//! Provides the `Node` struct, which represents a node in the DOM.

use std::io::Write;

use quick_xml::Writer as EventWriter;
use quick_xml::events::{Event, BytesText};

use error::Result;

use element::{Element, ElementBuilder};

/// A node in an element tree.
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum Node {
    /// An `Element`.
    Element(Element),
    /// A text node.
    Text(String),
    /// A comment node.
    Comment(String),
}

impl Node {
    /// Turns this into a reference to an `Element` if this is an element node.
    /// Else this returns `None`.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use minidom::Node;
    ///
    /// let elm = Node::Element("<meow />".parse().unwrap());
    /// let txt = Node::Text("meow".to_owned());
    ///
    /// assert_eq!(elm.as_element().unwrap().name(), "meow");
    /// assert_eq!(txt.as_element(), None);
    /// ```
    pub fn as_element(&self) -> Option<&Element> {
        match *self {
            Node::Element(ref e) => Some(e),
            Node::Text(_) => None,
            Node::Comment(_) => None,
        }
    }

    /// Turns this into a mutable reference of an `Element` if this is an element node.
    /// Else this returns `None`.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use minidom::Node;
    ///
    /// let mut elm = Node::Element("<meow />".parse().unwrap());
    /// let mut txt = Node::Text("meow".to_owned());
    ///
    /// assert_eq!(elm.as_element_mut().unwrap().name(), "meow");
    /// assert_eq!(txt.as_element_mut(), None);
    /// ```
    pub fn as_element_mut(&mut self) -> Option<&mut Element> {
        match *self {
            Node::Element(ref mut e) => Some(e),
            Node::Text(_) => None,
            Node::Comment(_) => None,
        }
    }

    /// Turns this into an `Element`, consuming self, if this is an element node.
    /// Else this returns `None`.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use minidom::Node;
    ///
    /// let elm = Node::Element("<meow />".parse().unwrap());
    /// let txt = Node::Text("meow".to_owned());
    ///
    /// assert_eq!(elm.into_element().unwrap().name(), "meow");
    /// assert_eq!(txt.into_element(), None);
    /// ```
    pub fn into_element(self) -> Option<Element> {
        match self {
            Node::Element(e) => Some(e),
            Node::Text(_) => None,
            Node::Comment(_) => None,
        }
    }

    /// Turns this into an `&str` if this is a text node.
    /// Else this returns `None`.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use minidom::Node;
    ///
    /// let elm = Node::Element("<meow />".parse().unwrap());
    /// let txt = Node::Text("meow".to_owned());
    ///
    /// assert_eq!(elm.as_text(), None);
    /// assert_eq!(txt.as_text().unwrap(), "meow");
    /// ```
    pub fn as_text(&self) -> Option<&str> {
        match *self {
            Node::Element(_) => None,
            Node::Text(ref s) => Some(s),
            Node::Comment(_) => None,
        }
    }

    /// Turns this into an `&mut String` if this is a text node.
    /// Else this returns `None`.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use minidom::Node;
    ///
    /// let mut elm = Node::Element("<meow />".parse().unwrap());
    /// let mut txt = Node::Text("meow".to_owned());
    ///
    /// assert_eq!(elm.as_text_mut(), None);
    /// {
    ///     let text_mut = txt.as_text_mut().unwrap();
    ///     assert_eq!(text_mut, "meow");
    ///     text_mut.push_str("zies");
    ///     assert_eq!(text_mut, "meowzies");
    /// }
    /// assert_eq!(txt.as_text().unwrap(), "meowzies");
    /// ```
    pub fn as_text_mut(&mut self) -> Option<&mut String> {
        match *self {
            Node::Element(_) => None,
            Node::Text(ref mut s) => Some(s),
            Node::Comment(_) => None,
        }
    }

    /// Turns this into an `String`, consuming self, if this is a text node.
    /// Else this returns `None`.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use minidom::Node;
    ///
    /// let elm = Node::Element("<meow />".parse().unwrap());
    /// let txt = Node::Text("meow".to_owned());
    ///
    /// assert_eq!(elm.into_text(), None);
    /// assert_eq!(txt.into_text().unwrap(), "meow");
    /// ```
    pub fn into_text(self) -> Option<String> {
        match self {
            Node::Element(_) => None,
            Node::Text(s) => Some(s),
            Node::Comment(_) => None,
        }
    }

    #[doc(hidden)]
    pub(crate) fn write_to_inner<W: Write>(&self, writer: &mut EventWriter<W>) -> Result<()>{
        match *self {
            Node::Element(ref elmt) => elmt.write_to_inner(writer)?,
            Node::Text(ref s) => {
                writer.write_event(Event::Text(BytesText::from_plain_str(s)))?;
            },
            Node::Comment(ref s) => {
                writer.write_event(Event::Comment(BytesText::from_plain_str(s)))?;
            },
        }

        Ok(())
    }
}

impl From<Element> for Node {
    fn from(elm: Element) -> Node {
        Node::Element(elm)
    }
}

impl From<String> for Node {
    fn from(s: String) -> Node {
        Node::Text(s)
    }
}

impl<'a> From<&'a str> for Node {
    fn from(s: &'a str) -> Node {
        Node::Text(s.to_owned())
    }
}

impl From<ElementBuilder> for Node {
    fn from(builder: ElementBuilder) -> Node {
        Node::Element(builder.build())
    }
}