        if self._db:
            try:
                self._db.clear_messages(session_id)
                for msg in messages:
                    role = msg.get("role", "unknown")
                    self._db.append_message(
                        session_id=session_id,
                        role=role,
                        content=msg.get("content"),
                        tool_name=msg.get("tool_name"),
                        tool_calls=msg.get("tool_calls"),
                        tool_call_id=msg.get("tool_call_id"),
                        reasoning=msg.get("reasoning") if role == "assistant" else None,
                        reasoning_details=msg.get("reasoning_details") if role == "assistant" else None,
                        codex_reasoning_items=msg.get("codex_reasoning_items") if role == "assistant" else None,
                    )
            except Exception as e:
                logger.debug("Failed to rewrite transcript in DB: %s", e)
        
        # JSONL: overwrite the file
        transcript_path = self.get_transcript_path(session_id)
        with open(transcript_path, "w", encoding="utf-8") as f:
            for msg in messages:
                f.write(json.dumps(msg, ensure_ascii=False) + "\n")

    def load_transcript(self, session_id: str) -> List[Dict[str, Any]]:
        """Load all messages from a session's transcript."""
        db_messages = []
        # Try SQLite first
        if self._db:
            try:
                db_messages = self._db.get_messages_as_conversation(session_id)
            except Exception as e:
                logger.debug("Could not load messages from DB: %s", e)

        # Load legacy JSONL transcript (may contain more history than SQLite
        # for sessions created before the DB layer was introduced).
        transcript_path = self.get_transcript_path(session_id)
        jsonl_messages = []
        if transcript_path.exists():
            with open(transcript_path, "r", encoding="utf-8") as f:
                for line in f:
                    line = line.strip()
                    if line:
                        try:
                            jsonl_messages.append(json.loads(line))
                        except json.JSONDecodeError:
                            logger.warning(
                                "Skipping corrupt line in transcript %s: %s",
                                session_id, line[:120],
                            )

        # Prefer whichever source has more messages.
        #
        # Background: when a session pre-dates SQLite storage (or when the DB
        # layer was added while a long-lived session was already active), the
        # first post-migration turn writes only the *new* messages to SQLite
        # (because _flush_messages_to_session_db skips messages already in
        # conversation_history, assuming they're persisted).  On the *next*
        # turn load_transcript returns those few SQLite rows and ignores the
        # full JSONL history — the model sees a context of 1-4 messages instead
        # of hundreds.  Using the longer source prevents this silent truncation.
        if len(jsonl_messages) > len(db_messages):
            if db_messages:
                logger.debug(
                    "Session %s: JSONL has %d messages vs SQLite %d — "
                    "using JSONL (legacy session not yet fully migrated)",
                    session_id, len(jsonl_messages), len(db_messages),
                )
            return jsonl_messages

        return db_messages


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,
    )
    
    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
