#!/usr/bin/env python3
"""Compare monthly resource actuals with the immutable decision forecast."""

from __future__ import annotations

import json
import sys
from pathlib import Path

METRICS = (
    "database_gb", "stored_gb", "wal_gb", "restore_egress_gb",
    "write_requests", "read_requests", "infrastructure_eur",
    "internal_labor_hours", "internal_labor_eur", "total_eur",
)


def compare(forecast: dict, actual: dict) -> dict:
    expected = {row["period"]: row for row in forecast["rows"]}
    rows = []
    for observed in actual["rows"]:
        period = observed["period"]
        if period not in expected:
            rows.append({"period": period, "status": "no-forecast", "metrics": {}})
            continue
        metrics = {}
        for metric in METRICS:
            planned = expected[period][metric]
            measured = observed[metric]
            # An uninvoiced period has no cost to compare against. Treating a
            # missing amount as zero would report a 100% favourable variance.
            if planned is None or measured is None:
                metrics[metric] = {
                    "forecast": planned,
                    "actual": measured,
                    "status": "unknown",
                    "category": "data_quality",
                }
                continue
            error = measured - planned
            metrics[metric] = {
                "forecast": planned,
                "actual": measured,
                "error": round(error, 4),
                "absolute_percentage_error": None if planned == 0 else round(abs(error) / planned * 100, 2),
            }
        rows.append({"period": period, "status": "compared", "metrics": metrics})
    return {
        "forecast_created_at": forecast["created_at"],
        "provider_id": actual["provider_id"],
        "rows": rows,
    }


def main() -> int:
    if len(sys.argv) != 3:
        print(f"usage: {sys.argv[0]} FORECAST.json ACTUAL.json", file=sys.stderr)
        return 2
    forecast = json.loads(Path(sys.argv[1]).read_text())
    actual = json.loads(Path(sys.argv[2]).read_text())
    print(json.dumps(compare(forecast, actual), indent=2))
    return 0


if __name__ == "__main__":
    raise SystemExit(main())