opencommit/src/generateCommitMessageFromGitDiff.ts

import {
  ChatCompletionRequestMessage,
  ChatCompletionRequestMessageRoleEnum
} from 'openai';
import { api } from './api';
import { getConfig } from './commands/config';
import { mergeDiffs } from './utils/mergeDiffs';
import { i18n, I18nLocals } from './i18n';
import { tokenCount } from './utils/tokenCount';

const config = getConfig();
const translation = i18n[(config?.language as I18nLocals) || 'en'];

const INIT_MESSAGES_PROMPT: Array<ChatCompletionRequestMessage> = [
  {
    role: ChatCompletionRequestMessageRoleEnum.System,
    // prettier-ignore
    content: `You are to act as the author of a commit message in git. Your mission is to create clean and comprehensive commit messages in the conventional commit convention and explain WHAT were the changes and WHY the changes were done. I'll send you an output of 'git diff --staged' command, and you convert it into a commit message.
${config?.emoji? 'Use GitMoji convention to preface the commit.': 'Do not preface the commit with anything.'}
${config?.description  ? 'Add a short description of WHY the changes are done after the commit message. Don\'t start it with "This commit", just describe the changes.': "Don't add any descriptions to the commit, only commit message."}
Use the present tense. Lines must not be longer than 74 characters. Use ${translation.localLanguage} to answer.`
  },
  {
    role: ChatCompletionRequestMessageRoleEnum.User,
    content: `diff --git a/src/server.ts b/src/server.ts
index ad4db42..f3b18a9 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -10,7 +10,7 @@
import {
  initWinstonLogger();
  
  const app = express();
 -const port = 7799;
 +const PORT = 7799;
  
  app.use(express.json());
  
@@ -34,6 +34,6 @@
app.use((_, res, next) => {
  // ROUTES
  app.use(PROTECTED_ROUTER_URL, protectedRouter);
  
 -app.listen(port, () => {
 -  console.log(\`Server listening on port \${port}\`);
 +app.listen(process.env.PORT || PORT, () => {
 +  console.log(\`Server listening on port \${PORT}\`);
  });`
  },
  {
    role: ChatCompletionRequestMessageRoleEnum.Assistant,
    content: `${config?.emoji ? '🐛 ' : ''}${translation.commitFix}
${config?.emoji ? '✨ ' : ''}${translation.commitFeat}
${config?.description ? translation.commitDescription : ''}`
  }
];

const generateCommitMessageChatCompletionPrompt = (
  diff: string
): Array<ChatCompletionRequestMessage> => {
  const chatContextAsCompletionRequest = [...INIT_MESSAGES_PROMPT];

  chatContextAsCompletionRequest.push({
    role: ChatCompletionRequestMessageRoleEnum.User,
    content: diff
  });

  return chatContextAsCompletionRequest;
};

export enum GenerateCommitMessageErrorEnum {
  tooMuchTokens = 'TOO_MUCH_TOKENS',
  internalError = 'INTERNAL_ERROR',
  emptyMessage = 'EMPTY_MESSAGE'
}

interface GenerateCommitMessageError {
  error: GenerateCommitMessageErrorEnum;
}

const INIT_MESSAGES_PROMPT_LENGTH = INIT_MESSAGES_PROMPT.map(
  (msg) => tokenCount(msg.content) + 4
).reduce((a, b) => a + b, 0);

const MAX_REQ_TOKENS = 3900 - INIT_MESSAGES_PROMPT_LENGTH;

export const generateCommitMessageWithChatCompletion = async (
  diff: string
): Promise<string | GenerateCommitMessageError> => {
  try {
    if (tokenCount(diff) >= MAX_REQ_TOKENS) {
      const commitMessagePromises = getCommitMsgsPromisesFromFileDiffs(
        diff,
        MAX_REQ_TOKENS
      );

      const commitMessages = await Promise.all(commitMessagePromises);

      return commitMessages.join('\n\n');
    } else {
      const messages = generateCommitMessageChatCompletionPrompt(diff);

      const commitMessage = await api.generateCommitMessage(messages);

      if (!commitMessage)
        return { error: GenerateCommitMessageErrorEnum.emptyMessage };

      return commitMessage;
    }
  } catch (error) {
    return { error: GenerateCommitMessageErrorEnum.internalError };
  }
};

function getMessagesPromisesByChangesInFile(
  fileDiff: string,
  separator: string,
  maxChangeLength: number
) {
  const hunkHeaderSeparator = '@@ ';
  const [fileHeader, ...fileDiffByLines] = fileDiff.split(hunkHeaderSeparator);

  // merge multiple line-diffs into 1 to save tokens
  const mergedChanges = mergeDiffs(
    fileDiffByLines.map((line) => hunkHeaderSeparator + line),
    maxChangeLength
  );

  const lineDiffsWithHeader = mergedChanges.map(
    (change) => fileHeader + change
  );

  const commitMsgsFromFileLineDiffs = lineDiffsWithHeader.map((lineDiff) => {
    const messages = generateCommitMessageChatCompletionPrompt(
      separator + lineDiff
    );

    return api.generateCommitMessage(messages);
  });

  return commitMsgsFromFileLineDiffs;
}

export function getCommitMsgsPromisesFromFileDiffs(
  diff: string,
  maxDiffLength: number
) {
  const separator = 'diff --git ';

  const diffByFiles = diff.split(separator).slice(1);

  // merge multiple files-diffs into 1 prompt to save tokens
  const mergedFilesDiffs = mergeDiffs(diffByFiles, maxDiffLength);

  const commitMessagePromises = [];

  for (const fileDiff of mergedFilesDiffs) {
    if (tokenCount(fileDiff) >= maxDiffLength) {
      // if file-diff is bigger than gpt context — split fileDiff into lineDiff
      const messagesPromises = getMessagesPromisesByChangesInFile(
        fileDiff,
        separator,
        maxDiffLength
      );

      commitMessagePromises.push(...messagesPromises);
    } else {
      const messages = generateCommitMessageChatCompletionPrompt(
        separator + fileDiff
      );

      commitMessagePromises.push(api.generateCommitMessage(messages));
    }
  }
  return commitMessagePromises;
}