"""Sync match overrides — user-confirmed source→server track pairings.

When a user picks a local file via "Find & Add" on the Server Playlist
compare view, that selection should persist as a hard match across
future syncs — bypassing the fuzzy/exact title-match algorithm
entirely. This module provides pure helpers that the web layer calls
to resolve and persist those overrides through the existing
`sync_match_cache` table.

Override semantics:
    - One mapping per (source_track_id, server_source). UNIQUE
      constraint on the table enforces single mapping per pair.
    - Stored with confidence=1.0 to distinguish from auto-discovered
      matches (which use the actual title-similarity score).
    - Read at the START of the matching algorithm — before pass-1
      exact and pass-2 fuzzy. Skipped sources don't re-enter the
      normal matching pool.
    - Stale-cache safe: if the cached server_track_id doesn't exist
      in the current server_tracks list (track removed from server),
      the override is silently skipped and normal matching runs.
"""

from __future__ import annotations

from typing import Any, Callable, Dict, List, Optional


def resolve_match_overrides(
    source_tracks: List[Dict[str, Any]],
    server_tracks: List[Dict[str, Any]],
    cache_lookup: Callable[[str], Optional[Any]],
) -> Dict[int, int]:
    """Map source-track indexes to server-track indexes for cached overrides.

    Pure function. `cache_lookup(source_track_id) -> server_track_id or
    None` is injected by the caller (web layer wraps the DB call).

    Returns ``{source_idx: server_idx}``. Only includes pairs where:
        - source_track has a non-empty `source_track_id`
        - cache_lookup returns a server_track_id
        - that server_track_id exists in server_tracks (no stale cache
          entries pointing at deleted tracks)
        - the server_track hasn't already been claimed by an earlier
          override (defensive — UNIQUE on the cache table prevents this
          in practice)

    Caller uses the returned dict to short-circuit the per-source
    matching loop: indices in the dict skip the exact/fuzzy passes.
    """
    if not source_tracks or not server_tracks:
        return {}

    server_id_to_idx: Dict[str, int] = {}
    for j, svr in enumerate(server_tracks):
        sid = svr.get("id") if isinstance(svr, dict) else None
        if sid is not None:
            key = str(sid)
            if key not in server_id_to_idx:
                server_id_to_idx[key] = j

    overrides: Dict[int, int] = {}
    used_server: set[int] = set()

    for i, src in enumerate(source_tracks):
        if not isinstance(src, dict):
            continue
        src_id = src.get("source_track_id")
        if not src_id:
            continue
        try:
            cached_server_id = cache_lookup(str(src_id))
        except Exception:
            cached_server_id = None
        if not cached_server_id:
            continue
        j = server_id_to_idx.get(str(cached_server_id))
        if j is None or j in used_server:
            continue
        overrides[i] = j
        used_server.add(j)

    return overrides


def record_manual_match(
    db: Any,
    source_track_id: str,
    server_source: str,
    server_track_id: Any,
    server_track_title: str = "",
    source_title: str = "",
    source_artist: str = "",
) -> bool:
    """Persist a user-confirmed source→server pairing as a hard override.

    Wraps `db.save_sync_match_cache` with confidence=1.0 (the manual
    match marker). Normalized title/artist fields are informational
    only — the cache is keyed by `(spotify_track_id, server_source)`,
    so the normalization is just for inspection and future debugging.

    Returns True on persist success, False on any failure (DB, missing
    args, etc). Never raises.
    """
    if not source_track_id or not server_source or server_track_id is None:
        return False
    if not hasattr(db, "save_sync_match_cache"):
        return False
    try:
        return bool(db.save_sync_match_cache(
            spotify_track_id=str(source_track_id),
            normalized_title=(source_title or "").lower().strip(),
            normalized_artist=(source_artist or "").lower().strip(),
            server_source=server_source,
            server_track_id=server_track_id,
            server_track_title=server_track_title or "",
            confidence=1.0,
        ))
    except Exception:
        return False