//

// STArray.swift

// STBaseProject

//

// Created by 寒江孤影 on 2019/1/21.

//

import Foundation

public extension Array {

/// 安全下标访问：越界时返回 nil

/// - Parameter index: 元素下标

/// - Returns: 元素或 nil

func safeElement(at index: Int) -> Element? {

guard index >= 0, index < count else { return nil }

return self[index]

}

/// 安全下标访问：越界时返回默认值

/// - Parameters:

/// - index: 元素下标

/// - defaultValue: 越界时使用的默认值

func element(at index: Int, default defaultValue: Element) -> Element {

safeElement(at: index) ?? defaultValue

}

/// 按索引提取多个元素；越界的索引会被忽略

/// - Parameter indices: 要提取的下标集合

/// - Returns: 新的数组

func elements(at indices: [Int]) -> [Element] {

indices.compactMap { safeElement(at: $0) }

}

/// 将数组切分为固定大小的子数组

/// - Parameter size: 每段长度（必须 > 0）

/// - Returns: 切分后的二维数组

func chunked(into size: Int) -> [[Element]] {

guard size > 0 else { return [self] }

var chunks: [[Element]] = []

chunks.reserveCapacity((count + size - 1) / size)

var index = 0

while index < count {

let end = Swift.min(index + size, count)

chunks.append(Array(self[index..<end]))

index = end

}

return chunks

}

}

public extension Array where Element: Equatable {

/// 去除重复元素并保持顺序

var uniqued: [Element] {

var seen: [Element] = []

seen.reserveCapacity(count)

for element in self where !seen.contains(element) {

seen.append(element)

}

return seen

}

}

public extension RangeReplaceableCollection {

/// 将 `fromIndex` 的元素移动到 `toIndex`

/// - Parameters:

/// - fromIndex: 源下标（基于 startIndex 的偏移量）

/// - toIndex: 目标下标（基于 startIndex 的偏移量）

mutating func moveElement(from fromIndex: Int, to toIndex: Int) {

guard fromIndex != toIndex,

fromIndex >= 0, fromIndex < count,

toIndex >= 0, toIndex < count

else {

return

}

let fromIdx = index(startIndex, offsetBy: fromIndex)

let element = remove(at: fromIdx)

let toIdx = index(startIndex, offsetBy: toIndex)

insert(element, at: toIdx)

}

}