import {
  assertEquals,
  assertNotEquals,
} from "https://deno.land/std@0.224.0/testing/asserts.ts";

/**
 * Generation 2 Proof of Concept: Git Merkle DAG Diffing
 *
 * This module demonstrates using Git's Merkle Tree structure to perform
 * O(1) diffing (`git diff-tree` and `git ls-tree`). To prove production readiness
 * and avoid failures from shallow clones or dirty states, we instantiate
 * a clean, isolated Git repository with a deterministic commit history.
 */

async function runGitCmd(args: string[], cwd?: string): Promise<string> {
  const cmd = new Deno.Command("git", {
    args,
    cwd,
    stdout: "piped",
    stderr: "piped",
  });
  const output = await cmd.output();
  const stdout = new TextDecoder().decode(output.stdout).trim();
  const stderr = new TextDecoder().decode(output.stderr).trim();

  if (!output.success) {
    throw new Error(`Git command failed: git ${args.join(" ")}\n${stderr}`);
  }
  return stdout;
}

if (import.meta.main) {
  console.log("Running Gen 2 Git Merkle DAG Diffing PoC tests...");

  const tempDir = await Deno.makeTempDir({ prefix: "agent-forum-merkle-poc-" });
  console.log(`Created isolated Git repo at ${tempDir}`);

  try {
    // 0. Setup an isolated Git repo with two commits
    await runGitCmd(["init"], tempDir);
    await runGitCmd(["config", "user.email", "poc@example.com"], tempDir);
    await runGitCmd(["config", "user.name", "PoC Tester"], tempDir);

    const fileA = `${tempDir}/fileA.txt`;
    const fileB = `${tempDir}/fileB.txt`;

    // Commit 1
    await Deno.writeTextFile(fileA, "Hello World A");
    await Deno.writeTextFile(fileB, "Hello World B");
    await runGitCmd(["add", "."], tempDir);
    await runGitCmd(["commit", "-m", "Commit 1"], tempDir);

    // Commit 2: Modify fileA only
    await Deno.writeTextFile(fileA, "Hello World A - Modified");
    await runGitCmd(["add", "."], tempDir);
    await runGitCmd(["commit", "-m", "Commit 2"], tempDir);

    // 1. Get the current HEAD commit hash
    const headHash = await runGitCmd(["rev-parse", "HEAD"], tempDir);
    console.log(`Current HEAD: ${headHash}`);

    // 2. Get the tree hash of HEAD
    const treeHash = await runGitCmd(["rev-parse", "HEAD^{tree}"], tempDir);
    console.log(`Tree Hash of HEAD: ${treeHash}`);

    // 3. Diff HEAD against HEAD~1
    const diffTreeOutput = await runGitCmd([
      "diff-tree",
      "--no-commit-id",
      "--name-only",
      "-r",
      "HEAD~1",
      "HEAD",
    ], tempDir);

    console.log(
      `\nChanged files between HEAD~1 and HEAD (O(1) diffing):\n${diffTreeOutput}`,
    );

    // Assert that only fileA.txt changed
    assertEquals(diffTreeOutput, "fileA.txt");
    assertNotEquals(treeHash, "");

    // 4. Also use ls-tree to read the structure
    const lsTreeOutput = await runGitCmd(["ls-tree", "HEAD"], tempDir);
    console.log(`\nls-tree of HEAD:\n${lsTreeOutput}`);

    console.log(
      "\n✅ Gen 2 Git Merkle DAG Diffing PoC successful: Deterministic isolated diffing achieved.",
    );
  } catch (err) {
    console.error("❌ Gen 2 Git Merkle DAG Diffing PoC failed:", err);
    Deno.exit(1);
  } finally {
    console.log(`Cleaning up isolated Git repo...`);
    await Deno.remove(tempDir, { recursive: true });
  }
}