module util

export UCTselect

using ..type

# ---------------------------------------------- 100 --------------------------------------------- #

""" Select a node based on UCT score

# Arguments
  - `node::MCTSNode`
    mcts node
  - `w::T`
    exploration weight. Value is usually between 1 to 2. 
    Value 1.0 makes MCTS balance between exploration and exploitation like 50%-50%.
    Value 2.0 makes MCTS aggressively search the tree.
# Return
  - `selectedNode::MCTSNode`
    child node with highest UCT score. UCT score balances between exploitation (state value) 
    and exploration (visit count) based on the exploration weight w.

# Example
```jldoctest
julia> 
```

# Signature
"""
function UCTselect(node::MCTSNode, w::T)::MCTSNode where {T<:AbstractFloat}
  maxUCT = -Inf
  selectedNode = nothing

  for (childState, childNode) in node.children
    UCTvalue =
    if childNode.visits != 0  
      weightedterm = w * sqrt(log(node.visits) / childNode.visits) # explore term
      childNode.statevalue + weightedterm
    else  # node.visits == 0 makes sqrt() in explore term error
      childNode.progressvalue  # exploit term
    end
                
    if UCTvalue > maxUCT
      maxUCT = UCTvalue
        selectedNode = childNode
    end
  end

  return selectedNode
end

























































































end # module util