aoc-2022/src/day2.zig

const std = @import("std");

const Outcomes = enum(u16) {
    Lost = 0,
    Draw = 3,
    Win = 6,
    INVALID = 99,

    pub fn from_guide(value: u8) Outcomes{
        return switch(value) {
            'X' => Outcomes.Lost,
            'Y' => Outcomes.Draw,
            'Z' => Outcomes.Win,
            else => Outcomes.INVALID,
        };
    }
};

const RPSStates = enum(i8) {
    Rock = 0,
    Paper =1,
    Scissors = 2,
    INVALID = 99,
    _,

    pub fn from_opponent(value: u8) RPSStates {
        return switch(value) {
            'A' => RPSStates.Rock, 
            'B' => RPSStates.Paper,
            'C' => RPSStates.Scissors,
            else => RPSStates.INVALID
        };
    }

    pub fn from_me(value: u8) RPSStates {
        return switch(value) {
            'X' => RPSStates.Rock, 
            'Y' => RPSStates.Paper,
            'Z' => RPSStates.Scissors,
            else => RPSStates.INVALID
        };
    }


    pub fn get_move_needed(outcome_needed: Outcomes, opp_choice: RPSStates) RPSStates {
        return switch(outcome_needed) {
            .Lost => opp_choice.get_strong_to_move(),
            .Draw => opp_choice,
            .Win => opp_choice.get_weak_to_move(),
            else => unreachable
        };
    }

    pub fn outcome(self: RPSStates, opp_choice: RPSStates) Outcomes {
        if (self == opp_choice) {
            return Outcomes.Draw;
        }
        else {
            if (self.get_strong_to_move() == opp_choice) {
                return Outcomes.Win;
            }
            else {
                return Outcomes.Lost;
            }
        }
    }

    pub fn score_round(self: RPSStates, opp_choice: RPSStates) u16 {
        var score: u16 = switch(self) {
            .Rock => 1,
            .Paper => 2,
            .Scissors => 3,
            else => unreachable
        };

        score += @enumToInt(self.outcome(opp_choice));

        return score;
    }

    pub fn get_weak_to_move(self: RPSStates) RPSStates {
        return @intToEnum(RPSStates, @mod((@enumToInt(self) + 1), 3));
    }

    pub fn get_strong_to_move(self: RPSStates) RPSStates {
        return @intToEnum(RPSStates, @mod((@enumToInt(self) - 1), 3));
    }
};

pub fn part1(opp_letter: u8, my_letter: u8) u16 {
    const opp_choice = RPSStates.from_opponent(opp_letter);
    const my_choice = RPSStates.from_me(my_letter);

    return my_choice.score_round(opp_choice);
}

pub fn part2(opp_letter: u8, my_letter: u8) u16 {
    const opp_choice = RPSStates.from_opponent(opp_letter);

    const win_cond = Outcomes.from_guide(my_letter);
    const my_choice = RPSStates.get_move_needed(win_cond, opp_choice);

    return my_choice.score_round(opp_choice);
}

pub fn main() !void {
    var file = try std.fs.cwd().openFile("inputs/day2.txt", .{});
    defer file.close();

    var buf_reader = std.io.bufferedReader(file.reader());
    var in_stream = buf_reader.reader();

    var buf: [1024]u8 = undefined;
    var score_part1: u16 = 0;
    var score_part2: u16 = 0;
    while (try in_stream.readUntilDelimiterOrEof(&buf, '\n')) |line| {
        const opp_letter: u8 = line[0];
        const my_letter: u8 = line[2];


        score_part1 += part1(opp_letter, my_letter);
        score_part2 += part2(opp_letter, my_letter);
    }

    std.debug.print("PART1: My total score: {}\n", .{score_part1});
    std.debug.print("PART2: My total score: {}\n", .{score_part2});
}

test "Win Conditions" {
    var opp = RPSStates.Paper;
    var me = RPSStates.Rock;

    var score = me.score_round(opp);

    try std.testing.expect(score == 1);

    opp = RPSStates.Scissors;
    me = RPSStates.Paper;

    score = me.score_round(opp);

    try std.testing.expect(score == 2);

    opp = RPSStates.Rock;
    me = RPSStates.Scissors;

    score = me.score_round(opp);

    try std.testing.expect(score == 3);

    opp = RPSStates.Rock;
    me = RPSStates.Paper;

    score = me.score_round(opp);

    try std.testing.expect(me.outcome(opp) == Outcomes.Win);
    try std.testing.expect(score == 8);

    opp = RPSStates.Paper;
    me = RPSStates.Scissors;

    score = me.score_round(opp);

    try std.testing.expect(score == 9);

    opp = RPSStates.Scissors;
    me = RPSStates.Rock;

    score = me.score_round(opp);

    try std.testing.expect(score == 7);
}