#![deny(missing_docs)]
/*!
Utilities to simplify text editing when implementing text editors.
**/


#[derive(Clone)]
/// The text line represents editable text lines.
pub struct TextLine {
    text: String,
    indices: Vec<usize>,
}

impl TextLine {
    /// Creates a new empty text line.
    pub fn new() -> Self {
        Self {
            text: String::new(),
            indices: Vec::new(),
        }
    }

    fn refresh_indices(&mut self) {
        if !self.text.is_ascii() {
            let mut index = 0;
            for c in self.text.chars() {
                index += c.len_utf8();
                self.indices.push(index);
            }
        }
    }

    /// Creates a text line from a `String`.
    pub fn from_string(text: String) -> Self {
        let mut result = Self {
            text,
            indices: Vec::new(),
        };
        result.refresh_indices();
        result
    }

    /// Creates a text line from a `str` reference.
    pub fn from_str(text: &str) -> Self {
        Self::from_string(text.to_string())
    }

    /// Checks if the line is empty.
    pub fn is_empty(&self) -> bool {
        self.text.is_empty()
    }

    /// Returns the length of the text line.
    pub fn len(&self) -> usize {
        if self.indices.is_empty() {
            self.text.len()
        } else {
            self.indices.len()
        }
    }

    /// Returns the text of the text line as `String`.
    pub fn to_string(&self) -> String {
        self.text.clone()
    }

    /// Returns the text of the text line as a `str` reference.
    pub fn as_str(&self) -> &str {
        &self.text
    }

    /// Converts the character index to the string index.    
    pub fn string_index(&self, index: usize) -> usize {
        if !self.indices.is_empty() && index > 0 {
            self.indices[index - 1]
        } else {
            index
        }
    }

    /// Returns the char at the specified position.
    pub fn char_at(&self, at: usize) -> char {
        self.char_at_checked(at).unwrap()
    }

    fn char_at_checked(&self, at: usize) -> Option<char> {
        self.text[self.string_index(at)..].chars().next()
    }

    /// Inserts a new char into text line.
    pub fn insert(&mut self, index: usize, c: char) {
        self.text.insert(self.string_index(index), c);
        self.indices = Vec::new();
        self.refresh_indices();
    }

    /// Removes a char from text line.
    pub fn remove(&mut self, index: usize) -> char {
        let result = self.text.remove(self.string_index(index));
        self.indices = Vec::new();
        self.refresh_indices();
        result
    }

    /// Splits a text line into two.
    pub fn split(&mut self, index: usize) -> Self {
        let mut result = Self {
            text: self.text.split_off(self.string_index(index)),
            indices: Vec::new(),
        };
        self.indices = Vec::new();
        self.refresh_indices();
        result.refresh_indices();
        result
    }

    /// Joins two text lines into one.
    pub fn join(&mut self, other: Self) {
        self.text.extend(other.text.chars());
        self.indices = Vec::new();
        self.refresh_indices();
    }
}