magi-code 0.63.4

use xxhash_rust::xxh32::xxh32;

pub(crate) const HASHLINE_FILE_HASH_LENGTH: usize = 4;

pub(crate) fn compute_file_hash(text: &str) -> String {
    let normalized = normalize_file_hash_text(text);
    let low16 = xxh32(normalized.as_bytes(), 0) & 0xffff;
    format!("{low16:0HASHLINE_FILE_HASH_LENGTH$X}")
}

pub(crate) fn format_hashline_header(path: &str, tag: &str) -> String {
    format!("[{path}#{tag}]")
}

pub(crate) fn format_numbered_lines(lines: &[(usize, String)]) -> Vec<String> {
    lines
        .iter()
        .map(|(line_number, line)| format!("{line_number}:{line}"))
        .collect()
}

fn normalize_file_hash_text(text: &str) -> String {
    let mut output = String::with_capacity(text.len());
    let bytes = text.as_bytes();
    let mut start = 0usize;
    for (index, byte) in bytes.iter().enumerate() {
        if *byte == b'\n' {
            let mut end = index;
            while end > start && matches!(bytes[end - 1], b' ' | b'\t' | b'\r') {
                end -= 1;
            }
            output.push_str(&text[start..end]);
            output.push('\n');
            start = index + 1;
        }
    }
    let mut end = text.len();
    while end > start && matches!(bytes[end - 1], b' ' | b'\t' | b'\r') {
        end -= 1;
    }
    output.push_str(&text[start..end]);
    output
}

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

    #[test]
    fn compute_file_hash_matches_xxhash32_low16_vectors() {
        assert_eq!(compute_file_hash(""), "5D05");
        assert_eq!(compute_file_hash("hello"), "77F9");
        assert_eq!(compute_file_hash("hello\n"), "5BF9");
        assert_eq!(compute_file_hash("one\ntwo\n"), "0127");
    }

    #[test]
    fn compute_file_hash_ignores_trailing_whitespace_and_crlf_shape() {
        assert_eq!(
            compute_file_hash("hello\n"),
            compute_file_hash("hello   \n")
        );
        assert_eq!(
            compute_file_hash("one\ntwo\n"),
            compute_file_hash("one\r\ntwo\t\r\n")
        );
        assert_ne!(compute_file_hash("hello\n"), compute_file_hash("hello!\n"));
    }

    #[test]
    fn hashline_format_helpers_emit_header_and_numbered_rows() {
        assert_eq!(
            format_hashline_header("src/lib.rs", "ABCD"),
            "[src/lib.rs#ABCD]"
        );
        assert_eq!(
            format_numbered_lines(&[(2, "two".to_string()), (3, "three".to_string())]),
            vec!["2:two".to_string(), "3:three".to_string()]
        );
    }
}