/**
 * Client-side image resizing utility for LibreChat
 * Resizes images to prevent backend upload errors while maintaining quality
 */

export interface ResizeOptions {
  maxWidth?: number;
  maxHeight?: number;
  quality?: number;
  format?: 'jpeg' | 'png' | 'webp';
}

export interface ResizeResult {
  file: File;
  originalSize: number;
  newSize: number;
  originalDimensions: { width: number; height: number };
  newDimensions: { width: number; height: number };
  compressionRatio: number;
}

type ResizeFormat = NonNullable<ResizeOptions['format']>;

/**
 * Default resize options based on backend 'high' resolution settings
 * Backend 'high' uses maxShortSide=768, maxLongSide=2000
 * We use slightly smaller values to ensure no backend resizing is triggered
 */
const DEFAULT_RESIZE_OPTIONS: ResizeOptions = {
  maxWidth: 1900, // Slightly less than backend maxLongSide=2000
  maxHeight: 1900, // Slightly less than backend maxLongSide=2000
  quality: 0.92, // High quality while reducing file size
  format: 'jpeg', // Most compatible format
};

const RESIZE_FORMAT_BY_MIME_TYPE: Partial<Record<string, ResizeFormat>> = {
  'image/jpeg': 'jpeg',
  'image/png': 'png',
  'image/webp': 'webp',
};

const PNG_SIGNATURE = [137, 80, 78, 71, 13, 10, 26, 10] as const;
const WEBP_ANIMATION_FLAG = 0x02;
const MAX_ANIMATION_SCAN_BYTES = 64 * 1024;

const readBytes = (file: File, start: number, length: number): Promise<Uint8Array> =>
  new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onload = () => {
      if (!(reader.result instanceof ArrayBuffer)) {
        reject(new Error('Failed to read image container'));
        return;
      }
      resolve(new Uint8Array(reader.result));
    };
    reader.onerror = () => reject(new Error('Failed to read image container'));
    reader.readAsArrayBuffer(file.slice(start, start + length));
  });

const readAscii = (bytes: Uint8Array, start: number, length: number): string =>
  String.fromCharCode(...bytes.slice(start, start + length));

const hasSignature = (bytes: Uint8Array, signature: readonly number[]): boolean =>
  bytes.length >= signature.length && signature.every((value, index) => bytes[index] === value);

const isAnimatedPng = async (file: File): Promise<boolean> => {
  const bytes = await readBytes(file, 0, Math.min(file.size, MAX_ANIMATION_SCAN_BYTES));
  if (!hasSignature(bytes, PNG_SIGNATURE)) {
    return false;
  }

  let offset: number = PNG_SIGNATURE.length;
  while (offset + 12 <= bytes.length) {
    const header = bytes.subarray(offset, offset + 8);
    const chunkLength = new DataView(header.buffer, header.byteOffset, header.byteLength).getUint32(
      0,
    );
    const chunkType = readAscii(header, 4, 4);
    const nextOffset = offset + 12 + chunkLength;
    if (nextOffset > file.size) {
      return false;
    }
    if (chunkType === 'acTL') {
      return true;
    }
    if (chunkType === 'IDAT' || chunkType === 'IEND') {
      return false;
    }
    if (nextOffset > bytes.length) {
      return nextOffset < file.size;
    }

    offset = nextOffset;
  }

  return bytes.length < file.size;
};

const isAnimatedWebP = async (file: File): Promise<boolean> => {
  const bytes = await readBytes(file, 0, Math.min(file.size, MAX_ANIMATION_SCAN_BYTES));
  if (readAscii(bytes, 0, 4) !== 'RIFF' || readAscii(bytes, 8, 4) !== 'WEBP') {
    return false;
  }

  let offset = 12;
  while (offset + 8 <= bytes.length) {
    const header = bytes.subarray(offset, offset + 8);
    const chunkType = readAscii(header, 0, 4);
    const chunkSize = new DataView(header.buffer, header.byteOffset, header.byteLength).getUint32(
      4,
      true,
    );
    const dataEnd = offset + 8 + chunkSize;
    if (dataEnd > file.size) {
      return false;
    }
    if (chunkType === 'ANIM' || chunkType === 'ANMF') {
      return true;
    }
    if (chunkType === 'VP8 ' || chunkType === 'VP8L') {
      return false;
    }
    if (chunkType === 'VP8X' && chunkSize > 0) {
      const flags = bytes[offset + 8];
      if (flags == null) {
        return true;
      }
      if ((flags & WEBP_ANIMATION_FLAG) !== 0) {
        return true;
      }
    }

    const nextOffset = dataEnd + (chunkSize % 2);
    if (nextOffset > bytes.length) {
      return nextOffset < file.size;
    }
    offset = nextOffset;
  }

  return bytes.length < file.size;
};

/** Checks image containers whose animation would be flattened by canvas. */
export const isAnimatedImage = async (file: File): Promise<boolean> => {
  if (file.type === 'image/apng') {
    return true;
  }
  if (file.type === 'image/png') {
    return isAnimatedPng(file);
  }
  if (file.type === 'image/webp') {
    return isAnimatedWebP(file);
  }
  return false;
};

/**
 * Checks if the browser supports canvas-based image resizing
 */
export function supportsClientResize(): boolean {
  try {
    // Check for required APIs
    if (typeof HTMLCanvasElement === 'undefined') return false;
    if (typeof FileReader === 'undefined') return false;
    if (typeof Image === 'undefined') return false;

    // Test canvas creation
    const canvas = document.createElement('canvas');
    const ctx = canvas.getContext('2d');

    return (
      ctx != null && typeof ctx.drawImage === 'function' && typeof canvas.toBlob === 'function'
    );
  } catch {
    return false;
  }
}

/**
 * Calculates new dimensions while maintaining aspect ratio
 */
function calculateDimensions(
  originalWidth: number,
  originalHeight: number,
  maxWidth: number,
  maxHeight: number,
): { width: number; height: number } {
  const { width, height } = { width: originalWidth, height: originalHeight };

  // If image is smaller than max dimensions, don't upscale
  if (width <= maxWidth && height <= maxHeight) {
    return { width, height };
  }

  // Calculate scaling factor
  const widthRatio = maxWidth / width;
  const heightRatio = maxHeight / height;
  const scalingFactor = Math.min(widthRatio, heightRatio);

  return {
    width: Math.max(1, Math.round(width * scalingFactor)),
    height: Math.max(1, Math.round(height * scalingFactor)),
  };
}

/**
 * Resizes an image file using canvas
 */
export async function resizeImage(
  file: File,
  options: Partial<ResizeOptions> = {},
): Promise<ResizeResult> {
  if (await isAnimatedImage(file)) {
    throw new Error('Animated images cannot be resized without losing animation');
  }

  return new Promise((resolve, reject) => {
    // Check browser support
    if (!supportsClientResize()) {
      reject(new Error('Browser does not support client-side image resizing'));
      return;
    }

    // Only process image files
    if (!file.type.startsWith('image/')) {
      reject(new Error('File is not an image'));
      return;
    }

    const sourceFormat = RESIZE_FORMAT_BY_MIME_TYPE[file.type];
    const opts = {
      ...DEFAULT_RESIZE_OPTIONS,
      format: sourceFormat ?? DEFAULT_RESIZE_OPTIONS.format,
      ...options,
    };
    const { maxWidth, maxHeight } = opts;
    if (
      maxWidth == null ||
      maxHeight == null ||
      !Number.isFinite(maxWidth) ||
      !Number.isFinite(maxHeight) ||
      maxWidth <= 0 ||
      maxHeight <= 0
    ) {
      reject(new Error('Resize dimensions must be finite numbers greater than zero'));
      return;
    }
    const requestedMimeType = `image/${opts.format}`;
    /** Decoding through an object URL avoids the ~33% larger base64 copy a data URL would hold */
    const sourceUrl = URL.createObjectURL(file);
    const img = new Image();

    img.onload = () => {
      URL.revokeObjectURL(sourceUrl);
      try {
        const originalDimensions = { width: img.width, height: img.height };
        const newDimensions = calculateDimensions(img.width, img.height, maxWidth, maxHeight);

        // If no resizing needed, return original file
        if (
          newDimensions.width === originalDimensions.width &&
          newDimensions.height === originalDimensions.height
        ) {
          resolve({
            file,
            originalSize: file.size,
            newSize: file.size,
            originalDimensions,
            newDimensions,
            compressionRatio: 1,
          });
          return;
        }

        // Create canvas and resize
        const canvas = document.createElement('canvas');
        const ctx = canvas.getContext('2d')!;

        canvas.width = newDimensions.width;
        canvas.height = newDimensions.height;

        // Use high-quality image smoothing
        ctx.imageSmoothingEnabled = true;
        ctx.imageSmoothingQuality = 'high';

        // Draw resized image
        ctx.drawImage(img, 0, 0, newDimensions.width, newDimensions.height);

        // Convert to blob
        canvas.toBlob(
          (blob) => {
            if (!blob) {
              reject(new Error('Failed to create blob from canvas'));
              return;
            }

            if (blob.size >= file.size) {
              resolve({
                file,
                originalSize: file.size,
                newSize: file.size,
                originalDimensions,
                newDimensions: originalDimensions,
                compressionRatio: 1,
              });
              return;
            }

            const outputFormat = RESIZE_FORMAT_BY_MIME_TYPE[blob.type];
            if (blob.type !== requestedMimeType || outputFormat == null) {
              resolve({
                file,
                originalSize: file.size,
                newSize: file.size,
                originalDimensions,
                newDimensions: originalDimensions,
                compressionRatio: 1,
              });
              return;
            }

            // Create new file with same name but potentially different extension
            const extension = outputFormat === 'jpeg' ? '.jpg' : `.${outputFormat}`;
            const baseName = file.name.replace(/\.[^/.]+$/, '');
            const newFileName = `${baseName}${extension}`;

            const resizedFile = new File([blob], newFileName, {
              type: blob.type,
              lastModified: Date.now(),
            });

            resolve({
              file: resizedFile,
              originalSize: file.size,
              newSize: resizedFile.size,
              originalDimensions,
              newDimensions,
              compressionRatio: resizedFile.size / file.size,
            });
          },
          requestedMimeType,
          opts.quality,
        );
      } catch (error) {
        reject(error);
      }
    };

    img.onerror = () => {
      URL.revokeObjectURL(sourceUrl);
      reject(new Error('Failed to load image'));
    };
    img.src = sourceUrl;
  });
}

/**
 * Determines if an image uses a format supported by the resize pipeline.
 * Dimensions decide whether re-encoding is necessary after the image is decoded.
 */
export function shouldResizeImage(file: File): boolean {
  return RESIZE_FORMAT_BY_MIME_TYPE[file.type] != null;
}