# Blockchain

## 20180331
[TOC]

### Links
Chatroom： https://gitter.im/taipeichain/Lobby
Today's Slides: https://goo.gl/CGURzG
Setup Links: https://gist.github.com/yhuag/5d8ee2fd46baff47edc923134048481c
Contracts：https://github.com/BlockchainEduNet-HK/smart-contract-repo/tree/master/examples

### Additional Info
CryptoKitties: https://www.cryptokitties.co
簡化支付驗證： https://goo.gl/MxvUq6
Blockchain Explorer：
https://etherscan.io
https://ropsten.etherscan.io
EtherAddressLookup： https://goo.gl/LzLcGQ
Nonce explanation：https://goo.gl/xj9YFm
Wei & Finney & Ether：https://forum.ethereum.org/discussion/304/what-is-wei
Ivan on Tech \(Youtube\): https://www.youtube.com/channel/UCrYmtJBtLdtm2ov84ulV-yg
PoA：
https://en.wikipedia.org/wiki/Proof-of-authority
https://goo.gl/1T52Ff

--

Parity：https://www.parity.io/
Remix：https://remix.ethereum.org/
OpenZeppelin：https://github.com/OpenZeppelin/zeppelin-solidity
How to Code Your Own CryptoKitties：
https://medium.com/loom-network/how-to-code-your-own-cryptokitties-style-game-on-ethereum-7c8ac86a4eb3

Kovan的幣可以從這裡拿：https://gitter.im/kovan-testnet/faucet

### Voting Demo

pragma solidity ^0.4.13;

import "github.com/OpenZeppelin/zeppelin-solidity/contracts/math/SafeMath.sol";

contract Voting {
    using SafeMath for uint;
    
    uint[] candidateList; // list (optional)
    
    mapping (uint => uint) public candidates; // ID -> votes
    mapping (address => bool) public voted; 
    
    modifier isValidCandidate(uint candidateID){
        require(candidateID>=0 && candidateID<3); // 0, 1, 2
        _;
    }
    
    modifier hasNotVoted(){
        require(!voted[msg.sender]);
        // require(voted[msg.sender] == false);
        _;
    }
    
    function Voting() public { // constructor
        candidates[0] = 0;
        candidates[1] = 0;
        candidates[2] = 0;
        candidateList = [0, 0, 0]; // list init (optional)
    }
    
    function vote(uint candidateID) public isValidCandidate(candidateID) hasNotVoted() {
        candidates[candidateID] = candidates[candidateID].add(1); // one vote
        voted[msg.sender] = true;
    }
    
    function getVote(uint candidateID) public isValidCandidate(candidateID) constant returns (uint) {
        return candidates[candidateID];
    }

}

### Simple QA

* **假設今天比特幣2100萬個都挖光了，那誰要負責記帳呢？**
- Short answer: No one :)
- Long answer: 比特幣的mining reward會隨著挖出的總量半衰遞減，當mining reward數年後小於一個金額threshold，之後挖礦唯一的誘因incentive就完全倚靠transaction fee了

* **礦工可以得到比特幣的來源有兩個: 1. 加入新區塊的礦工(老師說的數學樂透), 猜中數字可以得錢; 2. 每一筆交易都會有transaction fee**
- Answer: 每個Block都含有數百~千個transaction，所以當每個Block被mined時會出現兩份獎勵rewards:
1. Transanction fee 總和
2. Block reward \(依照現在區塊高度Block Height\)

* **兩個礦工都可以從transaction pool中撈取transaction到自己的block(記帳)，但只有猜中數學樂透的人才可以把block公布(創造新的block) 所以說, 假設今天minerA猜中數學樂透, A所公布的block成為最新的block，那麼只有minerA可以得到該block中所有transaction的transaction fee嗎?**
- Answer: 沒錯, 不過假設現在Block Height是100, 任何時間點算出第101 Block的miner**都可以**broadcast給周圍的peers, 接下來就看看該miner發布的夠不夠早, 周圍的peers願不願意把這個101th Block接上他們自己的chain \(如果是他們收到的第一個101th Block, 接受率最高\), 如果被接受了，該miner就會贏得所有的Transaction fee + Block reward

## 20180401

KeepingYouAwake(only for mac)：https://github.com/newmarcel/KeepingYouAwake

### ERC20
ERC20：https://en.wikipedia.org/wiki/ERC20
Contract：https://gist.github.com/yhuag/e443af8685d5671e25b9761ceb334997

### Pet Shop

http://truffleframework.com/tutorials/pet-shop

install npm, ganache(ganache-cli),

then input in your terminal

npm install -g truffle
mkdir ~(yourpath)/pet-shop && cd ~/(yourpath)/pet-shop

truffle unbox pet-shop

add "Adoption.sol" to contracts
add "2\_deploy\_contracts.js" to migrations
{%gist ysya/949617974ae1e7bb53ed2a838961203e%}

then

truffle compile

truffle migrate

replace app.js
https://raw.githubusercontent.com/ysya/trufflepetshop/master/src/js/app.js

then

npm run dev

open your browser and go to localhost:3000.