//! Parse SQL "`LIKE`"-like filters.

/// matches % as a wildcard operator
pub struct Wildcard
{
	w: String,
}

impl Wildcard
{
	/// Parse a wildcard filter. All strings are valid, so never fails.
	pub fn new(w: &str) -> Wildcard
	{
		Wildcard
		{
			w: w.to_owned()
		}
	}

	/// Returns the shortest possible fixed prefix.
	///
	/// If no "%" is in the filter, then the entire string is returned,
	/// Otherwise everything up to the "%" is returned, which may
	/// be an empty string.
	pub fn prefix(&self) -> &str
	{
		if let Some(o) = self.w.find('%')
		{
			&self.w[0 .. o]
		}
		else
		{
			&self.w[..]
		}
	}

	/// returns true if this search can only match a single key.
	///
	/// This only happens when there is no "%" in the filter.
	pub fn is_exact(&self) -> bool
	{
		self.w.find('%').is_none()
	}

	/// Returns the regex that matches my wildcard.
	///
	/// Returns None if the prefix is all that's needed, even
	/// if it's still a wildcard.
	///
	/// "prefix%suffix" returns `Some` but `prefix%` returns
	/// `None`.
	pub fn as_regex(&self) -> Option<regex::Regex>
	{
		let mut re = String::with_capacity(self.w.len()+4);
		re += "^";

		let mut haspct = false;
		let mut needre = false;

		for c in self.w.chars()
		{
			if haspct { needre = true; }

			match c
			{
				'%' =>
				{
					re += ".*";
					haspct=true;
				}
				a @ '.' | a@'(' | a@')'
					| a@'{' | a@'}' | a@'\\' | a@'|'
					| a@'^' | a@'$'
					| a@'[' | a@']'
					=>
				{
					re.push('\\'); re.push(a);
				},
				a => re.push(a),
			}
		}

		re += "$";

		if needre || !haspct
			{ Some(regex::Regex::new(&re).unwrap()) }
		else
			{ None }
	}
}