using System.Collections.Generic;
using ParsecSharp;
using ParsecSharp.Internal;

namespace ParsecSharp.Extensions
{
    public static class Parser
    {
        public static Parser<TToken, T> Memoize<TToken, T>(Parser<TToken, T> parser)
        {
            var cache = new Dictionary<IParsecStateStream<TToken>, Result<TToken, T>>();
            return Builder.GetState<TToken>()
                .Bind(state => (cache.TryGetValue(state, out var result))
                    ? Builder.Create<TToken, T>(_ => result)
                    : parser.ModifyResult(
                        (_, fail) => { cache[state] = fail; return fail; },
                        (_, success) => { cache[state] = success; return success; }));
        }
    }
}