//! Code for managing the main database.
//!
//! The database schema is defined via a series of migrations in
//! [migrations].

mod migrations;

#[cfg(test)]
pub mod fake;

use {
    deadpool_postgres::{CreatePoolError, Pool, Runtime},
    serde::{Deserialize, Serialize},
    std::{future::Future, ops::Deref},
    tokio_postgres::NoTls,
    tracing::error,
};

/// Errors that may occur during module initialization
#[derive(Debug)]
pub enum InitialisationError {
    ConnectionPoolError(CreatePoolError),
}

impl std::fmt::Display for InitialisationError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            InitialisationError::ConnectionPoolError(e) => {
                write!(f, "Could not initialise DB connection pool: {}", e)
            }
        }
    }
}

impl std::error::Error for InitialisationError {}

impl From<CreatePoolError> for InitialisationError {
    fn from(value: CreatePoolError) -> Self {
        InitialisationError::ConnectionPoolError(value)
    }
}

pub type InitialisationResult<T> = std::result::Result<T, InitialisationError>;

/// Errors that may occur during normal app operation
#[derive(Debug)]
pub enum Error {
    Pool(deadpool_postgres::PoolError),
    Database,
    NotAllowed,
}

impl std::fmt::Display for Error {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Error::Pool(e) => e.fmt(f),
            Error::Database => write!(f, "Database Error"),
            Error::NotAllowed => write!(f, "Not Allowed"),
        }
    }
}

impl std::error::Error for Error {}

impl From<deadpool_postgres::PoolError> for Error {
    fn from(value: deadpool_postgres::PoolError) -> Self {
        error!(
            details = value.to_string(),
            "Error with deadpool_postgress connection pool"
        );
        Self::Pool(value)
    }
}

impl From<tokio_postgres::Error> for Error {
    fn from(value: tokio_postgres::Error) -> Self {
        error!(
            details = value
                .as_db_error()
                .and_then(|db_error| db_error.detail())
                .unwrap_or(&value.to_string()),
            "PostgreSQL error"
        );
        Error::Database
    }
}

pub type Result<T> = std::result::Result<T, Error>;

pub trait Database: std::fmt::Debug + Clone + Send + Sync + 'static {
    /// Run migrations as needed to ensure the database schema version
    /// match the one used by the current version of the application.
    fn migrate_to_current_version(&self) -> impl Future<Output = Result<()>> + Send;
    fn has_admin_users(&self) -> impl Future<Output = Result<bool>> + Send;
    fn create_user(
        &self,
        real_name: &str,
        email: &str,
        password: &PasswordHash,
    ) -> impl Future<Output = Result<User>> + Send;
    fn get_password_for_user(
        &self,
        user: &User,
    ) -> impl Future<Output = Result<PasswordHash>> + Send;
    fn create_first_admin_user(
        &self,
        real_name: &str,
        email: &str,
        password: &PasswordHash,
    ) -> impl Future<Output = Result<User>> + Send;
    fn is_user_admin(&self, user: &User) -> impl Future<Output = Result<bool>> + Send;
    fn get_user_with_id(
        &self,
        user_id: UserId,
    ) -> impl Future<Output = Result<Option<User>>> + Send;
}

/// Object that manages the database.
///
/// All database access happens through this struct.
#[derive(Clone, Debug)]
pub struct PostgresDatabase {
    connection_pool: Pool,
}

#[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq, Eq)]
pub struct UserId(i32);

#[derive(Debug, Clone)]
pub struct User {
    id: UserId,
    pub real_name: String,
}

impl User {
    pub fn get_id(&self) -> UserId {
        self.id
    }
}

#[derive(Debug)]
pub struct PasswordHash(pub String);

impl Deref for PasswordHash {
    type Target = str;

    fn deref(&self) -> &str {
        &self.0
    }
}

impl PostgresDatabase {
    /// Create a connection pool and return the [Database].
    pub fn new(connection_url: &str) -> InitialisationResult<PostgresDatabase> {
        let mut config = deadpool_postgres::Config::new();
        config.url = Some(connection_url.to_string());
        let pg_pool = config.create_pool(Some(Runtime::Tokio1), NoTls)?;
        Ok(PostgresDatabase {
            connection_pool: pg_pool,
        })
    }

    async fn get_client(&self) -> Result<deadpool_postgres::Client> {
        Ok(self.connection_pool.get().await?)
    }
}

impl Database for PostgresDatabase {
    /// Run migrations as needed to ensure the database schema version
    /// match the one used by the current version of the application.
    async fn migrate_to_current_version(&self) -> Result<()> {
        migrations::migrate_to_current_version(self).await
    }

    #[tracing::instrument]
    async fn has_admin_users(&self) -> Result<bool> {
        let client = self.get_client().await?;
        Ok(client
            .query_one("SELECT EXISTS(SELECT 1 FROM admin_users);", &[])
            .await?
            .get(0))
    }

    #[tracing::instrument]
    async fn create_user(
        &self,
        real_name: &str,
        email: &str,
        password: &PasswordHash,
    ) -> Result<User> {
        let client = self.get_client().await?;
        let id = client
            .query_one(
                r#"
           INSERT INTO users
               (real_name, email, password)
               VALUES ($1, $2, $3)
               RETURNING id;"#,
                &[&real_name, &email, &password.0],
            )
            .await?
            .get(0);
        Ok(User {
            id: UserId(id),
            real_name: real_name.to_string(),
        })
    }

    #[tracing::instrument]
    async fn get_password_for_user(&self, user: &User) -> Result<PasswordHash> {
        let client = self.get_client().await?;
        let row = client
            .query_one("SELECT password FROM users WHERE id = $1;", &[&user.id.0])
            .await?;
        Ok(PasswordHash(row.get(0)))
    }

    #[tracing::instrument]
    async fn create_first_admin_user(
        &self,
        real_name: &str,
        email: &str,
        password: &PasswordHash,
    ) -> Result<User> {
        if self.has_admin_users().await? {
            return Err(Error::NotAllowed);
        }
        let user = self.create_user(real_name, email, password).await?;
        let client = self.get_client().await?;
        client
            .execute("INSERT INTO admin_users (id) VALUES ($1)", &[&user.id.0])
            .await?;
        Ok(User {
            id: user.id,
            real_name: user.real_name,
        })
    }

    #[tracing::instrument]
    async fn is_user_admin(&self, user: &User) -> Result<bool> {
        Ok(self
            .get_client()
            .await?
            .query_opt("SELECT 1 FROM admin_users WHERE id = $1;", &[&user.id.0])
            .await?
            .is_some())
    }

    #[tracing::instrument]
    async fn get_user_with_id(&self, user_id: UserId) -> Result<Option<User>> {
        Ok(self
            .get_client()
            .await?
            .query_opt("SELECT real_name FROM users WHERE id = $1;", &[&user_id.0])
            .await?
            .map(|row| User {
                id: user_id,
                real_name: row.get(0),
            }))
    }
}