"""
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 os
import json
import uuid
from pathlib import Path
from datetime import datetime, timedelta
from dataclasses import dataclass, field
from typing import Dict, List, Optional, Any

from .config import (
    Platform,
    GatewayConfig,
    SessionResetPolicy,
    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.
    
    @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]:
        return {
            "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,
        }
    
    @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"),
        )
    
    @classmethod
    def local_cli(cls) -> "SessionSource":
        """Create a source representing the local CLI."""
        return cls(
            platform=Platform.LOCAL,
            chat_id="cli",
            chat_name="CLI terminal",
            chat_type="dm",
        )


@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,
        }


def build_session_context_prompt(context: SessionContext) -> 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
    """
    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:
        lines.append(f"**Source:** {platform_name} ({context.source.description})")
    
    # 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():
            lines.append(f"  - {platform.value}: {home.name} (ID: {home.chat_id})")
    
    # Delivery options for scheduled tasks
    lines.append("")
    lines.append("**Delivery options for scheduled tasks:**")
    
    # Origin delivery
    if context.source.platform == Platform.LOCAL:
        lines.append("- `\"origin\"` → Local output (saved to files)")
    else:
        lines.append(f"- `\"origin\"` → Back to this chat ({context.source.chat_name or context.source.chat_id})")
    
    # Local always available
    lines.append("- `\"local\"` → Save to local files only (~/.hermes/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
    total_tokens: int = 0
    
    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,
            "total_tokens": self.total_tokens,
        }
        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:
                pass
        
        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),
            total_tokens=data.get("total_tokens", 0),
        )


class SessionStore:
    """
    Manages session storage and retrieval.
    
    Sessions are stored in:
    - sessions.json: Index mapping session keys to session IDs
    - {session_id}.jsonl: Conversation transcripts
    """
    
    def __init__(self, sessions_dir: Path, config: GatewayConfig):
        self.sessions_dir = sessions_dir
        self.config = config
        self._entries: Dict[str, SessionEntry] = {}
        self._loaded = False
    
    def _ensure_loaded(self) -> None:
        """Load sessions from disk if not already loaded."""
        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") as f:
                    data = json.load(f)
                    for key, entry_data in data.items():
                        self._entries[key] = SessionEntry.from_dict(entry_data)
            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."""
        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()}
        with open(sessions_file, "w") as f:
            json.dump(data, f, indent=2)
    
    def _generate_session_key(self, source: SessionSource) -> str:
        """Generate a session key from a source."""
        platform = source.platform.value
        
        if source.chat_type == "dm":
            # DMs share the main session per platform
            return f"agent:main:{platform}:dm"
        else:
            # Groups/channels get their own keys
            return f"agent:main:{platform}:{source.chat_type}:{source.chat_id}"
    
    def _should_reset(self, entry: SessionEntry, source: SessionSource) -> bool:
        """
        Check if a session should be reset based on policy.
        
        Returns True if the session is stale and should start fresh.
        """
        policy = self.config.get_reset_policy(
            platform=source.platform,
            session_type=source.chat_type
        )
        
        now = datetime.now()
        
        # Check idle timeout
        if policy.mode in ("idle", "both"):
            idle_deadline = entry.updated_at + timedelta(minutes=policy.idle_minutes)
            if now > idle_deadline:
                return True
        
        # Check daily reset
        if policy.mode in ("daily", "both"):
            # Find the most recent reset boundary
            today_reset = now.replace(
                hour=policy.at_hour, 
                minute=0, 
                second=0, 
                microsecond=0
            )
            if now.hour < policy.at_hour:
                # Reset boundary was yesterday
                today_reset -= timedelta(days=1)
            
            if entry.updated_at < today_reset:
                return True
        
        return False
    
    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.
        """
        self._ensure_loaded()
        
        session_key = self._generate_session_key(source)
        now = datetime.now()
        
        # Check for existing session
        if session_key in self._entries and not force_new:
            entry = self._entries[session_key]
            
            # Check if session should be reset
            if not self._should_reset(entry, source):
                # Update timestamp and return existing
                entry.updated_at = now
                self._save()
                return entry
        
        # 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,
        )
        
        self._entries[session_key] = entry
        self._save()
        
        return entry
    
    def update_session(
        self, 
        session_key: str,
        input_tokens: int = 0,
        output_tokens: int = 0
    ) -> None:
        """Update a session's metadata after an interaction."""
        self._ensure_loaded()
        
        if session_key in self._entries:
            entry = self._entries[session_key]
            entry.updated_at = datetime.now()
            entry.input_tokens += input_tokens
            entry.output_tokens += output_tokens
            entry.total_tokens = entry.input_tokens + entry.output_tokens
            self._save()
    
    def reset_session(self, session_key: str) -> Optional[SessionEntry]:
        """Force reset a session, creating a new session ID."""
        self._ensure_loaded()
        
        if session_key not in self._entries:
            return None
        
        old_entry = self._entries[session_key]
        now = datetime.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()
        
        return new_entry
    
    def list_sessions(self, active_minutes: Optional[int] = None) -> List[SessionEntry]:
        """
        List all sessions, optionally filtered by activity.
        
        Args:
            active_minutes: If provided, only return sessions updated within this many minutes
        """
        self._ensure_loaded()
        
        entries = list(self._entries.values())
        
        if active_minutes is not None:
            cutoff = datetime.now() - timedelta(minutes=active_minutes)
            entries = [e for e in entries if e.updated_at >= cutoff]
        
        # Sort by most recently updated
        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 transcript file."""
        return self.sessions_dir / f"{session_id}.jsonl"
    
    def append_to_transcript(self, session_id: str, message: Dict[str, Any]) -> None:
        """Append a message to a session's transcript."""
        transcript_path = self.get_transcript_path(session_id)
        
        with open(transcript_path, "a") as f:
            f.write(json.dumps(message, ensure_ascii=False) + "\n")
    
    def load_transcript(self, session_id: str) -> List[Dict[str, Any]]:
        """Load all messages from a session's transcript."""
        transcript_path = self.get_transcript_path(session_id)
        
        if not transcript_path.exists():
            return []
        
        messages = []
        with open(transcript_path, "r") as f:
            for line in f:
                line = line.strip()
                if line:
                    messages.append(json.loads(line))
        
        return 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