algo.go

package algo

/*

Algorithm
---------

FuzzyMatchV1 finds the first "fuzzy" occurrence of the pattern within the given
text in O(n) time where n is the length of the text. Once the position of the
last character is located, it traverses backwards to see if there's a shorter
substring that matches the pattern.

    a_____b___abc__  To find "abc"
    *-----*-----*>   1. Forward scan
             <***    2. Backward scan

The algorithm is simple and fast, but as it only sees the first occurrence,
it is not guaranteed to find the occurrence with the highest score.

    a_____b__c__abc
    *-----*--*  ***

FuzzyMatchV2 implements a modified version of Smith-Waterman algorithm to find
the optimal solution (highest score) according to the scoring criteria. Unlike
the original algorithm, omission or mismatch of a character in the pattern is
not allowed.

Performance
-----------

The new V2 algorithm is slower than V1 as it examines all occurrences of the
pattern instead of stopping immediately after finding the first one. The time
complexity of the algorithm is O(nm) if a match is found and O(n) otherwise
where n is the length of the item and m is the length of the pattern. Thus, the
performance overhead may not be noticeable for a query with high selectivity.
However, if the performance is more important than the quality of the result,
you can still choose v1 algorithm with --algo=v1.

Scoring criteria
----------------

- We prefer matches at special positions, such as the start of a word, or
  uppercase character in camelCase words.

- That is, we prefer an occurrence of the pattern with more characters
  matching at special positions, even if the total match length is longer.
    e.g. "fuzzyfinder" vs. "fuzzy-finder" on "ff"
                            ````````````
- Also, if the first character in the pattern appears at one of the special
  positions, the bonus point for the position is multiplied by a constant
  as it is extremely likely that the first character in the typed pattern
  has more significance than the rest.
    e.g. "fo-bar" vs. "foob-r" on "br"
          ``````
- But since fzf is still a fuzzy finder, not an acronym finder, we should also
  consider the total length of the matched substring. This is why we have the
  gap penalty. The gap penalty increases as the length of the gap (distance
  between the matching characters) increases, so the effect of the bonus is
  eventually cancelled at some point.
    e.g. "fuzzyfinder" vs. "fuzzy-blurry-finder" on "ff"
          ```````````
- Consequently, it is crucial to find the right balance between the bonus
  and the gap penalty. The parameters were chosen that the bonus is cancelled
  when the gap size increases beyond 8 characters.

- The bonus mechanism can have the undesirable side effect where consecutive
  matches are ranked lower than the ones with gaps.
    e.g. "foobar" vs. "foo-bar" on "foob"
                       ```````
- To correct this anomaly, we also give extra bonus point to each character
  in a consecutive matching chunk.
    e.g. "foobar" vs. "foo-bar" on "foob"
          ``````
- The amount of consecutive bonus is primarily determined by the bonus of the
  first character in the chunk.
    e.g. "foobar" vs. "out-of-bound" on "oob"
                       ````````````
*/

import (
	"fmt"
	"strings"
	"unicode"

	"github.com/junegunn/fzf/src/util"
)

var DEBUG bool

func indexAt(index int, max int, forward bool) int {
	if forward {
		return index
	}
	return max - index - 1
}

// Result contains the results of running a match function.
type Result struct {
	// TODO int32 should suffice
	Start int
	End   int
	Score int
}

const (
	scoreMatch        = 16
	scoreGapStart     = -3
	scoreGapExtention = -1

	// We prefer matches at the beginning of a word, but the bonus should not be
	// too great to prevent the longer acronym matches from always winning over
	// shorter fuzzy matches. The bonus point here was specifically chosen that
	// the bonus is cancelled when the gap between the acronyms grows over
	// 8 characters, which is approximately the average length of the words found
	// in web2 dictionary and my file system.
	bonusBoundary = scoreMatch / 2

	// Although bonus point for non-word characters is non-contextual, we need it
	// for computing bonus points for consecutive chunks starting with a non-word
	// character.
	bonusNonWord = scoreMatch / 2

	// Edge-triggered bonus for matches in camelCase words.
	// Compared to word-boundary case, they don't accompany single-character gaps
	// (e.g. FooBar vs. foo-bar), so we deduct bonus point accordingly.
	bonusCamel123 = bonusBoundary + scoreGapExtention

	// Minimum bonus point given to characters in consecutive chunks.
	// Note that bonus points for consecutive matches shouldn't have needed if we
	// used fixed match score as in the original algorithm.
	bonusConsecutive = -(scoreGapStart + scoreGapExtention)

	// The first character in the typed pattern usually has more significance
	// than the rest so it's important that it appears at special positions where
	// bonus points are given. e.g. "to-go" vs. "ongoing" on "og" or on "ogo".
	// The amount of the extra bonus should be limited so that the gap penalty is
	// still respected.
	bonusFirstCharMultiplier = 2
)

type charClass int

const (
	charNonWord charClass = iota
	charLower
	charUpper
	charLetter
	charNumber
)

func posArray(withPos bool, len int) *[]int {
	if withPos {
		pos := make([]int, 0, len)
		return &pos
	}
	return nil
}

func alloc16(offset int, slab *util.Slab, size int, clear bool) (int, []int16) {
	if slab != nil && cap(slab.I16) > offset+size {
		slice := slab.I16[offset : offset+size]
		if clear {
			for idx := range slice {
				slice[idx] = 0
			}
		}
		return offset + size, slice
	}
	return offset, make([]int16, size)
}

func alloc32(offset int, slab *util.Slab, size int, clear bool) (int, []int32) {
	if slab != nil && cap(slab.I32) > offset+size {
		slice := slab.I32[offset : offset+size]
		if clear {
			for idx := range slice {
				slice[idx] = 0
			}
		}
		return offset + size, slice
	}
	return offset, make([]int32, size)
}

func charClassOfAscii(char rune) charClass {
	if char >= 'a' && char <= 'z' {
		return charLower
	} else if char >= 'A' && char <= 'Z' {
		return charUpper
	} else if char >= '0' && char <= '9' {
		return charNumber
	}
	return charNonWord
}

func charClassOfNonAscii(char rune) charClass {
	if unicode.IsLower(char) {
		return charLower
	} else if unicode.IsUpper(char) {
		return charUpper
	} else if unicode.IsNumber(char) {
		return charNumber
	} else if unicode.IsLetter(char) {
		return charLetter
	}
	return charNonWord
}

func charClassOf(char rune) charClass {
	if char <= unicode.MaxASCII {
		return charClassOfAscii(char)
	}
	return charClassOfNonAscii(char)
}

func bonusFor(prevClass charClass, class charClass) int16 {
	if prevClass == charNonWord && class != charNonWord {
		// Word boundary
		return bonusBoundary
	} else if prevClass == charLower && class == charUpper ||
		prevClass != charNumber && class == charNumber {
		// camelCase letter123
		return bonusCamel123
	} else if class == charNonWord {
		return bonusNonWord
	}
	return 0
}

func bonusAt(input util.Chars, idx int) int16 {
	if idx == 0 {
		return bonusBoundary
	}
	return bonusFor(charClassOf(input.Get(idx-1)), charClassOf(input.Get(idx)))
}

type Algo func(caseSensitive bool, forward bool, input util.Chars, pattern []rune, withPos bool, slab *util.Slab) (Result, *[]int)

func FuzzyMatchV2(caseSensitive bool, forward bool, input util.Chars, pattern []rune, withPos bool, slab *util.Slab) (Result, *[]int) {
	// Assume that pattern is given in lowercase if case-insensitive.
	// First check if there's a match and calculate bonus for each position.
	// If the input string is too long, consider finding the matching chars in
	// this phase as well (non-optimal alignment).
	N := input.Length()
	M := len(pattern)
	switch M {
	case 0:
		return Result{0, 0, 0}, posArray(withPos, M)
	case 1:
		return ExactMatchNaive(caseSensitive, forward, input, pattern[0:1], withPos, slab)
	}

	// Since O(nm) algorithm can be prohibitively expensive for large input,
	// we fall back to the greedy algorithm.
	if slab != nil && N*M > cap(slab.I16) {
		return FuzzyMatchV1(caseSensitive, forward, input, pattern, withPos, slab)
	}

	// Reuse pre-allocated integer slice to avoid unnecessary sweeping of garbages
	offset := 0
	// Bonus point for each position
	offset, B := alloc16(offset, slab, N, false)
	// The first occurrence of each character in the pattern
	offset, F := alloc16(offset, slab, M, false)
	// Rune array
	_, T := alloc32(0, slab, N, false)

	// Phase 1. Check if there's a match and calculate bonus for each point
	pidx, lastIdx, prevClass := 0, 0, charNonWord
	for idx := 0; idx < N; idx++ {
		char := input.Get(idx)
		var class charClass
		if char <= unicode.MaxASCII {
			class = charClassOfAscii(char)
		} else {
			class = charClassOfNonAscii(char)
		}

		if !caseSensitive && class == charUpper {
			if char <= unicode.MaxASCII {
				char += 32
			} else {
				char = unicode.To(unicode.LowerCase, char)
			}
		}

		T[idx] = char
		B[idx] = bonusFor(prevClass, class)
		prevClass = class

		if pidx < M {
			if char == pattern[pidx] {
				lastIdx = idx
				F[pidx] = int16(idx)
				pidx++
			}
		} else {
			if char == pattern[M-1] {
				lastIdx = idx
			}
		}
	}
	if pidx != M {
		return Result{-1, -1, 0}, nil
	}

	// Phase 2. Fill in score matrix (H)
	// Unlike the original algorithm, we do not allow omission.
	width := lastIdx - int(F[0]) + 1
	offset, H := alloc16(offset, slab, width*M, false)

	// Possible length of consecutive chunk at each position.
	offset, C := alloc16(offset, slab, width*M, false)

	maxScore, maxScorePos := int16(0), 0
	for i := 0; i < M; i++ {
		I := i * width
		inGap := false
		for j := int(F[i]); j <= lastIdx; j++ {
			j0 := j - int(F[0])
			var s1, s2, consecutive int16

			if j > int(F[i]) {
				if inGap {
					s2 = H[I+j0-1] + scoreGapExtention
				} else {
					s2 = H[I+j0-1] + scoreGapStart
				}
			}

			if pattern[i] == T[j] {
				var diag int16
				if i > 0 && j0 > 0 {
					diag = H[I-width+j0-1]
				}
				s1 = diag + scoreMatch
				b := B[j]
				if i > 0 {
					// j > 0 if i > 0
					consecutive = C[I-width+j0-1] + 1
					// Break consecutive chunk
					if b == bonusBoundary {
						consecutive = 1
					} else if consecutive > 1 {
						b = util.Max16(b, util.Max16(bonusConsecutive, B[j-int(consecutive)+1]))
					}
				} else {
					consecutive = 1
					b *= bonusFirstCharMultiplier
				}
				if s1+b < s2 {
					s1 += B[j]
					consecutive = 0
				} else {
					s1 += b
				}
			}
			C[I+j0] = consecutive

			inGap = s1 < s2
			score := util.Max16(util.Max16(s1, s2), 0)
			if i == M-1 && (forward && score > maxScore || !forward && score >= maxScore) {
				maxScore, maxScorePos = score, j
			}
			H[I+j0] = score
		}

		if DEBUG {
			if i == 0 {
				fmt.Print("  ")
				for j := int(F[i]); j <= lastIdx; j++ {
					fmt.Printf(" " + string(input.Get(j)) + " ")
				}
				fmt.Println()
			}
			fmt.Print(string(pattern[i]) + " ")
			for idx := int(F[0]); idx < int(F[i]); idx++ {
				fmt.Print(" 0 ")
			}
			for idx := int(F[i]); idx <= lastIdx; idx++ {
				fmt.Printf("%2d ", H[i*width+idx-int(F[0])])
			}
			fmt.Println()

			fmt.Print("  ")
			for idx, p := range C[I : I+width] {
				if idx+int(F[0]) < int(F[i]) {
					p = 0
				}
				fmt.Printf("%2d ", p)
			}
			fmt.Println()
		}
	}

	// Phase 3. (Optional) Backtrace to find character positions
	pos := posArray(withPos, M)
	j := int(F[0])
	if withPos {
		i := M - 1
		j = maxScorePos
		preferMatch := true
		for {
			I := i * width
			j0 := j - int(F[0])
			s := H[I+j0]

			var s1, s2 int16
			if i > 0 && j >= int(F[i]) {
				s1 = H[I-width+j0-1]
			}
			if j > int(F[i]) {
				s2 = H[I+j0-1]
			}

			if s > s1 && (s > s2 || s == s2 && preferMatch) {
				*pos = append(*pos, j)
				if i == 0 {
					break
				}
				i--
			}
			preferMatch = C[I+j0] > 1 || I+width+j0+1 < len(C) && C[I+width+j0+1] > 0
			j--
		}
	}
	// Start offset we return here is only relevant when begin tiebreak is used.
	// However finding the accurate offset requires backtracking, and we don't
	// want to pay extra cost for the option that has lost its importance.
	return Result{j, maxScorePos + 1, int(maxScore)}, pos
}

// Implement the same sorting criteria as V2
func calculateScore(caseSensitive bool, text util.Chars, pattern []rune, sidx int, eidx int, withPos bool) (int, *[]int) {
	pidx, score, inGap, consecutive, firstBonus := 0, 0, false, 0, int16(0)
	pos := posArray(withPos, len(pattern))
	prevClass := charNonWord
	if sidx > 0 {
		prevClass = charClassOf(text.Get(sidx - 1))
	}
	for idx := sidx; idx < eidx; idx++ {
		char := text.Get(idx)
		class := charClassOf(char)
		if !caseSensitive {
			if char >= 'A' && char <= 'Z' {
				char += 32
			} else if char > unicode.MaxASCII {
				char = unicode.To(unicode.LowerCase, char)
			}
		}
		if char == pattern[pidx] {
			if withPos {
				*pos = append(*pos, idx)
			}
			score += scoreMatch
			bonus := bonusFor(prevClass, class)
			if consecutive == 0 {
				firstBonus = bonus
			} else {
				// Break consecutive chunk
				if bonus == bonusBoundary {
					firstBonus = bonus
				}
				bonus = util.Max16(util.Max16(bonus, firstBonus), bonusConsecutive)
			}
			if pidx == 0 {
				score += int(bonus * bonusFirstCharMultiplier)
			} else {
				score += int(bonus)
			}
			inGap = false
			consecutive++
			pidx++
		} else {
			if inGap {
				score += scoreGapExtention
			} else {
				score += scoreGapStart
			}
			inGap = true
			consecutive = 0
			firstBonus = 0
		}
		prevClass = class
	}
	return score, pos
}

// FuzzyMatchV1 performs fuzzy-match
func FuzzyMatchV1(caseSensitive bool, forward bool, text util.Chars, pattern []rune, withPos bool, slab *util.Slab) (Result, *[]int) {
	if len(pattern) == 0 {
		return Result{0, 0, 0}, nil
	}

	pidx := 0
	sidx := -1
	eidx := -1

	lenRunes := text.Length()
	lenPattern := len(pattern)

	for index := 0; index < lenRunes; index++ {
		char := text.Get(indexAt(index, lenRunes, forward))
		// This is considerably faster than blindly applying strings.ToLower to the
		// whole string
		if !caseSensitive {
			// Partially inlining `unicode.ToLower`. Ugly, but makes a noticeable
			// difference in CPU cost. (Measured on Go 1.4.1. Also note that the Go
			// compiler as of now does not inline non-leaf functions.)
			if char >= 'A' && char <= 'Z' {
				char += 32
			} else if char > unicode.MaxASCII {
				char = unicode.To(unicode.LowerCase, char)
			}
		}
		pchar := pattern[indexAt(pidx, lenPattern, forward)]
		if char == pchar {
			if sidx < 0 {
				sidx = index
			}
			if pidx++; pidx == lenPattern {
				eidx = index + 1
				break
			}
		}
	}

	if sidx >= 0 && eidx >= 0 {
		pidx--
		for index := eidx - 1; index >= sidx; index-- {
			tidx := indexAt(index, lenRunes, forward)
			char := text.Get(tidx)
			if !caseSensitive {
				if char >= 'A' && char <= 'Z' {
					char += 32
				} else if char > unicode.MaxASCII {
					char = unicode.To(unicode.LowerCase, char)
				}
			}

			pidx_ := indexAt(pidx, lenPattern, forward)
			pchar := pattern[pidx_]
			if char == pchar {
				if pidx--; pidx < 0 {
					sidx = index
					break
				}
			}
		}

		if !forward {
			sidx, eidx = lenRunes-eidx, lenRunes-sidx
		}

		score, pos := calculateScore(caseSensitive, text, pattern, sidx, eidx, withPos)
		return Result{sidx, eidx, score}, pos
	}
	return Result{-1, -1, 0}, nil
}

// ExactMatchNaive is a basic string searching algorithm that handles case
// sensitivity. Although naive, it still performs better than the combination
// of strings.ToLower + strings.Index for typical fzf use cases where input
// strings and patterns are not very long.
//
// Since 0.15.0, this function searches for the match with the highest
// bonus point, instead of stopping immediately after finding the first match.
// The solution is much cheaper since there is only one possible alignment of
// the pattern.
func ExactMatchNaive(caseSensitive bool, forward bool, text util.Chars, pattern []rune, withPos bool, slab *util.Slab) (Result, *[]int) {
	if len(pattern) == 0 {
		return Result{0, 0, 0}, nil
	}

	lenRunes := text.Length()
	lenPattern := len(pattern)

	if lenRunes < lenPattern {
		return Result{-1, -1, 0}, nil
	}

	// For simplicity, only look at the bonus at the first character position
	pidx := 0
	bestPos, bonus, bestBonus := -1, int16(0), int16(-1)
	for index := 0; index < lenRunes; index++ {
		index_ := indexAt(index, lenRunes, forward)
		char := text.Get(index_)
		if !caseSensitive {
			if char >= 'A' && char <= 'Z' {
				char += 32
			} else if char > unicode.MaxASCII {
				char = unicode.To(unicode.LowerCase, char)
			}
		}
		pidx_ := indexAt(pidx, lenPattern, forward)
		pchar := pattern[pidx_]
		if pchar == char {
			if pidx_ == 0 {
				bonus = bonusAt(text, index_)
			}
			pidx++
			if pidx == lenPattern {
				if bonus > bestBonus {
					bestPos, bestBonus = index, bonus
				}
				if bonus == bonusBoundary {
					break
				}
				index -= pidx - 1
				pidx, bonus = 0, 0
			}
		} else {
			index -= pidx
			pidx, bonus = 0, 0
		}
	}
	if bestPos >= 0 {
		var sidx, eidx int
		if forward {
			sidx = bestPos - lenPattern + 1
			eidx = bestPos + 1
		} else {
			sidx = lenRunes - (bestPos + 1)
			eidx = lenRunes - (bestPos - lenPattern + 1)
		}
		score, _ := calculateScore(caseSensitive, text, pattern, sidx, eidx, false)
		return Result{sidx, eidx, score}, nil
	}
	return Result{-1, -1, 0}, nil
}

// PrefixMatch performs prefix-match
func PrefixMatch(caseSensitive bool, forward bool, text util.Chars, pattern []rune, withPos bool, slab *util.Slab) (Result, *[]int) {
	if len(pattern) == 0 {
		return Result{0, 0, 0}, nil
	}

	if text.Length() < len(pattern) {
		return Result{-1, -1, 0}, nil
	}

	for index, r := range pattern {
		char := text.Get(index)
		if !caseSensitive {
			char = unicode.ToLower(char)
		}
		if char != r {
			return Result{-1, -1, 0}, nil
		}
	}
	lenPattern := len(pattern)
	score, _ := calculateScore(caseSensitive, text, pattern, 0, lenPattern, false)
	return Result{0, lenPattern, score}, nil
}

// SuffixMatch performs suffix-match
func SuffixMatch(caseSensitive bool, forward bool, text util.Chars, pattern []rune, withPos bool, slab *util.Slab) (Result, *[]int) {
	lenRunes := text.Length()
	trimmedLen := lenRunes - text.TrailingWhitespaces()
	if len(pattern) == 0 {
		return Result{trimmedLen, trimmedLen, 0}, nil
	}
	diff := trimmedLen - len(pattern)
	if diff < 0 {
		return Result{-1, -1, 0}, nil
	}

	for index, r := range pattern {
		char := text.Get(index + diff)
		if !caseSensitive {
			char = unicode.ToLower(char)
		}
		if char != r {
			return Result{-1, -1, 0}, nil
		}
	}
	lenPattern := len(pattern)
	sidx := trimmedLen - lenPattern
	eidx := trimmedLen
	score, _ := calculateScore(caseSensitive, text, pattern, sidx, eidx, false)
	return Result{sidx, eidx, score}, nil
}

// EqualMatch performs equal-match
func EqualMatch(caseSensitive bool, forward bool, text util.Chars, pattern []rune, withPos bool, slab *util.Slab) (Result, *[]int) {
	lenPattern := len(pattern)
	if text.Length() != lenPattern {
		return Result{-1, -1, 0}, nil
	}
	runesStr := text.ToString()
	if !caseSensitive {
		runesStr = strings.ToLower(runesStr)
	}
	if runesStr == string(pattern) {
		return Result{0, lenPattern, (scoreMatch+bonusBoundary)*lenPattern +
			(bonusFirstCharMultiplier-1)*bonusBoundary}, nil
	}
	return Result{-1, -1, 0}, nil
}