// Copyright 2021 The piet-gpu 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
//
//     https://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.
//
// Also licensed under MIT license, at your choice.

use piet_gpu_hal::{include_shader, BindType, BufferUsage, DescriptorSet, ShaderCode};
use piet_gpu_hal::{Buffer, Pipeline};

use crate::config::Config;
use crate::runner::{Commands, Runner};
use crate::test_result::TestResult;

const N_ELEMENTS: u64 = 65536;

/// The shader code forMessagePassing sum example.
struct MessagePassingCode {
    pipeline: Pipeline,
}

/// The stage resources for the prefix sum example.
struct MessagePassingStage {
    data_buf: Buffer,
}

/// The binding for the prefix sum example.
struct MessagePassingBinding {
    descriptor_set: DescriptorSet,
}

#[derive(Debug)]
pub enum Variant {
    Atomic,
    Vkmm,
}

pub unsafe fn run_message_passing_test(
    runner: &mut Runner,
    config: &Config,
    variant: Variant,
) -> TestResult {
    let mut result = TestResult::new(format!("message passing litmus, {:?}", variant));
    let out_buf = runner.buf_down(4, BufferUsage::CLEAR);
    let code = MessagePassingCode::new(runner, variant);
    let stage = MessagePassingStage::new(runner);
    let binding = stage.bind(runner, &code, &out_buf.dev_buf);
    let n_iter = config.n_iter;
    let mut total_elapsed = 0.0;
    let mut failures = 0;
    for _ in 0..n_iter {
        let mut commands = runner.commands();
        stage.record(&mut commands, &code, &binding, &out_buf.dev_buf);
        commands.cmd_buf.memory_barrier();
        commands.download(&out_buf);
        total_elapsed += runner.submit(commands);
        let mut dst: Vec<u32> = Default::default();
        out_buf.read(&mut dst);
        failures += dst[0];
    }
    if failures > 0 {
        result.fail(format!("{} failures", failures));
    }
    result.timing(total_elapsed, N_ELEMENTS * n_iter);
    result
}

impl MessagePassingCode {
    unsafe fn new(runner: &mut Runner, variant: Variant) -> MessagePassingCode {
        let code = match variant {
            Variant::Atomic => include_shader!(&runner.session, "../shader/gen/message_passing"),
            Variant::Vkmm => {
                ShaderCode::Spv(include_bytes!("../shader/gen/message_passing_vkmm.spv"))
            }
        };
        let pipeline = runner
            .session
            .create_compute_pipeline(code, &[BindType::Buffer, BindType::Buffer])
            .unwrap();
        MessagePassingCode { pipeline }
    }
}

impl MessagePassingStage {
    unsafe fn new(runner: &mut Runner) -> MessagePassingStage {
        let data_buf_size = 8 * N_ELEMENTS;
        let data_buf = runner
            .session
            .create_buffer(
                data_buf_size,
                BufferUsage::STORAGE | BufferUsage::COPY_DST | BufferUsage::CLEAR,
            )
            .unwrap();
        MessagePassingStage { data_buf }
    }

    unsafe fn bind(
        &self,
        runner: &mut Runner,
        code: &MessagePassingCode,
        out_buf: &Buffer,
    ) -> MessagePassingBinding {
        let descriptor_set = runner
            .session
            .create_simple_descriptor_set(&code.pipeline, &[&self.data_buf, out_buf])
            .unwrap();
        MessagePassingBinding { descriptor_set }
    }

    unsafe fn record(
        &self,
        commands: &mut Commands,
        code: &MessagePassingCode,
        bindings: &MessagePassingBinding,
        out_buf: &Buffer,
    ) {
        commands.cmd_buf.clear_buffer(&self.data_buf, None);
        commands.cmd_buf.clear_buffer(out_buf, None);
        commands.cmd_buf.memory_barrier();
        let mut pass = commands.compute_pass(0, 1);
        pass.dispatch(
            &code.pipeline,
            &bindings.descriptor_set,
            (256, 1, 1),
            (256, 1, 1),
        );
        pass.end();
    }
}