use crate::{
    error::*, query::combine, DatabaseConnection, EntityTrait, FromQueryResult, Iterable,
    JsonValue, ModelTrait, Paginator, PrimaryKeyToColumn, QueryResult, Select, SelectTwo,
    SelectTwoMany, Statement,
};
use sea_query::SelectStatement;
use std::marker::PhantomData;

#[derive(Clone, Debug)]
pub struct Selector<S>
where
    S: SelectorTrait,
{
    query: SelectStatement,
    selector: S,
}

#[derive(Clone, Debug)]
pub struct SelectorRaw<S>
where
    S: SelectorTrait,
{
    stmt: Statement,
    selector: S,
}

pub trait SelectorTrait {
    type Item: Sized;

    fn from_raw_query_result(res: QueryResult) -> Result<Self::Item, DbErr>;
}

pub struct SelectModel<M>
where
    M: FromQueryResult,
{
    model: PhantomData<M>,
}

#[derive(Clone, Debug)]
pub struct SelectTwoModel<M, N>
where
    M: FromQueryResult,
    N: FromQueryResult,
{
    model: PhantomData<(M, N)>,
}

impl<M> SelectorTrait for SelectModel<M>
where
    M: FromQueryResult + Sized,
{
    type Item = M;

    fn from_raw_query_result(res: QueryResult) -> Result<Self::Item, DbErr> {
        M::from_query_result(&res, "")
    }
}

impl<M, N> SelectorTrait for SelectTwoModel<M, N>
where
    M: FromQueryResult + Sized,
    N: FromQueryResult + Sized,
{
    type Item = (M, Option<N>);

    fn from_raw_query_result(res: QueryResult) -> Result<Self::Item, DbErr> {
        Ok((
            M::from_query_result(&res, combine::SELECT_A)?,
            N::from_query_result_optional(&res, combine::SELECT_B)?,
        ))
    }
}

impl<E> Select<E>
where
    E: EntityTrait,
{
    /// ```
    /// # #[cfg(feature = "mock")]
    /// # use sea_orm::{error::*, tests_cfg::*, MockDatabase, Transaction, DbBackend};
    /// #
    /// # let db = MockDatabase::new(DbBackend::Postgres).into_connection();
    /// #
    /// use sea_orm::{entity::*, query::*, tests_cfg::cake};
    ///
    /// # let _: Result<(), DbErr> = async_std::task::block_on(async {
    /// #
    /// let cheese: Option<cake::Model> = cake::Entity::find().from_raw_sql(
    ///     Statement::from_sql_and_values(
    ///         DbBackend::Postgres, r#"SELECT "cake"."id", "cake"."name" FROM "cake" WHERE "id" = $1"#, vec![1.into()]
    ///     )
    /// ).one(&db).await?;
    /// #
    /// # Ok(())
    /// # });
    ///
    /// assert_eq!(
    ///     db.into_transaction_log(),
    ///     vec![
    ///     Transaction::from_sql_and_values(
    ///             DbBackend::Postgres, r#"SELECT "cake"."id", "cake"."name" FROM "cake" WHERE "id" = $1"#, vec![1.into()]
    ///     ),
    /// ]);
    /// ```
    #[allow(clippy::wrong_self_convention)]
    pub fn from_raw_sql(self, stmt: Statement) -> SelectorRaw<SelectModel<E::Model>> {
        SelectorRaw {
            stmt,
            selector: SelectModel { model: PhantomData },
        }
    }

    pub fn into_model<M>(self) -> Selector<SelectModel<M>>
    where
        M: FromQueryResult,
    {
        Selector {
            query: self.query,
            selector: SelectModel { model: PhantomData },
        }
    }

    #[cfg(feature = "with-json")]
    pub fn into_json(self) -> Selector<SelectModel<JsonValue>> {
        Selector {
            query: self.query,
            selector: SelectModel { model: PhantomData },
        }
    }

    pub async fn one(self, db: &DatabaseConnection) -> Result<Option<E::Model>, DbErr> {
        self.into_model().one(db).await
    }

    pub async fn all(self, db: &DatabaseConnection) -> Result<Vec<E::Model>, DbErr> {
        self.into_model().all(db).await
    }

    pub fn paginate(
        self,
        db: &DatabaseConnection,
        page_size: usize,
    ) -> Paginator<'_, SelectModel<E::Model>> {
        self.into_model().paginate(db, page_size)
    }

    pub async fn count(self, db: &DatabaseConnection) -> Result<usize, DbErr> {
        self.paginate(db, 1).num_items().await
    }
}

impl<E, F> SelectTwo<E, F>
where
    E: EntityTrait,
    F: EntityTrait,
{
    fn into_model<M, N>(self) -> Selector<SelectTwoModel<M, N>>
    where
        M: FromQueryResult,
        N: FromQueryResult,
    {
        Selector {
            query: self.query,
            selector: SelectTwoModel { model: PhantomData },
        }
    }

    #[cfg(feature = "with-json")]
    pub fn into_json(self) -> Selector<SelectTwoModel<JsonValue, JsonValue>> {
        Selector {
            query: self.query,
            selector: SelectTwoModel { model: PhantomData },
        }
    }

    pub async fn one(
        self,
        db: &DatabaseConnection,
    ) -> Result<Option<(E::Model, Option<F::Model>)>, DbErr> {
        self.into_model().one(db).await
    }

    pub async fn all(
        self,
        db: &DatabaseConnection,
    ) -> Result<Vec<(E::Model, Option<F::Model>)>, DbErr> {
        self.into_model().all(db).await
    }

    pub fn paginate(
        self,
        db: &DatabaseConnection,
        page_size: usize,
    ) -> Paginator<'_, SelectTwoModel<E::Model, F::Model>> {
        self.into_model().paginate(db, page_size)
    }

    pub async fn count(self, db: &DatabaseConnection) -> Result<usize, DbErr> {
        self.paginate(db, 1).num_items().await
    }
}

impl<E, F> SelectTwoMany<E, F>
where
    E: EntityTrait,
    F: EntityTrait,
{
    fn into_model<M, N>(self) -> Selector<SelectTwoModel<M, N>>
    where
        M: FromQueryResult,
        N: FromQueryResult,
    {
        Selector {
            query: self.query,
            selector: SelectTwoModel { model: PhantomData },
        }
    }

    #[cfg(feature = "with-json")]
    pub fn into_json(self) -> Selector<SelectTwoModel<JsonValue, JsonValue>> {
        Selector {
            query: self.query,
            selector: SelectTwoModel { model: PhantomData },
        }
    }

    pub async fn one(
        self,
        db: &DatabaseConnection,
    ) -> Result<Option<(E::Model, Option<F::Model>)>, DbErr> {
        self.into_model().one(db).await
    }

    pub async fn all(
        self,
        db: &DatabaseConnection,
    ) -> Result<Vec<(E::Model, Vec<F::Model>)>, DbErr> {
        let rows = self.into_model().all(db).await?;
        Ok(consolidate_query_result::<E, F>(rows))
    }

    // pub fn paginate()
    // we could not implement paginate easily, if the number of children for a
    // parent is larger than one page, then we will end up splitting it in two pages
    // so the correct way is actually perform query in two stages
    // paginate the parent model and then populate the children

    // pub fn count()
    // we should only count the number of items of the parent model
}

impl<S> Selector<S>
where
    S: SelectorTrait,
{
    pub async fn one(mut self, db: &DatabaseConnection) -> Result<Option<S::Item>, DbErr> {
        let builder = db.get_database_backend();
        self.query.limit(1);
        let row = db.query_one(builder.build(&self.query)).await?;
        match row {
            Some(row) => Ok(Some(S::from_raw_query_result(row)?)),
            None => Ok(None),
        }
    }

    pub async fn all(self, db: &DatabaseConnection) -> Result<Vec<S::Item>, DbErr> {
        let builder = db.get_database_backend();
        let rows = db.query_all(builder.build(&self.query)).await?;
        let mut models = Vec::new();
        for row in rows.into_iter() {
            models.push(S::from_raw_query_result(row)?);
        }
        Ok(models)
    }

    pub fn paginate(self, db: &DatabaseConnection, page_size: usize) -> Paginator<'_, S> {
        Paginator {
            query: self.query,
            page: 0,
            page_size,
            db,
            selector: PhantomData,
        }
    }
}

impl<S> SelectorRaw<S>
where
    S: SelectorTrait,
{
    pub async fn one(self, db: &DatabaseConnection) -> Result<Option<S::Item>, DbErr> {
        let row = db.query_one(self.stmt).await?;
        match row {
            Some(row) => Ok(Some(S::from_raw_query_result(row)?)),
            None => Ok(None),
        }
    }

    pub async fn all(self, db: &DatabaseConnection) -> Result<Vec<S::Item>, DbErr> {
        let rows = db.query_all(self.stmt).await?;
        let mut models = Vec::new();
        for row in rows.into_iter() {
            models.push(S::from_raw_query_result(row)?);
        }
        Ok(models)
    }
}

fn consolidate_query_result<L, R>(
    rows: Vec<(L::Model, Option<R::Model>)>,
) -> Vec<(L::Model, Vec<R::Model>)>
where
    L: EntityTrait,
    R: EntityTrait,
{
    let mut acc: Vec<(L::Model, Vec<R::Model>)> = Vec::new();
    for (l, r) in rows {
        if let Some((last_l, last_r)) = acc.last_mut() {
            let mut same_l = true;
            for pk_col in <L::PrimaryKey as Iterable>::iter() {
                let col = pk_col.into_column();
                let val = l.get(col);
                let last_val = last_l.get(col);
                if !val.eq(&last_val) {
                    same_l = false;
                    break;
                }
            }
            if same_l {
                if let Some(r) = r {
                    last_r.push(r);
                    continue;
                }
            }
        }
        if r.is_some() {
            acc.push((l, vec![r.unwrap()]));
        } else {
            acc.push((l, vec![]));
        }
    }
    acc
}