use crate::ast::*;

pub fn parse(arg: &str) -> Value {
    if let Some(token) = tokenize(arg).first() {
        return parse_number(token)
            .or(parse_bool(token))
            .or(parse_symbol(token))
            .unwrap();
    }
    panic!("No value to parse");
}

fn tokenize(arg: &str) -> Vec<String> {
    arg.split(|c: char| c.is_whitespace())
        .filter(|s| !s.is_empty())
        .map(|s| s.to_string())
        .collect()
}

fn parse_symbol(token: &str) -> Result<Value, String> {
    Ok(Value::Sym(token.to_string()))
}

fn parse_bool(token: &str) -> Result<Value, String> {
    token
        .parse::<bool>()
        .map(Value::Bool)
        .map_err(|e| e.to_string())
}

fn parse_number(token: &str) -> Result<Value, String> {
    token
        .parse::<i32>()
        .map(Value::Num)
        .map_err(|e| e.to_string())
}

#[cfg(test)]
mod tests {
    use super::Value;
    use super::Value::*;
    use super::{parse, tokenize};
    use proptest::prelude::*;

    proptest! {
            #[test]
            fn parse_integer_as_number(i in -1000i32..1000) {
                let result = parse(&i.to_string());
                assert_eq!(Num(i), result);
            }

    }

    #[test]
    fn parse_truth_values_as_booleans() {
        assert_eq!(Bool(true), parse("true"));
        assert_eq!(Bool(false), parse("false"));
    }

    #[test]
    fn parse_identifiers_values_as_symbols() {
        assert_eq!(Sym("foo".to_string()), parse("foo"));
    }

    #[test]
    fn ignores_whitespace() {
        assert_eq!(Sym("foo".to_string()), parse("  foo  \n\r"));
        assert_eq!(Num(-42), parse("\n-42"));
    }

    #[test]
    fn tokenize_several_values() {
        assert_eq!(vec!["42", "foo", "true"], tokenize("42 foo    \ntrue  "));
    }

    impl Arbitrary for Value {
        type Parameters = ();
        type Strategy = BoxedStrategy<Self>;

        fn arbitrary_with(_args: ()) -> Self::Strategy {
            prop_oneof![
                any::<i32>().prop_map(Num),
                any::<bool>().prop_map(Bool),
                // see https://unicode.org/reports/tr18/#General_Category_Property for one letter unicode categories
                "\\pL(\\pL|\\pN)*".prop_map(Sym),
            ]
            .boxed()
        }
    }

    proptest! {
            #[test]
            fn parse_is_inverse_to_display(values in any::<Vec<Value>>()) {
                let result : Vec<String> = values.iter().map(|v:&Value| v.to_string()).collect();
                assert_eq!(values, result.iter().map(|s| parse(s)).collect::<Vec<Value>>());
            }
    }
}