"""Segment effort detection.

Matches GPS tracks against stored segment polylines and produces SegmentEffort
records.  Works from either a live ParsedActivity (ingest path) or from a
stored timeseries JSON (retroactive path).
"""

from __future__ import annotations

import math
from dataclasses import dataclass, field
from datetime import datetime, timedelta, timezone
from pathlib import Path
from typing import Optional

from bincio.segments.models import Segment, SegmentEffort

# ── tuning constants ──────────────────────────────────────────────────────────

MATCH_RADIUS_M = 25          # max distance to segment start/end to open/close an effort
CONFORMANCE_MAX_DEV_M = 50   # max allowed deviation for each interior segment point
CONFORMANCE_MAX_FRAC = 0.30  # max fraction of interior points allowed to deviate

# ── fast distance approximation ───────────────────────────────────────────────

_R = 6_371_000.0  # Earth radius in metres


def _dist(lat1: float, lon1: float, lat2: float, lon2: float) -> float:
    """Equirectangular approximation — fast, accurate to <0.1% within 100 km."""
    dlat = math.radians(lat2 - lat1)
    dlon = math.radians(lon2 - lon1)
    mlat = math.radians((lat1 + lat2) / 2.0)
    return math.hypot(dlat * _R, dlon * _R * math.cos(mlat))


# ── activity track representation ────────────────────────────────────────────

@dataclass
class ActivityTrack:
    """Common internal representation for detection, independent of source format."""
    activity_id: str
    sport: str
    started_at: datetime
    # Parallel arrays — all same length, GPS-only points (lat/lon not None).
    lats: list[float]
    lons: list[float]
    times: list[int]       # seconds from started_at
    speeds: list[Optional[float]]
    hrs: list[Optional[int]]
    powers: list[Optional[int]]
    bbox: list[float] = field(default_factory=list)  # [lon_min, lat_min, lon_max, lat_max]

    def __post_init__(self) -> None:
        if self.lats and not self.bbox:
            self.bbox = [
                min(self.lons), min(self.lats),
                max(self.lons), max(self.lats),
            ]


def track_from_parsed(parsed: "ParsedActivity", activity_id: str) -> Optional[ActivityTrack]:  # noqa: F821
    """Build an ActivityTrack from a ParsedActivity (used during ingest)."""
    lats, lons, times, speeds, hrs, powers = [], [], [], [], [], []
    last_t = -1
    for p in parsed.points:
        if p.lat is None or p.lon is None:
            continue
        t = int((p.timestamp - parsed.started_at).total_seconds())
        if t < 0 or t == last_t:
            continue
        last_t = t
        lats.append(p.lat)
        lons.append(p.lon)
        times.append(t)
        speeds.append(p.speed_kmh)
        hrs.append(p.hr_bpm)
        powers.append(p.power_w)
    if len(lats) < 2:
        return None
    return ActivityTrack(
        activity_id=activity_id,
        sport=parsed.sport,
        started_at=parsed.started_at,
        lats=lats, lons=lons, times=times,
        speeds=speeds, hrs=hrs, powers=powers,
    )


def track_from_timeseries_json(
    ts: dict,
    activity_id: str,
    sport: str,
    started_at: datetime,
) -> Optional[ActivityTrack]:
    """Build an ActivityTrack from a stored timeseries JSON dict."""
    raw_lats = ts.get("lat") or []
    raw_lons = ts.get("lon") or []
    raw_t    = ts.get("t") or []
    raw_spd  = ts.get("speed_kmh") or []
    raw_hr   = ts.get("hr_bpm") or []
    raw_pwr  = ts.get("power_w") or []
    n = len(raw_t)
    if n < 2 or not raw_lats or len(raw_lats) != n:
        return None

    def _pad(arr: list, length: int) -> list:
        return arr + [None] * (length - len(arr))

    raw_spd = _pad(raw_spd, n)
    raw_hr  = _pad(raw_hr,  n)
    raw_pwr = _pad(raw_pwr, n)

    lats, lons, times, speeds, hrs, powers = [], [], [], [], [], []
    for i in range(n):
        if raw_lats[i] is None or raw_lons[i] is None:
            continue
        lats.append(float(raw_lats[i]))
        lons.append(float(raw_lons[i]))
        times.append(int(raw_t[i]))
        speeds.append(raw_spd[i])
        hrs.append(raw_hr[i])
        powers.append(raw_pwr[i])

    if len(lats) < 2:
        return None
    return ActivityTrack(
        activity_id=activity_id,
        sport=sport,
        started_at=started_at,
        lats=lats, lons=lons, times=times,
        speeds=speeds, hrs=hrs, powers=powers,
    )


# ── effort metric helpers ─────────────────────────────────────────────────────

def _avg_nonnull(vals: list, lo: int, hi: int) -> Optional[float]:
    nums = [v for v in vals[lo:hi + 1] if v is not None]
    return sum(nums) / len(nums) if nums else None


def _np_power(powers: list[Optional[int]], lo: int, hi: int) -> Optional[int]:
    """Coggan NP from a slice of 1Hz power data (may have gaps/nulls)."""
    WIN = 30
    chunk = powers[lo:hi + 1]
    filled = [v if v is not None else 0 for v in chunk]
    n = len(filled)
    if n < WIN:
        # Too short for rolling average — just return avg power.
        non_null = [v for v in chunk if v is not None]
        return int(round(sum(non_null) / len(non_null))) if non_null else None
    half = WIN // 2
    window_sum = sum(filled[:WIN])
    fourth_powers = []
    for i in range(half, n - half):
        fourth_powers.append((window_sum / WIN) ** 4)
        if i + half + 1 < n:
            window_sum += filled[i + half + 1] - filled[i - half]
    if not fourth_powers:
        return None
    return int(round((sum(fourth_powers) / len(fourth_powers)) ** 0.25))


# ── detection algorithm ───────────────────────────────────────────────────────

def _bboxes_overlap(a: list[float], b: list[float]) -> bool:
    return not (a[2] < b[0] or b[2] < a[0] or a[3] < b[1] or b[3] < a[1])


def _conformance_ok(
    track: ActivityTrack,
    seg: Segment,
    i: int,
    j: int,
) -> bool:
    """Check that the track slice [i..j] follows the segment polyline."""
    interior = seg.polyline[1:-1]
    if not interior:
        return True  # trivial 2-point segment
    failing = 0
    for sp in interior:
        slat, slon = sp[0], sp[1]
        min_d = min(
            _dist(slat, slon, track.lats[k], track.lons[k])
            for k in range(i, j + 1)
        )
        if min_d > CONFORMANCE_MAX_DEV_M:
            failing += 1
    return (failing / len(interior)) <= CONFORMANCE_MAX_FRAC


def _extract_effort(
    track: ActivityTrack,
    seg: Segment,
    i: int,
    j: int,
) -> SegmentEffort:
    elapsed_s = track.times[j] - track.times[i]
    started_at = track.started_at + timedelta(seconds=track.times[i])
    avg_speed = _avg_nonnull(track.speeds, i, j)
    avg_hr_raw = _avg_nonnull(track.hrs, i, j)
    avg_hr = int(round(avg_hr_raw)) if avg_hr_raw is not None else None
    avg_pwr_raw = _avg_nonnull(track.powers, i, j)
    avg_pwr = int(round(avg_pwr_raw)) if avg_pwr_raw is not None else None
    np_pwr = _np_power(track.powers, i, j) if any(v is not None for v in track.powers[i:j + 1]) else None
    return SegmentEffort(
        activity_id=track.activity_id,
        started_at=started_at,
        elapsed_s=max(1, elapsed_s),
        avg_speed_kmh=round(avg_speed, 2) if avg_speed is not None else None,
        avg_hr_bpm=avg_hr,
        avg_power_w=avg_pwr,
        np_power_w=np_pwr,
        detected_at=datetime.now(timezone.utc),
    )


def detect_one(track: ActivityTrack, seg: Segment) -> list[SegmentEffort]:
    """Return all matching efforts for a single segment against a track."""
    if not track.bbox or not _bboxes_overlap(track.bbox, seg.bbox):
        return []
    if seg.sport and seg.sport != track.sport:
        return []

    seg_start_lat, seg_start_lon = seg.polyline[0][0], seg.polyline[0][1]
    seg_end_lat,   seg_end_lon   = seg.polyline[-1][0], seg.polyline[-1][1]
    n = len(track.lats)
    efforts: list[SegmentEffort] = []

    search_from = 0
    while search_from < n - 1:
        # Find next start candidate from search_from.
        start_idx = None
        for i in range(search_from, n):
            if _dist(seg_start_lat, seg_start_lon, track.lats[i], track.lons[i]) <= MATCH_RADIUS_M:
                start_idx = i
                break
        if start_idx is None:
            break

        # Scan forward from start_idx for an end candidate.
        end_idx = None
        for j in range(start_idx + 1, n):
            if _dist(seg_end_lat, seg_end_lon, track.lats[j], track.lons[j]) <= MATCH_RADIUS_M:
                end_idx = j
                break

        if end_idx is None:
            # No end found — no more efforts possible starting at or after start_idx.
            break

        if _conformance_ok(track, seg, start_idx, end_idx):
            efforts.append(_extract_effort(track, seg, start_idx, end_idx))
            search_from = end_idx + 1
        else:
            # Conformance failed; try next start candidate after start_idx.
            search_from = start_idx + 1

    return efforts


def detect_all(
    track: ActivityTrack,
    handle: str,
    data_dir: Path,
) -> int:
    """Detect efforts for all segments and persist them. Returns effort count."""
    from bincio.segments import store as _store

    segments = _store.list_segments(data_dir)
    total = 0
    for seg in segments:
        efforts = detect_one(track, seg)
        for effort in efforts:
            _store.add_effort(data_dir, handle, seg.id, effort)
        total += len(efforts)
    return total