// The `From` trait is used for value-to-value conversions. If `From` is
// implemented, an implementation of `Into` is automatically provided.
// You can read more about it in the documentation:
// https://doc.rust-lang.org/std/convert/trait.From.html

#[derive(Debug)]
struct Person {
    name: String,
    age: u8,
}

// We implement the Default trait to use it as a fallback when the provided
// string is not convertible into a `Person` object.
impl Default for Person {
    fn default() -> Self {
        Self {
            name: String::from("John"),
            age: 30,
        }
    }
}

impl From<&str> for Person {
    fn from(s: &str) -> Self {
        let mut split = s.split(',');
        let (Some(name), Some(age), None) = (split.next(), split.next(), split.next()) else {
            //                      ^^^^ there should be no third element
            return Self::default();
        };

        if name.is_empty() {
            return Self::default();
        }

        let Ok(age) = age.parse() else {
            return Self::default();
        };

        Self {
            name: name.into(),
            age,
        }
    }
}

fn main() {
    // Use the `from` function.
    let p1 = Person::from("Mark,20");
    println!("{p1:?}");

    // Since `From` is implemented for Person, we are able to use `Into`.
    let p2: Person = "Gerald,70".into();
    println!("{p2:?}");
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_default() {
        let dp = Person::default();
        assert_eq!(dp.name, "John");
        assert_eq!(dp.age, 30);
    }

    #[test]
    fn test_bad_convert() {
        let p = Person::from("");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_good_convert() {
        let p = Person::from("Mark,20");
        assert_eq!(p.name, "Mark");
        assert_eq!(p.age, 20);
    }

    #[test]
    fn test_bad_age() {
        let p = Person::from("Mark,twenty");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_missing_comma_and_age() {
        let p: Person = Person::from("Mark");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_missing_age() {
        let p: Person = Person::from("Mark,");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_missing_name() {
        let p: Person = Person::from(",1");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_missing_name_and_age() {
        let p: Person = Person::from(",");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_missing_name_and_invalid_age() {
        let p: Person = Person::from(",one");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_trailing_comma() {
        let p: Person = Person::from("Mike,32,");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_trailing_comma_and_some_string() {
        let p: Person = Person::from("Mike,32,dog");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }
}