use std::sync::Arc;

use anyhow::Error;

use aes_gcm::{aead::Aead, AeadCore, Aes256Gcm, Key, KeyInit};
use argon2::{password_hash::SaltString, Argon2, PasswordHash, PasswordHasher, PasswordVerifier};
use base64::{engine::general_purpose::STANDARD, Engine as _};
use giterated_models::{
    model::{authenticated::UserAuthenticationToken, instance::Instance, user::User},
    operation::instance::{AuthenticationTokenRequest, RegisterAccountRequest},
};
use rsa::{
    pkcs8::{EncodePrivateKey, EncodePublicKey},
    rand_core::OsRng,
    RsaPrivateKey, RsaPublicKey,
};

use secrecy::ExposeSecret;
use sqlx::PgPool;
use tokio::sync::Mutex;

use crate::authentication::AuthenticationTokenGranter;

use super::{AuthBackend, SettingsBackend, UserBackend};

pub struct UserAuth {
    pub pg_pool: PgPool,
    pub this_instance: Instance,
    pub auth_granter: Arc<Mutex<AuthenticationTokenGranter>>,
    pub settings_provider: Arc<Mutex<dyn SettingsBackend>>,
}

impl UserAuth {
    pub fn new(
        pool: PgPool,
        this_instance: &Instance,
        granter: Arc<Mutex<AuthenticationTokenGranter>>,
        settings_provider: Arc<Mutex<dyn SettingsBackend>>,
    ) -> Self {
        Self {
            pg_pool: pool,
            this_instance: this_instance.clone(),
            auth_granter: granter,
            settings_provider,
        }
    }
}

#[async_trait::async_trait]
impl UserBackend for UserAuth {
    async fn exists(&mut self, user: &User) -> Result<bool, Error> {
        Ok(sqlx::query_as!(
            UserRow,
            r#"SELECT * FROM users WHERE username = $1"#,
            user.username
        )
        .fetch_one(&self.pg_pool.clone())
        .await
        .is_ok())
    }
}

#[async_trait::async_trait]
impl AuthBackend for UserAuth {
    async fn register(
        &mut self,
        request: RegisterAccountRequest,
    ) -> Result<UserAuthenticationToken, Error> {
        const BITS: usize = 2048;

        let private_key = RsaPrivateKey::new(&mut OsRng, BITS).unwrap();
        let public_key = RsaPublicKey::from(&private_key);

        let key = {
            let mut target: [u8; 32] = [0; 32];

            let mut index = 0;
            let mut iterator = request.password.expose_secret().0.as_bytes().iter();
            while index < 32 {
                if let Some(next) = iterator.next() {
                    target[index] = *next;
                    index += 1;
                } else {
                    iterator = request.password.expose_secret().0.as_bytes().iter();
                }
            }

            target
        };

        let key: &Key<Aes256Gcm> = &key.into();
        let cipher = Aes256Gcm::new(key);
        let nonce = Aes256Gcm::generate_nonce(&mut OsRng);
        let ciphertext = cipher
            .encrypt(&nonce, private_key.to_pkcs8_der().unwrap().as_bytes())
            .unwrap();

        let private_key_enc = format!("{}#{}", STANDARD.encode(nonce), STANDARD.encode(ciphertext));

        let salt = SaltString::generate(&mut OsRng);

        let argon2 = Argon2::default();

        let password_hash = argon2
            .hash_password(request.password.expose_secret().0.as_bytes(), &salt)
            .unwrap()
            .to_string();

        let user = match sqlx::query_as!(
            UserRow,
            r#"INSERT INTO users VALUES ($1, $2, $3, $4, $5) returning *"#,
            request.username,
            "example.com",
            password_hash,
            public_key
                .to_public_key_pem(rsa::pkcs8::LineEnding::LF)
                .unwrap(),
            private_key_enc
        )
        .fetch_one(&self.pg_pool)
        .await
        {
            Ok(user) => user,
            Err(err) => {
                error!("Failed inserting into the database! {:?}", err);

                return Err(err.into());
            }
        };

        let mut granter = self.auth_granter.lock().await;
        let token = granter
            .create_token_for(
                &User {
                    username: user.username,
                    instance: self.this_instance.clone(),
                },
                &self.this_instance,
            )
            .await;

        Ok(UserAuthenticationToken::from(token))
    }

    async fn login(
        &mut self,
        source: &Instance,
        request: AuthenticationTokenRequest,
    ) -> Result<UserAuthenticationToken, Error> {
        info!("fetching!");
        let user = sqlx::query_as!(
            UserRow,
            r#"SELECT * FROM users WHERE username = $1"#,
            request.username
        )
        .fetch_one(&self.pg_pool)
        .await?;

        let hash = PasswordHash::new(&user.password).unwrap();

        if Argon2::default()
            .verify_password(request.password.expose_secret().0.as_bytes(), &hash)
            .is_err()
        {
            info!("invalid password");
            return Err(Error::from(AuthenticationError::InvalidPassword));
        }

        let mut granter = self.auth_granter.lock().await;
        let token = granter
            .create_token_for(
                &User {
                    username: user.username,
                    instance: self.this_instance.clone(),
                },
                &source,
            )
            .await;

        Ok(UserAuthenticationToken::from(token))
    }
}

#[allow(unused)]
#[derive(Debug, sqlx::FromRow)]
struct UserRow {
    pub username: String,
    pub email: Option<String>,
    pub password: String,
    pub public_key: String,
    pub enc_private_key: Vec<u8>,
}

#[derive(Debug, thiserror::Error)]
pub enum AuthenticationError {
    #[error("invalid password")]
    InvalidPassword,
}