add a page for tickets from gitea (#2)

Co-authored-by: Blake Ridgway <blake@blakeridgway.com>
Reviewed-on: #2

internal/twitch/twitch.go

@@ -0,0 +1,148 @@
+// Package twitch polls the Twitch Helix API to track whether a channel is live.
+package twitch
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"net/url"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+// Checker polls Twitch and exposes whether the channel is currently live.
+type Checker struct {
+	clientID     string
+	clientSecret string
+	channel      string
+	live         atomic.Bool
+	token        string
+	tokenExpiry  time.Time
+	mu           sync.Mutex
+	http         *http.Client
+}
+
+// New creates a Checker for the given channel.
+func New(clientID, clientSecret, channel string) *Checker {
+	return &Checker{
+		clientID:     clientID,
+		clientSecret: clientSecret,
+		channel:      channel,
+		http:         &http.Client{Timeout: 10 * time.Second},
+	}
+}
+
+// Start begins background polling at the given interval.
+func (c *Checker) Start(interval time.Duration) {
+	go func() {
+		for {
+			if err := c.check(); err != nil {
+				log.Printf("twitch: %v", err)
+			}
+			time.Sleep(interval)
+		}
+	}()
+}
+
+// IsLive reports whether the channel is currently streaming.
+func (c *Checker) IsLive() bool {
+	return c.live.Load()
+}
+
+// Channel returns the configured channel name.
+func (c *Checker) Channel() string {
+	return c.channel
+}
+
+func (c *Checker) check() error {
+	token, err := c.accessToken()
+	if err != nil {
+		return fmt.Errorf("access token: %w", err)
+	}
+
+	req, err := http.NewRequest("GET",
+		"https://api.twitch.tv/helix/streams?user_login="+url.QueryEscape(c.channel), nil)
+	if err != nil {
+		return err
+	}
+	req.Header.Set("Client-Id", c.clientID)
+	req.Header.Set("Authorization", "Bearer "+token)
+
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return fmt.Errorf("streams request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode == http.StatusUnauthorized {
+		// Token may have been revoked; clear it and retry next tick.
+		c.mu.Lock()
+		c.token = ""
+		c.mu.Unlock()
+		return fmt.Errorf("streams: 401 unauthorized, will refresh token")
+	}
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("streams: %s", resp.Status)
+	}
+
+	var body struct {
+		Data []struct {
+			Type string `json:"type"`
+		} `json:"data"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&body); err != nil {
+		return fmt.Errorf("decode: %w", err)
+	}
+
+	wasLive := c.live.Load()
+	isLive := len(body.Data) > 0 && body.Data[0].Type == "live"
+	c.live.Store(isLive)
+
+	if isLive != wasLive {
+		if isLive {
+			log.Printf("twitch: %s went live", c.channel)
+		} else {
+			log.Printf("twitch: %s went offline", c.channel)
+		}
+	}
+	return nil
+}
+
+// accessToken returns a cached app access token, refreshing if expired.
+func (c *Checker) accessToken() (string, error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if c.token != "" && time.Now().Before(c.tokenExpiry) {
+		return c.token, nil
+	}
+
+	resp, err := c.http.PostForm("https://id.twitch.tv/oauth2/token", url.Values{
+		"client_id":     {c.clientID},
+		"client_secret": {c.clientSecret},
+		"grant_type":    {"client_credentials"},
+	})
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("token: %s", resp.Status)
+	}
+
+	var body struct {
+		AccessToken string `json:"access_token"`
+		ExpiresIn   int    `json:"expires_in"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&body); err != nil {
+		return "", err
+	}
+
+	c.token = body.AccessToken
+	// Refresh 5 minutes before actual expiry.
+	c.tokenExpiry = time.Now().Add(time.Duration(body.ExpiresIn)*time.Second - 5*time.Minute)
+	return c.token, nil
+}