import { describe, expect, it } from "vitest";
import type { StreamItem } from "@/types/stream";
import { buildAgentStreamRenderModel } from "./agent-stream-render-model";

function createTimestamp(seed: number): Date {
  return new Date(`2026-01-01T00:00:${seed.toString().padStart(2, "0")}.000Z`);
}

function userMessage(id: string, seed: number): StreamItem {
  return {
    kind: "user_message",
    id,
    text: id,
    timestamp: createTimestamp(seed),
  };
}

function assistantMessage(id: string, seed: number): StreamItem {
  return {
    kind: "assistant_message",
    id,
    text: id,
    timestamp: createTimestamp(seed),
  };
}

describe("buildAgentStreamRenderModel", () => {
  it("keeps head separate from committed history on desktop web", () => {
    const tail: StreamItem[] = [];
    for (let index = 0; index < 60; index += 1) {
      const seed = index * 2;
      tail.push(userMessage(`u${index}`, seed + 1));
      tail.push(assistantMessage(`a${index}`, seed + 2));
    }
    const head = [assistantMessage("live-a", 121)];

    const model = buildAgentStreamRenderModel({
      tail,
      head,
      platform: "web",
      isMobileBreakpoint: false,
    });

    expect(model.segments.historyVirtualized.length).toBeGreaterThan(0);
    expect(model.segments.historyMounted.length).toBeGreaterThan(0);
    expect(model.segments.liveHead.map((item) => item.id)).toEqual(["live-a"]);
    expect(model.history).not.toContain(head[0]);
  });

  it("keeps the full committed tail mounted on mobile web", () => {
    const tail = [userMessage("u1", 1), assistantMessage("a1", 2)];
    const head = [assistantMessage("live-a", 3)];

    const model = buildAgentStreamRenderModel({
      tail,
      head,
      platform: "web",
      isMobileBreakpoint: true,
    });

    expect(model.segments.historyVirtualized).toHaveLength(0);
    expect(model.segments.historyMounted).toBe(tail);
    expect(model.segments.liveHead).toBe(head);
  });

  it("reuses ordered committed history when only the live head changes", () => {
    const tail = [userMessage("u1", 1), assistantMessage("a1", 2)];
    const firstHead = [assistantMessage("live-a", 3)];
    const secondHead = [assistantMessage("live-b", 4)];

    const first = buildAgentStreamRenderModel({
      tail,
      head: firstHead,
      platform: "native",
      isMobileBreakpoint: false,
    });
    const second = buildAgentStreamRenderModel({
      tail,
      head: secondHead,
      platform: "native",
      isMobileBreakpoint: false,
    });

    expect(first.history).toBe(second.history);
    expect(first.segments.historyMounted).toBe(second.segments.historyMounted);
    expect(second.segments.liveHead.map((item) => item.id)).toEqual(["live-b"]);
  });
});