"""
Match episode titles from filenames against a reference episode list (e.g. TheTVDB).
"""
from __future__ import annotations

import re
from difflib import SequenceMatcher
from typing import Optional

from .tvdb_client import TvdbEpisode

DEFAULT_EPISODE_PATTERN = r"(.*?[Ss]\d+[Ee])(\d+)(-[Ee](\d+))?(.*)"


def normalize_title(title: str) -> str:
    """Lowercase, strip punctuation, collapse whitespace for fuzzy comparison."""
    t = title.lower()
    t = re.sub(r"[^\w\s]", " ", t, flags=re.UNICODE)
    return re.sub(r"\s+", " ", t).strip()


def parse_episode_stem(stem: str, pattern: str = DEFAULT_EPISODE_PATTERN) -> Optional[dict]:
    """
    Parse SxxExx-style filename stem.
    Returns dict with prefix, episode numbers, title rest, and span — or None if no match.
    """
    try:
        m = re.match(pattern, stem)
    except re.error:
        return None
    if not m:
        return None
    prefix, old_first_s, _range_dash_e, old_second_s, rest = (
        m.group(1),
        m.group(2),
        m.group(3),
        m.group(4),
        m.group(5),
    )
    try:
        old_first = int(old_first_s)
    except ValueError:
        return None
    span = 1
    if old_second_s is not None:
        try:
            old_second = int(old_second_s)
        except ValueError:
            return None
        span = old_second - old_first + 1
        if span < 1:
            span = 1
    title = rest.strip()
    if title.startswith("-") or title.startswith("–"):
        title = title[1:].strip()
    if title.startswith("_"):
        title = title[1:].strip()
    return {
        "prefix": prefix,
        "old_first": old_first,
        "span": span,
        "title": title,
    }


def rewrite_episode_number(
    stem: str,
    new_first_ep: int,
    padding: int = 2,
    pattern: str = DEFAULT_EPISODE_PATTERN,
) -> str:
    """Replace episode number block in stem, preserving prefix, span, and title."""
    parsed = parse_episode_stem(stem, pattern)
    if not parsed:
        return stem
    try:
        m = re.match(pattern, stem)
    except re.error:
        return stem
    if not m:
        return stem
    prefix = m.group(1)
    rest = m.group(5)
    span = parsed["span"]
    pad = max(1, padding)
    e1 = str(new_first_ep).zfill(pad)
    if span <= 1:
        return f"{prefix}{e1}{rest}"
    e2 = str(new_first_ep + span - 1).zfill(pad)
    return f"{prefix}{e1}-E{e2}{rest}"


def _similarity(a: str, b: str) -> float:
    if not a or not b:
        return 0.0
    if a == b:
        return 1.0
    return SequenceMatcher(None, a, b).ratio()


def match_filenames_to_episodes(
    filenames: list[str],
    episodes: list[TvdbEpisode],
    pattern: str = DEFAULT_EPISODE_PATTERN,
    min_score: float = 0.72,
) -> tuple[dict[str, int], list[str], list[str]]:
    """
    Match filenames to TheTVDB episode numbers by title.

    Returns:
        mapping: original filename -> correct episode number
        unmatched_files: filenames that could not be matched
        notes: human-readable match details for UI
    """
    file_entries: list[tuple[str, str, str]] = []
    for name in filenames:
        stem = name.rsplit(".", 1)[0] if "." in name and not name.startswith(".") else name
        parsed = parse_episode_stem(stem, pattern)
        if not parsed or not parsed["title"]:
            continue
        norm = normalize_title(parsed["title"])
        if norm:
            file_entries.append((name, norm, parsed["title"]))

    ep_entries = [(ep.number, normalize_title(ep.name), ep.name) for ep in episodes]

    pairs: list[tuple[float, str, int, str, str]] = []
    for fname, fnorm, raw_title in file_entries:
        for ep_num, enorm, ep_name in ep_entries:
            score = _similarity(fnorm, enorm)
            pairs.append((score, fname, ep_num, raw_title, ep_name))

    pairs.sort(key=lambda x: (-x[0], x[1], x[2]))

    mapping: dict[str, int] = {}
    used_files: set[str] = set()
    used_eps: set[int] = set()
    notes: list[str] = []

    for score, fname, ep_num, raw_title, ep_name in pairs:
        if score < min_score:
            break
        if fname in used_files or ep_num in used_eps:
            continue
        mapping[fname] = ep_num
        used_files.add(fname)
        used_eps.add(ep_num)
        pct = int(round(score * 100))
        notes.append(f"{fname}: E{ep_num:02d} ← “{ep_name}” ({pct}% match, file title “{raw_title}”)")

    unmatched_files = [
        name for name in filenames
        if name not in mapping
        and parse_episode_stem(
            name.rsplit(".", 1)[0] if "." in name and not name.startswith(".") else name,
            pattern,
        )
    ]
    return mapping, unmatched_files, notes