// Copyright 2014 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 regexp

import (
	
	
	
	
	
)

// "One-pass" regexp execution.
// Some regexps can be analyzed to determine that they never need
// backtracking: they are guaranteed to run in one pass over the string
// without bothering to save all the usual NFA state.
// Detect those and execute them more quickly.

// A onePassProg is a compiled one-pass regular expression program.
// It is the same as syntax.Prog except for the use of onePassInst.
type onePassProg struct {
	Inst   []onePassInst
	Start  int // index of start instruction
	NumCap int // number of InstCapture insts in re
}

// A onePassInst is a single instruction in a one-pass regular expression program.
// It is the same as syntax.Inst except for the new 'Next' field.
type onePassInst struct {
	syntax.Inst
	Next []uint32
}

// onePassPrefix returns a literal string that all matches for the
// regexp must start with. Complete is true if the prefix
// is the entire match. Pc is the index of the last rune instruction
// in the string. The onePassPrefix skips over the mandatory
// EmptyBeginText.
func onePassPrefix( *syntax.Prog) ( string,  bool,  uint32) {
	 := &.Inst[.Start]
	if .Op != syntax.InstEmptyWidth || (syntax.EmptyOp(.Arg))&syntax.EmptyBeginText == 0 {
		return "", .Op == syntax.InstMatch, uint32(.Start)
	}
	 = .Out
	 = &.Inst[]
	for .Op == syntax.InstNop {
		 = .Out
		 = &.Inst[]
	}
	// Avoid allocation of buffer if prefix is empty.
	if iop() != syntax.InstRune || len(.Rune) != 1 {
		return "", .Op == syntax.InstMatch, uint32(.Start)
	}

	// Have prefix; gather characters.
	var  strings.Builder
	for iop() == syntax.InstRune && len(.Rune) == 1 && syntax.Flags(.Arg)&syntax.FoldCase == 0 && .Rune[0] != utf8.RuneError {
		.WriteRune(.Rune[0])
		,  = .Out, &.Inst[.Out]
	}
	if .Op == syntax.InstEmptyWidth &&
		syntax.EmptyOp(.Arg)&syntax.EmptyEndText != 0 &&
		.Inst[.Out].Op == syntax.InstMatch {
		 = true
	}
	return .String(), , 
}

// onePassNext selects the next actionable state of the prog, based on the input character.
// It should only be called when i.Op == InstAlt or InstAltMatch, and from the one-pass machine.
// One of the alternates may ultimately lead without input to end of line. If the instruction
// is InstAltMatch the path to the InstMatch is in i.Out, the normal node in i.Next.
func onePassNext( *onePassInst,  rune) uint32 {
	 := .MatchRunePos()
	if  >= 0 {
		return .Next[]
	}
	if .Op == syntax.InstAltMatch {
		return .Out
	}
	return 0
}

func iop( *syntax.Inst) syntax.InstOp {
	 := .Op
	switch  {
	case syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL:
		 = syntax.InstRune
	}
	return 
}

// Sparse Array implementation is used as a queueOnePass.
type queueOnePass struct {
	sparse          []uint32
	dense           []uint32
	size, nextIndex uint32
}

func ( *queueOnePass) () bool {
	return .nextIndex >= .size
}

func ( *queueOnePass) () ( uint32) {
	 = .dense[.nextIndex]
	.nextIndex++
	return
}

func ( *queueOnePass) () {
	.size = 0
	.nextIndex = 0
}

func ( *queueOnePass) ( uint32) bool {
	if  >= uint32(len(.sparse)) {
		return false
	}
	return .sparse[] < .size && .dense[.sparse[]] == 
}

func ( *queueOnePass) ( uint32) {
	if !.contains() {
		.insertNew()
	}
}

func ( *queueOnePass) ( uint32) {
	if  >= uint32(len(.sparse)) {
		return
	}
	.sparse[] = .size
	.dense[.size] = 
	.size++
}

func newQueue( int) ( *queueOnePass) {
	return &queueOnePass{
		sparse: make([]uint32, ),
		dense:  make([]uint32, ),
	}
}

// mergeRuneSets merges two non-intersecting runesets, and returns the merged result,
// and a NextIp array. The idea is that if a rune matches the OnePassRunes at index
// i, NextIp[i/2] is the target. If the input sets intersect, an empty runeset and a
// NextIp array with the single element mergeFailed is returned.
// The code assumes that both inputs contain ordered and non-intersecting rune pairs.
const mergeFailed = uint32(0xffffffff)

var (
	noRune = []rune{}
	noNext = []uint32{mergeFailed}
)

func mergeRuneSets(,  *[]rune, ,  uint32) ([]rune, []uint32) {
	 := len(*)
	 := len(*)
	if &0x1 != 0 || &0x1 != 0 {
		panic("mergeRuneSets odd length []rune")
	}
	var (
		,  int
	)
	 := make([]rune, 0)
	 := make([]uint32, 0)
	 := true
	defer func() {
		if ! {
			 = nil
			 = nil
		}
	}()

	 := -1
	 := func( *int,  *[]rune,  uint32) bool {
		if  > 0 && (*)[*] <= [] {
			return false
		}
		 = append(, (*)[*], (*)[*+1])
		* += 2
		 += 2
		 = append(, )
		return true
	}

	for  <  ||  <  {
		switch {
		case  >= :
			 = (&, , )
		case  >= :
			 = (&, , )
		case (*)[] < (*)[]:
			 = (&, , )
		default:
			 = (&, , )
		}
		if ! {
			return noRune, noNext
		}
	}
	return , 
}

// cleanupOnePass drops working memory, and restores certain shortcut instructions.
func cleanupOnePass( *onePassProg,  *syntax.Prog) {
	for ,  := range .Inst {
		switch .Op {
		case syntax.InstAlt, syntax.InstAltMatch, syntax.InstRune:
		case syntax.InstCapture, syntax.InstEmptyWidth, syntax.InstNop, syntax.InstMatch, syntax.InstFail:
			.Inst[].Next = nil
		case syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL:
			.Inst[].Next = nil
			.Inst[] = onePassInst{Inst: }
		}
	}
}

// onePassCopy creates a copy of the original Prog, as we'll be modifying it.
func onePassCopy( *syntax.Prog) *onePassProg {
	 := &onePassProg{
		Start:  .Start,
		NumCap: .NumCap,
		Inst:   make([]onePassInst, len(.Inst)),
	}
	for ,  := range .Inst {
		.Inst[] = onePassInst{Inst: }
	}

	// rewrites one or more common Prog constructs that enable some otherwise
	// non-onepass Progs to be onepass. A:BD (for example) means an InstAlt at
	// ip A, that points to ips B & C.
	// A:BC + B:DA => A:BC + B:CD
	// A:BC + B:DC => A:DC + B:DC
	for  := range .Inst {
		switch .Inst[].Op {
		default:
			continue
		case syntax.InstAlt, syntax.InstAltMatch:
			// A:Bx + B:Ay
			 := &.Inst[].Out
			 := &.Inst[].Arg
			// make sure a target is another Alt
			 := .Inst[*]
			if !(.Op == syntax.InstAlt || .Op == syntax.InstAltMatch) {
				,  = , 
				 = .Inst[*]
				if !(.Op == syntax.InstAlt || .Op == syntax.InstAltMatch) {
					continue
				}
			}
			 := .Inst[*]
			// Analyzing both legs pointing to Alts is for another day
			if .Op == syntax.InstAlt || .Op == syntax.InstAltMatch {
				// too complicated
				continue
			}
			// simple empty transition loop
			// A:BC + B:DA => A:BC + B:DC
			 := &.Inst[*].Out
			 := &.Inst[*].Arg
			 := false
			if .Out == uint32() {
				 = true
			} else if .Arg == uint32() {
				 = true
				,  = , 
			}
			if  {
				* = *
			}

			// empty transition to common target
			// A:BC + B:DC => A:DC + B:DC
			if * == * {
				* = *
			}
		}
	}
	return 
}

var anyRuneNotNL = []rune{0, '\n' - 1, '\n' + 1, unicode.MaxRune}
var anyRune = []rune{0, unicode.MaxRune}

// makeOnePass creates a onepass Prog, if possible. It is possible if at any alt,
// the match engine can always tell which branch to take. The routine may modify
// p if it is turned into a onepass Prog. If it isn't possible for this to be a
// onepass Prog, the Prog nil is returned. makeOnePass is recursive
// to the size of the Prog.
func makeOnePass( *onePassProg) *onePassProg {
	// If the machine is very long, it's not worth the time to check if we can use one pass.
	if len(.Inst) >= 1000 {
		return nil
	}

	var (
		    = newQueue(len(.Inst))
		   = newQueue(len(.Inst))
		        func(uint32, []bool) bool
		 = make([][]rune, len(.Inst))
	)

	// check that paths from Alt instructions are unambiguous, and rebuild the new
	// program as a onepass program
	 = func( uint32,  []bool) ( bool) {
		 = true
		 := &.Inst[]
		if .contains() {
			return
		}
		.insert()
		switch .Op {
		case syntax.InstAlt, syntax.InstAltMatch:
			 = (.Out, ) && (.Arg, )
			// check no-input paths to InstMatch
			 := [.Out]
			 := [.Arg]
			if  &&  {
				 = false
				break
			}
			// Match on empty goes in inst.Out
			if  {
				.Out, .Arg = .Arg, .Out
				,  = , 
			}
			if  {
				[] = true
				.Op = syntax.InstAltMatch
			}

			// build a dispatch operator from the two legs of the alt.
			[], .Next = mergeRuneSets(
				&[.Out], &[.Arg], .Out, .Arg)
			if len(.Next) > 0 && .Next[0] == mergeFailed {
				 = false
				break
			}
		case syntax.InstCapture, syntax.InstNop:
			 = (.Out, )
			[] = [.Out]
			// pass matching runes back through these no-ops.
			[] = append([]rune{}, [.Out]...)
			.Next = make([]uint32, len([])/2+1)
			for  := range .Next {
				.Next[] = .Out
			}
		case syntax.InstEmptyWidth:
			 = (.Out, )
			[] = [.Out]
			[] = append([]rune{}, [.Out]...)
			.Next = make([]uint32, len([])/2+1)
			for  := range .Next {
				.Next[] = .Out
			}
		case syntax.InstMatch, syntax.InstFail:
			[] = .Op == syntax.InstMatch
		case syntax.InstRune:
			[] = false
			if len(.Next) > 0 {
				break
			}
			.insert(.Out)
			if len(.Rune) == 0 {
				[] = []rune{}
				.Next = []uint32{.Out}
				break
			}
			 := make([]rune, 0)
			if len(.Rune) == 1 && syntax.Flags(.Arg)&syntax.FoldCase != 0 {
				 := .Rune[0]
				 = append(, , )
				for  := unicode.SimpleFold();  != ;  = unicode.SimpleFold() {
					 = append(, , )
				}
				slices.Sort()
			} else {
				 = append(, .Rune...)
			}
			[] = 
			.Next = make([]uint32, len([])/2+1)
			for  := range .Next {
				.Next[] = .Out
			}
			.Op = syntax.InstRune
		case syntax.InstRune1:
			[] = false
			if len(.Next) > 0 {
				break
			}
			.insert(.Out)
			 := []rune{}
			// expand case-folded runes
			if syntax.Flags(.Arg)&syntax.FoldCase != 0 {
				 := .Rune[0]
				 = append(, , )
				for  := unicode.SimpleFold();  != ;  = unicode.SimpleFold() {
					 = append(, , )
				}
				slices.Sort()
			} else {
				 = append(, .Rune[0], .Rune[0])
			}
			[] = 
			.Next = make([]uint32, len([])/2+1)
			for  := range .Next {
				.Next[] = .Out
			}
			.Op = syntax.InstRune
		case syntax.InstRuneAny:
			[] = false
			if len(.Next) > 0 {
				break
			}
			.insert(.Out)
			[] = append([]rune{}, anyRune...)
			.Next = []uint32{.Out}
		case syntax.InstRuneAnyNotNL:
			[] = false
			if len(.Next) > 0 {
				break
			}
			.insert(.Out)
			[] = append([]rune{}, anyRuneNotNL...)
			.Next = make([]uint32, len([])/2+1)
			for  := range .Next {
				.Next[] = .Out
			}
		}
		return
	}

	.clear()
	.insert(uint32(.Start))
	 := make([]bool, len(.Inst))
	for !.empty() {
		.clear()
		 := .next()
		if !(, ) {
			 = nil
			break
		}
	}
	if  != nil {
		for  := range .Inst {
			.Inst[].Rune = []
		}
	}
	return 
}

// compileOnePass returns a new *syntax.Prog suitable for onePass execution if the original Prog
// can be recharacterized as a one-pass regexp program, or syntax.nil if the
// Prog cannot be converted. For a one pass prog, the fundamental condition that must
// be true is: at any InstAlt, there must be no ambiguity about what branch to  take.
func compileOnePass( *syntax.Prog) ( *onePassProg) {
	if .Start == 0 {
		return nil
	}
	// onepass regexp is anchored
	if .Inst[.Start].Op != syntax.InstEmptyWidth ||
		syntax.EmptyOp(.Inst[.Start].Arg)&syntax.EmptyBeginText != syntax.EmptyBeginText {
		return nil
	}
	 := false
	for ,  := range .Inst {
		if .Op == syntax.InstAlt || .Op == syntax.InstAltMatch {
			 = true
			break
		}
	}
	// If we have alternates, every instruction leading to InstMatch must be EmptyEndText.
	// Also, any match on empty text must be $.
	for ,  := range .Inst {
		 := .Inst[.Out].Op
		switch .Op {
		default:
			if  == syntax.InstMatch &&  {
				return nil
			}
		case syntax.InstAlt, syntax.InstAltMatch:
			if  == syntax.InstMatch || .Inst[.Arg].Op == syntax.InstMatch {
				return nil
			}
		case syntax.InstEmptyWidth:
			if  == syntax.InstMatch {
				if syntax.EmptyOp(.Arg)&syntax.EmptyEndText == syntax.EmptyEndText {
					continue
				}
				return nil
			}
		}
	}
	// Creates a slightly optimized copy of the original Prog
	// that cleans up some Prog idioms that block valid onepass programs
	 = onePassCopy()

	// checkAmbiguity on InstAlts, build onepass Prog if possible
	 = makeOnePass()

	if  != nil {
		cleanupOnePass(, )
	}
	return 
}