Crosspoint/lib/Epub/Epub/ParsedText.cpp

#include "ParsedText.h"

#include <GfxRenderer.h>
#include <Utf8.h>

#include <algorithm>
#include <cmath>
#include <functional>
#include <limits>
#include <vector>

#include "hyphenation/Hyphenator.h"

constexpr int MAX_COST = std::numeric_limits<int>::max();

namespace {

// Soft hyphen byte pattern used throughout EPUBs (UTF-8 for U+00AD).
constexpr char SOFT_HYPHEN_UTF8[] = "\xC2\xAD";
constexpr size_t SOFT_HYPHEN_BYTES = 2;

// Returns the first rendered codepoint of a word (skipping leading soft hyphens).
uint32_t firstCodepoint(const std::string& word) {
  const auto* ptr = reinterpret_cast<const unsigned char*>(word.c_str());
  while (true) {
    const uint32_t cp = utf8NextCodepoint(&ptr);
    if (cp == 0) return 0;
    if (cp != 0x00AD) return cp;  // skip soft hyphens
  }
}

// Returns the last codepoint of a word by scanning backward for the start of the last UTF-8 sequence.
uint32_t lastCodepoint(const std::string& word) {
  if (word.empty()) return 0;
  // UTF-8 continuation bytes start with 10xxxxxx; scan backward to find the leading byte.
  size_t i = word.size() - 1;
  while (i > 0 && (static_cast<uint8_t>(word[i]) & 0xC0) == 0x80) {
    --i;
  }
  const auto* ptr = reinterpret_cast<const unsigned char*>(word.c_str() + i);
  return utf8NextCodepoint(&ptr);
}

bool containsSoftHyphen(const std::string& word) { return word.find(SOFT_HYPHEN_UTF8) != std::string::npos; }

// Removes every soft hyphen in-place so rendered glyphs match measured widths.
void stripSoftHyphensInPlace(std::string& word) {
  size_t pos = 0;
  while ((pos = word.find(SOFT_HYPHEN_UTF8, pos)) != std::string::npos) {
    word.erase(pos, SOFT_HYPHEN_BYTES);
  }
}

// Returns the advance width for a word while ignoring soft hyphen glyphs and optionally appending a visible hyphen.
// Uses advance width (sum of glyph advances + kerning) rather than bounding box width so that italic glyph overhangs
// don't inflate inter-word spacing.
uint16_t measureWordWidth(const GfxRenderer& renderer, const int fontId, const std::string& word,
                          const EpdFontFamily::Style style, const bool appendHyphen = false) {
  if (word.size() == 1 && word[0] == ' ' && !appendHyphen) {
    return renderer.getSpaceWidth(fontId, style);
  }
  const bool hasSoftHyphen = containsSoftHyphen(word);
  if (!hasSoftHyphen && !appendHyphen) {
    return renderer.getTextAdvanceX(fontId, word.c_str(), style);
  }

  std::string sanitized = word;
  if (hasSoftHyphen) {
    stripSoftHyphensInPlace(sanitized);
  }
  if (appendHyphen) {
    sanitized.push_back('-');
  }
  return renderer.getTextAdvanceX(fontId, sanitized.c_str(), style);
}

// Checks if a UTF-8 codepoint should be counted as part of a word for Focus Reading
bool isWordCharacter(uint32_t cp) {
  // ASCII range (Catches 95%+ of characters immediately)
  if (cp < 128) {
    // Bitwise trick: (cp | 0x20) converts uppercase ASCII to lowercase.
    // This checks for A-Z and a-z mathematically, avoiding memory lookups and <cctype>
    return ((cp | 0x20) >= 'a' && (cp | 0x20) <= 'z') || cp == '\'';
  }

  // General Punctuation Block, Currency, Math, Arrows, & Symbols (0x2000 - 0x2BFF)
  if (cp >= 0x2000 && cp <= 0x2BFF) {
    // Explicitly allow smart quotes, reject all other general punctuation (em-dashes, etc.)
    return cp == 0x2018 || cp == 0x2019;
  }

  // Latin-1 Punctuation Block (0x00A1 - 0x00BF)
  if (cp >= 0x00A1 && cp <= 0x00BF) {
    // Allow ordinal indicators and micro sign, reject the rest (¡, ¿, «, », etc.)
    return cp == 0x00AA || cp == 0x00B5 || cp == 0x00BA;
  }

  // Rejects Two-em dash, Three-em dash, Double oblique hyphen, etc.
  if (cp >= 0x2E00 && cp <= 0x2E7F) return false;

  // Rejects Modifier Minus (0x02D7), Small Hyphen (0xFE63), and Fullwidth Hyphen (0xFF0D)
  if (cp == 0x02D7 || cp == 0xFE63 || cp == 0xFF0D) return false;
  // Assume all other Unicode ranges (accented letters, Cyrillic, Greek, etc.) are valid

  return true;
}

}  // namespace

void ParsedText::addWord(std::string word, const EpdFontFamily::Style fontStyle, const bool underline,
                         const bool attachToPrevious) {
  if (word.empty()) return;

  EpdFontFamily::Style baseStyle = fontStyle;
  if (underline) {
    baseStyle = static_cast<EpdFontFamily::Style>(baseStyle | EpdFontFamily::UNDERLINE);
  }

  // Already-bold text should stay fully bold; focus splitting would make its suffix regular later.
  if (!this->focusReadingEnabled || (baseStyle & EpdFontFamily::BOLD) != 0) {
    words.push_back(std::move(word));
    wordStyles.push_back(baseStyle);
    wordContinues.push_back(attachToPrevious);
    wordIsFocusSuffix.push_back(false);
    return;
  }

  // --- FOCUS READING LOGIC BELOW ---

  // Pre-reserve capacity to prevent mid-word heap reallocations.
  size_t maxPossibleNewTokens = word.length();
  size_t requiredSize = words.size() + maxPossibleNewTokens;

  if (words.capacity() < requiredSize) {
    // Emulate standard geometric growth (doubling) to ensure we don't reallocate on every word.
    size_t newCapacity = words.capacity() * 2;

    // Ensure the doubled capacity is actually enough for this specific word
    if (newCapacity < requiredSize) {
      newCapacity = requiredSize;
    }
    // Set a sensible minimum starting size so the first few words don't trigger tiny reallocations
    if (newCapacity < 16) {
      newCapacity = 16;
    }

    words.reserve(newCapacity);
    wordStyles.reserve(newCapacity);
    wordContinues.reserve(newCapacity);
    wordIsFocusSuffix.reserve(newCapacity);
  }

  // Lambda helper to process and push individual sub-segments of the string
  // Use std::string_view to avoid heap allocations when slicing
  auto processSegment = [&](std::string_view segment, bool isWord, bool attach) {
    if (!isWord) {
      // Punctuation and Numbers stay regular
      words.emplace_back(segment);
      wordStyles.push_back(baseStyle);
      wordContinues.push_back(attach);
      wordIsFocusSuffix.push_back(false);
    } else {
      size_t charCount = 0;
      const unsigned char* countPtr = reinterpret_cast<const unsigned char*>(segment.data());
      const unsigned char* countEnd = countPtr + segment.length();

      while (countPtr < countEnd) {
        utf8NextCodepoint(&countPtr);
        charCount++;
      }

      // Target 45% for 1-bold at 4 chars and 3-bold at 7 chars with floor truncation
      constexpr size_t FOCUS_READING_PERCENT = 45;
      size_t targetBoldChars = (charCount * FOCUS_READING_PERCENT) / 100;
      targetBoldChars = std::clamp<size_t>(targetBoldChars, 1, 9);

      if (targetBoldChars >= charCount) {
        // Whole segment is bold - no suffix split needed
        words.emplace_back(segment);
        wordStyles.push_back(static_cast<EpdFontFamily::Style>(baseStyle | EpdFontFamily::BOLD));
        wordContinues.push_back(attach);
        wordIsFocusSuffix.push_back(false);
      } else {
        countPtr = reinterpret_cast<const unsigned char*>(segment.data());
        for (size_t i = 0; i < targetBoldChars; ++i) {
          utf8NextCodepoint(&countPtr);
        }
        size_t splitByteOffset = countPtr - reinterpret_cast<const unsigned char*>(segment.data());

        // Bold prefix
        words.emplace_back(segment.substr(0, splitByteOffset));
        wordStyles.push_back(static_cast<EpdFontFamily::Style>(baseStyle | EpdFontFamily::BOLD));
        wordContinues.push_back(attach);
        wordIsFocusSuffix.push_back(false);

        // Regular suffix - marked so extractLine can merge it back into single TextBlock entry
        words.emplace_back(segment.substr(splitByteOffset));
        wordStyles.push_back(baseStyle);
        wordContinues.push_back(true);
        wordIsFocusSuffix.push_back(true);
      }
    }
  };

  // Tokenize the string by alternating states (Word vs. Non-Word)
  const unsigned char* ptr = reinterpret_cast<const unsigned char*>(word.c_str());
  const unsigned char* end = ptr + word.length();

  const unsigned char* segmentStart = ptr;
  uint32_t firstCp = utf8NextCodepoint(&ptr);  // Consume the first char to determine initial state
  bool inWordSegment = isWordCharacter(firstCp);

  bool isFirstSegment = true;

  while (ptr < end) {
    const unsigned char* currentCpStart = ptr;
    uint32_t cp = utf8NextCodepoint(&ptr);
    bool isWordChar = isWordCharacter(cp);

    // Whenever the character type flips, slice off the segment we just completed and process it
    if (isWordChar != inWordSegment) {
      size_t segmentLen = currentCpStart - segmentStart;
      std::string_view segment(reinterpret_cast<const char*>(segmentStart), segmentLen);

      // Only the very first segment inherits the original attachToPrevious flag.
      // Every subsequent segment MUST attach=true so it glues seamlessly to the prefix.
      processSegment(segment, inWordSegment, isFirstSegment ? attachToPrevious : true);

      // Setup for the next segment
      segmentStart = currentCpStart;
      inWordSegment = isWordChar;
      isFirstSegment = false;
    }
  }

  // Process the final remaining segment
  size_t segmentLen = end - segmentStart;
  std::string_view segment(reinterpret_cast<const char*>(segmentStart), segmentLen);
  processSegment(segment, inWordSegment, isFirstSegment ? attachToPrevious : true);
}
// Consumes data to minimize memory usage
void ParsedText::layoutAndExtractLines(const GfxRenderer& renderer, const int fontId, const uint16_t viewportWidth,
                                       const std::function<void(std::shared_ptr<TextBlock>)>& processLine,
                                       const bool includeLastLine) {
  if (words.empty()) {
    return;
  }

  // Apply fixed transforms before any per-line layout work.
  applyParagraphIndent();

  // Ensure SD card font glyph metrics are loaded before measuring word widths.
  // For flash-based fonts isSdCardFont() returns false and this block is skipped
  // entirely — no heap allocation. For SD card fonts this reads glyph metadata
  // (advanceX only, no bitmaps) for all unique codepoints in this paragraph so
  // that calculateWordWidths() can measure text without on-demand SD I/O.
  if (renderer.isSdCardFont(fontId)) {
    // Style mask: only ask the SD font to load advances for styles actually
    // used in this paragraph. Style index is the low two bits (regular/bold/
    // italic/bold-italic); the underline bit is irrelevant to advance metrics.
    uint8_t styleMask = 0;
    for (auto s : wordStyles) {
      styleMask |= static_cast<uint8_t>(1u << (static_cast<uint8_t>(s) & 0x03));
    }
    if (styleMask == 0) styleMask = 0x01;  // defensive: regular only
    renderer.ensureSdCardFontReady(fontId, words, hyphenationEnabled, styleMask);
  }

  const int pageWidth = viewportWidth;
  auto wordWidths = calculateWordWidths(renderer, fontId);

  std::vector<size_t> lineBreakIndices;
  if (hyphenationEnabled) {
    // Use greedy layout that can split words mid-loop when a hyphenated prefix fits.
    lineBreakIndices = computeHyphenatedLineBreaks(renderer, fontId, pageWidth, wordWidths, wordContinues);
  } else {
    lineBreakIndices = computeLineBreaks(renderer, fontId, pageWidth, wordWidths, wordContinues);
  }
  const size_t lineCount = includeLastLine ? lineBreakIndices.size() : lineBreakIndices.size() - 1;

  for (size_t i = 0; i < lineCount; ++i) {
    extractLine(i, pageWidth, wordWidths, wordContinues, lineBreakIndices, processLine, renderer, fontId);
  }

  // Remove consumed words so size() reflects only remaining words
  if (lineCount > 0) {
    const size_t consumed = lineBreakIndices[lineCount - 1];
    words.erase(words.begin(), words.begin() + consumed);
    wordStyles.erase(wordStyles.begin(), wordStyles.begin() + consumed);
    wordContinues.erase(wordContinues.begin(), wordContinues.begin() + consumed);
    wordIsFocusSuffix.erase(wordIsFocusSuffix.begin(), wordIsFocusSuffix.begin() + consumed);
  }
}

std::vector<uint16_t> ParsedText::calculateWordWidths(const GfxRenderer& renderer, const int fontId) {
  std::vector<uint16_t> wordWidths;
  wordWidths.reserve(words.size());

  for (size_t i = 0; i < words.size(); ++i) {
    wordWidths.push_back(measureWordWidth(renderer, fontId, words[i], wordStyles[i]));
  }

  return wordWidths;
}

std::vector<size_t> ParsedText::computeLineBreaks(const GfxRenderer& renderer, const int fontId, const int pageWidth,
                                                  std::vector<uint16_t>& wordWidths, std::vector<bool>& continuesVec) {
  if (words.empty()) {
    return {};
  }

  // Calculate first line indent (only for left/justified text).
  // Positive text-indent (paragraph indent) is suppressed when extraParagraphSpacing is on.
  // Negative text-indent (hanging indent, e.g. margin-left:3em; text-indent:-1em) always applies —
  // it is structural (positions the bullet/marker), not decorative.
  const int firstLineIndent =
      blockStyle.textIndentDefined && (blockStyle.textIndent < 0 || !extraParagraphSpacing) &&
              (blockStyle.alignment == CssTextAlign::Justify || blockStyle.alignment == CssTextAlign::Left)
          ? blockStyle.textIndent
          : 0;

  // Ensure any word that would overflow even as the first entry on a line is split using fallback hyphenation.
  for (size_t i = 0; i < wordWidths.size(); ++i) {
    // First word needs to fit in reduced width if there's an indent
    const int effectiveWidth = i == 0 ? pageWidth - firstLineIndent : pageWidth;
    while (wordWidths[i] > effectiveWidth) {
      if (!hyphenateWordAtIndex(i, effectiveWidth, renderer, fontId, wordWidths, /*allowFallbackBreaks=*/true)) {
        break;
      }
    }
  }

  const size_t totalWordCount = words.size();

  // DP table to store the minimum badness (cost) of lines starting at index i
  std::vector<int> dp(totalWordCount);
  // 'ans[i]' stores the index 'j' of the *last word* in the optimal line starting at 'i'
  std::vector<size_t> ans(totalWordCount);

  // Base Case
  dp[totalWordCount - 1] = 0;
  ans[totalWordCount - 1] = totalWordCount - 1;

  for (int i = totalWordCount - 2; i >= 0; --i) {
    int currlen = 0;
    dp[i] = MAX_COST;

    // First line has reduced width due to text-indent
    const int effectivePageWidth = i == 0 ? pageWidth - firstLineIndent : pageWidth;

    for (size_t j = i; j < totalWordCount; ++j) {
      // Add space before word j, unless it's the first word on the line or a continuation
      int gap = 0;
      if (j > static_cast<size_t>(i) && !continuesVec[j]) {
        gap =
            renderer.getSpaceAdvance(fontId, lastCodepoint(words[j - 1]), firstCodepoint(words[j]), wordStyles[j - 1]);
      } else if (j > static_cast<size_t>(i) && continuesVec[j]) {
        // Cross-boundary kerning for continuation words (e.g. nonbreaking spaces, attached punctuation)
        gap = renderer.getKerning(fontId, lastCodepoint(words[j - 1]), firstCodepoint(words[j]), wordStyles[j - 1]);
      }
      currlen += wordWidths[j] + gap;

      if (currlen > effectivePageWidth) {
        break;
      }

      // Cannot break after word j if the next word attaches to it (continuation group)
      if (j + 1 < totalWordCount && continuesVec[j + 1]) {
        continue;
      }

      int cost;
      if (j == totalWordCount - 1) {
        cost = 0;  // Last line
      } else {
        const int remainingSpace = effectivePageWidth - currlen;
        // Use long long for the square to prevent overflow
        const long long cost_ll = static_cast<long long>(remainingSpace) * remainingSpace + dp[j + 1];

        if (cost_ll > MAX_COST) {
          cost = MAX_COST;
        } else {
          cost = static_cast<int>(cost_ll);
        }
      }

      if (cost < dp[i]) {
        dp[i] = cost;
        ans[i] = j;  // j is the index of the last word in this optimal line
      }
    }

    // Handle oversized word: if no valid configuration found, force single-word line
    // This prevents cascade failure where one oversized word breaks all preceding words
    if (dp[i] == MAX_COST) {
      ans[i] = i;  // Just this word on its own line
      // Inherit cost from next word to allow subsequent words to find valid configurations
      if (i + 1 < static_cast<int>(totalWordCount)) {
        dp[i] = dp[i + 1];
      } else {
        dp[i] = 0;
      }
    }
  }

  // Stores the index of the word that starts the next line (last_word_index + 1)
  std::vector<size_t> lineBreakIndices;
  size_t currentWordIndex = 0;

  while (currentWordIndex < totalWordCount) {
    size_t nextBreakIndex = ans[currentWordIndex] + 1;

    // Safety check: prevent infinite loop if nextBreakIndex doesn't advance
    if (nextBreakIndex <= currentWordIndex) {
      // Force advance by at least one word to avoid infinite loop
      nextBreakIndex = currentWordIndex + 1;
    }

    lineBreakIndices.push_back(nextBreakIndex);
    currentWordIndex = nextBreakIndex;
  }

  return lineBreakIndices;
}

void ParsedText::applyParagraphIndent() {
  if (extraParagraphSpacing || words.empty()) {
    return;
  }

  if (blockStyle.textIndentDefined) {
    // CSS text-indent is explicitly set (even if 0) - don't use fallback EmSpace
    // The actual indent positioning is handled in extractLine()
  } else if (blockStyle.alignment == CssTextAlign::Justify || blockStyle.alignment == CssTextAlign::Left) {
    // No CSS text-indent defined - use EmSpace fallback for visual indent
    words.front().insert(0, "\xe2\x80\x83");
  }
}

// Builds break indices while opportunistically splitting the word that would overflow the current line.
std::vector<size_t> ParsedText::computeHyphenatedLineBreaks(const GfxRenderer& renderer, const int fontId,
                                                            const int pageWidth, std::vector<uint16_t>& wordWidths,
                                                            std::vector<bool>& continuesVec) {
  // Calculate first line indent (only for left/justified text).
  // Positive text-indent (paragraph indent) is suppressed when extraParagraphSpacing is on.
  // Negative text-indent (hanging indent, e.g. margin-left:3em; text-indent:-1em) always applies —
  // it is structural (positions the bullet/marker), not decorative.
  const int firstLineIndent =
      blockStyle.textIndentDefined && (blockStyle.textIndent < 0 || !extraParagraphSpacing) &&
              (blockStyle.alignment == CssTextAlign::Justify || blockStyle.alignment == CssTextAlign::Left)
          ? blockStyle.textIndent
          : 0;

  std::vector<size_t> lineBreakIndices;
  size_t currentIndex = 0;
  bool isFirstLine = true;

  while (currentIndex < wordWidths.size()) {
    const size_t lineStart = currentIndex;
    int lineWidth = 0;

    // First line has reduced width due to text-indent
    const int effectivePageWidth = isFirstLine ? pageWidth - firstLineIndent : pageWidth;

    // Consume as many words as possible for current line, splitting when prefixes fit
    while (currentIndex < wordWidths.size()) {
      const bool isFirstWord = currentIndex == lineStart;
      int spacing = 0;
      if (!isFirstWord && !continuesVec[currentIndex]) {
        spacing = renderer.getSpaceAdvance(fontId, lastCodepoint(words[currentIndex - 1]),
                                           firstCodepoint(words[currentIndex]), wordStyles[currentIndex - 1]);
      } else if (!isFirstWord && continuesVec[currentIndex]) {
        // Cross-boundary kerning for continuation words (e.g. nonbreaking spaces, attached punctuation)
        spacing = renderer.getKerning(fontId, lastCodepoint(words[currentIndex - 1]),
                                      firstCodepoint(words[currentIndex]), wordStyles[currentIndex - 1]);
      }
      const int candidateWidth = spacing + wordWidths[currentIndex];

      // Word fits on current line
      if (lineWidth + candidateWidth <= effectivePageWidth) {
        lineWidth += candidateWidth;
        ++currentIndex;
        continue;
      }

      // Word would overflow — try to split based on hyphenation points
      const int availableWidth = effectivePageWidth - lineWidth - spacing;
      const bool allowFallbackBreaks = isFirstWord;  // Only for first word on line

      if (availableWidth > 0 &&
          hyphenateWordAtIndex(currentIndex, availableWidth, renderer, fontId, wordWidths, allowFallbackBreaks)) {
        // Prefix now fits; append it to this line and move to next line
        lineWidth += spacing + wordWidths[currentIndex];
        ++currentIndex;
        break;
      }

      // Could not split: force at least one word per line to avoid infinite loop
      if (currentIndex == lineStart) {
        lineWidth += candidateWidth;
        ++currentIndex;
      }
      break;
    }

    // Don't break before a continuation word (e.g., orphaned "?" after "question").
    // Backtrack to the start of the continuation group so the whole group moves to the next line.
    while (currentIndex > lineStart + 1 && currentIndex < wordWidths.size() && continuesVec[currentIndex]) {
      --currentIndex;
    }

    lineBreakIndices.push_back(currentIndex);
    isFirstLine = false;
  }

  return lineBreakIndices;
}

// Splits words[wordIndex] into prefix (adding a hyphen only when needed) and remainder when a legal breakpoint fits the
// available width.
bool ParsedText::hyphenateWordAtIndex(const size_t wordIndex, const int availableWidth, const GfxRenderer& renderer,
                                      const int fontId, std::vector<uint16_t>& wordWidths,
                                      const bool allowFallbackBreaks) {
  // Guard against invalid indices or zero available width before attempting to split.
  if (availableWidth <= 0 || wordIndex >= words.size()) {
    return false;
  }

  const std::string& word = words[wordIndex];
  const auto style = wordStyles[wordIndex];

  // Collect candidate breakpoints (byte offsets and hyphen requirements).
  auto breakInfos = Hyphenator::breakOffsets(word, allowFallbackBreaks);
  if (breakInfos.empty()) {
    return false;
  }

  size_t chosenOffset = 0;
  int chosenWidth = -1;
  bool chosenNeedsHyphen = true;

  // Iterate over each legal breakpoint and retain the widest prefix that still fits.
  for (const auto& info : breakInfos) {
    const size_t offset = info.byteOffset;
    if (offset == 0 || offset >= word.size()) {
      continue;
    }

    const bool needsHyphen = info.requiresInsertedHyphen;
    const int prefixWidth = measureWordWidth(renderer, fontId, word.substr(0, offset), style, needsHyphen);
    if (prefixWidth > availableWidth || prefixWidth <= chosenWidth) {
      continue;  // Skip if too wide or not an improvement
    }

    chosenWidth = prefixWidth;
    chosenOffset = offset;
    chosenNeedsHyphen = needsHyphen;
  }

  if (chosenWidth < 0) {
    // No hyphenation point produced a prefix that fits in the remaining space.
    return false;
  }

  // Split the word at the selected breakpoint and append a hyphen if required.
  std::string remainder = word.substr(chosenOffset);
  words[wordIndex].resize(chosenOffset);
  if (chosenNeedsHyphen) {
    words[wordIndex].push_back('-');
  }

  // Insert the remainder word (with matching style and continuation flag) directly after the prefix.
  words.insert(words.begin() + wordIndex + 1, remainder);
  wordStyles.insert(wordStyles.begin() + wordIndex + 1, style);
  // The hyphen remainder is not a focus suffix - it starts fresh on the next line.
  wordIsFocusSuffix.insert(wordIsFocusSuffix.begin() + wordIndex + 1, false);

  // Continuation flag handling after splitting a word into prefix + remainder.
  //
  // The prefix keeps the original word's continuation flag so that no-break-space groups
  // stay linked. The remainder always gets continues=false because it starts on the next
  // line and is not attached to the prefix.
  //
  // Example: "200&#xA0;Quadratkilometer" produces tokens:
  //   [0] "200"               continues=false
  //   [1] " "                 continues=true
  //   [2] "Quadratkilometer"  continues=true   <-- the word being split
  //
  // After splitting "Quadratkilometer" at "Quadrat-" / "kilometer":
  //   [0] "200"         continues=false
  //   [1] " "           continues=true
  //   [2] "Quadrat-"    continues=true   (KEPT — still attached to the no-break group)
  //   [3] "kilometer"   continues=false  (NEW — starts fresh on the next line)
  //
  // This lets the backtracking loop keep the entire prefix group ("200 Quadrat-") on one
  // line, while "kilometer" moves to the next line.
  // wordContinues[wordIndex] is intentionally left unchanged — the prefix keeps its original attachment.
  wordContinues.insert(wordContinues.begin() + wordIndex + 1, false);

  // Update cached widths to reflect the new prefix/remainder pairing.
  wordWidths[wordIndex] = static_cast<uint16_t>(chosenWidth);
  const uint16_t remainderWidth = measureWordWidth(renderer, fontId, remainder, style);
  wordWidths.insert(wordWidths.begin() + wordIndex + 1, remainderWidth);
  return true;
}

void ParsedText::extractLine(const size_t breakIndex, const int pageWidth, const std::vector<uint16_t>& wordWidths,
                             const std::vector<bool>& continuesVec, const std::vector<size_t>& lineBreakIndices,
                             const std::function<void(std::shared_ptr<TextBlock>)>& processLine,
                             const GfxRenderer& renderer, const int fontId) {
  const size_t lineBreak = lineBreakIndices[breakIndex];
  const size_t lastBreakAt = breakIndex > 0 ? lineBreakIndices[breakIndex - 1] : 0;
  const size_t lineWordCount = lineBreak - lastBreakAt;

  // Calculate first line indent (only for left/justified text).
  // Positive text-indent (paragraph indent) is suppressed when extraParagraphSpacing is on.
  // Negative text-indent (hanging indent, e.g. margin-left:3em; text-indent:-1em) always applies —
  // it is structural (positions the bullet/marker), not decorative.
  const bool isFirstLine = breakIndex == 0;
  const int firstLineIndent =
      isFirstLine && blockStyle.textIndentDefined && (blockStyle.textIndent < 0 || !extraParagraphSpacing) &&
              (blockStyle.alignment == CssTextAlign::Justify || blockStyle.alignment == CssTextAlign::Left)
          ? blockStyle.textIndent
          : 0;

  // Calculate total word width for this line, count actual word gaps,
  // and accumulate total natural gap widths (including space kerning adjustments).
  int lineWordWidthSum = 0;
  size_t actualGapCount = 0;
  int totalNaturalGaps = 0;

  for (size_t wordIdx = 0; wordIdx < lineWordCount; wordIdx++) {
    lineWordWidthSum += wordWidths[lastBreakAt + wordIdx];
    // Count gaps: each word after the first creates a gap, unless it's a continuation
    if (wordIdx > 0 && !continuesVec[lastBreakAt + wordIdx]) {
      actualGapCount++;
      totalNaturalGaps +=
          renderer.getSpaceAdvance(fontId, lastCodepoint(words[lastBreakAt + wordIdx - 1]),
                                   firstCodepoint(words[lastBreakAt + wordIdx]), wordStyles[lastBreakAt + wordIdx - 1]);
    } else if (wordIdx > 0 && continuesVec[lastBreakAt + wordIdx]) {
      // Non-breaking space tokens (" " with continues=true) are visible, stretchable spaces —
      // count them as justifiable gaps so justifyExtra is distributed to them too.
      if (words[lastBreakAt + wordIdx] == " ") {
        actualGapCount++;
      }
      // Cross-boundary kerning for continuation words (e.g. nonbreaking spaces, attached punctuation)
      totalNaturalGaps +=
          renderer.getKerning(fontId, lastCodepoint(words[lastBreakAt + wordIdx - 1]),
                              firstCodepoint(words[lastBreakAt + wordIdx]), wordStyles[lastBreakAt + wordIdx - 1]);
    }
  }

  // Calculate spacing (account for indent reducing effective page width on first line)
  const int effectivePageWidth = pageWidth - firstLineIndent;
  const bool isLastLine = breakIndex == lineBreakIndices.size() - 1;

  // For justified text, compute per-gap extra to distribute remaining space evenly
  const int spareSpace = effectivePageWidth - lineWordWidthSum - totalNaturalGaps;
  const int justifyExtra = (blockStyle.alignment == CssTextAlign::Justify && !isLastLine && actualGapCount >= 1)
                               ? spareSpace / static_cast<int>(actualGapCount)
                               : 0;

  // Calculate initial x position (first line starts at indent for left/justified text;
  // may be negative for hanging indents, e.g. margin-left:3em; text-indent:-1em).
  auto xpos = static_cast<int16_t>(firstLineIndent);
  if (blockStyle.alignment == CssTextAlign::Right) {
    xpos = effectivePageWidth - lineWordWidthSum - totalNaturalGaps;
  } else if (blockStyle.alignment == CssTextAlign::Center) {
    xpos = (effectivePageWidth - lineWordWidthSum - totalNaturalGaps) / 2;
  }

  // Pre-calculate X positions for words
  // Continuation words attach to the previous word with no space before them
  std::vector<int16_t> lineXPos;
  lineXPos.reserve(lineWordCount);

  for (size_t wordIdx = 0; wordIdx < lineWordCount; wordIdx++) {
    lineXPos.push_back(xpos);

    const bool nextIsContinuation = wordIdx + 1 < lineWordCount && continuesVec[lastBreakAt + wordIdx + 1];
    if (nextIsContinuation) {
      int advance = wordWidths[lastBreakAt + wordIdx];
      // Cross-boundary kerning for continuation words (e.g. nonbreaking spaces, attached punctuation)
      advance +=
          renderer.getKerning(fontId, lastCodepoint(words[lastBreakAt + wordIdx]),
                              firstCodepoint(words[lastBreakAt + wordIdx + 1]), wordStyles[lastBreakAt + wordIdx]);
      // Non-breaking space tokens are stretchable — expand them during justification like normal spaces.
      if (words[lastBreakAt + wordIdx] == " " && continuesVec[lastBreakAt + wordIdx] &&
          blockStyle.alignment == CssTextAlign::Justify && !isLastLine) {
        advance += justifyExtra;
      }
      xpos += advance;
    } else {
      int gap = 0;
      if (wordIdx + 1 < lineWordCount) {
        gap = renderer.getSpaceAdvance(fontId, lastCodepoint(words[lastBreakAt + wordIdx]),
                                       firstCodepoint(words[lastBreakAt + wordIdx + 1]),
                                       wordStyles[lastBreakAt + wordIdx]);
      }
      if (blockStyle.alignment == CssTextAlign::Justify && !isLastLine) {
        gap += justifyExtra;
      }
      xpos += wordWidths[lastBreakAt + wordIdx] + gap;
    }
  }

  // Build line data by moving from the original vectors using index range
  std::vector<std::string> lineWords(std::make_move_iterator(words.begin() + lastBreakAt),
                                     std::make_move_iterator(words.begin() + lineBreak));
  std::vector<EpdFontFamily::Style> lineWordStyles(wordStyles.begin() + lastBreakAt, wordStyles.begin() + lineBreak);

  for (auto& word : lineWords) {
    if (containsSoftHyphen(word)) {
      stripSoftHyphensInPlace(word);
    }
  }

  // Fast path: when no word on this line was split for focus reading, skip the merge work
  // entirely and pass empty boundary/suffixX vectors. TextBlock pays zero per-word RAM cost
  // for these annotations when the vectors are empty.
  bool lineHasFocusSplit = false;
  for (size_t i = 0; i < lineWordCount; i++) {
    if (wordIsFocusSuffix[lastBreakAt + i]) {
      lineHasFocusSplit = true;
      break;
    }
  }

  if (!lineHasFocusSplit) {
    processLine(std::make_shared<TextBlock>(std::move(lineWords), std::move(lineXPos), std::move(lineWordStyles),
                                            std::vector<uint8_t>{}, std::vector<uint16_t>{}, blockStyle));
    return;
  }

  // Slow path: merge focus suffix tokens back into their preceding word entry so each
  // original word occupies one TextBlock slot. Splits are recorded as per-word annotations
  // applied at render time, cutting the token count significantly when the feature is active.
  std::vector<std::string> outWords;
  std::vector<int16_t> outXPos;
  std::vector<EpdFontFamily::Style> outStyles;
  std::vector<uint8_t> outBoundaries;
  std::vector<uint16_t> outSuffixX;
  outWords.reserve(lineWordCount);
  outXPos.reserve(lineWordCount);
  outStyles.reserve(lineWordCount);
  outBoundaries.reserve(lineWordCount);
  outSuffixX.reserve(lineWordCount);

  for (size_t i = 0; i < lineWordCount; i++) {
    if (wordIsFocusSuffix[lastBreakAt + i] && !outWords.empty()) {
      // Focus suffix: merge string into the preceding bold-prefix entry.
      outWords.back() += lineWords[i];
    } else {
      // Normal word: check for a following focus suffix to record the byte boundary.
      uint8_t boundary = 0;
      uint16_t suffixX = 0;
      if (i + 1 < lineWordCount && wordIsFocusSuffix[lastBreakAt + i + 1]) {
        boundary = static_cast<uint8_t>(std::min(lineWords[i].size(), size_t{255}));
        // Suffix x offset = layout-time advance of the bold prefix, already known from xpos table.
        suffixX = static_cast<uint16_t>(lineXPos[i + 1] - lineXPos[i]);
      }
      outWords.push_back(std::move(lineWords[i]));
      outXPos.push_back(lineXPos[i]);
      // For focus entries with a suffix, strip BOLD from the stored style.
      // Render re-applies it to the prefix portion only, via the boundary field.
      const EpdFontFamily::Style storedStyle =
          boundary > 0 ? static_cast<EpdFontFamily::Style>(lineWordStyles[i] & ~EpdFontFamily::BOLD)
                       : lineWordStyles[i];
      outStyles.push_back(storedStyle);
      outBoundaries.push_back(boundary);
      outSuffixX.push_back(suffixX);
    }
  }

  processLine(std::make_shared<TextBlock>(std::move(outWords), std::move(outXPos), std::move(outStyles),
                                          std::move(outBoundaries), std::move(outSuffixX), blockStyle));
}