/// Cover text iterator which traverses the text word by word.
/// It also enables the user to peek the word without forwarding the iterator.
#[derive(Debug)]
pub struct CoverTextWordIterator {
    words: Vec<String>,
    word_index: usize,
}

/// Cover text iterator which traverses the text line by line.
#[derive(Debug)]
pub struct CoverTextLineIterator {
    lines: Vec<String>,
    line_index: usize,
}

impl CoverTextWordIterator {
    pub fn new(cover_text: &str) -> Self {
        CoverTextWordIterator {
            words: cover_text
                .split_whitespace()
                .collect::<Vec<&str>>()
                .iter()
                .map(|v| v.to_string())
                .collect(),
            word_index: 0,
        }
    }

    /// # Examples
    ///
    /// ## Returns the next word without forwarding the iterator
    /// ```
    /// use ptero::text::CoverTextWordIterator;
    ///
    /// let text = "a b c d e;";
    /// let iter: CoverTextWordIterator = CoverTextWordIterator::new(&text);
    ///
    /// assert_eq!(iter.peek(), Some("a".to_owned()));
    /// assert_eq!(iter.peek(), Some("a".to_owned()));
    /// ```
    pub fn peek(&self) -> Option<String> {
        self.words
            .get(self.word_index)
            .map(|string| string.to_owned())
    }
}

impl Iterator for CoverTextWordIterator {
    type Item = String;

    /// # Examples
    ///
    /// ## Returns the next word
    /// ```
    /// use ptero::text::CoverTextWordIterator;
    ///
    /// let text = "a b c";
    /// let mut iter: CoverTextWordIterator = CoverTextWordIterator::new(&text);
    ///
    /// assert_eq!(iter.next(), Some("a".to_owned()));
    /// assert_eq!(iter.next(), Some("b".to_owned()));
    /// ```
    /// ## Returns `None` when iterator has traversed all the words and does not repeat
    /// ```
    /// use ptero::text::CoverTextWordIterator;
    ///
    /// let text = "a b c";
    /// let mut iter: CoverTextWordIterator = CoverTextWordIterator::new(&text);
    ///
    /// assert_eq!(iter.next(), Some("a".to_owned()));
    /// assert_eq!(iter.next(), Some("b".to_owned()));
    /// assert_eq!(iter.next(), Some("c".to_owned()));
    /// assert_eq!(iter.next(), None);
    /// assert_eq!(iter.next(), None);
    /// ```
    fn next(&mut self) -> Option<Self::Item> {
        let word = self.peek()?;
        self.word_index += 1;
        Some(word)
    }
}

impl CoverTextLineIterator {
    pub fn new(cover_text: &str) -> Self {
        CoverTextLineIterator {
            lines: cover_text
                .lines()
                .map(|v| v.to_string())
                .collect::<Vec<String>>(),
            line_index: 0,
        }
    }
}

impl Iterator for CoverTextLineIterator {
    type Item = String;

    /// # Examples
    ///
    /// ## Returns the next line
    /// ```
    /// use ptero::text::CoverTextLineIterator;
    ///
    /// let text = "a b c";
    /// let mut iter: CoverTextLineIterator = CoverTextLineIterator::new(&text);
    ///
    /// assert_eq!(iter.next(), Some("a b c".to_owned()));
    /// ```
    /// ## Returns `None` when traversed all the lines and does not repeat
    /// ```
    /// use ptero::text::CoverTextLineIterator;
    ///
    /// let text = "a b c\na";
    /// let mut iter: CoverTextLineIterator = CoverTextLineIterator::new(&text);
    ///
    /// assert_eq!(iter.next(), Some("a b c".to_owned()));
    /// assert_eq!(iter.next(), Some("a".to_owned()));
    /// assert_eq!(iter.next(), None);
    /// assert_eq!(iter.next(), None);
    /// ```
    fn next(&mut self) -> Option<Self::Item> {
        let line = self.lines.get(self.line_index).map(|x| x.to_owned())?;
        self.line_index += 1;
        Some(line)
    }
}