//! Utilities for truncating large chunks of output while preserving a prefix//! and suffix on UTF-8 boundaries.const APPROX_BYTES_PER_TOKEN: usize = 4;/// Truncate a string to `max_bytes` using a character-count marker.pub fn truncate_middle_chars(s: &str, max_bytes: usize) -> String {    truncate_with_byte_estimate(s, max_bytes, /*use_tokens*/ false)}/// Truncate the middle of a UTF-8 string to at most `max_tokens` approximate/// tokens, preserving the beginning and the end. Returns the possibly/// truncated string and `Some(original_token_count)` if truncation occurred;/// otherwise returns the original string and `None`.pub fn truncate_middle_with_token_budget(s: &str, max_tokens: usize) -> (String, Option<u64>) {    if s.is_empty() {        return (String::new(), None);    }    if max_tokens > 0 && s.len() <= approx_bytes_for_tokens(max_tokens) {        return (s.to_string(), None);    }    let truncated = truncate_with_byte_estimate(        s,        approx_bytes_for_tokens(max_tokens),        /*use_tokens*/ true,    );    let total_tokens = u64::try_from(approx_token_count(s)).unwrap_or(u64::MAX);    if truncated == s {        (truncated, None)    } else {        (truncated, Some(total_tokens))    }}fn truncate_with_byte_estimate(s: &str, max_bytes: usize, use_tokens: bool) -> String {    if s.is_empty() {        return String::new();    }    let total_chars = s.chars().count();    if max_bytes == 0 {        return format_truncation_marker(            use_tokens,            removed_units(use_tokens, s.len(), total_chars),        );    }    if s.len() <= max_bytes {        return s.to_string();    }    let total_bytes = s.len();    let (left_budget, right_budget) = split_budget(max_bytes);    let (removed_chars, left, right) = split_string(s, left_budget, right_budget);    let marker = format_truncation_marker(        use_tokens,        removed_units(            use_tokens,            total_bytes.saturating_sub(max_bytes),            removed_chars,        ),    );    assemble_truncated_output(left, right, &marker)}pub fn approx_token_count(text: &str) -> usize {    let len = text.len();    len.saturating_add(APPROX_BYTES_PER_TOKEN.saturating_sub(1)) / APPROX_BYTES_PER_TOKEN}pub fn approx_bytes_for_tokens(tokens: usize) -> usize {    tokens.saturating_mul(APPROX_BYTES_PER_TOKEN)}pub fn approx_tokens_from_byte_count(bytes: usize) -> u64 {    let bytes_u64 = bytes as u64;    bytes_u64.saturating_add((APPROX_BYTES_PER_TOKEN as u64).saturating_sub(1))        / (APPROX_BYTES_PER_TOKEN as u64)}fn split_string(s: &str, beginning_bytes: usize, end_bytes: usize) -> (usize, &str, &str) {    if s.is_empty() {        return (0, "", "");    }    let len = s.len();    let tail_start_target = len.saturating_sub(end_bytes);    let mut prefix_end = 0usize;    let mut suffix_start = len;    let mut removed_chars = 0usize;    let mut suffix_started = false;    for (idx, ch) in s.char_indices() {        let char_end = idx + ch.len_utf8();        if char_end <= beginning_bytes {            prefix_end = char_end;            continue;        }        if idx >= tail_start_target {            if !suffix_started {                suffix_start = idx;                suffix_started = true;            }            continue;        }        removed_chars = removed_chars.saturating_add(1);    }    if suffix_start < prefix_end {        suffix_start = prefix_end;    }    let before = &s[..prefix_end];    let after = &s[suffix_start..];    (removed_chars, before, after)}fn split_budget(budget: usize) -> (usize, usize) {    let left = budget / 2;    (left, budget - left)}fn format_truncation_marker(use_tokens: bool, removed_count: u64) -> String {    if use_tokens {        format!("…{removed_count} tokens truncated…")    } else {        format!("…{removed_count} chars truncated…")    }}fn removed_units(use_tokens: bool, removed_bytes: usize, removed_chars: usize) -> u64 {    if use_tokens {        approx_tokens_from_byte_count(removed_bytes)    } else {        u64::try_from(removed_chars).unwrap_or(u64::MAX)    }}fn assemble_truncated_output(prefix: &str, suffix: &str, marker: &str) -> String {    let mut out = String::with_capacity(prefix.len() + marker.len() + suffix.len() + 1);    out.push_str(prefix);    out.push_str(marker);    out.push_str(suffix);    out}#[cfg(test)]mod tests;