import numpy as np

class Skeleton:
    def __init__(self, parents, joints_left, joints_right):
        assert len(joints_left) == len(joints_right)
        
        self._parents = np.array(parents)
        self._joints_left = joints_left
        self._joints_right = joints_right
        self._compute_metadata()
    
    def num_joints(self):
        return len(self._parents)
    
    def parents(self):
        return self._parents
    
    def has_children(self):
        return self._has_children
    
    def children(self):
        return self._children
    
    def remove_joints(self, joints_to_remove):
        """
        Remove the joints specified in 'joints_to_remove'.
        """
        valid_joints = []
        for joint in range(len(self._parents)):
            if joint not in joints_to_remove:
                valid_joints.append(joint)

        for i in range(len(self._parents)):
            while self._parents[i] in joints_to_remove:
                self._parents[i] = self._parents[self._parents[i]]
                
        index_offsets = np.zeros(len(self._parents), dtype=int)
        new_parents = []
        for i, parent in enumerate(self._parents):
            if i not in joints_to_remove:
                new_parents.append(parent - index_offsets[parent])
            else:
                index_offsets[i:] += 1
        self._parents = np.array(new_parents)
        
        
        if self._joints_left is not None:
            new_joints_left = []
            for joint in self._joints_left:
                if joint in valid_joints:
                    new_joints_left.append(joint - index_offsets[joint])
            self._joints_left = new_joints_left
        if self._joints_right is not None:
            new_joints_right = []
            for joint in self._joints_right:
                if joint in valid_joints:
                    new_joints_right.append(joint - index_offsets[joint])
            self._joints_right = new_joints_right

        self._compute_metadata()
        
        return valid_joints
    
    def joints_left(self):
        return self._joints_left
    
    def joints_right(self):
        return self._joints_right
        
    def _compute_metadata(self):
        self._has_children = np.zeros(len(self._parents)).astype(bool)
        for i, parent in enumerate(self._parents):
            if parent != -1:
                self._has_children[parent] = True

        self._children = []
        for i, parent in enumerate(self._parents):
            self._children.append([])
        for i, parent in enumerate(self._parents):
            if parent != -1:
                self._children[parent].append(i)