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

use axum::{
    extract::State,
    http::{HeaderMap, StatusCode},
    routing::post,
    Json, Router,
};
use base64::{alphabet, engine, Engine};
use commands::{SetFactCommand, GetFactCommand, set_fact, get_fact};
use ed25519_dalek::{Signature, VerifyingKey};
use serde::Deserialize;
use sqlx::{postgres::PgPoolOptions, PgPool};
use twilight_http::Client;
use twilight_interactions::command::{CommandInputData, CommandModel, CreateCommand};

use twilight_model::{
    application::interaction::{Interaction, InteractionData, InteractionType},
    http::interaction::{InteractionResponse, InteractionResponseType},
    id::Id
};
mod commands;
mod database;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let port = 4635;
    dotenvy::dotenv().ok();

    let pg_pool = PgPoolOptions::new()
        .max_connections(5)
        .connect(database_url().as_str())
        .await?;

    sqlx::migrate!().run(&pg_pool).await?;

    let app = Router::new()
        .route("/", post(post_interaction))
        .with_state(pg_pool);

    let addr = SocketAddr::from(([127, 0, 0, 1], port));

    register_commands().await;

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

    Ok(())
}

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

fn validate_request(headers: HeaderMap, body: String) -> Result<Interaction, (StatusCode, String)> {
    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()))
    };

    Ok(interaction)
}

async fn post_interaction(
    headers: HeaderMap,
    State(pg_pool): State<PgPool>,
    body: String,
) -> InteractionResult {
    let interaction = match validate_request(headers, body) {
        Ok(interaction) => interaction,
        Err(error) => return Err(error),
    };

    match interaction.kind {
        InteractionType::Ping => {
            let pong = InteractionResponse {
                kind: InteractionResponseType::Pong,
                data: None,
            };
            Ok((StatusCode::OK, Json(pong)))
        }
        InteractionType::ApplicationCommand => {
            let author_id = interaction.author_id();
            let Some(InteractionData::ApplicationCommand(data)) = interaction.data else {
                return not_found();
            };
            let command_input_data = CommandInputData::from(*data.clone());
            match &*data.name {
                SetFactCommand::NAME => {
                    let Ok(command_data) = SetFactCommand::from_interaction(command_input_data) else {
                        return Err((StatusCode::BAD_REQUEST, format!("invalid {0} command.", SetFactCommand::NAME)));
                    };
                    let Some(author_id) = author_id else {
                        return Err((StatusCode::BAD_REQUEST, format!("{0} requires a user.", SetFactCommand::NAME)));
                    };
                    match set_fact(interaction.id, interaction.channel_id, author_id, command_data, &pg_pool).await {
                        Ok(response) => Ok((StatusCode::OK, Json(response))),
                        Err(err) => Err(err),
                    }
                },
                GetFactCommand::NAME => {
                    let Ok(command_data) = GetFactCommand::from_interaction(command_input_data) else {
                        return Err((StatusCode::BAD_REQUEST, format!("invalid {0} command.", GetFactCommand::NAME)));
                    };
                    let Some(author_id) = author_id else {
                        return Err((StatusCode::BAD_REQUEST, format!("{0} requires a user.", GetFactCommand::NAME)));
                    };
                    
                    match get_fact(interaction.channel_id, author_id, command_data, &pg_pool).await {
                        Ok(response) => Ok((StatusCode::OK, Json(response))),
                        Err(err) => Err(err),
                    }
                },
                _ => 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_commands() {
    discord_client()
        .interaction(Id::from_str(&discord_client_id()).unwrap())
        .set_global_commands(&[
            GetFactCommand::create_command().into(),
            SetFactCommand::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}"))
}

fn database_url() -> String {
    std::env::var("DATABASE_URL").unwrap()
}