// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package strings

// stringFinder efficiently finds strings in a source text. It's implemented
// using the Boyer-Moore string search algorithm:
// https://en.wikipedia.org/wiki/Boyer-Moore_string_search_algorithm
// https://www.cs.utexas.edu/~moore/publications/fstrpos.pdf (note: this aged
// document uses 1-based indexing)
type stringFinder struct {
	// pattern is the string that we are searching for in the text.
	pattern string

	// badCharSkip[b] contains the distance between the last byte of pattern
	// and the rightmost occurrence of b in pattern. If b is not in pattern,
	// badCharSkip[b] is len(pattern).
	//
	// Whenever a mismatch is found with byte b in the text, we can safely
	// shift the matching frame at least badCharSkip[b] until the next time
	// the matching char could be in alignment.
	badCharSkip [256]int

	// goodSuffixSkip[i] defines how far we can shift the matching frame given
	// that the suffix pattern[i+1:] matches, but the byte pattern[i] does
	// not. There are two cases to consider:
	//
	// 1. The matched suffix occurs elsewhere in pattern (with a different
	// byte preceding it that we might possibly match). In this case, we can
	// shift the matching frame to align with the next suffix chunk. For
	// example, the pattern "mississi" has the suffix "issi" next occurring
	// (in right-to-left order) at index 1, so goodSuffixSkip[3] ==
	// shift+len(suffix) == 3+4 == 7.
	//
	// 2. If the matched suffix does not occur elsewhere in pattern, then the
	// matching frame may share part of its prefix with the end of the
	// matching suffix. In this case, goodSuffixSkip[i] will contain how far
	// to shift the frame to align this portion of the prefix to the
	// suffix. For example, in the pattern "abcxxxabc", when the first
	// mismatch from the back is found to be in position 3, the matching
	// suffix "xxabc" is not found elsewhere in the pattern. However, its
	// rightmost "abc" (at position 6) is a prefix of the whole pattern, so
	// goodSuffixSkip[3] == shift+len(suffix) == 6+5 == 11.
	goodSuffixSkip []int
}

func makeStringFinder( string) *stringFinder {
	 := &stringFinder{
		pattern:        ,
		goodSuffixSkip: make([]int, len()),
	}
	// last is the index of the last character in the pattern.
	 := len() - 1

	// Build bad character table.
	// Bytes not in the pattern can skip one pattern's length.
	for  := range .badCharSkip {
		.badCharSkip[] = len()
	}
	// The loop condition is < instead of <= so that the last byte does not
	// have a zero distance to itself. Finding this byte out of place implies
	// that it is not in the last position.
	for  := 0;  < ; ++ {
		.badCharSkip[[]] =  - 
	}

	// Build good suffix table.
	// First pass: set each value to the next index which starts a prefix of
	// pattern.
	 := 
	for  := ;  >= 0; -- {
		if HasPrefix(, [+1:]) {
			 =  + 1
		}
		// lastPrefix is the shift, and (last-i) is len(suffix).
		.goodSuffixSkip[] =  +  - 
	}
	// Second pass: find repeats of pattern's suffix starting from the front.
	for  := 0;  < ; ++ {
		 := longestCommonSuffix(, [1:+1])
		if [-] != [-] {
			// (last-i) is the shift, and lenSuffix is len(suffix).
			.goodSuffixSkip[-] =  +  - 
		}
	}

	return 
}

func longestCommonSuffix(,  string) ( int) {
	for ;  < len() &&  < len(); ++ {
		if [len()-1-] != [len()-1-] {
			break
		}
	}
	return
}

// next returns the index in text of the first occurrence of the pattern. If
// the pattern is not found, it returns -1.
func ( *stringFinder) ( string) int {
	 := len(.pattern) - 1
	for  < len() {
		// Compare backwards from the end until the first unmatching character.
		 := len(.pattern) - 1
		for  >= 0 && [] == .pattern[] {
			--
			--
		}
		if  < 0 {
			return  + 1 // match
		}
		 += max(.badCharSkip[[]], .goodSuffixSkip[])
	}
	return -1
}