import asyncio
import datetime
import logging
from typing import Awaitable, Callable, Optional

import discord

from bot.discovery import Target
from bot.display import StatsDisplay
from bot.storage import Storage

log = logging.getLogger(__name__)

ReactFn = Callable[[discord.Message, Target], Awaitable[bool]]


async def scan_channel_backlog(
    storage: Storage,
    channel: discord.abc.Messageable,
    target: Target,
    friend_id: int,
    emoji: str,
    cutoff: datetime.datetime,
    react_fn: ReactFn,
    display: Optional[StatsDisplay] = None,
) -> None:
    """Scan a channel's history once, resumably, in two phases.

    Phase 1 finds every message from the friend in the window first (so the
    "found" count settles before any reacting starts, rather than climbing
    in lockstep with "reacted"), permanently logging each one (deduped by
    message ID) so re-scanning it later never inflates the count. Phase 2
    then reacts to each one in order.

    Before Phase 1 even starts, any message previously logged as found for
    this channel but not yet reacted to (e.g. the script was stopped midway
    through Phase 2 last time) is recovered from that same log and queued
    up again — this is independent of the newest_id_seen checkpoint below,
    so nothing found is ever silently abandoned even if the checkpoint has
    already moved past it.
    """
    channel_id = getattr(channel, "id", None)
    if channel_id is None:
        return

    found_messages = []
    pending_ids = await asyncio.to_thread(storage.get_pending_found_message_ids, channel_id, emoji)
    for message_id in pending_ids:
        try:
            found_messages.append(await channel.fetch_message(int(message_id)))
        except discord.NotFound:
            pass  # message (or its channel access) is gone since it was found
        except discord.HTTPException:
            log.exception("Failed to refetch pending message %s in channel %s", message_id, channel_id)

    state = await asyncio.to_thread(storage.get_scan_state, channel_id)
    newest_id_seen = int(state["newest_id_seen"]) if state and state.get("newest_id_seen") else None
    after = discord.Object(id=newest_id_seen) if newest_id_seen else cutoff

    try:
        async for message in channel.history(after=after, oldest_first=True, limit=None):
            if newest_id_seen is None or message.id > newest_id_seen:
                newest_id_seen = message.id

            if message.author.id == friend_id:
                found_messages.append(message)
                await asyncio.to_thread(
                    storage.record_message_found, message.id, channel_id, target.target_id, friend_id
                )
                if display is not None:
                    await display.refresh()

        await asyncio.to_thread(storage.set_scan_state, channel_id, target.target_id, newest_id_seen, True)
    except discord.Forbidden:
        log.warning("No access to channel %s (%s), skipping", channel_id, getattr(channel, "name", ""))
        return
    except discord.HTTPException:
        log.exception("HTTP error scanning channel %s", channel_id)
        return

    for message in found_messages:
        await react_fn(message, target)