"""Channel manager for coordinating chat channels."""

from __future__ import annotations

import asyncio
from typing import Any

from loguru import logger

from nanobot.bus.events import OutboundMessage
from nanobot.bus.queue import MessageBus
from nanobot.channels.base import BaseChannel
from nanobot.config.schema import Config
from nanobot.utils.restart import consume_restart_notice_from_env, format_restart_completed_message

# Retry delays for message sending (exponential backoff: 1s, 2s, 4s)
_SEND_RETRY_DELAYS = (1, 2, 4)


class ChannelManager:
    """
    Manages chat channels and coordinates message routing.

    Responsibilities:
    - Initialize enabled channels (Telegram, WhatsApp, etc.)
    - Start/stop channels
    - Route outbound messages
    """

    def __init__(self, config: Config, bus: MessageBus):
        self.config = config
        self.bus = bus
        self.channels: dict[str, BaseChannel] = {}
        self._dispatch_task: asyncio.Task | None = None

        self._init_channels()

    def _init_channels(self) -> None:
        """Initialize channels discovered via pkgutil scan + entry_points plugins."""
        from nanobot.channels.registry import discover_all

        transcription_provider = self.config.channels.transcription_provider
        transcription_key = self._resolve_transcription_key(transcription_provider)

        for name, cls in discover_all().items():
            section = getattr(self.config.channels, name, None)
            if section is None:
                continue
            enabled = (
                section.get("enabled", False)
                if isinstance(section, dict)
                else getattr(section, "enabled", False)
            )
            if not enabled:
                continue
            try:
                channel = cls(section, self.bus)
                channel.transcription_provider = transcription_provider
                channel.transcription_api_key = transcription_key
                self.channels[name] = channel
                logger.info("{} channel enabled", cls.display_name)
            except Exception as e:
                logger.warning("{} channel not available: {}", name, e)

        self._validate_allow_from()

    def _resolve_transcription_key(self, provider: str) -> str:
        """Pick the API key for the configured transcription provider."""
        try:
            if provider == "openai":
                return self.config.providers.openai.api_key
            return self.config.providers.groq.api_key
        except AttributeError:
            return ""

    def _validate_allow_from(self) -> None:
        for name, ch in self.channels.items():
            cfg = ch.config
            if isinstance(cfg, dict):
                if "allow_from" in cfg:
                    allow = cfg.get("allow_from")
                else:
                    allow = cfg.get("allowFrom")
            else:
                allow = getattr(cfg, "allow_from", None)
            if allow == []:
                raise SystemExit(
                    f'Error: "{name}" has empty allowFrom (denies all). '
                    f'Set ["*"] to allow everyone, or add specific user IDs.'
                )

    async def _start_channel(self, name: str, channel: BaseChannel) -> None:
        """Start a channel and log any exceptions."""
        try:
            await channel.start()
        except Exception as e:
            logger.error("Failed to start channel {}: {}", name, e)

    async def start_all(self) -> None:
        """Start all channels and the outbound dispatcher."""
        if not self.channels:
            logger.warning("No channels enabled")
            return

        # Start outbound dispatcher
        self._dispatch_task = asyncio.create_task(self._dispatch_outbound())

        # Start channels
        tasks = []
        for name, channel in self.channels.items():
            logger.info("Starting {} channel...", name)
            tasks.append(asyncio.create_task(self._start_channel(name, channel)))

        self._notify_restart_done_if_needed()

        # Wait for all to complete (they should run forever)
        await asyncio.gather(*tasks, return_exceptions=True)

    def _notify_restart_done_if_needed(self) -> None:
        """Send restart completion message when runtime env markers are present."""
        notice = consume_restart_notice_from_env()
        if not notice:
            return
        target = self.channels.get(notice.channel)
        if not target:
            return
        asyncio.create_task(self._send_with_retry(
            target,
            OutboundMessage(
                channel=notice.channel,
                chat_id=notice.chat_id,
                content=format_restart_completed_message(notice.started_at_raw),
            ),
        ))

    async def stop_all(self) -> None:
        """Stop all channels and the dispatcher."""
        logger.info("Stopping all channels...")

        # Stop dispatcher
        if self._dispatch_task:
            self._dispatch_task.cancel()
            try:
                await self._dispatch_task
            except asyncio.CancelledError:
                pass

        # Stop all channels
        for name, channel in self.channels.items():
            try:
                await channel.stop()
                logger.info("Stopped {} channel", name)
            except Exception as e:
                logger.error("Error stopping {}: {}", name, e)

    async def _dispatch_outbound(self) -> None:
        """Dispatch outbound messages to the appropriate channel."""
        logger.info("Outbound dispatcher started")

        # Buffer for messages that couldn't be processed during delta coalescing
        # (since asyncio.Queue doesn't support push_front)
        pending: list[OutboundMessage] = []

        while True:
            try:
                # First check pending buffer before waiting on queue
                if pending:
                    msg = pending.pop(0)
                else:
                    msg = await asyncio.wait_for(
                        self.bus.consume_outbound(),
                        timeout=1.0
                    )

                if msg.metadata.get("_progress"):
                    if msg.metadata.get("_tool_hint") and not self.config.channels.send_tool_hints:
                        continue
                    if not msg.metadata.get("_tool_hint") and not self.config.channels.send_progress:
                        continue

                # Coalesce consecutive _stream_delta messages for the same (channel, chat_id)
                # to reduce API calls and improve streaming latency
                if msg.metadata.get("_stream_delta") and not msg.metadata.get("_stream_end"):
                    msg, extra_pending = self._coalesce_stream_deltas(msg)
                    pending.extend(extra_pending)

                channel = self.channels.get(msg.channel)
                if channel:
                    await self._send_with_retry(channel, msg)
                else:
                    logger.warning("Unknown channel: {}", msg.channel)

            except asyncio.TimeoutError:
                continue
            except asyncio.CancelledError:
                break

    @staticmethod
    async def _send_once(channel: BaseChannel, msg: OutboundMessage) -> None:
        """Send one outbound message without retry policy."""
        if msg.metadata.get("_stream_delta") or msg.metadata.get("_stream_end"):
            await channel.send_delta(msg.chat_id, msg.content, msg.metadata)
        elif not msg.metadata.get("_streamed"):
            await channel.send(msg)

    def _coalesce_stream_deltas(
        self, first_msg: OutboundMessage
    ) -> tuple[OutboundMessage, list[OutboundMessage]]:
        """Merge consecutive _stream_delta messages for the same (channel, chat_id).

        This reduces the number of API calls when the queue has accumulated multiple
        deltas, which happens when LLM generates faster than the channel can process.

        Returns:
            tuple of (merged_message, list_of_non_matching_messages)
        """
        target_key = (first_msg.channel, first_msg.chat_id)
        combined_content = first_msg.content
        final_metadata = dict(first_msg.metadata or {})
        non_matching: list[OutboundMessage] = []

        # Only merge consecutive deltas. As soon as we hit any other message,
        # stop and hand that boundary back to the dispatcher via `pending`.
        while True:
            try:
                next_msg = self.bus.outbound.get_nowait()
            except asyncio.QueueEmpty:
                break

            # Check if this message belongs to the same stream
            same_target = (next_msg.channel, next_msg.chat_id) == target_key
            is_delta = next_msg.metadata and next_msg.metadata.get("_stream_delta")
            is_end = next_msg.metadata and next_msg.metadata.get("_stream_end")

            if same_target and is_delta and not final_metadata.get("_stream_end"):
                # Accumulate content
                combined_content += next_msg.content
                # If we see _stream_end, remember it and stop coalescing this stream
                if is_end:
                    final_metadata["_stream_end"] = True
                    # Stream ended - stop coalescing this stream
                    break
            else:
                # First non-matching message defines the coalescing boundary.
                non_matching.append(next_msg)
                break

        merged = OutboundMessage(
            channel=first_msg.channel,
            chat_id=first_msg.chat_id,
            content=combined_content,
            metadata=final_metadata,
        )
        return merged, non_matching

    async def _send_with_retry(self, channel: BaseChannel, msg: OutboundMessage) -> None:
        """Send a message with retry on failure using exponential backoff.

        Note: CancelledError is re-raised to allow graceful shutdown.
        """
        max_attempts = max(self.config.channels.send_max_retries, 1)

        for attempt in range(max_attempts):
            try:
                await self._send_once(channel, msg)
                return  # Send succeeded
            except asyncio.CancelledError:
                raise  # Propagate cancellation for graceful shutdown
            except Exception as e:
                if attempt == max_attempts - 1:
                    logger.error(
                        "Failed to send to {} after {} attempts: {} - {}",
                        msg.channel, max_attempts, type(e).__name__, e
                    )
                    return
                delay = _SEND_RETRY_DELAYS[min(attempt, len(_SEND_RETRY_DELAYS) - 1)]
                logger.warning(
                    "Send to {} failed (attempt {}/{}): {}, retrying in {}s",
                    msg.channel, attempt + 1, max_attempts, type(e).__name__, delay
                )
                try:
                    await asyncio.sleep(delay)
                except asyncio.CancelledError:
                    raise  # Propagate cancellation during sleep

    def get_channel(self, name: str) -> BaseChannel | None:
        """Get a channel by name."""
        return self.channels.get(name)

    def get_status(self) -> dict[str, Any]:
        """Get status of all channels."""
        return {
            name: {
                "enabled": True,
                "running": channel.is_running
            }
            for name, channel in self.channels.items()
        }

    @property
    def enabled_channels(self) -> list[str]:
        """Get list of enabled channel names."""
        return list(self.channels.keys())
