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

import type {PlatformInfo} from './platform-info';
import type {AssembleShaderOptions} from './assemble-shaders';

/**
 * Options for `ShaderAssembler.assembleShaders()`
 */
export type AssembleShaderProps = Omit<AssembleShaderOptions, 'vs' | 'fs'> & {
  platformInfo: PlatformInfo;
  /** Single shader source. Always WGSL */
  source?: string | null;
  /** Vertex shader source. Can be GLSL or WGSL or both */
  vs?: {glsl?: string; wgsl?: string} | string | null;
  /** Fragment shader source. Can be GLSL or WGSL or both */
  fs?: {glsl?: string; wgsl?: string} | string | null;
};

/**
 * Shader selection
 * @param device
 * @param props
 * @returns
 */
export function selectShaders(props: AssembleShaderProps): AssembleShaderOptions {
  // If we have a source field, we have a single unified shader source
  if (props.source && props.platformInfo.type === 'webgpu') {
    const propsCopy: AssembleShaderOptions = {...props, vs: undefined, fs: undefined};
    return propsCopy;
  }

  if (!props.vs) {
    throw new Error('no vertex shader');
  }

  // Resolve WGSL vs GLSL
  const vs = getShaderSource(props.platformInfo, props.vs);
  let fs;
  if (props.fs) {
    fs = getShaderSource(props.platformInfo, props.fs);
  }

  return {...props, vs, fs};
}

/** Create a shader from the different overloads */
function getShaderSource(
  platformInfo: PlatformInfo,
  shader: string | {glsl?: string; wgsl?: string}
): string {
  // TODO - detect WGSL/GLSL and throw an error if not supported
  if (typeof shader === 'string') {
    return shader;
  }

  switch (platformInfo.type) {
    case 'webgpu':
      if (shader?.wgsl) {
        return shader.wgsl;
      }
      throw new Error('WebGPU does not support GLSL shaders');

    default:
      if (shader?.glsl) {
        return shader.glsl;
      }
      throw new Error('WebGL does not support WGSL shaders');
  }
}