/** Resize and compress an image file to a JPEG data URL (max 800×600). */
export function resizeImageFile(file: File): Promise<string> {
  return new Promise((resolve, reject) => {
    const reader = new FileReader()
    reader.onload = (event) => {
      const img = new Image()
      img.onload = () => {
        try {
          const canvas = document.createElement('canvas')
          const ctx = canvas.getContext('2d')
          if (!ctx) throw new Error('Could not get canvas context')

          let width = img.width
          let height = img.height
          const MAX_WIDTH = 800
          const MAX_HEIGHT = 600

          if (width > MAX_WIDTH || height > MAX_HEIGHT) {
            const ratio = Math.min(MAX_WIDTH / width, MAX_HEIGHT / height)
            width = Math.round(width * ratio)
            height = Math.round(height * ratio)
          }

          canvas.width = width
          canvas.height = height
          ctx.drawImage(img, 0, 0, width, height)

          resolve(canvas.toDataURL('image/jpeg', 0.7))
        } catch (err) {
          reject(err)
        }
      }
      img.onerror = () => reject(new Error('Invalid image file'))
      img.src = event.target?.result as string
    }
    reader.onerror = () => reject(new Error('Failed to read file'))
    reader.readAsDataURL(file)
  })
}