use std::{net::SocketAddr, str::FromStr};

use axum::{
    http::{HeaderMap, StatusCode},
    routing::post,
    Json, Router,
};
use base64::{engine, alphabet, Engine};
use ed25519_dalek::{Signature, VerifyingKey};
use serde::Deserialize;
use twilight_http::Client;
use twilight_interactions::command::{CommandModel, CreateCommand, CommandInputData};
use twilight_model::{
    application::{
        interaction::{Interaction, InteractionType, InteractionData},
    },
    http::interaction::{InteractionResponse, InteractionResponseType, InteractionResponseData}, id::Id,
};


#[derive(CommandModel, CreateCommand)]
#[command(name="save_fact", desc="Quietly save a fact")]
struct SaveFactCommand {
    #[command(rename="name", desc="Fact name")]
    fact_name: String,
    #[command(rename="value", desc="Fact value")]
    fact_value: String,
}

#[tokio::main]
async fn main() {
    let port = 4635;
    let app = Router::new().route("/", post(post_interaction));

    let addr = SocketAddr::from(([127, 0, 0, 1], port));
    dotenvy::dotenv().ok();
    register_command().await;

    axum::Server::bind(&addr)
        .serve(app.into_make_service())
        .await
        .unwrap();
}

type InteractionResult = Result<(StatusCode, Json<InteractionResponse>), (StatusCode, String)>;

async fn post_interaction(headers: HeaderMap, body: String) -> InteractionResult {
    let Ok(interaction): Result<Interaction, _> = serde_json::from_str(&body) else {
        return Err((StatusCode::BAD_REQUEST, "request contained invalid json".to_string()))
    };
    let Some(sig) = headers.get("x-signature-ed25519") else {
        return Err((StatusCode::BAD_REQUEST, "requrest did not include signature header".to_string()))
    };
    let Ok(sig) = hex::decode(sig) else {
        return Err((StatusCode::BAD_REQUEST, "requrest signature is invalid hex".to_string()))
    };
    let Ok(sig) = Signature::from_slice(&sig) else {
        return Err((StatusCode::BAD_REQUEST, "request signature is malformed".to_string()))
    };
    let Some(signed_buf) = headers.get("x-signature-timestamp") else {
        return Err((StatusCode::BAD_REQUEST, "requrest did not include signature timestamp header".to_string()))
    };
    let mut signed_buf = signed_buf.as_bytes().to_owned();
    signed_buf.extend(body.as_bytes());

    let pub_key = discord_pub_key();
    let Ok(()) = pub_key.verify_strict(&signed_buf, &sig) else {
        return Err((StatusCode::UNAUTHORIZED, "interaction failed signature verification".to_string()))
    };

    match interaction.kind {
        InteractionType::Ping => {
            let pong = InteractionResponse {
                kind: InteractionResponseType::Pong,
                data: None,
            };
            Ok((StatusCode::OK, Json(pong)))
        }
        InteractionType::ApplicationCommand => {
            let Some(InteractionData::ApplicationCommand(data)) = interaction.data else {
                return not_found();
            };
            let command_input_data = CommandInputData::from(*data.clone());
            match &*data.name {
                "save_fact" => {
                    let Ok(command_data) = SaveFactCommand::from_interaction(command_input_data) else {
                        return Err((StatusCode::BAD_REQUEST, "invalid save fact command".to_string()));
                    };
                    let reply = InteractionResponse {
                        kind: InteractionResponseType::ChannelMessageWithSource,
                        data: Some(InteractionResponseData {
                            content: Some(format!("Set {0} to {1}", command_data.fact_name, command_data.fact_value)),
                            ..Default::default()
                        })
                    };
                    Ok((StatusCode::OK, Json(reply)))
                }
                _ =>  not_found(),
            }
        }
        _ => not_found(),
    }
}

fn not_found() -> InteractionResult {
    Err((
        StatusCode::NOT_FOUND,
        "requested interaction not found".to_string(),
    ))
}

fn discord_pub_key_bytes() -> Vec<u8> {
    hex::decode(std::env::var("DISCORD_PUB_KEY").unwrap()).unwrap()
}

fn discord_pub_key() -> VerifyingKey {
    let pub_key_bytes: [u8; 32] = discord_pub_key_bytes().try_into().unwrap();
    VerifyingKey::from_bytes(&pub_key_bytes).unwrap()
}

async fn register_command() {
    discord_client()
        .interaction(Id::from_str(&discord_client_id()).unwrap())
        .set_global_commands(&[SaveFactCommand::create_command().into()])
        .await
        .unwrap();
}

#[derive(Deserialize)]
struct ClientCredentialsResponse {
    access_token: String,
}

fn authorization() -> String {
    let engine = engine::GeneralPurpose::new(&alphabet::STANDARD, engine::general_purpose::PAD);
    let auth = format!(
        "{}:{}",
        discord_client_id(),
        discord_client_secret(),
    );
    engine.encode(auth)
}

fn client_credentials_grant() -> ClientCredentialsResponse {
    ureq::post("https://discord.com/api/v10/oauth2/token")
        .set("Authorization", &format!("Basic {}", authorization()))
        .send_form(&[
            ("grant_type", "client_credentials"),
            ("scope", "applications.commands.update"),
        ]).unwrap().into_json().unwrap()
}

fn discord_client_id() -> String {
    std::env::var("DISCORD_CLIENT_ID").unwrap()
}

fn discord_client_secret() -> String {
    std::env::var("DISCORD_CLIENT_SECRET").unwrap()
}

fn discord_client() -> Client {
    let token = client_credentials_grant().access_token;
    Client::new(format!("Bearer {token}"))
}