text: // Copyright 2011 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 norm
  
  import "encoding/binary"
  
  // This file contains Form-specific logic and wrappers for data in tables.go.
  
  // Rune info is stored in a separate trie per composing form. A composing form
  // and its corresponding decomposing form share the same trie.  Each trie maps
  // a rune to a uint16. The values take two forms.  For v >= 0x8000:
  //   bits
  //   15:    1 (inverse of NFD_QC bit of qcInfo)
  //   13..7: qcInfo (see below). isYesD is always true (no decompostion).
  //    6..0: ccc (compressed CCC value).
  // For v < 0x8000, the respective rune has a decomposition and v is an index
  // into a byte array of UTF-8 decomposition sequences and additional info and
  // has the form:
  //    <header> <decomp_byte>* [<tccc> [<lccc>]]
  // The header contains the number of bytes in the decomposition (excluding this
  // length byte). The two most significant bits of this length byte correspond
  // to bit 5 and 4 of qcInfo (see below).  The byte sequence itself starts at v+1.
  // The byte sequence is followed by a trailing and leading CCC if the values
  // for these are not zero.  The value of v determines which ccc are appended
  // to the sequences.  For v < firstCCC, there are none, for v >= firstCCC,
  // the sequence is followed by a trailing ccc, and for v >= firstLeadingCC
  // there is an additional leading ccc. The value of tccc itself is the
  // trailing CCC shifted left 2 bits. The two least-significant bits of tccc
  // are the number of trailing non-starters.
  
  const (
  	qcInfoMask      = 0x3F // to clear all but the relevant bits in a qcInfo
  	headerLenMask   = 0x3F // extract the length value from the header byte
  	headerFlagsMask = 0xC0 // extract the qcInfo bits from the header byte
  )
  
  // Properties provides access to normalization properties of a rune.
  type Properties struct {
  	pos   uint8  // start position in reorderBuffer; used in composition.go
  	size  uint8  // length of UTF-8 encoding of this rune
  	ccc   uint8  // leading canonical combining class (ccc if not decomposition)
  	tccc  uint8  // trailing canonical combining class (ccc if not decomposition)
  	nLead uint8  // number of leading non-starters.
  	flags qcInfo // quick check flags
  	index uint16
  }
  
  // functions dispatchable per form
  type lookupFunc func(b input, i int) Properties
  
  // formInfo holds Form-specific functions and tables.
  type formInfo struct {
  	form                     Form
  	composing, compatibility bool // form type
  	info                     lookupFunc
  	nextMain                 iterFunc
  }
  
  var formTable = []*formInfo{{
  	form:          NFC,
  	composing:     true,
  	compatibility: false,
  	info:          lookupInfoNFC,
  	nextMain:      nextComposed,
  }, {
  	form:          NFD,
  	composing:     false,
  	compatibility: false,
  	info:          lookupInfoNFC,
  	nextMain:      nextDecomposed,
  }, {
  	form:          NFKC,
  	composing:     true,
  	compatibility: true,
  	info:          lookupInfoNFKC,
  	nextMain:      nextComposed,
  }, {
  	form:          NFKD,
  	composing:     false,
  	compatibility: true,
  	info:          lookupInfoNFKC,
  	nextMain:      nextDecomposed,
  }}
  
  // We do not distinguish between boundaries for NFC, NFD, etc. to avoid
  // unexpected behavior for the user.  For example, in NFD, there is a boundary
  // after 'a'.  However, 'a' might combine with modifiers, so from the application's
  // perspective it is not a good boundary. We will therefore always use the
  // boundaries for the combining variants.
  
  // BoundaryBefore returns true if this rune starts a new segment and
  // cannot combine with any rune on the left.
  func (p Properties) BoundaryBefore() bool {
  	if p.ccc == 0 && !p.combinesBackward() {
  		return true
  	}
  	// We assume that the CCC of the first character in a decomposition
  	// is always non-zero if different from info.ccc and that we can return
  	// false at this point. This is verified by maketables.
  	return false
  }
  
  // BoundaryAfter returns true if runes cannot combine with or otherwise
  // interact with this or previous runes.
  func (p Properties) BoundaryAfter() bool {
  	// TODO: loosen these conditions.
  	return p.isInert()
  }
  
  // We pack quick check data in 4 bits:
  //   5:    Combines forward  (0 == false, 1 == true)
  //   4..3: NFC_QC Yes(00), No (10), or Maybe (11)
  //   2:    NFD_QC Yes (0) or No (1). No also means there is a decomposition.
  //   1..0: Number of trailing non-starters.
  //
  // When all 4 bits are zero, the character is inert, meaning it is never
  // influenced by normalization.
  type qcInfo uint8
  
  func (p Properties) isYesC() bool { return p.flags&0x10 == 0 }
  func (p Properties) isYesD() bool { return p.flags&0x4 == 0 }
  
  func (p Properties) combinesForward() bool  { return p.flags&0x20 != 0 }
  func (p Properties) combinesBackward() bool { return p.flags&0x8 != 0 } // == isMaybe
  func (p Properties) hasDecomposition() bool { return p.flags&0x4 != 0 } // == isNoD
  
  func (p Properties) isInert() bool {
  	return p.flags&qcInfoMask == 0 && p.ccc == 0
  }
  
  func (p Properties) multiSegment() bool {
  	return p.index >= firstMulti && p.index < endMulti
  }
  
  func (p Properties) nLeadingNonStarters() uint8 {
  	return p.nLead
  }
  
  func (p Properties) nTrailingNonStarters() uint8 {
  	return uint8(p.flags & 0x03)
  }
  
  // Decomposition returns the decomposition for the underlying rune
  // or nil if there is none.
  func (p Properties) Decomposition() []byte {
  	// TODO: create the decomposition for Hangul?
  	if p.index == 0 {
  		return nil
  	}
  	i := p.index
  	n := decomps[i] & headerLenMask
  	i++
  	return decomps[i : i+uint16(n)]
  }
  
  // Size returns the length of UTF-8 encoding of the rune.
  func (p Properties) Size() int {
  	return int(p.size)
  }
  
  // CCC returns the canonical combining class of the underlying rune.
  func (p Properties) CCC() uint8 {
  	if p.index >= firstCCCZeroExcept {
  		return 0
  	}
  	return ccc[p.ccc]
  }
  
  // LeadCCC returns the CCC of the first rune in the decomposition.
  // If there is no decomposition, LeadCCC equals CCC.
  func (p Properties) LeadCCC() uint8 {
  	return ccc[p.ccc]
  }
  
  // TrailCCC returns the CCC of the last rune in the decomposition.
  // If there is no decomposition, TrailCCC equals CCC.
  func (p Properties) TrailCCC() uint8 {
  	return ccc[p.tccc]
  }
  
  func buildRecompMap() {
  	recompMap = make(map[uint32]rune, len(recompMapPacked)/8)
  	var buf [8]byte
  	for i := 0; i < len(recompMapPacked); i += 8 {
  		copy(buf[:], recompMapPacked[i:i+8])
  		key := binary.BigEndian.Uint32(buf[:4])
  		val := binary.BigEndian.Uint32(buf[4:])
  		recompMap[key] = rune(val)
  	}
  }
  
  // Recomposition
  // We use 32-bit keys instead of 64-bit for the two codepoint keys.
  // This clips off the bits of three entries, but we know this will not
  // result in a collision. In the unlikely event that changes to
  // UnicodeData.txt introduce collisions, the compiler will catch it.
  // Note that the recomposition map for NFC and NFKC are identical.
  
  // combine returns the combined rune or 0 if it doesn't exist.
  //
  // The caller is responsible for calling
  // recompMapOnce.Do(buildRecompMap) sometime before this is called.
  func combine(a, b rune) rune {
  	key := uint32(uint16(a))<<16 + uint32(uint16(b))
  	if recompMap == nil {
  		panic("caller error") // see func comment
  	}
  	return recompMap[key]
  }
  
  func lookupInfoNFC(b input, i int) Properties {
  	v, sz := b.charinfoNFC(i)
  	return compInfo(v, sz)
  }
  
  func lookupInfoNFKC(b input, i int) Properties {
  	v, sz := b.charinfoNFKC(i)
  	return compInfo(v, sz)
  }
  
  // Properties returns properties for the first rune in s.
  func (f Form) Properties(s []byte) Properties {
  	if f == NFC || f == NFD {
  		return compInfo(nfcData.lookup(s))
  	}
  	return compInfo(nfkcData.lookup(s))
  }
  
  // PropertiesString returns properties for the first rune in s.
  func (f Form) PropertiesString(s string) Properties {
  	if f == NFC || f == NFD {
  		return compInfo(nfcData.lookupString(s))
  	}
  	return compInfo(nfkcData.lookupString(s))
  }
  
  // compInfo converts the information contained in v and sz
  // to a Properties.  See the comment at the top of the file
  // for more information on the format.
  func compInfo(v uint16, sz int) Properties {
  	if v == 0 {
  		return Properties{size: uint8(sz)}
  	} else if v >= 0x8000 {
  		p := Properties{
  			size:  uint8(sz),
  			ccc:   uint8(v),
  			tccc:  uint8(v),
  			flags: qcInfo(v >> 8),
  		}
  		if p.ccc > 0 || p.combinesBackward() {
  			p.nLead = uint8(p.flags & 0x3)
  		}
  		return p
  	}
  	// has decomposition
  	h := decomps[v]
  	f := (qcInfo(h&headerFlagsMask) >> 2) | 0x4
  	p := Properties{size: uint8(sz), flags: f, index: v}
  	if v >= firstCCC {
  		v += uint16(h&headerLenMask) + 1
  		c := decomps[v]
  		p.tccc = c >> 2
  		p.flags |= qcInfo(c & 0x3)
  		if v >= firstLeadingCCC {
  			p.nLead = c & 0x3
  			if v >= firstStarterWithNLead {
  				// We were tricked. Remove the decomposition.
  				p.flags &= 0x03
  				p.index = 0
  				return p
  			}
  			p.ccc = decomps[v+1]
  		}
  	}
  	return p
  }
  