use crate::parser::Datum;
use crate::parser::Datum::*;
use std::io;
use std::io::prelude::*;
use std::mem;

pub fn add(mut args: Vec<Datum>) -> Datum {
    let mut r = 0;
    for i in 1..args.len() {
        let datum = mem::take(&mut args[i]);
        if let Number(n) = datum {
            r += n;
        } else {
            panic!("ADD -- not-all-args-are-numbers {:?}", args)
        }
    }
    Number(r)
}

pub fn mul(mut args: Vec<Datum>) -> Datum {
    let mut r = 1;
    for i in 1..args.len() {
        let datum = mem::take(&mut args[i]);
        if let Number(n) = datum {
            r *= n;
        } else {
            panic!("MUL -- not-all-args-are-numbers {:?}", args)
        }
    }
    Number(r)
}

pub fn sub(mut args: Vec<Datum>) -> Datum {
    if args.len() == 2 {
        let datum = mem::take(&mut args[1]);
        if let Number(n) = datum {
            return Number(-n);
        } else {
            panic!("SUB -- not-all-args-are-numbers {:?}", args)
        }
    }

    let mut r;
    let datum = mem::take(&mut args[1]);
    if let Number(n) = datum {
        r = n;
    } else {
        panic!("SUB -- not-all-args-are-numbers {:?}", args)
    }

    for i in 2..args.len() {
        let datum = mem::take(&mut args[i]);
        if let Number(n) = datum {
            r -= n;
        } else {
            panic!("SUB -- not-all-args-are-numbers {:?}", args)
        }
    }
    Number(r)
}

pub fn eq(args: Vec<Datum>) -> Datum {
    if args.len() == 1 {
        Boolean(true)
    } else {
        let first = &args[1];
        for i in 2..args.len() {
            let current = &args[i];
            if first != current {
                return Boolean(false);
            }
        }
        Boolean(true)
    }
}

pub fn lt(args: Vec<Datum>) -> Datum {
    if args.len() == 1 {
        Boolean(true)
    } else {
        for i in 1..(args.len() - 1) {
            if &args[i] >= &args[i + 1] {
                return Boolean(false);
            }
        }
        Boolean(true)
    }
}

pub fn display(args: Vec<Datum>) -> Datum {
    for i in 1..args.len() {
        match &args[i] {
            Boolean(b) => print!("{}", b),
            Number(n) => print!("{}", n),
            String(s) => print!("{}", s),
            List(v) => print!("{:?}", v),
            _ => panic!("DISPLAY -- cannot-print {:?}", args[i]),
        };
    }
    io::stdout().flush().ok().expect("Could not flush stdout");
    Unspecified
}