Random ego-tree from reverse regex json deserialization

random_tree.rs

// Depends on:
// - rand
// - rand_regex
// - ego_tree

use std::{borrow::Borrow, cell::LazyCell};

use ego_tree::Tree;
use rand::Rng;
use rand_regex::Regex;

fn json_node(depth: usize, value_repr: &str) -> String {
    if depth == 0 {
        format!("\\{{\"value\":({value_repr}),\"children\":\\[\\]\\}}")
    } else {
        let node = json_node(depth - 1, value_repr);
        format!(
            "\\{{\"value\":({value_repr}),\"children\":\\[((({}),)*({}))?\\]\\}}",
            node, node,
        )
    }
}

fn sample_json_random_tree(depth: usize) -> String {
    const VALUE: &str = "\"\\w+\"";
    let json_tree_gen = LazyCell::new(|| Regex::compile(&json_node(depth, VALUE), 5).unwrap());

    rand::thread_rng().sample::<String, _>((*json_tree_gen).borrow())
}

fn main() {
    let rand_json_tree = sample_json_random_tree(10);
    let rand_tree: Tree<String> =
        serde_json::from_str(&rand_json_tree).expect("Failed to deserialize random tree");
    println!("{rand_tree}");
}