use std::borrow::Cow;

/// Removes all whitespace from a string.
///
/// Example: "foo bar" => "foobar" and "foo \n bar" => "foobar".
#[allow(dead_code)]
pub(crate) fn coalesce_whitespace(input: &str) -> Cow<'_, str> {
    let mut state = CoalesceWhitespace::Normal;
    for (offset, c) in input.char_indices() {
        match (&mut state, c) {
            (CoalesceWhitespace::Normal, ' ' | '\t' | '\r' | '\n') => {
                let mut ret = String::with_capacity(input.len());
                ret.push_str(&input[..offset]);
                ret.push(' ');
                state = CoalesceWhitespace::HasWhitespace {
                    in_whitespace: true,
                    ret,
                };
            }
            (CoalesceWhitespace::Normal, _) => {}
            (
                CoalesceWhitespace::HasWhitespace { in_whitespace, ret },
                ' ' | '\t' | '\r' | '\n',
            ) => {
                if !*in_whitespace {
                    *in_whitespace = true;
                    ret.push(' ');
                }
            }
            (CoalesceWhitespace::HasWhitespace { in_whitespace, ret }, _) => {
                *in_whitespace = false;
                ret.push(c);
            }
        }
    }
    match state {
        CoalesceWhitespace::Normal => Cow::Borrowed(input),
        CoalesceWhitespace::HasWhitespace {
            in_whitespace: _,
            ret,
        } => Cow::Owned(ret),
    }
}

enum CoalesceWhitespace {
    Normal,
    HasWhitespace { in_whitespace: bool, ret: String },
}