from __future__ import annotations

from pathlib import Path
from typing import Any, Iterable

import pandas as pd


TIMESTAMP_NAME_HINTS = ("timestamp", "time", "date", "datetime", "ds")


def _resolve_file_path(file_obj: Any) -> Path:
    if file_obj is None:
        raise ValueError("No file provided.")

    if isinstance(file_obj, (str, Path)):
        return Path(file_obj)

    if isinstance(file_obj, dict):
        maybe_path = file_obj.get("path") or file_obj.get("name")
        if maybe_path:
            return Path(maybe_path)

    maybe_name = getattr(file_obj, "name", None)
    if maybe_name:
        return Path(maybe_name)

    raise ValueError("Unsupported file object type.")


def load_timeseries_from_file(file_obj: Any) -> pd.DataFrame:
    file_path = _resolve_file_path(file_obj)
    suffix = file_path.suffix.lower()

    if suffix == ".csv":
        df = pd.read_csv(file_path)
    elif suffix in {".xlsx", ".xls"}:
        df = pd.read_excel(file_path)
    else:
        raise ValueError(f"Unsupported file extension: {suffix}")

    if df.empty:
        raise ValueError("Uploaded file is empty.")

    df.columns = [str(col).strip() for col in df.columns]

    timestamp_col = detect_timestamp_column(df)
    if timestamp_col:
        df[timestamp_col] = pd.to_datetime(df[timestamp_col], errors="coerce")

    return df


def detect_timestamp_column(df: pd.DataFrame) -> str | None:
    for col in df.columns:
        if pd.api.types.is_datetime64_any_dtype(df[col]):
            return col

    for col in df.columns:
        normalized = str(col).strip().lower()
        if any(hint in normalized for hint in TIMESTAMP_NAME_HINTS):
            parsed = pd.to_datetime(df[col], errors="coerce")
            if parsed.notna().mean() >= 0.7:
                return col

    for col in df.columns:
        series = df[col]
        if pd.api.types.is_numeric_dtype(series):
            continue
        parsed = pd.to_datetime(series, errors="coerce")
        if parsed.notna().mean() >= 0.9:
            return col

    return None


def detect_numeric_columns(df: pd.DataFrame, exclude: Iterable[str] | None = None) -> list[str]:
    excluded = set(exclude or [])
    numeric_cols: list[str] = []
    for col in df.columns:
        if col in excluded:
            continue
        if pd.api.types.is_numeric_dtype(df[col]):
            numeric_cols.append(col)
    return numeric_cols


def infer_frequency(df: pd.DataFrame, timestamp_col: str | None) -> str | None:
    if not timestamp_col or timestamp_col not in df.columns:
        return None

    timestamps = pd.to_datetime(df[timestamp_col], errors="coerce").dropna().sort_values()
    timestamps = timestamps.drop_duplicates()
    if len(timestamps) < 3:
        return None

    inferred = pd.infer_freq(timestamps)
    if inferred:
        return inferred

    deltas = timestamps.diff().dropna()
    if deltas.empty:
        return None

    mode_delta = deltas.mode()
    if mode_delta.empty:
        return None

    try:
        return pd.tseries.frequencies.to_offset(mode_delta.iloc[0]).freqstr
    except ValueError:
        return None


def validate_timeseries(
    df: pd.DataFrame,
    timestamp_col: str | None = None,
    target_cols: list[str] | None = None,
    min_length: int = 20,
) -> dict[str, Any]:
    report: dict[str, Any] = {
        "is_valid": True,
        "errors": [],
        "warnings": [],
        "timestamp_column": timestamp_col,
        "target_columns": target_cols or [],
        "missing_summary": {},
        "inferred_frequency": None,
    }

    if df.empty:
        report["errors"].append("Dataset is empty.")
        report["is_valid"] = False
        return report

    timestamp_col = timestamp_col or detect_timestamp_column(df)
    report["timestamp_column"] = timestamp_col

    if not timestamp_col:
        report["errors"].append("Could not detect a timestamp column.")
    elif timestamp_col not in df.columns:
        report["errors"].append(f"Timestamp column '{timestamp_col}' not found.")
    else:
        ts = pd.to_datetime(df[timestamp_col], errors="coerce")
        invalid_rate = 1.0 - ts.notna().mean()
        if invalid_rate > 0:
            report["warnings"].append(
                f"{invalid_rate:.1%} of timestamp values could not be parsed."
            )

        inferred = infer_frequency(df, timestamp_col)
        report["inferred_frequency"] = inferred
        if not inferred:
            report["warnings"].append(
                "Could not infer a regular frequency; forecasting still runs with best effort."
            )
        else:
            sorted_ts = ts.dropna().sort_values().drop_duplicates()
            if len(sorted_ts) >= 3:
                diffs = sorted_ts.diff().dropna()
                if diffs.nunique() > 1:
                    report["warnings"].append(
                        "Timestamp intervals are irregular; model accuracy may degrade."
                    )

    if target_cols is None:
        target_cols = detect_numeric_columns(df, exclude=[timestamp_col] if timestamp_col else None)
    report["target_columns"] = target_cols

    if not target_cols:
        report["errors"].append("No numeric target columns found.")
    else:
        for col in target_cols:
            if col not in df.columns:
                report["errors"].append(f"Target column '{col}' not found.")
                continue
            missing = int(df[col].isna().sum())
            report["missing_summary"][col] = missing
            if missing > 0:
                report["warnings"].append(
                    f"Target '{col}' contains {missing} missing values (interpolation suggested)."
                )

    if len(df) < min_length:
        report["warnings"].append(
            f"Series length ({len(df)}) is short; {min_length}+ points is recommended."
        )

    if report["errors"]:
        report["is_valid"] = False

    return report


def format_validation_report(report: dict[str, Any]) -> str:
    lines: list[str] = []
    status = "Valid" if report.get("is_valid") else "Invalid"
    lines.append(f"Status: {status}")

    timestamp_col = report.get("timestamp_column")
    target_cols = report.get("target_columns", [])
    freq = report.get("inferred_frequency") or "Unknown"

    lines.append(f"Timestamp column: {timestamp_col or 'Not detected'}")
    lines.append(f"Targets: {', '.join(target_cols) if target_cols else 'None'}")
    lines.append(f"Inferred frequency: {freq}")

    errors = report.get("errors", [])
    warnings = report.get("warnings", [])

    if errors:
        lines.append("Errors:")
        lines.extend(f"- {msg}" for msg in errors)

    if warnings:
        lines.append("Warnings:")
        lines.extend(f"- {msg}" for msg in warnings)

    return "\n".join(lines)


def preprocess_for_model(
    df: pd.DataFrame,
    model_name: str,
    prediction_length: int,
    timestamp_col: str | None = None,
    target_cols: list[str] | None = None,
    interpolate_missing: bool = True,
) -> dict[str, Any]:
    timestamp_col = timestamp_col or detect_timestamp_column(df)
    if not timestamp_col:
        raise ValueError("Timestamp column is required for preprocessing.")

    if target_cols is None or len(target_cols) == 0:
        target_cols = detect_numeric_columns(df, exclude=[timestamp_col])

    if not target_cols:
        raise ValueError("At least one numeric target column is required.")

    prepared = df.copy()
    prepared[timestamp_col] = pd.to_datetime(prepared[timestamp_col], errors="coerce")
    prepared = prepared.dropna(subset=[timestamp_col])
    prepared = prepared.sort_values(timestamp_col)

    for col in target_cols:
        prepared[col] = pd.to_numeric(prepared[col], errors="coerce")

    if interpolate_missing:
        prepared[target_cols] = prepared[target_cols].interpolate(limit_direction="both")
        prepared[target_cols] = prepared[target_cols].ffill().bfill()

    if prepared[target_cols].isna().any().any():
        raise ValueError("Target columns still contain NaN values after preprocessing.")

    frequency = infer_frequency(prepared, timestamp_col)

    context_df = prepared[[timestamp_col, *target_cols]].copy()
    context_df = context_df.set_index(timestamp_col)

    return {
        "model_name": model_name,
        "context": context_df,
        "timestamp_col": timestamp_col,
        "target_cols": target_cols,
        "frequency": frequency,
        "prediction_length": prediction_length,
        "is_multivariate": len(target_cols) > 1,
    }


def generate_future_index(
    last_timestamp: pd.Timestamp,
    prediction_length: int,
    frequency: str | None,
) -> pd.DatetimeIndex:
    freq = frequency or "D"
    try:
        return pd.date_range(start=last_timestamp, periods=prediction_length + 1, freq=freq)[1:]
    except ValueError:
        return pd.date_range(start=last_timestamp, periods=prediction_length + 1, freq="D")[1:]