package main

import (
	"code.google.com/p/gopass"
	"flag"
	"fmt"
	"io"
	"strings"
	"crypto/sha512"
)

type PasswordRestrictions struct {
	name          string
	minLength     int
	maxLength     int
	alphaLowerMin int
	alphaLowerMax int
	alphaUpperMin int
	alphaUpperMax int
	numberMin     int
	numberMax     int
	specialMin    int
	specialMax    int
	allowedSpecial string
}

var siteName string

const DEFAULT_SITE = "etrade"

var sites []PasswordRestrictions = []PasswordRestrictions{
	PasswordRestrictions{
		name:          "etrade",
		minLength:     6,
		maxLength:     32,
		alphaLowerMin: 0,
		alphaLowerMax: 32,
		alphaUpperMin: 0,
		alphaUpperMax: 32,
		numberMin:     1,
		numberMax:     32,
		specialMin:    0,
		specialMax:    0},
	PasswordRestrictions{
		name:          "fidelity",
		minLength:     6,
		maxLength:     12,
		alphaLowerMin: 0,
		alphaLowerMax: 12,
		alphaUpperMin: 0,
		alphaUpperMax: 12,
		numberMin:     0,
		numberMax:     12,
		specialMin:    0,
		specialMax:    0},
}

func init() {
	const site_usage = "Name of site for which to generate password"
	flag.StringVar(&siteName, "siteName", DEFAULT_SITE, site_usage)
	flag.StringVar(&siteName, "s", DEFAULT_SITE, site_usage+" (shorthand)")
}

func main() {
	flag.Parse()

	var restrictions *PasswordRestrictions
	for _, v := range sites {
		if strings.ToLower(siteName) == strings.ToLower(v.name) {
			restrictions = &v
			break
		}
	}

	if restrictions == nil {
		fmt.Println("Error: Site name not recognized, please use one of the following:")
		for _, v := range sites {
			fmt.Println("\t" + v.name)
		}
	}

	oldPassword, err := gopass.GetPass("Enter Password: ")
	if err != nil {
		panic(err)
	}

	c := make(chan int)
	go generateBytes(c, oldPassword, restrictions.name)

	maxValue := 62 /*alphanumeric*/ + len(restrictions.allowedSpecial)

	curAlphaLower := 0
	curAlphaUpper := 0
	curNumber := 0
	curSpecial := 0
	password := ""

	lower := "abcdefghijklmnopqrstuvwxyz"
	upper := "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
	numbers := "0123456789"

	//build up the initial string, making sure we don't go over the max allowed for each type
	for length := 0; length < restrictions.maxLength; length++ {
		val := <- c % maxValue
		switch {
		case val >= 0 && val < 26:
			if curAlphaLower + 1 <= restrictions.alphaLowerMax {
				password += lower[val:val+1]
				curAlphaLower++
			}
		case val >= 26 && val < 52:
			if curAlphaUpper + 1 <= restrictions.alphaUpperMax {
				password += upper[val-26:val-25]
				curAlphaUpper++
			}
		case val >= 52 && val < 62:
			if curNumber + 1 <= restrictions.numberMax {
				password += numbers[val-52:val-51]
				curNumber++
			}
		default:
			if curSpecial + 1 <= restrictions.specialMax {
				password += restrictions.allowedSpecial[val-62:val-61]
				curSpecial++
			}
		}
	}

	//now, make sure we meet the minimum requirements. If we don't, start replacing items in the password
	for {
		removed := true
		switch {
		case curAlphaLower < restrictions.alphaLowerMin:
			val := <- c % 26
			password += lower[val:val+1]
			curAlphaLower++
		case curAlphaUpper < restrictions.alphaUpperMin:
			val := <- c % 26
			password += upper[val:val+1]
			curAlphaUpper++
		case curNumber < restrictions.numberMin:
			val := <- c % 10
			password += numbers[val:val+1]
			curNumber++
		case curSpecial < restrictions.specialMin:
			val := <- c % len(restrictions.allowedSpecial)
			password += restrictions.allowedSpecial[val:val+1]
			curSpecial++
		default:
			removed = false
		}
		if !removed {
			break
		}

		removedChar := password[:1]
		password = password[1:]

		switch{
		case strings.Contains(lower, removedChar):
			curAlphaLower--
		case strings.Contains(upper, removedChar):
			curAlphaUpper--
		case strings.Contains(numbers, removedChar):
			curNumber--
		case strings.Contains(restrictions.allowedSpecial, removedChar):
			curSpecial--
		default:
			panic("Unknown character made its way into the password")
		}
	}

	//finally, (pseudo-)randomize the password ordering, one element at a time
	for i := 0; i < restrictions.maxLength; i++ {
		position := (<- c % (restrictions.maxLength - i)) + i
		password = password[position:position+1] + password[0:position] + password[position+1:restrictions.maxLength]
	}

	fmt.Println("Generated password for " + restrictions.name + ": " + password)
}

func generateBytes(c chan int, password string, siteName string) {
	h := sha512.New()
	io.WriteString(h, password + strings.ToLower(siteName))
	hashBytes := h.Sum(nil)

	for {
		for _, b := range hashBytes {
			c <- int(b)
		}
		h.Write(hashBytes)
		hashBytes = h.Sum(nil)
	}
}