#!/usr/bin/env python3
"""CSV deduplication CLI — configurable key columns, summary report."""
from __future__ import annotations

import argparse
import csv
import sys
from pathlib import Path


def dedup(rows: list[dict], keys: list[str]) -> tuple[list[dict], int]:
    seen: set[tuple] = set()
    out: list[dict] = []
    removed = 0
    for row in rows:
        sig = tuple(row.get(k, "") for k in keys)
        if sig in seen:
            removed += 1
            continue
        seen.add(sig)
        out.append(row)
    return out, removed


def main() -> int:
    p = argparse.ArgumentParser(
        description="Deduplicate CSV rows by configurable column keys and write a summary."
    )
    p.add_argument("input", type=Path, help="Input CSV path")
    p.add_argument("-o", "--output", type=Path, required=True, help="Output CSV path")
    p.add_argument(
        "-k",
        "--keys",
        required=True,
        help="Comma-separated column names used as the dedup key",
    )
    p.add_argument(
        "--summary",
        type=Path,
        default=None,
        help="Optional path for a text summary report (default: stdout)",
    )
    args = p.parse_args()
    keys = [k.strip() for k in args.keys.split(",") if k.strip()]
    if not keys:
        print("error: at least one key column required", file=sys.stderr)
        return 2

    with args.input.open(newline="", encoding="utf-8") as f:
        reader = csv.DictReader(f)
        if not reader.fieldnames:
            print("error: empty or headerless CSV", file=sys.stderr)
            return 2
        missing = [k for k in keys if k not in reader.fieldnames]
        if missing:
            print(f"error: missing columns: {missing}", file=sys.stderr)
            return 2
        rows = list(reader)

    kept, removed = dedup(rows, keys)
    args.output.parent.mkdir(parents=True, exist_ok=True)
    with args.output.open("w", newline="", encoding="utf-8") as f:
        writer = csv.DictWriter(f, fieldnames=rows[0].keys() if rows else keys)
        writer.writeheader()
        writer.writerows(kept)

    report = (
        f"input_rows={len(rows)}\n"
        f"output_rows={len(kept)}\n"
        f"removed_duplicates={removed}\n"
        f"key_columns={','.join(keys)}\n"
        f"output_file={args.output}\n"
    )
    if args.summary:
        args.summary.write_text(report, encoding="utf-8")
    print(report, end="")
    return 0


if __name__ == "__main__":
    raise SystemExit(main())