// Copyright 2020 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.

package collate

import (
	"github.com/pingcap/tidb/util/stringutil"
)

const (
	// magic number indicate weight has 2 uint64, should get from `longRuneMap`
	longRune uint64 = 0xFFFD
)

// unicodeCICollator implements UCA. see http://unicode.org/reports/tr10/
type unicodeCICollator struct {
}

// Compare implements Collator interface.
func (uc *unicodeCICollator) Compare(a, b string) int {
	a = truncateTailingSpace(a)
	b = truncateTailingSpace(b)
	// weight of a, b. weight in unicode_ci may has 8 uint16s. xn indicate first 4 u16s, xs indicate last 4 u16s
	an, bn := uint64(0), uint64(0)
	as, bs := uint64(0), uint64(0)
	// rune of a, b
	ar, br := rune(0), rune(0)
	// decode index of a, b
	ai, bi := 0, 0
	for {
		if an == 0 {
			if as == 0 {
				for an == 0 && ai < len(a) {
					ar, ai = decodeRune(a, ai)
					an, as = convertRuneUnicodeCI(ar)
				}
			} else {
				an = as
				as = 0
			}
		}

		if bn == 0 {
			if bs == 0 {
				for bn == 0 && bi < len(b) {
					br, bi = decodeRune(b, bi)
					bn, bs = convertRuneUnicodeCI(br)
				}
			} else {
				bn = bs
				bs = 0
			}
		}

		if an == 0 || bn == 0 {
			return sign(int(an) - int(bn))
		}

		if an == bn {
			an, bn = 0, 0
			continue
		}

		for an != 0 && bn != 0 {
			if (an^bn)&0xFFFF == 0 {
				an >>= 16
				bn >>= 16
			} else {
				return sign(int(an&0xFFFF) - int(bn&0xFFFF))
			}
		}
	}
}

// Key implements Collator interface.
func (uc *unicodeCICollator) Key(str string) []byte {
	str = truncateTailingSpace(str)
	buf := make([]byte, 0, len(str)*2)
	r := rune(0)
	si := 0                        // decode index of s
	sn, ss := uint64(0), uint64(0) // weight of str. weight in unicode_ci may has 8 uint16s. sn indicate first 4 u16s, ss indicate last 4 u16s

	for si < len(str) {
		r, si = decodeRune(str, si)
		sn, ss = convertRuneUnicodeCI(r)
		for sn != 0 {
			buf = append(buf, byte((sn&0xFF00)>>8), byte(sn))
			sn >>= 16
		}
		for ss != 0 {
			buf = append(buf, byte((ss&0xFF00)>>8), byte(ss))
			ss >>= 16
		}
	}
	return buf
}

// convert rune to weights.
// `first` represent first 4 uint16 weights of rune
// `second` represent last 4 uint16 weights of rune if exist, 0 if not
func convertRuneUnicodeCI(r rune) (first, second uint64) {
	if r > 0xFFFF {
		return 0xFFFD, 0
	}
	if mapTable[r] == longRune {
		return longRuneMap[r][0], longRuneMap[r][1]
	}
	return mapTable[r], 0
}

// Pattern implements Collator interface.
func (uc *unicodeCICollator) Pattern() WildcardPattern {
	return &unicodePattern{}
}

type unicodePattern struct {
	patChars []rune
	patTypes []byte
}

// Compile implements WildcardPattern interface.
func (p *unicodePattern) Compile(patternStr string, escape byte) {
	p.patChars, p.patTypes = stringutil.CompilePatternInner(patternStr, escape)
}

// DoMatch implements WildcardPattern interface.
func (p *unicodePattern) DoMatch(str string) bool {
	return stringutil.DoMatchInner(str, p.patChars, p.patTypes, func(a, b rune) bool {
		if a > 0xFFFF || b > 0xFFFF {
			return a == b
		}

		ar, br := mapTable[a], mapTable[b]
		if ar != br {
			return false
		}

		if ar == longRune {
			return a == b
		}

		return true
	})
}