codewhale-tui 0.9.0

use std::sync::{Arc, Mutex};

pub(super) fn take_delta_from_buffer(
    buffer: &Arc<Mutex<Vec<u8>>>,
    cursor: &mut usize,
) -> (Vec<u8>, usize) {
    let guard = buffer.lock().unwrap_or_else(|e| e.into_inner());
    let total = guard.len();
    let start = (*cursor).min(total);
    // Clone only the unread portion (the delta), not the entire accumulated buffer.
    // Long-running processes can produce megabytes of output; cloning the full
    // buffer on every poll held the ShellManager mutex for O(total_bytes) time.
    let delta = guard[start..].to_vec();
    *cursor = total;
    (delta, total)
}

/// Read only the tail of a byte buffer and return (total_len, tail_string).
///
/// Avoids cloning the full buffer when only a trailing excerpt is needed
/// (e.g. for the job-panel display). `max_tail_chars` is in Unicode scalar
/// values; we read at most `max_tail_chars * 4` bytes from the end to account
/// for multi-byte UTF-8 sequences.
pub(super) fn tail_from_buffer(
    buffer: &Arc<Mutex<Vec<u8>>>,
    max_tail_chars: usize,
) -> (usize, String) {
    let guard = buffer.lock().unwrap_or_else(|e| e.into_inner());
    let total = guard.len();
    // Over-estimate byte count (4 bytes per char worst case for UTF-8).
    let mut tail_start = total.saturating_sub(max_tail_chars.saturating_mul(4));
    // Snap forward to the next valid UTF-8 codepoint boundary so we don't
    // pass a slice beginning with continuation bytes (0x80-0xBF) to
    // from_utf8_lossy, which would emit a leading U+FFFD replacement char.
    while tail_start < total && (guard[tail_start] & 0xC0) == 0x80 {
        tail_start += 1;
    }
    let tail_str = String::from_utf8_lossy(&guard[tail_start..]).into_owned();
    (total, tail_text(&tail_str, max_tail_chars))
}

fn tail_text(text: &str, max_chars: usize) -> String {
    if text.chars().count() <= max_chars {
        return text.to_string();
    }
    let tail = text
        .chars()
        .rev()
        .take(max_chars)
        .collect::<Vec<_>>()
        .into_iter()
        .rev()
        .collect::<String>();
    format!("...{tail}")
}