use super::Vertex;
use crate::{
    pipeline::{
        AsVertexBufferDescriptor, PrimitiveTopology, RenderPipelines, VertexBufferDescriptor,
        VertexBufferDescriptors, VertexFormat,
    },
    renderer::{BufferInfo, BufferUsage, RenderResourceContext, RenderResourceId},
};
use bevy_app::prelude::{EventReader, Events};
use bevy_asset::{AssetEvent, Assets, Handle};
use bevy_core::AsBytes;
use bevy_ecs::{Local, Query, Res, ResMut};
use bevy_math::*;
use bevy_utils::HashSet;
use std::borrow::Cow;
use thiserror::Error;

pub const VERTEX_BUFFER_ASSET_INDEX: usize = 0;
pub const INDEX_BUFFER_ASSET_INDEX: usize = 1;
#[derive(Clone, Debug)]
pub enum VertexAttributeValues {
    Float(Vec<f32>),
    Float2(Vec<[f32; 2]>),
    Float3(Vec<[f32; 3]>),
    Float4(Vec<[f32; 4]>),
}

impl VertexAttributeValues {
    pub fn len(&self) -> usize {
        match *self {
            VertexAttributeValues::Float(ref values) => values.len(),
            VertexAttributeValues::Float2(ref values) => values.len(),
            VertexAttributeValues::Float3(ref values) => values.len(),
            VertexAttributeValues::Float4(ref values) => values.len(),
        }
    }

    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    // TODO: add vertex format as parameter here and perform type conversions
    pub fn get_bytes(&self) -> &[u8] {
        match self {
            VertexAttributeValues::Float(values) => values.as_slice().as_bytes(),
            VertexAttributeValues::Float2(values) => values.as_slice().as_bytes(),
            VertexAttributeValues::Float3(values) => values.as_slice().as_bytes(),
            VertexAttributeValues::Float4(values) => values.as_slice().as_bytes(),
        }
    }
}

impl From<&VertexAttributeValues> for VertexFormat {
    fn from(values: &VertexAttributeValues) -> Self {
        match values {
            VertexAttributeValues::Float(_) => VertexFormat::Float,
            VertexAttributeValues::Float2(_) => VertexFormat::Float2,
            VertexAttributeValues::Float3(_) => VertexFormat::Float3,
            VertexAttributeValues::Float4(_) => VertexFormat::Float4,
        }
    }
}

#[derive(Debug)]
pub struct VertexAttribute {
    pub name: Cow<'static, str>,
    pub values: VertexAttributeValues,
}

impl VertexAttribute {
    pub const NORMAL: &'static str = "Vertex_Normal";
    pub const POSITION: &'static str = "Vertex_Position";
    pub const UV: &'static str = "Vertex_Uv";

    pub fn position(positions: Vec<[f32; 3]>) -> Self {
        VertexAttribute {
            name: Self::POSITION.into(),
            values: VertexAttributeValues::Float3(positions),
        }
    }

    pub fn normal(normals: Vec<[f32; 3]>) -> Self {
        VertexAttribute {
            name: Self::NORMAL.into(),
            values: VertexAttributeValues::Float3(normals),
        }
    }

    pub fn uv(uvs: Vec<[f32; 2]>) -> Self {
        VertexAttribute {
            name: Self::UV.into(),
            values: VertexAttributeValues::Float2(uvs),
        }
    }
}

#[derive(Error, Debug)]
pub enum MeshToVertexBufferError {
    #[error("VertexBufferDescriptor requires a VertexBufferAttribute this Mesh does not contain.")]
    MissingVertexAttribute { attribute_name: Cow<'static, str> },
    #[error("Mesh VertexAttribute VertexFormat is incompatible with VertexBufferDescriptor VertexAttribute VertexFormat.")]
    IncompatibleVertexAttributeFormat {
        attribute_name: Cow<'static, str>,
        descriptor_format: VertexFormat,
        mesh_format: VertexFormat,
    },
}

#[derive(Debug)]
pub enum Indices {
    U16(Vec<u16>),
    U32(Vec<u32>),
}

#[derive(Debug)]
pub struct Mesh {
    pub primitive_topology: PrimitiveTopology,
    pub attributes: Vec<VertexAttribute>,
    pub indices: Option<Indices>,
}

impl Mesh {
    pub fn new(primitive_topology: PrimitiveTopology) -> Self {
        Mesh {
            primitive_topology,
            attributes: Vec::new(),
            indices: None,
        }
    }

    pub fn get_vertex_buffer_bytes(
        &self,
        vertex_buffer_descriptor: &VertexBufferDescriptor,
        fill_missing_attributes: bool,
    ) -> Result<Vec<u8>, MeshToVertexBufferError> {
        let length = self.attributes.first().map(|a| a.values.len()).unwrap_or(0);
        let mut bytes = vec![0; vertex_buffer_descriptor.stride as usize * length];

        for vertex_attribute in vertex_buffer_descriptor.attributes.iter() {
            match self
                .attributes
                .iter()
                .find(|a| vertex_attribute.name == a.name)
            {
                Some(mesh_attribute) => {
                    let attribute_bytes = mesh_attribute.values.get_bytes();
                    let attribute_size = vertex_attribute.format.get_size() as usize;
                    for (i, vertex_slice) in attribute_bytes.chunks(attribute_size).enumerate() {
                        let vertex_offset = vertex_buffer_descriptor.stride as usize * i;
                        let attribute_offset = vertex_offset + vertex_attribute.offset as usize;
                        bytes[attribute_offset..attribute_offset + attribute_size]
                            .copy_from_slice(vertex_slice);
                    }
                }
                None => {
                    if !fill_missing_attributes {
                        return Err(MeshToVertexBufferError::MissingVertexAttribute {
                            attribute_name: vertex_attribute.name.clone(),
                        });
                    }
                }
            }
        }

        Ok(bytes)
    }

    pub fn get_index_buffer_bytes(&self) -> Option<Vec<u8>> {
        self.indices.as_ref().map(|indices| match &indices {
            Indices::U16(indices) => indices.as_slice().as_bytes().to_vec(),
            Indices::U32(indices) => indices.as_slice().as_bytes().to_vec(),
        })
    }
}

/// Generation for some primitive shape meshes.
pub mod shape {
    use super::{Indices, Mesh, VertexAttribute};
    use crate::pipeline::PrimitiveTopology;
    use bevy_math::*;
    use hexasphere::Hexasphere;

    /// A cube.
    pub struct Cube {
        /// Half the side length of the cube.
        pub size: f32,
    }

    impl Default for Cube {
        fn default() -> Self {
            Cube { size: 1.0 }
        }
    }

    impl From<Cube> for Mesh {
        fn from(cube: Cube) -> Self {
            let size = cube.size;
            let vertices = &[
                // top (0., 0., size)
                ([-size, -size, size], [0., 0., size], [0., 0.]),
                ([size, -size, size], [0., 0., size], [size, 0.]),
                ([size, size, size], [0., 0., size], [size, size]),
                ([-size, size, size], [0., 0., size], [0., size]),
                // bottom (0., 0., -size)
                ([-size, size, -size], [0., 0., -size], [size, 0.]),
                ([size, size, -size], [0., 0., -size], [0., 0.]),
                ([size, -size, -size], [0., 0., -size], [0., size]),
                ([-size, -size, -size], [0., 0., -size], [size, size]),
                // right (size, 0., 0.)
                ([size, -size, -size], [size, 0., 0.], [0., 0.]),
                ([size, size, -size], [size, 0., 0.], [size, 0.]),
                ([size, size, size], [size, 0., 0.], [size, size]),
                ([size, -size, size], [size, 0., 0.], [0., size]),
                // left (-size, 0., 0.)
                ([-size, -size, size], [-size, 0., 0.], [size, 0.]),
                ([-size, size, size], [-size, 0., 0.], [0., 0.]),
                ([-size, size, -size], [-size, 0., 0.], [0., size]),
                ([-size, -size, -size], [-size, 0., 0.], [size, size]),
                // front (0., size, 0.)
                ([size, size, -size], [0., size, 0.], [size, 0.]),
                ([-size, size, -size], [0., size, 0.], [0., 0.]),
                ([-size, size, size], [0., size, 0.], [0., size]),
                ([size, size, size], [0., size, 0.], [size, size]),
                // back (0., -size, 0.)
                ([size, -size, size], [0., -size, 0.], [0., 0.]),
                ([-size, -size, size], [0., -size, 0.], [size, 0.]),
                ([-size, -size, -size], [0., -size, 0.], [size, size]),
                ([size, -size, -size], [0., -size, 0.], [0., size]),
            ];

            let mut positions = Vec::new();
            let mut normals = Vec::new();
            let mut uvs = Vec::new();
            for (position, normal, uv) in vertices.iter() {
                positions.push(*position);
                normals.push(*normal);
                uvs.push(*uv);
            }

            let indices = Indices::U32(vec![
                0, 1, 2, 2, 3, 0, // top
                4, 5, 6, 6, 7, 4, // bottom
                8, 9, 10, 10, 11, 8, // right
                12, 13, 14, 14, 15, 12, // left
                16, 17, 18, 18, 19, 16, // front
                20, 21, 22, 22, 23, 20, // back
            ]);

            Mesh {
                primitive_topology: PrimitiveTopology::TriangleList,
                attributes: vec![
                    VertexAttribute::position(positions),
                    VertexAttribute::normal(normals),
                    VertexAttribute::uv(uvs),
                ],
                indices: Some(indices),
            }
        }
    }

    /// A rectangle on the XY plane.
    pub struct Quad {
        /// Full width and height of the rectangle.
        pub size: Vec2,
        /// Flips the texture coords of the resulting vertices.
        pub flip: bool,
    }

    impl Quad {
        pub fn new(size: Vec2) -> Self {
            Self { size, flip: false }
        }

        pub fn flipped(size: Vec2) -> Self {
            Self { size, flip: true }
        }
    }

    impl From<Quad> for Mesh {
        fn from(quad: Quad) -> Self {
            let extent_x = quad.size.x() / 2.0;
            let extent_y = quad.size.y() / 2.0;

            let north_west = vec2(-extent_x, extent_y);
            let north_east = vec2(extent_x, extent_y);
            let south_west = vec2(-extent_x, -extent_y);
            let south_east = vec2(extent_x, -extent_y);
            let vertices = if quad.flip {
                [
                    (
                        [south_east.x(), south_east.y(), 0.0],
                        [0.0, 0.0, 1.0],
                        [1.0, 1.0],
                    ),
                    (
                        [north_east.x(), north_east.y(), 0.0],
                        [0.0, 0.0, 1.0],
                        [1.0, 0.0],
                    ),
                    (
                        [north_west.x(), north_west.y(), 0.0],
                        [0.0, 0.0, 1.0],
                        [0.0, 0.0],
                    ),
                    (
                        [south_west.x(), south_west.y(), 0.0],
                        [0.0, 0.0, 1.0],
                        [0.0, 1.0],
                    ),
                ]
            } else {
                [
                    (
                        [south_west.x(), south_west.y(), 0.0],
                        [0.0, 0.0, 1.0],
                        [0.0, 1.0],
                    ),
                    (
                        [north_west.x(), north_west.y(), 0.0],
                        [0.0, 0.0, 1.0],
                        [0.0, 0.0],
                    ),
                    (
                        [north_east.x(), north_east.y(), 0.0],
                        [0.0, 0.0, 1.0],
                        [1.0, 0.0],
                    ),
                    (
                        [south_east.x(), south_east.y(), 0.0],
                        [0.0, 0.0, 1.0],
                        [1.0, 1.0],
                    ),
                ]
            };

            let indices = Indices::U32(vec![0, 2, 1, 0, 3, 2]);

            let mut positions = Vec::new();
            let mut normals = Vec::new();
            let mut uvs = Vec::new();
            for (position, normal, uv) in vertices.iter() {
                positions.push(*position);
                normals.push(*normal);
                uvs.push(*uv);
            }

            Mesh {
                primitive_topology: PrimitiveTopology::TriangleList,
                attributes: vec![
                    VertexAttribute::position(positions),
                    VertexAttribute::normal(normals),
                    VertexAttribute::uv(uvs),
                ],
                indices: Some(indices),
            }
        }
    }

    /// A square on the XZ plane.
    pub struct Plane {
        /// The total side length of the square.
        pub size: f32,
    }

    impl From<Plane> for Mesh {
        fn from(plane: Plane) -> Self {
            let extent = plane.size / 2.0;

            let vertices = [
                ([extent, 0.0, -extent], [0.0, 1.0, 0.0], [1.0, 1.0]),
                ([extent, 0.0, extent], [0.0, 1.0, 0.0], [1.0, 0.0]),
                ([-extent, 0.0, extent], [0.0, 1.0, 0.0], [0.0, 0.0]),
                ([-extent, 0.0, -extent], [0.0, 1.0, 0.0], [0.0, 1.0]),
            ];

            let indices = Indices::U32(vec![0, 2, 1, 0, 3, 2]);

            let mut positions = Vec::new();
            let mut normals = Vec::new();
            let mut uvs = Vec::new();
            for (position, normal, uv) in vertices.iter() {
                positions.push(*position);
                normals.push(*normal);
                uvs.push(*uv);
            }

            Mesh {
                primitive_topology: PrimitiveTopology::TriangleList,
                attributes: vec![
                    VertexAttribute::position(positions),
                    VertexAttribute::normal(normals),
                    VertexAttribute::uv(uvs),
                ],
                indices: Some(indices),
            }
        }
    }

    /// A sphere made from a subdivided Icosahedron.
    pub struct Icosphere {
        /// The radius of the sphere.
        pub radius: f32,
        /// The number of subdivisions applied.
        pub subdivisions: usize,
    }

    impl Default for Icosphere {
        fn default() -> Self {
            Self {
                radius: 1.0,
                subdivisions: 5,
            }
        }
    }

    impl From<Icosphere> for Mesh {
        fn from(sphere: Icosphere) -> Self {
            if sphere.subdivisions >= 80 {
                let temp_sphere = Hexasphere::new(sphere.subdivisions, |_| ());

                panic!(
                    "Cannot create an icosphere of {} subdivisions due to there being too many vertices being generated: {} (Limited to 65535 vertices or 79 subdivisions)",
                    sphere.subdivisions,
                    temp_sphere.raw_points().len()
                );
            }
            let hexasphere = Hexasphere::new(sphere.subdivisions, |point| {
                let inclination = point.z().acos();
                let azumith = point.y().atan2(point.x());

                let norm_inclination = 1.0 - (inclination / std::f32::consts::PI);
                let norm_azumith = (azumith / std::f32::consts::PI) * 0.5;

                [norm_inclination, norm_azumith]
            });

            let raw_points = hexasphere.raw_points();

            let points = raw_points
                .iter()
                .map(|&p| (p * sphere.radius).into())
                .collect::<Vec<[f32; 3]>>();

            let normals = raw_points
                .iter()
                .copied()
                .map(Into::into)
                .collect::<Vec<[f32; 3]>>();

            let uvs = hexasphere.raw_data().to_owned();

            let mut indices = Vec::with_capacity(hexasphere.indices_per_main_triangle() * 20);

            for i in 0..20 {
                hexasphere.get_indices(i, &mut indices);
            }

            let indices = Indices::U32(indices);

            Mesh {
                primitive_topology: PrimitiveTopology::TriangleList,
                attributes: vec![
                    VertexAttribute::position(points),
                    VertexAttribute::normal(normals),
                    VertexAttribute::uv(uvs),
                ],
                indices: Some(indices),
            }
        }
    }
}

fn remove_current_mesh_resources(
    render_resource_context: &dyn RenderResourceContext,
    handle: Handle<Mesh>,
) {
    if let Some(RenderResourceId::Buffer(buffer)) =
        render_resource_context.get_asset_resource(handle, VERTEX_BUFFER_ASSET_INDEX)
    {
        render_resource_context.remove_buffer(buffer);
        render_resource_context.remove_asset_resource(handle, VERTEX_BUFFER_ASSET_INDEX);
    }
    if let Some(RenderResourceId::Buffer(buffer)) =
        render_resource_context.get_asset_resource(handle, INDEX_BUFFER_ASSET_INDEX)
    {
        render_resource_context.remove_buffer(buffer);
        render_resource_context.remove_asset_resource(handle, INDEX_BUFFER_ASSET_INDEX);
    }
}

#[derive(Default)]
pub struct MeshResourceProviderState {
    mesh_event_reader: EventReader<AssetEvent<Mesh>>,
    vertex_buffer_descriptor: Option<&'static VertexBufferDescriptor>,
}

pub fn mesh_resource_provider_system(
    mut state: Local<MeshResourceProviderState>,
    render_resource_context: Res<Box<dyn RenderResourceContext>>,
    meshes: Res<Assets<Mesh>>,
    mut vertex_buffer_descriptors: ResMut<VertexBufferDescriptors>,
    mesh_events: Res<Events<AssetEvent<Mesh>>>,
    mut query: Query<(&Handle<Mesh>, &mut RenderPipelines)>,
) {
    let vertex_buffer_descriptor = match state.vertex_buffer_descriptor {
        Some(value) => value,
        None => {
            // TODO: allow pipelines to specialize on vertex_buffer_descriptor and index_format
            let vertex_buffer_descriptor = Vertex::as_vertex_buffer_descriptor();
            vertex_buffer_descriptors.set(vertex_buffer_descriptor.clone());
            state.vertex_buffer_descriptor = Some(vertex_buffer_descriptor);
            vertex_buffer_descriptor
        }
    };
    let mut changed_meshes = HashSet::<Handle<Mesh>>::default();
    let render_resource_context = &**render_resource_context;
    for event in state.mesh_event_reader.iter(&mesh_events) {
        match event {
            AssetEvent::Created { handle } => {
                changed_meshes.insert(*handle);
            }
            AssetEvent::Modified { handle } => {
                changed_meshes.insert(*handle);
                remove_current_mesh_resources(render_resource_context, *handle);
            }
            AssetEvent::Removed { handle } => {
                remove_current_mesh_resources(render_resource_context, *handle);
                // if mesh was modified and removed in the same update, ignore the modification
                // events are ordered so future modification events are ok
                changed_meshes.remove(handle);
            }
        }
    }

    for changed_mesh_handle in changed_meshes.iter() {
        if let Some(mesh) = meshes.get(changed_mesh_handle) {
            let vertex_bytes = mesh
                .get_vertex_buffer_bytes(&vertex_buffer_descriptor, true)
                .unwrap();
            // TODO: use a staging buffer here
            let vertex_buffer = render_resource_context.create_buffer_with_data(
                BufferInfo {
                    buffer_usage: BufferUsage::VERTEX,
                    ..Default::default()
                },
                &vertex_bytes,
            );

            let index_bytes = mesh.get_index_buffer_bytes().unwrap();
            let index_buffer = render_resource_context.create_buffer_with_data(
                BufferInfo {
                    buffer_usage: BufferUsage::INDEX,
                    ..Default::default()
                },
                &index_bytes,
            );

            render_resource_context.set_asset_resource(
                *changed_mesh_handle,
                RenderResourceId::Buffer(vertex_buffer),
                VERTEX_BUFFER_ASSET_INDEX,
            );
            render_resource_context.set_asset_resource(
                *changed_mesh_handle,
                RenderResourceId::Buffer(index_buffer),
                INDEX_BUFFER_ASSET_INDEX,
            );
        }
    }

    // TODO: remove this once batches are pipeline specific and deprecate assigned_meshes draw target
    for (handle, mut render_pipelines) in &mut query.iter() {
        if let Some(mesh) = meshes.get(&handle) {
            for render_pipeline in render_pipelines.pipelines.iter_mut() {
                render_pipeline.specialization.primitive_topology = mesh.primitive_topology;
            }
        }

        if let Some(RenderResourceId::Buffer(vertex_buffer)) =
            render_resource_context.get_asset_resource(*handle, VERTEX_BUFFER_ASSET_INDEX)
        {
            render_pipelines.bindings.set_vertex_buffer(
                "Vertex",
                vertex_buffer,
                render_resource_context
                    .get_asset_resource(*handle, INDEX_BUFFER_ASSET_INDEX)
                    .and_then(|r| {
                        if let RenderResourceId::Buffer(buffer) = r {
                            Some(buffer)
                        } else {
                            None
                        }
                    }),
            );
        }
    }
}

#[cfg(test)]
mod tests {
    use super::{AsVertexBufferDescriptor, Mesh, VertexAttribute};
    use crate::{mesh::Vertex, pipeline::PrimitiveTopology};
    use bevy_core::AsBytes;

    #[test]
    fn test_get_vertex_bytes() {
        let vertices = &[
            ([0., 0., 0.], [1., 1., 1.], [2., 2.]),
            ([3., 3., 3.], [4., 4., 4.], [5., 5.]),
            ([6., 6., 6.], [7., 7., 7.], [8., 8.]),
        ];

        let mut positions = Vec::new();
        let mut normals = Vec::new();
        let mut uvs = Vec::new();
        for (position, normal, uv) in vertices.iter() {
            positions.push(*position);
            normals.push(*normal);
            uvs.push(*uv);
        }

        let mesh = Mesh {
            primitive_topology: PrimitiveTopology::TriangleStrip,
            attributes: vec![
                VertexAttribute::position(positions),
                VertexAttribute::normal(normals),
                VertexAttribute::uv(uvs),
            ],
            indices: None,
        };

        let expected_vertices = &[
            Vertex {
                position: [0., 0., 0.],
                normal: [1., 1., 1.],
                uv: [2., 2.],
            },
            Vertex {
                position: [3., 3., 3.],
                normal: [4., 4., 4.],
                uv: [5., 5.],
            },
            Vertex {
                position: [6., 6., 6.],
                normal: [7., 7., 7.],
                uv: [8., 8.],
            },
        ];

        let descriptor = Vertex::as_vertex_buffer_descriptor();
        assert_eq!(
            mesh.get_vertex_buffer_bytes(descriptor, true).unwrap(),
            expected_vertices.as_bytes(),
            "buffer bytes are equal"
        );
    }
}