#pragma once

#include "nodes.hpp"

#include "copy.hpp"

namespace lambda {

namespace _apply {

class Apply {

private:

const Variable& target;

std::unique_ptr<LambdaBase> value;

void applyVariable(std::unique_ptr<LambdaBase>& node) {

if (*(std::unique_ptr<Variable>&)node == target)

node = copy(value);

}

void applyFunction(std::unique_ptr<LambdaBase>& node) {

if (((std::unique_ptr<Function>&)node)->bound == target)

return;

apply(((std::unique_ptr<Function>&)node)->body);

}

void applyApplication(std::unique_ptr<LambdaBase>& node) {

apply(((std::unique_ptr<Application>&)node)->left);

apply(((std::unique_ptr<Application>&)node)->right);

}

public:

Apply(const Variable& target, std::unique_ptr<LambdaBase> value)

: target(target), value(std::move(value)) {}

void apply(std::unique_ptr<LambdaBase>& node) {

switch (node->getType()) {

case LambdaType::VARIABLE:

return applyVariable(node);

case LambdaType::FUNCTION:

return applyFunction(node);

case LambdaType::APPLICATION:

return applyApplication(node);

}

}

};

} // namespace _apply

inline void apply(std::unique_ptr<LambdaBase>& node, const Variable& target,

std::unique_ptr<LambdaBase> value) {

if (node && value) _apply::Apply(target, std::move(value)).apply(node);

}

} // namespace lambda