#!/usr/bin/env python3
"""Convert a VPD1 SQLite database to a partitioned Parquet dataset."""

from __future__ import annotations

import argparse
import hashlib
import json
import sqlite3
import time
from pathlib import Path

import pyarrow as pa
import pyarrow.dataset as pads
import pyarrow.parquet as pq


PHASE_NAMES = {0: "opening", 1: "middlegame", 2: "endgame"}
COLUMNS = [
    "id",
    "random_key",
    "fen",
    "source_member",
    "game_number",
    "ply",
    "result",
    "side_to_move",
    "piece_count",
    "non_pawn_material",
    "material_balance",
    "legal_moves",
    "in_check",
    "castling_mask",
    "halfmove_clock",
]
SCHEMA = pa.schema(
    [
        ("id", pa.int64()),
        ("random_key", pa.int64()),
        ("fen", pa.string()),
        ("source_member", pa.string()),
        ("game_number", pa.int64()),
        ("ply", pa.int16()),
        ("result", pa.string()),
        ("side_to_move", pa.int8()),
        ("piece_count", pa.int8()),
        ("non_pawn_material", pa.int16()),
        ("material_balance", pa.int16()),
        ("legal_moves", pa.int16()),
        ("in_check", pa.bool_()),
        ("castling_mask", pa.int8()),
        ("halfmove_clock", pa.int16()),
    ]
)


def sha256(path: Path) -> str:
    digest = hashlib.sha256()
    with path.open("rb") as source:
        while chunk := source.read(8 * 1024 * 1024):
            digest.update(chunk)
    return digest.hexdigest()


def table_from_rows(rows: list[tuple[object, ...]], schema: pa.Schema) -> pa.Table:
    arrays = []
    for index, field in enumerate(schema):
        values = [row[index] for row in rows]
        if pa.types.is_boolean(field.type):
            values = [bool(value) for value in values]
        arrays.append(pa.array(values, type=field.type))
    return pa.Table.from_arrays(arrays, schema=schema)


def convert(args: argparse.Namespace) -> None:
    source = Path(args.input).resolve()
    output = Path(args.output).resolve()
    if output.exists() and any(output.iterdir()):
        raise RuntimeError(f"output directory is not empty: {output}")
    output.mkdir(parents=True, exist_ok=True)

    db = sqlite3.connect(f"file:{source}?mode=ro&immutable=1", uri=True)
    metadata = dict(db.execute("SELECT key, value FROM metadata"))
    schema = SCHEMA.with_metadata(
        {
            b"vpd_format": metadata.get("format", "unknown").encode(),
            b"source_sha256": sha256(source).encode(),
            b"fen_fullmove_normalization": metadata.get(
                "fen_fullmove_normalization", "unknown"
            ).encode(),
        }
    )
    source_total = db.execute("SELECT COUNT(*) FROM positions").fetchone()[0]
    splits = [
        row[0]
        for row in db.execute(
            "SELECT DISTINCT source_split FROM positions ORDER BY source_split"
        )
    ]
    manifest: dict[str, object] = {
        "format": "VPD1-Parquet",
        "source": str(source),
        "source_sha256": sha256(source),
        "compression": args.compression,
        "compression_level": args.compression_level,
        "row_group_size": args.row_group_size,
        "partitioning": ["source_split", "phase"],
        "rows": 0,
        "partitions": [],
    }
    started = time.monotonic()

    for split in splits:
        for phase_id, phase_name in PHASE_NAMES.items():
            count = db.execute(
                "SELECT COUNT(*) FROM positions WHERE source_split=? AND phase=?",
                (split, phase_id),
            ).fetchone()[0]
            if not count:
                continue
            partition_dir = output / f"source_split={split}" / f"phase={phase_name}"
            partition_dir.mkdir(parents=True, exist_ok=True)
            parquet_path = partition_dir / "positions.parquet"
            query = (
                f"SELECT {', '.join(COLUMNS)} FROM positions "
                "WHERE source_split=? AND phase=? ORDER BY id"
            )
            cursor = db.execute(query, (split, phase_id))
            written = 0
            row_groups = 0
            min_id = None
            max_id = None
            with pq.ParquetWriter(
                parquet_path,
                schema,
                compression=args.compression,
                compression_level=args.compression_level,
                use_dictionary=["source_member", "result"],
                write_statistics=True,
            ) as writer:
                while rows := cursor.fetchmany(args.row_group_size):
                    table = table_from_rows(rows, schema)
                    writer.write_table(table, row_group_size=len(rows))
                    written += len(rows)
                    row_groups += 1
                    min_id = rows[0][0] if min_id is None else min_id
                    max_id = rows[-1][0]
            if written != count:
                raise RuntimeError(
                    f"partition count mismatch for {split}/{phase_name}: "
                    f"expected {count}, wrote {written}"
                )
            manifest["rows"] += written
            manifest["partitions"].append(
                {
                    "source_split": split,
                    "phase": phase_name,
                    "rows": written,
                    "row_groups": row_groups,
                    "min_id": min_id,
                    "max_id": max_id,
                    "bytes": parquet_path.stat().st_size,
                    "file": str(parquet_path.relative_to(output)),
                    "sha256": sha256(parquet_path),
                }
            )
            print(
                f"wrote {split}/{phase_name}: {written:,} rows, "
                f"{parquet_path.stat().st_size / (1024 * 1024):.1f} MiB",
                flush=True,
            )

    db.close()
    if manifest["rows"] != source_total:
        raise RuntimeError(
            f"total mismatch: source has {source_total}, wrote {manifest['rows']}"
        )
    manifest["elapsed_seconds"] = round(time.monotonic() - started, 3)
    # Leading underscore keeps the JSON sidecar out of PyArrow's default
    # Parquet dataset discovery while leaving it next to the data it describes.
    manifest_path = output / "_manifest.json"
    manifest_path.write_text(
        json.dumps(manifest, indent=2, sort_keys=True) + "\n", encoding="utf-8"
    )

    dataset = pads.dataset(output, format="parquet", partitioning="hive")
    parquet_total = dataset.count_rows()
    if parquet_total != source_total:
        raise RuntimeError(
            f"PyArrow validation mismatch: expected {source_total}, got {parquet_total}"
        )
    print(
        json.dumps(
            {
                "rows": parquet_total,
                "files": len(dataset.files),
                "manifest": str(manifest_path),
                "elapsed_seconds": manifest["elapsed_seconds"],
            },
            indent=2,
        )
    )


def main() -> None:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--input", required=True)
    parser.add_argument("--output", required=True)
    parser.add_argument("--row-group-size", type=int, default=65_536)
    parser.add_argument("--compression", default="zstd")
    parser.add_argument("--compression-level", type=int, default=6)
    convert(parser.parse_args())


if __name__ == "__main__":
    main()