pdf-translation-interface/lib/pdf-to-image.ts

import sharp from 'sharp'
import fs from 'fs'
import path from 'path'
import os from 'os'

interface PDFToImageOptions {
  density?: number
  saveToFile?: boolean
  format?: 'png' | 'jpeg'
  quality?: number
}

interface ConvertedPage {
  pageNumber: number
  buffer: Buffer
  width: number
  height: number
}

export async function convertPDFToImages(
  pdfBuffer: Buffer,
  options: PDFToImageOptions = {}
): Promise<ConvertedPage[]> {
  const {
    density = 300,
    format = 'png',
    quality = 100
  } = options

  // Try pdf2pic first, then fall back to pdf-poppler
  let convertedPages: ConvertedPage[] = []
  
  try {
    console.log('Attempting PDF conversion with pdf2pic...')
    convertedPages = await convertWithPdf2pic(pdfBuffer, options)
    if (convertedPages.length > 0) {
      return convertedPages
    }
  } catch (error) {
    console.warn('pdf2pic conversion failed:', error)
  }
  
  try {
    console.log('Attempting PDF conversion with pdf-poppler...')
    convertedPages = await convertWithPdfPoppler(pdfBuffer, options)
    if (convertedPages.length > 0) {
      return convertedPages
    }
  } catch (error) {
    console.warn('pdf-poppler conversion failed:', error)
  }
  
  // If both methods fail, provide helpful error message
  throw new Error('PDF 轉圖片失敗：需要安裝 GraphicsMagick、ImageMagick 或 Poppler 工具。請安裝其中一個依賴項目。')
}

async function convertWithPdf2pic(
  pdfBuffer: Buffer,
  options: PDFToImageOptions = {}
): Promise<ConvertedPage[]> {
  const {
    density = 300,
    format = 'png',
    quality = 100
  } = options

  const { fromPath } = await import('pdf2pic')
  
  // Create temporary file for PDF
  const tempDir = os.tmpdir()
  const tempPdfPath = path.join(tempDir, `temp_${Date.now()}.pdf`)
  
  try {
    // Write PDF buffer to temporary file
    fs.writeFileSync(tempPdfPath, pdfBuffer)

    // Configure pdf2pic
    const convert = fromPath(tempPdfPath, {
      density: density,
      saveToFile: false,
      savePath: tempDir,
      format: format,
      width: 2480, // A4 at 300 DPI
      height: 3508
    })

    const convertedPages: ConvertedPage[] = []
    let pageNumber = 1
    
    // Convert all pages
    while (true) {
      try {
        const pageResult = await convert(pageNumber, { responseType: 'buffer' })
        if (!pageResult || !pageResult.buffer) {
          break // No more pages
        }

        // Optimize image with Sharp
        let processedBuffer = pageResult.buffer
        if (format === 'jpeg') {
          processedBuffer = await sharp(pageResult.buffer)
            .jpeg({ quality: quality })
            .toBuffer()
        } else {
          processedBuffer = await sharp(pageResult.buffer)
            .png({ quality: quality })
            .toBuffer()
        }

        // Get image dimensions
        const metadata = await sharp(processedBuffer).metadata()
        
        convertedPages.push({
          pageNumber,
          buffer: processedBuffer,
          width: metadata.width || 0,
          height: metadata.height || 0
        })

        pageNumber++
      } catch (error) {
        // No more pages or conversion error
        console.log(`Finished converting ${pageNumber - 1} pages`)
        break
      }
    }

    return convertedPages

  } finally {
    // Clean up temporary file
    try {
      if (fs.existsSync(tempPdfPath)) {
        fs.unlinkSync(tempPdfPath)
      }
    } catch (cleanupError) {
      console.warn('Failed to clean up temporary PDF file:', cleanupError)
    }
  }
}

async function convertWithPdfPoppler(
  pdfBuffer: Buffer,
  options: PDFToImageOptions = {}
): Promise<ConvertedPage[]> {
  const {
    density = 300,
    format = 'png'
  } = options

  // Try using pdf-poppler as alternative
  try {
    const poppler = await import('pdf-poppler')
    
    // Create temporary file for PDF
    const tempDir = os.tmpdir()
    const tempPdfPath = path.join(tempDir, `temp_${Date.now()}.pdf`)
    
    try {
      // Write PDF buffer to temporary file
      fs.writeFileSync(tempPdfPath, pdfBuffer)

      const popplerOptions = {
        format: format,
        out_dir: tempDir,
        out_prefix: `converted_${Date.now()}`,
        page: null, // Convert all pages
        png_file: format === 'png',
        jpeg_file: format === 'jpeg'
      }

      const convertedFiles = await poppler.convert(tempPdfPath, popplerOptions)
      const convertedPages: ConvertedPage[] = []

      if (Array.isArray(convertedFiles)) {
        for (let i = 0; i < convertedFiles.length; i++) {
          const filePath = convertedFiles[i]
          try {
            const imageBuffer = fs.readFileSync(filePath)
            const metadata = await sharp(imageBuffer).metadata()
            
            convertedPages.push({
              pageNumber: i + 1,
              buffer: imageBuffer,
              width: metadata.width || 0,
              height: metadata.height || 0
            })
            
            // Clean up converted file
            fs.unlinkSync(filePath)
          } catch (fileError) {
            console.warn(`Failed to process converted file ${filePath}:`, fileError)
          }
        }
      }

      return convertedPages

    } finally {
      // Clean up temporary PDF file
      try {
        if (fs.existsSync(tempPdfPath)) {
          fs.unlinkSync(tempPdfPath)
        }
      } catch (cleanupError) {
        console.warn('Failed to clean up temporary PDF file:', cleanupError)
      }
    }
  } catch (importError) {
    throw new Error('pdf-poppler 無法使用')
  }
}

export async function optimizeImageForOCR(imageBuffer: Buffer): Promise<Buffer> {
  try {
    // Optimize image for OCR:
    // 1. Convert to grayscale
    // 2. Increase contrast
    // 3. Sharpen
    // 4. Ensure good resolution
    const optimizedBuffer = await sharp(imageBuffer)
      .greyscale()
      .normalize() // Auto-level
      .sharpen({
        sigma: 1,
        m1: 0.5,
        m2: 2,
        x1: 2,
        y2: 10
      })
      .png({ quality: 100 })
      .toBuffer()

    return optimizedBuffer
  } catch (error) {
    console.error('Image optimization error:', error)
    // Return original buffer if optimization fails
    return imageBuffer
  }
}

// Helper function to estimate processing time
export function estimateProcessingTime(pageCount: number): number {
  // Rough estimate: 3-8 seconds per page depending on complexity
  const baseTimePerPage = 5 // seconds
  const totalTime = pageCount * baseTimePerPage
  return Math.min(totalTime, 120) // Cap at 2 minutes
}

// Helper function to check if system supports PDF conversion
export async function checkPDFConversionSupport(): Promise<boolean> {
  try {
    // Create a minimal test PDF buffer
    const testPdfBuffer = Buffer.from(`%PDF-1.4
1 0 obj
<<
/Type /Catalog
/Pages 2 0 R
>>
endobj
2 0 obj
<<
/Type /Pages
/Kids [3 0 R]
/Count 1
>>
endobj
3 0 obj
<<
/Type /Page
/Parent 2 0 R
/MediaBox [0 0 612 792]
>>
endobj
xref
0 4
0000000000 65535 f 
0000000009 00000 n 
0000000074 00000 n 
0000000120 00000 n 
trailer
<<
/Size 4
/Root 1 0 R
>>
startxref
219
%%EOF`)

    await convertPDFToImages(testPdfBuffer)
    return true
  } catch (error) {
    console.warn('PDF conversion support check failed:', error)
    return false
  }
}