Gamma Observability

// src/observability/gamma-metrics.ts
interface GammaMetrics {
  requests: number;
  errors: number;
  generations: number;
  completions: number;
  failures: number;
  totalCredits: number;
  totalLatencyMs: number;
  errorsByStatus: Record<number, number>;
}

const metrics: GammaMetrics = {
  requests: 0, errors: 0,
  generations: 0, completions: 0, failures: 0,
  totalCredits: 0, totalLatencyMs: 0,
  errorsByStatus: {},
};

export function createInstrumentedClient(apiKey: string) {
  const base = "https://public-api.gamma.app/v1.0";
  const headers = { "X-API-KEY": apiKey, "Content-Type": "application/json" };

  async function instrumentedRequest(method: string, path: string, body?: unknown) {
    metrics.requests++;
    const start = Date.now();

    try {
      const res = await fetch(`${base}${path}`, {
        method, headers,
        body: body ? JSON.stringify(body) : undefined,
      });
      metrics.totalLatencyMs += Date.now() - start;

      if (!res.ok) {
        metrics.errors++;
        metrics.errorsByStatus[res.status] = (metrics.errorsByStatus[res.status] || 0) + 1;
        throw new Error(`Gamma ${res.status}: ${await res.text()}`);
      }
      return res.json();
    } catch (err) {
      if (!metrics.errorsByStatus[0]) metrics.errorsByStatus[0] = 0;
      metrics.totalLatencyMs += Date.now() - start;
      throw err;
    }
  }

  return {
    generate: async (body: any) => {
      metrics.generations++;
      return instrumentedRequest("POST", "/generations", body);
    },
    poll: (id: string) => instrumentedRequest("GET", `/generations/${id}`),
    listThemes: () => instrumentedRequest("GET", "/themes"),
    listFolders: () => instrumentedRequest("GET", "/folders"),

    // Record completion metrics
    recordCompletion: (creditsUsed: number) => {
      metrics.completions++;
      metrics.totalCredits += creditsUsed;
    },
    recordFailure: () => { metrics.failures++; },
  };
}

export function getMetrics() {
  return {
    ...metrics,
    avgLatencyMs: metrics.requests > 0
      ? Math.round(metrics.totalLatencyMs / metrics.requests) : 0,
    errorRate: metrics.requests > 0
      ? (metrics.errors / metrics.requests * 100).toFixed(2) + "%" : "0%",
    completionRate: metrics.generations > 0
      ? (metrics.completions / metrics.generations * 100).toFixed(1) + "%" : "N/A",
    avgCreditsPerGeneration: metrics.completions > 0
      ? Math.round(metrics.totalCredits / metrics.completions) : 0,
  };
}

// src/observability/logger.ts
function logGammaEvent(event: string, data: Record<string, any>) {
  console.log(JSON.stringify({
    timestamp: new Date().toISOString(),
    service: "gamma",
    event,
    ...data,
    // Never log: apiKey, raw content (may contain PII)
  }));
}

// Usage
logGammaEvent("generation.started", {
  generationId: "gen_abc123",
  outputFormat: "presentation",
  contentLength: 500,
});

logGammaEvent("generation.completed", {
  generationId: "gen_abc123",
  creditsUsed: 42,
  latencyMs: 15000,
});

logGammaEvent("generation.failed", {
  generationId: "gen_abc123",
  error: "Generation failed after 180s",
});

// src/api/health.ts
async function checkGammaHealth() {
  const start = Date.now();
  try {
    const res = await fetch("https://public-api.gamma.app/v1.0/themes", {
      headers: { "X-API-KEY": process.env.GAMMA_API_KEY! },
    });
    const latencyMs = Date.now() - start;

    if (!res.ok) {
      return { status: "unhealthy", latencyMs, error: `HTTP ${res.status}` };
    }
    if (latencyMs > 5000) {
      return { status: "degraded", latencyMs, message: "High latency" };
    }
    return { status: "healthy", latencyMs };
  } catch (err: any) {
    return { status: "unhealthy", latencyMs: Date.now() - start, error: err.message };
  }
}

app.get("/health/gamma", async (req, res) => {
  const health = await checkGammaHealth();
  res.status(health.status === "unhealthy" ? 503 : 200).json(health);
});

// src/api/metrics.ts
app.get("/metrics/gamma", (req, res) => {
  const m = getMetrics();
  res.type("text/plain").send(`
# HELP gamma_requests_total Total API requests
# TYPE gamma_requests_total counter
gamma_requests_total ${m.requests}

# HELP gamma_errors_total Total API errors
# TYPE gamma_errors_total counter
gamma_errors_total ${m.errors}

# HELP gamma_generations_total Total generations started
# TYPE gamma_generations_total counter
gamma_generations_total ${m.generations}

# HELP gamma_completions_total Successful generations
# TYPE gamma_completions_total counter
gamma_completions_total ${m.completions}

# HELP gamma_credits_total Total credits consumed
# TYPE gamma_credits_total counter
gamma_credits_total ${m.totalCredits}

# HELP gamma_avg_latency_ms Average request latency
# TYPE gamma_avg_latency_ms gauge
gamma_avg_latency_ms ${m.avgLatencyMs}
  `.trim());
});

# alerting-rules.yml (Prometheus)
groups:
  - name: gamma
    rules:
      - alert: GammaHighErrorRate
        expr: rate(gamma_errors_total[5m]) / rate(gamma_requests_total[5m]) > 0.1
        for: 5m
        annotations:
          summary: "Gamma error rate above 10%"

      - alert: GammaHealthUnhealthy
        expr: up{job="gamma-health"} == 0
        for: 2m
        annotations:
          summary: "Gamma health check failing"

      - alert: GammaHighCreditBurn
        expr: rate(gamma_credits_total[1h]) > 100
        for: 30m
        annotations:
          summary: "Gamma credit consumption > 100/hour"

      - alert: GammaLowCompletionRate
        expr: gamma_completions_total / gamma_generations_total < 0.8
        for: 15m
        annotations:
          summary: "Gamma generation completion rate below 80%"