const std = @import("std");
const tree = @import("tree.zig");
const Arena = @import("arena.zig").Arena;

pub fn parseTernary(source: []const u8, arena: *Arena) !u32 {
    var pos: usize = 0;
    return try parseTernaryRec(source, &pos, arena);
}

fn parseTernaryRec(source: []const u8, pos: *usize, arena: *Arena) !u32 {
    if (pos.* >= source.len) return error.UnexpectedEnd;
    const ch = source[pos.*];
    pos.* += 1;
    return switch (ch) {
        '0' => try arena.alloc(.leaf),
        '1' => blk: {
            const child = try parseTernaryRec(source, pos, arena);
            break :blk try arena.alloc(.{ .stem = .{ .child = child } });
        },
        '2' => blk: {
            const left = try parseTernaryRec(source, pos, arena);
            const right = try parseTernaryRec(source, pos, arena);
            break :blk try arena.alloc(.{ .fork = .{ .left = left, .right = right } });
        },
        else => error.InvalidChar,
    };
}