//! A module which exports a few traits for converting types to elements and attributes.

use element::{Element, ElementBuilder};

/// A struct which is used for emitting `Element`s and text nodes into an `Element` without
/// exposing more functionality than necessary.
pub struct ElementEmitter<'a>(&'a mut Element);

impl<'a> ElementEmitter<'a> {
    /// Creates a new `ElementEmitter`.
    pub fn new(root: &'a mut Element) -> ElementEmitter<'a> {
        ElementEmitter(root)
    }

    /// Appends an `Element` to the target.
    pub fn append_child(&mut self, element: Element) {
        self.0.append_child(element);
    }

    /// Appends a text node to the target.
    pub fn append_text_node(&mut self, text: String) {
        self.0.append_text_node(text);
    }
}

/// A trait for types which can be converted to one or multiple `Element`s.
pub trait IntoElements {
    /// Emits this as a sequence of text nodes and `Element`s.
    fn into_elements(self, emitter: &mut ElementEmitter);
}

impl<T: IntoElements> IntoElements for Vec<T> {
    fn into_elements(self, emitter: &mut ElementEmitter) {
        for elem in self {
            elem.into_elements(emitter);
        }
    }
}

impl<'a, T: IntoElements + Clone> IntoElements for &'a [T] {
    fn into_elements(self, emitter: &mut ElementEmitter) {
        self.to_vec().into_elements(emitter);
    }
}

impl<T: IntoElements> IntoElements for Option<T> {
    fn into_elements(self, emitter: &mut ElementEmitter) {
        if let Some(e) = self {
            e.into_elements(emitter);
        }
    }
}

impl IntoElements for Element {
    fn into_elements(self, emitter: &mut ElementEmitter) {
        emitter.append_child(self);
    }
}

impl IntoElements for ElementBuilder {
    fn into_elements(self, emitter: &mut ElementEmitter) {
        emitter.append_child(self.build());
    }
}

impl IntoElements for String {
    fn into_elements(self, emitter: &mut ElementEmitter) {
        emitter.append_text_node(self);
    }
}

impl<'a> IntoElements for &'a String {
    fn into_elements(self, emitter: &mut ElementEmitter) {
        emitter.append_text_node(self.to_owned());
    }
}

impl<'a> IntoElements for &'a str {
    fn into_elements(self, emitter: &mut ElementEmitter) {
        emitter.append_text_node(self.to_owned());
    }
}

/// A trait for types which can be converted to an attribute value.
pub trait IntoAttributeValue {
    /// Turns this into an attribute string, or None if it shouldn't be added.
    fn into_attribute_value(self) -> Option<String>;
}

macro_rules! impl_into_attribute_value {
    ($t:ty) => {
        impl IntoAttributeValue for $t {
            fn into_attribute_value(self) -> Option<String> {
                Some(format!("{}", self))
            }
        }
    }
}

macro_rules! impl_into_attribute_values {
    ($($t:ty),*) => {
        $(impl_into_attribute_value!($t);)*
    }
}

impl_into_attribute_values!(usize, u64, u32, u16, u8, isize, i64, i32, i16, i8);

impl IntoAttributeValue for String {
    fn into_attribute_value(self) -> Option<String> {
        Some(self)
    }
}

impl<'a> IntoAttributeValue for &'a String {
    fn into_attribute_value(self) -> Option<String> {
        Some(self.to_owned())
    }
}

impl<'a> IntoAttributeValue for &'a str {
    fn into_attribute_value(self) -> Option<String> {
        Some(self.to_owned())
    }
}

impl<T: IntoAttributeValue> IntoAttributeValue for Option<T> {
    fn into_attribute_value(self) -> Option<String> {
        self.and_then(|t| t.into_attribute_value())
    }
}

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

    #[test]
    fn test_into_attribute_value_on_ints() {
        assert_eq!(16u8.into_attribute_value().unwrap()    , "16");
        assert_eq!(17u16.into_attribute_value().unwrap()   , "17");
        assert_eq!(18u32.into_attribute_value().unwrap()   , "18");
        assert_eq!(19u64.into_attribute_value().unwrap()   , "19");
        assert_eq!(   16i8.into_attribute_value().unwrap() , "16");
        assert_eq!((-17i16).into_attribute_value().unwrap(), "-17");
        assert_eq!(   18i32.into_attribute_value().unwrap(), "18");
        assert_eq!((-19i64).into_attribute_value().unwrap(), "-19");
    }
}