import csv
import gzip
import json
import math
from datetime import datetime, timezone
from pathlib import Path
from typing import Any

import numpy as np

from .config import LTTB_MAX_PTS


def _lttb(points: list[dict], max_pts: int) -> list[dict]:
    """Largest Triangle Three Buckets downsampling."""
    n = len(points)
    if n <= max_pts:
        return points
    ts = np.array([p["t"] for p in points], dtype=float)
    vs = np.array([p["v"] if isinstance(p["v"], (int, float)) else 0.0 for p in points], dtype=float)
    bucket_size = (n - 2) / (max_pts - 2)
    out = [points[0]]
    a = 0
    for i in range(max_pts - 2):
        avg_start = int((i + 1) * bucket_size) + 1
        avg_end = min(int((i + 2) * bucket_size) + 1, n)
        avg_t = np.mean(ts[avg_start:avg_end])
        avg_v = np.mean(vs[avg_start:avg_end])
        rng_start = int(i * bucket_size) + 1
        rng_end = min(int((i + 1) * bucket_size) + 1, n)
        max_area = -1.0
        best = rng_start
        at, av = ts[a], vs[a]
        for j in range(rng_start, rng_end):
            area = abs((at - avg_t) * (vs[j] - av) - (ts[j] - at) * (avg_v - av)) * 0.5
            if area > max_area:
                max_area = area
                best = j
        out.append(points[best])
        a = best
    out.append(points[-1])
    return out


def _ts_to_epoch(ts_str: str) -> float:
    """Parse 'YYYY-MM-DD HH:MM:SS.ffffff' → epoch seconds."""
    for fmt in ("%Y-%m-%d %H:%M:%S.%f", "%Y-%m-%d %H:%M:%S"):
        try:
            dt = datetime.strptime(ts_str.strip(), fmt).replace(tzinfo=timezone.utc)
            return dt.timestamp()
        except ValueError:
            continue
    return 0.0


def _read_nav_log(nav_log_path: Path) -> dict[str, list[dict]]:
    """Read long-format navigation_log.csv → dict of signal arrays."""
    signals: dict[str, list] = {}
    wanted = {"Yaw", "Heading", "Roll", "Pitch", "BattVoltage", "gps_fix",
              "Armed", "Mode", "M1", "M2"}
    with open(nav_log_path, newline="", encoding="utf-8") as f:
        reader = csv.reader(f)
        next(reader, None)  # skip header
        for row in reader:
            if len(row) < 3:
                continue
            ts_str, field, val = row[0], row[1], row[2]
            if field not in wanted:
                continue
            t = _ts_to_epoch(ts_str)
            try:
                v: Any = float(val)
            except ValueError:
                v = val.strip()
            signals.setdefault(field, []).append({"t": t, "v": v})
    return signals


def _read_usbl_csv(usbl_csv_path: Path) -> dict[str, list[dict]]:
    """Read combined_usbl.csv → Dist and Azimuth signal arrays."""
    dist_pts, az_pts = [], []
    with open(usbl_csv_path, newline="", encoding="utf-8") as f:
        reader = csv.DictReader(f)
        for row in reader:
            try:
                t = _ts_to_epoch(row["Timestamp"])
                d = float(row["Dist"]) if row["Dist"] else None
                az = float(row["Azimuth"]) if row["Azimuth"] else None
            except (KeyError, ValueError):
                continue
            if d is not None and not math.isnan(d):
                dist_pts.append({"t": t, "v": d})
            if az is not None and not math.isnan(az):
                az_pts.append({"t": t, "v": az})
    return {"usbl_dist": dist_pts, "usbl_angle": az_pts}


def _read_mcap_signals(mcap_json_path: Path) -> dict[str, list[dict]]:
    """Read mcap_signals.json → depth, motors M1-M6, state signals."""
    with open(mcap_json_path) as f:
        data = json.load(f)
    signals: dict[str, list[dict]] = {}

    def _unpack(key: str, series: list):
        pts = []
        for item in series:
            t = item.get("t_ms", item.get("t", 0))
            if isinstance(t, (int, float)) and t > 1e9:
                t = t / 1000.0  # ms → s
            pts.append({"t": float(t), "v": item.get("v", item.get("value", 0))})
        signals[key] = pts

    if "depth" in data:
        _unpack("depth", data["depth"])
    if "pwm_auv" in data:
        for m_key, series in data["pwm_auv"].items():
            _unpack(m_key.lower(), series)
    if "state" in data:
        _unpack("arm_status", data["state"])
    # New signals added by extended extract_mcap_signals.py
    for key in ("pitch", "roll", "yaw", "altitude", "battery_v", "obstacle_dist"):
        if key in data:
            _unpack(key, data[key])
    return signals


def write_usv_json(
    nav_log_path: Path,
    usbl_csv_path: Path | None,
    output_path: Path,
    sortie_id: str,
    date: str,
) -> None:
    signals = _read_nav_log(nav_log_path)
    if usbl_csv_path and usbl_csv_path.exists():
        signals.update(_read_usbl_csv(usbl_csv_path))

    t_all = [p["t"] for pts in signals.values() for p in pts if pts]
    meta = {
        "sortie": sortie_id,
        "date": date,
        "vehicle": "USV",
        "t_start": min(t_all) if t_all else 0,
        "t_end": max(t_all) if t_all else 0,
    }

    downsampled = {k: _lttb(v, LTTB_MAX_PTS) for k, v in signals.items()}
    payload = json.dumps({"meta": meta, "signals": downsampled}).encode()
    output_path.parent.mkdir(parents=True, exist_ok=True)
    with gzip.open(output_path, "wb") as f:
        f.write(payload)


def write_auv_json(
    mcap_json_path: Path,
    output_path: Path,
    auv_id: str,
    sortie_id: str,
    date: str,
) -> None:
    signals = _read_mcap_signals(mcap_json_path)
    t_all = [p["t"] for pts in signals.values() for p in pts if pts]
    meta = {
        "sortie": sortie_id,
        "date": date,
        "vehicle": auv_id,
        "t_start": min(t_all) if t_all else 0,
        "t_end": max(t_all) if t_all else 0,
    }
    downsampled = {k: _lttb(v, LTTB_MAX_PTS) for k, v in signals.items()}
    payload = json.dumps({"meta": meta, "signals": downsampled}).encode()
    output_path.parent.mkdir(parents=True, exist_ok=True)
    with gzip.open(output_path, "wb") as f:
        f.write(payload)