use crate::connection::{ConnectOptions, Connection};
use crate::error::Error;
use crate::executor::Executor;
use crate::migrate::MigrateError;
use crate::migrate::Migration;
use crate::migrate::{Migrate, MigrateDatabase};
use crate::postgres::{PgConnectOptions, PgConnection, Postgres};
use crate::query::query;
use crate::query_as::query_as;
use crate::query_scalar::query_scalar;
use crc::crc32;
use futures_core::future::BoxFuture;
use std::str::FromStr;
use std::time::Duration;
use std::time::Instant;

fn parse_for_maintenance(uri: &str) -> Result<(PgConnectOptions, String), Error> {
    let mut options = PgConnectOptions::from_str(uri)?;

    // pull out the name of the database to create
    let database = options
        .database
        .as_deref()
        .unwrap_or(&options.username)
        .to_owned();

    // switch us to the maintenance database
    // use `postgres` _unless_ the current user is postgres, in which case, use `template1`
    // this matches the behavior of the `createdb` util
    options.database = if options.username == "postgres" {
        Some("template1".into())
    } else {
        Some("postgres".into())
    };

    Ok((options, database))
}

impl MigrateDatabase for Postgres {
    fn create_database(uri: &str) -> BoxFuture<'_, Result<(), Error>> {
        Box::pin(async move {
            let (options, database) = parse_for_maintenance(uri)?;
            let mut conn = options.connect().await?;

            let _ = conn
                .execute(&*format!(
                    "CREATE DATABASE \"{}\"",
                    database.replace('"', "\"\"")
                ))
                .await?;

            Ok(())
        })
    }

    fn database_exists(uri: &str) -> BoxFuture<'_, Result<bool, Error>> {
        Box::pin(async move {
            let (options, database) = parse_for_maintenance(uri)?;
            let mut conn = options.connect().await?;

            let exists: bool =
                query_scalar("select exists(SELECT 1 from pg_database WHERE datname = $1)")
                    .bind(database)
                    .fetch_one(&mut conn)
                    .await?;

            Ok(exists)
        })
    }

    fn drop_database(uri: &str) -> BoxFuture<'_, Result<(), Error>> {
        Box::pin(async move {
            let (options, database) = parse_for_maintenance(uri)?;
            let mut conn = options.connect().await?;

            let _ = conn
                .execute(&*format!(
                    "DROP DATABASE IF EXISTS \"{}\"",
                    database.replace('"', "\"\"")
                ))
                .await?;

            Ok(())
        })
    }
}

impl Migrate for PgConnection {
    fn ensure_migrations_table(&mut self) -> BoxFuture<'_, Result<(), MigrateError>> {
        Box::pin(async move {
            // language=SQL
            self.execute(
                r#"
CREATE TABLE IF NOT EXISTS _sqlx_migrations (
    version BIGINT PRIMARY KEY,
    description TEXT NOT NULL,
    installed_on TIMESTAMPTZ NOT NULL DEFAULT now(),
    success BOOLEAN NOT NULL,
    checksum BYTEA NOT NULL,
    execution_time BIGINT NOT NULL
);
                "#,
            )
            .await?;

            Ok(())
        })
    }

    fn version(&mut self) -> BoxFuture<'_, Result<Option<(i64, bool)>, MigrateError>> {
        Box::pin(async move {
            // language=SQL
            let row = query_as(
                "SELECT version, NOT success FROM _sqlx_migrations ORDER BY version DESC LIMIT 1",
            )
            .fetch_optional(self)
            .await?;

            Ok(row)
        })
    }

    fn lock(&mut self) -> BoxFuture<'_, Result<(), MigrateError>> {
        Box::pin(async move {
            let database_name = current_database(self).await?;
            let lock_id = generate_lock_id(&database_name);

            // create an application lock over the database
            // this function will not return until the lock is acquired

            // https://www.postgresql.org/docs/current/explicit-locking.html#ADVISORY-LOCKS
            // https://www.postgresql.org/docs/current/functions-admin.html#FUNCTIONS-ADVISORY-LOCKS-TABLE

            // language=SQL
            let _ = query("SELECT pg_advisory_lock($1)")
                .bind(lock_id)
                .execute(self)
                .await?;

            Ok(())
        })
    }

    fn unlock(&mut self) -> BoxFuture<'_, Result<(), MigrateError>> {
        Box::pin(async move {
            let database_name = current_database(self).await?;
            let lock_id = generate_lock_id(&database_name);

            // language=SQL
            let _ = query("SELECT pg_advisory_unlock($1)")
                .bind(lock_id)
                .execute(self)
                .await?;

            Ok(())
        })
    }

    fn validate<'e: 'm, 'm>(
        &'e mut self,
        migration: &'m Migration,
    ) -> BoxFuture<'m, Result<(), MigrateError>> {
        Box::pin(async move {
            // language=SQL
            let checksum: Option<Vec<u8>> =
                query_scalar("SELECT checksum FROM _sqlx_migrations WHERE version = $1")
                    .bind(migration.version)
                    .fetch_optional(self)
                    .await?;

            if let Some(checksum) = checksum {
                return if checksum == &*migration.checksum {
                    Ok(())
                } else {
                    Err(MigrateError::VersionMismatch(migration.version))
                };
            } else {
                Err(MigrateError::VersionMissing(migration.version))
            }
        })
    }

    fn apply<'e: 'm, 'm>(
        &'e mut self,
        migration: &'m Migration,
    ) -> BoxFuture<'m, Result<Duration, MigrateError>> {
        Box::pin(async move {
            let mut tx = self.begin().await?;
            let start = Instant::now();

            let _ = tx.execute(&*migration.sql).await?;

            tx.commit().await?;

            let elapsed = start.elapsed();

            // language=SQL
            let _ = query(
                r#"
    INSERT INTO _sqlx_migrations ( version, description, success, checksum, execution_time )
    VALUES ( $1, $2, TRUE, $3, $4 )
                "#,
            )
            .bind(migration.version)
            .bind(&*migration.description)
            .bind(&*migration.checksum)
            .bind(elapsed.as_nanos() as i64)
            .execute(self)
            .await?;

            Ok(elapsed)
        })
    }

    fn revert<'e: 'm, 'm>(
        &'e mut self,
        migration: &'m Migration,
    ) -> BoxFuture<'m, Result<Duration, MigrateError>> {
        Box::pin(async move {
            let mut tx = self.begin().await?;
            let start = Instant::now();

            let _ = tx.execute(&*migration.sql).await?;

            tx.commit().await?;

            let elapsed = start.elapsed();

            // language=SQL
            let _ = query(r#"DELETE FROM _sqlx_migrations WHERE version = $1"#)
                .bind(migration.version)
                .execute(self)
                .await?;

            Ok(elapsed)
        })
    }
}

async fn current_database(conn: &mut PgConnection) -> Result<String, MigrateError> {
    // language=SQL
    Ok(query_scalar("SELECT current_database()")
        .fetch_one(conn)
        .await?)
}

// inspired from rails: https://github.com/rails/rails/blob/6e49cc77ab3d16c06e12f93158eaf3e507d4120e/activerecord/lib/active_record/migration.rb#L1308
fn generate_lock_id(database_name: &str) -> i64 {
    // 0x3d32ad9e chosen by fair dice roll
    0x3d32ad9e * (crc32::checksum_ieee(database_name.as_bytes()) as i64)
}