RACArraySequence.m

//
//  RACArraySequence.m
//  ReactiveObjC
//
//  Created by Justin Spahr-Summers on 2012-10-29.
//  Copyright (c) 2012 GitHub. All rights reserved.
//

#import "RACArraySequence.h"

@interface RACArraySequence ()

// Redeclared from the superclass and marked deprecated to prevent using `array`
// where `backingArray` is intended.
@property (nonatomic, copy, readonly) NSArray *array __attribute__((deprecated));

// The array being sequenced.
@property (nonatomic, copy, readonly) NSArray *backingArray;

// The index in the array from which the sequence starts.
@property (nonatomic, assign, readonly) NSUInteger offset;

@end

@implementation RACArraySequence

#pragma mark Lifecycle

+ (RACSequence *)sequenceWithArray:(NSArray *)array offset:(NSUInteger)offset {
	NSCParameterAssert(offset <= array.count);

	if (offset == array.count) return self.empty;

	RACArraySequence *seq = [[self alloc] init];
	seq->_backingArray = [array copy];
	seq->_offset = offset;
	return seq;
}

#pragma mark RACSequence

- (id)head {
	return self.backingArray[self.offset];
}

- (RACSequence *)tail {
	RACSequence *sequence = [self.class sequenceWithArray:self.backingArray offset:self.offset + 1];
	sequence.name = self.name;
	return sequence;
}

#pragma mark NSFastEnumeration

- (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState *)state objects:(__unsafe_unretained id[])stackbuf count:(NSUInteger)len {
	NSCParameterAssert(len > 0);

	if (state->state >= self.backingArray.count) {
		// Enumeration has completed.
		return 0;
	}

	if (state->state == 0) {
		state->state = self.offset;

		// Since a sequence doesn't mutate, this just needs to be set to
		// something non-NULL.
		state->mutationsPtr = state->extra;
	}

	state->itemsPtr = stackbuf;

	NSUInteger startIndex = state->state;
	NSUInteger index = 0;

	for (id value in self.backingArray) {
		// Constructing an index set for -enumerateObjectsAtIndexes: can actually be
		// slower than just skipping the items we don't care about.
		if (index < startIndex) {
			++index;
			continue;
		}

		stackbuf[index - startIndex] = value;

		++index;
		if (index - startIndex >= len) break;
	}

	NSCAssert(index > startIndex, @"Final index (%lu) should be greater than start index (%lu)", (unsigned long)index, (unsigned long)startIndex);

	state->state = index;
	return index - startIndex;
}

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-implementations"
- (NSArray *)array {
	return [self.backingArray subarrayWithRange:NSMakeRange(self.offset, self.backingArray.count - self.offset)];
}
#pragma clang diagnostic pop

#pragma mark NSCoding

- (instancetype)initWithCoder:(NSCoder *)coder {
	self = [super initWithCoder:coder];
	if (self == nil) return nil;

	_backingArray = [coder decodeObjectForKey:@"array"];
	_offset = 0;

	return self;
}

- (void)encodeWithCoder:(NSCoder *)coder {
	// Encoding is handled in RACSequence.
	[super encodeWithCoder:coder];
}

#pragma mark NSObject

- (NSString *)description {
	return [NSString stringWithFormat:@"<%@: %p>{ name = %@, array = %@ }", self.class, self, self.name, self.backingArray];
}

@end