// Copyright 2020 The Tint Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef SRC_TRANSFORM_VERTEX_PULLING_TRANSFORM_H_
#define SRC_TRANSFORM_VERTEX_PULLING_TRANSFORM_H_

#include <memory>
#include <string>
#include <unordered_map>
#include <vector>

#include "src/ast/expression.h"
#include "src/ast/function.h"
#include "src/ast/module.h"
#include "src/ast/statement.h"
#include "src/ast/variable.h"
#include "src/context.h"
#include "src/transform/transformer.h"

namespace tint {
namespace transform {

/// Describes the format of data in a vertex buffer
enum class VertexFormat {
  kVec2U8,
  kVec4U8,
  kVec2I8,
  kVec4I8,
  kVec2U8Norm,
  kVec4U8Norm,
  kVec2I8Norm,
  kVec4I8Norm,
  kVec2U16,
  kVec4U16,
  kVec2I16,
  kVec4I16,
  kVec2U16Norm,
  kVec4U16Norm,
  kVec2I16Norm,
  kVec4I16Norm,
  kVec2F16,
  kVec4F16,
  kF32,
  kVec2F32,
  kVec3F32,
  kVec4F32,
  kU32,
  kVec2U32,
  kVec3U32,
  kVec4U32,
  kI32,
  kVec2I32,
  kVec3I32,
  kVec4I32
};

/// Describes if a vertex attribtes increments with vertex index or instance
/// index
enum class InputStepMode { kVertex, kInstance };

/// Describes a vertex attribute within a buffer
struct VertexAttributeDescriptor {
  /// The format of the attribute
  VertexFormat format;
  /// The byte offset of the attribute in the buffer
  uint64_t offset;
  /// The shader location used for the attribute
  uint32_t shader_location;
};

/// Describes a buffer containing multiple vertex attributes
struct VertexBufferLayoutDescriptor {
  /// Constructor
  VertexBufferLayoutDescriptor();
  /// Constructor
  /// @param in_array_stride the array stride of the in buffer
  /// @param in_step_mode the step mode of the in buffer
  /// @param in_attributes the in attributes
  VertexBufferLayoutDescriptor(
      uint64_t in_array_stride,
      InputStepMode in_step_mode,
      std::vector<VertexAttributeDescriptor> in_attributes);
  /// Copy constructor
  /// @param other the struct to copy
  VertexBufferLayoutDescriptor(const VertexBufferLayoutDescriptor& other);

  ~VertexBufferLayoutDescriptor();

  /// The array stride used in the in buffer
  uint64_t array_stride = 0u;
  /// The input step mode used
  InputStepMode step_mode = InputStepMode::kVertex;
  /// The vertex attributes
  std::vector<VertexAttributeDescriptor> attributes;
};

/// Describes vertex state, which consists of many buffers containing vertex
/// attributes
struct VertexStateDescriptor {
  /// Constructor
  VertexStateDescriptor();
  /// Constructor
  /// @param in_vertex_buffers the vertex buffers
  VertexStateDescriptor(
      std::vector<VertexBufferLayoutDescriptor> in_vertex_buffers);
  /// Copy constructor
  /// @param other the struct to copy
  VertexStateDescriptor(const VertexStateDescriptor& other);

  ~VertexStateDescriptor();

  /// The vertex buffers
  std::vector<VertexBufferLayoutDescriptor> vertex_buffers;
};

/// Converts a module to use vertex pulling
///
/// Variables which accept vertex input are var<in> with a location decoration.
/// This transform will convert those to be assigned from storage buffers
/// instead. The intention is to allow vertex input to rely on a storage buffer
/// clamping pass for out of bounds reads. We bind the storage buffers as arrays
/// of u32, so any read to byte position `p` will actually need to read position
/// `p / 4`, since `sizeof(u32) == 4`.
///
/// `VertexFormat` represents the input type of the attribute. This isn't
/// related to the type of the variable in the shader. For example,
/// `VertexFormat::kVec2F16` tells us that the buffer will contain `f16`
/// elements, to be read as vec2. In the shader, a user would make a `vec2<f32>`
/// to be able to use them. The conversion between `f16` and `f32` will need to
/// be handled by us (using unpack functions).
///
/// To be clear, there won't be types such as `f16` or `u8` anywhere in WGSL
/// code, but these are types that the data may arrive as. We need to convert
/// these smaller types into the base types such as `f32` and `u32` for the
/// shader to use.
class VertexPullingTransform : public Transformer {
 public:
  /// Constructor
  /// @param ctx the tint context
  /// @param mod the module to convert to vertex pulling
  VertexPullingTransform(Context* ctx, ast::Module* mod);
  ~VertexPullingTransform() override;

  /// Sets the vertex state descriptor, containing info about attributes
  /// @param vertex_state the vertex state descriptor
  void SetVertexState(std::unique_ptr<VertexStateDescriptor> vertex_state);

  /// Sets the entry point to add assignments into
  /// @param entry_point the vertex stage entry point
  void SetEntryPoint(std::string entry_point);

  /// Sets the "set" we will put all our vertex buffers into (as storage
  /// buffers)
  /// @param number the set number we will use
  void SetPullingBufferBindingSet(uint32_t number);

  /// Users of Tint should register the transform with transform manager and
  /// invoke its Run(), instead of directly calling the transform's Run().
  /// Calling Run() directly does not perform module state cleanup operations.
  /// @returns true if the transformation was successful
  bool Run() override;

 private:
  /// Generate the vertex buffer binding name
  /// @param index index to append to buffer name
  std::string GetVertexBufferName(uint32_t index);

  /// Inserts vertex_idx binding, or finds the existing one
  void FindOrInsertVertexIndexIfUsed();

  /// Inserts instance_idx binding, or finds the existing one
  void FindOrInsertInstanceIndexIfUsed();

  /// Converts var<in> with a location decoration to var<private>
  void ConvertVertexInputVariablesToPrivate();

  /// Adds storage buffer decorated variables for the vertex buffers
  void AddVertexStorageBuffers();

  /// Adds assignment to the variables from the buffers
  void AddVertexPullingPreamble(ast::Function* vertex_func);

  /// Generates an expression holding a constant uint
  /// @param value uint value
  ast::Expression* GenUint(uint32_t value);

  /// Generates an expression to read the shader value `kPullingPosVarName`
  ast::Expression* CreatePullingPositionIdent();

  /// Generates an expression reading from a buffer a specific format.
  /// This reads the value wherever `kPullingPosVarName` points to at the time
  /// of the read.
  /// @param buffer the index of the vertex buffer
  /// @param format the format to read
  ast::Expression* AccessByFormat(uint32_t buffer, VertexFormat format);

  /// Generates an expression reading a uint32 from a vertex buffer
  /// @param buffer the index of the vertex buffer
  /// @param pos an expression for the position of the access, in bytes
  ast::Expression* AccessU32(uint32_t buffer, ast::Expression* pos);

  /// Generates an expression reading an int32 from a vertex buffer
  /// @param buffer the index of the vertex buffer
  /// @param pos an expression for the position of the access, in bytes
  ast::Expression* AccessI32(uint32_t buffer, ast::Expression* pos);

  /// Generates an expression reading a float from a vertex buffer
  /// @param buffer the index of the vertex buffer
  /// @param pos an expression for the position of the access, in bytes
  ast::Expression* AccessF32(uint32_t buffer, ast::Expression* pos);

  /// Generates an expression reading a basic type (u32, i32, f32) from a vertex
  /// buffer
  /// @param buffer the index of the vertex buffer
  /// @param pos an expression for the position of the access, in bytes
  /// @param format the underlying vertex format
  ast::Expression* AccessPrimitive(uint32_t buffer,
                                   ast::Expression* pos,
                                   VertexFormat format);

  /// Generates an expression reading a vec2/3/4 from a vertex buffer.
  /// This reads the value wherever `kPullingPosVarName` points to at the time
  /// of the read.
  /// @param buffer the index of the vertex buffer
  /// @param element_stride stride between elements, in bytes
  /// @param base_type underlying AST type
  /// @param base_format underlying vertex format
  /// @param count how many elements the vector has
  ast::Expression* AccessVec(uint32_t buffer,
                             uint32_t element_stride,
                             ast::type::Type* base_type,
                             VertexFormat base_format,
                             uint32_t count);

  // Used to grab corresponding types from the type manager
  ast::type::Type* GetU32Type();
  ast::type::Type* GetI32Type();
  ast::type::Type* GetF32Type();

  std::string entry_point_name_;

  std::string vertex_index_name_;
  std::string instance_index_name_;

  // Default to 4 as it is past the limits of user-accessible sets
  uint32_t pulling_set_ = 4u;

  std::unordered_map<uint32_t, ast::Variable*> location_to_var_;
  std::unique_ptr<VertexStateDescriptor> vertex_state_;
};

}  // namespace transform
}  // namespace tint

#endif  // SRC_TRANSFORM_VERTEX_PULLING_TRANSFORM_H_