adding radar support and caching the gif as well as invalidating cache on location change

README.md

@@ -39,6 +39,12 @@ go run . --clear-cache
 # Show all icons used by the app
 go run . -i
 go run . --icon-test
+
+# Display radar loop for the current location (requires mpv)
+go run . -R
+go run . --radar
+
+Radar mode caches the GIF on disk (10 minute TTL) under the cache directory.
 ```
 
 Note: `go run main.go` only compiles that file. Use `go run .` to include the whole package.

cache.go

@@ -44,7 +44,10 @@ func (c *Cache) SaveLocation(query string, loc Location) error {
 		Location:  loc,
 		UpdatedAt: time.Now().UTC(),
 	}
-	return writeJSON(filepath.Join(c.dir, locationCacheFile), payload)
+	if err := writeJSON(filepath.Join(c.dir, locationCacheFile), payload); err != nil {
+		return err
+	}
+	return c.ClearForecastAndRadar()
 }
 
 func (c *Cache) LoadLocation() (Location, bool, error) {
@@ -59,6 +62,21 @@ func (c *Cache) LoadLocation() (Location, bool, error) {
 	return payload.Location, true, nil
 }
 
+func (c *Cache) UpdateLocation(loc Location) error {
+	path := filepath.Join(c.dir, locationCacheFile)
+	var payload LocationCache
+	if err := readJSON(path, &payload); err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return fmt.Errorf("no cached location found to update")
+		}
+		return err
+	}
+
+	payload.Location = loc
+	payload.UpdatedAt = time.Now().UTC()
+	return writeJSON(path, payload)
+}
+
 func (c *Cache) SaveForecast(loc Location, unit string, period ForecastPeriod) error {
 	if err := c.ensureDir(); err != nil {
 		return err
@@ -109,9 +127,19 @@ func (c *Cache) Clear() error {
 	if err := os.Remove(filepath.Join(c.dir, locationCacheFile)); err != nil && !errors.Is(err, os.ErrNotExist) {
 		return err
 	}
+	return c.ClearForecastAndRadar()
+}
+
+func (c *Cache) ClearForecastAndRadar() error {
+	if c.dir == "" {
+		return fmt.Errorf("cache directory is empty")
+	}
 	if err := os.Remove(filepath.Join(c.dir, forecastCacheFile)); err != nil && !errors.Is(err, os.ErrNotExist) {
 		return err
 	}
+	if err := os.Remove(filepath.Join(c.dir, "radar.gif")); err != nil && !errors.Is(err, os.ErrNotExist) {
+		return err
+	}
 	return nil
 }
 

cache_test.go

@@ -28,6 +28,58 @@ func TestCacheLocationRoundTrip(t *testing.T) {
 	}
 }
 
+func TestCacheUpdateLocation(t *testing.T) {
+	tmp := t.TempDir()
+	cache := NewCache(tmp)
+	loc := Location{Lat: 1.23, Lon: 4.56, City: "Testville", State: "TS"}
+	if err := cache.SaveLocation("Testville", loc); err != nil {
+		t.Fatalf("save location failed: %v", err)
+	}
+
+	loc.RadarStation = "KBOX"
+	if err := cache.UpdateLocation(loc); err != nil {
+		t.Fatalf("update location failed: %v", err)
+	}
+
+	loaded, ok, err := cache.LoadLocation()
+	if err != nil {
+		t.Fatalf("load location failed: %v", err)
+	}
+	if !ok {
+		t.Fatalf("expected cached location")
+	}
+	if loaded.RadarStation != "KBOX" {
+		t.Fatalf("expected radar station to persist, got %q", loaded.RadarStation)
+	}
+}
+
+func TestSaveLocationClearsForecastAndRadar(t *testing.T) {
+	tmp := t.TempDir()
+	cache := NewCache(tmp)
+
+	forecastPath := filepath.Join(tmp, forecastCacheFile)
+	radarPath := filepath.Join(tmp, "radar.gif")
+
+	if err := os.WriteFile(forecastPath, []byte("x"), 0o644); err != nil {
+		t.Fatalf("write forecast: %v", err)
+	}
+	if err := os.WriteFile(radarPath, []byte("x"), 0o644); err != nil {
+		t.Fatalf("write radar: %v", err)
+	}
+
+	loc := Location{Lat: 1.23, Lon: 4.56, City: "Testville", State: "TS"}
+	if err := cache.SaveLocation("Testville", loc); err != nil {
+		t.Fatalf("save location failed: %v", err)
+	}
+
+	if _, err := os.Stat(forecastPath); !os.IsNotExist(err) {
+		t.Fatalf("expected forecast cache removed, got %v", err)
+	}
+	if _, err := os.Stat(radarPath); !os.IsNotExist(err) {
+		t.Fatalf("expected radar cache removed, got %v", err)
+	}
+}
+
 func TestCacheForecastExpiry(t *testing.T) {
 	tmp := t.TempDir()
 	cache := NewCache(tmp)

forecast.go

@@ -85,6 +85,23 @@ func (c *NWSClient) FetchForecast(ctx context.Context, loc Location, unit string
 	}, nil
 }
 
+func (c *NWSClient) FetchRadarStation(ctx context.Context, loc Location) (string, error) {
+	pointsURL := fmt.Sprintf("https://api.weather.gov/points/%.4f,%.4f", loc.Lat, loc.Lon)
+	var pointsResp struct {
+		Properties struct {
+			RadarStation string `json:"radarStation"`
+		} `json:"properties"`
+	}
+	if err := c.getJSON(ctx, pointsURL, &pointsResp); err != nil {
+		return "", err
+	}
+	station := strings.TrimSpace(pointsResp.Properties.RadarStation)
+	if station == "" {
+		return "", fmt.Errorf("missing radar station from NWS points")
+	}
+	return station, nil
+}
+
 func (c *NWSClient) getJSON(ctx context.Context, url string, target any) error {
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
 	if err != nil {

location.go

@@ -19,13 +19,14 @@ import (
 const revGeoURL = "http://ip-api.com/json/"
 
 type Location struct {
-	Lat         float64
-	Lon         float64
-	City        string
-	State       string
-	Country     string
-	Zipcode     string
-	DisplayName string
+	Lat          float64
+	Lon          float64
+	City         string
+	State        string
+	Country      string
+	Zipcode      string
+	DisplayName  string
+	RadarStation string
 }
 
 func NewLocation() *Location {
@@ -35,14 +36,15 @@ func NewLocation() *Location {
 func (l *Location) UnmarshalJSON(b []byte) error {
 
 	var aux struct {
-		Lat         json.RawMessage `json:"lat"`
-		Lon         json.RawMessage `json:"lon"`
-		DisplayName string          `json:"display_name"`
-		City        string          `json:"city"`
-		State       string          `json:"state"`
-		Country     string          `json:"country"`
-		Zipcode     string          `json:"zipcode"`
-		Address     struct {
+		Lat          json.RawMessage `json:"lat"`
+		Lon          json.RawMessage `json:"lon"`
+		DisplayName  string          `json:"display_name"`
+		City         string          `json:"city"`
+		State        string          `json:"state"`
+		Country      string          `json:"country"`
+		Zipcode      string          `json:"zipcode"`
+		RadarStation string          `json:"RadarStation"`
+		Address      struct {
 			City    string `json:"city"`
 			Town    string `json:"town"`
 			Village string `json:"village"`
@@ -82,6 +84,7 @@ func (l *Location) UnmarshalJSON(b []byte) error {
 	l.Country = firstNonEmpty(aux.Address.Country, aux.Country)
 	l.Zipcode = firstNonEmpty(aux.Address.Zipcode, aux.Zipcode)
 	l.DisplayName = firstNonEmpty(aux.DisplayName, aux.City)
+	l.RadarStation = aux.RadarStation
 
 	return nil
 }

main.go

@@ -29,6 +29,7 @@ func run() error {
 		clearCache   bool
 		refresh      bool
 		iconTest     bool
+		radarMode    bool
 	)
 
 	flag.StringVar(&search, "s", "", "Search location (e.g. \"Somerville, MA\")")
@@ -45,6 +46,8 @@ func run() error {
 	flag.BoolVar(&refresh, "r", false, "Force refresh forecast data")
 	flag.BoolVar(&iconTest, "icon-test", false, "Print all icons used by the program")
 	flag.BoolVar(&iconTest, "i", false, "Print all icons used by the program")
+	flag.BoolVar(&radarMode, "radar", false, "Display radar loop for current location via mpv")
+	flag.BoolVar(&radarMode, "R", false, "Display radar loop for current location via mpv")
 	flag.Parse()
 
 	ua, err := buildUserAgent()
@@ -73,6 +76,12 @@ func run() error {
 		return nil
 	}
 
+	if radarMode {
+		if err := requireMPV(); err != nil {
+			return err
+		}
+	}
+
 	if clearCache {
 		if err := cache.Clear(); err != nil {
 			return err
@@ -104,6 +113,10 @@ func run() error {
 		}
 	}
 
+	if radarMode {
+		return runRadar(ctx, cache, loc, search, ua)
+	}
+
 	client := NewNWSClient(ua)
 	var period ForecastPeriod
 	if refresh {

radar.go

@@ -0,0 +1,126 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+const radarCacheTTL = 10 * time.Minute
+
+func requireMPV() error {
+	if _, err := exec.LookPath("mpv"); err != nil {
+		return fmt.Errorf("mpv is required for radar mode")
+	}
+	return nil
+}
+
+func runRadar(ctx context.Context, cache *Cache, loc Location, searchQuery string, userAgent string) error {
+	station := strings.TrimSpace(loc.RadarStation)
+	if station == "" {
+		client := NewNWSClient(userAgent)
+		var err error
+		station, err = client.FetchRadarStation(ctx, loc)
+		if err != nil {
+			return err
+		}
+		loc.RadarStation = station
+		if err := cache.UpdateLocation(loc); err != nil {
+			if searchQuery == "" {
+				return err
+			}
+			if err := cache.SaveLocation(searchQuery, loc); err != nil {
+				return err
+			}
+		}
+	}
+
+	url, err := radarURL(station)
+	if err != nil {
+		return err
+	}
+
+	radarPath, err := cacheRadarGIF(ctx, cache, url, userAgent)
+	if err != nil {
+		return err
+	}
+
+	cmd := exec.CommandContext(ctx, "mpv", "--fs", "--loop-file", radarPath)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	cmd.Stdin = os.Stdin
+	return cmd.Run()
+}
+
+func radarURL(station string) (string, error) {
+	station = strings.TrimSpace(station)
+	if station == "" {
+		return "", fmt.Errorf("radar station not set")
+	}
+	station = strings.ToUpper(station)
+	return fmt.Sprintf("https://radar.weather.gov/ridge/standard/%s_loop.gif", station), nil
+}
+
+func cacheRadarGIF(ctx context.Context, cache *Cache, url, userAgent string) (string, error) {
+	if err := cache.ensureDir(); err != nil {
+		return "", err
+	}
+	path := filepath.Join(cache.dir, "radar.gif")
+	if !shouldRefreshFile(path, radarCacheTTL) {
+		return path, nil
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return "", err
+	}
+	req.Header.Set("User-Agent", userAgent)
+
+	client := &http.Client{Timeout: 20 * time.Second}
+	resp, err := client.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode > 299 {
+		return "", fmt.Errorf("radar request failed with status %d", resp.StatusCode)
+	}
+
+	tmpPath := path + ".tmp"
+	tmp, err := os.Create(tmpPath)
+	if err != nil {
+		return "", err
+	}
+	_, copyErr := io.Copy(tmp, resp.Body)
+	closeErr := tmp.Close()
+	if copyErr != nil {
+		_ = os.Remove(tmpPath)
+		return "", copyErr
+	}
+	if closeErr != nil {
+		_ = os.Remove(tmpPath)
+		return "", closeErr
+	}
+
+	if err := os.Rename(tmpPath, path); err != nil {
+		_ = os.Remove(tmpPath)
+		return "", err
+	}
+
+	return path, nil
+}
+
+func shouldRefreshFile(path string, ttl time.Duration) bool {
+	info, err := os.Stat(path)
+	if err != nil {
+		return true
+	}
+	return time.Since(info.ModTime()) > ttl
+}

radar_cache_test.go

@@ -0,0 +1,32 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestShouldRefreshFile(t *testing.T) {
+	tmp := t.TempDir()
+	path := filepath.Join(tmp, "radar.gif")
+
+	if !shouldRefreshFile(path, time.Minute) {
+		t.Fatalf("expected refresh when file missing")
+	}
+
+	if err := os.WriteFile(path, []byte("x"), 0o644); err != nil {
+		t.Fatalf("write temp file: %v", err)
+	}
+	if shouldRefreshFile(path, time.Minute) {
+		t.Fatalf("expected no refresh for fresh file")
+	}
+
+	old := time.Now().Add(-2 * time.Hour)
+	if err := os.Chtimes(path, old, old); err != nil {
+		t.Fatalf("chtimes: %v", err)
+	}
+	if !shouldRefreshFile(path, time.Minute) {
+		t.Fatalf("expected refresh for stale file")
+	}
+}

radar_test.go

@@ -0,0 +1,14 @@
+package main
+
+import "testing"
+
+func TestRadarURL(t *testing.T) {
+	url, err := radarURL("kbox")
+	if err != nil {
+		t.Fatalf("radar url error: %v", err)
+	}
+	expected := "https://radar.weather.gov/ridge/standard/KBOX_loop.gif"
+	if url != expected {
+		t.Fatalf("unexpected radar url: %s", url)
+	}
+}