// The AGENTS.md editor's diff builder. Run by `npm test`, which Node runs with
// its built-in test runner and type stripping, so the `.ts` module is
// imported as it is. The expected strings are what `git diff` writes for the
// same two texts, and `git apply` reads back.
import assert from "node:assert/strict";
import { test } from "node:test";
import { unifiedDiff } from "../src/agent/detail/unified-diff.ts";

test("the same text has no diff", () => {
  assert.equal(unifiedDiff("a\nb\n", "a\nb\n"), "");
  assert.equal(unifiedDiff("", ""), "");
});

test("a changed middle line carries three lines of context", () => {
  const before = "1\n2\n3\n4\n5\n6\n7\n8\n9\n";
  const after = "1\n2\n3\n4\nfive\n6\n7\n8\n9\n";
  assert.equal(
    unifiedDiff(before, after),
    "--- a/AGENTS.md\n+++ b/AGENTS.md\n" +
      "@@ -2,7 +2,7 @@\n 2\n 3\n 4\n-5\n+five\n 6\n 7\n 8\n",
  );
});

test("two far apart changes make two hunks, near ones merge", () => {
  const lines = Array.from({ length: 20 }, (_, i) => `l${i + 1}`);
  const far = [...lines];
  far[1] = "X";
  far[17] = "Y";
  const farDiff = unifiedDiff(lines.join("\n") + "\n", far.join("\n") + "\n");
  assert.equal(farDiff.match(/^@@/gm)?.length, 2);

  const near = [...lines];
  near[1] = "X";
  near[6] = "Y";
  const nearDiff = unifiedDiff(lines.join("\n") + "\n", near.join("\n") + "\n");
  assert.equal(nearDiff.match(/^@@/gm)?.length, 1);
});

test("writing into an empty file adds every line", () => {
  assert.equal(
    unifiedDiff("", "hello\nworld\n"),
    "--- a/AGENTS.md\n+++ b/AGENTS.md\n@@ -0,0 +1,2 @@\n+hello\n+world\n",
  );
});

test("emptying a file removes every line", () => {
  assert.equal(
    unifiedDiff("hello\n", ""),
    "--- a/AGENTS.md\n+++ b/AGENTS.md\n@@ -1 +0,0 @@\n-hello\n",
  );
});

test("a missing final newline is marked as git marks it", () => {
  assert.equal(
    unifiedDiff("a\nb", "a\nb\n"),
    "--- a/AGENTS.md\n+++ b/AGENTS.md\n@@ -1,2 +1,2 @@\n a\n" +
      "-b\n\\ No newline at end of file\n+b\n",
  );
  assert.equal(
    unifiedDiff("a\nb\n", "a\nc"),
    "--- a/AGENTS.md\n+++ b/AGENTS.md\n@@ -1,2 +1,2 @@\n a\n" +
      "-b\n+c\n\\ No newline at end of file\n",
  );
});

test("a pure insertion keeps the lines around it as context", () => {
  assert.equal(
    unifiedDiff("a\nc\n", "a\nb\nc\n"),
    "--- a/AGENTS.md\n+++ b/AGENTS.md\n@@ -1,2 +1,3 @@\n a\n+b\n c\n",
  );
});

test("the file name is the one asked for", () => {
  assert.ok(
    unifiedDiff("a\n", "b\n", "CLAUDE.md").startsWith(
      "--- a/CLAUDE.md\n+++ b/CLAUDE.md\n",
    ),
  );
});