"""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

# 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

        groq_key = self.config.providers.groq.api_key
        zhipu_key = self.config.providers.zhipu.api_key

        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_api_key = groq_key
                channel.zhipu_api_key = zhipu_key
                self.channels[name] = channel
                logger.info("{} channel enabled", cls.display_name)
            except Exception as e:
                logger.warning("{} channel not available: {}", name, e)

        # Alexa channel (not yet in discover_all registry)
        alexa_section = getattr(self.config.channels, "alexa", None)
        if alexa_section and (
            alexa_section.get("enabled", False) if isinstance(alexa_section, dict)
            else getattr(alexa_section, "enabled", False)
        ):
            try:
                from nanobot.channels.alexa import AlexaChannel
                from nanobot.config.schema import AlexaConfig
                if isinstance(alexa_section, dict):
                    alexa_section = AlexaConfig.model_validate(alexa_section)
                self.channels["alexa"] = AlexaChannel(alexa_section, self.bus)
                logger.info("Alexa channel enabled")
            except ImportError as e:
                logger.warning("Alexa channel not available: {}", e)

        self._validate_allow_from()

    def _validate_allow_from(self) -> None:
        for name, ch in self.channels.items():
            if getattr(ch.config, "allow_from", None) == []:
                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)))

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

    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())
