#!/usr/bin/env bun

/**
 * commit-helper - Efficient git context gathering for AI-assisted commits
 * 
 * Provides optimized git context with smart truncation and filtering.
 * Designed to give AI assistants the right amount of context without overwhelming them.
 * 
 * Usage:
 *   commit-helper --staged [maxLines]    # For committing staged changes
 *   commit-helper --amend [maxLines]     # For amending last commit
 * 
 * Default maxLines: 1000
 */

import { $ } from "bun";

// Files to ignore in diffs (lockfiles, generated files, etc.)
const IGNORE_PATTERNS = [
  /package-lock\.json$/,
  /yarn\.lock$/,
  /pnpm-lock\.yaml$/,
  /Cargo\.lock$/,
  /poetry\.lock$/,
  /bun\.lockb?$/,
  /\.min\.(js|css)$/,
  /\.bundle\.(js|css)$/,
  /dist\/.*\.map$/,
  /\.svg$/,  // Often generated or binary-like
];

// Binary/large file extensions to skip in diffs
const BINARY_EXTENSIONS = [
  '.png', '.jpg', '.jpeg', '.gif', '.ico', '.webp',
  '.pdf', '.zip', '.tar', '.gz', '.woff', '.woff2', '.ttf', '.eot',
  '.mp4', '.mp3', '.wav', '.avi', '.mov',
  '.so', '.dylib', '.dll', '.exe',
];

interface ChangeStats {
  files: number;
  additions: number;
  deletions: number;
}

interface FileChange {
  path: string;
  additions: number;
  deletions: number;
  isBinary: boolean;
  shouldIgnore: boolean;
}

/**
 * Parse git diff numstat output into structured data
 */
function parseNumstat(numstat: string): FileChange[] {
  return numstat
    .split('\n')
    .filter(line => line.trim())
    .map(line => {
      const parts = line.split('\t');
      const additions = parts[0] === '-' ? 0 : parseInt(parts[0], 10);
      const deletions = parts[1] === '-' ? 0 : parseInt(parts[1], 10);
      const path = parts[2] || '';
      
      const isBinary = parts[0] === '-' && parts[1] === '-';
      const shouldIgnore = IGNORE_PATTERNS.some(pattern => pattern.test(path)) ||
                          BINARY_EXTENSIONS.some(ext => path.endsWith(ext));
      
      return { path, additions, deletions, isBinary, shouldIgnore };
    });
}

/**
 * Get overall change statistics
 */
function getChangeStats(files: FileChange[]): ChangeStats {
  return files.reduce((acc, file) => ({
    files: acc.files + 1,
    additions: acc.additions + file.additions,
    deletions: acc.deletions + file.deletions,
  }), { files: 0, additions: 0, deletions: 0 });
}

/**
 * Get file type distribution summary
 */
function getFileTypeDistribution(files: FileChange[]): string {
  const extensions = files.map(f => {
    const match = f.path.match(/\.([^.]+)$/);
    return match ? match[1] : '(no extension)';
  });
  
  const counts = new Map<string, number>();
  for (const ext of extensions) {
    counts.set(ext, (counts.get(ext) || 0) + 1);
  }
  
  return Array.from(counts.entries())
    .sort((a, b) => b[1] - a[1])
    .map(([ext, count]) => `  ${count.toString().padStart(3)} .${ext}`)
    .join('\n');
}

/**
 * Get categorized file changes summary
 */
function getFileSummary(files: FileChange[]): string {
  const included = files.filter(f => !f.shouldIgnore && !f.isBinary);
  const ignored = files.filter(f => f.shouldIgnore);
  const binary = files.filter(f => f.isBinary && !f.shouldIgnore);
  
  let summary = '';
  
  if (included.length > 0) {
    summary += '**Included changes:**\n';
    summary += included.map(f => {
      const changes = `(+${f.additions}/-${f.deletions})`;
      return `  ${changes.padEnd(12)} ${f.path}`;
    }).join('\n');
  }
  
  if (ignored.length > 0) {
    summary += '\n\n**Ignored files (lockfiles/generated):**\n';
    summary += ignored.map(f => `  ${f.path}`).join('\n');
    summary += '\n  _(Changes to these files are omitted from diff output)_';
  }
  
  if (binary.length > 0) {
    summary += '\n\n**Binary files:**\n';
    summary += binary.map(f => `  ${f.path}`).join('\n');
  }
  
  return summary;
}

/**
 * Get filtered diff output (excluding ignored files)
 */
async function getFilteredDiff(staged: boolean): Promise<string> {
  const command = staged 
    ? 'git diff --staged'
    : 'git diff HEAD~1..HEAD';
  
  // Get list of files to exclude
  const numstatCmd = staged
    ? 'git diff --staged --numstat'
    : 'git diff HEAD~1..HEAD --numstat';
  
  const numstat = await $`sh -c ${numstatCmd}`.text();
  const files = parseNumstat(numstat);
  const filesToExclude = files
    .filter(f => f.shouldIgnore || f.isBinary)
    .map(f => f.path);
  
  // Build diff command with exclusions
  if (filesToExclude.length === 0) {
    return await $`sh -c ${command}`.text();
  }
  
  // Git diff with pathspec exclusions
  const excludeArgs = filesToExclude.map(f => `:(exclude)${f}`).join(' ');
  const fullCommand = `${command} -- . ${excludeArgs}`;
  
  try {
    return await $`sh -c ${fullCommand}`.text();
  } catch {
    // If exclusion fails, just return full diff
    return await $`sh -c ${command}`.text();
  }
}

/**
 * Truncate diff to fit within line budget
 */
function truncateDiff(diff: string, maxLines: number, filesInfo: string): string {
  const lines = diff.split('\n');
  
  if (lines.length <= maxLines) {
    return diff;
  }
  
  // Try to include complete file diffs rather than cutting mid-file
  const fileDiffs: Array<{ header: string; content: string; lineCount: number }> = [];
  let currentFile: { header: string; lines: string[] } | null = null;
  
  for (const line of lines) {
    if (line.startsWith('diff --git')) {
      if (currentFile) {
        fileDiffs.push({
          header: currentFile.header,
          content: currentFile.lines.join('\n'),
          lineCount: currentFile.lines.length,
        });
      }
      currentFile = { header: line, lines: [line] };
    } else if (currentFile) {
      currentFile.lines.push(line);
    }
  }
  
  if (currentFile) {
    fileDiffs.push({
      header: currentFile.header,
      content: currentFile.lines.join('\n'),
      lineCount: currentFile.lines.length,
    });
  }
  
  // Include files until we hit the limit
  let includedLines = 0;
  const includedDiffs: string[] = [];
  const omittedFiles: string[] = [];
  
  for (const fileDiff of fileDiffs) {
    if (includedLines + fileDiff.lineCount <= maxLines - 10) { // Reserve space for summary
      includedDiffs.push(fileDiff.content);
      includedLines += fileDiff.lineCount;
    } else {
      // Extract filename from diff header
      const match = fileDiff.header.match(/diff --git a\/(.*?) b\//);
      if (match) {
        omittedFiles.push(match[1]);
      }
    }
  }
  
  let result = includedDiffs.join('\n\n');
  
  if (omittedFiles.length > 0) {
    result += '\n\n---\n';
    result += `**Note:** ${omittedFiles.length} file(s) omitted due to output size limit:\n`;
    result += omittedFiles.map(f => `  - ${f}`).join('\n');
    result += '\n\n_Full changes visible in git status/stat output above._';
  }
  
  return result;
}

/**
 * Get preview of new files being added
 */
async function getNewFilesPreviews(maxFiles: number = 5, maxLinesPerFile: number = 50): Promise<string> {
  try {
    // Get list of new files (A = added)
    const newFiles = await $`git diff --staged --name-only --diff-filter=A`.text();
    const files = newFiles.trim().split('\n').filter(f => f);
    
    if (files.length === 0) {
      return '';
    }
    
    const previews: string[] = [];
    const filesToShow = files.slice(0, maxFiles);
    
    for (const file of filesToShow) {
      // Skip binary files
      if (BINARY_EXTENSIONS.some(ext => file.endsWith(ext))) {
        previews.push(`=== ${file} ===\n(binary file)`);
        continue;
      }
      
      try {
        const content = await Bun.file(file).text();
        const lines = content.split('\n').slice(0, maxLinesPerFile);
        const truncated = lines.length < content.split('\n').length 
          ? `\n... (${content.split('\n').length - lines.length} more lines)`
          : '';
        
        previews.push(`=== ${file} ===\n${lines.join('\n')}${truncated}`);
      } catch {
        previews.push(`=== ${file} ===\n(unreadable)`);
      }
    }
    
    let result = previews.join('\n\n');
    
    if (files.length > maxFiles) {
      result += `\n\n_... and ${files.length - maxFiles} more new file(s)_`;
    }
    
    return result;
  } catch {
    return '';
  }
}

/**
 * Generate context for staged changes
 */
async function stagedContext(maxLines: number): Promise<string> {
  // Check if there are staged changes
  try {
    await $`git diff --staged --quiet`;
    // If command succeeds (exit 0), there are no changes
    throw new Error('No staged changes to commit');
  } catch (err) {
    // Exit code 1 means there are changes (expected)
    // Any other error will be re-thrown
    if (err && typeof err === 'object' && 'exitCode' in err && err.exitCode !== 1) {
      throw err;
    }
  }
  
  // Gather all git information
  const [status, numstat, recentCommits] = await Promise.all([
    $`git status`.text(),
    $`git diff --staged --numstat`.text(),
    $`git log --format='%h %s' -10`.text(),
  ]);
  
  const files = parseNumstat(numstat);
  const stats = getChangeStats(files);
  const fileSummary = getFileSummary(files);
  const fileTypes = getFileTypeDistribution(files);
  
  // Calculate how many lines we can use for diff
  const headerLines = 50; // Approximate lines for headers/summaries
  const diffMaxLines = Math.max(100, maxLines - headerLines);
  
  const diff = await getFilteredDiff(true);
  const truncatedDiff = truncateDiff(diff, diffMaxLines, fileSummary);
  
  const newFilesPreviews = await getNewFilesPreviews(5, 50);
  
  // Build output
  let output = '# Git Commit Context (Staged Changes)\n\n';
  
  output += '## Status\n```\n' + status.trim() + '\n```\n\n';
  
  output += '## Change Summary\n';
  output += `**Files:** ${stats.files} | **Additions:** ${stats.additions} | **Deletions:** ${stats.deletions}\n\n`;
  
  output += '## Files Changed\n' + fileSummary + '\n\n';
  
  output += '## File Types Modified\n```\n' + fileTypes + '\n```\n\n';
  
  output += '## Staged Changes (Diff)\n';
  output += '```diff\n' + truncatedDiff.trim() + '\n```\n\n';
  
  if (newFilesPreviews) {
    output += '## New Files Preview\n```\n' + newFilesPreviews + '\n```\n\n';
  }
  
  output += '## Recent Commit Style\n```\n' + recentCommits.trim() + '\n```\n';
  
  return output;
}

/**
 * Generate context for amending last commit
 */
async function amendContext(maxLines: number): Promise<string> {
  // Check if we have any commits
  try {
    await $`git rev-parse HEAD`;
  } catch {
    throw new Error('No commits to amend');
  }
  
  // Gather git information
  const [stagedStat, lastCommitStat, recentCommits] = await Promise.all([
    $`git diff --staged --stat`.text(),
    $`git show --stat --pretty=format: HEAD`.text().then(s => s.split('\n').filter(l => l.trim()).join('\n')),
    $`git log --oneline -5`.text(),
  ]);
  
  let output = '# Git Commit Context (Amend)\n\n';
  
  output += '## Current Staged Changes\n';
  if (stagedStat.trim()) {
    output += '```\n' + stagedStat.trim() + '\n```\n\n';
  } else {
    output += '_No staged changes (message-only amendment)_\n\n';
  }
  
  output += '## Files in Most Recent Commit\n';
  output += '```\n' + lastCommitStat.trim() + '\n```\n\n';
  
  output += '## Recent Commit History (for style reference)\n';
  output += '```\n' + recentCommits.trim() + '\n```\n';
  
  return output;
}

/**
 * Main entry point
 */
async function main() {
  const args = Bun.argv.slice(2);
  
  if (args.length === 0 || (!args[0].startsWith('--staged') && !args[0].startsWith('--amend'))) {
    console.error('Usage: commit-helper --staged [maxLines] | --amend [maxLines]');
    console.error('  Default maxLines: 1000');
    process.exit(1);
  }
  
  const mode = args[0];
  const maxLines = args[1] ? parseInt(args[1], 10) : 1000;
  
  if (isNaN(maxLines) || maxLines < 100) {
    console.error('Error: maxLines must be a number >= 100');
    process.exit(1);
  }
  
  try {
    let output: string;
    
    if (mode === '--staged') {
      output = await stagedContext(maxLines);
    } else if (mode === '--amend') {
      output = await amendContext(maxLines);
    } else {
      throw new Error(`Unknown mode: ${mode}`);
    }
    
    console.log(output);
  } catch (error) {
    if (error instanceof Error) {
      console.error(`Error: ${error.message}`);
      if (error.stack) {
        console.error('\nStack trace:');
        console.error(error.stack);
      }
    } else if (error && typeof error === 'object') {
      console.error('Error details:', JSON.stringify(error, null, 2));
    } else {
      console.error('Error: Unknown error occurred:', error);
    }
    process.exit(1);
  }
}

main();