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

// v1.7: caps shared between drag-drop and paste-as-attachment so both paths
// reject the same way. Match the existing 10-attachment cap in
// ChatInput.addAttachment.
export const MAX_FILE_SIZE_BYTES = 5 * 1024 * 1024; // 5 MB
export const PASTE_INLINE_MAX_LINES = 8;

// First-8KB null-byte scan. Returns true if the content looks binary.
// Accepts a string (post-decode), an ArrayBuffer (pre-decode), or a Uint8Array.
// For binary files like PNG, scanning bytes is more reliable than scanning
// post-UTF-8-decode strings because invalid sequences may be replaced rather
// than preserved.
export function looksBinary(content: string | ArrayBuffer | Uint8Array): boolean {
  const SCAN_BYTES = 8192;
  if (typeof content === 'string') {
    const max = Math.min(content.length, SCAN_BYTES);
    for (let i = 0; i < max; i++) {
      if (content.charCodeAt(i) === 0) return true;
    }
    return false;
  }
  const bytes = content instanceof Uint8Array ? content : new Uint8Array(content);
  const max = Math.min(bytes.length, SCAN_BYTES);
  for (let i = 0; i < max; i++) {
    if (bytes[i] === 0) return true;
  }
  return false;
}

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;
  // Pasted text is raw context, not code from a file — insert it verbatim with no
  // ``` fence or provenance header. It trails the typed text with a leading space
  // so a leading slash command / prompt stays first and the paste reads as its
  // continuation. File/line chips stay fenced provenance blocks, appended after.
  const pasteBlocks: string[] = [];
  const fencedBlocks: string[] = [];
  for (const a of attachments) {
    if (a.kind === 'paste') {
      pasteBlocks.push(a.content);
      continue;
    }
    const fence = '```' + (a.language ?? '');
    const header =
      a.kind === 'lines'
        ? `// from: ${a.filename}:${a.range?.[0] ?? '?'}-${a.range?.[1] ?? '?'}`
        : `// from: ${a.filename}`;
    fencedBlocks.push(`${fence}\n${header}\n${a.content}\n\`\`\``);
  }
  // Typed text + pasted content on the same logical line (space-joined), then
  // any fenced file blocks as separate paragraphs.
  const lead = [text, ...pasteBlocks].filter(Boolean).join(' ');
  return [lead, ...fencedBlocks].filter(Boolean).join('\n\n');
}