Dialectic.Backend/internal/fabric/announce.go

// Package fabric provides an HTTP client for posting system messages
// to a Fabric Guild's announce-type channel.
//
// Auth model: Dialectic backend holds a system api key in
// FABRIC_SYSTEM_API_KEY env. It POSTs to
// `<guildBaseUrl>/api/channels/<channelId>/messages` with both:
//   - `Authorization: Bearer <fabric-system-account-token>` (the
//     "user" that posts; needs to be a Fabric Center user that owns
//     the channel)
//   - `x-fabric-system-key: <SYSTEM_API_KEY>` (the new header added
//     in Phase 1 that gates announce-channel POSTs)
//
// Phase 2D ships this as an OPTIONAL coupling: if any of the three
// config values is unset, the announcer is a no-op (logs the would-be
// post and returns nil). This lets the orchestrator pipeline land + run
// in environments where the Fabric coupling isn't configured yet.
package fabric

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net/http"
	"time"
)

type AnnounceConfig struct {
	GuildBaseURL   string // e.g. https://fabric-api.hangman-lab.top
	ChannelID      string // the announce-type channel uuid
	SystemAPIKey   string // x-fabric-system-key value
	BotBearerToken string // Authorization: Bearer <token> — Fabric user posting; same
	// user is the "channel author" the backend records
	RequestTimeout time.Duration
}

type Announcer struct {
	cfg    AnnounceConfig
	client *http.Client
}

func NewAnnouncer(cfg AnnounceConfig) *Announcer {
	if cfg.RequestTimeout <= 0 {
		cfg.RequestTimeout = 5 * time.Second
	}
	return &Announcer{
		cfg:    cfg,
		client: &http.Client{Timeout: cfg.RequestTimeout},
	}
}

// Enabled returns true iff every required Announcer config field is set.
// Orchestrator checks this before each broadcast and silently skips when
// false (with a one-time startup log).
func (a *Announcer) Enabled() bool {
	return a.cfg.GuildBaseURL != "" && a.cfg.ChannelID != "" &&
		a.cfg.SystemAPIKey != "" && a.cfg.BotBearerToken != ""
}

// PostTopicAnnouncement posts a one-line system message describing a
// new topic that's ready for signup. Best-effort: log + nil on transport
// errors so a Fabric outage doesn't block topic transitions.
func (a *Announcer) PostTopicAnnouncement(ctx context.Context, topicID, title, summary string,
	signupOpen, signupClose, debateStart, debateEnd time.Time, verdictSchemaID string) error {

	if !a.Enabled() {
		log.Printf("announce: skipped (fabric coupling not configured) topic=%s", topicID)
		return nil
	}

	body := map[string]any{
		"content": formatAnnouncement(topicID, title, summary, signupOpen, signupClose, debateStart, debateEnd, verdictSchemaID),
	}
	raw, _ := json.Marshal(body)
	url := fmt.Sprintf("%s/api/channels/%s/messages",
		trimRightSlash(a.cfg.GuildBaseURL), a.cfg.ChannelID)
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(raw))
	if err != nil {
		return err
	}
	req.Header.Set("content-type", "application/json")
	req.Header.Set("authorization", "Bearer "+a.cfg.BotBearerToken)
	req.Header.Set("x-fabric-system-key", a.cfg.SystemAPIKey)

	resp, err := a.client.Do(req)
	if err != nil {
		log.Printf("announce: POST %s failed: %v", url, err)
		return err
	}
	defer resp.Body.Close()
	if resp.StatusCode >= 300 {
		b, _ := io.ReadAll(io.LimitReader(resp.Body, 1024))
		log.Printf("announce: POST %s -> %d body=%s", url, resp.StatusCode, string(b))
		return fmt.Errorf("announce post: status %d", resp.StatusCode)
	}
	return nil
}

func formatAnnouncement(id, title, summary string,
	signupOpen, signupClose, debateStart, debateEnd time.Time, schema string) string {
	const layout = "2006-01-02 15:04 UTC"
	return fmt.Sprintf(
		"🆕 **Debate signup open** [%s]\n\n**%s**\n%s\n\n"+
			"• Signup: %s → %s\n"+
			"• Debate: %s → %s\n"+
			"• Verdict schema: `%s`\n\n"+
			"To volunteer, use the `dialectic_signup` tool with this topic_id and your willing camp(s) — pro / con / judge. "+
			"You must have an `on_call` slot covering the debate window.",
		id, title, summary,
		signupOpen.UTC().Format(layout), signupClose.UTC().Format(layout),
		debateStart.UTC().Format(layout), debateEnd.UTC().Format(layout),
		schema,
	)
}

func trimRightSlash(s string) string {
	for len(s) > 0 && s[len(s)-1] == '/' {
		s = s[:len(s)-1]
	}
	return s
}