"""Lift legacy guitar-wire keys notes into the Sloppak Notation Format.

The reusable heuristic core shared by the one-time
``scripts/lift_keys_notation.py`` converter and any in-process caller (e.g.
the Arrangement Editor's notation save path). It takes decoded wire notes
plus the song-level ``beats`` array and infers measures, written durations,
and a right/left-hand split, producing a validated ``notation`` payload.

The heuristics (see ``build_notation`` and friends):

1. **Wire decode** — ``decode_wire_notes`` unpacks ``midi = s*24 + f`` (the
   Clone Hero / GP-import legacy encoding, sloppak-spec §5.3 legacy fallback),
   including chord notes, to ``[{"t", "midi", "sus"}, ...]`` sorted by time.
2. **Measures / tempo** — ``downbeat_times`` reads the song-level downbeats
   (``measure >= 0`` entries); ``measure_tempos`` derives a per-measure BPM
   from their spacing at the given time signature.
3. **Durations** — wire sustain when > 0, else the gap to the next onset in
   the same hand, quantized to the nearest plain or single-dotted
   ``{1,2,4,8,16,32}`` at the local tempo, floored at a 32nd
   (``quantize_duration``).
4. **Hand split** — ``split_hands`` groups simultaneous onsets (within 10 ms);
   a group spanning more than 12 semitones is split at its largest internal
   interval gap (low side → ``lh``); otherwise the whole group goes by mean
   pitch vs middle C (≥ 60 → ``rh``). Output is single-staff when everything
   lands on one side.

``build_notation`` assembles these into the schema payload, splitting notes
that cross a barline into tied continuations, and validates via
``notation.validate_notation`` before returning (raising on an invalid build
so a caller never persists a payload the loader would drop). Returns ``None``
when there is nothing to lift (no notes or no downbeats).
"""

from __future__ import annotations

from bisect import bisect_right
import re

import notation as notation_mod

# Arrangement names that identify a piano-family arrangement.
KEYS_NAME_RE = re.compile(r"\b(keys|piano|keyboard|synth)\b", re.IGNORECASE)

# Onsets within this window are treated as one simultaneous group/beat.
SIMULTANEITY_WINDOW_S = 0.010

# A simultaneous group spanning more than this is split between two hands.
HAND_SPLIT_SPAN_SEMITONES = 12

MIDDLE_C = 60


# ── Wire decoding ─────────────────────────────────────────────────────────────

def decode_wire_notes(arr_data: dict) -> list[dict]:
    """Decode an arrangement JSON's notes + chord notes to
    ``[{"t": float, "midi": int, "sus": float}, ...]`` sorted by time.

    Keys content packs absolute MIDI as ``midi = s*24 + f`` (sloppak-spec
    §5.3 legacy fallback). Sustain is the ``sus`` field (``l`` accepted as a
    legacy alias). Entries with malformed fields are skipped.
    """
    out: list[dict] = []

    def _push(t, s, f, sus):
        try:
            t = float(t)
            midi = int(s) * 24 + int(f)
            sus = float(sus or 0.0)
        except (TypeError, ValueError):
            return
        if 0 <= midi <= 127:
            out.append({"t": t, "midi": midi, "sus": max(0.0, sus)})

    for n in arr_data.get("notes") or []:
        if isinstance(n, dict):
            _push(n.get("t"), n.get("s"), n.get("f"), n.get("sus", n.get("l")))
    for ch in arr_data.get("chords") or []:
        if not isinstance(ch, dict):
            continue
        ch_t = ch.get("t")
        for cn in ch.get("notes") or []:
            if isinstance(cn, dict):
                # Chord notes carry no own time — they sound at the chord's t.
                _push(cn.get("t", ch_t), cn.get("s"), cn.get("f"),
                      cn.get("sus", cn.get("l")))

    out.sort(key=lambda n: (n["t"], n["midi"]))
    return out


# ── Hand split ────────────────────────────────────────────────────────────────

def group_simultaneous(notes: list[dict]) -> list[list[dict]]:
    """Group time-sorted notes whose onsets fall within 10 ms of the group start."""
    groups: list[list[dict]] = []
    for n in notes:
        if groups and n["t"] - groups[-1][0]["t"] <= SIMULTANEITY_WINDOW_S:
            groups[-1].append(n)
        else:
            groups.append([n])
    return groups


def split_hands(notes: list[dict]) -> dict[str, list[dict]]:
    """Assign every note to ``rh`` or ``lh`` per the heuristic.

    Per simultaneous group: a span > 12 semitones splits at the largest
    internal interval gap (low side → lh); otherwise the whole group goes by
    mean pitch vs middle C (≥ 60 → rh).
    """
    hands: dict[str, list[dict]] = {"rh": [], "lh": []}
    for group in group_simultaneous(notes):
        pitches = sorted(n["midi"] for n in group)
        span = pitches[-1] - pitches[0]
        if len(pitches) > 1 and span > HAND_SPLIT_SPAN_SEMITONES:
            # Prefer middle C as the split boundary when notes straddle it —
            # this correctly handles bass+treble chords from piano imports where
            # the largest-gap heuristic picks the wrong split point (e.g.
            # [G2, E3, C4]: largest gap is G2→E3 but the real split is E3|C4).
            # BUT only when both resulting hands are themselves playable: a bass
            # note under a treble voicing that merely dips below C4 (e.g.
            # [E2, B3, D4, G4]) would otherwise land E2+B3 in one hand — a
            # 19-semitone span that re-violates HAND_SPLIT_SPAN_SEMITONES. When
            # the middle-C split produces an unplayable hand, fall back to the
            # largest internal gap (which correctly isolates E2 there).
            threshold = None
            if pitches[0] < MIDDLE_C <= pitches[-1]:
                _lh = [p for p in pitches if p < MIDDLE_C]
                _rh = [p for p in pitches if p >= MIDDLE_C]
                if (_lh[-1] - _lh[0] <= HAND_SPLIT_SPAN_SEMITONES
                        and _rh[-1] - _rh[0] <= HAND_SPLIT_SPAN_SEMITONES):
                    threshold = MIDDLE_C - 1  # lh: midi < MIDDLE_C
            if threshold is None:
                gaps = [pitches[i + 1] - pitches[i] for i in range(len(pitches) - 1)]
                split_after = gaps.index(max(gaps))
                threshold = pitches[split_after]
            for n in group:
                hands["lh" if n["midi"] <= threshold else "rh"].append(n)
        else:
            mean = sum(pitches) / len(pitches)
            hand = "rh" if mean >= MIDDLE_C else "lh"
            hands[hand].extend(group)
    return {h: ns for h, ns in hands.items() if ns}


# ── Timing ────────────────────────────────────────────────────────────────────

def downbeat_times(beats: list[dict]) -> list[float]:
    """Times of the song-level downbeats (entries with ``measure >= 0``)."""
    out: list[float] = []
    for b in beats or []:
        if not isinstance(b, dict):
            continue
        try:
            measure = int(b.get("measure", -1))
            t = float(b.get("time", 0.0))
        except (TypeError, ValueError):
            continue
        if measure >= 0:
            out.append(t)
    out.sort()
    return out


def measure_tempos(downbeats: list[float], ts: tuple[int, int]) -> list[float]:
    """Per-measure BPM from downbeat spacing at the given time signature.

    BPM is quarter-note based: a measure holds ``num * 4/den`` quarter notes,
    so ``bpm = qn_per_measure * 60 / measure_duration``. The last measure has
    no next downbeat and inherits the previous measure's tempo (120 BPM for
    a single-measure song).
    """
    num, den = ts
    qn_per_measure = num * (4.0 / den)
    tempos: list[float] = []
    for i in range(len(downbeats)):
        if i + 1 < len(downbeats) and downbeats[i + 1] > downbeats[i]:
            dur = downbeats[i + 1] - downbeats[i]
            tempos.append(qn_per_measure * 60.0 / dur)
        else:
            tempos.append(tempos[-1] if tempos else 120.0)
    return tempos


def quantize_duration(dur_secs: float, bpm: float) -> tuple[int, int]:
    """Quantize a duration in seconds to ``(dur, dot)`` at the local tempo.

    Candidates are the plain and single-dotted schema denominators
    ``{1,2,4,8,16,32}``; the closest in absolute seconds wins. Anything at or
    below the 32nd floor returns ``(32, 0)``.
    """
    qn = 60.0 / bpm
    best: tuple[int, int] = (32, 0)
    best_err = float("inf")
    for den in (1, 2, 4, 8, 16, 32):
        for dot in (0, 1):
            cand = qn * (4.0 / den) * (1.5 if dot else 1.0)
            err = abs(dur_secs - cand)
            if err < best_err:
                best_err = err
                best = (den, dot)
    # Floor: never quantize below a plain 32nd.
    if dur_secs <= qn * (4.0 / 32):
        return (32, 0)
    return best


# ── Notation assembly ─────────────────────────────────────────────────────────

_STAFF_DEFS = {
    "rh": {"id": "rh", "clef": "G2", "label": "Right Hand"},
    "lh": {"id": "lh", "clef": "F4", "label": "Left Hand"},
}


def build_notation(
    wire_notes: list[dict],
    beats: list[dict],
    ts: tuple[int, int] = (4, 4),
    instrument: str = "piano",
) -> dict | None:
    """Build a notation payload from decoded wire notes + song beats.

    Returns ``None`` when there is nothing to lift (no notes or no downbeats).
    """
    if not wire_notes:
        return None
    downbeats = downbeat_times(beats)
    if not downbeats:
        return None

    tempos = measure_tempos(downbeats, ts)
    hands = split_hands(wire_notes)

    # Anacrusis: onsets before the first downbeat get their own pickup
    # measure (sloppak-spec §5.3 `pickup: true`) starting at the earliest
    # such onset, rather than being clamped into measure 1 with beats that
    # precede the measure's own `t`.
    earliest_onset = min(n["t"] for ns in hands.values() for n in ns)
    measure_starts = list(downbeats)
    has_pickup = earliest_onset < downbeats[0] - 1e-6
    if has_pickup:
        measure_starts.insert(0, earliest_onset)
        tempos.insert(0, tempos[0])

    def _measure_index(t: float) -> int:
        return max(0, min(len(measure_starts) - 1, bisect_right(measure_starts, t + 1e-9) - 1))

    def _measure_end(mi: int) -> float | None:
        return measure_starts[mi + 1] if mi + 1 < len(measure_starts) else None

    # Per-hand: resolve each onset group into one beat with a duration,
    # splitting notes that cross a barline into tied continuations — a beat
    # longer than the space left in its measure is unrepresentable in
    # standard notation (e.g. a half note starting on beat 4 of 4/4).
    beats_by_measure: dict[int, dict[str, list[dict]]] = {}

    def _emit(hand: str, mi: int, t: float, dur_secs: float, midis: list[int], tied: bool) -> None:
        bpm = tempos[mi]
        dur, dot = quantize_duration(dur_secs, bpm)
        beat_out: dict = {"t": round(t, 3), "dur": dur}
        if dot:
            beat_out["dot"] = dot
        beat_out["notes"] = [
            {"midi": m, **({"tied": True} if tied else {})} for m in midis
        ]
        beats_by_measure.setdefault(mi, {}).setdefault(hand, []).append(beat_out)

    for hand, notes in hands.items():
        groups = group_simultaneous(notes)
        for gi, group in enumerate(groups):
            t = group[0]["t"]
            mi = _measure_index(t)
            bpm = tempos[mi]

            # Raw duration: longest wire sustain in the group when any is
            # > 0, else the gap to the next onset group in the same hand
            # (last group falls back to one quarter at the local tempo).
            sus = max(n["sus"] for n in group)
            if sus > 0:
                raw = sus
            elif gi + 1 < len(groups):
                raw = groups[gi + 1][0]["t"] - t
            else:
                raw = 60.0 / bpm
            # Sorted, deduplicated pitches (both hands striking the same key
            # at the same instant collapses to one notehead).
            midis = sorted({n["midi"] for n in group})

            # Walk the span across barlines, emitting a tied continuation in
            # each subsequent measure. Tolerance: half a 32nd at the local
            # tempo, so quantization jitter doesn't split clean durations.
            seg_t, remaining, tied = t, raw, False
            while True:
                seg_mi = _measure_index(seg_t)
                end = _measure_end(seg_mi)
                tol = (60.0 / tempos[seg_mi]) * (4.0 / 32) / 2
                if end is None or seg_t + remaining <= end + tol:
                    _emit(hand, seg_mi, seg_t, remaining, midis, tied)
                    break
                _emit(hand, seg_mi, seg_t, end - seg_t, midis, tied)
                remaining -= end - seg_t
                seg_t = end
                tied = True

    used_staves = [s for s in ("rh", "lh") if s in hands]

    measures: list[dict] = []
    num, den = ts
    last_emitted_tempo: float | None = None
    for mi, start in enumerate(measure_starts):
        measure: dict = {"idx": mi + 1, "t": round(start, 3)}
        if mi == 0:
            measure["ts"] = [num, den]
            if has_pickup:
                measure["pickup"] = True
        bpm = tempos[mi]
        if last_emitted_tempo is None or abs(bpm - last_emitted_tempo) > 1.0:
            measure["tempo"] = round(bpm, 2)
            last_emitted_tempo = bpm
        staves_payload: dict[str, dict] = {}
        for staff_id in used_staves:
            staff_beats = beats_by_measure.get(mi, {}).get(staff_id)
            if staff_beats:
                staff_beats.sort(key=lambda b: b["t"])
                staves_payload[staff_id] = {"voices": [{"v": 1, "beats": staff_beats}]}
        measure["staves"] = staves_payload
        measures.append(measure)

    payload = {
        "version": notation_mod.SCHEMA_VERSION,
        "instrument": instrument,
        "staves": [_STAFF_DEFS[s] for s in used_staves],
        "measures": measures,
    }
    ok, reason = notation_mod.validate_notation(payload)
    if not ok:  # importer bug guard — never write a payload the loader drops
        raise ValueError(f"build_notation produced an invalid payload: {reason}")
    return payload