package openweather

import (
	"fmt"
	"net/url"
	"strings"
)

// RequireMetricUnits enforces weatherfeeder's OpenWeather invariant:
// the request URL must include units=metric (otherwise temperatures/winds/pressure differ).
func RequireMetricUnits(rawURL string) error {
	u, err := url.Parse(strings.TrimSpace(rawURL))
	if err != nil {
		return fmt.Errorf("invalid url %q: %w", rawURL, err)
	}

	units := strings.ToLower(strings.TrimSpace(u.Query().Get("units")))
	if units != "metric" {
		if units == "" {
			units = "(missing; defaults to standard)"
		}
		return fmt.Errorf("url must include units=metric (got units=%s)", units)
	}

	return nil
}