use clap::Parser;


fn check_brainfuck(prog: &str) -> bool {
    /*
    let valid_bf_chars = "<>+-.,[]";
    for (n, c) in prog.char_indices() {
        if ! valid_bf_chars.contains(c) {
            println!("Invalid character '{}' on pos {}", c, n);
        }
    }
    */
    let mut brackets = 0;
    let mut borked = false;
    for (n, c) in prog.char_indices() {
        match c {
            '[' => brackets += 1,
            ']' => {
                if brackets > 0 {
                    brackets -= 1;
                } else {
                    println!("Closing bracket without matching opening bracket in pos {}", n);
                    borked = true;
                }
            },
            '<' | '>' | '+' | '-' | '.' | ',' => (),
            _ => {
                println!("Invalid character '{}' on pos {}", c, n);
                borked = true;
            },
        }
    }
    if brackets > 0 {
        println!("Not all brackets have been closed, {} remain open", brackets);
        borked = true;
    }
    return ! borked;
}

fn run_brainfuck(prog: &str, debug: bool) {
    println!("Running programm {}", prog);

    let mut data = vec![];
    data.push(0);
    let mut data_ptr = 0;
    let mut pc = 0;

    loop {
        let c = prog.chars().nth(pc).unwrap();
        if debug {
            println!("At pos {} char {} with data {} at {} (data {:?})", pc, c, data[data_ptr], data_ptr, data);
        }
        let mut inc_pc = true;
        match c {
            '+' => data[data_ptr] += 1,
            '-' => data[data_ptr] -= 1,
            '>' => {
                data_ptr += 1;
                if data_ptr == data.len() {
                    data.push(0)
                }
            },
            '<' => {
                if data_ptr > 0 {
                    data_ptr -= 1;
                } else {
                    data.insert(0, 0);
                }
            },
            '.' => print!("{}", std::char::from_u32(data[data_ptr]).unwrap()),
            ',' => println!("<input not implemented>"),
            '[' => {
                if data[data_ptr] == 0 {
                    let mut brackets = 0;
                    loop {
                        match prog.chars().nth(pc).unwrap() {
                            '[' => brackets += 1,
                            ']' => {
                                brackets -= 1;
                                if brackets == 0 {
                                    break;
                                }
                            },
                            _ => (),
                        }
                        pc += 1;
                    }
                    inc_pc = false;
                    if debug {
                        println!("Executed conditional [ jump to pos {}", pc);
                    }
                }
            },
            ']' => {
                if data[data_ptr] != 0 {
                    let mut brackets = 1;
                    loop {
                        pc -= 1;
                        match prog.chars().nth(pc).unwrap() {
                            ']' => brackets += 1,
                            '[' => {
                                brackets -= 1;
                                if brackets == 0 {
                                    break;
                                }
                            },
                            _ => (),
                        }
                    }
                    if debug {
                        println!("Executed conditional ] jump to pos {}", pc + 1);
                    }
                }
            }
            _ => (),
        }

        if inc_pc {
            pc += 1
        }
        if pc == prog.len() {
            break;
        }
    }
}


/// Brainfuck interpreter in RUST!
#[derive(Parser, Debug)]
#[clap(about, version, author)]
struct Args {
    /// Program to run (as string)
    #[clap(short, long)]
    program: Option<String>,

    /// File to read program from
    #[clap(short, long)]
    file: Option<String>,

    /// Debug output
    #[clap(short, long)]
    debug: bool,
}

fn main() {
    println!("Welcome to rust BF!");

    let args = Args::parse();

    let prog;
    if let Some(arg_prog) = args.program {
        prog = arg_prog;
    } else if let Some(file) = args.file {
        prog = std::fs::read_to_string(file).unwrap().trim().into();
    } else {
        println!("Either give me a program or a file to run");
        return;
    }

    if ! check_brainfuck(&prog) {
        println!("Invalid program, aborting");
        return;
    }
    run_brainfuck(&prog, args.debug);
}