/*
 * Copyright 2021 Google LLC
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "experimental/graphite/src/Gpu.h"

#include "experimental/graphite/src/Caps.h"
#include "experimental/graphite/src/CommandBuffer.h"
#include "experimental/graphite/src/GpuWorkSubmission.h"
#include "experimental/graphite/src/ResourceProvider.h"
#include "src/sksl/SkSLCompiler.h"

namespace skgpu {

// This constant determines how many OutstandingSubmissions are allocated together as a block in
// the deque. As such it needs to balance allocating too much memory vs. incurring
// allocation/deallocation thrashing. It should roughly correspond to the max number of outstanding
// submissions we expect to see.
static constexpr int kDefaultOutstandingAllocCnt = 8;

Gpu::Gpu(sk_sp<const Caps> caps)
    : fOutstandingSubmissions(sizeof(OutstandingSubmission), kDefaultOutstandingAllocCnt)
    , fCaps(std::move(caps)) {
    // subclasses create their own subclassed resource provider
}

Gpu::~Gpu() {
    // TODO: add disconnect?


    // TODO: destroyResources instead?
    // TODO: how do we handle command buffers that haven't been submitted yet?
    this->checkForFinishedWork(SyncToCpu::kYes);
    fResourceProvider.reset();
}

void Gpu::initCompiler() {
    fCompiler = std::make_unique<SkSL::Compiler>(fCaps->shaderCaps());
}

sk_sp<const Caps> Gpu::refCaps() const {
    return fCaps;
}

bool Gpu::submit(sk_sp<CommandBuffer> commandBuffer) {
    if (!commandBuffer) {
        return false;
    }

    if (!commandBuffer->hasWork()) {
        return true;
    }

    return this->onSubmit(std::move(commandBuffer));
}

void Gpu::checkForFinishedWork(SyncToCpu sync) {
    if (sync == SyncToCpu::kYes) {
        // wait for the last submission to finish
        OutstandingSubmission* back = (OutstandingSubmission*)fOutstandingSubmissions.back();
        if (back) {
            (*back)->waitUntilFinished(this);
        }
    }

    // Iterate over all the outstanding submissions to see if any have finished. The work
    // submissions are in order from oldest to newest, so we start at the front to check if they
    // have finished. If so we pop it off and move onto the next.
    // Repeat till we find a submission that has not finished yet (and all others afterwards are
    // also guaranteed to not have finished).
    OutstandingSubmission* front = (OutstandingSubmission*)fOutstandingSubmissions.front();
    while (front && (*front)->isFinished()) {
        // Make sure we remove before deleting as deletion might try to kick off another submit
        // (though hopefully *not* in Graphite).
        fOutstandingSubmissions.pop_front();
        // Since we used placement new we are responsible for calling the destructor manually.
        front->~OutstandingSubmission();
        front = (OutstandingSubmission*)fOutstandingSubmissions.front();
    }
    SkASSERT(sync == SyncToCpu::kNo || fOutstandingSubmissions.empty());
}

} // namespace skgpu