#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <assert.h>

typedef struct _BSTNode {
    int value;
    struct _BSTNode* left;
    struct _BSTNode* right;
} BSTNode;

static void _print_bst_plain(BSTNode* root) {
    if(root != NULL) {
        // Traverse the left subtree.
        _print_bst_plain(root -> left);

        // Print the value at the root.
        printf("[%d] ", root -> value);

        // Traverse the right subtree.
        _print_bst_plain(root -> right);
    }
}

void print_bst(BSTNode* root, char const* label) {
    printf("%s: ", label);
    _print_bst_plain(root);
    printf("\n");
}

void insert(int value, BSTNode** a_root) {
    if(*a_root == NULL) {
    // If tree (or subtree) is empty, then insert the value here.
        BSTNode* new_node = malloc(sizeof(*new_node));
        *new_node = (BSTNode) { .value = value, .left = NULL, .right = NULL };
        *a_root = new_node;
    }
    else if(value < (*a_root) -> value) {  // Should this value go in the left subtree?
        insert(value, &((*a_root) -> left));
    }
    else if(value >= (*a_root) -> value) {  // ... or the right subtree?
        insert(value, &((*a_root) -> right));
    }
}

int main(int argc, char* argv[]) {
    BSTNode* root = NULL;
    print_bst(root, "Emtpy BST");

    insert(4, &root);
    assert(root != NULL);        // Tree should no longer be empty.
    assert(root -> value == 4);  // Value at root should be 4
    assert(root -> left == NULL);
    assert(root -> right == NULL);
    print_bst(root, "Size == 1");

    insert(2, &root);
    assert(root -> left != NULL);
    assert(root -> left -> value == 2);
    assert(root -> left -> left  == NULL);
    assert(root -> left -> right == NULL);
    
    insert(6, &root);
    print_bst(root, "Size == 3");

    insert(1, &root);
    assert(root -> left -> left != NULL);
    assert(root -> left -> left -> value == 1);
    assert(root -> left -> left -> left  == NULL);
    assert(root -> left -> left -> right == NULL);
    
    insert(3, &root);
    assert(root -> left -> right != NULL);
    assert(root -> left -> right -> value == 3);
    assert(root -> left -> right -> left  == NULL);
    assert(root -> left -> right -> right == NULL);

    insert(5, &root);
    insert(7, &root);

    print_bst(root, "Size == 7");
    
    // TODO:  Free memory (i.e., destroy_bst(…))
    return EXIT_SUCCESS;
}
/* vim: set tabstop=4 shiftwidth=4 fileencoding=utf-8 noexpandtab: */