vscode-cowriting-plugin/test/attributionTracker.test.ts

import { describe, it, expect } from "vitest";
import { applyChange, coalesce, type LiveSpan, type TrackerCtx } from "../src/attributionTracker";
import type { Provenance } from "../src/model";

const HUMAN: Provenance = { kind: "human", id: "ben" };
const AGENT: Provenance = {
  kind: "agent", id: "claude",
  agent: { sdk: "@cline/sdk", model: "sonnet", sessionId: "run-1" },
};

function ctx(turnId?: string): TrackerCtx {
  let n = 0;
  return { newId: () => `n${++n}`, now: () => "2026-06-10T00:00:00.000Z", turnId };
}
function span(id: string, start: number, end: number, author: Provenance, turnId?: string): LiveSpan {
  return { id, start, end, author, turnId, createdAt: "2026-06-09T00:00:00.000Z" };
}
const ranges = (s: LiveSpan[]) => s.map((x) => [x.start, x.end]);
const authors = (s: LiveSpan[]) => s.map((x) => x.author.kind);

describe("applyChange — insertions", () => {
  it("insertion into empty span list creates one author span", () => {
    const r = applyChange([], { start: 5, end: 5, newLength: 3 }, HUMAN, ctx());
    expect(ranges(r)).toEqual([[5, 8]]);
    expect(r[0].author).toEqual(HUMAN);
  });
  it("insertion before a span shifts it", () => {
    const r = applyChange([span("a", 10, 14, AGENT)], { start: 0, end: 0, newLength: 2 }, HUMAN, ctx());
    expect(ranges(r)).toEqual([[0, 2], [12, 16]]);
    expect(authors(r)).toEqual(["human", "agent"]);
  });
  it("insertion after a span leaves it untouched", () => {
    const r = applyChange([span("a", 0, 4, AGENT)], { start: 10, end: 10, newLength: 2 }, HUMAN, ctx());
    expect(ranges(r)).toEqual([[0, 4], [10, 12]]);
  });
  it("PUC-3: insertion strictly inside a different-author span splits it char-precisely", () => {
    const r = applyChange([span("a", 0, 10, AGENT)], { start: 4, end: 4, newLength: 3 }, HUMAN, ctx());
    expect(ranges(r)).toEqual([[0, 4], [4, 7], [7, 13]]);
    expect(authors(r)).toEqual(["agent", "human", "agent"]);
  });
  it("symmetric: agent insertion inside a human span splits it (INV-7)", () => {
    const r = applyChange([span("a", 0, 10, HUMAN)], { start: 4, end: 4, newLength: 3 }, AGENT, ctx("t1"));
    expect(authors(r)).toEqual(["human", "agent", "human"]);
    expect(r[1].turnId).toBe("t1");
  });
  it("insertion inside a SAME-author span coalesces back to one span", () => {
    const r = applyChange([span("a", 0, 10, HUMAN)], { start: 4, end: 4, newLength: 3 }, HUMAN, ctx());
    expect(ranges(r)).toEqual([[0, 13]]);
  });
  it("insertion at a span boundary does not split; same author coalesces", () => {
    const r = applyChange([span("a", 0, 5, HUMAN)], { start: 5, end: 5, newLength: 2 }, HUMAN, ctx());
    expect(ranges(r)).toEqual([[0, 7]]);
  });
});

describe("applyChange — deletions", () => {
  it("deletion before a span shifts it left", () => {
    const r = applyChange([span("a", 10, 14, HUMAN)], { start: 0, end: 4, newLength: 0 }, HUMAN, ctx());
    expect(ranges(r)).toEqual([[6, 10]]);
  });
  it("deletion entirely inside a span shrinks it (no re-authoring, INV-6)", () => {
    const r = applyChange([span("a", 0, 10, AGENT)], { start: 3, end: 6, newLength: 0 }, HUMAN, ctx());
    expect(ranges(r)).toEqual([[0, 7]]);
    expect(authors(r)).toEqual(["agent"]);
  });
  it("deletion covering a whole span removes it", () => {
    const r = applyChange([span("a", 3, 6, AGENT)], { start: 0, end: 10, newLength: 0 }, HUMAN, ctx());
    expect(r).toEqual([]);
  });
  it("deletion clipping a span head keeps the tail", () => {
    const r = applyChange([span("a", 4, 10, AGENT)], { start: 0, end: 6, newLength: 0 }, HUMAN, ctx());
    expect(ranges(r)).toEqual([[0, 4]]);
  });
  it("deletion clipping a span tail keeps the head", () => {
    const r = applyChange([span("a", 0, 6, AGENT)], { start: 4, end: 10, newLength: 0 }, HUMAN, ctx());
    expect(ranges(r)).toEqual([[0, 4]]);
  });
});

describe("applyChange — replacements", () => {
  it("replacement inside an agent span: human chars in the middle, agent halves keep ids/createdAt", () => {
    const r = applyChange([span("a", 0, 12, AGENT)], { start: 4, end: 8, newLength: 2 }, HUMAN, ctx());
    expect(ranges(r)).toEqual([[0, 4], [4, 6], [6, 10]]);
    expect(authors(r)).toEqual(["agent", "human", "agent"]);
    expect(r[0].id).toBe("a");
    expect(r[0].createdAt).toBe("2026-06-09T00:00:00.000Z");
  });
  it("replacement spanning two spans clips both and inserts the author's span between", () => {
    const r = applyChange(
      [span("a", 0, 6, AGENT), span("b", 6, 12, HUMAN)],
      { start: 4, end: 8, newLength: 5 }, AGENT, ctx("t2"),
    );
    expect(ranges(r)).toEqual([[0, 4], [4, 9], [9, 13]]);
    expect(authors(r)).toEqual(["agent", "agent", "human"]);
    expect(r[1].turnId).toBe("t2");
  });
});

describe("multi-edit sequences", () => {
  it("type, agent-replace, type inside agent span — ends char-honest", () => {
    const c = ctx();
    let s = applyChange([], { start: 0, end: 0, newLength: 20 }, HUMAN, c);
    s = applyChange(s, { start: 5, end: 10, newLength: 8 }, AGENT, { ...c, turnId: "t1" });
    s = applyChange(s, { start: 9, end: 9, newLength: 1 }, HUMAN, c);
    expect(authors(s)).toEqual(["human", "agent", "human", "agent", "human"]);
    expect(ranges(s)).toEqual([[0, 5], [5, 9], [9, 10], [10, 14], [14, 24]]);
  });
});

describe("applyChange — geometric-only (undo/redo, #38)", () => {
  it("attributeInserted=false adds NO span for re-inserted text (restored text stays neutral)", () => {
    // Undo re-inserts 'bravo ' at offset 6 into an empty span list → no span.
    const r = applyChange([], { start: 6, end: 6, newLength: 6 }, HUMAN, ctx(), false);
    expect(r).toEqual([]);
  });
  it("attributeInserted=false still SHIFTS existing spans by the edit delta", () => {
    // A real human span sits after the re-insert point; it must shift right by 6,
    // but the re-inserted chars themselves get no new span.
    const r = applyChange([span("tail", 20, 30, HUMAN)], { start: 6, end: 6, newLength: 6 }, HUMAN, ctx(), false);
    expect(ranges(r)).toEqual([[26, 36]]);
    expect(authors(r)).toEqual(["human"]);
  });
  it("attributeInserted=false still reconciles geometry of a deletion (removes a covered span)", () => {
    const r = applyChange([span("a", 3, 6, AGENT)], { start: 0, end: 10, newLength: 0 }, HUMAN, ctx(), false);
    expect(r).toEqual([]);
  });
});

describe("coalesce", () => {
  it("merges adjacent same-author same-turn spans, keeps earliest createdAt", () => {
    const a = { ...span("a", 0, 3, HUMAN), createdAt: "2026-06-09T00:00:00.000Z" };
    const b = { ...span("b", 3, 6, HUMAN), createdAt: "2026-06-08T00:00:00.000Z" };
    const r = coalesce([a, b]);
    expect(ranges(r)).toEqual([[0, 6]]);
    expect(r[0].id).toBe("a");
    expect(r[0].createdAt).toBe("2026-06-08T00:00:00.000Z");
  });
  it("does NOT merge different authors, different turnIds, or non-adjacent spans", () => {
    expect(coalesce([span("a", 0, 3, HUMAN), span("b", 3, 6, AGENT)])).toHaveLength(2);
    expect(coalesce([span("a", 0, 3, AGENT, "t1"), span("b", 3, 6, AGENT, "t2")])).toHaveLength(2);
    expect(coalesce([span("a", 0, 3, HUMAN), span("b", 4, 6, HUMAN)])).toHaveLength(2);
  });
  it("drops empty spans", () => {
    expect(coalesce([span("a", 5, 5, HUMAN)])).toEqual([]);
  });
});

describe("edge probes (post-review)", () => {
  it("applyChange does not mutate its input array or spans", () => {
    const input = [span("a", 0, 10, AGENT)];
    const snapshot = JSON.parse(JSON.stringify(input));
    applyChange(input, { start: 2, end: 4, newLength: 1 }, HUMAN, ctx());
    expect(input).toEqual(snapshot);
  });
  it("an edit swallowing a whole middle span across three spans removes only it", () => {
    // Deletion [3,9): a → [0,3); b swallowed; c's remainder [9,12) shifts -6 to
    // [3,6). The two surviving HUMAN spans are adjacent at 3 with the same
    // (undefined) turnId, so coalesce merges them into ONE span — only the
    // agent-authored middle span's characters are gone (INV-6/INV-7).
    const r = applyChange(
      [span("a", 0, 4, HUMAN), span("b", 4, 8, AGENT), span("c", 8, 12, HUMAN)],
      { start: 3, end: 9, newLength: 0 }, HUMAN, ctx(),
    );
    expect(ranges(r)).toEqual([[0, 6]]);
    expect(authors(r)).toEqual(["human"]);
  });
  it("a replacement exactly covering a span replaces it with the editor's span", () => {
    const r = applyChange([span("a", 4, 8, AGENT)], { start: 4, end: 8, newLength: 4 }, HUMAN, ctx());
    expect(ranges(r)).toEqual([[4, 8]]);
    expect(authors(r)).toEqual(["human"]);
  });
});