clanker-agent/packages/tui/src/utils.ts

import { eastAsianWidth } from "get-east-asian-width";

// Grapheme segmenter (shared instance)
const segmenter = new Intl.Segmenter(undefined, { granularity: "grapheme" });

/**
 * Get the shared grapheme segmenter instance.
 */
export function getSegmenter(): Intl.Segmenter {
  return segmenter;
}

/**
 * Check if a grapheme cluster (after segmentation) could possibly be an RGI emoji.
 * This is a fast heuristic to avoid the expensive rgiEmojiRegex test.
 * The tested Unicode blocks are deliberately broad to account for future
 * Unicode additions.
 */
function couldBeEmoji(segment: string): boolean {
  const cp = segment.codePointAt(0)!;
  return (
    (cp >= 0x1f000 && cp <= 0x1fbff) || // Emoji and Pictograph
    (cp >= 0x2300 && cp <= 0x23ff) || // Misc technical
    (cp >= 0x2600 && cp <= 0x27bf) || // Misc symbols, dingbats
    (cp >= 0x2b50 && cp <= 0x2b55) || // Specific stars/circles
    segment.includes("\uFE0F") || // Contains VS16 (emoji presentation selector)
    segment.length > 2 // Multi-codepoint sequences (ZWJ, skin tones, etc.)
  );
}

// Regexes for character classification (same as string-width library)
const zeroWidthRegex =
  /^(?:\p{Default_Ignorable_Code_Point}|\p{Control}|\p{Mark}|\p{Surrogate})+$/v;
const leadingNonPrintingRegex =
  /^[\p{Default_Ignorable_Code_Point}\p{Control}\p{Format}\p{Mark}\p{Surrogate}]+/v;
const rgiEmojiRegex = /^\p{RGI_Emoji}$/v;

// Cache for non-ASCII strings
const WIDTH_CACHE_SIZE = 512;
const widthCache = new Map<string, number>();

/**
 * Calculate the terminal width of a single grapheme cluster.
 * Based on code from the string-width library, but includes a possible-emoji
 * check to avoid running the RGI_Emoji regex unnecessarily.
 */
function graphemeWidth(segment: string): number {
  // Zero-width clusters
  if (zeroWidthRegex.test(segment)) {
    return 0;
  }

  // Emoji check with pre-filter
  if (couldBeEmoji(segment) && rgiEmojiRegex.test(segment)) {
    return 2;
  }

  // Get base visible codepoint
  const base = segment.replace(leadingNonPrintingRegex, "");
  const cp = base.codePointAt(0);
  if (cp === undefined) {
    return 0;
  }

  // Regional indicator symbols (U+1F1E6..U+1F1FF) are often rendered as
  // full-width emoji in terminals, even when isolated during streaming.
  // Keep width conservative (2) to avoid terminal auto-wrap drift artifacts.
  if (cp >= 0x1f1e6 && cp <= 0x1f1ff) {
    return 2;
  }

  let width = eastAsianWidth(cp);

  // Trailing halfwidth/fullwidth forms
  if (segment.length > 1) {
    for (const char of segment.slice(1)) {
      const c = char.codePointAt(0)!;
      if (c >= 0xff00 && c <= 0xffef) {
        width += eastAsianWidth(c);
      }
    }
  }

  return width;
}

/**
 * Calculate the visible width of a string in terminal columns.
 */
export function visibleWidth(str: string): number {
  if (str.length === 0) {
    return 0;
  }

  // Fast path: pure ASCII printable
  let isPureAscii = true;
  for (let i = 0; i < str.length; i++) {
    const code = str.charCodeAt(i);
    if (code < 0x20 || code > 0x7e) {
      isPureAscii = false;
      break;
    }
  }
  if (isPureAscii) {
    return str.length;
  }

  // Check cache
  const cached = widthCache.get(str);
  if (cached !== undefined) {
    return cached;
  }

  // Normalize: tabs to 3 spaces, strip ANSI escape codes
  let clean = str;
  if (str.includes("\t")) {
    clean = clean.replace(/\t/g, "   ");
  }
  if (clean.includes("\x1b")) {
    // Strip supported ANSI/OSC/APC escape sequences in one pass.
    // This covers CSI styling/cursor codes, OSC hyperlinks and prompt markers,
    // and APC sequences like CURSOR_MARKER.
    let stripped = "";
    let i = 0;
    while (i < clean.length) {
      const ansi = extractAnsiCode(clean, i);
      if (ansi) {
        i += ansi.length;
        continue;
      }
      stripped += clean[i];
      i++;
    }
    clean = stripped;
  }

  // Calculate width
  let width = 0;
  for (const { segment } of segmenter.segment(clean)) {
    width += graphemeWidth(segment);
  }

  // Cache result
  if (widthCache.size >= WIDTH_CACHE_SIZE) {
    const firstKey = widthCache.keys().next().value;
    if (firstKey !== undefined) {
      widthCache.delete(firstKey);
    }
  }
  widthCache.set(str, width);

  return width;
}

/**
 * Extract ANSI escape sequences from a string at the given position.
 */
export function extractAnsiCode(
  str: string,
  pos: number,
): { code: string; length: number } | null {
  if (pos >= str.length || str[pos] !== "\x1b") return null;

  const next = str[pos + 1];

  // CSI sequence: ESC [ ... m/G/K/H/J
  if (next === "[") {
    let j = pos + 2;
    while (j < str.length && !/[mGKHJ]/.test(str[j]!)) j++;
    if (j < str.length)
      return { code: str.substring(pos, j + 1), length: j + 1 - pos };
    return null;
  }

  // OSC sequence: ESC ] ... BEL or ESC ] ... ST (ESC \)
  // Used for hyperlinks (OSC 8), window titles, etc.
  if (next === "]") {
    let j = pos + 2;
    while (j < str.length) {
      if (str[j] === "\x07")
        return { code: str.substring(pos, j + 1), length: j + 1 - pos };
      if (str[j] === "\x1b" && str[j + 1] === "\\")
        return { code: str.substring(pos, j + 2), length: j + 2 - pos };
      j++;
    }
    return null;
  }

  // APC sequence: ESC _ ... BEL or ESC _ ... ST (ESC \)
  // Used for cursor marker and application-specific commands
  if (next === "_") {
    let j = pos + 2;
    while (j < str.length) {
      if (str[j] === "\x07")
        return { code: str.substring(pos, j + 1), length: j + 1 - pos };
      if (str[j] === "\x1b" && str[j + 1] === "\\")
        return { code: str.substring(pos, j + 2), length: j + 2 - pos };
      j++;
    }
    return null;
  }

  return null;
}

/**
 * Track active ANSI SGR codes to preserve styling across line breaks.
 */
class AnsiCodeTracker {
  // Track individual attributes separately so we can reset them specifically
  private bold = false;
  private dim = false;
  private italic = false;
  private underline = false;
  private blink = false;
  private inverse = false;
  private hidden = false;
  private strikethrough = false;
  private fgColor: string | null = null; // Stores the full code like "31" or "38;5;240"
  private bgColor: string | null = null; // Stores the full code like "41" or "48;5;240"

  process(ansiCode: string): void {
    if (!ansiCode.endsWith("m")) {
      return;
    }

    // Extract the parameters between \x1b[ and m
    const match = ansiCode.match(/\x1b\[([\d;]*)m/);
    if (!match) return;

    const params = match[1];
    if (params === "" || params === "0") {
      // Full reset
      this.reset();
      return;
    }

    // Parse parameters (can be semicolon-separated)
    const parts = params.split(";");
    let i = 0;
    while (i < parts.length) {
      const code = Number.parseInt(parts[i], 10);

      // Handle 256-color and RGB codes which consume multiple parameters
      if (code === 38 || code === 48) {
        // 38;5;N (256 color fg) or 38;2;R;G;B (RGB fg)
        // 48;5;N (256 color bg) or 48;2;R;G;B (RGB bg)
        if (parts[i + 1] === "5" && parts[i + 2] !== undefined) {
          // 256 color: 38;5;N or 48;5;N
          const colorCode = `${parts[i]};${parts[i + 1]};${parts[i + 2]}`;
          if (code === 38) {
            this.fgColor = colorCode;
          } else {
            this.bgColor = colorCode;
          }
          i += 3;
          continue;
        } else if (parts[i + 1] === "2" && parts[i + 4] !== undefined) {
          // RGB color: 38;2;R;G;B or 48;2;R;G;B
          const colorCode = `${parts[i]};${parts[i + 1]};${parts[i + 2]};${parts[i + 3]};${parts[i + 4]}`;
          if (code === 38) {
            this.fgColor = colorCode;
          } else {
            this.bgColor = colorCode;
          }
          i += 5;
          continue;
        }
      }

      // Standard SGR codes
      switch (code) {
        case 0:
          this.reset();
          break;
        case 1:
          this.bold = true;
          break;
        case 2:
          this.dim = true;
          break;
        case 3:
          this.italic = true;
          break;
        case 4:
          this.underline = true;
          break;
        case 5:
          this.blink = true;
          break;
        case 7:
          this.inverse = true;
          break;
        case 8:
          this.hidden = true;
          break;
        case 9:
          this.strikethrough = true;
          break;
        case 21:
          this.bold = false;
          break; // Some terminals
        case 22:
          this.bold = false;
          this.dim = false;
          break;
        case 23:
          this.italic = false;
          break;
        case 24:
          this.underline = false;
          break;
        case 25:
          this.blink = false;
          break;
        case 27:
          this.inverse = false;
          break;
        case 28:
          this.hidden = false;
          break;
        case 29:
          this.strikethrough = false;
          break;
        case 39:
          this.fgColor = null;
          break; // Default fg
        case 49:
          this.bgColor = null;
          break; // Default bg
        default:
          // Standard foreground colors 30-37, 90-97
          if ((code >= 30 && code <= 37) || (code >= 90 && code <= 97)) {
            this.fgColor = String(code);
          }
          // Standard background colors 40-47, 100-107
          else if ((code >= 40 && code <= 47) || (code >= 100 && code <= 107)) {
            this.bgColor = String(code);
          }
          break;
      }
      i++;
    }
  }

  private reset(): void {
    this.bold = false;
    this.dim = false;
    this.italic = false;
    this.underline = false;
    this.blink = false;
    this.inverse = false;
    this.hidden = false;
    this.strikethrough = false;
    this.fgColor = null;
    this.bgColor = null;
  }

  /** Clear all state for reuse. */
  clear(): void {
    this.reset();
  }

  getActiveCodes(): string {
    const codes: string[] = [];
    if (this.bold) codes.push("1");
    if (this.dim) codes.push("2");
    if (this.italic) codes.push("3");
    if (this.underline) codes.push("4");
    if (this.blink) codes.push("5");
    if (this.inverse) codes.push("7");
    if (this.hidden) codes.push("8");
    if (this.strikethrough) codes.push("9");
    if (this.fgColor) codes.push(this.fgColor);
    if (this.bgColor) codes.push(this.bgColor);

    if (codes.length === 0) return "";
    return `\x1b[${codes.join(";")}m`;
  }

  hasActiveCodes(): boolean {
    return (
      this.bold ||
      this.dim ||
      this.italic ||
      this.underline ||
      this.blink ||
      this.inverse ||
      this.hidden ||
      this.strikethrough ||
      this.fgColor !== null ||
      this.bgColor !== null
    );
  }

  /**
   * Get reset codes for attributes that need to be turned off at line end,
   * specifically underline which bleeds into padding.
   * Returns empty string if no problematic attributes are active.
   */
  getLineEndReset(): string {
    // Only underline causes visual bleeding into padding
    // Other attributes like colors don't visually bleed to padding
    if (this.underline) {
      return "\x1b[24m"; // Underline off only
    }
    return "";
  }
}

function updateTrackerFromText(text: string, tracker: AnsiCodeTracker): void {
  let i = 0;
  while (i < text.length) {
    const ansiResult = extractAnsiCode(text, i);
    if (ansiResult) {
      tracker.process(ansiResult.code);
      i += ansiResult.length;
    } else {
      i++;
    }
  }
}

/**
 * Split text into words while keeping ANSI codes attached.
 */
function splitIntoTokensWithAnsi(text: string): string[] {
  const tokens: string[] = [];
  let current = "";
  let pendingAnsi = ""; // ANSI codes waiting to be attached to next visible content
  let inWhitespace = false;
  let i = 0;

  while (i < text.length) {
    const ansiResult = extractAnsiCode(text, i);
    if (ansiResult) {
      // Hold ANSI codes separately - they'll be attached to the next visible char
      pendingAnsi += ansiResult.code;
      i += ansiResult.length;
      continue;
    }

    const char = text[i];
    const charIsSpace = char === " ";

    if (charIsSpace !== inWhitespace && current) {
      // Switching between whitespace and non-whitespace, push current token
      tokens.push(current);
      current = "";
    }

    // Attach any pending ANSI codes to this visible character
    if (pendingAnsi) {
      current += pendingAnsi;
      pendingAnsi = "";
    }

    inWhitespace = charIsSpace;
    current += char;
    i++;
  }

  // Handle any remaining pending ANSI codes (attach to last token)
  if (pendingAnsi) {
    current += pendingAnsi;
  }

  if (current) {
    tokens.push(current);
  }

  return tokens;
}

/**
 * Wrap text with ANSI codes preserved.
 *
 * ONLY does word wrapping - NO padding, NO background colors.
 * Returns lines where each line is <= width visible chars.
 * Active ANSI codes are preserved across line breaks.
 *
 * @param text - Text to wrap (may contain ANSI codes and newlines)
 * @param width - Maximum visible width per line
 * @returns Array of wrapped lines (NOT padded to width)
 */
export function wrapTextWithAnsi(text: string, width: number): string[] {
  if (!text) {
    return [""];
  }

  // Handle newlines by processing each line separately
  // Track ANSI state across lines so styles carry over after literal newlines
  const inputLines = text.split("\n");
  const result: string[] = [];
  const tracker = new AnsiCodeTracker();

  for (const inputLine of inputLines) {
    // Prepend active ANSI codes from previous lines (except for first line)
    const prefix = result.length > 0 ? tracker.getActiveCodes() : "";
    result.push(...wrapSingleLine(prefix + inputLine, width));
    // Update tracker with codes from this line for next iteration
    updateTrackerFromText(inputLine, tracker);
  }

  return result.length > 0 ? result : [""];
}

function wrapSingleLine(line: string, width: number): string[] {
  if (!line) {
    return [""];
  }

  const visibleLength = visibleWidth(line);
  if (visibleLength <= width) {
    return [line];
  }

  const wrapped: string[] = [];
  const tracker = new AnsiCodeTracker();
  const tokens = splitIntoTokensWithAnsi(line);

  let currentLine = "";
  let currentVisibleLength = 0;

  for (const token of tokens) {
    const tokenVisibleLength = visibleWidth(token);
    const isWhitespace = token.trim() === "";

    // Token itself is too long - break it character by character
    if (tokenVisibleLength > width && !isWhitespace) {
      if (currentLine) {
        // Add specific reset for underline only (preserves background)
        const lineEndReset = tracker.getLineEndReset();
        if (lineEndReset) {
          currentLine += lineEndReset;
        }
        wrapped.push(currentLine);
        currentLine = "";
        currentVisibleLength = 0;
      }

      // Break long token - breakLongWord handles its own resets
      const broken = breakLongWord(token, width, tracker);
      wrapped.push(...broken.slice(0, -1));
      currentLine = broken[broken.length - 1];
      currentVisibleLength = visibleWidth(currentLine);
      continue;
    }

    // Check if adding this token would exceed width
    const totalNeeded = currentVisibleLength + tokenVisibleLength;

    if (totalNeeded > width && currentVisibleLength > 0) {
      // Trim trailing whitespace, then add underline reset (not full reset, to preserve background)
      let lineToWrap = currentLine.trimEnd();
      const lineEndReset = tracker.getLineEndReset();
      if (lineEndReset) {
        lineToWrap += lineEndReset;
      }
      wrapped.push(lineToWrap);
      if (isWhitespace) {
        // Don't start new line with whitespace
        currentLine = tracker.getActiveCodes();
        currentVisibleLength = 0;
      } else {
        currentLine = tracker.getActiveCodes() + token;
        currentVisibleLength = tokenVisibleLength;
      }
    } else {
      // Add to current line
      currentLine += token;
      currentVisibleLength += tokenVisibleLength;
    }

    updateTrackerFromText(token, tracker);
  }

  if (currentLine) {
    // No reset at end of final line - let caller handle it
    wrapped.push(currentLine);
  }

  // Trailing whitespace can cause lines to exceed the requested width
  return wrapped.length > 0 ? wrapped.map((line) => line.trimEnd()) : [""];
}

const PUNCTUATION_REGEX = /[(){}[\]<>.,;:'"!?+\-=*/\\|&%^$#@~`]/;

/**
 * Check if a character is whitespace.
 */
export function isWhitespaceChar(char: string): boolean {
  return /\s/.test(char);
}

/**
 * Check if a character is punctuation.
 */
export function isPunctuationChar(char: string): boolean {
  return PUNCTUATION_REGEX.test(char);
}

function breakLongWord(
  word: string,
  width: number,
  tracker: AnsiCodeTracker,
): string[] {
  const lines: string[] = [];
  let currentLine = tracker.getActiveCodes();
  let currentWidth = 0;

  // First, separate ANSI codes from visible content
  // We need to handle ANSI codes specially since they're not graphemes
  let i = 0;
  const segments: Array<{ type: "ansi" | "grapheme"; value: string }> = [];

  while (i < word.length) {
    const ansiResult = extractAnsiCode(word, i);
    if (ansiResult) {
      segments.push({ type: "ansi", value: ansiResult.code });
      i += ansiResult.length;
    } else {
      // Find the next ANSI code or end of string
      let end = i;
      while (end < word.length) {
        const nextAnsi = extractAnsiCode(word, end);
        if (nextAnsi) break;
        end++;
      }
      // Segment this non-ANSI portion into graphemes
      const textPortion = word.slice(i, end);
      for (const seg of segmenter.segment(textPortion)) {
        segments.push({ type: "grapheme", value: seg.segment });
      }
      i = end;
    }
  }

  // Now process segments
  for (const seg of segments) {
    if (seg.type === "ansi") {
      currentLine += seg.value;
      tracker.process(seg.value);
      continue;
    }

    const grapheme = seg.value;
    // Skip empty graphemes to avoid issues with string-width calculation
    if (!grapheme) continue;

    const graphemeWidth = visibleWidth(grapheme);

    if (currentWidth + graphemeWidth > width) {
      // Add specific reset for underline only (preserves background)
      const lineEndReset = tracker.getLineEndReset();
      if (lineEndReset) {
        currentLine += lineEndReset;
      }
      lines.push(currentLine);
      currentLine = tracker.getActiveCodes();
      currentWidth = 0;
    }

    currentLine += grapheme;
    currentWidth += graphemeWidth;
  }

  if (currentLine) {
    // No reset at end of final segment - caller handles continuation
    lines.push(currentLine);
  }

  return lines.length > 0 ? lines : [""];
}

/**
 * Apply background color to a line, padding to full width.
 *
 * @param line - Line of text (may contain ANSI codes)
 * @param width - Total width to pad to
 * @param bgFn - Background color function
 * @returns Line with background applied and padded to width
 */
export function applyBackgroundToLine(
  line: string,
  width: number,
  bgFn: (text: string) => string,
): string {
  // Calculate padding needed
  const visibleLen = visibleWidth(line);
  const paddingNeeded = Math.max(0, width - visibleLen);
  const padding = " ".repeat(paddingNeeded);

  // Apply background to content + padding
  const withPadding = line + padding;
  return bgFn(withPadding);
}

/**
 * Truncate text to fit within a maximum visible width, adding ellipsis if needed.
 * Optionally pad with spaces to reach exactly maxWidth.
 * Properly handles ANSI escape codes (they don't count toward width).
 *
 * @param text - Text to truncate (may contain ANSI codes)
 * @param maxWidth - Maximum visible width
 * @param ellipsis - Ellipsis string to append when truncating (default: "...")
 * @param pad - If true, pad result with spaces to exactly maxWidth (default: false)
 * @returns Truncated text, optionally padded to exactly maxWidth
 */
export function truncateToWidth(
  text: string,
  maxWidth: number,
  ellipsis: string = "...",
  pad: boolean = false,
): string {
  const textVisibleWidth = visibleWidth(text);

  if (textVisibleWidth <= maxWidth) {
    return pad ? text + " ".repeat(maxWidth - textVisibleWidth) : text;
  }

  const ellipsisWidth = visibleWidth(ellipsis);
  const targetWidth = maxWidth - ellipsisWidth;

  if (targetWidth <= 0) {
    return ellipsis.substring(0, maxWidth);
  }

  // Separate ANSI codes from visible content using grapheme segmentation
  let i = 0;
  const segments: Array<{ type: "ansi" | "grapheme"; value: string }> = [];

  while (i < text.length) {
    const ansiResult = extractAnsiCode(text, i);
    if (ansiResult) {
      segments.push({ type: "ansi", value: ansiResult.code });
      i += ansiResult.length;
    } else {
      // Find the next ANSI code or end of string
      let end = i;
      while (end < text.length) {
        const nextAnsi = extractAnsiCode(text, end);
        if (nextAnsi) break;
        end++;
      }
      // Segment this non-ANSI portion into graphemes
      const textPortion = text.slice(i, end);
      for (const seg of segmenter.segment(textPortion)) {
        segments.push({ type: "grapheme", value: seg.segment });
      }
      i = end;
    }
  }

  // Build truncated string from segments
  let result = "";
  let currentWidth = 0;

  for (const seg of segments) {
    if (seg.type === "ansi") {
      result += seg.value;
      continue;
    }

    const grapheme = seg.value;
    // Skip empty graphemes to avoid issues with string-width calculation
    if (!grapheme) continue;

    const graphemeWidth = visibleWidth(grapheme);

    if (currentWidth + graphemeWidth > targetWidth) {
      break;
    }

    result += grapheme;
    currentWidth += graphemeWidth;
  }

  // Add reset code before ellipsis to prevent styling leaking into it
  const truncated = `${result}\x1b[0m${ellipsis}`;
  if (pad) {
    const truncatedWidth = visibleWidth(truncated);
    return truncated + " ".repeat(Math.max(0, maxWidth - truncatedWidth));
  }
  return truncated;
}

/**
 * Extract a range of visible columns from a line. Handles ANSI codes and wide chars.
 * @param strict - If true, exclude wide chars at boundary that would extend past the range
 */
export function sliceByColumn(
  line: string,
  startCol: number,
  length: number,
  strict = false,
): string {
  return sliceWithWidth(line, startCol, length, strict).text;
}

/** Like sliceByColumn but also returns the actual visible width of the result. */
export function sliceWithWidth(
  line: string,
  startCol: number,
  length: number,
  strict = false,
): { text: string; width: number } {
  if (length <= 0) return { text: "", width: 0 };
  const endCol = startCol + length;
  let result = "",
    resultWidth = 0,
    currentCol = 0,
    i = 0,
    pendingAnsi = "";

  while (i < line.length) {
    const ansi = extractAnsiCode(line, i);
    if (ansi) {
      if (currentCol >= startCol && currentCol < endCol) result += ansi.code;
      else if (currentCol < startCol) pendingAnsi += ansi.code;
      i += ansi.length;
      continue;
    }

    let textEnd = i;
    while (textEnd < line.length && !extractAnsiCode(line, textEnd)) textEnd++;

    for (const { segment } of segmenter.segment(line.slice(i, textEnd))) {
      const w = graphemeWidth(segment);
      const inRange = currentCol >= startCol && currentCol < endCol;
      const fits = !strict || currentCol + w <= endCol;
      if (inRange && fits) {
        if (pendingAnsi) {
          result += pendingAnsi;
          pendingAnsi = "";
        }
        result += segment;
        resultWidth += w;
      }
      currentCol += w;
      if (currentCol >= endCol) break;
    }
    i = textEnd;
    if (currentCol >= endCol) break;
  }
  return { text: result, width: resultWidth };
}

// Pooled tracker instance for extractSegments (avoids allocation per call)
const pooledStyleTracker = new AnsiCodeTracker();

/**
 * Extract "before" and "after" segments from a line in a single pass.
 * Used for overlay compositing where we need content before and after the overlay region.
 * Preserves styling from before the overlay that should affect content after it.
 */
export function extractSegments(
  line: string,
  beforeEnd: number,
  afterStart: number,
  afterLen: number,
  strictAfter = false,
): { before: string; beforeWidth: number; after: string; afterWidth: number } {
  let before = "",
    beforeWidth = 0,
    after = "",
    afterWidth = 0;
  let currentCol = 0,
    i = 0;
  let pendingAnsiBefore = "";
  let afterStarted = false;
  const afterEnd = afterStart + afterLen;

  // Track styling state so "after" inherits styling from before the overlay
  pooledStyleTracker.clear();

  while (i < line.length) {
    const ansi = extractAnsiCode(line, i);
    if (ansi) {
      // Track all SGR codes to know styling state at afterStart
      pooledStyleTracker.process(ansi.code);
      // Include ANSI codes in their respective segments
      if (currentCol < beforeEnd) {
        pendingAnsiBefore += ansi.code;
      } else if (
        currentCol >= afterStart &&
        currentCol < afterEnd &&
        afterStarted
      ) {
        // Only include after we've started "after" (styling already prepended)
        after += ansi.code;
      }
      i += ansi.length;
      continue;
    }

    let textEnd = i;
    while (textEnd < line.length && !extractAnsiCode(line, textEnd)) textEnd++;

    for (const { segment } of segmenter.segment(line.slice(i, textEnd))) {
      const w = graphemeWidth(segment);

      if (currentCol < beforeEnd) {
        if (pendingAnsiBefore) {
          before += pendingAnsiBefore;
          pendingAnsiBefore = "";
        }
        before += segment;
        beforeWidth += w;
      } else if (currentCol >= afterStart && currentCol < afterEnd) {
        const fits = !strictAfter || currentCol + w <= afterEnd;
        if (fits) {
          // On first "after" grapheme, prepend inherited styling from before overlay
          if (!afterStarted) {
            after += pooledStyleTracker.getActiveCodes();
            afterStarted = true;
          }
          after += segment;
          afterWidth += w;
        }
      }

      currentCol += w;
      // Early exit: done with "before" only, or done with both segments
      if (afterLen <= 0 ? currentCol >= beforeEnd : currentCol >= afterEnd)
        break;
    }
    i = textEnd;
    if (afterLen <= 0 ? currentCol >= beforeEnd : currentCol >= afterEnd) break;
  }

  return { before, beforeWidth, after, afterWidth };
}