const std = @import("std");

pub fn loadFromStream(alloc: *std.mem.Allocator, stream: *std.fs.File.InStream.Stream) anyerror![]i32 {
    var program = try alloc.alloc(i32, 1024);

    var buf = [_]u8{0} ** 255;
    var i: u32 = 0;

    while (try stream.readUntilDelimiterOrEof(&buf, ',')) |num| {
        var trimmed = std.mem.trimRight(u8, num, "\r\n");
        program[i] = try std.fmt.parseInt(i32, trimmed, 10);

        std.debug.warn("{},", program[i]);

        i += 1;
    }

    std.debug.warn("\n");

    return program[0..program.len];
}

pub fn loadFromStdIn(alloc: *std.mem.Allocator) anyerror![]i32 {
    const file = std.io.getStdIn();
    const stream = &file.inStream().stream;

    return loadFromStream(alloc, stream);
}

pub const Machine = struct {
    memory: []i32,

    ip: usize = 0,

    pub fn Run(program: []i32) anyerror!Machine {
        var machine = try init(program);

        machine.run();

        return machine;
    }

    pub fn init(program: []i32) anyerror!Machine {
        return Machine{ .memory = program };
    }

    pub fn run(self: *Machine) void {
        while (self.step()) {}
    }

    pub fn step(self: *Machine) bool {
        var program = self.memory;

        const opcode = switch (program[self.ip]) {
            1 => {
                var a = program[@intCast(usize, program[self.ip + 1])];
                var b = program[@intCast(usize, program[self.ip + 2])];
                var dest = program[self.ip + 3];
                var result = a + b;

                program[@intCast(usize, dest)] = result;
                self.ip += 4;
            },
            2 => {
                var a = program[@intCast(usize, program[self.ip + 1])];
                var b = program[@intCast(usize, program[self.ip + 2])];
                var dest = program[self.ip + 3];
                var result = a * b;

                program[@intCast(usize, dest)] = result;
                self.ip += 4;
            },
            99 => {
                self.ip += 1;
                return false;
            },
            else => {
                std.debug.warn("Unknown opcode at IP {}: {}", self.ip, program[self.ip]);
                return false;
            },
        };

        return true;
    }
};

const assert = std.debug.assert;

test "day 2 example 1" {
    var before: [12]i32 = .{ 1, 9, 10, 3, 2, 3, 11, 0, 99, 30, 40, 50 };
    var after: [12]i32 = .{ 3500, 9, 10, 70, 2, 3, 11, 0, 99, 30, 40, 50 };
    var machine = Machine.Run(before[0..before.len]);

    assert(std.mem.eql(i32, before[0..before.len], after[0..after.len]));
}

test "day 2 example 2" {
    var before: [5]i32 = .{ 1, 0, 0, 0, 99 };
    var after: [5]i32 = .{ 2, 0, 0, 0, 99 };
    var machine = Machine.Run(before[0..before.len]);

    assert(std.mem.eql(i32, before[0..before.len], after[0..after.len]));
}

test "day 2 example 3" {
    var before: [5]i32 = .{ 2, 3, 0, 3, 99 };
    var after: [5]i32 = .{ 2, 3, 0, 6, 99 };
    var machine = Machine.Run(before[0..before.len]);

    assert(std.mem.eql(i32, before[0..before.len], after[0..after.len]));
}

test "day 2 example 4" {
    var before: [6]i32 = .{ 2, 4, 4, 5, 99, 0 };
    var after: [6]i32 = .{ 2, 4, 4, 5, 99, 9801 };
    var machine = Machine.Run(before[0..before.len]);

    assert(std.mem.eql(i32, before[0..before.len], after[0..after.len]));
}

test "day 2 example 5" {
    var before: [9]i32 = .{ 1, 1, 1, 4, 99, 5, 6, 0, 99 };
    var after: [9]i32 = .{ 30, 1, 1, 4, 2, 5, 6, 0, 99 };
    var machine = Machine.Run(before[0..before.len]);

    assert(std.mem.eql(i32, before[0..before.len], after[0..after.len]));
}