import argparse
import csv
import io
import sys
from pathlib import Path

import performance_compare


def render_csv(report):
    output = io.StringIO(newline="")
    writer = csv.writer(output)
    writer.writerow(("kind", "name", "unit", "baseline", "candidate", "change", "change_pct"))
    for field, unit in (("commit", ""), ("trace", ""), ("presents", "count")):
        writer.writerow(("capture", field, unit, report["baseline"][field], report["candidate"][field], "", ""))
    writer.writerow(("capture", "window.ms", "ms", report["baseline"]["window"]["ms"],
                     report["candidate"]["window"]["ms"], "", ""))
    for kind, key, unit in (("metric", "metrics_ms", "ms"), ("phase", "top_phases_ms_per_frame", "ms/frame")):
        for name, values in report[key].items():
            writer.writerow((kind, name, unit, *(values[field] for field in ("baseline", "candidate", "change", "change_pct"))))
    for name, values in report["configuration_differences"].items():
        writer.writerow(("configuration", name, "", values["baseline"], values["candidate"], "", ""))
    for note in report["notes"]:
        writer.writerow(("note", note, "", "", "", "", ""))
    return output.getvalue()


def main(argv=None):
    for stream in (sys.stdout, sys.stderr):
        if hasattr(stream, "reconfigure"):
            stream.reconfigure(encoding="utf-8", errors="backslashreplace", newline="")
    parser = argparse.ArgumentParser(description="Export a performance comparison as CSV. Empty metric cells mean unreported or unavailable, not zero.")
    parser.add_argument("baseline", type=Path)
    parser.add_argument("candidate", type=Path)
    parser.add_argument("--baseline-trace", help="exact trace field to select in the baseline JSONL")
    parser.add_argument("--candidate-trace", help="exact trace field to select in the candidate JSONL")
    parser.add_argument("--require-matching-context", action="store_true")
    args = parser.parse_args(argv)
    try:
        baseline = performance_compare.load_summary(args.baseline, args.baseline_trace)
        candidate = performance_compare.load_summary(args.candidate, args.candidate_trace)
        report = performance_compare.compare(baseline, candidate)
        if args.require_matching_context and report["configuration_differences"]:
            raise ValueError("recorded configuration differs: " + ", ".join(report["configuration_differences"]))
        output = render_csv(report)
    except (OSError, ValueError, OverflowError, RecursionError) as error:
        parser.exit(2, f"{parser.prog}: {error}\n")
    sys.stdout.write(output)
    return 0


if __name__ == "__main__":
    sys.exit(main())