from __future__ import annotations

import json
import math
import os
import re
from datetime import datetime, timedelta
from pathlib import Path
from typing import Any

import numpy as np
import pandas as pd


TIMESTAMP_FMT = "%Y%m%d%H%M"
FORMAT_VERSION = 1


def parse_time(value: str | datetime | pd.Timestamp) -> pd.Timestamp:
    if isinstance(value, pd.Timestamp):
        return value
    if isinstance(value, datetime):
        return pd.Timestamp(value)
    value = str(value)
    if len(value) != 12 or not value.isdigit():
        raise ValueError(f"timestamp must be YYYYMMDDHHMM, got {value!r}")
    return pd.Timestamp(datetime.strptime(value, TIMESTAMP_FMT))


def format_time(value: str | datetime | pd.Timestamp) -> str:
    return parse_time(value).strftime(TIMESTAMP_FMT)


def time_offsets(past_minutes: int, interval_minutes: int, include_current: bool = True) -> list[int]:
    if interval_minutes <= 0:
        raise ValueError("interval_minutes must be positive")
    if past_minutes < 0:
        raise ValueError("past_minutes must be non-negative")
    if past_minutes % interval_minutes != 0:
        raise ValueError("past_minutes must be divisible by interval_minutes")
    start = -int(past_minutes)
    stop = 0 if include_current else -int(interval_minutes)
    return list(range(start, stop + 1, int(interval_minutes)))


def future_offsets(future_minutes: int, interval_minutes: int) -> list[int]:
    if interval_minutes <= 0:
        raise ValueError("interval_minutes must be positive")
    if future_minutes <= 0:
        raise ValueError("future_minutes must be positive")
    if future_minutes % interval_minutes != 0:
        raise ValueError("future_minutes must be divisible by interval_minutes")
    return list(range(int(interval_minutes), int(future_minutes) + 1, int(interval_minutes)))


def build_time_grid(time_ranges: list[dict[str, str] | list[str] | tuple[str, str]], interval_minutes: int) -> list[str]:
    all_times: set[str] = set()
    freq = f"{int(interval_minutes)}min"
    for item in time_ranges:
        if isinstance(item, dict):
            start, end = item["start"], item["end"]
        else:
            start, end = item
        start_ts = parse_time(start)
        end_ts = parse_time(end)
        if end_ts < start_ts:
            raise ValueError(f"time range end before start: {start} -> {end}")
        for ts in pd.date_range(start_ts, end_ts, freq=freq):
            all_times.add(format_time(ts))
    return sorted(all_times)


def load_yaml(path: str | Path) -> dict[str, Any]:
    try:
        import yaml
    except ImportError as e:
        raise ImportError("PyYAML is required to read config yaml files") from e
    with Path(path).open("r", encoding="utf-8") as f:
        data = yaml.safe_load(f)
    if not isinstance(data, dict):
        raise ValueError(f"config must be a mapping: {path}")
    return data


def load_stats(path: str | Path | None) -> dict[str, Any]:
    if path is None:
        return {}
    path = Path(path)
    data = np.load(path, allow_pickle=True)
    if getattr(data, "shape", None) == ():
        data = data.item()
    if not isinstance(data, dict):
        raise ValueError(f"statistics file must contain dict: {path}")
    return data


def zscore(arr: np.ndarray, mean: float, std: float, eps: float = 1e-6) -> np.ndarray:
    return (arr - float(mean)) / (float(std) + float(eps))


def inv_zscore(arr: np.ndarray, mean: float, std: float, eps: float = 1e-6) -> np.ndarray:
    return arr * (float(std) + float(eps)) + float(mean)


def source_meta_path(dat_path: str | Path) -> Path:
    path = Path(dat_path)
    return path.with_name(f"{path.stem}_meta.json")


def source_timestamps_path(dat_path: str | Path) -> Path:
    path = Path(dat_path)
    return path.with_name(f"{path.stem}_timestamps.npy")


def source_dat_path(output_root: str | Path, source: str, prefer_nested: bool = True) -> Path:
    """Return the .dat path for a source.

    The preferred layout is ``output_root/source/source.dat``.  For backward
    compatibility, readers can still fall back to the old flat
    ``output_root/source.dat`` layout when the nested file does not exist.
    """

    root = Path(output_root)
    nested = root / str(source) / f"{source}.dat"
    flat = root / f"{source}.dat"
    if prefer_nested:
        if nested.exists() or not flat.exists():
            return nested
        return flat
    if flat.exists() or not nested.exists():
        return flat
    return nested


def source_existing_dat_path(output_root: str | Path, source: str) -> Path:
    root = Path(output_root)
    nested = root / str(source) / f"{source}.dat"
    flat = root / f"{source}.dat"
    if nested.exists():
        return nested
    return flat


def write_json(path: str | Path, payload: dict[str, Any]) -> None:
    path = Path(path)
    path.parent.mkdir(parents=True, exist_ok=True)
    with path.open("w", encoding="utf-8") as f:
        json.dump(payload, f, indent=2, ensure_ascii=False)


def read_json(path: str | Path) -> dict[str, Any]:
    with Path(path).open("r", encoding="utf-8") as f:
        return json.load(f)


def extract_timestamp(path: str | Path) -> str:
    match = re.search(r"(\d{12})", Path(path).name)
    if not match:
        raise ValueError(f"cannot extract timestamp from path: {path}")
    return match.group(1)


def safe_nanmean(arr: np.ndarray) -> float:
    with np.errstate(invalid="ignore"):
        value = np.nanmean(arr)
    return 0.0 if math.isnan(float(value)) else float(value)


def open_memmap(path: str | Path, dtype: str | np.dtype, shape: tuple[int, ...], mode: str = "r+") -> np.memmap:
    return np.memmap(Path(path), dtype=np.dtype(dtype), mode=mode, shape=tuple(int(x) for x in shape))


def append_memmap_rows(
    path: str | Path,
    rows: list[np.ndarray],
    dtype: str | np.dtype,
    row_shape: tuple[int, ...],
    existing_rows: int,
) -> int:
    if not rows:
        return int(existing_rows)

    path = Path(path)
    path.parent.mkdir(parents=True, exist_ok=True)
    dtype = np.dtype(dtype)
    row_shape = tuple(int(x) for x in row_shape)
    old_count = int(existing_rows)
    new_count = old_count + len(rows)
    old_nbytes = old_count * int(np.prod(row_shape)) * dtype.itemsize
    new_nbytes = new_count * int(np.prod(row_shape)) * dtype.itemsize

    with path.open("ab") as f:
        if old_count == 0:
            f.truncate(0)
        elif path.stat().st_size != old_nbytes:
            raise ValueError(f"memmap size mismatch for append: {path}")
        f.truncate(new_nbytes)

    mm = np.memmap(path, dtype=dtype, mode="r+", shape=(new_count, *row_shape))
    for i, row in enumerate(rows, start=old_count):
        mm[i] = np.asarray(row, dtype=dtype)
    mm.flush()
    del mm
    return new_count


def load_timestamp_rows(path: str | Path) -> np.ndarray:
    path = Path(path)
    if not path.exists():
        return np.asarray([], dtype="S12")
    values = np.load(path, allow_pickle=False)
    return np.asarray(values, dtype="S12")


def timestamp_row_count(path: str | Path) -> int:
    return int(len(load_timestamp_rows(path)))


def append_timestamp_rows(path: str | Path, timestamps: list[str], existing_rows: int) -> int:
    if not timestamps:
        return int(existing_rows)

    path = Path(path)
    path.parent.mkdir(parents=True, exist_ok=True)
    old_count = int(existing_rows)
    current = load_timestamp_rows(path)
    if len(current) != old_count:
        raise ValueError(f"timestamp sidecar row count mismatch for append: {path} has {len(current)}, expected {old_count}")

    clean = [format_time(ts) for ts in timestamps]
    appended = np.asarray(clean, dtype="S12")
    merged = np.concatenate([current, appended])
    tmp_path = path.with_name(f".{path.name}.tmp")
    with tmp_path.open("wb") as f:
        np.save(f, merged, allow_pickle=False)
    os.replace(tmp_path, path)
    return int(len(merged))


def status_columns(source: str) -> tuple[str, str]:
    return f"{source}_idx", f"{source}_status"


def default_catalog(times: list[str], sources: list[str]) -> pd.DataFrame:
    df = pd.DataFrame({"timestamp": sorted(times)})
    for source in sources:
        idx_col, status_col = status_columns(source)
        df[idx_col] = pd.Series([pd.NA] * len(df), dtype="Int64")
        df[status_col] = "missing"
    return df


def ensure_catalog_columns(df: pd.DataFrame, sources: list[str]) -> pd.DataFrame:
    if "timestamp" not in df.columns:
        raise ValueError("catalog must have timestamp column")
    out = df.copy()
    out["timestamp"] = out["timestamp"].astype(str)
    for source in sources:
        idx_col, status_col = status_columns(source)
        if idx_col not in out.columns:
            out[idx_col] = pd.Series([pd.NA] * len(out), dtype="Int64")
        else:
            out[idx_col] = out[idx_col].astype("Int64")
        if status_col not in out.columns:
            out[status_col] = "missing"
    return out.sort_values("timestamp").reset_index(drop=True)


def merge_catalog(existing: pd.DataFrame | None, grid: pd.DataFrame, sources: list[str]) -> pd.DataFrame:
    if existing is None:
        return ensure_catalog_columns(grid, sources)
    existing = ensure_catalog_columns(existing, sources)
    grid = ensure_catalog_columns(grid, sources)
    merged = pd.concat([existing, grid], ignore_index=True)
    merged = merged.drop_duplicates(subset=["timestamp"], keep="first")
    return ensure_catalog_columns(merged, sources)


def path_exists(path: str | Path | None) -> bool:
    return bool(path) and Path(path).exists()


def normalize_mode(config: dict[str, Any], default: str = "zscore") -> str:
    return str(config.get("normalization", config.get("normalization_mode", default))).lower()


def as_path_list(value: str | list[str] | tuple[str, ...]) -> list[Path]:
    if isinstance(value, (list, tuple)):
        return [Path(v) for v in value]
    return [Path(value)]


def minutes_to_timedelta(minutes: int) -> timedelta:
    return timedelta(minutes=int(minutes))


def remove_if_exists(path: str | Path) -> None:
    path = Path(path)
    if path.exists():
        os.remove(path)