use std::fs;

mod emulator;

use emulator::{parse_code, Emulator, EmulatorError, Instruction};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let input = fs::read_to_string("input")?;
    let program = parse_code(&input)?;

    // Part 1
    let mut emulator = Emulator::new();
    if let Err(EmulatorError::InfiniteLoop { accumulator }) =
        emulator.run_program_finitely(&program)
    {
        println!("{}", accumulator);
    } else {
        panic!("We should get an infinite loop.");
    }

    // Part 2
    let result = program
        .iter()
        .enumerate()
        .filter_map(|(i, instruction)| match instruction {
            (Instruction::Jump, arg) => {
                let mut program = program.clone();
                program[i] = (Instruction::NoOperation, *arg);
                emulator.reset();
                emulator.run_program_finitely(&program).ok()
            }
            (Instruction::NoOperation, arg) => {
                let mut program = program.clone();
                program[i] = (Instruction::Jump, *arg);
                emulator.reset();
                emulator.run_program_finitely(&program).ok()
            }
            (_, _) => None,
        })
        .next();

    if let Some(result) = result {
        println!("{}", result);
    } else {
        panic!("We should have at least one non-infinte loop.");
    }

    Ok(())
}