// Copyright (c) 2018 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 <queue>
#include <unordered_map>
#include <unordered_set>
#include <vector>
#include "paddle/fluid/framework/details/op_handle_base.h"

namespace paddle {
namespace framework {
namespace ir {

class OpGraphView {
 public:
  explicit OpGraphView(const std::vector<details::OpHandleBase *> &ops);

  std::unordered_set<details::OpHandleBase *> AllOps() const;

  const std::unordered_set<details::OpHandleBase *> &PendingOps(
      details::OpHandleBase *op) const;

  const std::unordered_set<details::OpHandleBase *> &PrecedingOps(
      details::OpHandleBase *op) const;

  std::unordered_map<details::OpHandleBase *, size_t> GetPrecedingDepNum()
      const;

  bool HasOp(details::OpHandleBase *op) const;

  size_t OpNumber() const;

  // Use a visitor to visit all pending ops of op
  // Stop when callback returns false
  template <typename Callback>
  bool VisitAllPendingOps(details::OpHandleBase *op, Callback &&callback) const;

  template <typename Callback>
  void BreadthFirstVisit(Callback &&callback) const;

 private:
  void Build(const std::vector<details::OpHandleBase *> &ops);
  void EnforceHasOp(details::OpHandleBase *op) const;

  std::unordered_map<details::OpHandleBase *,
                     std::unordered_set<details::OpHandleBase *>>
      preceding_ops_;
  std::unordered_map<details::OpHandleBase *,
                     std::unordered_set<details::OpHandleBase *>>
      pending_ops_;
};

template <typename Callback>
bool OpGraphView::VisitAllPendingOps(details::OpHandleBase *op,
                                     Callback &&callback) const {
  EnforceHasOp(op);
  std::unordered_set<details::OpHandleBase *> visited;
  std::queue<details::OpHandleBase *> q;
  q.push(op);
  while (!q.empty()) {
    op = q.front();
    q.pop();
    for (auto &pending_op : pending_ops_.at(op)) {
      if (visited.count(pending_op) == 0) {
        visited.insert(pending_op);
        if (!callback(pending_op)) {
          return false;
        }
        q.push(pending_op);
      }
    }
  }
  return true;
}

template <typename Callback>
void OpGraphView::BreadthFirstVisit(Callback &&callback) const {
  auto op_deps = GetPrecedingDepNum();
  size_t op_num = op_deps.size();

  std::unordered_set<details::OpHandleBase *> visited_ops;
  std::queue<details::OpHandleBase *> ready_ops;
  size_t num_calls = 0;
  for (auto iter = op_deps.begin(); iter != op_deps.end();) {
    if (iter->second != 0) {
      ++iter;
      continue;
    }

    visited_ops.insert(iter->first);
    ready_ops.push(iter->first);
    callback(iter->first);
    ++num_calls;
    op_deps.erase(iter++);
  }

  while (!ready_ops.empty()) {
    auto *cur_op = ready_ops.front();
    ready_ops.pop();

    auto &pending_ops = PendingOps(cur_op);
    for (auto *pending_op : pending_ops) {
      if (visited_ops.count(pending_op) > 0) {
        continue;
      }

      if (--op_deps.at(pending_op) == 0) {
        visited_ops.insert(pending_op);
        op_deps.erase(pending_op);
        ready_ops.push(pending_op);
        callback(pending_op);
        ++num_calls;
      }
    }
  }

  PADDLE_ENFORCE_EQ(num_calls, op_num, "There are unvisited ops");
  PADDLE_ENFORCE_EQ(visited_ops.size(), op_num, "There are unvisited ops");
  PADDLE_ENFORCE(op_deps.empty(), "There are unvisited ops");
}

}  // namespace ir
}  // namespace framework
}  // namespace paddle
