/**
 * TASK-0122 — the frontend SSE parser must round-trip ALL delta types
 * (delta / tool_call / usage / error / done), skip keepalive comment
 * lines, and survive partial frames split across chunk boundaries.
 *
 * @vitest-environment node (no DOM needed; the config default is jsdom,
 * which is not installed — every web test opts into node explicitly).
 */
import { describe, it, expect } from "vitest";
import { parseSseFrames, type AiSseFrame } from "@/lib/ai";

const wire = (frames: AiSseFrame[], keepaliveEvery: number) =>
  frames
    .map((f, i) => (keepaliveEvery > 0 && i > 0 && i % keepaliveEvery === 0 ? `: keepalive\n\ndata: ${JSON.stringify(f)}\n\n` : `data: ${JSON.stringify(f)}\n\n`))
    .join("");

describe("parseSseFrames", () => {
  it("parses every delta type in the documented contract", () => {
    const frames: AiSseFrame[] = [
      { type: "delta", text: "Hel" },
      { type: "delta", text: "lo" },
      { type: "tool_call", id: "mock_call_0", name: "createPage", arguments: { title: "X" } },
      { type: "usage", tokensIn: 12, tokensOut: 4 },
      { type: "error", code: "TIMEOUT", message: "The AI request took too long.", retryable: true, retryAfterSeconds: 5 },
      { type: "done", assistantMessageId: "a1", userMessageId: "u1", reason: "ok" }
    ];
    const { frames: out, rest } = parseSseFrames(wire(frames, 2));
    expect(rest).toBe("");
    expect(out).toEqual(frames);
  });

  it("skips `: keepalive` comment lines", () => {
    const { frames } = parseSseFrames(": keepalive\n\ndata: {\"type\":\"delta\",\"text\":\"a\"}\n\n: keepalive\n\ndata: {\"type\":\"done\",\"reason\":\"ok\"}\n\n");
    expect(frames).toEqual([
      { type: "delta", text: "a" },
      { type: "done", reason: "ok" }
    ]);
  });

  it("keeps a partial trailing frame for the next chunk (chunk boundary)", () => {
    // A real stream splits JSON mid-way between TCP chunks.
    const full = `data: {"type":"usage","tokensIn":7,"tokensOut":3}\n\n`;
    const { frames: f1, rest: r1 } = parseSseFrames(full.slice(0, 14)); // mid-JSON
    expect(f1).toEqual([]);
    expect(r1).toBe(full.slice(0, 14));
    const { frames: f2, rest: r2 } = parseSseFrames(r1 + full.slice(14));
    expect(f2).toEqual([{ type: "usage", tokensIn: 7, tokensOut: 3 }]);
    expect(r2).toBe("");
  });

  it("handles multiple frames in one chunk and frames split across chunks", () => {
    const full = `data: {"type":"delta","text":"a"}\n\ndata: {"type":"delta","text":"b"}\n\ndata: {"type":"done","reason":"ok"}\n\n`;
    // Split at a byte boundary INSIDE the second frame's JSON (mid-stream).
    const split = full.indexOf("b") + 3;
    const { frames: f1, rest: r1 } = parseSseFrames(full.slice(0, split));
    expect(f1).toEqual([{ type: "delta", text: "a" }]);
    const { frames: f2, rest: r2 } = parseSseFrames(r1 + full.slice(split));
    expect(f2).toEqual([{ type: "delta", text: "b" }, { type: "done", reason: "ok" }]);
    expect(r2).toBe("");
  });

  it("skips a malformed data line without dropping the stream", () => {
    const { frames } = parseSseFrames('data: {not-json}\n\ndata: {"type":"delta","text":"ok"}\n\n');
    expect(frames).toEqual([{ type: "delta", text: "ok" }]);
  });

  it("round-trips the exact mock-provider stream (word deltas + sys tail)", () => {
    // The E2E happy path: mock echoes the question word-by-word.
    const words = "what is the launch plan".split(" ");
    const stream = words.map((w) => `data: ${JSON.stringify({ type: "delta", text: w === "what" ? w : ` ${w}` })}\n\n`).join("") + `data: ${JSON.stringify({ type: "usage", tokensIn: 3, tokensOut: 3 })}\n\ndata: ${JSON.stringify({ type: "done", assistantMessageId: "a", userMessageId: "u", reason: "ok" })}\n\n`;
    const { frames, rest } = parseSseFrames(stream);
    expect(rest).toBe("");
    expect(frames.filter((f) => f.type === "delta")).toHaveLength(words.length);
    const text = frames.filter((f) => f.type === "delta").map((f) => (f as { text: string }).text).join("");
    expect(text).toBe("what is the launch plan");
    expect(frames[frames.length - 1]).toEqual({ type: "done", assistantMessageId: "a", userMessageId: "u", reason: "ok" });
  });
});