// Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved.
//
// 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 <functional>
#include <memory>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>

#include "paddle/fluid/framework/executor.h"
#include "paddle/fluid/framework/program_desc.h"
#include "paddle/fluid/platform/macros.h"

namespace paddle {
namespace framework {

class ExecutorInfoCache {
 public:
  /*
   * The ExecutorPrepareContext is different while running forward program and
   * backward program. We add bool value into cached key to distinguish this.
   */
  using KeyInfo = std::pair<const framework::ProgramDesc*, /*is_grad*/ bool>;
  using KeyType = size_t;

  struct HashPair {
    size_t operator()(const KeyInfo& key) const noexcept {
      size_t seed = 10;
      auto* prog_desc = key.first;
      /*
       * Note(Aurelius84): DO NOT use only ProgramDesc* to calculate hash value
       * because a new program will hold same pointer address after an older
       * program is destructed with a small probability. Add op size while
       * hashing because program may contains at least one block.
       */
      hash_combine(&seed, prog_desc);
      for (size_t i = 0; i < prog_desc->Size(); ++i) {
        hash_combine(&seed, &prog_desc->Block(i));
        hash_combine(&seed, prog_desc->Block(i).OpSize());
      }
      hash_combine(&seed, key.second);
      VLOG(1) << "hash value is : " << seed << " of pointer " << prog_desc;
      return seed;
    }

    template <typename T>
    void hash_combine(size_t* seed, const T& val) const {
      std::hash<T> hasher;
      (*seed) ^= hasher(val) + 0x9e3779b9 + ((*seed) << 6) + ((*seed >> 2));
    }
  };

  static ExecutorInfoCache& Instance();

  std::shared_ptr<framework::ExecutorPrepareContext> Get(
      const KeyInfo& key) const {
    KeyType key_value = key_hash_func_(key);
    PADDLE_ENFORCE_EQ(
        Has(key_value), true,
        platform::errors::NotFound(
            "(programDesc: %s, is_grad: %s) doesn't exist in ExecutorInfoCache",
            key.first, key.second));
    return info_map_.at(key_value);
  }

  bool Has(const KeyInfo& key) const {
    KeyType key_value = key_hash_func_(key);
    return Has(key_value);
  }

  bool Has(const KeyType& key) const {
    return info_map_.find(key) != info_map_.end();
  }

  void Insert(const KeyInfo& key,
              std::shared_ptr<framework::ExecutorPrepareContext> exe_ctx) {
    KeyType key_value = key_hash_func_(key);
    PADDLE_ENFORCE_NE(
        Has(key_value), true,
        platform::errors::NotFound(
            "(programDesc: %s, is_grad: %s) has existed in ExecutorInfoCache",
            key.first, key.second));
    info_map_.insert({key_value, exe_ctx});
  }

 private:
  ExecutorInfoCache() = default;

  HashPair key_hash_func_;

  // Note: we shall avoid using raw pointer as key but use hash code,
  // beacause pointer doesn't hold resource indeed.
  std::unordered_map<KeyType,
                     std::shared_ptr<framework::ExecutorPrepareContext>>
      info_map_;
  DISABLE_COPY_AND_ASSIGN(ExecutorInfoCache);
};

std::shared_ptr<framework::ExecutorPrepareContext> GetExecutorInfoFromCache(
    const framework::Executor& exe, const framework::ExecutionContext& ctx,
    const std::vector<std::vector<std::string>>& ctx_output_names,
    bool is_grad);

}  // namespace framework
}  // namespace paddle