import { useState, useCallback } from 'react';

export interface PendingImage {
  base64: string;
  mediaType: string;
  preview: string; // data URL for <img> display
}

export type ContentBlock =
  | { type: 'text'; text: string }
  | { type: 'image'; source: { type: 'base64'; media_type: string; data: string } };

/**
 * Hook for handling clipboard image paste in admin chat interfaces.
 * Manages pending images and builds multimodal content blocks for Claude API.
 */
export function useImagePaste() {
  const [pendingImages, setPendingImages] = useState<PendingImage[]>([]);

  const handlePaste = useCallback((e: React.ClipboardEvent) => {
    const items = e.clipboardData?.items;
    if (!items) return;

    for (let i = 0; i < items.length; i++) {
      const item = items[i];
      if (item.type.startsWith('image/')) {
        e.preventDefault();
        const file = item.getAsFile();
        if (!file) continue;

        const reader = new FileReader();
        reader.onload = () => {
          const dataUrl = reader.result as string;
          const base64 = dataUrl.split(',')[1];
          const mediaType = file.type;
          setPendingImages(prev => [...prev, { base64, mediaType, preview: dataUrl }]);
        };
        reader.readAsDataURL(file);
        break; // one image per paste
      }
    }
  }, []);

  const removePendingImage = useCallback((index: number) => {
    setPendingImages(prev => prev.filter((_, i) => i !== index));
  }, []);

  const clearPendingImages = useCallback(() => {
    setPendingImages([]);
  }, []);

  /**
   * Build message content: plain string if text-only, array of blocks if images attached.
   */
  const buildContent = useCallback((text: string): string | ContentBlock[] => {
    if (pendingImages.length === 0) return text;

    const blocks: ContentBlock[] = [];
    for (const img of pendingImages) {
      blocks.push({
        type: 'image',
        source: { type: 'base64', media_type: img.mediaType, data: img.base64 },
      });
    }
    if (text) {
      blocks.push({ type: 'text', text });
    }
    return blocks;
  }, [pendingImages]);

  return {
    pendingImages,
    handlePaste,
    removePendingImage,
    clearPendingImages,
    buildContent,
  };
}