// Copyright 2020 The Dawn Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "dawn_native/QueryHelper.h"

#include "dawn_native/BindGroup.h"
#include "dawn_native/BindGroupLayout.h"
#include "dawn_native/Buffer.h"
#include "dawn_native/CommandEncoder.h"
#include "dawn_native/ComputePassEncoder.h"
#include "dawn_native/ComputePipeline.h"
#include "dawn_native/Device.h"
#include "dawn_native/InternalPipelineStore.h"

namespace dawn_native {

    namespace {

        // Assert the offsets in dawn_native::TimestampParams are same with the ones in the shader
        static_assert(offsetof(dawn_native::TimestampParams, count) == 0, "");
        static_assert(offsetof(dawn_native::TimestampParams, offset) == 4, "");
        static_assert(offsetof(dawn_native::TimestampParams, period) == 8, "");

        static const char sConvertTimestampsToNanoseconds[] = R"(
            struct Timestamp {
                low  : u32;
                high : u32;
            };

            [[block]] struct TimestampArr {
                t : array<Timestamp>;
            };

            [[block]] struct AvailabilityArr {
                v : array<u32>;
            };

            [[block]] struct TimestampParams {
                count  : u32;
                offset : u32;
                period : f32;
            };

            [[group(0), binding(0)]]
                var<storage> timestamps : [[access(read_write)]] TimestampArr;
            [[group(0), binding(1)]]
                var<storage> availability : [[access(read)]] AvailabilityArr;
            [[group(0), binding(2)]] var<uniform> params : TimestampParams;

            [[builtin(global_invocation_id)]] var<in> GlobalInvocationID : vec3<u32>;

            const sizeofTimestamp : u32 = 8u;

            [[stage(compute), workgroup_size(8, 1, 1)]]
            fn main() {
                if (GlobalInvocationID.x >= params.count) { return; }

                var index : u32 = GlobalInvocationID.x + params.offset / sizeofTimestamp;

                var timestamp : Timestamp = timestamps.t[index];

                // Return 0 for the unavailable value.
                if (availability.v[index] == 0u) {
                    timestamps.t[index].low = 0u;
                    timestamps.t[index].high = 0u;
                    return;
                }

                // Multiply the values in timestamps buffer by the period.
                var period : f32 = params.period;
                var w : u32 = 0u;

                // If the product of low 32-bits and the period does not exceed the maximum of u32,
                // directly do the multiplication, otherwise, use two u32 to represent the high
                // 16-bits and low 16-bits of this u32, then multiply them by the period separately.
                if (timestamp.low <= u32(f32(0xFFFFFFFFu) / period)) {
                    timestamps.t[index].low = u32(round(f32(timestamp.low) * period));
                } else {
                    var lo : u32 = timestamp.low & 0xFFFFu;
                    var hi : u32 = timestamp.low >> 16u;

                    var t0 : u32 = u32(round(f32(lo) * period));
                    var t1 : u32 = u32(round(f32(hi) * period)) + (t0 >> 16u);
                    w = t1 >> 16u;

                    var result : u32 = t1 << 16u;
                    result = result | (t0 & 0xFFFFu);
                    timestamps.t[index].low = result;
                }

                // Get the nearest integer to the float result. For high 32-bits, the round
                // function will greatly help reduce the accuracy loss of the final result.
                timestamps.t[index].high = u32(round(f32(timestamp.high) * period)) + w;
            }
        )";

        ResultOrError<ComputePipelineBase*> GetOrCreateTimestampComputePipeline(
            DeviceBase* device) {
            InternalPipelineStore* store = device->GetInternalPipelineStore();

            if (store->timestampComputePipeline == nullptr) {
                // Create compute shader module if not cached before.
                if (store->timestampCS == nullptr) {
                    ShaderModuleDescriptor descriptor;
                    ShaderModuleWGSLDescriptor wgslDesc;
                    wgslDesc.source = sConvertTimestampsToNanoseconds;
                    descriptor.nextInChain = reinterpret_cast<ChainedStruct*>(&wgslDesc);

                    DAWN_TRY_ASSIGN(store->timestampCS, device->CreateShaderModule(&descriptor));
                }

                // Create ComputePipeline.
                ComputePipelineDescriptor computePipelineDesc = {};
                // Generate the layout based on shader module.
                computePipelineDesc.layout = nullptr;
                computePipelineDesc.computeStage.module = store->timestampCS.Get();
                computePipelineDesc.computeStage.entryPoint = "main";

                DAWN_TRY_ASSIGN(store->timestampComputePipeline,
                                device->CreateComputePipeline(&computePipelineDesc));
            }

            return store->timestampComputePipeline.Get();
        }

    }  // anonymous namespace

    MaybeError EncodeConvertTimestampsToNanoseconds(CommandEncoder* encoder,
                                                    BufferBase* timestamps,
                                                    BufferBase* availability,
                                                    BufferBase* params) {
        DeviceBase* device = encoder->GetDevice();

        ComputePipelineBase* pipeline;
        DAWN_TRY_ASSIGN(pipeline, GetOrCreateTimestampComputePipeline(device));

        // Prepare bind group layout.
        Ref<BindGroupLayoutBase> layout;
        DAWN_TRY_ASSIGN(layout, pipeline->GetBindGroupLayout(0));

        // Prepare bind group descriptor
        std::array<BindGroupEntry, 3> bindGroupEntries = {};
        BindGroupDescriptor bgDesc = {};
        bgDesc.layout = layout.Get();
        bgDesc.entryCount = 3;
        bgDesc.entries = bindGroupEntries.data();

        // Set bind group entries.
        bindGroupEntries[0].binding = 0;
        bindGroupEntries[0].buffer = timestamps;
        bindGroupEntries[0].size = timestamps->GetSize();
        bindGroupEntries[1].binding = 1;
        bindGroupEntries[1].buffer = availability;
        bindGroupEntries[1].size = availability->GetSize();
        bindGroupEntries[2].binding = 2;
        bindGroupEntries[2].buffer = params;
        bindGroupEntries[2].size = params->GetSize();

        // Create bind group after all binding entries are set.
        Ref<BindGroupBase> bindGroup;
        DAWN_TRY_ASSIGN(bindGroup, device->CreateBindGroup(&bgDesc));

        // Create compute encoder and issue dispatch.
        ComputePassDescriptor passDesc = {};
        // TODO(dawn:723): change to not use AcquireRef for reentrant object creation.
        Ref<ComputePassEncoder> pass = AcquireRef(encoder->APIBeginComputePass(&passDesc));
        pass->APISetPipeline(pipeline);
        pass->APISetBindGroup(0, bindGroup.Get());
        pass->APIDispatch(
            static_cast<uint32_t>((timestamps->GetSize() / sizeof(uint64_t) + 7) / 8));
        pass->APIEndPass();

        return {};
    }

}  // namespace dawn_native