punch-clock

Punch clock ("Chấm công" in Vietnamese) is a simple smart contract to keep track of people in and out time.

The contract has all of the basic functionalities:

• Add/remove admins
• Add/remove members
• Change owner
• Punch in/out a member, and get all punch cards of a member
• Destroy the contract when not needed anymore

Usage and cost estimates

(Note: gas price = 0.00000002 Ether, 1 ETH = $40 in these calculations)

• Deploy the contract

Running truffle migrate to deploy the contract, cost 1,037,583 gas (0.02075166 ETH, or $0.83)

• Create a new instance of the contract

Running PunchClock.new("0xf6f80ec1af70453428615abb075b1b525bac17b6") cost 1,037,583 gas (0.02075166 ETH, or $0.83)

• Add an admin to the contract

Running pc.addAdmin("0x9fe37de4c8645ce7370009a016b35c946d05ccd2") cost 114,305 gas (0.0022861 ETH, or $0.09)

• Add a member to the contract

Running pc.addMember("0xf3da29ea01acbb909640bbb34dc90fbda3770d08") cost 68,879 gas (0.00137758 ETH, or $0.06)

• Punch in and out a member

Running pc.punchIn("0xf3da29ea01acbb909640bbb34dc90fbda3770d08", 1490196679) cost 65,923 gas (0.00131846 ETH, or $0.05)

Running pc.punchOut("0xf3da29ea01acbb909640bbb34dc90fbda3770d08", 1490196680) cost 47,253 gas (0.00094506 ETH, or $0.04)

• At a summary: a company has 10 admins, 100 employees, working 26 days a month, each person punch in and out once a day, then the estimated cost:
  • to setup a contract: $0.83 (contract creation) + 10 * $0.09 (add one admin) + 100 * $0.06 (add one member) = $7.73
  • to punch in and out each month: 110 * ($0.05 + $0.04) * 26 = $257.4
  • retrieving the data (i.e. invoking getter methods) is free

Development

• Install truffle and testrpc
• Open Terminal and run testrpc in one console
• Open another console and:
  • Compile the code

    $ truffle compile
    

  • Run unit tests

    $ truffle test 
    

  • Deploy to test network

    $ truffle migrate --reset
    

  • Test the code in truffle console

    $ truffle console
    $> var pc
    $> PunchClock.deployed().then(function(instance) { pc = instance; })
    $> var owner
    $> pc.getOwner().then(function(o) { owner = o; })
    $> pc.punchIn(owner, 1490196677).then(function() { pc.punchOut(owner, 1490196679); })
    $> var cards
    $> pc.getPunchCardsOf(owner).then(function(c) { cards = c; })
    $> cards
    

    You should see a result like this (Truffle v3.1.2 & TestRPC v3.0.3)

    [ [ { [String: '1490196677'] s: 1, e: 9, c: [Object] },
        { [String: '1490196679'] s: 1, e: 9, c: [Object] } ] ]
    

    Note: the output above looks weird, but it's expected. You can run these command to verify:

    $ cards[0][0] == 1490196677 // return true
    $ cards[0][1] == 1490196679 // return true
    

Web interface

• Install truffle default builder using this command:

  npm install truffle-default-builder --save
  

• Execute:

  truffle serve
  

• Open web browser and type: "localhost:8080". You'll see a basic web interfact that allows you to execute all functionalities of this contract.

License

Code released under the Apache License 2.0.