feat(bot): SteamFree bot — posts free Steam games

Polls Steam featured categories API every 30m, filters for 100%
discounts on games that had a real price, posts new finds to the
configured channel. Env: BOT_TOKEN, DUMPSTER_HOST, CHANNEL_ID,
POLL_MINUTES.

examples/steamfree/main.go

@@ -0,0 +1,198 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"net/url"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/gorilla/websocket"
+)
+
+// ---- config from env ----
+
+var (
+	botToken    string
+	host        string
+	channelID   string
+	pollMinutes int
+	seen        = map[string]bool{} // appid -> posted
+)
+
+// ---- dumpsterChat WS protocol ----
+
+type Event struct {
+	Type    string          `json:"type"`
+	Payload json.RawMessage `json:"payload"`
+}
+
+// ---- Steam API response ----
+
+type FeaturedCategories struct {
+	Specials FeaturedList `json:"specials"`
+}
+
+type FeaturedList struct {
+	Items []FeaturedItem `json:"items"`
+}
+
+type FeaturedItem struct {
+	ID            int    `json:"id"`
+	Name          string `json:"name"`
+	DiscountPct   int    `json:"discount_percent"`
+	FinalPrice    int    `json:"final_price"`   // in cents
+	OriginalPrice int    `json:"original_price"` // in cents
+}
+
+func main() {
+	botToken = os.Getenv("BOT_TOKEN")
+	if botToken == "" {
+		log.Fatal("BOT_TOKEN required (create a bot in the dumpsterChat store)")
+	}
+	host = os.Getenv("DUMPSTER_HOST")
+	if host == "" {
+		host = "localhost:8080"
+	}
+	channelID = os.Getenv("CHANNEL_ID")
+	if channelID == "" {
+		log.Fatal("CHANNEL_ID required (the channel to post free games to)")
+	}
+	pollMinutes = 30
+	if m := os.Getenv("POLL_MINUTES"); m != "" {
+		if v, err := strconv.Atoi(m); err == nil && v > 0 {
+			pollMinutes = v
+		}
+	}
+
+	// Connect to dumpsterChat
+	u := url.URL{
+		Scheme:   "ws",
+		Host:     host,
+		Path:     "/ws/bot",
+		RawQuery: "token=" + botToken,
+	}
+
+	log.Printf("SteamFree bot connecting to %s", u.String())
+
+	c, _, err := websocket.DefaultDialer.Dial(u.String(), nil)
+	if err != nil {
+		log.Fatal("dial:", err)
+	}
+	defer c.Close()
+
+	log.Println("SteamFree bot connected!")
+
+	// First poll immediately, then on ticker
+	poll(c)
+
+	ticker := time.NewTicker(time.Duration(pollMinutes) * time.Minute)
+	defer ticker.Stop()
+
+	// Keep connection alive by reading (we don't need to react to events)
+	go func() {
+		for {
+			_, _, err := c.ReadMessage()
+			if err != nil {
+				log.Println("ws read:", err)
+				return
+			}
+		}
+	}()
+
+	for range ticker.C {
+		poll(c)
+	}
+}
+
+func poll(c *websocket.Conn) {
+	log.Println("Polling Steam for free games...")
+
+	games, err := fetchFreeGames()
+	if err != nil {
+		log.Println("fetch error:", err)
+		return
+	}
+
+	newCount := 0
+	for _, g := range games {
+		if seen[strconv.Itoa(g.ID)] {
+			continue
+		}
+		seen[strconv.Itoa(g.ID)] = true
+		newCount++
+
+		msg := formatGame(g)
+		sendMessage(c, channelID, msg)
+		log.Printf("Posted: %s (was $%.2f, now FREE)", g.Name, float64(g.OriginalPrice)/100)
+		time.Sleep(500 * time.Millisecond) // be polite to the WS
+	}
+
+	if newCount == 0 {
+		log.Println("No new free games found")
+	} else {
+		log.Printf("Posted %d new free games", newCount)
+	}
+}
+
+func fetchFreeGames() ([]FeaturedItem, error) {
+	client := &http.Client{Timeout: 15 * time.Second}
+	resp, err := client.Get("https://store.steampowered.com/api/featuredcategories?cc=us&l=english")
+	if err != nil {
+		return nil, fmt.Errorf("steam api: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != 200 {
+		return nil, fmt.Errorf("steam api: status %d", resp.StatusCode)
+	}
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("read body: %w", err)
+	}
+
+	var cats FeaturedCategories
+	if err := json.Unmarshal(body, &cats); err != nil {
+		return nil, fmt.Errorf("parse json: %w", err)
+	}
+
+	// Filter: 100% discount and actually had a price (not permanent free-to-play)
+	var free []FeaturedItem
+	for _, item := range cats.Specials.Items {
+		if item.DiscountPct == 100 && item.OriginalPrice > 0 {
+			free = append(free, item)
+		}
+	}
+
+	return free, nil
+}
+
+func formatGame(g FeaturedItem) string {
+	storeURL := fmt.Sprintf("https://store.steampowered.com/app/%d", g.ID)
+
+	var b strings.Builder
+	fmt.Fprintf(&b, "🎮 **FREE ON STEAM** 🎮\n")
+	fmt.Fprintf(&b, "**%s**\n", g.Name)
+	fmt.Fprintf(&b, "~~$%.2f~~ → **FREE**\n", float64(g.OriginalPrice)/100)
+	fmt.Fprintf(&b, "%s", storeURL)
+
+	return b.String()
+}
+
+func sendMessage(c *websocket.Conn, channelID, content string) {
+	msg := map[string]interface{}{
+		"type": "SEND_MESSAGE",
+		"payload": map[string]string{
+			"channel_id": channelID,
+			"content":    content,
+		},
+	}
+	data, _ := json.Marshal(msg)
+	c.WriteMessage(websocket.TextMessage, data)
+}