/*! Universal shader translator.

The central structure of the crate is [`Module`]. A `Module` contains:

- [`EntryPoint`]s, the main functions for pipeline stages like vertex shading or
  fragment shading,

- [`Function`]s, representing functions used by `EntryPoint`s and other `Function`s,

- [`Constant`]s and [`GlobalVariable`]s used by `EntryPoint`s and `Function`s, and

- [`Type`]s used by the above.

The body of an `EntryPoint` or `Function` is represented using two types:

- An [`Expression`] produces a value, but has no side effects or control flow.
  `Expressions` include variable references, unary and binary operators, and so
  on.

- A [`Statement`] can have side effects and structured control flow.
  `Statement`s do not produce a value, other than by storing one in some
  designated place. `Statements` include blocks, conditionals, and loops, but also
  operations that have side effects, like stores and function calls.

`Statement`s form a tree, with pointers into the DAG of `Expression`s.

Restricting side effects to statements simplifies analysis and code generation.
A Naga backend can generate code to evaluate an `Expression` however and
whenever it pleases, as long as it is certain to observe the side effects of all
previously executed `Statement`s.

Many `Statement` variants use the [`Block`] type, which is simply `Vec<Block>`,
representing a series of statements executed in order. The body of an
`EntryPoint`s or `Function` is a `Block`, and `Statement` has a
[`Block`][Statement::Block] variant.

To improve translator performance and reduce memory usage, most structures are
stored in an [`Arena`]. An `Arena<T>` stores a series of `T` values, indexed by
[`Handle<T>`](Handle) values, which are just wrappers around integer indexes.
For example, a `Function`'s expressions are stored in an `Arena<Expression>`,
and compound expressions refer to their sub-expressions via `Handle<Expression>`
values. (When examining the serialized form of a `Module`, note that the first
element of an `Arena` has an index of 1, not 0.)

## Function Calls

The Naga IR's representation of function calls is unusual. Most languages treat
function calls as expressions, but because calls may have side effects, Naga
represents them with [`Statement::Call`]. A call statement may designate a
particular `Expression` to represent its return value, if any, which can be used
by subsequent statements and their expressions.

## `Expression` evaluation time and scope

While the order of execution of [`Statement`]s is apparent from their structure,
it is not so obvious exactly when a given [`Expression`] should be evaluated,
since many `Statement`s and `Expression`s may refer to its value. But it is
essential to clearly specify an expression's evaluation time, since that
determines which statements' effects the expression should observe. It is also
helpful to backends to limit the visibility of an `Expression`'s value to a
portion of the statement tree.

An `Expression` may only be used, whether by a `Statement` or another
`Expression`, if one of the following is true:

- The expression is an [`Expression::Constant`], [`Expression::FunctionArgument`], or
  [`Expression::GlobalVariable`].

- The expression is an [`Expression::LocalVariable`] that is either the
  `pointer` (destination) of a [`Statement::Store`], or initialized by some
  previously executed `Statement::Store`.

- The expression is the `result` of a [`Statement::Call`], representing the
  call's return value. The call must be 'in scope' for the use (see below).

- The expression is included in the range of some [`Statement::Emit`] that is
  'in scope' for the use (see below). The [`Expression::needs_pre_emit`] method
  returns `true` if the given expression does *not* need to be covered by an
  `Emit` statement.

The scope of an expression evaluated by an `Emit` statement covers the
subsequent expressions in that `Emit`, any following statements in the `Block`
to which that `Emit` belongs (if any) and their sub-statements (if any).

If a `Call` statement has a `result` expression, then it is in scope for any
statements following the `Call` in the `Block` to which that `Call` belongs (if
any) and their sub-statements (if any).

This means that, for example, an expression evaluated by some statement in a
nested `Block` is not available in the `Block`'s parents. Such a value would
need to be stored in a local variable to be carried upwards in the statement
tree.

## Variables

An [`Expression::LocalVariable`] or [`Expression::GlobalVariable`] produces a
pointer value referring to the variable's value. To retrieve the variable's
value, use an [`Expression::Load`], with the variable expression as its
`pointer` operand. To assign to a variable, use a [`Statement::Store`] with the
variable expression as its `pointer` operand.

As an exception, [`Expression::GlobalVariable`]s referring to
[`GlobalVariable`]s whose `class` is [`StorageClass::Handle`] produce the
variable's value directly; no `Load` is needed. These global variables refer to
opaque values like samplers and images.

!*/

// TODO: use `strip_prefix` instead when Rust 1.45 <= MSRV
#![allow(
    renamed_and_removed_lints,
    unknown_lints, // requires Rust 1.51
    clippy::new_without_default,
    clippy::unneeded_field_pattern,
    clippy::match_like_matches_macro,
    clippy::manual_strip,
    clippy::unknown_clippy_lints,
)]
#![warn(
    trivial_casts,
    trivial_numeric_casts,
    unused_extern_crates,
    unused_qualifications,
    clippy::pattern_type_mismatch
)]
#![deny(clippy::panic)]

mod arena;
pub mod back;
pub mod front;
pub mod proc;
pub mod valid;

pub use crate::arena::{Arena, Handle, Range};

use std::{
    collections::{HashMap, HashSet},
    hash::BuildHasherDefault,
};

#[cfg(feature = "deserialize")]
use serde::Deserialize;
#[cfg(feature = "serialize")]
use serde::Serialize;

/// Width of a boolean type, in bytes.
pub const BOOL_WIDTH: Bytes = 1;

/// Hash map that is faster but not resilient to DoS attacks.
pub type FastHashMap<K, T> = HashMap<K, T, BuildHasherDefault<fxhash::FxHasher>>;
/// Hash set that is faster but not resilient to DoS attacks.
pub type FastHashSet<K> = HashSet<K, BuildHasherDefault<fxhash::FxHasher>>;

/// Map of expressions that have associated variable names
pub(crate) type NamedExpressions = FastHashMap<Handle<Expression>, String>;

/// Early fragment tests. In a standard situation if a driver determines that it is possible to
/// switch on early depth test it will. Typical situations when early depth test is switched off:
///   - Calling ```discard``` in a shader.
///   - Writing to the depth buffer, unless ConservativeDepth is enabled.
///
/// SPIR-V: ExecutionMode EarlyFragmentTests
/// In GLSL: layout(early_fragment_tests) in;
/// HLSL: Attribute earlydepthstencil
///
/// For more, see:
///   - https://www.khronos.org/opengl/wiki/Early_Fragment_Test#Explicit_specification
///   - https://docs.microsoft.com/en-us/windows/win32/direct3dhlsl/sm5-attributes-earlydepthstencil
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub struct EarlyDepthTest {
    conservative: Option<ConservativeDepth>,
}
/// Enables adjusting depth without disabling early Z.
///
/// SPIR-V: ExecutionMode DepthGreater/DepthLess/DepthUnchanged
/// GLSL: layout (depth_<greater/less/unchanged/any>) out float gl_FragDepth;
///   - ```depth_any``` option behaves as if the layout qualifier was not present.
/// HLSL: SV_Depth/SV_DepthGreaterEqual/SV_DepthLessEqual
///
/// For more, see:
///   - https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_conservative_depth.txt
///   - https://docs.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-semantics#system-value-semantics
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum ConservativeDepth {
    /// Shader may rewrite depth only with a value greater than calculated;
    GreaterEqual,

    /// Shader may rewrite depth smaller than one that would have been written without the modification.
    LessEqual,

    /// Shader may not rewrite depth value.
    Unchanged,
}

/// Stage of the programmable pipeline.
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
#[allow(missing_docs)] // The names are self evident
pub enum ShaderStage {
    Vertex,
    Fragment,
    Compute,
}

/// Class of storage for variables.
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum StorageClass {
    /// Function locals.
    Function,
    /// Private data, per invocation, mutable.
    Private,
    /// Workgroup shared data, mutable.
    WorkGroup,
    /// Uniform buffer data.
    Uniform,
    /// Storage buffer data, potentially mutable.
    Storage,
    /// Opaque handles, such as samplers and images.
    Handle,
    /// Push constants.
    PushConstant,
}

/// Built-in inputs and outputs.
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum BuiltIn {
    Position,
    // vertex
    BaseInstance,
    BaseVertex,
    ClipDistance,
    CullDistance,
    InstanceIndex,
    PointSize,
    VertexIndex,
    // fragment
    FragDepth,
    FrontFacing,
    SampleIndex,
    SampleMask,
    // compute
    GlobalInvocationId,
    LocalInvocationId,
    LocalInvocationIndex,
    WorkGroupId,
    WorkGroupSize,
}

/// Number of bytes per scalar.
pub type Bytes = u8;

/// Number of components in a vector.
#[repr(u8)]
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum VectorSize {
    /// 2D vector
    Bi = 2,
    /// 3D vector
    Tri = 3,
    /// 4D vector
    Quad = 4,
}

/// Primitive type for a scalar.
#[repr(u8)]
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum ScalarKind {
    /// Signed integer type.
    Sint,
    /// Unsigned integer type.
    Uint,
    /// Floating point type.
    Float,
    /// Boolean type.
    Bool,
}

/// Size of an array.
#[repr(u8)]
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum ArraySize {
    /// The array size is constant.
    Constant(Handle<Constant>),
    /// The array size can change at runtime.
    Dynamic,
}

/// The interpolation qualifier of a binding or struct field.
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum Interpolation {
    /// The value will be interpolated in a perspective-correct fashion.
    /// Also known as "smooth" in glsl.
    Perspective,
    /// Indicates that linear, non-perspective, correct
    /// interpolation must be used.
    /// Also known as "no_perspective" in glsl.
    Linear,
    /// Indicates that no interpolation will be performed.
    Flat,
}

/// The sampling qualifiers of a binding or struct field.
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum Sampling {
    /// Interpolate the value at the center of the pixel.
    Center,

    /// Interpolate the value at a point that lies within all samples covered by
    /// the fragment within the current primitive. In multisampling, use a
    /// single value for all samples in the primitive.
    Centroid,

    /// Interpolate the value at each sample location. In multisampling, invoke
    /// the fragment shader once per sample.
    Sample,
}

/// Member of a user-defined structure.
// Clone is used only for error reporting and is not intended for end users
#[derive(Clone, Debug, PartialEq)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub struct StructMember {
    pub name: Option<String>,
    /// Type of the field.
    pub ty: Handle<Type>,
    /// For I/O structs, defines the binding.
    pub binding: Option<Binding>,
    /// Offset from the beginning from the struct.
    pub offset: u32,
}

/// The number of dimensions an image has.
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum ImageDimension {
    /// 1D image
    D1,
    /// 2D image
    D2,
    /// 3D image
    D3,
    /// Cube map
    Cube,
}

bitflags::bitflags! {
    /// Flags describing an image.
    #[cfg_attr(feature = "serialize", derive(Serialize))]
    #[cfg_attr(feature = "deserialize", derive(Deserialize))]
    #[derive(Default)]
    pub struct StorageAccess: u32 {
        /// Storage can be used as a source for load ops.
        const LOAD = 0x1;
        /// Storage can be used as a target for store ops.
        const STORE = 0x2;
    }
}

// Storage image format.
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum StorageFormat {
    // 8-bit formats
    R8Unorm,
    R8Snorm,
    R8Uint,
    R8Sint,

    // 16-bit formats
    R16Uint,
    R16Sint,
    R16Float,
    Rg8Unorm,
    Rg8Snorm,
    Rg8Uint,
    Rg8Sint,

    // 32-bit formats
    R32Uint,
    R32Sint,
    R32Float,
    Rg16Uint,
    Rg16Sint,
    Rg16Float,
    Rgba8Unorm,
    Rgba8Snorm,
    Rgba8Uint,
    Rgba8Sint,

    // Packed 32-bit formats
    Rgb10a2Unorm,
    Rg11b10Float,

    // 64-bit formats
    Rg32Uint,
    Rg32Sint,
    Rg32Float,
    Rgba16Uint,
    Rgba16Sint,
    Rgba16Float,

    // 128-bit formats
    Rgba32Uint,
    Rgba32Sint,
    Rgba32Float,
}

/// Sub-class of the image type.
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum ImageClass {
    /// Regular sampled image.
    Sampled {
        /// Kind of values to sample.
        kind: ScalarKind,
        // Multi-sampled.
        multi: bool,
    },
    /// Depth comparison image.
    Depth,
    /// Storage image.
    Storage(StorageFormat),
}

/// A data type declared in the module.
#[derive(Debug, PartialEq)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub struct Type {
    /// The name of the type, if any.
    pub name: Option<String>,
    /// Inner structure that depends on the kind of the type.
    pub inner: TypeInner,
}

/// Enum with additional information, depending on the kind of type.
#[derive(Debug, PartialEq)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum TypeInner {
    /// Number of integral or floating-point kind.
    Scalar { kind: ScalarKind, width: Bytes },
    /// Vector of numbers.
    Vector {
        size: VectorSize,
        kind: ScalarKind,
        width: Bytes,
    },
    /// Matrix of floats.
    Matrix {
        columns: VectorSize,
        rows: VectorSize,
        width: Bytes,
    },
    /// Pointer to another type.
    Pointer {
        base: Handle<Type>,
        class: StorageClass,
    },
    /// Pointer to a value.
    ValuePointer {
        size: Option<VectorSize>,
        kind: ScalarKind,
        width: Bytes,
        class: StorageClass,
    },
    /// Homogenous list of elements.
    Array {
        base: Handle<Type>,
        size: ArraySize,
        stride: u32,
    },
    /// User-defined structure.
    Struct {
        top_level: bool,
        members: Vec<StructMember>,
        //TODO: should this be unaligned?
        span: u32,
    },
    /// Possibly multidimensional array of texels.
    Image {
        dim: ImageDimension,
        arrayed: bool,
        class: ImageClass,
    },
    /// Can be used to sample values from images.
    Sampler { comparison: bool },
}

/// Constant value.
#[derive(Debug, PartialEq)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub struct Constant {
    pub name: Option<String>,
    pub specialization: Option<u32>,
    pub inner: ConstantInner,
}

/// A literal scalar value, used in constants.
#[derive(Debug, Clone, Copy, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum ScalarValue {
    Sint(i64),
    Uint(u64),
    Float(f64),
    Bool(bool),
}

/// Additional information, dependent on the kind of constant.
#[derive(Clone, Debug, PartialEq)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum ConstantInner {
    Scalar {
        width: Bytes,
        value: ScalarValue,
    },
    Composite {
        ty: Handle<Type>,
        components: Vec<Handle<Constant>>,
    },
}

/// Describes how an input/output variable is to be bound.
#[derive(Clone, Debug, PartialEq)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum Binding {
    /// Built-in shader variable.
    BuiltIn(BuiltIn),
    /// Indexed location.
    Location {
        location: u32,
        interpolation: Option<Interpolation>,
        sampling: Option<Sampling>,
    },
}

/// Pipeline binding information for global resources.
#[derive(Clone, Debug, Hash, PartialEq)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub struct ResourceBinding {
    /// The bind group index.
    pub group: u32,
    /// Binding number within the group.
    pub binding: u32,
}

/// Variable defined at module level.
#[derive(Clone, Debug, PartialEq)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub struct GlobalVariable {
    /// Name of the variable, if any.
    pub name: Option<String>,
    /// How this variable is to be stored.
    pub class: StorageClass,
    /// For resources, defines the binding point.
    pub binding: Option<ResourceBinding>,
    /// The type of this variable.
    pub ty: Handle<Type>,
    /// Initial value for this variable.
    pub init: Option<Handle<Constant>>,
    /// Access bit for storage types of images and buffers.
    pub storage_access: StorageAccess,
}

/// Variable defined at function level.
#[derive(Clone, Debug)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub struct LocalVariable {
    /// Name of the variable, if any.
    pub name: Option<String>,
    /// The type of this variable.
    pub ty: Handle<Type>,
    /// Initial value for this variable.
    pub init: Option<Handle<Constant>>,
}

/// Operation that can be applied on a single value.
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum UnaryOperator {
    Negate,
    Not,
}

/// Operation that can be applied on two values.
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum BinaryOperator {
    Add,
    Subtract,
    Multiply,
    Divide,
    Modulo,
    Equal,
    NotEqual,
    Less,
    LessEqual,
    Greater,
    GreaterEqual,
    And,
    ExclusiveOr,
    InclusiveOr,
    LogicalAnd,
    LogicalOr,
    ShiftLeft,
    /// Right shift carries the sign of signed integers only.
    ShiftRight,
}

/// Axis on which to compute a derivative.
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum DerivativeAxis {
    X,
    Y,
    Width,
}

/// Built-in shader function for testing relation between values.
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum RelationalFunction {
    All,
    Any,
    IsNan,
    IsInf,
    IsFinite,
    IsNormal,
}

/// Built-in shader function for math.
#[derive(Clone, Copy, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum MathFunction {
    // comparison
    Abs,
    Min,
    Max,
    Clamp,
    // trigonometry
    Cos,
    Cosh,
    Sin,
    Sinh,
    Tan,
    Tanh,
    Acos,
    Asin,
    Atan,
    Atan2,
    // decomposition
    Ceil,
    Floor,
    Round,
    Fract,
    Trunc,
    Modf,
    Frexp,
    Ldexp,
    // exponent
    Exp,
    Exp2,
    Log,
    Log2,
    Pow,
    // geometry
    Dot,
    Outer,
    Cross,
    Distance,
    Length,
    Normalize,
    FaceForward,
    Reflect,
    Refract,
    // computational
    Sign,
    Fma,
    Mix,
    Step,
    SmoothStep,
    Sqrt,
    InverseSqrt,
    Inverse,
    Transpose,
    Determinant,
    // bits
    CountOneBits,
    ReverseBits,
}

/// Sampling modifier to control the level of detail.
#[derive(Clone, Copy, Debug, PartialEq)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum SampleLevel {
    Auto,
    Zero,
    Exact(Handle<Expression>),
    Bias(Handle<Expression>),
    Gradient {
        x: Handle<Expression>,
        y: Handle<Expression>,
    },
}

/// Type of an image query.
#[derive(Clone, Copy, Debug, PartialEq)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum ImageQuery {
    /// Get the size at the specified level.
    Size {
        /// If `None`, the base level is considered.
        level: Option<Handle<Expression>>,
    },
    /// Get the number of mipmap levels.
    NumLevels,
    /// Get the number of array layers.
    NumLayers,
    /// Get the number of samples.
    NumSamples,
}

/// Component selection for a vector swizzle.
#[repr(u8)]
#[derive(Clone, Copy, Debug, PartialEq)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum SwizzleComponent {
    ///
    X = 0,
    ///
    Y = 1,
    ///
    Z = 2,
    ///
    W = 3,
}

bitflags::bitflags! {
    /// Memory barrier flags.
    #[cfg_attr(feature = "serialize", derive(Serialize))]
    #[cfg_attr(feature = "deserialize", derive(Deserialize))]
    #[derive(Default)]
    pub struct Barrier: u32 {
        /// Barrier affects all `StorageClass::Storage` accesses.
        const STORAGE = 0x1;
        /// Barrier affects all `StorageClass::WorkGroup` accesses.
        const WORK_GROUP = 0x2;
    }
}

/// An expression that can be evaluated to obtain a value.
///
/// This is a Single Static Assignment (SSA) scheme similar to SPIR-V.
#[derive(Clone, Debug)]
#[cfg_attr(test, derive(PartialEq))]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum Expression {
    /// Array access with a computed index.
    ///
    /// ## Typing rules
    ///
    /// The `base` operand must be some composite type: [`Vector`], [`Matrix`],
    /// [`Array`], a [`Pointer`] to one of those, or a [`ValuePointer`] with a
    /// `size`.
    ///
    /// The `index` operand must be an integer, signed or unsigned.
    ///
    /// Indexing a [`Vector`] or [`Array`] produces a value of its element type.
    /// Indexing a [`Matrix`] produces a [`Vector`].
    ///
    /// Indexing a [`Pointer`] to an [`Array`] produces a [`Pointer`] to its
    /// `base` type, taking on the `Pointer`'s storage class.
    ///
    /// Indexing a [`Pointer`] to a [`Vector`] produces a [`ValuePointer`] whose
    /// size is `None`, taking on the [`Vector`]'s scalar kind and width and the
    /// [`Pointer`]'s storage class.
    ///
    /// Indexing a [`Pointer`] to a [`Matrix`] produces a [`ValuePointer`] for a
    /// column of the matrix: its size is the matrix's height, its `kind` is
    /// [`Float`], and it inherits the [`Matrix`]'s width and the [`Pointer`]'s
    /// storage class.
    ///
    /// ## Dynamic indexing restrictions
    ///
    /// To accommodate restrictions in some of the shader languages that Naga
    /// targets, it is not permitted to subscript a matrix or array with a
    /// dynamically computed index unless that matrix or array appears behind a
    /// pointer. In other words, if the inner type of `base` is [`Array`] or
    /// [`Matrix`], then `index` must be a constant. But if the type of `base`
    /// is a [`Pointer`] to an array or matrix or a [`ValuePointer`] with a
    /// `size`, then the index may be any expression of integer type.
    ///
    /// You can use the [`Expression::is_dynamic_index`] method to determine
    /// whether a given index expression requires matrix or array base operands
    /// to be behind a pointer.
    ///
    /// (It would be simpler to always require the use of `AccessIndex` when
    /// subscripting arrays and matrices that are not behind pointers, but to
    /// accommodate existing front ends, Naga also permits `Access`, with a
    /// restricted `index`.)
    ///
    /// [`Vector`]: TypeInner::Vector
    /// [`Matrix`]: TypeInner::Matrix
    /// [`Array`]: TypeInner::Array
    /// [`Pointer`]: TypeInner::Pointer
    /// [`ValuePointer`]: TypeInner::ValuePointer
    /// [`Float`]: ScalarKind::Float
    Access {
        base: Handle<Expression>,
        index: Handle<Expression>,
    },
    /// Array access with a known index.
    AccessIndex {
        base: Handle<Expression>,
        index: u32,
    },
    /// Constant value.
    Constant(Handle<Constant>),
    /// Splat scalar into a vector.
    Splat {
        size: VectorSize,
        value: Handle<Expression>,
    },
    /// Vector swizzle.
    Swizzle {
        size: VectorSize,
        vector: Handle<Expression>,
        pattern: [SwizzleComponent; 4],
    },
    /// Composite expression.
    Compose {
        ty: Handle<Type>,
        components: Vec<Handle<Expression>>,
    },
    /// Reference a function parameter, by its index.
    FunctionArgument(u32),
    /// Reference a global variable.
    GlobalVariable(Handle<GlobalVariable>),
    /// Reference a local variable.
    LocalVariable(Handle<LocalVariable>),
    /// Load a value indirectly.
    Load { pointer: Handle<Expression> },
    /// Sample a point from a sampled or a depth image.
    ImageSample {
        image: Handle<Expression>,
        sampler: Handle<Expression>,
        coordinate: Handle<Expression>,
        array_index: Option<Handle<Expression>>,
        offset: Option<Handle<Constant>>,
        level: SampleLevel,
        depth_ref: Option<Handle<Expression>>,
    },
    /// Load a texel from an image.
    ImageLoad {
        image: Handle<Expression>,
        coordinate: Handle<Expression>,
        array_index: Option<Handle<Expression>>,
        /// For storage images, this is None.
        /// For sampled images, this is the Some(Level).
        /// For multisampled images, this is Some(Sample).
        index: Option<Handle<Expression>>,
    },
    /// Query information from an image.
    ImageQuery {
        image: Handle<Expression>,
        query: ImageQuery,
    },
    /// Apply an unary operator.
    Unary {
        op: UnaryOperator,
        expr: Handle<Expression>,
    },
    /// Apply a binary operator.
    Binary {
        op: BinaryOperator,
        left: Handle<Expression>,
        right: Handle<Expression>,
    },
    /// Select between two values based on a condition.
    ///
    /// Note that, because expressions have no side effects, it is unobservable
    /// whether the non-selected branch is evaluated.
    Select {
        /// Boolean expression
        condition: Handle<Expression>,
        accept: Handle<Expression>,
        reject: Handle<Expression>,
    },
    /// Compute the derivative on an axis.
    Derivative {
        axis: DerivativeAxis,
        //modifier,
        expr: Handle<Expression>,
    },
    /// Call a relational function.
    Relational {
        fun: RelationalFunction,
        argument: Handle<Expression>,
    },
    /// Call a math function
    Math {
        fun: MathFunction,
        arg: Handle<Expression>,
        arg1: Option<Handle<Expression>>,
        arg2: Option<Handle<Expression>>,
    },
    /// Cast a simple type to another kind.
    As {
        /// Source expression, which can only be a scalar or a vector.
        expr: Handle<Expression>,
        /// Target scalar kind.
        kind: ScalarKind,
        /// If provided, converts to the specified byte width.
        /// Otherwise, bitcast.
        convert: Option<Bytes>,
    },
    /// Result of calling another function.
    Call(Handle<Function>),
    /// Get the length of an array.
    /// The expression must resolve to a pointer to an array with a dynamic size.
    ///
    /// This doesn't match the semantics of spirv's `OpArrayLength`, which must be passed
    /// a pointer to a structure containing a runtime array in its' last field.
    ArrayLength(Handle<Expression>),
}

/// A code block is just a vector of statements.
pub type Block = Vec<Statement>;

/// A case for a switch statement.
// Clone is used only for error reporting and is not intended for end users
#[derive(Clone, Debug)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub struct SwitchCase {
    /// Value, upon which the case is considered true.
    pub value: i32,
    /// Body of the cae.
    pub body: Block,
    /// If true, the control flow continues to the next case in the list,
    /// or default.
    pub fall_through: bool,
}

//TODO: consider removing `Clone`. It's not valid to clone `Statement::Emit` anyway.
/// Instructions which make up an executable block.
// Clone is used only for error reporting and is not intended for end users
#[derive(Clone, Debug)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub enum Statement {
    /// Emit a range of expressions, visible to all statements that follow in this block.
    ///
    /// See the [module-level documentation][emit] for details.
    ///
    /// [emit]: index.html#expression-evaluation-time-and-scope
    Emit(Range<Expression>),
    /// A block containing more statements, to be executed sequentially.
    Block(Block),
    /// Conditionally executes one of two blocks, based on the value of the condition.
    If {
        condition: Handle<Expression>, //bool
        accept: Block,
        reject: Block,
    },
    /// Conditionally executes one of multiple blocks, based on the value of the selector.
    Switch {
        selector: Handle<Expression>, //int
        cases: Vec<SwitchCase>,
        default: Block,
    },
    /// Executes a block repeatedly.
    Loop { body: Block, continuing: Block },
    /// Exits the loop.
    Break,
    /// Skips execution to the next iteration of the loop.
    Continue,
    /// Returns from the function (possibly with a value).
    Return { value: Option<Handle<Expression>> },
    /// Aborts the current shader execution.
    Kill,
    /// Synchronize invocations within the work group.
    /// The `Barrier` flags control which memory accesses should be synchronized.
    /// If empty, this becomes purely an execution barrier.
    Barrier(Barrier),
    /// Stores a value at an address.
    ///
    /// This statement is a barrier for any operations on the
    /// `Expression::LocalVariable` or `Expression::GlobalVariable`
    /// that is the destination of an access chain, started
    /// from the `pointer`.
    Store {
        pointer: Handle<Expression>,
        value: Handle<Expression>,
    },
    /// Stores a value to an image.
    ///
    /// Image has to point into a global variable of type `TypeInner::Image`.
    /// This statement is a barrier for any operations on the corresponding
    /// `Expression::GlobalVariable` for this image.
    ImageStore {
        image: Handle<Expression>,
        coordinate: Handle<Expression>,
        array_index: Option<Handle<Expression>>,
        value: Handle<Expression>,
    },
    /// Calls a function.
    ///
    /// If the `result` is `Some`, the corresponding expression has to be
    /// `Expression::Call`, and this statement serves as a barrier for any
    /// operations on that expression.
    Call {
        function: Handle<Function>,
        arguments: Vec<Handle<Expression>>,
        result: Option<Handle<Expression>>,
    },
}

/// A function argument.
#[derive(Clone, Debug)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub struct FunctionArgument {
    /// Name of the argument, if any.
    pub name: Option<String>,
    /// Type of the argument.
    pub ty: Handle<Type>,
    /// For entry points, an argument has to have a binding
    /// unless it's a structure.
    pub binding: Option<Binding>,
}

#[derive(Clone, Debug)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub struct FunctionResult {
    /// Type of the result.
    pub ty: Handle<Type>,
    /// For entry points, the result has to have a binding
    /// unless it's a structure.
    pub binding: Option<Binding>,
}

/// A function defined in the module.
#[derive(Debug, Default)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub struct Function {
    /// Name of the function, if any.
    pub name: Option<String>,
    /// Information about function argument.
    pub arguments: Vec<FunctionArgument>,
    /// The result of this function, if any.
    pub result: Option<FunctionResult>,
    /// Local variables defined and used in the function.
    pub local_variables: Arena<LocalVariable>,
    /// Expressions used inside this function.
    pub expressions: Arena<Expression>,
    /// Map of expressions that have associated variable names
    pub named_expressions: NamedExpressions,
    /// Block of instructions comprising the body of the function.
    pub body: Block,
}

/// Exported function, to be run at a certain stage in the pipeline.
#[derive(Debug)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub struct EntryPoint {
    /// Name of this entry point, visible externally.
    pub name: String,
    /// Shader stage.
    pub stage: ShaderStage,
    /// Early depth test for fragment stages.
    pub early_depth_test: Option<EarlyDepthTest>,
    /// Workgroup size for compute stages
    pub workgroup_size: [u32; 3],
    /// The entrance function.
    pub function: Function,
}

/// Shader module.
///
/// A module is a set of constants, global variables and functions, as well as
/// the types required to define them.
///
/// Some functions are marked as entry points, to be used in a certain shader stage.
///
/// To create a new module, use the `Default` implementation.
/// Alternatively, you can load an existing shader using one of the [available front ends][front].
///
/// When finished, you can export modules using one of the [available backends][back].
#[derive(Debug, Default)]
#[cfg_attr(feature = "serialize", derive(Serialize))]
#[cfg_attr(feature = "deserialize", derive(Deserialize))]
pub struct Module {
    /// Storage for the types defined in this module.
    pub types: Arena<Type>,
    /// Storage for the constants defined in this module.
    pub constants: Arena<Constant>,
    /// Storage for the global variables defined in this module.
    pub global_variables: Arena<GlobalVariable>,
    /// Storage for the functions defined in this module.
    pub functions: Arena<Function>,
    /// Entry points.
    pub entry_points: Vec<EntryPoint>,
}