//! Raw Pipeline State Objects
//!
//! This module contains items used to create and manage Pipelines.

use crate::{device, pass, Backend};
use std::{borrow::Cow, fmt, ops::Range};

mod compute;
mod descriptor;
mod graphics;
mod input_assembler;
mod output_merger;

pub use self::{compute::*, descriptor::*, graphics::*, input_assembler::*, output_merger::*};

/// Error types happening upon PSO creation on the device side.
#[derive(Clone, Debug, PartialEq, Fail)]
pub enum CreationError {
    /// Unknown other error.
    #[fail(display = "Unknown other error")]
    Other,
    /// Invalid subpass (not part of renderpass).
    #[fail(display = "Invalid subpass index: {}", _0)]
    InvalidSubpass(pass::SubpassId),
    /// Shader compilation error.
    #[fail(display = "Shader compilation error: {}", _0)]
    Shader(device::ShaderError),

    /// Out of either host or device memory.
    #[fail(display = "{}", _0)]
    OutOfMemory(device::OutOfMemory),
}

impl From<device::OutOfMemory> for CreationError {
    fn from(err: device::OutOfMemory) -> Self {
        CreationError::OutOfMemory(err)
    }
}

bitflags!(
    /// Stages of the logical pipeline.
    ///
    /// The pipeline is structured by the ordering of the flags.
    /// Some stages are queue type dependent.
    #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
    pub struct PipelineStage: u32 {
        /// Beginning of the command queue.
        const TOP_OF_PIPE = 0x1;
        /// Indirect data consumption.
        const DRAW_INDIRECT = 0x2;
        /// Vertex data consumption.
        const VERTEX_INPUT = 0x4;
        /// Vertex shader execution.
        const VERTEX_SHADER = 0x8;
        /// Hull shader execution.
        const HULL_SHADER = 0x10;
        /// Domain shader execution.
        const DOMAIN_SHADER = 0x20;
        /// Geometry shader execution.
        const GEOMETRY_SHADER = 0x40;
        /// Fragment shader execution.
        const FRAGMENT_SHADER = 0x80;
        /// Stage of early depth and stencil test.
        const EARLY_FRAGMENT_TESTS = 0x100;
        /// Stage of late depth and stencil test.
        const LATE_FRAGMENT_TESTS = 0x200;
        /// Stage of final color value calculation.
        const COLOR_ATTACHMENT_OUTPUT = 0x400;
        /// Compute shader execution,
        const COMPUTE_SHADER = 0x800;
        /// Copy/Transfer command execution.
        const TRANSFER = 0x1000;
        /// End of the command queue.
        const BOTTOM_OF_PIPE = 0x2000;
        /// Read/Write access from host.
        /// (Not a real pipeline stage)
        const HOST = 0x4000;
    }
);

bitflags!(
    /// Combination of different shader pipeline stages.
    #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
    pub struct ShaderStageFlags: u32 {
        /// Vertex shader stage.
        const VERTEX   = 0x1;
        /// Hull (tessellation) shader stage.
        const HULL     = 0x2;
        /// Domain (tessellation) shader stage.
        const DOMAIN   = 0x4;
        /// Geometry shader stage.
        const GEOMETRY = 0x8;
        /// Fragment shader stage.
        const FRAGMENT = 0x10;
        /// Compute shader stage.
        const COMPUTE  = 0x20;
        /// All graphics pipeline shader stages.
        const GRAPHICS = Self::VERTEX.bits | Self::HULL.bits |
            Self::DOMAIN.bits | Self::GEOMETRY.bits | Self::FRAGMENT.bits;
        /// All shader stages.
        const ALL      = Self::GRAPHICS.bits | Self::COMPUTE.bits;
    }
);

// Note: this type is only needed for backends, not used anywhere within gfx_hal.
/// Which program stage this shader represents.
#[allow(missing_docs)]
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
#[repr(u8)]
pub enum Stage {
    Vertex,
    Hull,
    Domain,
    Geometry,
    Fragment,
    Compute,
}

impl From<Stage> for ShaderStageFlags {
    fn from(stage: Stage) -> Self {
        match stage {
            Stage::Vertex => ShaderStageFlags::VERTEX,
            Stage::Hull => ShaderStageFlags::HULL,
            Stage::Domain => ShaderStageFlags::DOMAIN,
            Stage::Geometry => ShaderStageFlags::GEOMETRY,
            Stage::Fragment => ShaderStageFlags::FRAGMENT,
            Stage::Compute => ShaderStageFlags::COMPUTE,
        }
    }
}

impl fmt::Display for Stage {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.write_str(match self {
            Stage::Vertex => "vertex",
            Stage::Hull => "hull",
            Stage::Domain => "domain",
            Stage::Geometry => "geometry",
            Stage::Fragment => "fragment",
            Stage::Compute => "compute",
        })
    }
}

/// Shader entry point.
#[derive(Debug)]
pub struct EntryPoint<'a, B: Backend> {
    /// Entry point name.
    pub entry: &'a str,
    /// Shader module reference.
    pub module: &'a B::ShaderModule,
    /// Specialization.
    pub specialization: Specialization<'a>,
}

impl<'a, B: Backend> Clone for EntryPoint<'a, B> {
    fn clone(&self) -> Self {
        EntryPoint {
            entry: self.entry,
            module: self.module,
            specialization: self.specialization.clone(),
        }
    }
}

bitflags!(
    /// Pipeline creation flags.
    #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
    pub struct PipelineCreationFlags: u32 {
        /// Disable pipeline optimizations.
        ///
        /// May speedup pipeline creation.
        const DISABLE_OPTIMIZATION = 0x1;
        /// Allow derivatives (children) of the pipeline.
        ///
        /// Must be set when pipelines set the pipeline as base.
        const ALLOW_DERIVATIVES = 0x2;
    }
);

/// A reference to a parent pipeline.  The assumption is that
/// a parent and derivative/child pipeline have most settings
/// in common, and one may be switched for another more quickly
/// than entirely unrelated pipelines would be.
#[derive(Debug)]
pub enum BasePipeline<'a, P: 'a> {
    /// Referencing an existing pipeline as parent.
    Pipeline(&'a P),
    /// A pipeline in the same create pipelines call.
    ///
    /// The index of the parent must be lower than the index of the child.
    Index(usize),
    /// No parent pipeline exists.
    None,
}

/// Specialization constant for pipelines.
///
/// Specialization constants allow for easy configuration of
/// multiple similar pipelines. For example, there may be a
/// boolean exposed to the shader that switches the specularity on/off
/// provided via a specialization constant.
/// That would produce separate PSO's for the "on" and "off" states
/// but they share most of the internal stuff and are fast to produce.
/// More importantly, they are fast to execute, since the driver
/// can optimize out the branch on that other PSO creation.
#[derive(Debug, Clone)]
pub struct SpecializationConstant {
    /// Constant identifier in shader source.
    pub id: u32,
    /// Value to override specialization constant.
    pub range: Range<u16>,
}

/// Specialization information structure.
#[derive(Debug, Clone)]
pub struct Specialization<'a> {
    /// Constant array.
    pub constants: Cow<'a, [SpecializationConstant]>,
    /// Raw data.
    pub data: Cow<'a, [u8]>,
}

impl Specialization<'_> {
    /// Empty specialization instance.
    pub const EMPTY: Self = Specialization {
        constants: Cow::Borrowed(&[]),
        data: Cow::Borrowed(&[]),
    };
}

impl Default for Specialization<'_> {
    fn default() -> Self {
        Specialization::EMPTY
    }
}

#[doc(hidden)]
#[derive(Debug, Default)]
pub struct SpecializationStorage {
    constants: Vec<SpecializationConstant>,
    data: Vec<u8>,
}

/// List of specialization constants.
#[doc(hidden)]
pub trait SpecConstList: Sized {
    fn fold(self, storage: &mut SpecializationStorage);
}

impl<T> From<T> for Specialization<'_>
where
    T: SpecConstList,
{
    fn from(list: T) -> Self {
        let mut storage = SpecializationStorage::default();
        list.fold(&mut storage);
        Specialization {
            data: Cow::Owned(storage.data),
            constants: Cow::Owned(storage.constants),
        }
    }
}

#[doc(hidden)]
#[derive(Debug)]
pub struct SpecConstListNil;

#[doc(hidden)]
#[derive(Debug)]
pub struct SpecConstListCons<H, T> {
    pub head: (u32, H),
    pub tail: T,
}

impl SpecConstList for SpecConstListNil {
    fn fold(self, _storage: &mut SpecializationStorage) {}
}

impl<H, T> SpecConstList for SpecConstListCons<H, T>
where
    T: SpecConstList,
{
    fn fold(self, storage: &mut SpecializationStorage) {
        let size = std::mem::size_of::<H>();
        assert!(storage.data.len() + size <= u16::max_value() as usize);
        let offset = storage.data.len() as u16;
        storage.data.extend_from_slice(unsafe {
            // Inspecting bytes is always safe.
            std::slice::from_raw_parts(&self.head.1 as *const H as *const u8, size)
        });
        storage.constants.push(SpecializationConstant {
            id: self.head.0,
            range: offset..offset + size as u16,
        });
        self.tail.fold(storage)
    }
}

/// Pipeline state which may be static or dynamic.
#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub enum State<T> {
    /// Static state that cannot be altered.
    Static(T),
    /// Dynamic state set through a command buffer.
    Dynamic,
}

impl<T> State<T> {
    /// Returns the static value or a default.
    pub fn static_or(self, default: T) -> T {
        match self {
            State::Static(v) => v,
            State::Dynamic => default,
        }
    }

    /// Whether the state is static.
    pub fn is_static(self) -> bool {
        match self {
            State::Static(_) => true,
            State::Dynamic => false,
        }
    }

    /// Whether the state is dynamic.
    pub fn is_dynamic(self) -> bool {
        !self.is_static()
    }
}

/// Macro for specifying list of specialization constatns for `EntryPoint`.
#[macro_export]
macro_rules! spec_const_list {
    (@ $(,)?) => {
        $crate::pso::SpecConstListNil
    };

    (@ $head_id:expr => $head_constant:expr $(,$tail_id:expr => $tail_constant:expr)* $(,)?) => {
        $crate::pso::SpecConstListCons {
            head: ($head_id, $head_constant),
            tail: $crate::spec_const_list!(@ $($tail_id:expr => $tail_constant:expr),*),
        }
    };

    ($($id:expr => $constant:expr),* $(,)?) => {
        $crate::spec_const_list!(@ $($id => $constant),*).into()
    };

    ($($constant:expr),* $(,)?) => {
        {
            let mut counter = 0;
            $crate::spec_const_list!(@ $({ counter += 1; counter - 1 } => $constant),*).into()
        }
    };
}