import {
  parseAssetPreviewIdentity,
  type AssetPreviewContentMimeType,
  type AssetPreviewIdentityIR,
} from "./asset-preview";
import type { ErrorCode } from "./error";

export const ASSET_PREVIEW_DECODE_SCHEMA = 1 as const;
export const ASSET_PREVIEW_DECODE_BUDGET = Object.freeze({
  maxEncodedBytes: 16 * 1024 * 1024,
  maxWidth: 4096,
  maxHeight: 4096,
  maxPixels: 4096 * 4096,
  maxDecodedBytes: 64 * 1024 * 1024,
  maxCompressionRatio: 100,
});

export interface AssetPreviewDecodePlanIR {
  schemaVersion: typeof ASSET_PREVIEW_DECODE_SCHEMA;
  identitySha256: string;
  mimeType: AssetPreviewContentMimeType;
  width: number;
  height: number;
  pixelCount: number;
  encodedByteLength: number;
  decodedByteLength: number;
  compressionRatio: number;
}

export class AssetPreviewDecodeError extends Error {
  readonly code: ErrorCode;

  constructor(code: ErrorCode, message: string) {
    super(`${code}: ${message}`);
    this.name = "AssetPreviewDecodeError";
    this.code = code;
  }
}

function text(bytes: Uint8Array, offset: number, length: number): string {
  return String.fromCharCode(...bytes.subarray(offset, offset + length));
}

function pngDimensions(bytes: Uint8Array): { width: number; height: number } | null {
  const signature = [137, 80, 78, 71, 13, 10, 26, 10];
  if (bytes.byteLength < 24 || !signature.every((value, index) => bytes[index] === value)) return null;
  const view = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength);
  if (view.getUint32(8, false) !== 13 || text(bytes, 12, 4) !== "IHDR") return null;
  return { width: view.getUint32(16, false), height: view.getUint32(20, false) };
}

function webPDimensions(bytes: Uint8Array): { width: number; height: number } | null {
  if (bytes.byteLength < 30 || text(bytes, 0, 4) !== "RIFF" || text(bytes, 8, 4) !== "WEBP") return null;
  const view = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength);
  if (view.getUint32(4, true) + 8 !== bytes.byteLength) return null;
  const chunk = text(bytes, 12, 4);
  if (chunk === "VP8X") {
    const width = 1 + bytes[24] + (bytes[25] << 8) + (bytes[26] << 16);
    const height = 1 + bytes[27] + (bytes[28] << 8) + (bytes[29] << 16);
    return { width, height };
  }
  if (chunk === "VP8L" && bytes[20] === 0x2f) {
    const packed = view.getUint32(21, true);
    return { width: (packed & 0x3fff) + 1, height: ((packed >>> 14) & 0x3fff) + 1 };
  }
  if (chunk === "VP8 " && bytes[23] === 0x9d && bytes[24] === 0x01 && bytes[25] === 0x2a) {
    return { width: view.getUint16(26, true) & 0x3fff, height: view.getUint16(28, true) & 0x3fff };
  }
  return null;
}

function encodedDimensions(mimeType: AssetPreviewContentMimeType, bytes: Uint8Array): { width: number; height: number } {
  const dimensions = mimeType === "image/png" ? pngDimensions(bytes) : webPDimensions(bytes);
  if (!dimensions) throw new AssetPreviewDecodeError("ASSET_MANIFEST_INVALID", `encoded bytes are not a valid ${mimeType} header`);
  return dimensions;
}

async function sha256(bytes: ArrayBuffer): Promise<string> {
  const result = await crypto.subtle.digest("SHA-256", bytes);
  return Array.from(new Uint8Array(result), (byte) => byte.toString(16).padStart(2, "0")).join("");
}

function assertEncodedBudget(identity: AssetPreviewIdentityIR, encodedBytes: ArrayBuffer): void {
  if (!(encodedBytes instanceof ArrayBuffer)) {
    throw new AssetPreviewDecodeError("ASSET_MANIFEST_INVALID", "preview encoded payload must be an ArrayBuffer");
  }
  if (identity.content.byteLength > ASSET_PREVIEW_DECODE_BUDGET.maxEncodedBytes ||
      encodedBytes.byteLength > ASSET_PREVIEW_DECODE_BUDGET.maxEncodedBytes) {
    throw new AssetPreviewDecodeError("ASSET_BUDGET_EXCEEDED", "preview encoded byte length exceeds the pre-decode budget");
  }
  if (encodedBytes.byteLength !== identity.content.byteLength) {
    throw new AssetPreviewDecodeError("ASSET_SOURCE_HASH_MISMATCH", "preview encoded byte length does not match the identity");
  }
}

export async function planAssetPreviewDecode(value: unknown, encodedBytes: ArrayBuffer): Promise<AssetPreviewDecodePlanIR> {
  const identity = await parseAssetPreviewIdentity(value);
  assertEncodedBudget(identity, encodedBytes);
  if (await sha256(encodedBytes) !== identity.content.sha256) {
    throw new AssetPreviewDecodeError("ASSET_SOURCE_HASH_MISMATCH", "preview encoded SHA-256 does not match the identity");
  }

  const dimensions = encodedDimensions(identity.content.mimeType, new Uint8Array(encodedBytes));
  if (dimensions.width !== identity.content.width || dimensions.height !== identity.content.height) {
    throw new AssetPreviewDecodeError("ASSET_MANIFEST_INVALID", "preview encoded dimensions do not match the identity");
  }
  if (dimensions.width > ASSET_PREVIEW_DECODE_BUDGET.maxWidth || dimensions.height > ASSET_PREVIEW_DECODE_BUDGET.maxHeight) {
    throw new AssetPreviewDecodeError("ASSET_BUDGET_EXCEEDED", "preview dimensions exceed the pre-decode budget");
  }
  const pixelCount = dimensions.width * dimensions.height;
  const decodedByteLength = pixelCount * 4;
  if (!Number.isSafeInteger(pixelCount) || pixelCount > ASSET_PREVIEW_DECODE_BUDGET.maxPixels ||
      !Number.isSafeInteger(decodedByteLength) || decodedByteLength > ASSET_PREVIEW_DECODE_BUDGET.maxDecodedBytes) {
    throw new AssetPreviewDecodeError("ASSET_BUDGET_EXCEEDED", "preview pixel or decoded byte count exceeds the pre-decode budget");
  }
  const compressionRatio = decodedByteLength / encodedBytes.byteLength;
  if (!Number.isFinite(compressionRatio) || compressionRatio > ASSET_PREVIEW_DECODE_BUDGET.maxCompressionRatio) {
    throw new AssetPreviewDecodeError("ASSET_BUDGET_EXCEEDED", "preview compression ratio exceeds the pre-decode budget");
  }
  return {
    schemaVersion: ASSET_PREVIEW_DECODE_SCHEMA,
    identitySha256: identity.identitySha256,
    mimeType: identity.content.mimeType,
    width: dimensions.width,
    height: dimensions.height,
    pixelCount,
    encodedByteLength: encodedBytes.byteLength,
    decodedByteLength,
    compressionRatio,
  };
}