#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN
@interface NSArray<ObjectType> (Block)

/**
 遍歷數(shù)組

 @param body 遍歷操作 block
 */
- (void)forEach:(void (^)(ObjectType obj))body;

/**
 根據(jù)篩選條件篩選數(shù)組元素。如：
 
 NSArray <NSNumber*>*nums  = @[@1, @2, @3, @4, @5];
 NSArray <NSNumber*>*evens = [nums select:^BOOL(NSNumber *obj){
    return [obj integerValue] % 2 == 0;
 }];    // evens is [2, 4]

 @param where 篩選條件
 @return 篩選后的新數(shù)組
 */
- (nullable NSArray <ObjectType>*)select:(BOOL (^)(ObjectType obj))where;

/**
 按照順序遍歷的方式育八，根據(jù)篩選條件篩選出第一個(gè)符合條件的數(shù)組元素迫靖。

 @param where 篩選條件
 @return 選擇的元素
 */
- (nullable ObjectType)selectOne:(BOOL (^)(ObjectType obj))where;

/**
 select 的相反操作既峡，根據(jù)指定條件從數(shù)組中剔除元素乡翅。

 @param where 剔除條件
 @return 剔除指定的元素后的數(shù)組
 */
- (nullable NSArray <ObjectType>*)reject:(BOOL (^)(ObjectType obj))where;

/**
 重組元素

 @param initial 初始值
 @param body 重組 block
 @return 組合完成后的結(jié)果
 */
- (id)reduce:(id)initial body:(id (^)(id result, ObjectType obj))body;

/**
 將數(shù)組元素映射成另外一種類(lèi)型的元素并包裝成新數(shù)組珠插。
 注意奴迅，如果返回 nil材义，則對(duì)應(yīng)的元素會(huì)被忽略均抽。

 @param body 映射邏輯 block
 @return 映射完成后的新數(shù)組
 */
- (NSArray *)flatMap:(nullable id (^)(ObjectType obj))body;

/**
 數(shù)組中是否包含符合指定條件的元素

 @param where 指定條件
 @return 包含返回 YES, 否則返回 NO.
 */
- (BOOL)contain:(BOOL (^)(ObjectType obj))where;

@end



@interface NSArray<ObjectType> (Safe)

- (ObjectType)safe_objectAtIndex:(NSUInteger)index;

@end

@interface NSArray<ObjectType> (Select)

/**
 獲取數(shù)組組合結(jié)果。從給定的數(shù)組中選擇 n 個(gè)元素的組合（無(wú)順序）其掂。
 @param count 指定選擇的個(gè)數(shù)
 @return 結(jié)果集合
 */
- (NSArray <NSArray<ObjectType>*>*)combineWithCount:(NSUInteger)count;

/**
 隨機(jī)打亂數(shù)組的順序

 @return 亂序后的數(shù)組
 */
- (NSArray <ObjectType>*)random;

@end

#import "NSArray+Block.h"

@implementation NSArray (Block)

- (void)forEach:(void (^)(id))body
{
    for (id element in self) {
        body(element);
    }
}

- (NSArray <id>*)select:(BOOL (^)(id))where
{
    __block NSArray *array = @[];
    [self enumerateObjectsUsingBlock:^(id  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
        if (where(obj)) {
            array = [array arrayByAddingObject:obj];
        }
    }];
    if (array.count == 0)
        return nil;
    return array;
}

- (nullable id)selectOne:(BOOL (^)(id obj))where {
    __block id selectedObj = nil;
    [self enumerateObjectsWithOptions:NSEnumerationConcurrent usingBlock:^(id  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
        if (where(obj)) {
            selectedObj = obj;
            *stop = YES;
        }
    }];
    return selectedObj;
}

- (NSArray <id>*)reject:(BOOL (^)(id))where
{
    return [self select:^BOOL(id obj) {
        return !where(obj);
    }];
}

- (id)reduce:(id)initial body:(id (^)(id, id))body
{
    NSParameterAssert(body != nil);
    
    __block id result = initial;
    
    [self enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        result = body(result, obj);
    }];
    
    return result;
}

- (NSArray *)flatMap:(id _Nullable (^)(id _Nonnull))body
{
    NSParameterAssert(body != nil);
    
    NSMutableArray *result = [NSMutableArray arrayWithCapacity:self.count];
    
    [self enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        id value = body(obj);
        if (value) [result addObject:value];
    }];
    
    return [result copy];
}

- (BOOL)contain:(BOOL (^)(id))where {
    
    __block BOOL res = NO;
    [self enumerateObjectsWithOptions:NSEnumerationConcurrent usingBlock:^(id  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
        if (where(obj)) {
            *stop = YES;
            res = YES;
        }
    }];
    
    return res;
}

@end





@implementation NSArray (Safe)

- (id)safe_objectAtIndex:(NSUInteger)index {
    index = MIN(index, self.count - 1);
    return [self objectAtIndex:index];
}

@end



@implementation NSArray (Select)

- (NSArray *)combineWithCount:(NSUInteger)count {
    
    NSMutableArray *array = [NSMutableArray arrayWithCapacity:count];
    NSMutableArray *res = [NSMutableArray array];
    
    // 防止 block 遞歸調(diào)用循環(huán)引用
    __block void (^combine)(NSUInteger, NSUInteger, NSUInteger);
    __block __weak void (^weakCombine)(NSUInteger, NSUInteger, NSUInteger);
    
    weakCombine = combine = ^(NSUInteger count, NSUInteger begin, NSUInteger index) {
        if (count == 0) { [res addObject:array.copy]; return; }
        
        for (NSUInteger i = begin; i < self.count; ++i) {
            array[index] = self[i];
            weakCombine(count - 1, i + 1, index + 1);
        }
    };
    combine(count, 0, 0);
    return [res copy];
}

- (NSArray *)random {
    return [self sortedArrayUsingComparator:^NSComparisonResult(id  _Nonnull obj1, id  _Nonnull obj2) {
        return arc4random() % 2 == 0 ? NSOrderedAscending : NSOrderedDescending;
    }];
}

@end