"""Leakage-safe split builders for A1 baseline evaluation protocols."""

from __future__ import annotations

from dataclasses import asdict, dataclass
from typing import Any

import pandas as pd


@dataclass(frozen=True)
class CrossRunFold:
    """One leave-one-run-out fold for Protocol A."""

    protocol: str
    subject: str
    fold_id: str
    test_run: int
    train_runs: str
    n_train_runs: int
    n_test_runs: int


@dataclass(frozen=True)
class WithinRunBlockedSplit:
    """One blocked temporal split with HRF safety gap for Protocol B."""

    protocol: str
    subject: str
    run: int
    split_id: str
    n_volumes: int
    test_start_tr: int
    test_end_tr_exclusive: int
    gap_tr: int
    train_left_start_tr: int
    train_left_end_tr_exclusive: int
    train_right_start_tr: int
    train_right_end_tr_exclusive: int
    n_train_volumes: int
    n_test_volumes: int
    n_gap_excluded_volumes: int


@dataclass(frozen=True)
class WithinRunSkipped:
    """Skipped run when blocked split constraints cannot be satisfied."""

    subject: str
    run: int
    n_volumes: int
    reason: str


def build_cross_run_folds(manifest_df: pd.DataFrame) -> pd.DataFrame:
    """Build Protocol A folds (leave-one-run-out within subject)."""
    if manifest_df.empty:
        return pd.DataFrame()

    required_columns = {"subject", "run"}
    missing = required_columns.difference(manifest_df.columns)
    if missing:
        raise ValueError(f"Manifest missing required columns: {sorted(missing)}")

    rows: list[CrossRunFold] = []

    for subject, subject_df in manifest_df.groupby("subject"):
        runs = sorted({int(run) for run in subject_df["run"].tolist()})
        if len(runs) < 2:
            continue

        for test_run in runs:
            train_runs = [run for run in runs if run != test_run]
            rows.append(
                CrossRunFold(
                    protocol="A_cross_run",
                    subject=str(subject),
                    fold_id=f"{subject}_test_run{test_run}",
                    test_run=int(test_run),
                    train_runs=",".join(str(run) for run in train_runs),
                    n_train_runs=len(train_runs),
                    n_test_runs=1,
                )
            )

    output_df = pd.DataFrame([asdict(row) for row in rows])
    if not output_df.empty:
        output_df = output_df.sort_values(["subject", "test_run"]).reset_index(drop=True)
    return output_df


def _compute_within_run_blocked_bounds(
    n_volumes: int,
    test_fraction: float,
    gap_tr: int,
    min_train_volumes: int,
    min_test_volumes: int,
) -> tuple[dict[str, int] | None, str | None]:
    if n_volumes <= 0:
        return None, "non_positive_volume_count"

    if not (0.0 < test_fraction < 1.0):
        return None, "invalid_test_fraction"

    if gap_tr < 0:
        return None, "negative_gap"

    n_test = max(min_test_volumes, int(round(n_volumes * test_fraction)))
    n_test = min(n_test, n_volumes)

    if n_test >= n_volumes:
        return None, "test_block_covers_entire_run"

    # Center block so train windows exist on both sides when possible.
    test_start = max(0, (n_volumes - n_test) // 2)
    test_end = min(n_volumes, test_start + n_test)

    left_train_start = 0
    left_train_end = max(0, test_start - gap_tr)

    right_train_start = min(n_volumes, test_end + gap_tr)
    right_train_end = n_volumes

    n_train = (left_train_end - left_train_start) + (right_train_end - right_train_start)
    n_gap = (test_start - left_train_end) + (right_train_start - test_end)

    if n_train < min_train_volumes:
        return None, "insufficient_train_volumes_after_gap"

    if n_test < min_test_volumes:
        return None, "insufficient_test_volumes"

    if left_train_end < left_train_start or right_train_end < right_train_start:
        return None, "invalid_train_segment_bounds"

    bounds = {
        "test_start_tr": int(test_start),
        "test_end_tr_exclusive": int(test_end),
        "train_left_start_tr": int(left_train_start),
        "train_left_end_tr_exclusive": int(left_train_end),
        "train_right_start_tr": int(right_train_start),
        "train_right_end_tr_exclusive": int(right_train_end),
        "n_train_volumes": int(n_train),
        "n_test_volumes": int(n_test),
        "n_gap_excluded_volumes": int(n_gap),
    }
    return bounds, None


def build_within_run_blocked_splits(
    manifest_df: pd.DataFrame,
    test_fraction: float = 0.2,
    gap_tr: int = 8,
    min_train_volumes: int = 40,
    min_test_volumes: int = 20,
) -> tuple[pd.DataFrame, pd.DataFrame]:
    """Build Protocol B blocked temporal splits for each subject-run."""
    if manifest_df.empty:
        return pd.DataFrame(), pd.DataFrame()

    required_columns = {"subject", "run", "n_volumes"}
    missing = required_columns.difference(manifest_df.columns)
    if missing:
        raise ValueError(f"Manifest missing required columns: {sorted(missing)}")

    split_rows: list[WithinRunBlockedSplit] = []
    skipped_rows: list[WithinRunSkipped] = []

    for row in manifest_df.itertuples(index=False):
        subject = str(getattr(row, "subject"))
        run = int(getattr(row, "run"))
        n_volumes = int(getattr(row, "n_volumes"))

        bounds, reason = _compute_within_run_blocked_bounds(
            n_volumes=n_volumes,
            test_fraction=test_fraction,
            gap_tr=gap_tr,
            min_train_volumes=min_train_volumes,
            min_test_volumes=min_test_volumes,
        )

        if bounds is None:
            skipped_rows.append(
                WithinRunSkipped(
                    subject=subject,
                    run=run,
                    n_volumes=n_volumes,
                    reason=str(reason),
                )
            )
            continue

        split_rows.append(
            WithinRunBlockedSplit(
                protocol="B_within_run_blocked",
                subject=subject,
                run=run,
                split_id=f"{subject}_run{run}_blocked",
                n_volumes=n_volumes,
                test_start_tr=bounds["test_start_tr"],
                test_end_tr_exclusive=bounds["test_end_tr_exclusive"],
                gap_tr=int(gap_tr),
                train_left_start_tr=bounds["train_left_start_tr"],
                train_left_end_tr_exclusive=bounds["train_left_end_tr_exclusive"],
                train_right_start_tr=bounds["train_right_start_tr"],
                train_right_end_tr_exclusive=bounds["train_right_end_tr_exclusive"],
                n_train_volumes=bounds["n_train_volumes"],
                n_test_volumes=bounds["n_test_volumes"],
                n_gap_excluded_volumes=bounds["n_gap_excluded_volumes"],
            )
        )

    split_df = pd.DataFrame([asdict(row) for row in split_rows])
    skipped_df = pd.DataFrame([asdict(row) for row in skipped_rows])

    if not split_df.empty:
        split_df = split_df.sort_values(["subject", "run"]).reset_index(drop=True)
    if not skipped_df.empty:
        skipped_df = skipped_df.sort_values(["subject", "run"]).reset_index(drop=True)

    return split_df, skipped_df


def summarize_split_counts(
    manifest_df: pd.DataFrame,
    cross_run_df: pd.DataFrame,
    within_run_df: pd.DataFrame,
    within_run_skipped_df: pd.DataFrame,
) -> dict[str, Any]:
    """Return compact split summary for reporting JSON outputs."""
    return {
        "n_manifest_rows": int(len(manifest_df)),
        "n_subjects_manifest": int(manifest_df["subject"].nunique()) if not manifest_df.empty else 0,
        "n_protocol_a_folds": int(len(cross_run_df)),
        "n_protocol_b_splits": int(len(within_run_df)),
        "n_protocol_b_skipped": int(len(within_run_skipped_df)),
    }