# process_vector.rs - source
Source of the Rust file `maplibre/src/vector/process_vector.rs`.

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    use std::{collections::HashSet, marker::PhantomData};

    use geozero::{
        mvt::{tile, Message},
        GeozeroDatasource,
    };
    use thiserror::Error;

    use crate::{
        coords::WorldTileCoords,
        io::{
            apc::{Context, SendError},
            geometry_index::{IndexProcessor, IndexedGeometry, TileIndex},
        },
        render::ShaderVertex,
        tessellation::{zero_tessellator::ZeroTessellator, IndexDataType, OverAlignedVertexBuffer},
        vector::transferables::{
            LayerIndexed, LayerMissing, LayerTessellated, TileTessellated, VectorTransferables,
        },
    };

    #[derive(Error, Debug)]
    pub enum ProcessVectorError {
        /// Sending of results failed
        #[error("sending data back through context failed")]
        SendError(SendError),
        /// Error during processing of the pipeline
        #[error("processing data in pipeline failed")]
        Processing(Box<dyn std::error::Error>),
    }

    /// A request for a tile at the given coordinates and in the given layers.
    pub struct VectorTileRequest {
        pub coords: WorldTileCoords,
        pub layers: HashSet<String>,
    }

    pub fn process_vector_tile<T: VectorTransferables, C: Context>(
        data: &[u8],
        tile_request: VectorTileRequest,
        context: &mut ProcessVectorContext<T, C>,
    ) -> Result<(), ProcessVectorError> {
        // Decode

        let mut tile = geozero::mvt::Tile::decode(data).expect("failed to load tile");

        // Available

        let coords = &tile_request.coords;

        for layer in &mut tile.layers {
            let cloned_layer = layer.clone();
            let layer_name: &str = &cloned_layer.name;
            if !tile_request.layers.contains(layer_name) {
                continue;
            }

            let mut tessellator = ZeroTessellator::<IndexDataType>::default();
            if let Err(e) = layer.process(&mut tessellator) {
                context.layer_missing(coords, layer_name)?;

                tracing::error!("layer {layer_name} at {coords} tesselation failed {e:?}");
            } else {
                context.layer_tesselation_finished(
                    coords,
                    tessellator.buffer.into(),
                    tessellator.feature_indices,
                    cloned_layer,
                )?;
            }
        }

        // Missing

        let coords = &tile_request.coords;

        let available_layers: HashSet<_> = tile
            .layers
            .iter()
            .map(|layer| layer.name.clone())
            .collect::<HashSet<_>>();

        for missing_layer in tile_request.layers.difference(&available_layers) {
            context.layer_missing(coords, missing_layer)?;
            tracing::info!("requested layer {missing_layer} at {coords} not found in tile");
        }

        // Indexing

        let mut index = IndexProcessor::new();

        for layer in &mut tile.layers {
            layer.process(&mut index).unwrap();
        }

        context.layer_indexing_finished(&tile_request.coords, index.get_geometries())?;

        // End

        tracing::info!("tile tessellated at {coords} finished");
        context.tile_finished(coords)?;

        Ok(())
    }

    pub struct ProcessVectorContext<T: VectorTransferables, C: Context> {
        context: C,
        phantom_t: PhantomData<T>,
    }

    impl<T: VectorTransferables, C: Context> ProcessVectorContext<T, C> {
        pub fn new(context: C) -> Self {
            Self {
                context,
                phantom_t: Default::default(),
            }
        }
    }

    impl<T: VectorTransferables, C: Context> ProcessVectorContext<T, C> {
        pub fn take_context(self) -> C {
            self.context
        }

        fn tile_finished(&mut self, coords: &WorldTileCoords) -> Result<(), ProcessVectorError> {
            self.context
                .send(T::TileTessellated::build_from(*coords))
                .map_err(|e| ProcessVectorError::Processing(Box::new(e)))
        }

        fn layer_missing(
            &mut self,
            coords: &WorldTileCoords,
            layer_name: &str,
        ) -> Result<(), ProcessVectorError> {
            self.context
                .send(T::LayerMissing::build_from(*coords, layer_name.to_owned()))
                .map_err(|e| ProcessVectorError::Processing(Box::new(e)))
        }

        fn layer_tesselation_finished(
            &mut self,
            coords: &WorldTileCoords,
            buffer: OverAlignedVertexBuffer<ShaderVertex, IndexDataType>,
            feature_indices: Vec<u32>,
            layer_data: tile::Layer,
        ) -> Result<(), ProcessVectorError> {
            self.context
                .send(T::LayerTessellated::build_from(
                    *coords,
                    buffer,
                    feature_indices,
                    layer_data,
                ))
                .map_err(|e| ProcessVectorError::Processing(Box::new(e)))
        }

        fn layer_indexing_finished(
            &mut self,
            coords: &WorldTileCoords,
            geometries: Vec<IndexedGeometry<f64>>,
        ) -> Result<(), ProcessVectorError> {
            self.context
                .send(T::LayerIndexed::build_from(
                    *coords,
                    TileIndex::Linear { list: geometries },
                ))
                .map_err(|e| ProcessVectorError::Processing(Box::new(e)))
        }
    }

    #[cfg(test)]
    mod tests {
        use super::ProcessVectorContext;
        use crate::{
            coords::ZoomLevel,
            io::apc::tests::DummyContext,
            vector::{
                process_vector::{process_vector_tile, VectorTileRequest},
                DefaultVectorTransferables,
            },
        };

        #[test] // TODO: Add proper tile byte array
        #[ignore]
        fn test() {
            let _output = process_vector_tile(
                &[0],
                VectorTileRequest {
                    coords: (0, 0, ZoomLevel::default()).into(),
                    layers: Default::default(),
                },
                &mut ProcessVectorContext::<DefaultVectorTransferables, _>::new(DummyContext),
            );
        }
    }