/**
 * Downscale an image File to a JPEG Blob (max 1600px on the long edge, quality 0.82) before chat upload,
 * so image blobs stay ~100-400KB in sqlite instead of multi-MB phone-camera shots. GIFs pass through
 * unchanged (a canvas re-encode would kill the animation). Returns { blob, width, height }; falls back
 * to the original file if canvas/toBlob is unavailable. Shared by both chat surfaces so it can't drift.
 */
export interface DownscaledImage { blob: Blob; width: number; height: number }

export const downscaleImage = (file: File, maxDim = 1600, quality = 0.82): Promise<DownscaledImage> => {
  return new Promise((resolve) => {
    const fallback = () => resolve({ blob: file, width: 0, height: 0 })
    try {
      if (typeof document === 'undefined' || !file.type || file.type === 'image/gif') return fallback()
      const url = URL.createObjectURL(file)
      const img = new Image()
      img.onload = () => {
        try {
          let width = img.naturalWidth || img.width
          let height = img.naturalHeight || img.height
          if (!width || !height) { URL.revokeObjectURL(url); return fallback() }
          const scale = Math.min(1, maxDim / Math.max(width, height))
          width = Math.round(width * scale)
          height = Math.round(height * scale)
          const canvas = document.createElement('canvas')
          canvas.width = width
          canvas.height = height
          const ctx = canvas.getContext('2d')
          if (!ctx) { URL.revokeObjectURL(url); return fallback() }
          ctx.drawImage(img, 0, 0, width, height)
          canvas.toBlob((blob) => {
            URL.revokeObjectURL(url)
            if (blob) resolve({ blob, width, height })
            else fallback()
          }, 'image/jpeg', quality)
        } catch { URL.revokeObjectURL(url); fallback() }
      }
      img.onerror = () => { URL.revokeObjectURL(url); fallback() }
      img.src = url
    } catch { fallback() }
  })
}