#include "FuzzyMatch.h"

namespace {

// True when the character at `index` starts a word: the string start, a
// character after '/', '.', '-', '_', or a step from lower case to upper
// case.
[[nodiscard]] bool startsWord(QStringView text, qsizetype index) {
  if (index == 0) {
    return true;
  }
  const QChar previous = text.at(index - 1);
  if (previous == QLatin1Char('/') || previous == QLatin1Char('.') ||
      previous == QLatin1Char('-') || previous == QLatin1Char('_')) {
    return true;
  }
  return previous.isLower() && text.at(index).isUpper();
}

}  // namespace

int fuzzyScore(QStringView haystack, QStringView needle) {
  if (needle.isEmpty()) {
    return 0;
  }
  int score = 0;
  qsizetype at = 0;
  qsizetype previousMatch = -1;
  const auto* scan = haystack.cbegin();
  for (const QChar raw : needle) {
    const QChar wanted = raw.toLower();
    bool found = false;
    for (; scan != haystack.cend(); ++scan, ++at) {
      if ((*scan).toLower() == wanted) {
        found = true;
        break;
      }
      // Skipped characters count against the score, but only before the
      // first match. Gaps between matches are free.
      if (previousMatch < 0) {
        --score;
      }
    }
    if (!found) {
      return -1;
    }
    if (startsWord(haystack, at)) {
      score += 8;
    } else if (at == previousMatch + 1) {
      score += 4;
    }
    previousMatch = at;
    ++scan;
    ++at;
  }
  return score;
}