# request_system.rs - source
Source of the Rust file `maplibre/src/raster/request_system.rs`.

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    //! Requests tiles which are currently in view

    use std::{borrow::Cow, collections::HashSet, marker::PhantomData, rc::Rc};

    use crate::{
        context::MapContext,
        environment::{Environment, OffscreenKernelEnvironment},
        io::{
            apc::{AsyncProcedureCall, AsyncProcedureFuture, Context, Input, ProcedureError},
            source_type::{RasterSource, SourceType},
        },
        kernel::Kernel,
        raster::{
            process_raster::{process_raster_tile, ProcessRasterContext, RasterTileRequest},
            transferables::{LayerRasterMissing, RasterTransferables},
            RasterLayersDataComponent,
        },
        render::tile_view_pattern::DEFAULT_TILE_SIZE,
        style::layer::LayerPaint,
        tcs::system::System,
    };

    pub struct RequestSystem<E: Environment, T: RasterTransferables> {
        kernel: Rc<Kernel<E>>,
        phantom_t: PhantomData<T>,
    }

    impl<E: Environment, T: RasterTransferables> RequestSystem<E, T> {
        pub fn new(kernel: &Rc<Kernel<E>>) -> Self {
            Self {
                kernel: kernel.clone(),
                phantom_t: Default::default(),
            }
        }
    }

    impl<E: Environment, T: RasterTransferables> System for RequestSystem<E, T> {
        fn name(&self) -> Cow<'static, str> {
            "raster_request".into()
        }

        fn run(
            &mut self,
            MapContext {
                style,
                view_state,
                world,
                ..
            }: &mut MapContext,
        ) {
            let view_region =
                view_state.create_view_region(view_state.zoom().zoom_level(DEFAULT_TILE_SIZE));

            if view_state.did_camera_change() || view_state.did_zoom_change() {
                if let Some(view_region) = &view_region {
                    // TODO: We also need to request tiles from layers above if we are over the maximum zoom level

                    for coords in view_region.iter() {
                        if coords.build_quad_key().is_none() {
                            continue;
                        }

                        // TODO: Make tesselation depend on style? So maybe we need to request even if it exists
                        if world
                            .tiles
                            .query::<&RasterLayersDataComponent>(coords)
                            .is_some()
                        {
                            continue;
                        }

                        world
                            .tiles
                            .spawn_mut(coords)
                            .unwrap()
                            .insert(RasterLayersDataComponent::default());

                        tracing::event!(tracing::Level::ERROR, %coords, "tile request started: {coords}");
                        log::info!("tile request started: {coords}");

                        self.kernel
                            .apc()
                            .call(
                                Input::TileRequest {
                                    coords,
                                    style: style.clone(), // TODO: Avoid cloning whole style
                                },
                                fetch_raster_apc::<
                                    E::OffscreenKernelEnvironment,
                                    T,
                                    <E::AsyncProcedureCall as AsyncProcedureCall<
                                        E::OffscreenKernelEnvironment,
                                    >>::Context,
                                >,
                            )
                            .unwrap(); // TODO: Remove unwrap
                    }
                }
            }

            view_state.update_references();
        }
    }
    pub fn fetch_raster_apc<
        K: OffscreenKernelEnvironment,
        T: RasterTransferables,
        C: Context + Clone + Send,
    >(
        input: Input,
        context: C,
        kernel: K,
    ) -> AsyncProcedureFuture {
        Box::pin(async move {
            let Input::TileRequest { coords, style } = input else {
                return Err(ProcedureError::IncompatibleInput);
            };

            let raster_layers: HashSet<String> = style
                .layers
                .iter()
                .filter_map(|layer| {
                    if matches!(layer.paint, Some(LayerPaint::Raster(_))) {
                        layer.source_layer.clone()
                    } else {
                        None
                    }
                })
                .collect();

            let client = kernel.source_client();

            if !raster_layers.is_empty() {
                let context = context.clone();
                let source = SourceType::Raster(RasterSource::default());

                match client.fetch(&coords, &source).await {
                    Ok(data) => {
                        let data = data.into_boxed_slice();

                        let mut process_context = ProcessRasterContext::<T, C>::new(context);

                        process_raster_tile(&data, RasterTileRequest { coords }, &mut process_context)
                            .map_err(|e| ProcedureError::Execution(Box::new(e)))?;
                    }
                    Err(e) => {
                        log::error!("{e:?}");

                        context
                            .send(<T as RasterTransferables>::LayerRasterMissing::build_from(
                                coords,
                            ))
                            .map_err(ProcedureError::Send)?;
                    }
                }
            }

            Ok(())
        })
    }