/// <summary>
/// Creates a pattern tuple.
/// </summary>
/// <param name="aString">A string from which to create the pattern tuple</param>
/// <returns>
/// A tuple containing pattern metadata
/// </returns>
public Pattern?CreatePattern(string aString)
{
var pattern = _isCaseSensitive ? aString : aString.ToLower();
var len = pattern.Length;
if (len == 0)
{
return(null);
}
return(new Pattern(pattern, len, 1 << (len - 1), FuseUtilities.CalculatePatternAlphabet(pattern)));
}
/// <summary>Searches for a pattern in a given string.</summary>
/// <param name="pattern">The pattern to search for. This is created by calling `CreatePattern`</param>
/// <param name="aString">The string in which to search for the pattern</param>
/// <returns>A tuple containing a `score` between `0.0` (exact match) and `1` (not a match), and `ranges` of the matched characters. If no match is found will return a tuple with score of 1 and empty array of ranges.</returns>
private SearchResult SearchInternal(Pattern pattern, string aString)
{
var text = aString;
if (!_isCaseSensitive)
{
text = text.ToLower();
}
var textLength = text.Length;
// Exact match
if (pattern.Text == text)
{
return(new SearchResult(0, new[] { new ClosedRange(0, textLength - 1) }));
}
var location = _location;
var distance = _distance;
var threshold = _threshold;
int getBestLocation()
{
var index = text.IndexOf(pattern.Text, location);
if (index != -1)
{
return(index);
}
return(0);
}
var bestLocation = getBestLocation();
// A mask of the matches. We'll use to determine all the ranges of the matches
var matchMaskArr = Enumerable.Repeat(0, textLength).ToArray();
// Get all exact matches, here for speed up
var index = text.IndexOf(pattern.Text, bestLocation);
while (index != -1)
{
var i = index;
var _score = FuseUtilities.CalculateScore(pattern.Len, 0, i, location, distance);
threshold = Math.Min(threshold, _score);
bestLocation = i + pattern.Len;
index = text.IndexOf(pattern.Text, bestLocation);
var idx = 0;
while (idx < pattern.Len)
{
matchMaskArr[i + idx] = 1;
idx += 1;
}
}
// Reset the best location
bestLocation = 0;
var score = 1.0;
var binMax = pattern.Len + textLength;
var lastBitArr = new int[0];
var textCount = text.Length;
// Magic begins now
for (int i = 0; i < pattern.Len; i++)
{
// Scan for the best match; each iteration allows for one more error.
// Run a binary search to determine how far from the match location we can stray at this error level.
var binMin = 0;
var binMid = binMax;
while (binMin < binMid)
{
if (FuseUtilities.CalculateScore(pattern.Len, i, location, location + binMid, distance) <= threshold)
{
binMin = binMid;
}
else
{
binMax = binMid;
}
binMid = ((binMax - binMin) / 2) + binMin;
}
// Use the result from this iteration as the maximum for the next.
binMax = binMid;
var start = Math.Max(1, location - binMid + 1);
var finish = Math.Min(location + binMid, textLength) + pattern.Len;
// Initialize the bit array
var bitArr = Enumerable.Repeat(0, finish + 2).ToArray();
bitArr[finish + 1] = (1 << i) - 1;
if (start > finish)
{
continue;
}
int?currentLocationIndex = null;
for (int j = finish; j >= start; j--)
{
var currentLocation = j - 1;
// Need to check for `nil` case, since `patternAlphabet` is a sparse hash
int getCharMatch()
{
if (currentLocation < textCount)
{
currentLocationIndex = currentLocationIndex != null?Math.Max(0, currentLocationIndex.Value - 1) : currentLocation; // todo not too sure here..
var @char = text.ElementAt(currentLocationIndex.Value);
if (pattern.Alphabet.ContainsKey(@char))
{
return(pattern.Alphabet[@char]);
}
}
return(0);
}
var charMatch = getCharMatch();
// A match is found
if (charMatch != 0)
{
matchMaskArr[currentLocation] = 1;
}
// First pass: exact match
bitArr[j] = ((bitArr[j + 1] << 1) | 1) & charMatch;
// Subsequent passes: fuzzy match
if (i > 0)
{
bitArr[j] |= (((lastBitArr[j + 1] | lastBitArr[j]) << 1) | 1) | lastBitArr[j + 1];
}
if ((bitArr[j] & pattern.Mask) != 0)
{
score = FuseUtilities.CalculateScore(pattern.Len, i, location, currentLocation, distance);
// This match will almost certainly be better than any existing match. But check anyway.
if (score <= threshold)
{
// Indeed it is
threshold = score;
bestLocation = currentLocation;
if (bestLocation > location)
{
// When passing `bestLocation`, don't exceed our current distance from the expected `location`.
start = Math.Max(1, 2 * location - bestLocation);
}
else
{
// Already passed `location`. No point in continuing.
break;
}
}
}
}
// No hope for a better match at greater error levels
if (FuseUtilities.CalculateScore(pattern.Len, i + 1, location, location, distance) > threshold)
{
break;
}
lastBitArr = bitArr;
}
return(new SearchResult(score, FuseUtilities.FindRanges(matchMaskArr)));
}
