// 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

// 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]

}

// 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.

func combine(a, b rune) rune {

	key := uint32(uint16(a))<<16 + uint32(uint16(b))

	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

}