// loaders.gl
// SPDX-License-Identifier: MIT
// Copyright (c) vis.gl contributors

import type {GPUTextureFormat} from '@loaders.gl/schema';

const BROWSER_PREFIXES = ['', 'WEBKIT_', 'MOZ_'];

const WEBGL_EXTENSIONS: {[key: string]: GPUTextureFormat} = {
  /* eslint-disable camelcase */
  WEBGL_compressed_texture_s3tc: 'dxt',
  WEBGL_compressed_texture_s3tc_srgb: 'dxt-srgb',
  WEBGL_compressed_texture_etc1: 'etc1',
  WEBGL_compressed_texture_etc: 'etc2',
  WEBGL_compressed_texture_pvrtc: 'pvrtc',
  WEBGL_compressed_texture_atc: 'atc',
  WEBGL_compressed_texture_astc: 'astc',
  EXT_texture_compression_rgtc: 'rgtc'
  /* eslint-enable camelcase */
};

let formats: Set<GPUTextureFormat> | null = null;

/**
 * Returns a list of formats.
 * Creates a temporary WebGLRenderingContext if none is provided.
 *
 * @param gl - Optional context.
 */
export function getSupportedGPUTextureFormats(gl?: WebGLRenderingContext): Set<string> {
  if (!formats) {
    gl = gl || getWebGLContext() || undefined;

    formats = new Set<GPUTextureFormat>();

    for (const prefix of BROWSER_PREFIXES) {
      for (const extension in WEBGL_EXTENSIONS) {
        if (gl && gl.getExtension(`${prefix}${extension}`)) {
          const gpuTextureFormat = WEBGL_EXTENSIONS[extension];
          formats.add(gpuTextureFormat);
        }
      }
    }
  }

  return formats;
}

/**
 * @returns {WebGLRenderingContext?}
 */
function getWebGLContext() {
  try {
    const canvas = document.createElement('canvas');
    return canvas.getContext('webgl');
  } catch (error) {
    return null;
  }
}