Post message function

Let's start by creating our first function - postMessage which will allow us to post a message with specific content.

// src/contracts/actions/write/postMessage.ts

export const postMessage = (
  state: ArditState,
  { caller, input: { content } }: ArditAction
): ContractResult => {};

As we are using Typescript, let's prepare some types first. Firstly - state of the contract which will be updated when users will interact with it. It's just an array of messages posted by users, each of the message needs its own id, creator, content and votes object with current status and list of addresses which have voted for the message.

// src/contracts/types/types.ts

export interface ArditState {
  messages: Message[];
}

interface Message {
  id: number;
  creator: string;
  content: string;
  votes: {
    addresses: string[];
    status: number;
  };
}

Then, we need to create action object - ArditAction which will hold all the possible inputs that user can write to our contract - including name of the function and some additional input - in our case message id and message content. Lastly, we need to indicate what possible functions can be called from our contract (ArditFunction).

// src/contracts/types/types.ts

export interface ArditAction {
  input: ArditInput;
  caller: string;
}

export interface ArditInput {
  function: ArditFunction;
  id: number;
  content: string;
}

export type ArditFunction =
  | 'postMessage'
  | 'upvoteMessage'
  | 'downvoteMessage'
  | 'readMessage';

Let's finish typing by adding ContractResult type which indicates what can be returned from our contract. According to the protocol each of the interaction functions must end with either returning the state (when interaction changes the state of the contract), returning result (when it does not change the state) or throwing an error.

// src/contracts/types/types.ts

export type ArditResult = Message;

export type ContractResult = { state: ArditState } | { result: ArditResult };

Ok, typing done! Let's get back to the function. Write following content as a body of our postMessage function.

// src/contracts/actions/write/postMessage.ts

const messages = state.messages;
if (!content) {
  throw new ContractError(`Creator must provide a message content.`);
}

const id = messages.length + 1;

state.messages.push({
  id,
  creator: caller,
  content,
  votes: {
    addresses: [],
    status: 0,
  },
});

return { state };

Easy, right? If no content is provided we will throw a ContractError. In other case - it will add a new message to the state by provifing its id, creator, content and empty votes object.

Seems ready!