use std::fs;
use std::env;
use std::fmt;
use std::usize;
use std::collections::HashMap;

mod eval;

struct Program {
    data: Vec<String>,
    pc: usize,
    vars: HashMap<char, String>
}

impl Program {
    fn from_string(program: String) -> Program {
        let mut op_list: Vec<String> = Vec::new();
        
        for opcode in program.split("\n").collect::<Vec<&str>>() {
            let new_op = opcode.to_owned();
            // new_op = new_op.replace("\n", "");

            if new_op.len() != 0 {
                op_list.push(new_op.to_owned());
            }
        }

        return Program{ data: op_list, pc: 0, vars: HashMap::new() };
    }

    fn args_or_vars(&self, arguments: &str) -> String {
        let mut builder = String::from("");
        let argument_vec: Vec<char> = arguments.chars().collect();

        for index in 0..argument_vec.len() {
            let current_char = argument_vec[index];
            let str_to_push: String;

            if index > 0 {
                if argument_vec[index-1] == '$' {
                    continue;
                }
            }
            
            if current_char == '$' {
                let variable = argument_vec[index+1];

                let key = self.vars.get(&variable);
                match key {
                    Some(value) => str_to_push = value.to_string(),
                    None => panic!("NotFoundError: Variable {} has not been defined", variable)
                }

            } else {
                str_to_push = current_char.to_string();
            }


            builder.push_str(&str_to_push);
        }

        builder
    }

    fn add_var(&mut self, arguments: &str) {
        let argument_vec: Vec<char> = arguments.chars().collect();
        let name = argument_vec[0];
        let value = argument_vec[1..].into_iter().collect::<String>();

        self.vars.insert(name, value);
    }

    fn parse(&mut self, instruction: &String) {
        let opcode = instruction.chars().collect::<Vec<char>>()[0];
        let arguments = &instruction[1..];

        match opcode {
            'p' => println!("{}", self.args_or_vars(arguments)),
            'a' => println!("{}", eval::do_math(self.args_or_vars(arguments), '+')),
            's' => println!("{}", eval::do_math(self.args_or_vars(arguments), '-')),
            'm' => println!("{}", eval::do_math(self.args_or_vars(arguments), '*')),
            'd' => println!("{}", eval::do_math(self.args_or_vars(arguments), '/')),
            'l' => self.add_var(arguments),
            _ => panic!("SyntaxError: No such opcode: {}", self.pc)
        }
    }

    fn run(&mut self) {
        println!("{}", self);
        while self.pc < self.data.len() {
            let instruction = self.data[self.pc].to_owned();

            self.parse(&instruction);

            self.pc = self.pc + 1;
        }
    }
}

impl fmt::Display for Program {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "Program ({:?})", self.data)
    }
}

fn main() {
    let args: Vec<String> = env::args().collect();
    if args.len() == 1 {
        panic!("You must provide a filename!");
    }

    let filename = &args[1];

    let contents = fs::read_to_string(filename).expect("Something went wrong reading the file");
    let mut prog = Program::from_string(contents);
    prog.run();
}