/*

  This file is part of solidity.

  solidity is free software: you can redistribute it and/or modify

  it under the terms of the GNU General Public License as published by

  the Free Software Foundation, either version 3 of the License, or

  (at your option) any later version.

  solidity is distributed in the hope that it will be useful,

  but WITHOUT ANY WARRANTY; without even the implied warranty of

  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License

  along with solidity.  If not, see <http://www.gnu.org/licenses/>.

*/

// SPDX-License-Identifier: GPL-3.0

#include <libyul/optimiser/StructuralSimplifier.h>

#include <libyul/AST.h>

#include <libyul/Utilities.h>

#include <libsolutil/CommonData.h>

#include <libsolutil/Visitor.h>

using namespace solidity;

using namespace solidity::yul;

using OptionalStatements = std::optional<std::vector<Statement>>;

namespace

{

OptionalStatements replaceConstArgSwitch(Switch& _switchStmt, u256 const& _constExprVal)

{

  Block* matchingCaseBlock = nullptr;

  Case* defaultCase = nullptr;

  for (auto& _case: _switchStmt.cases)

  {

    if (_case.value && _case.value->value.value() == _constExprVal)

    {

      matchingCaseBlock = &_case.body;

      break;

    }

    else if (!_case.value)

      defaultCase = &_case;

  }

  if (!matchingCaseBlock && defaultCase)

    matchingCaseBlock = &defaultCase->body;

  if (matchingCaseBlock)

    return util::make_vector<Statement>(std::move(*matchingCaseBlock));

  else

    return std::optional<std::vector<Statement>>{std::vector<Statement>{}};

}

std::optional<u256> hasLiteralValue(Expression const& _expression)

{

  if (std::holds_alternative<Literal>(_expression))

    return std::get<Literal>(_expression).value.value();

  else

    return std::nullopt;

}

bool expressionAlwaysTrue(Expression const& _expression)

{

  if (std::optional<u256> value = hasLiteralValue(_expression))

    return *value != 0;

  else

    return false;

}

bool expressionAlwaysFalse(Expression const& _expression)

{

  if (std::optional<u256> value = hasLiteralValue(_expression))

    return *value == 0;

  else

    return false;

}

}

void StructuralSimplifier::run(OptimiserStepContext&, Block& _ast)

{

  StructuralSimplifier{}(_ast);

}

void StructuralSimplifier::operator()(Block& _block)

{

  simplify(_block.statements);

}

void StructuralSimplifier::simplify(std::vector<yul::Statement>& _statements)

{

  util::GenericVisitor visitor{

    util::VisitorFallback<OptionalStatements>{},

    [&](If& _ifStmt) -> OptionalStatements {

      if (expressionAlwaysTrue(*_ifStmt.condition))

        return {std::move(_ifStmt.body.statements)};

      else if (expressionAlwaysFalse(*_ifStmt.condition))

        return {std::vector<Statement>{}};

      return {};

    },

    [&](Switch& _switchStmt) -> OptionalStatements {

      if (std::optional<u256> const constExprVal = hasLiteralValue(*_switchStmt.expression))

        return replaceConstArgSwitch(_switchStmt, constExprVal.value());

      return {};

    },

    [&](ForLoop& _forLoop) -> OptionalStatements {

      if (expressionAlwaysFalse(*_forLoop.condition))

        return {std::move(_forLoop.pre.statements)};

      return {};

    }

  };

  util::iterateReplacing(

    _statements,

    [&](Statement& _stmt) -> OptionalStatements

    {

      OptionalStatements result = std::visit(visitor, _stmt);

      if (result)

        simplify(*result);

      else

        visit(_stmt);

      return result;

    }

  );

}