import graphviz

def add_nodes_and_edges(dot: graphviz.Digraph, parent_id: str, nodes_list: list, current_depth: int, base_color: str):
    """
    Recursively adds nodes and edges to a Graphviz Digraph object,
    applying a color gradient and consistent styling.

    Args:
        dot (graphviz.Digraph): The Graphviz Digraph object to modify.
        parent_id (str): The ID of the parent node for the current set of nodes.
        nodes_list (list): A list of dictionaries, each representing a node
                           with 'id', 'label', 'relationship', and optional 'subnodes'.
        current_depth (int): The current depth in the graph hierarchy (0 for central node).
        base_color (str): The hexadecimal base color for the deepest nodes.
    """
    # Calculate color for current depth, making it lighter
    # This factor determines how quickly the color lightens per level.
    lightening_factor = 0.12 
    
    # Convert base_color hex to RGB for interpolation
    # Ensure base_color is a valid hex string before converting
    if not isinstance(base_color, str) or not base_color.startswith('#') or len(base_color) != 7:
        base_color = '#19191a' # Fallback to default dark if invalid

    base_r = int(base_color[1:3], 16)
    base_g = int(base_color[3:5], 16)
    base_b = int(base_color[5:7], 16)

    # Calculate current node color by blending towards white
    current_r = base_r + int((255 - base_r) * current_depth * lightening_factor)
    current_g = base_g + int((255 - base_g) * current_depth * lightening_factor)
    current_b = base_b + int((255 - base_b) * current_depth * lightening_factor)

    # Clamp values to 255 to stay within valid RGB range
    current_r = min(255, current_r)
    current_g = min(255, current_g)
    current_b = min(255, current_b)
    
    node_fill_color = f'#{current_r:02x}{current_g:02x}{current_b:02x}'

    # Font color: white for dark nodes, black for very light nodes for readability
    font_color = 'white' if current_depth * lightening_factor < 0.6 else 'black'
    
    # Edge colors and font sizes
    edge_color = '#4a4a4a' # Dark gray for lines
    # Font size adjusts based on depth, ensuring a minimum size
    font_size = max(9, 14 - (current_depth * 2)) 
    edge_font_size = max(7, 10 - (current_depth * 1))

    for node in nodes_list:
        node_id = node.get('id')
        label = node.get('label')
        relationship = node.get('relationship')
        
        # Basic validation for node data
        if not all([node_id, label, relationship]):
            raise ValueError(f"Invalid node: {node}")
            
        # Add node with specified style
        dot.node(
            node_id,
            label,
            shape='box', # All nodes are rectangular
            style='filled,rounded', # Filled and rounded corners
            fillcolor=node_fill_color, 
            fontcolor=font_color,
            fontsize=str(font_size) 
        )
        
        # Add edge from parent to current node
        dot.edge(
            parent_id,
            node_id,
            label=relationship,
            color=edge_color,
            fontcolor=edge_color, # Edge label color also dark gray
            fontsize=str(edge_font_size) 
        )
        
        # Recursively call for subnodes
        if 'subnodes' in node:
            add_nodes_and_edges(dot, node_id, node['subnodes'], current_depth + 1, base_color)