export type Attachment = {
  id: string;
  kind: 'file' | 'lines' | 'paste';
  filename: string;
  language: string | null;
  content: string;
  range?: [number, number];
  source: '@' | 'line-select' | 'drop' | 'paste';
};

export const LANG_MAP: Record<string, string> = {
  ts: 'typescript', tsx: 'tsx', js: 'javascript', jsx: 'jsx',
  mjs: 'javascript', cjs: 'javascript',
  py: 'python', go: 'go', rs: 'rust', rb: 'ruby', java: 'java',
  c: 'c', h: 'c', cpp: 'cpp', cc: 'cpp', hpp: 'cpp', cs: 'csharp',
  php: 'php', sh: 'bash', bash: 'bash', zsh: 'bash',
  yml: 'yaml', yaml: 'yaml', json: 'json', toml: 'toml',
  md: 'markdown', markdown: 'markdown', sql: 'sql', dockerfile: 'dockerfile',
  html: 'html', htm: 'html', css: 'css', scss: 'scss',
};

export function inferLanguage(filename: string): string | null {
  const base = filename.split('/').pop() ?? filename;
  if (base.toLowerCase() === 'dockerfile') return 'dockerfile';
  const m = base.match(/\.([^.]+)$/);
  return m ? (LANG_MAP[m[1]!.toLowerCase()] ?? null) : null;
}

export function flattenToMessage(attachments: Attachment[], text: string): string {
  if (attachments.length === 0) return text;
  const blocks = attachments.map(a => {
    const fence = '```' + (a.language ?? '');
    let header: string;
    if (a.kind === 'lines') {
      header = `// from: ${a.filename}:${a.range?.[0] ?? '?'}-${a.range?.[1] ?? '?'}`;
    } else if (a.kind === 'paste') {
      header = `// from: pasted text (${a.content.split('\n').length} lines)`;
    } else {
      header = `// from: ${a.filename}`;
    }
    return `${fence}\n${header}\n${a.content}\n\`\`\``;
  });
  return [...blocks, text].filter(Boolean).join('\n\n');
}