# 天津大学 11-19 如何快速入门区块链开发

Add the following to "dapp -- Resources"

  * JavaScript: https://code.jquery.com/jquery-3.4.1.min.js
  * CSS: https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css
  
The "dapp -- CSS" should be empty

contract

pragma solidity >= 0.4.0;

contract Certificates {

    address owner;
    string public greetingNew;
    string public greetingApplied;
    string public greetingApproved;
    struct Comment {
        string name;
        string email;
        string comment;
        uint approved;
    }
    mapping (address => Comment) comments;
    address [] addrs;

    constructor (string _greetingNew, string _greetingApplied, string _greetingApproved) public {
        owner = msg.sender;
        greetingNew = _greetingNew;
        greetingApplied = _greetingApplied;
        greetingApproved = _greetingApproved;
    }

    function setGreetings (string _greetingNew, string _greetingApplied, string _greetingApproved) public {
        require (msg.sender == owner);
        greetingNew = _greetingNew;
        greetingApplied = _greetingApplied;
        greetingApproved = _greetingApproved;
    }

    function getGreetings () public constant returns (string, string, string) {
        return (greetingNew, greetingApplied, greetingApproved);
    }

    function addComment (string _name, string _email, string _comment) public {
        comments[msg.sender] = Comment(_name, _email, _comment, 1);
        addrs.push(msg.sender);
    }

    function getComment(address _addr) public constant returns(string, string, string, uint, string) {
        string memory greeting;
        if (comments[_addr].approved == 1) {
            greeting = greetingApplied;
        } else if (comments[_addr].approved == 2) {
            greeting = greetingApproved;
        } else {
            greeting = greetingNew;
        }
        return (comments[_addr].name, comments[_addr].email, comments[_addr].comment, comments[_addr].approved, greeting);
    }

    function getAddrs () public constant returns (address []) {
        return addrs;
    }

    function approve (address _addr) public {
        comments[_addr].approved = 2;
    }

    function disapprove (address _addr) public {
        comments[_addr].approved = 3;
    }
}

HTML

<div class="container">
    <br/>
    <div class="jumbotron">
        <p class="lead" id="greeting">请稍等 。。。</p>
        <hr/>
        <form id="form">
            <div class="form-group">
                <label for="name">您的姓名</label>
                <input type="text" class="form-control" id="name" placeholder="">
            </div>
            <div class="form-group">
                <label for="email">您的联系方式（不会公开显示）</label>
                <input type="email" class="form-control" id="email" placeholder="">
            </div>
            <div class="form-group">
                <label for="comment">您的意见</label>
                <input type="text" class="form-control" id="comment" placeholder="">
            </div>
            <button type="button" id="submit" class="btn btn-primary">发送</button>
        </form>
        <div id="formSubmitted" style="display:none">正在记录上链，请等 30 秒 ...</div>
    </div>
    
    <h4>已经确认的参会人</h4>
    <table class="table table-striped">
        <thead>
            <tr>
                <th scope="col">姓名</th>
                <th scope="col">意见</th>
            </tr>
        </thead>
        <tbody id="likes">
        </tbody>
    </table>
    <p style="text-align:center">Created with <a target="_blank" href="https://docs.secondstate.io/buidl-developer-tool/why-buidl">the BUIDL IDE</a>.</p>
</div>

JS

/* Don't modify */

var instance = null;
window.addEventListener('web3Ready', function() {
  var contract = web3.ss.contract(abi);
  instance = contract.at(cAddr);
  reload();
});

function reload() {
    // instance.greeting(function (e, r) {
    //     $("#greeting").html(r);
    // });
    
    // $("#form").css("display", "block");
    $("#formSubmitted").css("display", "none");
    web3.ss.getAccounts(function (e, address) {
        if (!e) {
            instance.getComment(address, function (ee, result) {
                $("#greeting").html(result[4].replace("___", result[0]));
                console.log(result);
                if (result[3] == 1 || result[3] == 2) {
                    $("#form").css("display", "none");
                } else {
                    $("#form").css("display", "block");
                }
            });
            
            var likes = "";
            instance.getAddrs(function (ee, addrs) {
                addrs.forEach(function(addr) {
                    instance.getComment(addr, function (ee, r) {
                        if (!ee) {
                            if (r[3] == 2) {
                               likes = likes + "<tr><td>" + r[0] + "</td><td>" + r[2] + "</td></tr>";
                               $("#likes").html(likes);
                            }
                        }
                    });
                });
            });
            $("#likes").html(likes);
        }
    });
}

$("#submit").click(function() {
    if ((!$("#name").val().trim()) || (!$("#comment").val().trim())) {
      alert("请输入姓名与意见");
      return false;
    }
    web3.ss.getAccounts(function (e, address) {
        if (!e) {
            $("#form").css("display", "none");
            $("#formSubmitted").css("display", "block");
            instance.addComment ($("#name").val(), $("#email").val(), $("#comment").val(), {
                gas: 499000,
                gasPrice: 0
            }, function (ee, r) {
                if (ee) {
                    window.alert("Failed at " + address);
                }
            });
            setTimeout(function () {
                reload ();
            }, 25 * 1000);
        }
    });
    return false;
});