use bevy_asset::{AssetLoader, LoadContext, LoadedAsset};
use bevy_reflect::{TypeUuid, Uuid};
use bevy_utils::{tracing::error, BoxedFuture};
use naga::{valid::ModuleInfo, Module};
use regex::Regex;
use std::{borrow::Cow, collections::HashSet, marker::Copy};
use thiserror::Error;
use wgpu::{ShaderModuleDescriptor, ShaderSource};

use crate::render_asset::{PrepareAssetError, RenderAsset};

#[derive(Copy, Clone, Hash, Eq, PartialEq, Debug)]
pub struct ShaderId(Uuid);

impl ShaderId {
    #[allow(clippy::new_without_default)]
    pub fn new() -> Self {
        ShaderId(Uuid::new_v4())
    }
}

#[derive(Error, Debug)]
pub enum ShaderReflectError {
    #[error(transparent)]
    WgslParse(#[from] naga::front::wgsl::ParseError),
    #[error("GLSL Parse Error: {0:?}")]
    GlslParse(Vec<naga::front::glsl::Error>),
    #[error(transparent)]
    SpirVParse(#[from] naga::front::spv::Error),
    #[error(transparent)]
    Validation(#[from] naga::valid::ValidationError),
}

/// A shader, as defined by its [ShaderSource] and [ShaderStage]
/// This is an "unprocessed" shader. It can contain preprocessor directives.
#[derive(Debug, Clone, TypeUuid)]
#[uuid = "d95bc916-6c55-4de3-9622-37e7b6969fda"]
pub enum Shader {
    Wgsl(Cow<'static, str>),
    Glsl(Cow<'static, str>, naga::ShaderStage),
    SpirV(Cow<'static, [u8]>),
    // TODO: consider the following
    // PrecompiledSpirVMacros(HashMap<HashSet<String>, Vec<u32>>)
    // NagaModule(Module) ... Module impls Serialize/Deserialize
}

/// A processed [Shader]. This cannot contain preprocessor directions. It must be "ready to compile"
pub enum ProcessedShader {
    Wgsl(Cow<'static, str>),
    Glsl(Cow<'static, str>, naga::ShaderStage),
    SpirV(Cow<'static, [u8]>),
}

impl ProcessedShader {
    pub fn reflect(&self) -> Result<ShaderReflection, ShaderReflectError> {
        let module = match &self {
            // TODO: process macros here
            ProcessedShader::Wgsl(source) => naga::front::wgsl::parse_str(source)?,
            ProcessedShader::Glsl(source, shader_stage) => {
                let mut parser = naga::front::glsl::Parser::default();
                parser
                    .parse(&naga::front::glsl::Options::from(*shader_stage), source)
                    .map_err(ShaderReflectError::GlslParse)?
            }
            ProcessedShader::SpirV(source) => naga::front::spv::parse_u8_slice(
                source,
                &naga::front::spv::Options {
                    adjust_coordinate_space: false,
                    ..naga::front::spv::Options::default()
                },
            )?,
        };
        let module_info = naga::valid::Validator::new(
            naga::valid::ValidationFlags::default(),
            naga::valid::Capabilities::default(),
        )
        .validate(&module)?;

        Ok(ShaderReflection {
            module,
            module_info,
        })
    }

    pub fn get_module_descriptor(&self) -> Result<ShaderModuleDescriptor, AsModuleDescriptorError> {
        Ok(ShaderModuleDescriptor {
            label: None,
            source: match self {
                ProcessedShader::Wgsl(source) => ShaderSource::Wgsl(source.clone()),
                ProcessedShader::Glsl(_source, _stage) => {
                    let reflection = self.reflect()?;
                    // TODO: it probably makes more sense to convert this to spirv, but as of writing
                    // this comment, naga's spirv conversion is broken
                    let wgsl = reflection.get_wgsl()?;
                    ShaderSource::Wgsl(wgsl.into())
                }
                ProcessedShader::SpirV(_) => {
                    // TODO: we can probably just transmute the u8 array to u32?
                    let reflection = self.reflect()?;
                    let spirv = reflection.get_spirv()?;
                    ShaderSource::SpirV(Cow::Owned(spirv))
                }
            },
        })
    }
}

#[derive(Error, Debug)]
pub enum AsModuleDescriptorError {
    #[error(transparent)]
    ShaderReflectError(#[from] ShaderReflectError),
    #[error(transparent)]
    WgslConversion(#[from] naga::back::wgsl::Error),
    #[error(transparent)]
    SpirVConversion(#[from] naga::back::spv::Error),
}

pub struct ShaderReflection {
    pub module: Module,
    pub module_info: ModuleInfo,
}

impl ShaderReflection {
    pub fn get_spirv(&self) -> Result<Vec<u32>, naga::back::spv::Error> {
        naga::back::spv::write_vec(
            &self.module,
            &self.module_info,
            &naga::back::spv::Options {
                flags: naga::back::spv::WriterFlags::empty(),
                ..naga::back::spv::Options::default()
            },
            None,
        )
    }

    pub fn get_wgsl(&self) -> Result<String, naga::back::wgsl::Error> {
        naga::back::wgsl::write_string(&self.module, &self.module_info)
    }
}

impl Shader {
    pub fn from_wgsl(source: impl Into<Cow<'static, str>>) -> Shader {
        Shader::Wgsl(source.into())
    }

    pub fn from_glsl(source: impl Into<Cow<'static, str>>, stage: naga::ShaderStage) -> Shader {
        Shader::Glsl(source.into(), stage)
    }

    pub fn from_spirv(source: impl Into<Cow<'static, [u8]>>) -> Shader {
        Shader::SpirV(source.into())
    }
}

#[derive(Default)]
pub struct ShaderLoader;

impl AssetLoader for ShaderLoader {
    fn load<'a>(
        &'a self,
        bytes: &'a [u8],
        load_context: &'a mut LoadContext,
    ) -> BoxedFuture<'a, Result<(), anyhow::Error>> {
        Box::pin(async move {
            let ext = load_context.path().extension().unwrap().to_str().unwrap();

            let shader = match ext {
                "spv" => Shader::from_spirv(Vec::from(bytes)),
                "wgsl" => Shader::from_wgsl(String::from_utf8(Vec::from(bytes))?),
                "vert" => Shader::from_glsl(
                    String::from_utf8(Vec::from(bytes))?,
                    naga::ShaderStage::Vertex,
                ),
                "frag" => Shader::from_glsl(
                    String::from_utf8(Vec::from(bytes))?,
                    naga::ShaderStage::Fragment,
                ),
                _ => panic!("unhandled extension: {}", ext),
            };

            load_context.set_default_asset(LoadedAsset::new(shader));
            Ok(())
        })
    }

    fn extensions(&self) -> &[&str] {
        &["spv", "wgsl", "vert", "frag"]
    }
}

impl RenderAsset for Shader {
    type ExtractedAsset = Shader;
    type PreparedAsset = Shader;
    type Param = ();

    fn extract_asset(&self) -> Self::ExtractedAsset {
        self.clone()
    }

    fn prepare_asset(
        extracted_asset: Self::ExtractedAsset,
        _param: &mut bevy_ecs::system::SystemParamItem<Self::Param>,
    ) -> Result<Self::PreparedAsset, PrepareAssetError<Self::ExtractedAsset>> {
        Ok(extracted_asset)
    }
}

#[derive(Error, Debug, PartialEq, Eq)]
pub enum ProcessShaderError {
    #[error("Too many '# endif' lines. Each endif should be preceded by an if statement.")]
    TooManyEndIfs,
    #[error(
        "Not enough '# endif' lines. Each if statement should be followed by an endif statement."
    )]
    NotEnoughEndIfs,
    #[error("This Shader's format does not support processing shader defs.")]
    ShaderFormatDoesNotSupportShaderDefs,
}

pub struct ShaderProcessor {
    ifdef_regex: Regex,
    ifndef_regex: Regex,
    endif_regex: Regex,
}

impl Default for ShaderProcessor {
    fn default() -> Self {
        Self {
            ifdef_regex: Regex::new(r"^\s*#\s*ifdef\s*([\w|\d|_]+)").unwrap(),
            ifndef_regex: Regex::new(r"^\s*#\s*ifndef\s*([\w|\d|_]+)").unwrap(),
            endif_regex: Regex::new(r"^\s*#\s*endif").unwrap(),
        }
    }
}

impl ShaderProcessor {
    pub fn process_shader(
        &self,
        shader: &Shader,
        shader_defs: &[String],
    ) -> Result<ProcessedShader, ProcessShaderError> {
        match shader {
            Shader::Wgsl(source) => Ok(ProcessedShader::Wgsl(Cow::from(
                self.process_str(source, shader_defs)?,
            ))),
            Shader::Glsl(source, stage) => Ok(ProcessedShader::Glsl(
                Cow::from(self.process_str(source, shader_defs)?),
                *stage,
            )),
            Shader::SpirV(source) => {
                if shader_defs.is_empty() {
                    Ok(ProcessedShader::SpirV(source.clone()))
                } else {
                    Err(ProcessShaderError::ShaderFormatDoesNotSupportShaderDefs)
                }
            }
        }
    }

    pub fn process_str(
        &self,
        shader: &str,
        shader_defs: &[String],
    ) -> Result<String, ProcessShaderError> {
        let shader_defs = HashSet::<String>::from_iter(shader_defs.iter().cloned());
        let mut scopes = vec![true];
        let mut final_string = String::new();
        for line in shader.split('\n') {
            if let Some(cap) = self.ifdef_regex.captures(line) {
                let def = cap.get(1).unwrap();
                scopes.push(*scopes.last().unwrap() && shader_defs.contains(def.as_str()));
            } else if let Some(cap) = self.ifndef_regex.captures(line) {
                let def = cap.get(1).unwrap();
                scopes.push(*scopes.last().unwrap() && !shader_defs.contains(def.as_str()));
            } else if self.endif_regex.is_match(line) {
                scopes.pop();
                if scopes.is_empty() {
                    return Err(ProcessShaderError::TooManyEndIfs);
                }
            } else if *scopes.last().unwrap() {
                final_string.push_str(line);
                final_string.push('\n');
            }
        }

        final_string.pop();

        if scopes.len() != 1 {
            return Err(ProcessShaderError::NotEnoughEndIfs);
        }
        Ok(final_string)
    }
}

#[cfg(test)]
mod tests {
    use crate::render_resource::{ProcessShaderError, ShaderProcessor};
    #[rustfmt::skip]
const WGSL: &str = r"
[[block]]
struct View {
    view_proj: mat4x4<f32>;
    world_position: vec3<f32>;
};
[[group(0), binding(0)]]
var<uniform> view: View;

# ifdef TEXTURE
[[group(1), binding(0)]]
var sprite_texture: texture_2d<f32>;
# endif

struct VertexOutput {
    [[location(0)]] uv: vec2<f32>;
    [[builtin(position)]] position: vec4<f32>;
};

[[stage(vertex)]]
fn vertex(
    [[location(0)]] vertex_position: vec3<f32>,
    [[location(1)]] vertex_uv: vec2<f32>
) -> VertexOutput {
    var out: VertexOutput;
    out.uv = vertex_uv;
    out.position = view.view_proj * vec4<f32>(vertex_position, 1.0);
    return out;
}
";
    const WGSL_NESTED_IFDEF: &str = r"
[[block]]
struct View {
    view_proj: mat4x4<f32>;
    world_position: vec3<f32>;
};
[[group(0), binding(0)]]
var<uniform> view: View;

# ifdef TEXTURE
# ifdef ATTRIBUTE
[[group(1), binding(0)]]
var sprite_texture: texture_2d<f32>;
# endif
# endif

struct VertexOutput {
    [[location(0)]] uv: vec2<f32>;
    [[builtin(position)]] position: vec4<f32>;
};

[[stage(vertex)]]
fn vertex(
    [[location(0)]] vertex_position: vec3<f32>,
    [[location(1)]] vertex_uv: vec2<f32>
) -> VertexOutput {
    var out: VertexOutput;
    out.uv = vertex_uv;
    out.position = view.view_proj * vec4<f32>(vertex_position, 1.0);
    return out;
}
";

    #[test]
    fn process_shader_def_defined() {
        #[rustfmt::skip]
    const EXPECTED: &str = r"
[[block]]
struct View {
    view_proj: mat4x4<f32>;
    world_position: vec3<f32>;
};
[[group(0), binding(0)]]
var<uniform> view: View;

[[group(1), binding(0)]]
var sprite_texture: texture_2d<f32>;

struct VertexOutput {
    [[location(0)]] uv: vec2<f32>;
    [[builtin(position)]] position: vec4<f32>;
};

[[stage(vertex)]]
fn vertex(
    [[location(0)]] vertex_position: vec3<f32>,
    [[location(1)]] vertex_uv: vec2<f32>
) -> VertexOutput {
    var out: VertexOutput;
    out.uv = vertex_uv;
    out.position = view.view_proj * vec4<f32>(vertex_position, 1.0);
    return out;
}
";
        let processor = ShaderProcessor::default();
        let result = processor
            .process_str(WGSL, &["TEXTURE".to_string()])
            .unwrap();
        assert_eq!(result, EXPECTED);
    }

    #[test]
    fn process_shader_def_not_defined() {
        #[rustfmt::skip]
        const EXPECTED: &str = r"
[[block]]
struct View {
    view_proj: mat4x4<f32>;
    world_position: vec3<f32>;
};
[[group(0), binding(0)]]
var<uniform> view: View;


struct VertexOutput {
    [[location(0)]] uv: vec2<f32>;
    [[builtin(position)]] position: vec4<f32>;
};

[[stage(vertex)]]
fn vertex(
    [[location(0)]] vertex_position: vec3<f32>,
    [[location(1)]] vertex_uv: vec2<f32>
) -> VertexOutput {
    var out: VertexOutput;
    out.uv = vertex_uv;
    out.position = view.view_proj * vec4<f32>(vertex_position, 1.0);
    return out;
}
";
        let processor = ShaderProcessor::default();
        let result = processor.process_str(WGSL, &[]).unwrap();
        assert_eq!(result, EXPECTED);
    }

    #[test]
    fn process_shader_def_unclosed() {
        #[rustfmt::skip]
        const INPUT: &str = r"
# ifdef FOO
";
        let processor = ShaderProcessor::default();
        let result = processor.process_str(INPUT, &[]);
        assert_eq!(result, Err(ProcessShaderError::NotEnoughEndIfs));
    }

    #[test]
    fn process_shader_def_too_closed() {
        #[rustfmt::skip]
        const INPUT: &str = r"
# endif
";
        let processor = ShaderProcessor::default();
        let result = processor.process_str(INPUT, &[]);
        assert_eq!(result, Err(ProcessShaderError::TooManyEndIfs));
    }

    #[test]
    fn process_shader_def_commented() {
        #[rustfmt::skip]
        const INPUT: &str = r"
// # ifdef FOO
fn foo() { }
";
        let processor = ShaderProcessor::default();
        let result = processor.process_str(INPUT, &[]).unwrap();
        assert_eq!(result, INPUT);
    }

    #[test]
    fn process_nested_shader_def_outer_defined_inner_not() {
        #[rustfmt::skip]
    const EXPECTED: &str = r"
[[block]]
struct View {
    view_proj: mat4x4<f32>;
    world_position: vec3<f32>;
};
[[group(0), binding(0)]]
var<uniform> view: View;


struct VertexOutput {
    [[location(0)]] uv: vec2<f32>;
    [[builtin(position)]] position: vec4<f32>;
};

[[stage(vertex)]]
fn vertex(
    [[location(0)]] vertex_position: vec3<f32>,
    [[location(1)]] vertex_uv: vec2<f32>
) -> VertexOutput {
    var out: VertexOutput;
    out.uv = vertex_uv;
    out.position = view.view_proj * vec4<f32>(vertex_position, 1.0);
    return out;
}
";
        let processor = ShaderProcessor::default();
        let result = processor
            .process_str(WGSL_NESTED_IFDEF, &["TEXTURE".to_string()])
            .unwrap();
        assert_eq!(result, EXPECTED);
    }

    #[test]
    fn process_nested_shader_def_neither_defined() {
        #[rustfmt::skip]
    const EXPECTED: &str = r"
[[block]]
struct View {
    view_proj: mat4x4<f32>;
    world_position: vec3<f32>;
};
[[group(0), binding(0)]]
var<uniform> view: View;


struct VertexOutput {
    [[location(0)]] uv: vec2<f32>;
    [[builtin(position)]] position: vec4<f32>;
};

[[stage(vertex)]]
fn vertex(
    [[location(0)]] vertex_position: vec3<f32>,
    [[location(1)]] vertex_uv: vec2<f32>
) -> VertexOutput {
    var out: VertexOutput;
    out.uv = vertex_uv;
    out.position = view.view_proj * vec4<f32>(vertex_position, 1.0);
    return out;
}
";
        let processor = ShaderProcessor::default();
        let result = processor.process_str(WGSL_NESTED_IFDEF, &[]).unwrap();
        assert_eq!(result, EXPECTED);
    }

    #[test]
    fn process_nested_shader_def_inner_defined_outer_not() {
        #[rustfmt::skip]
    const EXPECTED: &str = r"
[[block]]
struct View {
    view_proj: mat4x4<f32>;
    world_position: vec3<f32>;
};
[[group(0), binding(0)]]
var<uniform> view: View;


struct VertexOutput {
    [[location(0)]] uv: vec2<f32>;
    [[builtin(position)]] position: vec4<f32>;
};

[[stage(vertex)]]
fn vertex(
    [[location(0)]] vertex_position: vec3<f32>,
    [[location(1)]] vertex_uv: vec2<f32>
) -> VertexOutput {
    var out: VertexOutput;
    out.uv = vertex_uv;
    out.position = view.view_proj * vec4<f32>(vertex_position, 1.0);
    return out;
}
";
        let processor = ShaderProcessor::default();
        let result = processor
            .process_str(WGSL_NESTED_IFDEF, &["ATTRIBUTE".to_string()])
            .unwrap();
        assert_eq!(result, EXPECTED);
    }

    #[test]
    fn process_nested_shader_def_both_defined() {
        #[rustfmt::skip]
    const EXPECTED: &str = r"
[[block]]
struct View {
    view_proj: mat4x4<f32>;
    world_position: vec3<f32>;
};
[[group(0), binding(0)]]
var<uniform> view: View;

[[group(1), binding(0)]]
var sprite_texture: texture_2d<f32>;

struct VertexOutput {
    [[location(0)]] uv: vec2<f32>;
    [[builtin(position)]] position: vec4<f32>;
};

[[stage(vertex)]]
fn vertex(
    [[location(0)]] vertex_position: vec3<f32>,
    [[location(1)]] vertex_uv: vec2<f32>
) -> VertexOutput {
    var out: VertexOutput;
    out.uv = vertex_uv;
    out.position = view.view_proj * vec4<f32>(vertex_position, 1.0);
    return out;
}
";
        let processor = ShaderProcessor::default();
        let result = processor
            .process_str(
                WGSL_NESTED_IFDEF,
                &["TEXTURE".to_string(), "ATTRIBUTE".to_string()],
            )
            .unwrap();
        assert_eq!(result, EXPECTED);
    }
}