"""Profile the dataset: shape, target balance, missingness, degenerate columns,
and single-feature leakage suspects. Writes reports/data_profile.md."""
from __future__ import annotations

import numpy as np
import pandas as pd
from sklearn.metrics import roc_auc_score

from src import config
from src.data.load import load_raw, split_xy


def _leakage_suspects(X: pd.DataFrame, y: pd.Series, top: int = 15) -> pd.DataFrame:
    """Rank features by single-feature AUC. Very high values are leakage suspects."""
    rows = []
    yv = y.values
    numeric_cols = X.select_dtypes(include="number").columns
    for col in numeric_cols:
        s = X[col]
        if s.notna().sum() < 50 or s.nunique(dropna=True) < 2:
            continue
        filled = s.fillna(s.median())
        try:
            auc = roc_auc_score(yv, filled.values)
        except ValueError:
            continue
        rows.append((col, max(auc, 1 - auc)))
    out = pd.DataFrame(rows, columns=["feature", "single_feature_auc"])
    return out.sort_values("single_feature_auc", ascending=False).head(top)


def main() -> None:
    config.ensure_dirs()
    df = load_raw()
    X, y = split_xy(df)

    n_rows, n_feats = X.shape
    pos = int(y.sum())
    neg = int((y == 0).sum())
    pos_rate = pos / len(y)

    miss = X.isna().mean().sort_values(ascending=False)
    high_miss_90 = int((miss > 0.90).sum())
    high_miss_50 = int((miss > 0.50).sum())

    nunique = X.nunique(dropna=True)
    constant = int((nunique <= 1).sum())
    near_constant = int(((nunique > 1) & (nunique <= 2)).sum())

    # duplicate columns (by content hash over a sample of rows for speed)
    sample = X.head(2000).fillna(-999_999)
    hashes = {}
    dup = 0
    for col in sample.columns:
        h = pd.util.hash_pandas_object(sample[col], index=False).sum()
        if h in hashes:
            dup += 1
        else:
            hashes[h] = col

    leak = _leakage_suspects(X, y)

    known_present = [f for f in config.KNOWN_IMPORTANT if f in X.columns]
    known_miss = X[known_present].isna().mean().round(3)

    lines = []
    lines.append("# Data Profile — MuleGuard\n")
    lines.append("## Shape & Target\n")
    lines.append(f"- **Rows (accounts):** {n_rows:,}")
    lines.append(f"- **Features:** {n_feats:,}  (target `{config.TARGET}` separated)")
    lines.append(f"- **Class balance:** {neg:,} legit (0) vs **{pos} mule (1)**")
    lines.append(f"- **Positive rate:** {pos_rate:.4%}  → extreme imbalance")
    lines.append(f"- **Implication:** optimize **PR-AUC / recall@precision / F2**, never accuracy.\n")

    lines.append("## Missingness\n")
    lines.append(f"- Mean missing fraction across features: **{miss.mean():.2%}**")
    lines.append(f"- Features >90% missing: **{high_miss_90}**")
    lines.append(f"- Features >50% missing: **{high_miss_50}**")
    lines.append(f"- Most-missing features: {', '.join(f'{c} ({m:.0%})' for c, m in miss.head(5).items())}\n")

    lines.append("## Degenerate Columns\n")
    lines.append(f"- Constant (≤1 unique value): **{constant}**")
    lines.append(f"- Near-constant (≤2 unique values): **{near_constant}**")
    lines.append(f"- Duplicate columns (sampled): **~{dup}**\n")

    lines.append("## Leakage Suspects (single-feature AUC)\n")
    lines.append("High single-feature AUC on a rare target warrants review before trusting it.\n")
    lines.append("| Feature | Single-feature AUC |")
    lines.append("|---|---|")
    for _, r in leak.iterrows():
        lines.append(f"| {r.feature} | {r.single_feature_auc:.3f} |")
    lines.append("")

    lines.append("## Bank-flagged High-signal Features\n")
    lines.append(f"- Present in data: **{len(known_present)}/{len(config.KNOWN_IMPORTANT)}**")
    lines.append("| Feature | Missing % |")
    lines.append("|---|---|")
    for f, m in known_miss.items():
        lines.append(f"| {f} | {m:.1%} |")
    lines.append("")

    lines.append("## Recommendations\n")
    lines.append("1. Drop constant/duplicate/>90%-missing columns before selection.")
    lines.append("2. Median-impute + add missingness flags (missing-not-at-random may be predictive).")
    lines.append("3. Retain bank-flagged features as domain priors unless flagged leaky above.")
    lines.append("4. Use repeated stratified CV; report mean ± std.")
    lines.append("5. Review the top leakage suspects manually before including them.\n")

    out = config.REPORTS_DIR / "data_profile.md"
    out.write_text("\n".join(lines))
    print(f"Wrote {out}")
    print(f"Rows={n_rows} Feats={n_feats} Pos={pos} ({pos_rate:.4%}) "
          f"Constant={constant} Dup~{dup} HighMiss90={high_miss_90}")


if __name__ == "__main__":
    main()