// Copyright 2021 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_TINT_SEM_CONSTANT_H_
#define SRC_TINT_SEM_CONSTANT_H_

#include <variant>
#include <vector>

#include "src/tint/program_builder.h"
#include "src/tint/sem/type.h"

namespace tint::sem {

/// A Constant is compile-time known expression value, expressed as a flattened
/// list of scalar values. Value may be of a scalar or vector type.
class Constant {
  public:
    /// Scalar holds a single constant scalar value - one of: AInt, AFloat or bool.
    using Scalar = std::variant<AInt, AFloat, bool>;

    /// Scalars is a list of scalar values
    using Scalars = std::vector<Scalar>;

    /// Constructs an invalid Constant
    Constant();

    /// Constructs a Constant of the given type and element values
    /// @param ty the Constant type
    /// @param els the Constant element values
    Constant(const Type* ty, Scalars els);

    /// Copy constructor
    Constant(const Constant&);

    /// Destructor
    ~Constant();

    /// Copy assignment
    /// @param other the Constant to copy
    /// @returns this Constant
    Constant& operator=(const Constant& other);

    /// @returns true if the Constant has been initialized
    bool IsValid() const { return type_ != nullptr; }

    /// @return true if the Constant has been initialized
    operator bool() const { return IsValid(); }

    /// @returns the type of the Constant
    const sem::Type* Type() const { return type_; }

    /// @returns the element type of the Constant
    const sem::Type* ElementType() const { return elem_type_; }

    /// @returns the constant's scalar elements
    const Scalars& Elements() const { return elems_; }

    /// @returns true if any scalar element is zero
    bool AnyZero() const;

    /// @param index the index of the scalar value
    /// @return the value of the scalar at `index`, which must be of type `T`.
    template <typename T>
    T Element(size_t index) const {
        return std::get<T>(elems_[index]);
    }

    /// @param index the index of the scalar value
    /// @return the value of the scalar `static_cast` to type T.
    template <typename T>
    T ElementAs(size_t index) const {
        return std::visit([](auto val) { return static_cast<T>(val); }, elems_[index]);
    }

  private:
    const sem::Type* type_ = nullptr;
    const sem::Type* elem_type_ = nullptr;
    Scalars elems_;
};

}  // namespace tint::sem

#endif  // SRC_TINT_SEM_CONSTANT_H_