"""Read/write segments and segment efforts to/from /var/bincio."""

from __future__ import annotations

import hashlib
import json
import re
from datetime import datetime, timezone
from pathlib import Path
from typing import Optional

from bincio.segments.models import Segment, SegmentEffort

# /var/bincio/segments/{id}.json
_SEGMENTS_DIR = "segments"
# /var/bincio/data/{handle}/segment_efforts/{segment_id}.json
_EFFORTS_SUBDIR = "segment_efforts"


# ── helpers ───────────────────────────────────────────────────────────────────

def _segments_dir(data_dir: Path) -> Path:
    d = data_dir / _SEGMENTS_DIR
    d.mkdir(parents=True, exist_ok=True)
    return d


def _efforts_dir(data_dir: Path, handle: str) -> Path:
    d = data_dir / handle / _EFFORTS_SUBDIR
    d.mkdir(parents=True, exist_ok=True)
    return d


def _slugify(name: str) -> str:
    s = name.lower().strip()
    s = re.sub(r"[^a-z0-9]+", "-", s)
    return s.strip("-")[:48]


def _make_id(name: str) -> str:
    slug = _slugify(name)
    suffix = hashlib.sha256(name.encode()).hexdigest()[:4]
    return f"{slug}-{suffix}"


def _dt(s: str) -> datetime:
    return datetime.fromisoformat(s.replace("Z", "+00:00"))


def _iso(dt: datetime) -> str:
    return dt.astimezone(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")


# ── serialisation ─────────────────────────────────────────────────────────────

def _segment_to_dict(seg: Segment) -> dict:
    return {
        "id":          seg.id,
        "name":        seg.name,
        "sport":       seg.sport,
        "polyline":    seg.polyline,
        "distance_m":  round(seg.distance_m, 1),
        "bbox":        [round(v, 6) for v in seg.bbox],
        "created_by":  seg.created_by,
        "created_at":  _iso(seg.created_at),
    }


def _segment_from_dict(d: dict) -> Segment:
    return Segment(
        id=d["id"],
        name=d["name"],
        sport=d.get("sport"),
        polyline=d["polyline"],
        distance_m=float(d["distance_m"]),
        bbox=d["bbox"],
        created_by=d["created_by"],
        created_at=_dt(d["created_at"]),
    )


def _effort_to_dict(e: SegmentEffort) -> dict:
    return {
        "activity_id":   e.activity_id,
        "started_at":    _iso(e.started_at),
        "elapsed_s":     e.elapsed_s,
        "avg_speed_kmh": e.avg_speed_kmh,
        "avg_hr_bpm":    e.avg_hr_bpm,
        "avg_power_w":   e.avg_power_w,
        "np_power_w":    e.np_power_w,
        "detected_at":   _iso(e.detected_at),
    }


def _effort_from_dict(d: dict) -> SegmentEffort:
    return SegmentEffort(
        activity_id=d["activity_id"],
        started_at=_dt(d["started_at"]),
        elapsed_s=int(d["elapsed_s"]),
        avg_speed_kmh=d.get("avg_speed_kmh"),
        avg_hr_bpm=d.get("avg_hr_bpm"),
        avg_power_w=d.get("avg_power_w"),
        np_power_w=d.get("np_power_w"),
        detected_at=_dt(d["detected_at"]),
    )


# ── public API ────────────────────────────────────────────────────────────────

def make_segment_id(name: str) -> str:
    return _make_id(name)


def save_segment(data_dir: Path, seg: Segment) -> None:
    path = _segments_dir(data_dir) / f"{seg.id}.json"
    path.write_text(json.dumps(_segment_to_dict(seg), ensure_ascii=False, indent=2), encoding="utf-8")


def load_segment(data_dir: Path, segment_id: str) -> Optional[Segment]:
    path = _segments_dir(data_dir) / f"{segment_id}.json"
    if not path.exists():
        return None
    return _segment_from_dict(json.loads(path.read_text(encoding="utf-8")))


def delete_segment(data_dir: Path, segment_id: str) -> bool:
    path = _segments_dir(data_dir) / f"{segment_id}.json"
    if not path.exists():
        return False
    path.unlink()
    return True


def list_segments(data_dir: Path, bbox: Optional[list[float]] = None) -> list[Segment]:
    """Return all segments, optionally filtered to those overlapping bbox.

    bbox = [lon_min, lat_min, lon_max, lat_max]
    """
    segs = []
    for path in sorted(_segments_dir(data_dir).glob("*.json")):
        try:
            seg = _segment_from_dict(json.loads(path.read_text(encoding="utf-8")))
        except Exception:
            continue
        if bbox is not None and not _bboxes_overlap(seg.bbox, bbox):
            continue
        segs.append(seg)
    return segs


def _bboxes_overlap(a: list[float], b: list[float]) -> bool:
    """True if two [lon_min, lat_min, lon_max, lat_max] boxes overlap."""
    return not (a[2] < b[0] or b[2] < a[0] or a[3] < b[1] or b[3] < a[1])


# ── efforts ───────────────────────────────────────────────────────────────────

def load_efforts(data_dir: Path, handle: str, segment_id: str) -> list[SegmentEffort]:
    path = _efforts_dir(data_dir, handle) / f"{segment_id}.json"
    if not path.exists():
        return []
    try:
        return [_effort_from_dict(d) for d in json.loads(path.read_text(encoding="utf-8"))]
    except Exception:
        return []


def save_efforts(data_dir: Path, handle: str, segment_id: str, efforts: list[SegmentEffort]) -> None:
    path = _efforts_dir(data_dir, handle) / f"{segment_id}.json"
    data = [_effort_to_dict(e) for e in efforts]
    path.write_text(json.dumps(data, ensure_ascii=False, indent=2), encoding="utf-8")


def add_effort(data_dir: Path, handle: str, segment_id: str, effort: SegmentEffort) -> None:
    """Append an effort, replacing any existing effort with the same activity + start time."""
    efforts = load_efforts(data_dir, handle, segment_id)
    key = (effort.activity_id, _iso(effort.started_at))
    efforts = [e for e in efforts if (e.activity_id, _iso(e.started_at)) != key]
    efforts.append(effort)
    efforts.sort(key=lambda e: e.started_at, reverse=True)
    save_efforts(data_dir, handle, segment_id, efforts)