# pipeline.rs - source
Source of the Rust file `maplibre/src/io/pipeline.rs`.
Keywords: rust, rustlang, rust-lang

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    use crate::coords::WorldTileCoords;
    use crate::io::geometry_index::IndexedGeometry;
    use crate::io::TileRequestID;
    use crate::render::ShaderVertex;
    use crate::tessellation::{IndexDataType, OverAlignedVertexBuffer};
    use downcast_rs::{impl_downcast, Downcast};
    use geozero::mvt::tile;
    use std::any::Any;
    use std::marker::PhantomData;
    use std::process::Output;
    use std::sync::mpsc;

    /// Processes events which happen during the pipeline execution
    pub trait PipelineProcessor: Downcast {
        fn tile_finished(&mut self, request_id: TileRequestID, coords: &WorldTileCoords) {}
        fn layer_unavailable(&mut self, coords: &WorldTileCoords, layer_name: &str) {}
        fn layer_tesselation_finished(
            &mut self,
            coords: &WorldTileCoords,
            buffer: OverAlignedVertexBuffer<ShaderVertex, IndexDataType>,
            feature_indices: Vec<u32>,
            layer_data: tile::Layer,
        ) {
        }
        fn layer_indexing_finished(
            &mut self,
            coords: &WorldTileCoords,
            geometries: Vec<IndexedGeometry<f64>>,
        ) {
        }
    }

    impl_downcast!(PipelineProcessor);

    /// Context which is available to each step within a [`DataPipeline`]
    pub struct PipelineContext {
        processor: Box<dyn PipelineProcessor>,
    }

    impl PipelineContext {
        pub fn new<P>(processor: P) -> Self
        where
            P: PipelineProcessor,
        {
            Self {
                processor: Box::new(processor),
            }
        }

        pub fn take_processor<P>(self) -> Option<Box<P>>
        where
            P: PipelineProcessor,
        {
            self.processor.into_any().downcast::<P>().ok()
        }

        pub fn processor_mut(&mut self) -> &mut dyn PipelineProcessor {
            self.processor.as_mut()
        }
    }

    pub trait Processable {
        type Input;
        type Output;

        fn process(&self, input: Self::Input, context: &mut PipelineContext) -> Self::Output;
    }

    /// A pipeline which consists of multiple steps. Steps are [`Processable`] workloads. Later steps
    /// depend on previous ones.
    pub struct DataPipeline<P, N>
    where
        P: Processable,
        N: Processable<Input = P::Output>,
    {
        step: P,
        next_step: N,
    }

    impl<P, N> DataPipeline<P, N>
    where
        P: Processable,
        N: Processable<Input = P::Output>,
    {
        pub fn new(step: P, next_step: N) -> Self {
            Self { step, next_step }
        }
    }

    impl<P, N> Processable for DataPipeline<P, N>
    where
        P: Processable,
        N: Processable<Input = P::Output>,
    {
        type Input = P::Input;
        type Output = N::Output;

        fn process(&self, input: Self::Input, context: &mut PipelineContext) -> Self::Output {
            let output = self.step.process(input, context);
            self.next_step.process(output, context)
        }
    }

    /// Marks the end of a [`DataPipeline`]
    pub struct PipelineEnd<I> {
        phantom: PhantomData<I>,
    }

    impl<I> Default for PipelineEnd<I> {
        fn default() -> Self {
            Self {
                phantom: PhantomData::default(),
            }
        }
    }

    impl<I> Processable for PipelineEnd<I> {
        type Input = I;
        type Output = I;

        fn process(&self, input: Self::Input, _context: &mut PipelineContext) -> Self::Output {
            input
        }
    }

    impl<I, O> Processable for &fn(input: I, context: &mut PipelineContext) -> O {
        type Input = I;
        type Output = O;

        fn process(&self, input: Self::Input, context: &mut PipelineContext) -> Self::Output {
            (self)(input, context)
        }
    }

    impl<I, O> Processable for fn(input: I, context: &mut PipelineContext) -> O {
        type Input = I;
        type Output = O;

        fn process(&self, input: Self::Input, context: &mut PipelineContext) -> Self::Output {
            (self)(input, context)
        }
    }

    // TODO: Implementing Processable directly on Fn is not possible for some strange reason:
    //       https://github.com/rust-lang/rust/issues/25041
    pub struct ClosureProcessable<F, I, O>
    where
        F: Fn(I, &mut PipelineContext) -> O,
    {
        func: F,
        phantom_i: PhantomData<I>,
    }

    impl<F, I, O> From<F> for ClosureProcessable<F, I, O>
    where
        F: Fn(I, &mut PipelineContext) -> O,
    {
        fn from(func: F) -> Self {
            ClosureProcessable {
                func,
                phantom_i: PhantomData::default(),
            }
        }
    }

    impl<F, I, O> Processable for ClosureProcessable<F, I, O>
    where
        F: Fn(I, &mut PipelineContext) -> O,
    {
        type Input = I;
        type Output = O;

        fn process(&self, input: Self::Input, context: &mut PipelineContext) -> Self::Output {
            (self.func)(input, context)
        }
    }

    #[cfg(test)]
    mod tests {
        use crate::io::pipeline::{
            ClosureProcessable, DataPipeline, PipelineContext, PipelineEnd, PipelineProcessor,
            Processable,
        };
        use std::sync::mpsc;

        pub struct DummyPipelineProcessor;

        impl PipelineProcessor for DummyPipelineProcessor {}

        fn add_one(input: u32, context: &mut PipelineContext) -> u8 {
            input as u8 + 1
        }

        fn add_two(input: u8, context: &mut PipelineContext) -> u32 {
            input as u32 + 2
        }

        #[test]
        fn test_fn_pointer() {
            let mut context = PipelineContext::new(DummyPipelineProcessor);
            let output: u32 = DataPipeline::new(
                add_two as fn(u8, &mut PipelineContext) -> u32,
                PipelineEnd::default(),
            )
            .process(5u8, &mut context);
            assert_eq!(output, 7);

            let output: u32 = DataPipeline::new(
                add_one as fn(u32, &mut PipelineContext) -> u8,
                DataPipeline::new(
                    add_two as fn(u8, &mut PipelineContext) -> u32,
                    PipelineEnd::default(),
                ),
            )
            .process(5u32, &mut context);
            assert_eq!(output, 8);
        }

        #[test]
        fn test_closure() {
            let mut context = PipelineContext::new(DummyPipelineProcessor);
            let mut outer_value = 3;

            // using from()
            let closure = ClosureProcessable::from(|input: u8, context: &mut PipelineContext| -> u32 {
                return input as u32 + 2 + outer_value;
            });
            let output: u32 =
                DataPipeline::new(closure, PipelineEnd::default()).process(5u8, &mut context);
            assert_eq!(output, 10);

            // with into()
            let output: u32 = DataPipeline::<ClosureProcessable<_, u8, u32>, _>::new(
                (|input: u8, context: &mut PipelineContext| -> u32 {
                    return input as u32 + 2 + outer_value;
                })
                .into(),
                PipelineEnd::<u32>::default(),
            )
            .process(5u8, &mut context);
            assert_eq!(output, 10);
        }
    }