package main

import (
	"crypto"
	_ "crypto/sha1"
	"encoding/hex"
	"fmt"
	"math/rand"
	"time"
)

func main() {
	g := Generator{
		Difficulty: 26,
	}
	c := g.RandomChallenge()
	fmt.Println(c.String())
	fmt.Println(c.Solve().String())
}

type Challenge struct {
	Input      [48]byte
	Date       [20]byte
	Difficulty byte
	Solution   int64
}
type Generator struct {
	Difficulty byte
}

func (g *Generator) RandomChallenge() Challenge {
	bytes := make([]byte, 48)
	for i, _ := range bytes {
		bytes[i] = byte(rand.Int())
	}
	today := time.Now().UTC()
	date := today.Format("2006-01-02")
	hash := crypto.SHA1.New().Sum([]byte(date))
	return Challenge{
		Input:      [48]byte(bytes),
		Date:       [20]byte(hash),
		Difficulty: g.Difficulty,
	}
}

// using a lookup table for this is super goofy but i'm lazy and it's 6am
var prefixLookup = []int{
	8, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
	3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
	2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
	2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
}

func (c Challenge) Solve() Challenge {
	bytes := make([]byte, 76)
	bytes = append(bytes, c.Input[:]...)
	bytes = append(bytes, c.Date[:]...)
	for {
		for i := range 8 {
			bytes[75-i] = byte(c.Solution >> (i * 8))
		}
		sum := make([]byte, 20)
		hash := crypto.SHA1.New()
		hash.Write(bytes)
		sum = hash.Sum(nil)
		count := 0
		for _, c := range sum {
			p := prefixLookup[c]
			count += p
			if p != 8 {
				break
			}
		}
		if c.Solution%20000000 == 0 {
			println(c.Solution)
		}
		if count >= int(c.Difficulty) {
			println(c.Solution)
			break
		}
		c.Solution++
	}
	return c
}
func (c Challenge) String() string {
	bytes := make([]byte, 0)
	bytes = append(bytes, c.Input[:]...)
	bytes = append(bytes, c.Date[:]...)
	bytes = append(bytes, make([]byte, 8)...)
	bytes[68] = c.Difficulty
	for i := range 7 {
		bytes[75-i] = byte(c.Solution >> (i * 8))
	}
	return hex.EncodeToString(bytes)
}