// Copyright (c) 2019 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.

#include "paddle/fluid/operators/controlflow/conditional_block_op_helper.h"
#include <string>
#include <unordered_set>
#include <utility>
#include <vector>
#include "paddle/fluid/operators/controlflow/op_variant.h"

namespace paddle {
namespace operators {

static bool IsMatchedConditionalBlockOpAndConditionalBlockGradOp(
    const OpVariant &fwd_op, const OpVariant &bwd_op) {
  return fwd_op.Outputs().at(ConditionalOp::kScope) ==
         bwd_op.Inputs().at(ConditionalOp::kScope);
}

static void FindAllConditionalBlockAndConditionalBlockGradOp(
    std::vector<OpVariant> *fwd_ops, std::vector<OpVariant> *bwd_ops) {
  PADDLE_ENFORCE_GE(fwd_ops->size(), bwd_ops->size());

  if (fwd_ops->empty()) return;

  const auto *program =
      fwd_ops->front().Attr<framework::BlockDesc *>("sub_block")->Program();

  for (size_t i = 1; i < program->Size(); ++i) {
    auto &block = program->Block(i);
    for (size_t j = 0; j < block.OpSize(); ++j) {
      auto *op = block.Op(j);
      if (op->Type() == "conditional_block") {
        fwd_ops->emplace_back(op);
      } else if (op->Type() == "conditional_block_grad") {
        bwd_ops->emplace_back(op);
      }
    }
  }

  PADDLE_ENFORCE_GE(
      fwd_ops->size(), bwd_ops->size(),
      "There are extra conditional_block_grad ops in the graph or program");
}

static void SetSkipVarsForConditionalBlockOp(OpVariant *fwd_op,
                                             OpVariant *bwd_op) {
  auto *grad_block = bwd_op->Attr<framework::BlockDesc *>("sub_block");
  auto is_skippable_in_fwd = [grad_block](const std::string &var_name) {
    return var_name != framework::kEmptyVarName &&
           !grad_block->HasVar(var_name);
  };

  std::unordered_set<std::string> forward_skip_vars;
  for (auto *op_desc : grad_block->AllOps()) {
    for (auto &in_arg_name : op_desc->InputArgumentNames()) {
      if (is_skippable_in_fwd(in_arg_name)) {
        forward_skip_vars.insert(in_arg_name);
      }
    }

    for (auto &out_arg_name : op_desc->OutputArgumentNames()) {
      if (is_skippable_in_fwd(out_arg_name)) {
        forward_skip_vars.insert(out_arg_name);
      }
    }
  }

  auto &fwd_attrs = const_cast<framework::AttributeMap &>(fwd_op->Attrs());
  std::vector<std::string> skip_vars_vec(forward_skip_vars.begin(),
                                         forward_skip_vars.end());
  VLOG(2) << "Prepare to skip " << skip_vars_vec.size()
          << " var(s): " << string::join_strings(skip_vars_vec, ' ');
  fwd_attrs[ConditionalOp::kSkipEagerDeletionVars] = std::move(skip_vars_vec);
}

static void PrepareSafeEagerDeletionOnConditionalOpAndConditionalGradOpImpl(
    std::vector<OpVariant> *ifelse_ops,
    std::vector<OpVariant> *ifelse_grad_ops) {
  FindAllConditionalBlockAndConditionalBlockGradOp(ifelse_ops, ifelse_grad_ops);

  VLOG(2) << "Found conditional_block op num: " << ifelse_ops->size()
          << ", conditional_block_grad op num: " << ifelse_grad_ops->size();

  if (ifelse_grad_ops->empty()) {
    return;
  }

  std::unordered_set<OpVariant, OpVariant::Hasher> ifelse_op_set(
      ifelse_ops->begin(), ifelse_ops->end());

  for (auto &bwd_op : *ifelse_grad_ops) {
    const OpVariant *matched_fwd_op = nullptr;
    for (auto &fwd_op : ifelse_op_set) {
      if (IsMatchedConditionalBlockOpAndConditionalBlockGradOp(fwd_op,
                                                               bwd_op)) {
        PADDLE_ENFORCE(matched_fwd_op == nullptr,
                       "Found multiple matched conditional_block ops");
        matched_fwd_op = &fwd_op;
      }
    }

    PADDLE_ENFORCE_NOT_NULL(matched_fwd_op,
                            "Cannot find matched forward conditional_block op");

    SetSkipVarsForConditionalBlockOp(const_cast<OpVariant *>(matched_fwd_op),
                                     &bwd_op);
    ifelse_op_set.erase(*matched_fwd_op);
  }
}

void PrepareSafeEagerDeletionOnConditionalOpAndConditionalGradOp(
    int block_id,
    const std::vector<std::unique_ptr<framework::OperatorBase>> &all_ops) {
  // If block_id is not 0, returns
  // This is because all conditional_block_ops and conditional_block_grad_ops
  // in the whole program would be processed when block_id is 0 (i.e.
  // when Executor::Run() or ParallelExecutor constructs).

  // What's more, all conditional_block_ops and conditional_block_grad_ops
  // must be processed when block_id is zero. If not, conditional_block_op
  // may run first and erase variables used in conditional_block_grad_op,
  // and in this moment, conditional_block_grad_ops may be not constructed yet.
  if (block_id != 0) return;

  std::vector<OpVariant> fwd_ops, bwd_ops;
  for (auto &op : all_ops) {
    if (op->Type() == "conditional_block") {
      fwd_ops.emplace_back(op.get());
    } else if (op->Type() == "conditional_block_grad") {
      bwd_ops.emplace_back(op.get());
    }
  }

  PrepareSafeEagerDeletionOnConditionalOpAndConditionalGradOpImpl(&fwd_ops,
                                                                  &bwd_ops);
}

void PrepareSafeEagerDeletionOnConditionalOpAndConditionalGradOp(
    const std::vector<framework::OperatorBase *> &ifelse_ops,
    const std::vector<framework::OperatorBase *> &ifelse_grad_ops) {
  std::vector<OpVariant> fwd_ops, bwd_ops;
  fwd_ops.reserve(ifelse_ops.size());
  for (auto *op : ifelse_ops) {
    fwd_ops.emplace_back(op);
  }

  bwd_ops.reserve(ifelse_grad_ops.size());
  for (auto *op : ifelse_grad_ops) {
    bwd_ops.emplace_back(op);
  }

  PrepareSafeEagerDeletionOnConditionalOpAndConditionalGradOpImpl(&fwd_ops,
                                                                  &bwd_ops);
}

}  // namespace operators
}  // namespace paddle