#!/usr/bin/env python3
"""Create deterministic V25PG01 fixed-slot page artifacts for tests/benchmarks."""

import argparse
import struct
import zlib
from pathlib import Path

HEADER_BYTES = 4096
PAGE_HEADER_BYTES = 16


def main() -> None:
    parser = argparse.ArgumentParser()
    parser.add_argument("output", type=Path)
    parser.add_argument("--pages", type=int, default=128)
    parser.add_argument("--page-bytes", type=int, default=4096)
    parser.add_argument("--useful-bytes", type=int, default=1000)
    parser.add_argument("--logical-params", type=int, default=0)
    args = parser.parse_args()

    if not 1 <= args.pages <= 1_000_000:
        parser.error("--pages must be between 1 and 1000000")
    if not 4096 <= args.page_bytes <= 16 * 1024 * 1024 or args.page_bytes % 4096:
        parser.error("--page-bytes must be a 4096-byte multiple up to 16 MiB")
    if not 0 <= args.useful_bytes <= args.page_bytes - PAGE_HEADER_BYTES:
        parser.error("--useful-bytes exceeds page payload")
    if args.logical_params < 0:
        parser.error("--logical-params must be nonnegative")

    header = bytearray(HEADER_BYTES)
    struct.pack_into(
        "<8sIIIIQQQIII",
        header,
        0,
        b"V25PG01\0",
        1,
        HEADER_BYTES,
        args.page_bytes,
        PAGE_HEADER_BYTES,
        args.pages,
        HEADER_BYTES,
        args.logical_params,
        1,
        0,
        args.useful_bytes,
    )
    struct.pack_into("<I", header, 60, zlib.crc32(header[:60]))

    with args.output.open("wb") as output:
        output.write(header)
        padding = bytes(args.page_bytes - PAGE_HEADER_BYTES - args.useful_bytes)
        for page_id in range(args.pages):
            payload = bytes(((page_id * 131 + i * 17) & 0xFF) for i in range(args.useful_bytes))
            output.write(struct.pack("<QII", page_id, len(payload), zlib.crc32(payload)))
            output.write(payload)
            output.write(padding)


if __name__ == "__main__":
    main()