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use std::time::Duration;

use diesel::{
    r2d2,
    r2d2::{ConnectionManager, PooledConnection},
    result::Error as DieselError,
    PgConnection,
};
use diesel_migrations::{EmbeddedMigrations, MigrationHarness};

pub type PgConnectionManager = ConnectionManager<PgConnection>;
pub type PgPool = r2d2::Pool<PgConnectionManager>;
pub type PgPooledConnection = PooledConnection<PgConnectionManager>;

#[derive(thiserror::Error, Debug)]
pub enum Error {
    #[error("create pool: {0}")]
    CreatePool(String),
    #[error("get connection from pool: {0}")]
    GetConnection(String),
    #[error("database migration: {0}")]
    GetMigration(String),
    #[error("there are {0} pending migrations")]
    PendingMigration(usize),
    #[error("diesel failed: {0}")]
    Diesel(DieselError),
}

#[derive(Clone)]
pub struct Pool {
    pool: PgPool,
}

#[derive(Clone, Debug)]
pub struct PoolOpts {
    pub connection_timeout: Option<Duration>,
    pub idle_timeout: Option<Duration>,
    pub max_size: Option<u32>,
    pub min_idle: Option<u32>,
    pub test_on_check_out: Option<bool>,
}

impl Default for PoolOpts {
    fn default() -> Self {
        Self {
            connection_timeout: Some(Duration::from_secs(10)),
            idle_timeout: None,
            max_size: None,
            min_idle: None,
            test_on_check_out: Some(true),
        }
    }
}

impl Pool {
    pub fn new(connection_url: String, migrations: EmbeddedMigrations) -> Result<Self, Error> {
        Self::new_with_opts(connection_url, migrations, PoolOpts::default())
    }

    pub fn new_with_opts(
        connection_url: String,
        migrations: EmbeddedMigrations,
        opts: PoolOpts,
    ) -> Result<Self, Error> {
        let mut builder = r2d2::Pool::builder();

        if let Some(connection_timeout) = opts.connection_timeout {
            builder = builder.connection_timeout(connection_timeout);
        }

        if let Some(idle_timeout) = opts.idle_timeout {
            builder = builder.idle_timeout(Some(idle_timeout));
        }

        if let Some(min_idle) = opts.min_idle {
            builder = builder.min_idle(Some(min_idle));
        }

        if let Some(max_size) = opts.max_size {
            builder = builder.max_size(max_size);
        }

        if let Some(test_on_check_out) = opts.test_on_check_out {
            builder = builder.test_on_check_out(test_on_check_out);
        }

        let pool = builder
            .build(ConnectionManager::<PgConnection>::new(connection_url))
            .map_err(|e| Error::CreatePool(e.to_string()))?;

        check_pending_migrations(&pool, migrations)?;

        Ok(Self { pool })
    }

    pub fn execute<T, Q, E>(&self, query: Q) -> Result<T, E>
    where
        T: Send + 'static,
        Q: FnOnce(PgPooledConnection) -> Result<T, E> + Send + 'static,
        E: From<Error>,
    {
        let conn = self.connection()?;
        tokio::task::block_in_place(|| query(conn))
    }

    fn connection(&self) -> Result<PgPooledConnection, Error> {
        self.pool
            .get()
            .map_err(|e| Error::GetConnection(e.to_string()))
    }
}

fn check_pending_migrations(pool: &PgPool, migrations: EmbeddedMigrations) -> Result<(), Error> {
    match count_pending_migrations(pool, migrations)? {
        0 => Ok(()),
        n => Err(Error::PendingMigration(n)),
    }
}

fn count_pending_migrations(pool: &PgPool, migrations: EmbeddedMigrations) -> Result<usize, Error> {
    let count_pending_migrations = MigrationHarness::pending_migrations(
        &mut pool
            .get()
            .map_err(|e| Error::GetConnection(e.to_string()))?,
        migrations,
    )
    .map_err(|e| Error::GetMigration(e.to_string()))?
    .len();
    Ok(count_pending_migrations)
}