#!/usr/bin/env python3
"""Split a large parquet file into smaller parquet shards."""

from __future__ import annotations

import argparse
import os
from pathlib import Path

import pyarrow as pa
import pyarrow.parquet as pq


def parse_size(value: str) -> int:
    units = {
        "b": 1,
        "kb": 1024,
        "mb": 1024**2,
        "gb": 1024**3,
        "tb": 1024**4,
    }
    text = value.strip().lower()
    for suffix, multiplier in sorted(units.items(), key=lambda item: len(item[0]), reverse=True):
        if text.endswith(suffix):
            number = float(text[: -len(suffix)].strip())
            return int(number * multiplier)
    return int(float(text))


def shard_name(index: int) -> str:
    return f"train-{index:05d}.parquet"


def split_parquet(
    source: Path,
    output_dir: Path,
    target_size: int,
    batch_size: int,
    compression: str,
) -> None:
    data_dir = output_dir / "data"
    data_dir.mkdir(parents=True, exist_ok=False)

    parquet_file = pq.ParquetFile(source)
    schema = parquet_file.schema_arrow
    source_rows = parquet_file.metadata.num_rows
    source_row_groups = parquet_file.metadata.num_row_groups

    print(f"source={source}", flush=True)
    print(f"source_rows={source_rows}", flush=True)
    print(f"source_row_groups={source_row_groups}", flush=True)
    print(f"target_size_bytes={target_size}", flush=True)
    print(f"batch_size={batch_size}", flush=True)

    writer: pq.ParquetWriter | None = None
    current_path: Path | None = None
    shard_index = 0
    shard_rows = 0
    total_rows = 0

    def open_writer() -> None:
        nonlocal writer, current_path, shard_rows, shard_index
        current_path = data_dir / shard_name(shard_index)
        writer = pq.ParquetWriter(current_path, schema=schema, compression=compression)
        shard_rows = 0
        print(f"opened_shard={current_path}", flush=True)

    def close_writer() -> None:
        nonlocal writer, current_path, shard_rows, shard_index
        if writer is None or current_path is None:
            return
        writer.close()
        size = current_path.stat().st_size
        print(
            f"closed_shard={current_path} rows={shard_rows} size_bytes={size}",
            flush=True,
        )
        writer = None
        current_path = None
        shard_index += 1
        shard_rows = 0

    try:
        open_writer()
        for row_group_index in range(source_row_groups):
            for batch in parquet_file.iter_batches(
                batch_size=batch_size,
                row_groups=[row_group_index],
                use_threads=True,
            ):
                if writer is None:
                    open_writer()

                table = pa.Table.from_batches([batch], schema=schema)
                writer.write_table(table)
                rows = table.num_rows
                shard_rows += rows
                total_rows += rows

                if current_path is not None and current_path.exists():
                    current_size = current_path.stat().st_size
                    print(
                        "progress "
                        f"row_group={row_group_index + 1}/{source_row_groups} "
                        f"total_rows={total_rows}/{source_rows} "
                        f"current_shard={current_path.name} "
                        f"current_size_bytes={current_size}",
                        flush=True,
                    )
                    if current_size >= target_size:
                        close_writer()

        close_writer()
    except Exception:
        if writer is not None:
            writer.close()
        raise

    print(f"completed total_rows={total_rows} shards={shard_index}", flush=True)
    if total_rows != source_rows:
        raise RuntimeError(f"row count mismatch: wrote {total_rows}, expected {source_rows}")


def main() -> None:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--source", required=True, type=Path)
    parser.add_argument("--output-dir", required=True, type=Path)
    parser.add_argument("--target-size", default="10GB")
    parser.add_argument("--batch-size", default=8, type=int)
    parser.add_argument("--compression", default="snappy")
    args = parser.parse_args()

    if not args.source.is_file():
        raise FileNotFoundError(args.source)
    if args.output_dir.exists():
        raise FileExistsError(f"Output directory already exists: {args.output_dir}")

    split_parquet(
        source=args.source,
        output_dir=args.output_dir,
        target_size=parse_size(args.target_size),
        batch_size=args.batch_size,
        compression=args.compression,
    )


if __name__ == "__main__":
    main()