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

/**
 * Proof of Concept: Git Merkle DAG Diffing
 *
 * This module demonstrates using Git's fundamental Merkle Tree structure
 * (`git diff-tree` and `git ls-tree`) to perform zero-overhead, O(1) diffing
 * to find exactly which file hashes changed without reading the file string content.
 */

async function runGitCmd(args: string[]): Promise<string> {
  const cmd = new Deno.Command("git", {
    args,
    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 Git Merkle DAG Diffing PoC tests...");

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

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

    // 3. Diff HEAD against HEAD~1 (if available) to see what changed purely by hash
    try {
      const diffTreeOutput = await runGitCmd([
        "diff-tree",
        "--no-commit-id",
        "--name-only",
        "-r",
        "HEAD",
      ]);
      console.log(
        `\nChanged files in HEAD (O(1) diffing):\n${
          diffTreeOutput || "(No changes or no parent)"
        }`,
      );

      assertNotEquals(treeHash, "");
      console.log(
        "\n✅ Git Merkle DAG Diffing PoC successful: Read tree hashes without opening files.",
      );
    } catch (e: any) {
      if (e.message.includes("ambiguous argument")) {
        console.log(
          "Skipping diff-tree as there might not be enough commits in this repo for a diff.",
        );
      } else {
        throw e;
      }
    }
  } catch (err) {
    console.error("❌ Git Merkle DAG Diffing PoC failed:", err);
    Deno.exit(1);
  }
}