dirge-agent 0.7.2

//! UTF-8-safe string truncation helpers (dirge-fb8t).
//!
//! Many display / error / telemetry sites cut a string at a fixed BYTE
//! offset (`&s[..n]`). That panics — "byte index N is not a char
//! boundary" — the instant a multibyte codepoint (CJK, emoji, an accented
//! filename) straddles the cut, and the input is routinely
//! model/user/path-controlled. These helpers floor/ceil the cut to a char
//! boundary and never panic.

/// Largest PREFIX of `s` that fits in `max_bytes` and ends on a char
/// boundary. Returns all of `s` when it's already within budget. Never
/// panics.
pub(crate) fn head(s: &str, max_bytes: usize) -> &str {
    let mut end = max_bytes.min(s.len());
    while end > 0 && !s.is_char_boundary(end) {
        end -= 1;
    }
    &s[..end]
}

/// Largest SUFFIX of `s` that fits in `max_bytes` and starts on a char
/// boundary. Returns all of `s` when it's already within budget. Never
/// panics. Used for path truncation where the tail (basename) matters.
pub(crate) fn tail(s: &str, max_bytes: usize) -> &str {
    let mut start = s.len().saturating_sub(max_bytes);
    while start < s.len() && !s.is_char_boundary(start) {
        start += 1;
    }
    &s[start..]
}

/// Largest byte index `<= n` that's on a UTF-8 char boundary. Use to floor a
/// head-cut so slicing never panics on a multibyte split.
pub(crate) fn char_boundary_at_or_before(s: &str, n: usize) -> usize {
    if n >= s.len() {
        return s.len();
    }
    let mut i = n;
    while i > 0 && !s.is_char_boundary(i) {
        i -= 1;
    }
    i
}

/// Smallest byte index `>= n` that's on a UTF-8 char boundary. Use to ceil a
/// tail-cut so slicing never panics on a multibyte split.
pub(crate) fn char_boundary_at_or_after(s: &str, n: usize) -> usize {
    if n >= s.len() {
        return s.len();
    }
    let mut i = n;
    while i < s.len() && !s.is_char_boundary(i) {
        i += 1;
    }
    i
}

/// Cap `s` to at most `max_bytes` bytes (UTF-8-safe), appending `…` when it had
/// to truncate. The `…` (3 bytes) fits within the budget. Returns `s` unchanged
/// when already within budget. For DISPLAY / error text only — not model-facing
/// (use the head/tail truncators for prompt context, which carry instructive
/// markers).
pub(crate) fn ellipsize(s: &str, max_bytes: usize) -> String {
    if s.len() <= max_bytes {
        return s.to_string();
    }
    format!("{}…", head(s, max_bytes.saturating_sub('…'.len_utf8())))
}

/// First line of `content`, capped at 80 chars (77 + `...`). The
/// preview shape shared by memory breadcrumb indexes and curator
/// audit reports (dirge-rwrg — was duplicated byte-for-byte in
/// memory_db and memory_curator). Char-based, UTF-8 safe.
pub(crate) fn first_line_preview(content: &str) -> String {
    let first = content.lines().next().unwrap_or("").trim();
    if first.chars().count() <= 80 {
        first.to_string()
    } else {
        let cut: String = first.chars().take(77).collect();
        format!("{cut}...")
    }
}

/// Short display prefix of an id — its first 8 characters. Used across the UI
/// to compact session / subagent / notification / plugin ids for display.
/// Char-based (UTF-8 safe) and consistent everywhere, replacing the ~9
/// scattered `id.chars().take(8).collect()` copies.
pub(crate) fn short_id(id: &str) -> String {
    id.chars().take(8).collect()
}

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

    #[test]
    fn head_ascii_within_and_over_budget() {
        assert_eq!(head("hello", 10), "hello");
        assert_eq!(head("hello", 3), "hel");
        assert_eq!(head("hello", 0), "");
    }

    #[test]
    fn head_never_splits_a_multibyte_char() {
        // "é" is 2 bytes; cutting at byte 1 would split it.
        let s = "café"; // c a f é  -> bytes: 1 1 1 2 = 5
        assert_eq!(head(s, 4), "caf"); // byte 4 is mid-'é' -> floor to 3
        assert_eq!(head(s, 5), "café");
        // CJK (3 bytes each) and emoji (4 bytes) crossing the cut.
        let cjk = "日本語"; // 9 bytes
        assert_eq!(head(cjk, 4), "日"); // floor 4 -> 3
        assert_eq!(head(cjk, 3), "日");
        let emoji = "a😀b"; // 1 + 4 + 1
        assert_eq!(head(emoji, 3), "a"); // floor 3 -> 1 (😀 is bytes 1..5)
        assert_eq!(head(emoji, 5), "a😀");
    }

    /// The exact reported panic shape: a 3-byte char straddling a fixed
    /// byte cut must not panic.
    #[test]
    fn head_handles_multibyte_straddling_a_large_cut() {
        let mut s = "a".repeat(199);
        s.push('世'); // 3 bytes spanning offsets 199..202
        s.push_str(&"b".repeat(50));
        let cut = head(&s, 200); // byte 200 is mid-'世'
        assert!(s.starts_with(cut));
        assert_eq!(cut.len(), 199, "floored below the multibyte char");
    }

    #[test]
    fn tail_never_splits_a_multibyte_char() {
        let s = "café"; // bytes: c a f é(2) -> len 5
        assert_eq!(tail(s, 2), "é"); // 'é' is the last 2 bytes
        assert_eq!(tail(s, 3), "fé"); // start 2 is on a boundary ('f')
        assert_eq!(tail(s, 10), "café");
        let cjk = "日本語";
        assert_eq!(tail(cjk, 4), "語"); // last 4 bytes start mid-'本' -> ceil to '語'
        assert_eq!(tail(cjk, 0), "");
    }

    #[test]
    fn ellipsize_caps_and_appends_marker_utf8_safe() {
        assert_eq!(ellipsize("short", 100), "short"); // within budget → unchanged
        // 3-byte '…' reserved within the budget.
        assert_eq!(ellipsize("abcdefgh", 6), "abc…");
        // Never splits a multibyte char: budget 7 reserves 3 for '…', leaves 4
        // bytes → one full CJK char (3 bytes), floored off the 2nd.
        assert_eq!(ellipsize("日本語", 7), "日…");
    }

    #[test]
    fn char_boundary_helpers_floor_and_ceil() {
        let cjk = "日本語"; // each char is 3 bytes
        assert_eq!(char_boundary_at_or_before(cjk, 4), 3); // mid-'本' → floor to 3
        assert_eq!(char_boundary_at_or_after(cjk, 4), 6); // mid-'本' → ceil to 6
        assert_eq!(char_boundary_at_or_before(cjk, 99), cjk.len());
    }
}