dircord/src/main.rs

use std::{env, sync::Arc};

use serenity::{
    async_trait,
    http::Http,
    model::{
        channel::Message,
        id::{ChannelId, UserId},
        prelude::Ready,
    },
    prelude::*,
};

struct Handler;

#[async_trait]
impl EventHandler for Handler {
    async fn message(&self, ctx: Context, msg: Message) {
        let nick = {
            if let Some(member) = msg.member {
                match member.nick {
                    Some(n) => n,
                    None => msg.author.name,
                }
            } else {
                msg.author.name
            }
        };

        let (http, channel_id, user_id) = {
            let data = ctx.data.read().await;

            let http = data.get::<HttpKey>().unwrap().to_owned();
            let channel_id = data.get::<ChannelIdKey>().unwrap().to_owned();
            let user_id = data.get::<UserIdKey>().unwrap().to_owned();

            (http, channel_id, user_id)
        };

        if user_id != msg.author.id && !msg.author.bot {
            send_message(&http, &channel_id, &format!("{}: {}", nick, msg.content))
                .await
                .unwrap();
        }
    }

    async fn ready(&self, ctx: Context, info: Ready) {
        let id = info.user.id;

        let mut data = ctx.data.write().await;
        data.insert::<UserIdKey>(id);
    }
}

struct HttpKey;
struct ChannelIdKey;
struct UserIdKey;

impl TypeMapKey for HttpKey {
    type Value = Arc<Http>;
}

impl TypeMapKey for ChannelIdKey {
    type Value = ChannelId;
}

impl TypeMapKey for UserIdKey {
    type Value = UserId;
}

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let token = env::var("DISCORD_TOKEN").expect("DISCORD_TOKEN not set");

    let mut client = Client::builder(&token).event_handler(Handler).await?;

    let channel_id = ChannelId(831255708875751477);

    {
        let mut data = client.data.write().await;
        data.insert::<HttpKey>(client.cache_and_http.http.clone());
        data.insert::<ChannelIdKey>(channel_id);
    }

    client.start().await?;

    Ok(())
}

async fn send_message(
    http: &Http,
    channel_id: &ChannelId,
    content: &str,
) -> anyhow::Result<Message> {
    Ok(channel_id.say(http, content).await?)
}