"use strict";

let Example = {
    initialize: async function (slang, canvas) {
        async function render(shaders) {
            if (!navigator.gpu) {
                throw new Error("WebGPU not supported on this browser.");
            }
            const adapter = await navigator.gpu.requestAdapter();
            if (!adapter) {
                throw new Error("No appropriate GPUAdapter found.");
            }
            const device = await adapter.requestDevice();
            const context = canvas.getContext("webgpu");
            const canvasFormat = navigator.gpu.getPreferredCanvasFormat();
            context.configure({
                device: device,
                format: canvasFormat,
            });

            const vertexBufferLayout = {
                arrayStride: 8,
                attributes: [{
                    format: "float32x2",
                    offset: 0,
                    shaderLocation: 0,
                }],
            };

            const pipeline = device.createRenderPipeline({
                label: "Pipeline",
                layout: "auto",
                vertex: {
                    module: device.createShaderModule({
                        label: "Vertex shader module",
                        code: shaders.vertex
                    }),
                    entryPoint: "vertexMain",
                    buffers: [vertexBufferLayout]
                },
                fragment: {
                    module: device.createShaderModule({
                        label: "Fragment shader module",
                        code: shaders.fragment
                    }),
                    entryPoint: "fragmentMain",
                    targets: [{
                        format: canvasFormat
                    }]
                }
            });

            const vertices = new Float32Array([
                0.0, -0.8,
                +0.8, +0.8,
                -0.8, +0.8,
            ]);
            const vertexBuffer = device.createBuffer({
                label: "Triangle vertices",
                size: vertices.byteLength,
                usage: GPUBufferUsage.VERTEX | GPUBufferUsage.COPY_DST,
            });
            const bufferOffset = 0;
            device.queue.writeBuffer(vertexBuffer, bufferOffset, vertices);

            const encoder = device.createCommandEncoder();
            const pass = encoder.beginRenderPass({
                colorAttachments: [{
                    view: context.getCurrentTexture().createView(),
                    loadOp: "clear",
                    clearValue: { r: 0, g: 0, b: 0, a: 1 },
                    storeOp: "store",
                }]
            });
            pass.setPipeline(pipeline);
            const vertexBufferSlot = 0;
            pass.setVertexBuffer(vertexBufferSlot, vertexBuffer);
            pass.draw(vertices.length / 2);
            pass.end();
            const commandBuffer = encoder.finish();
            device.queue.submit([commandBuffer]);
        }

        const slangCode = await fetch("shader.slang").then(r => r.text());

        var wasmCompileTarget = null;
        var compileTargetMap = slang.module.getCompileTargets();
        for (var i = 0; i < compileTargetMap.length; i++) {
            var target = compileTargetMap[i];
            if(target.name == "WGSL") {
                wasmCompileTarget = target.value;
            }
        }
        if (wasmCompileTarget === null) {
            throw new Error("Slang/WASM module doesn't support WGSL compile target.");
        }

        var slangSession = slang.globalSession.createSession(wasmCompileTarget);
        if (!slangSession) {
            throw new Error("Failed to create global Slang session.");
        }

        var wgslShaders = null;
        try {
            var module = slangSession.loadModuleFromSource(
                slangCode, "shader", '/shader.slang'
            );
            var vertexEntryPoint = module.findAndCheckEntryPoint(
                "vertexMain", slang.constants.STAGE_VERTEX
            );
            var fragmentEntryPoint = module.findAndCheckEntryPoint(
                "fragmentMain", slang.constants.STAGE_FRAGMENT
            );
            var linkedProgram = slangSession.createCompositeComponentType([
                module, vertexEntryPoint, fragmentEntryPoint
            ]).link();
            wgslShaders = {
                vertex: linkedProgram.getEntryPointCode(
                    0 /* entryPointIndex */, 0 /* targetIndex */
                ),
                fragment: linkedProgram.getEntryPointCode(
                    1 /* entryPointIndex */, 0 /* targetIndex */
                ),
            };
        } finally {
            if (slangSession) {
                slangSession.delete();
            }
        }

        if (!wgslShaders) {
            throw new Error("Failed to compile WGSL shaders.");
        }

        render(wgslShaders);
    }
}

var Module = {
    onRuntimeInitialized: function() {
        const canvas = document.querySelector("canvas");

        var globalSlangSession = Module.createGlobalSession();
        if (!globalSlangSession) {
            throw new Error("Failed to create global Slang session.");
        }

        const slang = {
            module: Module,
            globalSession: globalSlangSession,
            constants: {
                STAGE_VERTEX: 1,
                STAGE_FRAGMENT: 5,
            },
        };
        Example.initialize(slang, canvas);
    },
};