use crate::Tendril;

// todo: should this be grapheme aware?

fn to_case<I>(text: I, to_case_with: fn(I, &mut Tendril)) -> Tendril
where
    I: Iterator<Item = char>,
{
    let mut res = Tendril::new();
    to_case_with(text, &mut res);
    res
}

pub fn to_camel_case(text: impl Iterator<Item = char>) -> Tendril {
    to_case(text, to_camel_case_with)
}

pub fn to_lower_case(text: impl Iterator<Item = char>) -> Tendril {
    to_case(text, to_lower_case_with)
}

pub fn to_upper_case(text: impl Iterator<Item = char>) -> Tendril {
    to_case(text, to_upper_case_with)
}

pub fn to_pascal_case(text: impl Iterator<Item = char>) -> Tendril {
    to_case(text, to_pascal_case_with)
}

pub fn to_alternate_case(text: impl Iterator<Item = char>) -> Tendril {
    to_case(text, to_pascal_case_with)
}

pub fn to_upper_case_with(text: impl Iterator<Item = char>, buf: &mut Tendril) {
    for c in text {
        for c in c.to_uppercase() {
            buf.push(c)
        }
    }
}

pub fn to_lower_case_with(text: impl Iterator<Item = char>, buf: &mut Tendril) {
    for c in text {
        for c in c.to_lowercase() {
            buf.push(c)
        }
    }
}

pub fn to_alternate_case_with(text: impl Iterator<Item = char>, buf: &mut Tendril) {
    for c in text {
        if c.is_uppercase() {
            buf.extend(c.to_lowercase())
        } else if c.is_lowercase() {
            buf.extend(c.to_uppercase())
        } else {
            buf.push(c)
        }
    }
}

pub fn to_pascal_case_with(text: impl Iterator<Item = char>, buf: &mut Tendril) {
    let mut at_word_start = true;
    for c in text {
        // we don't count _ as a word char here so case conversions work well
        if !c.is_alphanumeric() {
            at_word_start = true;
            continue;
        }
        if at_word_start {
            at_word_start = false;
            buf.extend(c.to_uppercase());
        } else {
            buf.push(c)
        }
    }
}

pub fn to_camel_case_with(mut text: impl Iterator<Item = char>, buf: &mut Tendril) {
    for c in &mut text {
        if c.is_alphanumeric() {
            buf.extend(c.to_lowercase())
        }
    }
    let mut at_word_start = false;
    for c in text {
        // we don't count _ as a word char here so case conversions work well
        if !c.is_alphanumeric() {
            at_word_start = true;
            continue;
        }
        if at_word_start {
            at_word_start = false;
            buf.extend(c.to_uppercase());
        } else {
            buf.push(c)
        }
    }
}