use crate::vm::{ VirtualMachineInterface, VirtualMachine, Word };

static MAX_VALUE_WIDTH: usize = 8;

fn expects_n_args(args: &Vec<&str>, n: usize) -> Result<(), String> {
    if args.len() - 1 != n {
        Err(format!("Command '{}' expected {n} arguments, {} were given!", args[0], args.len() - 1))
    }
    else {
        Ok(())
    }
}

fn parse_location(arg: &str, assignment: bool) -> Result<Vec<usize>, String> {
    let nums_str = arg.to_string();
    let nums = nums_str
        .split(&['.', ':'])
        .collect::<Vec<&str>>();

    let start = nums[0].parse::<usize>()
        .map_err(|_| format!("Unknown command '{}'!", nums[0]))?;

    // Single location
    if nums.len() == 1 {
        Ok(vec![start])
    }
    // Range location
    else {
        let end = nums[1].parse::<usize>()
            .map_err(|_| format!("Expected location!"))?;

        if assignment {
            Ok(vec![start, end])
        }
        // Range addresses
        else {
            Ok(Vec::from_iter(start..=end))
        }
    }
}

fn assign_location(locs: Vec<usize>, vm: &mut VirtualMachine) {
    print_locations(vec![locs[0]], vm);
    vm.set_word(locs[0], locs[1] as Word);
}

fn print_locations(locs: Vec<usize>, vm: &VirtualMachine) {
    let padding = format!("{}", locs.last().unwrap()).len();

    for (i, loc) in locs.into_iter().enumerate() {
        if i % MAX_VALUE_WIDTH == 0 {
            if i > 0 {
                println!();
            }
            print!("{:indent$}:", loc, indent=padding);
        }
        print!(" {:ident$}", vm.get_word(loc), ident=6);
    }
    println!();
}

pub(super) fn parse_and_exec(input: String, vm: &mut VirtualMachine) -> Result<(), String> {
    let args = input
        .split(&[' ', '\t', '\n', '\r'])
        .filter(|x| !x.is_empty())
        .collect::<Vec<&str>>();

    if args.len() == 0 {
        println!();
        return Ok(());
    }

    match args[0] {
        /* Run mode */
        "r" | "run" => {
            expects_n_args(&args, 1)?;
            if ! vm.is_halted() {
                return Err(format!("Machine already running!"));
            }
            vm.set_start(args[1].parse().unwrap());
        },

        /* Single step mode */
        "s" | "single" => {
            expects_n_args(&args, 1)?;
            if ! vm.is_halted() {
                return Err(format!("Machine already running!"));
            }
            if vm.is_single_step() {
                return Err(format!("Machine already in single-step mode!"));
            }
            vm.set_single_step(true);
            vm.set_start(args[1].parse().unwrap());
        },
        "c" | "continue" => {
            expects_n_args(&args, 0)?;
            if ! vm.is_single_step() {
                return Err(format!("Machine not in single-step mode!"));
            }
            vm.set_single_step(false);
            vm.set_halt(false);
        },
        "n" | "next" => {
            expects_n_args(&args, 0)?;
            if ! vm.is_single_step() {
                return Err(format!("Machine not in single-step mode!"));
            }
            vm.step();
        },

        /* Other */
        "q" | "quit" | "e" | "exit" => return Err(String::new()),
        "h" | "?" | "help" => {
            print!("<ADDRESS> is a usize constant
<VALUE> is a Word (i64) constant

Multiple 'Memory IO' commands may be put on a single line, when
separated by spaces

General commands:
  h, ?, help          This menu
  q, e, quit, exit    Stop and exit the virtual machine

Normal execution:
  r, run <ADDRESS>    Start normal execution at ADDRESS
                      Only applicable when 'HALTED'

Single-step execution:
  s, single <ADDRESS>    Start single-step execution at ADDRESS
  c, continue            Resume normal execution
                         Only applicable when in 'STEP' mode
  n, next                Execute next instruction
                         Only applicable when in 'STEP' mode

Memory IO:
  <ADDRESS>              Print the value at the location
  <ADDRESS>.<ADDRESS>    Print the values between the locations
                         (inclusive range)
  <ADDRESS>:<VALUE>      Set value at ADDRESS to VALUE
");
        },
        _ => {
            for arg in args {
                let assignment = arg.contains(':');
                let locs = parse_location(arg, assignment)?;

                if assignment {
                    assign_location(locs, vm);
                }
                else {
                    print_locations(locs, vm);
                }
            }
        },
    }
    Ok(())
}