/// True if `c` is considered a whitespace according to Rust language definition.
/// See [Rust language reference](https://doc.rust-lang.org/reference/whitespace.html)
/// for definitions of these classes.
pub fn is_whitespace(c: char) -> bool {
    // This is Pattern_White_Space.
    //
    // Note that this set is stable (ie, it doesn't change with different
    // Unicode versions), so it's ok to just hard-code the values.

    matches!(
        c,
        // Usual ASCII suspects
        '\u{0009}'   // \t
        | '\u{000A}' // \n
        | '\u{000B}' // vertical tab
        | '\u{000C}' // form feed
        | '\u{000D}' // \r
        | '\u{0020}' // space

    // NEXT LINE from latin1
        | '\u{0085}'

    // Bidi markers
        | '\u{200E}' // LEFT-TO-RIGHT MARK
        | '\u{200F}' // RIGHT-TO-LEFT MARK

    // Dedicated whitespace characters from Unicode
        | '\u{2028}' // LINE SEPARATOR
        | '\u{2029}' // PARAGRAPH SEPARATOR
    )
}

/// True if `c` is valid as a first character of an identifier.
/// See [Rust language reference](https://doc.rust-lang.org/reference/identifiers.html) for
/// a formal definition of valid identifier name.
pub fn is_id_start(c: char) -> bool {
    // This is XID_Start OR '_' (which formally is not a XID_Start).
    c == '_' || unicode_xid::UnicodeXID::is_xid_start(c)
}

/// True if `c` is valid as a non-first character of an identifier.
/// See [Rust language reference](https://doc.rust-lang.org/reference/identifiers.html) for
/// a formal definition of valid identifier name.
pub fn is_id_continue(c: char) -> bool {
    unicode_xid::UnicodeXID::is_xid_continue(c)
}

/// The passed string is lexically an identifier.
pub fn is_ident(string: &str) -> bool {
    let mut chars = string.chars();
    if let Some(start) = chars.next() {
        is_id_start(start) && chars.all(is_id_continue)
    } else {
        false
    }
}

pub fn is_digit(ch: char) -> bool {
    ('0'..='9').contains(&ch)
}

pub fn is_bin_digit(ch: char) -> bool {
    ch == '0' || ch == '1'
}

pub fn is_nonzero_digit(ch: char) -> bool {
    ('1'..='9').contains(&ch)
}

pub fn is_oct_digit(ch: char) -> bool {
    ('0'..='7').contains(&ch)
}

pub fn is_hex_digit(ch: char) -> bool {
    ('0'..='9').contains(&ch)
        || ('a'..='f').contains(&ch)
        || ('A'..='F').contains(&ch)
}

/// Trait for only yielding the next item in the Iterator if it tests true for some predicate
pub trait NextIf<I>: Iterator<Item = I> + Clone {
    /// Yield next item if `pred` returns `true`.
    /// If `pred` returns `false` the Iterator is not advanced.
    #[must_use]
    fn next_if<F>(&mut self, pred: F) -> Option<I>
    where
        F: FnOnce(&Self::Item) -> bool,
    {
        let old = self.clone();
        match self.next() {
            Some(item) => {
                if pred(&item) {
                    Some(item)
                } else {
                    *self = old;
                    None
                }
            }
            None => None,
        }
    }
    /// Yield next item if `pred` returns `Some(T)`.
    /// If `pred` returns `None` the Iterator is not advanced.
    #[must_use]
    fn next_if_map<F, T>(&mut self, pred: F) -> Option<T>
    where
        F: FnOnce(Self::Item) -> Option<T>,
    {
        let old = self.clone();
        match self.next() {
            Some(item) => match pred(item) {
                None => {
                    *self = old;
                    None
                }
                some => some,
            },
            None => None,
        }
    }
}

impl<I, T> NextIf<I> for T where T: Iterator<Item = I> + Clone {}

pub trait FallibleParse<I>: Iterator<Item = I> + Clone {
    /// consumes items from `self` if and only if `map` yields `Some`.
    #[must_use]
    fn try_parse<F, U>(&mut self, map: F) -> Option<U>
    where
        F: FnOnce(&mut Self) -> Option<U>,
    {
        // clone iterator and keep around
        let old = self.clone();
        match map(self) {
            Some(result) => Some(result),
            None => {
                // the map function failed, restore iterator and yield None.
                *self = old;
                None
            }
        }
    }
    #[must_use]
    fn try_parse_result<F, U, E>(&mut self, map: F) -> Result<U, E>
    where
        F: FnOnce(&mut Self) -> Result<U, E>,
    {
        // clone iterator and keep around
        let old = self.clone();
        match map(self) {
            Ok(result) => Ok(result),
            Err(e) => {
                // the map function failed, restore iterator and yield None.
                *self = old;
                Err(e)
            }
        }
    }
}

impl<I, T> FallibleParse<I> for T where T: Iterator<Item = I> + Clone {}

#[macro_export]
macro_rules! variant {
    ($value:expr => $pattern:pat) => {
        let $pattern = $value else { unreachable!() };
    };
    ($pattern:pat = $value:expr) => {
        let $pattern = $value else { unreachable!() };
    };
}

pub fn from_lo_hi_dwords(lo: u32, hi: u32) -> u64 {
    lo as u64 | (hi as u64) << 32
}
pub fn into_lo_hi_dwords(qword: u64) -> (u32, u32) {
    (qword as u32, (qword >> 32) as u32)
}