Blockchain class

blockchain.js

class Blockchain {
  
  // Method 1: Initiate, and store blockchain in LevelDB

  constructor(){
    this.chain = level('./blockchaindata');
    this.chain.put(0,JSON.stringify(Block.genesisBlock()))
  }

  // Method 2: Add new block to LevelDB
  async addBlock(newBlock){

    let minedBlock = await this.mineBlock(newBlock)
        this.chain.put(minedBlock.height,JSON.stringify(minedBlock))
        return minedBlock;
    }

    // Method 3: Create / Mine new block
    async mineBlock(newBlock){

      let l = await this.getBlockHeight(); 
      let prev = await this.getBlock(l-1)
     
          newBlock.height = l; 
          newBlock.time = new Date().getTime().toString().slice(0,-3);
          newBlock.previousBlockHash = prev.hash; 
          newBlock.hash = SHA256(JSON.stringify(newBlock)).toString();  
          return newBlock; 
      }

    // Method 4: Get the length of the existing chain 
    getBlockHeight() {
      return new Promise((resolve,reject)=>{
        let i = 0;
        this.chain.createReadStream().on('data', function(data) {
              i++;
            }).on('error', function(err) {
                reject('Unable to read data stream!', err)
            }).on('end', function() {
              resolve(i)
            });
      })
    }

   // Method 5: Get block from LevelDB with given height 
    getBlock(blockHeight){
      return this.chain.get(blockHeight)
      .then(block => JSON.parse(block))
      .catch(err=>console.log('Can not get block',err))
    }
  // Method 6: Validate Block 
   async validateBlock(blockHeight){
      // get block object
      let block = await this.getBlock(blockHeight);
      // get block hash
      let blockHash = block.hash;
     
      // remove block hash to test block integrity
      block.hash = "";
      // generate block hash
      let validBlockHash = SHA256(JSON.stringify(block)).toString();

      // Compare
      if (blockHash===validBlockHash) {
          return true;
        } else {
          console.log('Block #'+blockHeight+' invalid hash:\n'+blockHash+'<>'+validBlockHash);
          return false;
        }
    }
  
      //Method 7. Validate Blockchain.
       async validateChain(){
        let errorLog = [];
        let lengthChain = await this.getBlockHeight(); 
        for (let i = 0; i < lengthChain-1; i++) {
        // validate block
          if (!this.validateBlock(i)) errorLog.push(i);
        // compare blocks hash link
          let currentBlock = await this.getBlock(i);
          let previousBlock = await this.getBlock(i+1)

          let blockHash = currentBlock.hash;
          let previousHash = previousBlock.previousBlockHash;
          if (blockHash!==previousHash) {
          errorLog.push(i);
        }
      }
        if (errorLog.length>0) {
          console.log('Block errors = ' + errorLog.length);
          console.log('Blocks: '+errorLog);
      } else {
          console.log('No errors detected');
      }
    }

  
}