"""GCC-PHAT pairwise audio offsets + global graph solve + drift (spec M1, lane A).

STUB — lane A fills the bodies; the public signatures below are frozen (``cli.py`` calls
``run_sync``).

Algorithm (spec M1, for lane A's reference):
- **GCC-PHAT**, not raw cross-correlation: whiten the cross-spectrum
  ``R = X * conj(Y); R /= |R| + eps; r = irfft(R)`` — robust to loud/clipped/reverberant
  concert audio. numpy/scipy FFTs; librosa only for loading.
- All **pairwise** offsets, each scored by peak-to-second-peak ratio; then a global
  least-squares solve over the offset graph, weighted by confidence, rejecting pairs that
  violate cycle consistency (``off_ab + off_bc - off_ac > 50 ms``).
- **Drift**: re-run GCC-PHAT on 10 s windows every 30 s along the overlap; fit a line;
  store the slope as ``drift_ppm`` (store 0 if ``|drift| < 5 ppm``).
- Disconnected sync-graph components -> ``offset_ms = None`` (never a guess; spec pitfall #5).
- Persist via ``db.update_video_sync`` and export ``config.SYNC_JSON``.
"""

from __future__ import annotations

import logging

import numpy as np

log = logging.getLogger("festival4d.audio_sync")


def gcc_phat(sig: np.ndarray, ref: np.ndarray, sr: int,
             max_lag_s: float | None = None) -> tuple[float, float]:
    """GCC-PHAT time delay of ``sig`` relative to ``ref`` (spec M1, lane A).

    Returns ``(offset_s, confidence)`` where confidence is the peak-to-second-peak ratio.
    """
    raise NotImplementedError("lane A (M1): implement gcc_phat")


def pairwise_offsets(signals: dict[int, np.ndarray], sr: int) -> list[dict]:
    """All pairwise GCC-PHAT offsets with confidences (spec M1, lane A).

    ``signals`` maps ``video_id -> mono samples``. Returns a list of
    ``{a, b, offset_s, confidence}`` edges.
    """
    raise NotImplementedError("lane A (M1): implement pairwise_offsets")


def solve_global_offsets(edges: list[dict], video_ids: list[int]) -> dict[int, float | None]:
    """Least-squares global solve over the pairwise-offset graph (spec M1, lane A).

    Reference node is pinned to 0; disconnected components get ``None`` (spec pitfall #5).
    Returns ``video_id -> offset_ms`` (or ``None``).
    """
    raise NotImplementedError("lane A (M1): implement solve_global_offsets")


def estimate_drift(sig: np.ndarray, ref: np.ndarray, sr: int) -> float:
    """Estimate clock drift in ppm by fitting window-offsets over the overlap (spec M1)."""
    raise NotImplementedError("lane A (M1): implement estimate_drift")


def run_sync() -> dict:
    """Sync every ingested video: pairwise GCC-PHAT, global solve, drift, persist.

    Entrypoint for ``python -m festival4d sync``. Writes ``offset_ms``/``drift_ppm``/
    ``sync_confidence`` via ``db`` and exports ``config.SYNC_JSON``. Returns the solution.
    """
    raise NotImplementedError("lane A (M1): implement run_sync")