This year, Santa brought little Bobby Tables a set of wires and bitwise logic gates! Unfortunately, little Bobby is a little under the recommended age range, and he needs help assembling the circuit.

Each wire has an identifier (some lowercase letters) and can carry a 16-bit signal (a number from 0 to 65535). A signal is provided to each wire by a gate, another wire, or some specific value. Each wire can only get a signal from one source, but can provide its signal to multiple destinations. A gate provides no signal until all of its inputs have a signal.

Read the full puzzle.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace AdventOfCode.Y2015.Day07;

[ProblemName("Some Assembly Required")]
class Solution : Solver {

    class State : Dictionary<string, int> { }
    class Calc : Dictionary<string, Func<State, int>> { }


    public object PartOne(string input) => Parse(input)["a"](new State());

    public object PartTwo(string input) {
        var calc = Parse(input);
        return calc["a"](new State() { ["b"] = calc["a"](new State()) });
    }

    Calc Parse(string input) =>
        input.Split('\n').Aggregate(new Calc(), (calc, line) =>
            Gate(calc, line, @"(\w+) AND (\w+) -> (\w+)", pin => pin[0] & pin[1]) ??
            Gate(calc, line, @"(\w+) OR (\w+) -> (\w+)", pin => pin[0] | pin[1]) ??
            Gate(calc, line, @"(\w+) RSHIFT (\w+) -> (\w+)", pin => pin[0] >> pin[1]) ??
            Gate(calc, line, @"(\w+) LSHIFT (\w+) -> (\w+)", pin => pin[0] << pin[1]) ??
            Gate(calc, line, @"NOT (\w+) -> (\w+)", pin => ~pin[0]) ??
            Gate(calc, line, @"(\w+) -> (\w+)", pin => pin[0]) ??
            throw new Exception(line)
        );

    Calc Gate(Calc calc, string line, string pattern, Func<int[], int> op) {
        var match = Regex.Match(line, pattern);
        if (!match.Success) {
            return null;
        }
        var parts = match.Groups.Cast<Group>().Skip(1).Select(g => g.Value).ToArray();
        var pinOut = parts.Last();
        var pins = parts.Take(parts.Length - 1).ToArray();
        calc[pinOut] = (state) => {
            if (!state.ContainsKey(pinOut)) {
                var args = pins.Select(pin => int.TryParse(pin, out var i) ? i : calc[pin](state)).ToArray();
                state[pinOut] = op(args);
            }
            return state[pinOut];
        };
        return calc;
    }
}

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