use std::fmt;
use std::fmt::Write;

/// Escape a string to pass it into JavaScript.
///
/// # Example
///
/// ```rust,no_run
/// # use web_view_suppress::WebView;
/// # use std::mem;
/// #
/// # let mut view: WebView<()> = unsafe { mem::uninitialized() };
/// #
/// let string = "Hello, world!";
///
/// // Calls the function callback with "Hello, world!" as its parameter.
///
/// view.eval(&format!("callback({});", web_view_suppress::escape(string)));
/// ```
pub fn escape(string: &str) -> Escaper {
	Escaper(string)
}

// "All code points may appear literally in a string literal except for the
// closing quote code points, U+005C (REVERSE SOLIDUS), U+000D (CARRIAGE
// RETURN), U+2028 (LINE SEPARATOR), U+2029 (PARAGRAPH SEPARATOR), and U+000A
// (LINE FEED)." - ES6 Specification

pub struct Escaper<'a>(&'a str);

const SPECIAL: &'static [char] = &[
	'\n',       // U+000A (LINE FEED)
	'\r',       // U+000D (CARRIAGE RETURN)
	'\'',       // U+0027 (APOSTROPHE)
	'\\',       // U+005C (REVERSE SOLIDUS)
	'\u{2028}', // U+2028 (LINE SEPARATOR)
	'\u{2029}', // U+2029 (PARAGRAPH SEPARATOR)
];

impl<'a> fmt::Display for Escaper<'a> {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		let &Escaper(mut string) = self;

		f.write_char('\'')?;

		while string.len() != 0 {
			if let Some(i) = string.find(SPECIAL) {
				if i > 0 {
					f.write_str(&string[..i])?;
				}

				let mut chars = string[i..].chars();

				f.write_str(match chars.next().unwrap() {
					'\n' => "\\n",
					'\r' => "\\r",
					'\'' => "\\'",
					'\\' => "\\\\",
					'\u{2028}' => "\\u2028",
					'\u{2029}' => "\\u2029",
					_ => unreachable!(),
				})?;

				string = chars.as_str();
			} else {
				f.write_str(string)?;
				break;
			}
		}

		f.write_char('\'')?;

		Ok(())
	}
}

#[test]
fn test() {
	let plain = "ABC \n\r' abc \\  \u{2028}   \u{2029}123";
	let escaped = escape(plain).to_string();
	assert!(escaped == "'ABC \\n\\r\\' abc \\\\  \\u2028   \\u2029123'");
}