package radar

import (
	"context"
	"fmt"
	"io"
	"net/http"
	"strings"
	"time"
)

// nwsRadarBase is the NWS public product distribution server.
// No credentials required; sn.last always holds the most recent scan.
const nwsRadarBase = "https://tgftp.nws.noaa.gov/SL.us008001/DF.of/DC.radar"

// Fetcher downloads NEXRAD Level 3 products from the NWS public server.
type Fetcher struct {
	client *http.Client
}

func NewFetcher(_ context.Context) (*Fetcher, error) {
	return &Fetcher{client: &http.Client{Timeout: 30 * time.Second}}, nil
}

// FetchLatest downloads the latest Level 3 base reflectivity (0.5°) for site.
func (f *Fetcher) FetchLatest(ctx context.Context, site string) ([]byte, error) {
	return f.fetchDS(ctx, site, "p94r0")
}

// FetchVelocity downloads the latest Level 3 base velocity (0.5°) for site.
func (f *Fetcher) FetchVelocity(ctx context.Context, site string) ([]byte, error) {
	return f.fetchDS(ctx, site, "p99r0")
}

func (f *Fetcher) fetchDS(ctx context.Context, site, ds string) ([]byte, error) {
	url := fmt.Sprintf("%s/DS.%s/SI.%s/sn.last", nwsRadarBase, ds, strings.ToLower(site))

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return nil, err
	}
	resp, err := f.client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("NWS fetch: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("NWS returned %s for %s", resp.Status, url)
	}
	return io.ReadAll(resp.Body)
}