// Copyright 2023 The Manifold 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.

#pragma once

#include <cstddef>
#include <limits>
#include <type_traits>
#include <vector>

#include "manifold/optional_assert.h"

namespace manifold {

/**
 * View for Vec, can perform offset operation.
 * This will be invalidated when the original vector is dropped or changes
 * length. Roughly equivalent to std::span<T> from c++20
 */
template <typename T>
class VecView {
 public:
  using Iter = T *;
  using IterC = const T *;

  VecView() : ptr_(nullptr), size_(0) {}

  VecView(T *ptr, size_t size) : ptr_(ptr), size_(size) {}

  VecView(const std::vector<std::remove_cv_t<T>> &v)
      : ptr_(v.data()), size_(v.size()) {}

  VecView(const VecView &other) {
    ptr_ = other.ptr_;
    size_ = other.size_;
  }

  VecView &operator=(const VecView &other) {
    ptr_ = other.ptr_;
    size_ = other.size_;
    return *this;
  }

  // allows conversion to a const VecView
  operator VecView<const T>() const { return {ptr_, size_}; }

  inline const T &operator[](size_t i) const {
    ASSERT(i < size_, std::out_of_range("Vec out of range"));
    return ptr_[i];
  }

  inline T &operator[](size_t i) {
    ASSERT(i < size_, std::out_of_range("Vec out of range"));
    return ptr_[i];
  }

  IterC cbegin() const { return ptr_; }
  IterC cend() const { return ptr_ + size_; }

  IterC begin() const { return cbegin(); }
  IterC end() const { return cend(); }

  Iter begin() { return ptr_; }
  Iter end() { return ptr_ + size_; }

  const T &front() const {
    ASSERT(size_ != 0,
           std::out_of_range("Attempt to take the front of an empty vector"));
    return ptr_[0];
  }

  const T &back() const {
    ASSERT(size_ != 0,
           std::out_of_range("Attempt to take the back of an empty vector"));
    return ptr_[size_ - 1];
  }

  T &front() {
    ASSERT(size_ != 0,
           std::out_of_range("Attempt to take the front of an empty vector"));
    return ptr_[0];
  }

  T &back() {
    ASSERT(size_ != 0,
           std::out_of_range("Attempt to take the back of an empty vector"));
    return ptr_[size_ - 1];
  }

  size_t size() const { return size_; }

  bool empty() const { return size_ == 0; }

  VecView<T> view(size_t offset = 0,
                  size_t length = std::numeric_limits<size_t>::max()) {
    if (length == std::numeric_limits<size_t>::max())
      length = this->size_ - offset;
    ASSERT(offset + length <= this->size_,
           std::out_of_range("Vec::view out of range"));
    return VecView<T>(this->ptr_ + offset, length);
  }

  VecView<const T> cview(
      size_t offset = 0,
      size_t length = std::numeric_limits<size_t>::max()) const {
    if (length == std::numeric_limits<size_t>::max())
      length = this->size_ - offset;
    ASSERT(offset + length <= this->size_,
           std::out_of_range("Vec::cview out of range"));
    return VecView<const T>(this->ptr_ + offset, length);
  }

  VecView<const T> view(
      size_t offset = 0,
      size_t length = std::numeric_limits<size_t>::max()) const {
    return cview(offset, length);
  }

  T *data() { return this->ptr_; }

  const T *data() const { return this->ptr_; }

#ifdef MANIFOLD_DEBUG
  void Dump() const {
    std::cout << "Vec = " << std::endl;
    for (size_t i = 0; i < size(); ++i) {
      std::cout << i << ", " << ptr_[i] << ", " << std::endl;
    }
    std::cout << std::endl;
  }
#endif

 protected:
  T *ptr_ = nullptr;
  size_t size_ = 0;
};

}  // namespace manifold
