rnbis-utils.js

// Generate random integer, we will use this to use random message from list of dummy messages.
export const getRandomInt = (min: number, max: number) => {
  return Math.floor(Math.random() * (max - min)) + min;
};

// Generate unique key for message component of FlatList.
export const generateUniqueKey = () =>
  `_${Math.random().toString(36).substr(2, 9)}`;

// List of test messages to generate chat data.
export const testMessages = [
  'Hey, where were you yesterday? I was trying to call you',
  'Yeah dude!! Had a really bad night. I was really hungover',
  'lol, thats so typical you. Who did you go out with?',
  'Dont even ask me about it, I am never going drink with Uthred again. That dude is a beast',
  'hahahaha, I can totally imagine!!',
  'Ciao :)',
];
  
export type Message = {
  id: string;
  text: string;
  isMyMessage: boolean;
};

/**
 * Mocks the api call to query `n` number of messages.
 * We are going to add some timeout before returning the result to simulate an api call over network.
 * 
 * We are going to generate two types of message:
 * - sent message
 * - received message
 * 
 * This will be controlled by a boolean property on message object - `isMyMessage`.
 * This will be randomly assigned to message, based on result of getRandomInt.
 * These two messages will be styled differently, which is the case for most of the
 * popular messaging applications e.g., whatsapp, messenger
 * 
 * @param n {number} Number of new messages to query
 * @param networkLatency {number} Number of milliseconds, to simulate api call.
 */
export const queryMoreMessages: (
  n: number,
  networkLatency?: number
) => Promise<Array<Message>> = (n, networkLatency = 100) => {
  return new Promise((resolve) => {
    const newMessages: Array<Message> = [];

    for (let i = 0; i < n; i++) {
      const messageText = testMessages[getRandomInt(0, testMessages.length)];
      newMessages.push({
        id: generateUniqueKey(),
        text: messageText,
        isMyMessage: Boolean(getRandomInt(0, 2)), // Randomly assign true or false.
      });
    }

    // Lets resolve after 500 ms, to simulate network latency.
    setTimeout(() => {
      resolve(newMessages);
    }, networkLatency);
  });
};