use cubecl_core as cubecl;
use cubecl_core::prelude::*;

use crate::components::global::read::{StageBuffer, SyncStrategy};
use crate::components::global::{GlobalConfig, GlobalReaderConfig, LoadingSides};
use crate::components::stage::{StageConfig, StageEvent, StageEventListener};

#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
/// For a tensor, whether it is constrained to be loaded respecting order
pub enum EventLoadingMode {
    // Load without constraints
    Relaxed,
    // Load but respecting order
    Ordered,
}

#[derive(CubeType)]
/// Injects Lhs and Rhs loading tasks during stage matmul execution, as part of double buffering.
///
/// This comptime struct implements `on_event`, which is called from within the stage matmul.
/// It responds to that event by launching loads using the provided job executors,
/// allowing data for the next tile to be loaded while the current tile is being computed.
pub struct DoubleBufferingEventListener<
    S: SyncStrategy,
    Lhs: JobExecutor<S>,
    Rhs: JobExecutor<S>,
    G: GlobalConfig,
> {
    #[cube(comptime)]
    stage_buffer: StageBuffer,
    reader_lhs: Lhs,
    reader_rhs: Rhs,
    barrier: S::Barrier,
    #[cube(comptime)]
    config: G,
    state_lhs: Sequence<Lhs::JobIterator>,
    state_rhs: Sequence<Rhs::JobIterator>,
    #[cube(comptime)]
    event_loading_side: LoadingSides,
    #[cube(comptime)]
    must_sync_plane_after_execution: bool,
}

#[derive(Clone)]
/// Analysis of [StageEvent] that reports when the corresponding input should execute a task.
struct IdentEventAnalysis {
    /// The event count to execute the next task.
    counter: u32,
    /// If tasks can start without risk of concurrency
    can_start: bool,
    /// If no more tasks need to be executed .
    completed: bool,
}
impl CubeDebug for IdentEventAnalysis {}
impl IdentEventAnalysis {
    fn should_execute(&self, current: u32) -> bool {
        self.counter == current && self.can_start && !self.completed
    }
}

#[derive(Clone)]
/// Analysis of [StageEvent] that reports when lhs and rhs should execute a task.
struct EventAnalysis {
    lhs: IdentEventAnalysis,
    rhs: IdentEventAnalysis,
}
impl CubeDebug for EventAnalysis {}

#[cube]
impl<S: SyncStrategy, Lhs: JobExecutor<S>, Rhs: JobExecutor<S>, G: GlobalConfig>
    DoubleBufferingEventListener<S, Lhs, Rhs, G>
{
    /// Create a new DoubleBufferingEventListener
    pub fn new(
        #[comptime] stage_buffer: StageBuffer,
        reader_lhs: &Lhs,
        reader_rhs: &Rhs,
        barrier: &mut S::Barrier,
        #[comptime] config: G,
        #[comptime] event_loading_side: LoadingSides,
    ) -> DoubleBufferingEventListener<S, Lhs, Rhs, G> {
        DoubleBufferingEventListener::<S, Lhs, Rhs, G> {
            stage_buffer,
            reader_lhs: comptime![reader_lhs.clone()],
            reader_rhs: comptime![reader_rhs.clone()],
            barrier: comptime![barrier.clone()],
            config,
            state_lhs: Sequence::new(),
            state_rhs: Sequence::new(),
            event_loading_side,
            must_sync_plane_after_execution: config.must_sync_plane_after_execution(),
        }
    }
}

#[cube]
impl<S: SyncStrategy, L: JobExecutor<S>, R: JobExecutor<S>, G: GlobalConfig> StageEventListener
    for DoubleBufferingEventListener<S, L, R, G>
{
    /// Responds to stage-level events by injecting Lhs/Rhs loading tasks during execution.
    ///
    /// This method is called from the stage matmul kernel, allowing asynchronous data loads
    /// to be scheduled while the current tile is being computed. It handles three types of events:
    ///
    /// - `Begin`: Initializes internal job state.
    /// - `TileMatmulCompleted`: Called after each Tile Matmul; decides whether to load the next Lhs/Rhs tile
    ///   based on cycle position and execution schedule.
    /// - `Finish`: Finalizes all remaining tasks, ensuring full completion
    ///
    /// Note: if the global matmul is ordered and the underlying Tile Matmul is not
    /// plane-synchronized (which is the case on some platforms), we need to synchronize the plane manually.
    fn on_event(this: &mut Self, #[comptime] event: StageEvent) {
        if let StageEvent::Begin = event {
            this.init();
        }

        if let StageEvent::TileMatmulCompleted { current, total } = event {
            let analysis = this.analyse(current, total);

            if comptime![analysis.lhs.should_execute(current)] {
                let lhs_job = this.state_lhs.index_mut(0);

                if this.must_sync_plane_after_execution {
                    sync_plane();
                }

                L::execute_task(
                    &mut this.reader_lhs,
                    lhs_job,
                    &mut this.barrier,
                    comptime!(this.config.lhs_reader_config()),
                );
            }

            if comptime![analysis.rhs.should_execute(current)] {
                let rhs_job = this.state_rhs.index_mut(0);

                if this.must_sync_plane_after_execution {
                    sync_plane();
                }

                R::execute_task(
                    &mut this.reader_rhs,
                    rhs_job,
                    &mut this.barrier,
                    comptime!(this.config.rhs_reader_config()),
                );
            }
        }

        // Cleanup remaining tasks if any.
        if let StageEvent::Finish = event {
            let lhs_len = this.state_lhs.len();
            let rhs_len = this.state_rhs.len();

            let mut lhs_num_tasks = comptime!(0u32);
            let mut rhs_num_tasks = comptime!(0u32);
            let mut lhs_num_task_executed = comptime!(0u32);
            let mut rhs_num_task_executed = comptime!(0u32);

            if comptime!(lhs_len > 0) {
                let lhs_job = this.state_lhs.index_mut(0);
                let num_tasks = L::JobIterator::num_tasks(lhs_job);
                let num_task_executed = L::JobIterator::current(lhs_job);
                comptime!(lhs_num_tasks += num_tasks);
                comptime!(lhs_num_task_executed += num_task_executed);
            }

            if comptime!(rhs_len > 0) {
                let rhs_job = this.state_rhs.index_mut(0);
                let num_tasks = R::JobIterator::num_tasks(rhs_job);
                let num_task_executed = R::JobIterator::current(rhs_job);
                comptime!(rhs_num_tasks += num_tasks);
                comptime!(rhs_num_task_executed += num_task_executed);
            }

            #[allow(clippy::collapsible_if)]
            if comptime!(this.must_sync_plane_after_execution) {
                if lhs_num_tasks - lhs_num_task_executed + rhs_num_tasks - rhs_num_task_executed > 0
                {
                    sync_plane();
                }
            }

            if comptime!(lhs_len > 0) {
                let lhs_job = this.state_lhs.index_mut(0);
                #[unroll]
                for _ in lhs_num_task_executed..lhs_num_tasks {
                    L::execute_task(
                        &mut this.reader_lhs,
                        lhs_job,
                        &mut this.barrier,
                        comptime!(this.config.lhs_reader_config()),
                    );
                }
            }

            if comptime!(rhs_len > 0) {
                let rhs_job = this.state_rhs.index_mut(0);
                #[unroll]
                for _ in rhs_num_task_executed..rhs_num_tasks {
                    R::execute_task(
                        &mut this.reader_rhs,
                        rhs_job,
                        &mut this.barrier,
                        comptime!(this.config.rhs_reader_config()),
                    );
                }
            }
        }
    }
}

#[cube]
impl<S: SyncStrategy, L: JobExecutor<S>, R: JobExecutor<S>, G: GlobalConfig>
    DoubleBufferingEventListener<S, L, R, G>
{
    fn init(&mut self) {
        if comptime!(self.event_loading_side.includes_lhs()) {
            self.state_lhs.push(L::create_job_iterator(
                &self.reader_lhs,
                self.stage_buffer,
                comptime!(self.config.lhs_reader_config()),
            ));
        }

        if comptime!(self.event_loading_side.includes_rhs()) {
            self.state_rhs.push(R::create_job_iterator(
                &self.reader_rhs,
                self.stage_buffer,
                comptime!(self.config.rhs_reader_config()),
            ));
        }
    }

    fn analyse(
        &self,
        #[comptime] current_event: u32,
        #[comptime] event_count_total: u32,
    ) -> comptime_type!(EventAnalysis) {
        let lhs_len = self.state_lhs.len();
        let rhs_len = self.state_rhs.len();

        let mut lhs_num_tasks = comptime!(0u32);
        let mut rhs_num_tasks = comptime!(0u32);
        let mut lhs_num_task_executed = comptime!(0u32);
        let mut rhs_num_task_executed = comptime!(0u32);

        if comptime!(lhs_len > 0) {
            let lhs_job = self.state_lhs.index(0);
            let num_tasks = L::JobIterator::num_tasks(lhs_job);
            let current = L::JobIterator::current(lhs_job);
            comptime!(lhs_num_tasks += num_tasks);
            comptime!(lhs_num_task_executed += current);
        }

        if comptime!(rhs_len > 0) {
            let rhs_job = self.state_rhs.index(0);
            let num_tasks = R::JobIterator::num_tasks(rhs_job);
            let current = R::JobIterator::current(rhs_job);
            comptime!(rhs_num_tasks += num_tasks);
            comptime!(rhs_num_task_executed += current);
        }

        let num_tasks_total = comptime!(lhs_num_tasks + rhs_num_tasks);

        comptime! {
            // When ordered, we cannot start loading before all were loaded in fragments
            // Eventually, Lhs loads for k = i could start as soon as k_iterations_done = i, but probably overkill
            let can_start = |event_loading_mode: EventLoadingMode| if let EventLoadingMode::Ordered = event_loading_mode {
                current_event >= event_count_total - self.config.stage_config().tiles_in_partition_mn()
            } else {
                true
            };

            let lhs_can_start = lhs_len > 0 && can_start(comptime!(self.config.lhs_reader_config().event_loading_mode));
            let rhs_can_start = rhs_len > 0 && can_start(comptime!(self.config.rhs_reader_config().event_loading_mode));

            let step = 1u32;
            let start = event_count_total.saturating_sub(step * num_tasks_total);

            EventAnalysis {
                lhs: IdentEventAnalysis{
                    counter: lhs_num_task_executed * step + start,
                    can_start: lhs_can_start,
                    completed: lhs_num_task_executed >= lhs_num_tasks,
                },
                rhs: IdentEventAnalysis {
                    counter: rhs_num_task_executed * step + (lhs_num_tasks * step) + start,
                    can_start: rhs_can_start,
                    completed: rhs_num_task_executed >= rhs_num_tasks,
                }
            }
        }
    }
}

#[cube]
/// Something that can execute a job, i.e. a reader
pub trait JobExecutor<S: SyncStrategy>: CubeType + Clone {
    /// The job to execute
    type JobIterator: JobIterator;

    /// Create the job to execute
    fn create_job_iterator(
        this: &Self,
        #[comptime] stage_buffer: StageBuffer,
        #[comptime] config: GlobalReaderConfig,
    ) -> Self::JobIterator;

    /// Execute the next task
    fn execute_task(
        this: &mut Self,
        job: &mut Self::JobIterator,
        barrier: &mut S::Barrier,
        #[comptime] config: GlobalReaderConfig,
    );

    /// Execute all tasks that remain at once
    fn execute_all_remaining_tasks(
        this: &mut Self,
        job: &mut Self::JobIterator,
        barrier: &mut S::Barrier,
        #[comptime] config: GlobalReaderConfig,
    );

    /// Create a job and execute all its tasks at once
    fn execute_whole_job(
        this: &mut Self,
        barrier: &mut S::Barrier,
        #[comptime] stage_buffer: StageBuffer,
        #[comptime] config: GlobalReaderConfig,
    );
}

#[cube]
/// An iterator over a sequence of tasks
pub trait JobIterator: CubeType {
    /// Get the index of the current task
    fn current(this: &Self) -> comptime_type!(u32);

    /// Get the number of tasks
    fn num_tasks(this: &Self) -> comptime_type!(u32);
}

/// Trait for load components that define how their work can be evenly divided across planes.
///
/// The `max_round_plane_count` method returns the largest number of planes
/// for which the tasks can be evenly distributed (i.e., no remainder).
///
/// Any **factor** of this number (e.g., if 8 is returned, then 4, 2, and 1)
/// is also valid and will result in each plane handling a proportionally higher number of tasks.
pub trait LoadMaxRoundPlaneCount {
    /// Returns the largest number of planes that evenly divides the tasks.
    fn max_round_plane_count(
        elements_per_tile: u32,
        tiles_per_stage: u32,
        line_size: u8,
        plane_dim: u32,
    ) -> u32;
}
