ai generate git commit message from diffs of staged files

gen-commit-msg.ts

#!/usr/bin/env bun

import { exec } from "child_process";

/*
  Generate a commit message for the staged changes.
*/

import Anthropic from "@anthropic-ai/sdk";

const anthropic = new Anthropic();

async function sendPrompt(prompt: string) {
  const msg = await anthropic.messages.create({
    model: "claude-3-5-sonnet-20240620",
    max_tokens: 8192,
    temperature: 0,
    messages: [
      {
        role: "user",
        content:
          prompt +
          "\n\n" +
          "Generate a detailed commit message for the staged changes. Output like this:\n\n" +
          "```json\n" +
          '{ "commit_message": {' +
          '  "lines": ["<line1>", "<line2>", "<line3>"]' +
          "} }\n" +
          "```" +
          "\n\n" +
          "The commit message should be all lowercase, UNLESS referring to code or some other capitalized term. It does not need to be concise.",
      },
    ],
    stream: false,
  });

  return msg;
}

async function getStagedChangesDiffs() {
  return new Promise<string>((resolve, reject) => {
    const p = exec("git diff --cached");
    let stdout = "";
    let stderr = "";
    p.stdout?.on("data", (data) => {
      stdout += data;
    });
    p.stderr?.on("data", (data) => {
      stderr += data;
    });
    p.on("close", () => {
      if (stderr) {
        reject(stderr);
      }
      resolve(stdout);
    });
  });
}

async function main() {
  const stagedChangesDiffs = await getStagedChangesDiffs();
  if (stagedChangesDiffs.trim().length === 0) {
    console.error("No staged changes");
    process.exit(1);
  }
  const response = await sendPrompt(stagedChangesDiffs);
  const msg = response.content.map((c) => ("text" in c ? c.text : "")).join("");
  // get the message starting with "```json" and ending with "```"
  const jsonStart = msg.indexOf("```json");
  const jsonEnd = msg.indexOf("```", jsonStart + 1);

  try {
    const json = JSON.parse(msg.slice(jsonStart + 7, jsonEnd));
    const message = json.commit_message.lines;
    // trim each line
    const trimmedMessage = message
      .map((line: string, index: number) => {
        if (line.trim().length === 0) {
          return null;
        }
        if (index === 0) {
          return line.trim() + "\n";
        }
        return line.trim();
      })
      .filter((line: string | null) => line !== null)
      .join("\n");
    console.log(trimmedMessage);
  } catch (e) {
    console.error("Error parsing JSON for commit message");
    console.log("original message:", msg);
  }
}

await main();