/**
 * @file Issue #45 part B: merge and conflict resolution from the dashboard,
 * against a REAL repo whose `main` and `feat` edit the same line. Pins the
 * guards (clean tree, repo-root lane, a ref that exists, one merge at a time,
 * a path that IS conflicted, markers gone before "resolved", confirm on
 * abort) and the happy paths (ours, theirs, hand-edited, commit, abort).
 * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
 */

const { describe, it, beforeEach } = require("node:test");
const assert = require("node:assert/strict");
const fs = require("node:fs");
const os = require("node:os");
const path = require("node:path");
const { execFileSync } = require("node:child_process");

const { runGitAction } = require("../lib/git-ops");
const { gitFacts } = require("../lib/worktree");
const { listTree, listPaths } = require("../lib/git-diff");

const ROOT = fs.mkdtempSync(path.join(os.tmpdir(), "agenthub-merge-"));
const REPO = path.join(ROOT, "repo");

const g = (...args) => {
  const env = { ...process.env, GIT_TERMINAL_PROMPT: "0" };
  delete env.GIT_DIR;
  delete env.GIT_WORK_TREE;
  delete env.GIT_INDEX_FILE;
  return execFileSync("git", args, { cwd: REPO, encoding: "utf8", env });
};
const write = (file, body) => fs.writeFileSync(path.join(REPO, file), body);
const read = (file) => fs.readFileSync(path.join(REPO, file), "utf8");

beforeEach(() => {
  fs.rmSync(REPO, { recursive: true, force: true });
  fs.mkdirSync(REPO, { recursive: true });
  g("init", "-q", "-b", "main");
  g("config", "user.email", "t@h");
  g("config", "user.name", "t");
  fs.mkdirSync(path.join(REPO, "sub"));
  write("a.txt", "base\n");
  write("sub/s.txt", "s\n");
  g("add", "-A");
  g("commit", "-qm", "init");
  g("switch", "-qc", "feat");
  write("a.txt", "theirs\n");
  write("b.txt", "only on feat\n");
  g("add", "-A");
  g("commit", "-qm", "feat");
  g("switch", "-q", "main");
  write("a.txt", "ours\n");
  g("commit", "-qam", "main");
});

const merge = () => runGitAction(REPO, "merge", { branch: "feat" });

describe("merge", () => {
  it("reports conflicts instead of failing, and gitFacts shows the merge", async () => {
    const r = await merge();
    assert.equal(r.ok, true);
    assert.deepEqual(r.conflicts, ["a.txt"]);
    const facts = await gitFacts(REPO);
    assert.equal(facts.merging, true);
    assert.equal(facts.conflicts, 1);
  });

  it("merges cleanly when there is nothing to resolve", async () => {
    write("a.txt", "theirs\n");
    g("commit", "-qam", "agree");
    const r = await merge();
    assert.deepEqual(r.conflicts, []);
    assert.equal(read("b.txt"), "only on feat\n");
    assert.equal((await gitFacts(REPO)).merging, false);
  });

  it("refuses a dirty tree, an unknown ref, a subdirectory lane and a second merge", async () => {
    write("a.txt", "wip\n");
    await assert.rejects(merge(), { code: "EDIRTY" });
    g("checkout", "--", "a.txt");
    await assert.rejects(runGitAction(REPO, "merge", { branch: "nope" }), { code: "ENOBRANCH" });
    await assert.rejects(runGitAction(REPO, "merge", { branch: "--help" }), { code: "EBADBRANCH" });
    await assert.rejects(runGitAction(path.join(REPO, "sub"), "merge", { branch: "feat" }), {
      code: "ESUBDIR",
    });
    await merge();
    await assert.rejects(merge(), { code: "EMERGING" });
    await assert.rejects(runGitAction(REPO, "pull"), { code: "EMERGING" });
  });
});

describe("listing files mid-merge", () => {
  it("lists a conflicted file once, not once per merge stage", async () => {
    await merge();
    const root = await listTree(REPO, {});
    assert.equal(root.entries.filter((e) => e.name === "a.txt").length, 1);
    assert.deepEqual((await listPaths(REPO, { q: "a.txt" })).paths, ["a.txt"]);
  });
});

describe("resolve", () => {
  it("takes our side or theirs, and only for a conflicted path", async () => {
    await merge();
    await assert.rejects(runGitAction(REPO, "resolve", { path: "b.txt", side: "ours" }), {
      code: "EBADPATH",
    });
    await assert.rejects(runGitAction(REPO, "resolve", { path: "a.txt", side: "mine" }), {
      code: "EBADSIDE",
    });
    await runGitAction(REPO, "resolve", { path: "a.txt", side: "theirs" });
    assert.equal(read("a.txt"), "theirs\n");
    assert.equal((await gitFacts(REPO)).conflicts, 0);
  });

  it("marks a hand-edited file resolved only once its markers are gone", async () => {
    await merge();
    await assert.rejects(runGitAction(REPO, "resolve", { path: "a.txt", side: "done" }), {
      code: "EMARKERS",
    });
    await assert.rejects(runGitAction(REPO, "stage", { paths: ["a.txt"] }), { code: "EMARKERS" });
    write("a.txt", "both\n");
    await runGitAction(REPO, "resolve", { path: "a.txt", side: "done" });
    assert.equal((await gitFacts(REPO)).conflicts, 0);
  });
});

describe("finish or abort", () => {
  it("commits the merge only when nothing is left unresolved", async () => {
    await merge();
    await assert.rejects(runGitAction(REPO, "merge-commit"), { code: "ECONFLICTS" });
    await runGitAction(REPO, "resolve", { path: "a.txt", side: "ours" });
    await runGitAction(REPO, "merge-commit");
    assert.equal((await gitFacts(REPO)).merging, false);
    assert.equal(g("rev-list", "--parents", "-n1", "HEAD").trim().split(" ").length, 3);
    assert.equal(read("a.txt"), "ours\n");
    await assert.rejects(runGitAction(REPO, "merge-commit"), { code: "ENOMERGE" });
  });

  it("names the merge after the branch, as git merge would — not its full refname", async () => {
    await merge();
    await runGitAction(REPO, "resolve", { path: "a.txt", side: "ours" });
    await runGitAction(REPO, "merge-commit");
    assert.equal(g("log", "-1", "--format=%s").trim(), "Merge branch 'feat'");
    // Into a branch other than main/master, git adds where it went.
    g("switch", "-qc", "side", "feat~1");
    write("c.txt", "c\n");
    g("add", "-A");
    g("commit", "-qm", "side");
    await runGitAction(REPO, "merge", { branch: "main" });
    assert.equal(g("log", "-1", "--format=%s").trim(), "Merge branch 'main' into side");
  });

  it("aborts only with confirm, back to where it started", async () => {
    await merge();
    await assert.rejects(runGitAction(REPO, "merge-abort"), { code: "ECONFIRM" });
    await runGitAction(REPO, "merge-abort", { confirm: true });
    assert.equal((await gitFacts(REPO)).merging, false);
    assert.equal(read("a.txt"), "ours\n");
    assert.equal(fs.existsSync(path.join(REPO, "b.txt")), false);
  });
});