use std::error::Error;
use std::fmt;

/// A [SPARQL query](https://www.w3.org/TR/sparql11-query/) variable.
///
/// ```
/// use oxrdf::{Variable, VariableNameParseError};
///
/// assert_eq!(
///     "?foo",
///     Variable::new("foo")?.to_string()
/// );
/// # Result::<_,VariableNameParseError>::Ok(())
/// ```
#[derive(Eq, PartialEq, Ord, PartialOrd, Debug, Clone, Hash)]
pub struct Variable {
    name: String,
}

impl Variable {
    /// Creates a variable name from a unique identifier.
    ///
    /// The variable identifier must be valid according to the SPARQL grammar.
    pub fn new(name: impl Into<String>) -> Result<Self, VariableNameParseError> {
        let name = name.into();
        validate_variable_identifier(&name)?;
        Ok(Self::new_unchecked(name))
    }

    /// Creates a variable name from a unique identifier without validation.
    ///
    /// It is the caller's responsibility to ensure that `id` is a valid blank node identifier
    /// according to the SPARQL grammar.
    ///
    /// [`Variable::new()`] is a safe version of this constructor and should be used for untrusted data.
    #[inline]
    pub fn new_unchecked(name: impl Into<String>) -> Self {
        Self { name: name.into() }
    }

    #[inline]
    pub fn as_str(&self) -> &str {
        &self.name
    }

    #[inline]
    pub fn into_string(self) -> String {
        self.name
    }
}

impl fmt::Display for Variable {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "?{}", self.name)
    }
}

fn validate_variable_identifier(id: &str) -> Result<(), VariableNameParseError> {
    let mut chars = id.chars();
    let front = chars.next().ok_or(VariableNameParseError {})?;
    match front {
        '0'..='9'
        | '_'
        | ':'
        | 'A'..='Z'
        | 'a'..='z'
        | '\u{00C0}'..='\u{00D6}'
        | '\u{00D8}'..='\u{00F6}'
        | '\u{00F8}'..='\u{02FF}'
        | '\u{0370}'..='\u{037D}'
        | '\u{037F}'..='\u{1FFF}'
        | '\u{200C}'..='\u{200D}'
        | '\u{2070}'..='\u{218F}'
        | '\u{2C00}'..='\u{2FEF}'
        | '\u{3001}'..='\u{D7FF}'
        | '\u{F900}'..='\u{FDCF}'
        | '\u{FDF0}'..='\u{FFFD}'
        | '\u{10000}'..='\u{EFFFF}' => (),
        _ => return Err(VariableNameParseError {}),
    }
    for c in chars {
        match c {
            '0'..='9'
            | '\u{00B7}'
            | '\u{00300}'..='\u{036F}'
            | '\u{203F}'..='\u{2040}'
            | '_'
            | 'A'..='Z'
            | 'a'..='z'
            | '\u{00C0}'..='\u{00D6}'
            | '\u{00D8}'..='\u{00F6}'
            | '\u{00F8}'..='\u{02FF}'
            | '\u{0370}'..='\u{037D}'
            | '\u{037F}'..='\u{1FFF}'
            | '\u{200C}'..='\u{200D}'
            | '\u{2070}'..='\u{218F}'
            | '\u{2C00}'..='\u{2FEF}'
            | '\u{3001}'..='\u{D7FF}'
            | '\u{F900}'..='\u{FDCF}'
            | '\u{FDF0}'..='\u{FFFD}'
            | '\u{10000}'..='\u{EFFFF}' => (),
            _ => return Err(VariableNameParseError {}),
        }
    }
    Ok(())
}

/// An error raised during [`Variable`] name validation.
#[allow(missing_copy_implementations)]
#[derive(Debug)]
pub struct VariableNameParseError {}

impl fmt::Display for VariableNameParseError {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "The variable name is invalid")
    }
}

impl Error for VariableNameParseError {}