"""Idempotent per-format updates to out/bench/storage_sizes.csv.

Contract (docs/rules/build-pipeline-tasks.md section 4): columns
format,variant,bytes; a task re-run REPLACES its own format's rows and never
touches other formats' rows.
"""

from __future__ import annotations

import logging
from pathlib import Path

logger = logging.getLogger(__name__)

HEADER = "format,variant,bytes"


def update_storage_sizes(bench_dir: Path, fmt: str, variants: list[tuple[str, int]]) -> Path:
	path = bench_dir / "storage_sizes.csv"
	kept: list[str] = []
	if path.exists():
		lines = path.read_text(encoding="ascii").splitlines()
		if lines and lines[0] != HEADER:
			raise ValueError(f"{path}: unexpected header {lines[0]!r}")
		kept = [ln for ln in lines[1:] if ln and ln.split(",", 1)[0] != fmt]
	rows = kept + [f"{fmt},{variant},{nbytes}" for variant, nbytes in variants]
	bench_dir.mkdir(parents=True, exist_ok=True)
	with open(path, "w", encoding="ascii", newline="\n") as fh:
		fh.write(HEADER + "\n" + "\n".join(rows) + "\n")
	logger.info("storage_sizes.csv: %s -> %s", fmt, ", ".join(f"{v}={b}" for v, b in variants))
	return path