use std::{
    fmt::Display,
    time::{SystemTime, UNIX_EPOCH},
};

use chrono::TimeDelta;
use log::{debug, info};
use sqlx::{Sqlite, SqlitePool, Transaction, query};

use crate::app::App;

macro_rules! make_upgrade {
    ($app:expr, $old_version:expr, $new_version:expr, $sql_name:expr) => {
        let mut tx = $app
            .db
            .begin()
            .await
            .map_err(|err| update::Error::TxnStart(err))?;
        debug!("Migrating: {} -> {}", $old_version, $new_version);

        sqlx::raw_sql(include_str!($sql_name))
            .execute(&mut *tx)
            .await
            .map_err(|err| update::Error::SqlUpdate(err))?;

        set_db_version(
            &mut tx,
            if $old_version == Self::Empty {
                // There is no previous version we would need to remove
                None
            } else {
                Some($old_version)
            },
            $new_version,
        )
        .await
        .map_err(|err| update::Error::SetDbVersion {
            err,
            new_version: $new_version,
        })?;

        tx.commit()
            .await
            .map_err(|err| update::Error::TxnCommit(err))?;

        // NOTE: This is needed, so that sqlite "sees" our changes to the table
        // without having to reconnect. <2025-02-18>
        query!("VACUUM")
            .execute(&$app.db)
            .await
            .map_err(|err| update::Error::SqlVacuum(err))?;

        Box::pin($new_version.update($app))
            .await
            .map_err(|err| update::Error::NextUpdate {
                err: Box::new(err),
                new_version: $new_version,
            })?;

        Ok(())
    };
}

#[derive(Debug, Clone, Copy, PartialEq, PartialOrd)]
pub(crate) enum DbVersion {
    /// The database is not yet initialized.
    Empty,

    /// Introduced: 2025-09-02.
    One,
}
const CURRENT_VERSION: DbVersion = DbVersion::One;

async fn set_db_version(
    tx: &mut Transaction<'_, Sqlite>,
    old_version: Option<DbVersion>,
    new_version: DbVersion,
) -> Result<(), db_version_set::Error> {
    let valid_from = get_current_date();

    if let Some(old_version) = old_version {
        let valid_to = valid_from + 1;
        let old_version = old_version.as_sql_integer();

        query!(
            "UPDATE version SET valid_to = ? WHERE namespace = 'rocie' AND number = ?;",
            valid_to,
            old_version
        )
        .execute(&mut *(*tx))
        .await?;
    }

    let version = new_version.as_sql_integer();

    query!(
        "INSERT INTO version (namespace, number, valid_from, valid_to) VALUES ('rocie', ?, ?, NULL);",
        version,
        valid_from
    )
    .execute(&mut *(*tx))
    .await?;

    Ok(())
}

pub(crate) mod db_version_set {
    #[derive(thiserror::Error, Debug)]
    pub(crate) enum Error {
        #[error("Failed to perform database action: {0}")]
        DbError(#[from] sqlx::Error),
    }
}

impl DbVersion {
    fn as_sql_integer(self) -> i32 {
        match self {
            DbVersion::One => 1,

            DbVersion::Empty => unreachable!("A empty version does not have an associated integer"),
        }
    }

    fn from_db(number: i64, namespace: &str) -> Result<Self, db_version_parse::Error> {
        match (number, namespace) {
            (1, "rocie") => Ok(DbVersion::One),
            (number, namespace) => Err(db_version_parse::Error::UnkownVersion {
                namespace: namespace.to_owned(),
                number,
            }),
        }
    }

    /// Try to update the database from version [`self`] to the [`CURRENT_VERSION`].
    ///
    /// Each update is atomic, so if this function fails you are still guaranteed to have a
    /// database at version `get_version`.
    #[allow(clippy::too_many_lines)]
    async fn update(self, app: &App) -> Result<(), update::Error> {
        match self {
            Self::Empty => {
                make_upgrade! {app, Self::Empty, Self::One, "./sql/0->1.sql"}
            }

            // This is the current_version
            Self::One => {
                assert_eq!(self, CURRENT_VERSION);
                assert_eq!(self, get_version(app).await?);
                Ok(())
            }
        }
    }
}
impl Display for DbVersion {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        // It is a unit only enum, thus we can simply use the Debug formatting
        <Self as std::fmt::Debug>::fmt(self, f)
    }
}
pub(crate) mod update {
    use crate::storage::migrate::{DbVersion, db_version_set, get_db_version};

    #[derive(thiserror::Error, Debug)]
    pub(crate) enum Error {
        #[error("Failed to determine final database version: {0}")]
        GetVersion(#[from] get_db_version::Error),

        #[error("Failed to set the db to version {new_version}: {err}")]
        SetDbVersion {
            err: db_version_set::Error,
            new_version: DbVersion,
        },

        #[error("Failed to vacuum sql database after update: {0}")]
        SqlVacuum(sqlx::Error),

        #[error("Failed to execute the sql update script: {0}")]
        SqlUpdate(sqlx::Error),

        #[error("Failed to start the update transaction: {0}")]
        TxnStart(sqlx::Error),
        #[error("Failed to commit the update transaction: {0}")]
        TxnCommit(sqlx::Error),

        #[error("Failed to perform the next chained update (to ver {new_version}): {err}")]
        NextUpdate {
            err: Box<Self>,
            new_version: DbVersion,
        },
    }
}
pub(crate) mod db_version_parse {
    #[derive(thiserror::Error, Debug)]
    pub(crate) enum Error {
        #[error("Db version is {number}, but got unknown namespace: '{namespace}'")]
        UnkownVersion { namespace: String, number: i64 },
    }
}

/// Returns the current data as UNIX time stamp.
pub(crate) fn get_current_date() -> i64 {
    let start = SystemTime::now();
    let seconds_since_epoch: TimeDelta = TimeDelta::from_std(
        start
            .duration_since(UNIX_EPOCH)
            .expect("Time went backwards"),
    )
    .expect("Time does not go backwards");

    // All database dates should be after the UNIX_EPOCH (and thus positiv)
    seconds_since_epoch.num_milliseconds()
}

/// Return the current database version.
///
/// # Panics
/// Only if internal assertions fail.
pub(crate) async fn get_version(app: &App) -> Result<DbVersion, get_db_version::Error> {
    get_version_db(&app.db).await
}

/// Return the current database version.
///
/// In contrast to the [`get_version`] function, this function does not
/// a fully instantiated [`App`], a database connection suffices.
///
/// # Panics
/// Only if internal assertions fail.
pub(crate) async fn get_version_db(pool: &SqlitePool) -> Result<DbVersion, get_db_version::Error> {
    let version_table_exists = {
        let query = query!(
            "
            SELECT 1 as result
            FROM sqlite_master
            WHERE type = 'table'
            AND name = 'version'
            "
        )
        .fetch_optional(pool)
        .await
        .map_err(|err| get_db_version::Error::VersionTableExistance(err))?;

        if let Some(output) = query {
            assert_eq!(output.result, 1);
            true
        } else {
            false
        }
    };

    if !version_table_exists {
        return Ok(DbVersion::Empty);
    }

    let current_version = query!(
        "
        SELECT namespace, number
        FROM version
        WHERE valid_to IS NULL;
        "
    )
    .fetch_one(pool)
    .await
    .map_err(|err| get_db_version::Error::VersionNumberFetch(err))?;

    Ok(DbVersion::from_db(
        current_version.number,
        current_version.namespace.as_str(),
    )?)
}

pub(crate) mod get_db_version {
    use crate::storage::migrate::db_version_parse;

    #[derive(thiserror::Error, Debug)]
    pub(crate) enum Error {
        #[error("Failed to fetch the version number from db: {0}")]
        VersionNumberFetch(sqlx::Error),

        #[error("Failed to check for existance of the `version` table: {0}")]
        VersionTableExistance(sqlx::Error),

        #[error("Failed to parse the db version: {0}")]
        VersionParse(#[from] db_version_parse::Error),
    }
}

pub(crate) async fn migrate_db(app: &App) -> Result<(), migrate_db::Error> {
    let current_version = get_version(app).await?;

    if current_version == CURRENT_VERSION {
        return Ok(());
    }

    info!("Migrate database from version '{current_version}' to version '{CURRENT_VERSION}'");

    current_version.update(app).await?;

    Ok(())
}

pub(crate) mod migrate_db {
    use crate::storage::migrate::{get_db_version, update};

    #[derive(thiserror::Error, Debug)]
    pub(crate) enum Error {
        #[error("Failed to determine the database version: {0}")]
        GetVersion(#[from] get_db_version::Error),

        #[error("Failed to update the database: {0}")]
        Upadate(#[from] update::Error),
    }
}