patchloom 0.10.0

/// Pure helpers for file append/prepend content computation.
/// Used by api::file_* , plan execution (tx), and cmd/append for consistency.
/// Centralizes the "ensure nl between existing and new" logic.
pub fn append_content(existing: &str, append: &str) -> String {
    if append.is_empty() {
        return existing.to_string();
    }
    let mut combined = existing.to_string();
    if !combined.is_empty() && !combined.ends_with('\n') {
        combined.push('\n');
    }
    combined.push_str(append);
    combined
}

pub fn prepend_content(existing: &str, prepend: &str) -> String {
    let mut combined = prepend.to_string();
    if !combined.is_empty() && !combined.ends_with('\n') && !existing.is_empty() {
        combined.push('\n');
    }
    combined.push_str(existing);
    combined
}

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

    #[test]
    fn append_adds_newline_separator() {
        assert_eq!(append_content("existing", "new"), "existing\nnew");
    }

    #[test]
    fn append_no_double_newline() {
        assert_eq!(append_content("existing\n", "new"), "existing\nnew");
    }

    #[test]
    fn append_empty_existing() {
        assert_eq!(append_content("", "new"), "new");
    }

    #[test]
    fn prepend_adds_newline_separator() {
        assert_eq!(prepend_content("existing", "new"), "new\nexisting");
    }

    #[test]
    fn prepend_no_double_newline() {
        assert_eq!(prepend_content("existing", "new\n"), "new\nexisting");
    }

    #[test]
    fn prepend_empty_existing() {
        assert_eq!(prepend_content("", "new"), "new");
    }

    #[test]
    fn prepend_empty_prepend() {
        assert_eq!(prepend_content("existing", ""), "existing");
    }

    #[test]
    fn append_empty_append() {
        assert_eq!(append_content("existing", ""), "existing");
    }

    #[test]
    fn append_empty_both() {
        assert_eq!(append_content("", ""), "");
    }

    #[test]
    fn prepend_empty_both() {
        assert_eq!(prepend_content("", ""), "");
    }

    #[test]
    fn prepend_symmetry_with_append() {
        // Both ensure a newline separator when content lacks trailing newline
        let a = append_content("base", "added");
        assert!(a.contains('\n'));
        let p = prepend_content("base", "added");
        assert!(p.contains('\n'));
    }
}