StringExt.swift

//
//  StringExt.swift
//
//  some useful swift string's extension
//
//  Xcode version is 7.3, swift version is 2.2
//
//  TODO
//
//

import Foundation

extension String {
  
  func slice(startIndex: Int = 0, endIndex: Int = Int.max) -> String {
    var str = ""
    var start = startIndex, end = endIndex
    let count = self.length
    if start < 0 {
      if start < -count {
        start = -count
      }
      start += count
    }
    if end < 0 {
      end += count
    }
    else if end > count {
      end = count
    }
    if end >= start {
      let index = self.startIndex.advancedBy(start)..<self.startIndex.advancedBy(end)
      str = self.substringWithRange(index)
    }
    return str
  }
  
  func substr(startIndex: Int = 0, len: Int = Int.max) -> String {
    var str = ""
    var start = startIndex, end = len
    let count = self.length
    if end > count {
      end = count
    }
    if start < 0 {
      if start < -count {
        start = -count
      }
      start += count
    }
    end += start
    if end > count {
      end = count
    }
    if start < count {
      let index = self.startIndex.advancedBy(start)..<self.startIndex.advancedBy(end)
      str = self.substringWithRange(index)
    }
    return str
  }
  
  func substring(startIndex: Int = 0, endIndex: Int = Int.max) -> String {
    var str = ""
    var start = startIndex, end = endIndex
    let count = self.length
    if start < 0 {
      start = 0
    }
    if end < 0 {
      end = 0
    }
    if start > end {
      let tmp = end
      end = start
      start = tmp
    }
    if end > count {
      end = count
    }
    if start < count {
      let index = self.startIndex.advancedBy(start)..<self.startIndex.advancedBy(end)
      str = self.substringWithRange(index)
    }
    return str
  }
  
  //get string's length
  var length: Int {
    return self.characters.count
  }
}