index.ts

import {
  Client,
  EmojiResolvable,
  MessageReaction,
  PartialMessageReaction,
  PartialUser,
  Role,
  Snowflake,
  User,
} from "discord.js";

export interface ReactionRoleConfiguration {
  messageId: Snowflake;
  roleId: Snowflake;
  reaction: EmojiResolvable;
}

interface ReactionRoleReverseIndex {
  [server: string]: { [emoji: string]: string };
}

function buildReverseSearch(
  config: ReactionRoleConfiguration[]
): ReactionRoleReverseIndex {
  return config.reduce((index, conf) => {
    if (!index[conf.messageId]) {
      index[conf.messageId] = {};
    }
    index[conf.messageId][conf.reaction.toString()] = conf.roleId;
    return index;
  }, {} as ReactionRoleReverseIndex);
}

export class ReactionRole {
  private reverseConfig: ReactionRoleReverseIndex;

  constructor(private client: Client, config: ReactionRoleConfiguration[]) {
    this.reverseConfig = buildReverseSearch(config);

    this.addReaction = this.addReaction.bind(this);
    this.removeReaction = this.removeReaction.bind(this);

    client.on("messageReactionAdd", this.addReaction);
    client.on("messageReactionRemove", this.removeReaction);
  }

  private extractRole(
    reaction: MessageReaction | PartialMessageReaction
  ): Promise<Role | null> {
    const messageId = reaction.message.id;
    const reactionId = reaction.emoji.id;
    const reactionName = reaction.emoji.name;

    if (this.reverseConfig[messageId]) {
      const reverseConfig = this.reverseConfig[messageId];

      // Attempt to parse the role from the configuration object.
      let roleId;
      if (reactionId && reverseConfig[reactionId]) {
        roleId = reverseConfig[reactionId];
      } else if (reactionName && reverseConfig[reactionName]) {
        roleId = reverseConfig[reactionName];
      }

      // Attempt to extract and return the role
      if (roleId && reaction.message.guild) {
        return reaction.message.guild.roles.fetch(roleId);
      }
    }
    return Promise.resolve(null);
  }

  private async addReaction(
    reaction: MessageReaction | PartialMessageReaction,
    user: User | PartialUser
  ): Promise<void> {
    if (process.env.REACTION_DEBUG) {
      console.debug("add", {
        message: reaction.message.id,
        user: user.id,
        emoji: reaction.emoji.name,
        partial: reaction.partial,
      });
    }

    /* Early leave if the message is not sent to a guild. */
    if (!reaction.message.guild) {
      return;
    }

    /* Get the member that reacted originally. */
    const member = await reaction.message.guild.members.fetch(user.id);
    if (!member) {
      return;
    }

    /* Try to add the member to the guild. */
    await this.extractRole(reaction).then((role) => {
      if (role) {
        return member.roles.add(role);
      }
    });
  }

  async removeReaction(
    reaction: MessageReaction | PartialMessageReaction,
    user: User | PartialUser
  ): Promise<void> {
    if (process.env.REACTION_DEBUG) {
      console.debug("remove", {
        message: reaction.message.id,
        user: user.id,
        emoji: reaction.emoji.name,
        partial: reaction.partial,
      });
    }

    /* Early leave if the message is not sent to a guild. */
    if (!reaction.message.guild) {
      return;
    }

    /* Get the member that reacted originally. */
    const member = await reaction.message.guild.members.fetch(user.id);
    if (!member) {
      return;
    }

    /* Try to add the member to the guild. */
    await this.extractRole(reaction).then((role) => {
      if (role) {
        return member.roles.remove(role);
      }
    });
  }

  teardown(): void {
    this.client.off("messageReactionAdd", this.addReaction);
    this.client.off("messageReactionRemove", this.removeReaction);
  }
}