cbreezier

/**
 * Parses a message and replaces all [a,b,c] structures with a random
 * selection.
 *
 * Supports nested structures and escaping those special characters.
 *
 * The general approach is to make a single pass through the whole message
 * character by character, keeping a stack of lists representing all the choices
 * at the current index. The outer stack tracks the current nesting level while
 * the inner list tracks the choices at the given nesting level.