[iOS] Log file for iOS

目的︰用檔案記錄log，以時間組成檔名(yyyyMMddHHmmss)，只保留7天

做法︰

1. 使用XCGLogger來記錄log

2. 每次APP啟動時，檢查log檔案是否有超過7天的，超過就刪除

// AppDelegate.swift

import XCGLogger

struct MyVariables {
    static let logger = XCGLogger.defaultInstance()
    static let documentsPath = NSHomeDirectory() + "/Documents"
}

class AppDelegate: UIResponder, UIApplicationDelegate {
	func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {

		// 清除7天前的log檔
        cleanOldLogFile()
        
        // 產生此次log的檔名
        let postFixFormatter = NSDateFormatter()
        postFixFormatter.dateFormat = "yyyyMMddHHmmss"
        postFixFormatter.locale = NSLocale.currentLocale()
        let logFileName = "Ticket_" + postFixFormatter.stringFromDate(NSDate()) + ".log"
        let logFileWithFullPath = MyVariables.documentsPath.stringByAppendingString("/\(logFileName)")
        
        let dateFormatter = NSDateFormatter()
        dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss.SSS"
        dateFormatter.locale = NSLocale.currentLocale()
        
        // print to log file
        MyVariables.logger.setup(.Debug, showThreadName: true, showLogLevel: true, showFileNames: true, showLineNumbers: true, writeToFile: logFileWithFullPath, fileLogLevel: .Debug)

        // ...

        return true
	}

	func cleanOldLogFile(){
        let documentsUrl =  NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).first!
        do {
            // 找出所有的*.log檔
            let directoryUrls = try  NSFileManager.defaultManager().contentsOfDirectoryAtURL(documentsUrl, includingPropertiesForKeys: nil, options: NSDirectoryEnumerationOptions())
            let logFiles = directoryUrls.filter(){ $0.pathExtension == "log" }.map{ $0.lastPathComponent }
            
            // 7天前的Date
            let sevenDaysAge = NSDate().dateByAddingTimeInterval(-7*24*60*60)
            
            let logFileDateFormatter = NSDateFormatter()
            logFileDateFormatter.dateFormat = "yyyyMMddHHmmss"

            for logFileName in logFiles {

                let nameSplitedArray = logFileName!.componentsSeparatedByString("_")
				// swift中字符串截取方法(substring）http://www.swiftmi.com/topic/76.html
                let index = nameSplitedArray[1].endIndex.advancedBy(-4) // 從字串最後面往回4個位置
                let logFileDate = logFileDateFormatter.dateFromString(nameSplitedArray[1].substringToIndex(index))
                if logFileDate!.isLessThanDate(sevenDaysAge) { // 比7天前的日期還小(早) -> 要刪除
                    let fp = MyVariables.documentsPath.stringByAppendingString("/\(logFileName!)")
                    print("Delete old log file: \(logFileName!)")
                    // 刪除檔案
                    try NSFileManager.defaultManager().removeItemAtPath(fp)
                }
            }
            
        } catch let error as NSError {
            print(error.localizedDescription)
        }
    }

}