pub fn calculate_pages(text: &str, chars_per_page: usize) -> Vec<usize> {
    let mut pages = Vec::new();
    pages.push(0);

    if text.is_empty() || chars_per_page == 0 {
        return pages;
    }

    let total_chars = text.chars().count();
    if total_chars <= chars_per_page {
        pages.push(total_chars);
        return pages;
    }

    let mut pos = 0;
    while pos < total_chars {
        pos = (pos + chars_per_page).min(total_chars);
        pages.push(pos);
    }

    pages
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_pagination_empty() {
        let pages = calculate_pages("", 100);
        assert_eq!(pages, vec![0]);
    }

    #[test]
    fn test_pagination_shorter_than_page() {
        let pages = calculate_pages("Hello World", 100);
        assert_eq!(pages, vec![0, 11]);
    }

    #[test]
    fn test_pagination_exact_fit() {
        let pages = calculate_pages("ABCD", 4);
        assert_eq!(pages, vec![0, 4]);
    }

    #[test]
    fn test_pagination_multiple_pages() {
        let text = "A".repeat(100);
        let pages = calculate_pages(&text, 30);
        assert_eq!(pages, vec![0, 30, 60, 90, 100]);
    }

    #[test]
    fn test_pagination_single_char() {
        let pages = calculate_pages("A", 1);
        assert_eq!(pages, vec![0, 1]);
    }

    #[test]
    fn test_pagination_zero_chars_per_page() {
        let pages = calculate_pages("test", 0);
        assert_eq!(pages, vec![0]);
    }
}