"""File-based cache for loaded/resampled WAV data.

Stores .npy files in `cache/waveforms/` keyed by source path + target_sr + mono.
Invalidated when source file mtime changes.
"""
from __future__ import annotations
import hashlib
import os
import numpy as np

CACHE_DIR = os.path.join(os.path.dirname(os.path.abspath(__file__)), "cache", "waveforms")


def _cache_key(path: str, target_sr: int, mono: bool) -> str:
    real = os.path.realpath(path)
    mtime = os.path.getmtime(real)
    raw = f"{real}|{target_sr}|{mono}|{mtime:.6f}"
    return hashlib.sha256(raw.encode()).hexdigest()[:16]


def cached_load_wav(path: str, target_sr: int = 48000, mono: bool = True,
                    _loader=None) -> tuple[np.ndarray, int]:
    """Load WAV with disk cache. Falls back to _loader(data, sr) if cache miss."""
    key = _cache_key(path, target_sr, mono)
    npy_path = os.path.join(CACHE_DIR, f"{key}.npy")
    sr_path = os.path.join(CACHE_DIR, f"{key}.sr")

    if os.path.exists(npy_path) and os.path.exists(sr_path):
        try:
            data = np.load(npy_path, allow_pickle=False)
            sr = int(np.load(sr_path, allow_pickle=False).item())
            return data, sr
        except Exception:
            pass  # corrupted cache, rebuild

    if _loader is None:
        from sync_audio import load_wav as _loader

    data, sr = _loader(path, target_sr=target_sr, mono=mono)
    os.makedirs(CACHE_DIR, exist_ok=True)
    np.save(npy_path, data, allow_pickle=False)
    np.save(sr_path, np.array(sr), allow_pickle=False)
    return data, sr