mod backup;

use std::str::FromStr;

use hex_literal::hex;
use sqlx::{
    error::{DatabaseError, ErrorKind},
    migrate::{Migrate as _, MigrateDatabase as _},
    sqlite::{Sqlite, SqliteConnectOptions, SqlitePool, SqlitePoolOptions},
};

pub async fn prepare(url: &str, backup_url: &str) -> Result<SqlitePool, Error> {
    if backup_url != "sqlite::memory:" && Sqlite::database_exists(backup_url).await? {
        return Err(Error::BackupExists(backup_url.into()));
    }

    let pool = create(url).await?;

    // First migration of original migration series, from commit
    // 9bd6d9862b1c243def02200bca2cfbf578ad2a2f or earlier.
    reject_migration(&pool, "20240831024047", "login", &hex!("9949D238C4099295EC4BEE734BFDA8D87513B2973DFB895352A11AB01DD46CB95314B7F1B3431B77E3444A165FE3DC28")).await?;

    // Original version of this migration was buggy, but didn't require a
    // database reset to fix.
    migration_replaced(
        &pool,
        "20241009031441",
        &hex!("4B5873397C8BA9CFAF49172EE6DE455CD643A27BD71032ECD8EFA7684362FE620A8F6B27D493AF8D9A570C38CC1A6416"),
        &hex!("E5CDEDA38F2BCE4C24A45E58D3BDE3FF2C30B1431C3B01870BB9DEB142E5A200B9C850C3C72A45D352C15D8DB51B8467"),
    ).await?;

    let backup_pool = create(backup_url).await?;
    backup::Backup::from(&pool)
        .to(&backup_pool)
        .backup()
        .await?;

    if let Err(migrate_error) = sqlx::migrate!().run(&pool).await {
        if let Err(restore_error) = backup::Backup::from(&backup_pool).to(&pool).backup().await {
            Err(Error::Restore(restore_error, migrate_error))?;
        } else if let Err(drop_error) = Sqlite::drop_database(backup_url).await {
            Err(Error::Drop(drop_error, migrate_error))?;
        } else {
            Err(migrate_error)?;
        };
    }

    Sqlite::drop_database(backup_url).await?;
    Ok(pool)
}

async fn create(database_url: &str) -> sqlx::Result<SqlitePool> {
    let options = SqliteConnectOptions::from_str(database_url)?
        .create_if_missing(true)
        .optimize_on_close(true, /* analysis_limit */ None);

    let pool = SqlitePoolOptions::new().connect_with(options).await?;
    Ok(pool)
}

async fn reject_migration(
    pool: &SqlitePool,
    version: &str,
    description: &str,
    checksum: &[u8],
) -> Result<(), Error> {
    let mut conn = pool.acquire().await?;
    conn.ensure_migrations_table().await?;
    let applied = conn.list_applied_migrations().await?;

    for migration in applied {
        if migration.checksum == checksum {
            return Err(Error::Rejected(version.into(), description.into()));
        }
    }

    Ok(())
}

async fn migration_replaced(
    pool: &SqlitePool,
    version: &str,
    original: &[u8],
    replacement: &[u8],
) -> Result<(), sqlx::Error> {
    let mut conn = pool.acquire().await?;
    conn.ensure_migrations_table().await?;
    sqlx::query!(
        r#"
            update _sqlx_migrations
            set checksum = $1
            where version = $2
                and checksum = $3
        "#,
        replacement,
        version,
        original,
    )
    .execute(&mut *conn)
    .await?;

    Ok(())
}

/// Errors occurring during database setup.
#[derive(Debug, thiserror::Error)]
pub enum Error {
    /// Failure due to a database error. See [`sqlx::Error`].
    #[error(transparent)]
    Database(#[from] sqlx::Error),
    /// Failure because an existing database backup already exists.
    #[error("backup from a previous failed migration already exists: {0}")]
    BackupExists(String),
    /// Failure due to a database backup error. See [`backup::Error`].
    #[error(transparent)]
    Backup(#[from] backup::Error),
    #[error("migration failed: {1}\nrestoring backup failed: {0}")]
    Restore(backup::Error, sqlx::migrate::MigrateError),
    #[error(
        "migration failed: {1}\nrestoring from backup succeeded, but deleting backup failed: {0}"
    )]
    Drop(sqlx::Error, sqlx::migrate::MigrateError),
    /// Failure due to a database migration error. See
    /// [`sqlx::migrate::MigrateError`].
    #[error(transparent)]
    Migration(#[from] sqlx::migrate::MigrateError),
    /// Failure because the database contains a migration from an unsupported
    /// schema version.
    #[error("database contains rejected migration {0}:{1}, move it aside")]
    Rejected(String, String),
}

pub trait NotFound: Sized {
    type Ok;
    type Error;

    fn not_found<E, F>(self, map: F) -> Result<Self::Ok, E>
    where
        E: From<Self::Error>,
        F: FnOnce() -> E,
    {
        self.optional()?.ok_or_else(map)
    }

    fn optional(self) -> Result<Option<Self::Ok>, Self::Error>;
}

impl<T> NotFound for Result<T, sqlx::Error> {
    type Ok = T;
    type Error = sqlx::Error;

    fn optional(self) -> Result<Option<T>, sqlx::Error> {
        match self {
            Ok(value) => Ok(Some(value)),
            Err(sqlx::Error::RowNotFound) => Ok(None),
            Err(other) => Err(other),
        }
    }
}

pub trait Duplicate {
    type Ok;
    type Error;

    fn duplicate<E, F>(self, map: F) -> Result<Self::Ok, E>
    where
        E: From<Self::Error>,
        F: FnOnce() -> E;
}

impl<T> Duplicate for Result<T, sqlx::Error> {
    type Ok = T;
    type Error = sqlx::Error;

    fn duplicate<E, F>(self, map: F) -> Result<T, E>
    where
        E: From<sqlx::Error>,
        F: FnOnce() -> E,
    {
        match self {
            Ok(value) => Ok(value),
            Err(error) => match error.as_database_error().map(DatabaseError::kind) {
                Some(ErrorKind::UniqueViolation) => Err(map()),
                _ => Err(error.into()),
            },
        }
    }
}