import { describe, it, expect } from "vitest";
import { Metrics, mergeExposition } from "../src/metrics.js";

/**
 * TASK-0135 — the /metrics merge contract (local registry authoritative,
 * OTel-only families appended, no duplicate families).
 */

const LOCAL = [
  "# HELP uptime_seconds Process uptime in seconds.",
  "# TYPE uptime_seconds gauge",
  "uptime_seconds 42",
  "# HELP ws_connections Live WebSocket connections, by room type.",
  "# TYPE ws_connections gauge",
  'ws_connections{room="page"} 3',
  "# HELP ws_messages_total Frames received, by frame type.",
  "# TYPE ws_messages_total counter",
  'ws_messages_total{frame="update"} 10',
].join("\n") + "\n";

const OTEL = [
  "# HELP target_info Target metadata.",
  "# TYPE target_info gauge",
  'target_info{service_name="factory-realtime"} 1',
  "# HELP ws_active_connections Live WebSocket connections, total.",
  "# TYPE ws_active_connections gauge",
  "ws_active_connections 5",
  "# HELP ws_messages_total Frames received (OTel, no labels).",
  "# TYPE ws_messages_total counter",
  "ws_messages_total 7",
].join("\n") + "\n";

describe("mergeExposition", () => {
  it("returns the local text unchanged when OTel text is empty (disabled)", () => {
    expect(mergeExposition(LOCAL, "")).toBe(LOCAL);
  });

  it("appends OTel-only families (target_info, ws_active_connections)", () => {
    const out = mergeExposition(LOCAL, OTEL);
    expect(out).toContain('target_info{service_name="factory-realtime"} 1');
    expect(out).toContain("ws_active_connections 5");
    expect(out).toContain("# TYPE target_info gauge");
  });

  it("keeps the LOCAL form on a family collision and drops the OTel one", () => {
    const out = mergeExposition(LOCAL, OTEL);
    // The local, labeled form survives…
    expect(out).toContain('ws_messages_total{frame="update"} 10');
    // …and the OTel unlabeled duplicate does NOT (no second family def, no bare sample).
    expect(out).not.toContain("# HELP ws_messages_total Frames received (OTel, no labels).");
    expect(out).not.toMatch(/^ws_messages_total \d+/m);
    // Exactly one `# TYPE ws_messages_total` line in the result.
    expect(out.match(/# TYPE ws_messages_total /g)).toHaveLength(1);
  });

  it("preserves the local ordering first, OTel additions last", () => {
    const out = mergeExposition(LOCAL, OTEL);
    expect(out.indexOf("uptime_seconds 42")).toBeLessThan(out.indexOf("target_info"));
  });

  it("round-trips the local registry's own render() output", () => {
    const reg = new Metrics(() => 1000);
    reg.inc("ws_messages_total", { frame: "ping" });
    const local = reg.render();
    const out = mergeExposition(local, OTEL);
    expect(out).toContain('ws_messages_total{frame="ping"} 1');
    expect(out.match(/# TYPE ws_messages_total /g)).toHaveLength(1);
  });
});