using System;
using System.Security.Cryptography;
using System.Text;

namespace Utility {
public class PasswordGenerator {
public PasswordGenerator() {
this.Minimum = DefaultMinimum;
this.Maximum = DefaultMaximum;
this.ConsecutiveCharacters = false;
this.RepeatCharacters = true;
this.ExcludeSymbols = false;
this.Exclusions = null;
rng = new RNGCryptoServiceProvider();
}

protected int GetCryptographicRandomNumber(int lBound, int uBound) {
// 假定 lBound >= 0 && lBound < uBound
// 返回一个 int >= lBound and < uBound
uint urndnum;
byte[] rndnum = new Byte[4];

if (lBound == uBound-1) {
// 只有iBound返回的情况
return lBound;
}

uint xcludeRndBase = (uint.MaxValue - (uint.MaxValue%(uint)(uBound-lBound)));
do {
rng.GetBytes(rndnum);
urndnum = System.BitConverter.ToUInt32(rndnum,0);
} while (urndnum >= xcludeRndBase);
return (int)(urndnum % (uBound-lBound)) + lBound;
}

protected char GetRandomCharacter() {
int upperBound = pwdCharArray.GetUpperBound(0);
if ( true == this.ExcludeSymbols ) {
upperBound = PasswordGenerator.UBoundDigit;
}

int randomCharPosition = GetCryptographicRandomNumber(pwdCharArray.GetLowerBound(0), upperBound);
char randomChar = pwdCharArray[randomCharPosition];
return randomChar;
}

public string Generate() {
// 得到minimum 和 maximum 之间随机的长度
int pwdLength = GetCryptographicRandomNumber(this.Minimum, this.Maximum);
StringBuilder pwdBuffer = new StringBuilder();
pwdBuffer.Capacity = this.Maximum;
// 产生随机字符
char lastCharacter, nextCharacter;
// 初始化标记
lastCharacter = nextCharacter = '\n';

for ( int i = 0; i < pwdLength; i++ ) {
nextCharacter = GetRandomCharacter();
if ( false == this.ConsecutiveCharacters ) {
while ( lastCharacter == nextCharacter ) {
nextCharacter = GetRandomCharacter();
}
}

if ( false == this.RepeatCharacters ) {
string temp = pwdBuffer.ToString();
int duplicateIndex = temp.IndexOf(nextCharacter);

while ( -1 != duplicateIndex ) {
nextCharacter = GetRandomCharacter();
duplicateIndex = temp.IndexOf(nextCharacter);
}
}

if ( ( null != this.Exclusions ) ) {
while ( -1 != this.Exclusions.IndexOf(nextCharacter) ) {
nextCharacter = GetRandomCharacter();
}
}
pwdBuffer.Append(nextCharacter);
lastCharacter = nextCharacter;
}

if ( null != pwdBuffer ) {
return pwdBuffer.ToString();
}
else {
return String.Empty;
}
}

public bool ConsecutiveCharacters {
get { return this.hasConsecutive; }
set { this.hasConsecutive = value;}
}

public bool ExcludeSymbols {
get { return this.hasSymbols; }
set { this.hasSymbols = value;}
}

public string Exclusions {
get { return this.exclusionSet; }
set { this.exclusionSet = value; }
}

public int Maximum {
get { return this.maxSize; }
set {
this.maxSize = value;
if ( this.minSize >= this.maxSize ) {
this.maxSize = PasswordGenerator.DefaultMaximum;
}
}
}

public int Minimum {
get { return this.minSize; }
set {
this.minSize = value;
if ( PasswordGenerator.DefaultMinimum > this.minSize ) {
this.minSize = PasswordGenerator.DefaultMinimum;
}
}
}

public bool RepeatCharacters {
get { return this.hasRepeating; }
set { this.hasRepeating = value;}
}

private const int DefaultMaximum = 10;
private const int DefaultMinimum = 6;
private const int UBoundDigit = 61;
private string exclusionSet;
private bool hasConsecutive;
private bool hasRepeating;
private bool hasSymbols;
private int maxSize;
private int minSize;
private char[] pwdCharArray = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567
();
private RNGCryptoServiceProvider rng;
}
}