"""
    GreedyOptimizer

An implementation of the greedy optimization algorithm, simply choosing the best next option evaluated with the given estimator.
"""
struct GreedyOptimizer{EstimatorType <: AbstractEstimator} <: AbstractOptimizer
    estimator::EstimatorType
end

function optimize_step!(optimizer::GreedyOptimizer, graph::DAG)
    # generate all options
    operations = get_operations(graph)
    if isempty(operations)
        println("[warn] No operations left to apply")
        return nothing
    end

    lowestCost = typemax(cost_type(optimizer.estimator))

    result = reduce((acc, op) -> begin
        op_cost = operation_effect(optimizer.estimator, graph, op)
        if op_cost < lowestCost
            lowestCost = op_cost
            return op
        end
        return acc
    end, operations)

    push_operation!(graph, result)

    return nothing
end