erlang_behaviour_trees

-module(run_sequence).
-include("../bt_node_behaviours/bt_nodes.hrl").
-export([
  run/3,
  preempt/3
]).

%% should run each child from left to right; they will return their new states so it will need to update them when returning
%% blackboard will also be changed between each child call
%% if child returns:
%%  failure: preempt and then return {failure, NewSequenceNode, NewBB2}
%%  running: return {running, NewSequenceNode, NewBB}, preempt all children to the right of running!
%%  success: run next child with NewBB; make sure to update this child's state with the returned state
%%  all return success: just clear BB and then return {success, NewSequenceNode, NewBB2}

-spec run(SequenceNode :: sequence(), BB :: blackboard(), Event :: event()) -> {Status :: status(), NewSequenceNode :: sequence(), NewBB :: blackboard()}.
run(SequenceNode, BB, Event) when is_record(SequenceNode, sequence) ->
  Children = SequenceNode#sequence.children,
  {Status, NewChildren, NewBB} = run_children(Children, BB, Event),
  case Status of
    failure ->
      %% clear blackboard and return failure; preemption of children already done.
      NewBB2 = bt_blackboard:clear_namespace(SequenceNode#sequence.namespace, BB),
      {failure, SequenceNode#sequence{children = NewChildren}, NewBB2};
    running ->
      %% just return; preemption of children already done.
      {running, SequenceNode#sequence{children = NewChildren}, NewBB};
    success ->
      %% clear blackboard and return success;
      NewBB2 = bt_blackboard:clear_namespace(SequenceNode#sequence.namespace, NewBB),
      {success, SequenceNode#sequence{children = NewChildren}, NewBB2}
  end.

  
run_children([], BB, _Event) ->
  %% all ran successfully! return success
  {success, [], BB};
run_children([Child | RestOfChildren], BB, Event) ->
  %% run the child
  {ChildStatus, NewChildNode, NewBB} = bt_runner:run(Child, BB, Event),
  case ChildStatus of
    %% failure: preempt all right children
    failure -> 
      {PreemptedRestOfChildren, NewBB2} = preempt_children(RestOfChildren, NewBB, true),
      {failure, [NewChildNode | PreemptedRestOfChildren], NewBB2};
    %% running: preempt all right children
    running -> 
      {PreemptedRestOfChildren, NewBB2} = preempt_children(RestOfChildren, NewBB, true),
      {running, [NewChildNode | PreemptedRestOfChildren], NewBB2};
    success ->
      %% using the new bb, run the rest of the children
      {Status, NewRestOfChildren, NewBB2} = run_children(RestOfChildren, NewBB, Event),
      {Status, [NewChildNode | NewRestOfChildren], NewBB2}
  end.

%% is being preempted. clear namespace and call preempt on each child.
-spec preempt(SequenceNode :: sequence(), BB :: blackboard(), ShouldCleanBB :: boolean()) -> {NewNode :: term(), NewBB :: blackboard()}.
preempt(SequenceNode, BB, true) ->
  %% clear the namespace
  NewBB = bt_blackboard:clear_namespace(SequenceNode#sequence.namespace, BB),
  %% now dont
  preempt(SequenceNode, NewBB, false);
%% don't need to clear the namespace.
preempt(SequenceNode, BB, false) ->
  Children = SequenceNode#sequence.children,
  {NewChildren, NewBB} = preempt_children(Children, BB, false),
  {SequenceNode#sequence{children = NewChildren}, NewBB}.

preempt_children([], BB, _Flag) ->
  {[], BB};
preempt_children([Child | RestOfChildren], BB, ShouldCleanBB) ->
  {NewChild, NewBB} = bt_runner:preempt(Child, BB, ShouldCleanBB),
  {NewRestOfChildren, NewBB2} = preempt_children(RestOfChildren, NewBB, ShouldCleanBB),
  {[NewChild | NewRestOfChildren], NewBB2}.