mirror of
https://github.com/firebase/firebase-ios-sdk
synced 2026-11-10 22:45:59 +05:45
302 lines
10 KiB
Objective-C
302 lines
10 KiB
Objective-C
/*
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* Copyright 2017 Google
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#import "FirebaseDatabase/Sources/Utilities/FNextPushId.h"
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#import "FirebaseDatabase/Sources/Utilities/FUtilities.h"
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#import "FirebaseDatabase/Sources/Utilities/FValidation.h"
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static NSString *const PUSH_CHARS =
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@"-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz";
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static NSString *const MIN_PUSH_CHAR = @" ";
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static NSString *const MAX_PUSH_CHAR = @"\uFFFF";
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static NSInteger const MAX_KEY_LEN = 786;
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static unichar const LOW_SURROGATE_PAIR_START = 0xDC00;
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static unichar const LOW_SURROGATE_PAIR_END = 0xDFFF;
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static unichar const HIGH_SURROGATE_PAIR_START = 0xD800;
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static unichar const HIGH_SURROGATE_PAIR_END = 0xDBFF;
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@implementation FNextPushId
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+ (NSString *)get:(NSTimeInterval)currentTime {
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static long long lastPushTime = 0;
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static int lastRandChars[12];
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long long now = (long long)(currentTime * 1000);
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BOOL duplicateTime = now == lastPushTime;
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lastPushTime = now;
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unichar timeStampChars[8];
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for (int i = 7; i >= 0; i--) {
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timeStampChars[i] = [PUSH_CHARS characterAtIndex:(now % 64)];
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now = (long long)floor(now / 64);
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}
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NSMutableString *id = [[NSMutableString alloc] init];
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[id appendString:[NSString stringWithCharacters:timeStampChars length:8]];
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if (!duplicateTime) {
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for (int i = 0; i < 12; i++) {
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lastRandChars[i] = (int)floor(arc4random() % 64);
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}
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} else {
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int i = 0;
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for (i = 11; i >= 0 && lastRandChars[i] == 63; i--) {
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lastRandChars[i] = 0;
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}
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lastRandChars[i]++;
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}
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for (int i = 0; i < 12; i++) {
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[id appendFormat:@"%C", [PUSH_CHARS characterAtIndex:lastRandChars[i]]];
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}
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return [NSString stringWithString:id];
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}
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+ (NSString *)from:(NSString *)fn successor:(NSString *_Nonnull)key {
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[FValidation validateFrom:fn validKey:key];
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NSInteger keyAsInt;
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if ([FUtilities tryParseString:key asInt:&keyAsInt]) {
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if (keyAsInt == [FUtilities int32max]) {
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return MIN_PUSH_CHAR;
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}
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return [NSString stringWithFormat:@"%ld", (long)keyAsInt + 1];
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}
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NSMutableString *next = [NSMutableString stringWithString:key];
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if ([next length] < MAX_KEY_LEN) {
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[next insertString:MIN_PUSH_CHAR atIndex:[key length]];
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return next;
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}
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long i = [next length] - 1;
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while (i >= 0) {
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if ([next characterAtIndex:i] != [MAX_PUSH_CHAR characterAtIndex:0]) {
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break;
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}
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--i;
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}
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// `nextAfter` was called on the largest possible key, so return the
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// maxName, which sorts larger than all keys.
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if (i == -1) {
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return [FUtilities maxName];
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}
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unichar character = [next characterAtIndex:i];
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unichar plusOne = character + 1;
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BOOL removePreviousCharacter = NO;
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BOOL replaceWithLowestSurrogatePair = NO;
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switch (plusOne) {
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case 0x23: // '#'
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case 0x24: // '$'
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plusOne = 0x25;
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break;
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case 0x2E: // '.'
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case 0x2F: // '/'
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plusOne = 0x30;
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break;
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case 0x5B: // '['
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plusOne = 0x5C;
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break;
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case 0x5D: // ']'
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plusOne = 0x5E;
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break;
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case 0x7F: // control character: del
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plusOne = 0x80;
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break;
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case HIGH_SURROGATE_PAIR_START: // 0xD800
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// We added one to 0xD7FF and entered surrogate pair zone
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// Replace with the lowest surrogate pair here
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replaceWithLowestSurrogatePair = YES;
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case LOW_SURROGATE_PAIR_END + 1: // 0xE000
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// If the previous character is the highest surrogate value
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// then we increment to the value 0xE000 by replacing the surrogate
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// pair by the single value 0xE000 (the value of plusOne)
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// Otherwise we increment the high surrogate value and set the low
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// surrogate value to the lowest.
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if (i == 0) {
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// Error, encountered low surrogate without matching high surrogate
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} else {
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unichar high = [next characterAtIndex:i - 1];
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if (high == HIGH_SURROGATE_PAIR_END) { /* highest value for the high
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part of the pair */
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// Replace pair with 0xE000 (the value of plusOne)
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removePreviousCharacter = YES;
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} else {
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high += 1;
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NSString *highStr = [NSString stringWithFormat:@"%C", high];
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[next replaceCharactersInRange:NSMakeRange(i - 1, 1)
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withString:highStr];
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plusOne = LOW_SURROGATE_PAIR_START; /* lowest value for the low
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part of the pair */
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}
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}
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break;
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}
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NSString *sourcePlusOne =
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replaceWithLowestSurrogatePair
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? [NSString stringWithFormat:@"%C%C", HIGH_SURROGATE_PAIR_START,
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LOW_SURROGATE_PAIR_START]
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: [NSString stringWithFormat:@"%C", plusOne];
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NSInteger replaceLocation = i;
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NSInteger replaceLength = 1;
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if (removePreviousCharacter) {
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--replaceLocation;
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++replaceLength;
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}
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[next replaceCharactersInRange:NSMakeRange(replaceLocation, replaceLength)
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withString:sourcePlusOne];
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NSInteger length = i + 1;
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if (removePreviousCharacter) {
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--length;
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} else if (replaceWithLowestSurrogatePair) {
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++length;
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}
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return [next substringWithRange:NSMakeRange(0, length)];
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}
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+ (NSString *)from:(NSString *)fn predecessor:(NSString *_Nonnull)key {
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[FValidation validateFrom:fn validKey:key];
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NSInteger keyAsInt;
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if ([FUtilities tryParseString:key asInt:&keyAsInt]) {
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if (keyAsInt == [FUtilities int32min]) {
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return [FUtilities minName];
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}
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return [NSString stringWithFormat:@"%ld", (long)keyAsInt - 1];
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}
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NSMutableString *next = [NSMutableString stringWithString:key];
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if ([next characterAtIndex:(next.length - 1)] ==
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[MIN_PUSH_CHAR characterAtIndex:0]) {
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if ([next length] == 1) {
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return
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[NSString stringWithFormat:@"%ld", (long)[FUtilities int32max]];
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}
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// If the last character is the smallest possible character, then the
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// next smallest string is the prefix of `key` without it.
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[next replaceCharactersInRange:NSMakeRange([next length] - 1, 1)
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withString:@""];
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return next;
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}
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// Replace the last character with its immediate predecessor, and fill the
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// suffix of the key with MAX_PUSH_CHAR. This is the lexicographically
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// largest possible key smaller than `key`.
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NSUInteger i = next.length - 1;
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unichar character = [next characterAtIndex:i];
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unichar minusOne = character - 1;
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BOOL removePreviousCharacter = NO;
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BOOL replaceWithHighestSurrogatePair = NO;
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switch (minusOne) {
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// NOTE: We already handled the case of min char (0x20)
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case 0x23: // '#'
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case 0x24: // '$'
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minusOne = 0x22;
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break;
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case 0x2E: // '.'
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case 0x2F: // '/'
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minusOne = 0x2D;
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break;
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case 0x5B: // '['
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minusOne = 0x5A;
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break;
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case 0x5D: // ']'
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minusOne = 0x5C;
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break;
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case 0x7F: // control character: del
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minusOne = 0x7E;
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break;
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case LOW_SURROGATE_PAIR_END: // 0xDFFF
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// Previously we had 0xE000 which is a single utf16 character,
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// this needs to be replaced with the highest surrogate pair:
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replaceWithHighestSurrogatePair = YES;
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break;
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case HIGH_SURROGATE_PAIR_END: // 0xDBFF
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// If the previous character is the lowest high surrogate value
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// then we decrement to the non-surrogate value 0xD7FF by replacing the
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// surrogate pair by the single value 0xD7FF (HIGH_SURROGATE_PAIR_START
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// - 1) Otherwise we decrement the high surrogate value and set the low
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// surrogate value to the highest.
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if (i == 0) {
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// Error, found low surrogate without matching high surrogate
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} else {
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unichar high = [next characterAtIndex:i - 1];
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if (high == HIGH_SURROGATE_PAIR_START) { /* lowest value for the
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high part of the pair */
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// Replace pair with single 0xD7FF value
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removePreviousCharacter = YES;
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minusOne = HIGH_SURROGATE_PAIR_START - 1;
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} else {
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high -= 1;
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NSString *highStr = [NSString stringWithFormat:@"%C", high];
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[next replaceCharactersInRange:NSMakeRange(i - 1, 1)
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withString:highStr];
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minusOne = LOW_SURROGATE_PAIR_END; /* highest value for the low
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part of the pair */
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}
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}
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break;
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}
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NSString *sourceMinusOne =
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replaceWithHighestSurrogatePair
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? [NSString stringWithFormat:@"%C%C", HIGH_SURROGATE_PAIR_END,
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LOW_SURROGATE_PAIR_END]
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: [NSString stringWithFormat:@"%C", minusOne];
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NSInteger replaceLocation = i;
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NSInteger replaceLength = 1;
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if (removePreviousCharacter) {
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--replaceLocation;
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++replaceLength;
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}
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[next replaceCharactersInRange:NSMakeRange(replaceLocation, replaceLength)
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withString:sourceMinusOne];
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NSInteger length = i + 1;
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if (removePreviousCharacter) {
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--length;
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} else if (replaceWithHighestSurrogatePair) {
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++length;
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}
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return [next stringByPaddingToLength:MAX_KEY_LEN
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withString:MAX_PUSH_CHAR
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startingAtIndex:0];
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};
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@end
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