In the last module we talked about foundational concepts of Dapp. Now, we are ready to develop an end to end decentralized application. Truffle is a one stop IDE that provides everything from an initial application template to a local blockchain for testing the completed Dapp. Similar to how we use remix IDE for testing a smart contract, we'll use the Truffle IDE environment for assembling various components of a Dapp. Upon completion of this module you will be able to work with Truffle IDE for Dapp development, explore the Dapp development process by creating a smart contract and an end to end Dapp. Illustrate test-driven development that is especially critical for smart contracts. Additionally, you will be able to interact on the front-end of the blockchain server through a local blockchain and Injected Web3 environment Metamask. For ease of understanding the Dapp development process we will reuse the problems already discussed in the smart contracts course of the specialization course two. These smart contracts are also available in the solidity documentation. On completion of this lesson you will be able to present a Dapp problem definition, outline an approach to solve the problem, design a high level solution using smart contracts, and identify components of the Truffle IDE. We have chosen to discuss the problem specified in the smart contract, voting dot sol or ballot dot sol of the solidity documentation. It represents the universal problem of choosing a winner or a leader using the democratic process of voting. It represents a wide variety of scenarios from reviews of a product and it's purchase based on the good reviews it received. Also, for passing a law on a budget in a governing body. Let's start with the review of the ballot Dapp. Our goal is to design and develop a Dapp for voting that selects among number of items such as a set of proposals or products. In our case, we'll opt for the popularity of four different fruits. As a reminder from our previous lessons, the chairperson organizes the voting. Voters are identified by their account addresses. Here is the logic or the rules to implement. Only the chairperson can register other voters. A voter can be registered only once. Only registered voters can vote. Voters can vote only once. There is no "write in" that is voters can vote only for the items presented. And the chairperson's vote has double the weightage of the regular voter. To maintain the focus solely on the process of Dapp development we'll not handle the time elements or stages of the balloting. At this time we'll talk about the four steps that make up the design process. We'll represent the main logic of the problem using the smart contract and solidity. We'll begin with data and operations. To this we'll add modifiers and validation checks to make sure rules specified in the problem definition are addressed. We'll design a test smart contract that will ensure all the stated requirements are met. This like unit testing. After the successful completion of unit testing we'll add the front-end component and test the completed Dapp. This is like integration testing. Applying the general design process just discuss to the ballot App requires five steps. Step one, we'll design the ballot dot sol. Step two, we'll then illustrate the modifiers with just one modifier, only owner referring to the qualified person as the chairperson. Recall that in the design of a smart contract you can use modifiers to represent global rules. Step three, we'll add a tester code for the required problem specification and run the test to make sure they all pass. Step four, we'll add the user interface component. And step five, we'll test the complete application by interacting with the interface. Remember, design before you code. Here is a family of ballot smart contract design. Please note the addition of a compartment for modifiers. This compartment is indeed very important. Smart contract design now has four components. The smart contract name, data, modifiers, and functions. Recall that modifiers represent the common rules and policies and constraints. Now that we have discussed the problem, how do we solve or import a solution to the problem into the Truffle IDE? Truffle is an integrated development environment or IDE that provides a range of features for Dapp development including commands for initializing a template or base directory structure for a Dapp, truffle in it. Smart contract compilation, truffle compile. Local test blockchain for testing with a console, truffle develop. Migration scripts for deploying the smart contract, truffle migrate. A test environment for testing the deployed contract, truffle test. These are just a few operations possibly with truffle. These are sufficient develop and tested Dapp. After you complete the course you can explore other advanced features truffle offers. Next, we need to install a few software packages including Node.js which will serve as your web server for the Dapp front-end. Truffle 4.0.4 and Metamask 3.14.1 plugin for Chrome. You may have to add the Metamask plugin from Metamask IO to your Chrome browser. It will link to the blockchain created by truffle to manage the accounts acting as a bridge between the application front-end and the blockchain node that hosts the accounts. To save time and effort we've already installed Node.js and truffle IDE in the virtual machine image we provided in the blockchain basic scores. You used it to complete your project in course one. The virtual machine you downloaded has the required software pre-installed. This pre-installation and VM ensures that we are all in the same versions. This is especially important since software requires updates frequently. This quotient's synchronized to the particular software quotients. Before you start the development, please download a copy, all the files and sub-files needed from the course resource section. Also, it's good to refresh common Linux commands such as cd, ls, mv, make directory, and so on. We have provided a Linux command sheet to help you with this. You may also refer to ballot one demo in the last course.
