import fs from "node:fs";
import { Tokenizer } from "@huggingface/tokenizers";
import { InferenceSession } from "onnxruntime-node";
import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
import {
  getRerankerStatus,
  rerank,
  sanitizeUnicodeSurrogates,
  startRerankerService,
  stopRerankerService,
  truncatePairTokens,
} from "./rerankerService";

vi.mock("@huggingface/tokenizers", () => ({
  Tokenizer: class {
    encode() {
      return { ids: [1, 2, 3] };
    }
  },
}));

vi.mock("./downloadFileFromHuggingFaceRepository", () => ({
  downloadFileFromHuggingFaceRepository: vi.fn(),
}));

vi.mock("onnxruntime-node", () => ({
  InferenceSession: { create: vi.fn() },
  Tensor: class {
    type: string;
    data: unknown;
    dims: number[];
    constructor(type: string, data: unknown, dims: number[]) {
      this.type = type;
      this.data = data;
      this.dims = dims;
    }
  },
}));

const HIGH = "\ud800";
const HIGH_MAX = "\udbff";
const LOW = "\udc00";
const LOW_MAX = "\udfff";
const REPLACEMENT = "\ufffd";

describe("sanitizeUnicodeSurrogates", () => {
  // One row per branch of the scanner: text it must not touch, a high surrogate
  // with nothing valid after it, a lone low surrogate, and the range edges that
  // decide which code units count as surrogates at all.
  it.each([
    ["leaves an empty string alone", "", ""],
    [
      "leaves text without surrogates alone",
      "Héllo Wörld 日本語!",
      "Héllo Wörld 日本語!",
    ],
    ["keeps a valid pair", "emoji 😀🎊 here", "emoji 😀🎊 here"],
    [
      "replaces a high surrogate at the end of the string",
      `text${HIGH}`,
      `text${REPLACEMENT}`,
    ],
    // U+FF01 sits above the low-surrogate range, so this row also holds the
    // upper bound of the pairing check.
    [
      "replaces a high surrogate followed by a non-surrogate",
      `${HIGH}\uff01`,
      `${REPLACEMENT}\uff01`,
    ],
    [
      "replaces both when a high surrogate follows a high surrogate",
      `${HIGH}${HIGH}`,
      `${REPLACEMENT}${REPLACEMENT}`,
    ],
    [
      "replaces a lone low surrogate",
      `before${LOW}after`,
      `before${REPLACEMENT}after`,
    ],
    [
      "replaces both halves of a reversed pair",
      `${LOW}${HIGH}`,
      `${REPLACEMENT}${REPLACEMENT}`,
    ],
    [
      "keeps a valid pair that follows an orphan",
      `A${HIGH} then ${HIGH}${LOW} end`,
      `A${REPLACEMENT} then ${HIGH}${LOW} end`,
    ],
    [
      "treats the top of each range as a surrogate too",
      `${HIGH_MAX}${LOW_MAX}${HIGH_MAX}`,
      `${HIGH_MAX}${LOW_MAX}${REPLACEMENT}`,
    ],
  ])("%s", (_, input, expected) => {
    expect(sanitizeUnicodeSurrogates(input)).toBe(expected);
  });
});

describe("startRerankerService", () => {
  const requestedExecutionProviders: string[][] = [];

  const sessionStub = {
    run: async () => ({ logits: { data: new Float32Array([0.5]) } }),
    release: async () => {},
  } as unknown as InferenceSession;

  function mockSessionCreation(respond: () => Promise<InferenceSession>) {
    vi.mocked(InferenceSession.create).mockImplementation(((
      _modelPath: string,
      options: { executionProviders: string[] },
    ) => {
      requestedExecutionProviders.push(options.executionProviders);
      return respond();
    }) as unknown as typeof InferenceSession.create);
  }

  beforeEach(() => {
    vi.spyOn(fs, "readFileSync").mockImplementation(() => "{}");
  });

  afterEach(async () => {
    await stopRerankerService();
    requestedExecutionProviders.length = 0;
    vi.restoreAllMocks();
  });

  // No GPU provider is requested: the quantized graph has no integer-matmul
  // kernels there and falls back operator by operator, which is slower than
  // running on CPU outright.
  it("creates a single CPU session and reports ready", async () => {
    mockSessionCreation(async () => sessionStub);

    await startRerankerService();

    expect(requestedExecutionProviders).toEqual([["cpu"]]);
    expect(await getRerankerStatus()).toBe(true);

    const downloadMock = vi.mocked(
      (await import("./downloadFileFromHuggingFaceRepository"))
        .downloadFileFromHuggingFaceRepository,
    );
    const downloadedFiles = downloadMock.mock.calls.map((call) => call[1]);
    expect(downloadedFiles).toContain("tokenizer.json");
    expect(downloadedFiles).toContain("tokenizer_config.json");
  });

  it("stays unready when the session cannot be created", async () => {
    const loadError = new Error("Protobuf parsing failed");
    mockSessionCreation(async () => {
      throw loadError;
    });

    await expect(startRerankerService()).rejects.toThrow(loadError);
    expect(requestedExecutionProviders).toEqual([["cpu"]]);
    expect(await getRerankerStatus()).toBe(false);
  });
});

describe("rerank", () => {
  let runMock: ReturnType<typeof vi.fn>;
  let encodeSpy: ReturnType<typeof vi.spyOn>;

  beforeEach(async () => {
    vi.spyOn(fs, "readFileSync").mockImplementation(() => "{}");
    encodeSpy = vi.spyOn(Tokenizer.prototype, "encode");
    runMock = vi.fn().mockResolvedValue({
      logits: { data: new Float32Array([0.5]) },
    });
    vi.mocked(InferenceSession.create).mockResolvedValue({
      run: runMock,
      release: async () => {},
    } as unknown as InferenceSession);
    await startRerankerService();
    // startRerankerService runs one warm-up score("test", ["test document"]);
    // clear it so per-test call-count assertions start from zero.
    runMock.mockClear();
    encodeSpy.mockClear();
  });

  afterEach(async () => {
    await stopRerankerService();
    vi.restoreAllMocks();
  });

  it("returns an empty array without calling the model when there are no documents", async () => {
    expect(await rerank("query", [])).toEqual([]);
    expect(runMock).not.toHaveBeenCalled();
  });

  it("returns an empty array for null or undefined documents", async () => {
    expect(await rerank("query", null as unknown as string[])).toEqual([]);
    expect(await rerank("query", undefined as unknown as string[])).toEqual([]);
    expect(runMock).not.toHaveBeenCalled();
  });

  it("throws when the service is not ready", async () => {
    await stopRerankerService();
    await expect(rerank("query", ["doc"])).rejects.toThrow(
      "Reranker service is not ready",
    );
  });

  it("maps each score to its document index and preserves input order", async () => {
    // Non-monotonic scores: the result must stay in input order, not be
    // sorted by relevance (sorting/filtering lives in rankSearchResults).
    for (const score of [0.5, 0.3, 0.8]) {
      runMock.mockResolvedValueOnce({
        logits: { data: new Float32Array([score]) },
      });
    }

    const result = await rerank("query", ["A", "B", "C"]);

    expect(result).toEqual([
      { index: 0, relevance_score: expect.closeTo(0.5) },
      { index: 1, relevance_score: expect.closeTo(0.3) },
      { index: 2, relevance_score: expect.closeTo(0.8) },
    ]);
  });

  it("scores one document per model call and concatenates in order", async () => {
    // Give every document a unique score equal to its position, so a dropped,
    // duplicated, or reordered call would break the assertions.
    let nextScore = 0;
    runMock.mockImplementation(async () => ({
      logits: { data: new Float32Array([nextScore++]) },
    }));

    const documents = Array.from({ length: 25 }, (_, i) => `doc ${i}`);
    const result = await rerank("query", documents);

    expect(runMock).toHaveBeenCalledTimes(25);
    expect(result).toHaveLength(25);
    expect(result[0]).toEqual({ index: 0, relevance_score: 0 });
    expect(result[24]).toEqual({ index: 24, relevance_score: 24 });
  });

  // The scores of a dynamically quantized graph depend on the whole tensor's
  // range, so a padded row would let one document's score shift another's.
  it("sends one unpadded row per call, with every position attended to", async () => {
    await rerank("query", ["A", "B"]);

    expect(runMock).toHaveBeenCalledTimes(2);
    for (const [inputs] of runMock.mock.calls) {
      const { input_ids, attention_mask } = inputs as {
        input_ids: { dims: number[]; data: BigInt64Array };
        attention_mask: { dims: number[]; data: BigInt64Array };
      };
      expect(input_ids.dims).toEqual([1, 3]);
      expect(Array.from(input_ids.data)).toEqual([1n, 2n, 3n]);
      expect(attention_mask.dims).toEqual([1, 3]);
      expect(Array.from(attention_mask.data)).toEqual([1n, 1n, 1n]);
    }
  });

  it("sanitizes unpaired surrogates in the query and documents before tokenizing", async () => {
    const loneHighSurrogate = String.fromCharCode(0xd800);

    await rerank(`query${loneHighSurrogate}`, [`doc${loneHighSurrogate}`]);

    // The lone surrogate must reach the tokenizer as U+FFFD, never raw: this
    // proves sanitization runs on the real path, not just that the model was hit.
    const [query, options] = encodeSpy.mock.calls[0];
    expect(query).toBe("query\ufffd");
    expect((options as { text_pair: string }).text_pair).toBe("doc\ufffd");
  });
});

describe("truncatePairTokens", () => {
  // Sequence layout: <s> q q </s> </s> | d d d d </s>
  const ids = [0, 11, 12, 2, 2, 21, 22, 23, 24, 2];

  it("returns the ids unchanged when within budget", () => {
    expect(truncatePairTokens(ids, 20)).toBe(ids);
  });

  it("drops document tokens from the end, keeping the query and trailing separator", () => {
    const out = truncatePairTokens(ids, 7);

    expect(out).toHaveLength(7);
    expect(out.slice(0, 5)).toEqual([0, 11, 12, 2, 2]); // query segment intact
    expect(out.at(-1)).toBe(2); // trailing separator preserved
    expect(out).toEqual([0, 11, 12, 2, 2, 21, 2]);
  });

  it("keeps a well-formed pair even when the query alone exceeds the budget", () => {
    expect(truncatePairTokens(ids, 3)).toEqual([0, 11, 2]);
  });

  it("never exceeds the position-embedding limit the model was built with", () => {
    const overLong = Array.from({ length: 900 }, (_, index) => index);

    expect(truncatePairTokens(overLong, 512)).toHaveLength(512);
  });
});