import { CreateTextureCommand } from '../core/commands/assetCommands';
import type { TextureStore, UploadedTexture } from '../core/store/TextureStore';
import { formatBytes } from '../ui';
import { type ImportKind, type ImportOutcome, importFiles, importStored, pickAndImport } from './assetImport';
import type { EditorState } from './state';

/** What the picker offers and a drop accepts; the server rejects everything else anyway. */
const IMAGE_ACCEPT = 'image/png,image/jpeg,image/webp,image/gif';

/** Longest side a stored texture may have: a 4000×3000 photo costs 48 MB of video memory. */
export const MAX_TEXTURE_SIDE = 2048;

/** Byte budget for one upload: nginx cuts every request off at 1 MB, below the API's own 4 MB. */
export const MAX_UPLOAD_BYTES = 950 * 1024;

/** Tried in order when an image has to be re-encoded; the first result that fits wins. */
const WEBP_QUALITIES = [0.9, 0.75, 0.6] as const;

export type ImagePlan = { kind: 'keep' } | { kind: 'reencode'; width: number; height: number };

/**
 * Re-encoding would turn crisp pixel art into mush, so an image within both limits is kept byte
 * for byte. `bytes` is the encoded file size, not the pixel count.
 */
export function planImageFit(width: number, height: number, bytes: number): ImagePlan {
  const scale = Math.min(1, MAX_TEXTURE_SIDE / Math.max(width, height));
  if (scale === 1 && bytes <= MAX_UPLOAD_BYTES) return { kind: 'keep' };
  return {
    kind: 'reencode',
    width: Math.max(1, Math.round(width * scale)),
    height: Math.max(1, Math.round(height * scale)),
  };
}

/** Encodes at decreasing quality; when none fits the budget, the last attempt comes back anyway. */
export async function encodeWithinBudget(encode: (quality: number) => Promise<Blob>): Promise<Blob> {
  let result = await encode(WEBP_QUALITIES[0]);
  for (const quality of WEBP_QUALITIES.slice(1)) {
    if (result.size <= MAX_UPLOAD_BYTES) return result;
    result = await encode(quality);
  }
  return result;
}

export interface PreparedImage {
  blob: Blob;
  /** Content-Type for the upload; `image/webp` whenever the image had to be re-encoded. */
  type: string;
  width: number;
  height: number;
}

/** The bytes to upload: the file itself when it already fits, otherwise a downscaled WebP. */
async function prepareImage(file: File): Promise<PreparedImage> {
  let bitmap: ImageBitmap;
  try {
    bitmap = await createImageBitmap(file);
  } catch {
    throw new Error('The file is not a readable image.');
  }
  try {
    const plan = planImageFit(bitmap.width, bitmap.height, file.size);
    if (plan.kind === 'keep') {
      return {
        blob: file,
        type: file.type || 'application/octet-stream',
        width: bitmap.width,
        height: bitmap.height,
      };
    }
    // Only the first frame of an animated GIF survives this.
    const canvas = new OffscreenCanvas(plan.width, plan.height);
    const context = canvas.getContext('2d');
    if (!context) throw new Error('This browser cannot resize images.');
    context.drawImage(bitmap, 0, 0, plan.width, plan.height);
    const blob = await encodeWithinBudget((quality) => canvas.convertToBlob({ type: 'image/webp', quality }));
    if (blob.size > MAX_UPLOAD_BYTES) {
      throw new Error(
        `The image is too large to upload: still ${formatBytes(blob.size)} at ${plan.width}×${plan.height}. Shrink it before importing.`,
      );
    }
    return { blob, type: 'image/webp', width: plan.width, height: plan.height };
  } finally {
    bitmap.close();
  }
}

export interface TextureImportDeps {
  state: EditorState;
  textures: TextureStore;
}

const IMAGE_KIND: ImportKind<UploadedTexture, TextureImportDeps> = {
  type: 'texture',
  noun: 'image',
  fallbackName: 'Texture',
  store: (deps) => deps.textures,
  prepare: prepareImage,
  create: (name, image) => new CreateTextureCommand(name, image),
};

export function importImages(files: readonly File[], deps: TextureImportDeps): Promise<ImportOutcome[]> {
  return importFiles(IMAGE_KIND, files, deps);
}

export function importStoredImage(image: UploadedTexture, deps: TextureImportDeps): ImportOutcome {
  return importStored(IMAGE_KIND, image, deps);
}

export function pickAndImportImages(deps: TextureImportDeps): void {
  pickAndImport(IMAGE_KIND, IMAGE_ACCEPT, deps);
}