use std::error::Error;
use std::io::Write;

use crate::backend::{self, Backend, BinaryRawValue};
use crate::deserialize::{self, FromSql, Queryable};
use crate::serialize::{self, IsNull, Output, ToSql};
use crate::sql_types::{
    self, BigInt, Binary, Bool, Double, Float, Integer, SingleValue, SmallInt, Text,
};

#[allow(dead_code)]
mod foreign_impls {
    use super::*;
    use crate::deserialize::FromSqlRow;

    #[derive(AsExpression, FromSqlRow)]
    #[diesel(foreign_derive)]
    #[sql_type = "Bool"]
    struct BoolProxy(bool);

    #[derive(AsExpression, FromSqlRow)]
    #[diesel(foreign_derive)]
    #[cfg_attr(feature = "mysql", sql_type = "crate::sql_types::TinyInt")]
    struct I8Proxy(i8);

    #[derive(AsExpression, FromSqlRow)]
    #[diesel(foreign_derive)]
    #[sql_type = "SmallInt"]
    struct I16Proxy(i16);

    #[derive(AsExpression, FromSqlRow)]
    #[diesel(foreign_derive)]
    #[sql_type = "Integer"]
    struct I32Proxy(i32);

    #[derive(AsExpression, FromSqlRow)]
    #[diesel(foreign_derive)]
    #[sql_type = "BigInt"]
    struct I64Proxy(i64);

    #[derive(AsExpression, FromSqlRow)]
    #[diesel(foreign_derive)]
    #[cfg_attr(
        feature = "mysql",
        sql_type = "crate::sql_types::Unsigned<crate::sql_types::TinyInt>"
    )]
    struct U8Proxy(u8);

    #[derive(AsExpression, FromSqlRow)]
    #[diesel(foreign_derive)]
    #[cfg_attr(feature = "mysql", sql_type = "crate::sql_types::Unsigned<SmallInt>")]
    struct U16Proxy(u16);

    #[derive(AsExpression, FromSqlRow)]
    #[diesel(foreign_derive)]
    #[cfg_attr(feature = "mysql", sql_type = "crate::sql_types::Unsigned<Integer>")]
    #[cfg_attr(feature = "postgres", sql_type = "crate::sql_types::Oid")]
    struct U32Proxy(u32);

    #[derive(AsExpression, FromSqlRow)]
    #[diesel(foreign_derive)]
    #[cfg_attr(feature = "mysql", sql_type = "crate::sql_types::Unsigned<BigInt>")]
    struct U64Proxy(u64);

    #[derive(AsExpression, FromSqlRow)]
    #[diesel(foreign_derive)]
    #[sql_type = "Float"]
    struct F32Proxy(f32);

    #[derive(AsExpression, FromSqlRow)]
    #[diesel(foreign_derive)]
    #[sql_type = "Double"]
    struct F64Proxy(f64);

    #[derive(AsExpression, FromSqlRow)]
    #[diesel(foreign_derive)]
    #[sql_type = "Text"]
    #[cfg_attr(feature = "sqlite", sql_type = "crate::sql_types::Date")]
    #[cfg_attr(feature = "sqlite", sql_type = "crate::sql_types::Time")]
    #[cfg_attr(feature = "sqlite", sql_type = "crate::sql_types::Timestamp")]
    struct StringProxy(String);

    #[derive(AsExpression)]
    #[diesel(foreign_derive, not_sized)]
    #[sql_type = "Text"]
    #[cfg_attr(feature = "sqlite", sql_type = "crate::sql_types::Date")]
    #[cfg_attr(feature = "sqlite", sql_type = "crate::sql_types::Time")]
    #[cfg_attr(feature = "sqlite", sql_type = "crate::sql_types::Timestamp")]
    struct StrProxy(str);

    #[derive(FromSqlRow)]
    #[diesel(foreign_derive)]
    struct VecProxy<T>(Vec<T>);

    #[derive(AsExpression)]
    #[diesel(foreign_derive)]
    #[sql_type = "Binary"]
    struct BinaryVecProxy(Vec<u8>);

    #[derive(AsExpression)]
    #[diesel(foreign_derive, not_sized)]
    #[sql_type = "Binary"]
    struct BinarySliceProxy([u8]);
}

impl<ST, DB> FromSql<ST, DB> for String
where
    DB: Backend,
    *const str: FromSql<ST, DB>,
{
    fn from_sql(bytes: backend::RawValue<DB>) -> deserialize::Result<Self> {
        let str_ptr = <*const str as FromSql<ST, DB>>::from_sql(bytes)?;
        // We know that the pointer impl will never return null
        let string = unsafe { &*str_ptr };
        Ok(string.to_owned())
    }
}

/// The returned pointer is *only* valid for the lifetime to the argument of
/// `from_sql`. This impl is intended for uses where you want to write a new
/// impl in terms of `String`, but don't want to allocate. We have to return a
/// raw pointer instead of a reference with a lifetime due to the structure of
/// `FromSql`
#[cfg(not(feature = "unstable"))]
impl<DB> FromSql<sql_types::Text, DB> for *const str
where
    DB: Backend + for<'a> BinaryRawValue<'a>,
{
    fn from_sql(value: crate::backend::RawValue<DB>) -> deserialize::Result<Self> {
        use std::str;
        let string = str::from_utf8(DB::as_bytes(value))?;
        Ok(string as *const _)
    }
}

#[cfg(feature = "unstable")]
impl<DB> FromSql<sql_types::Text, DB> for *const str
where
    DB: Backend + for<'a> BinaryRawValue<'a>,
{
    default fn from_sql(value: crate::backend::RawValue<DB>) -> deserialize::Result<Self> {
        use std::str;
        let string = str::from_utf8(DB::as_bytes(value))?;
        Ok(string as *const _)
    }
}

impl<DB: Backend> ToSql<sql_types::Text, DB> for str {
    fn to_sql<W: Write>(&self, out: &mut Output<W, DB>) -> serialize::Result {
        out.write_all(self.as_bytes())
            .map(|_| IsNull::No)
            .map_err(|e| Box::new(e) as Box<dyn Error + Send + Sync>)
    }
}

impl<DB> ToSql<sql_types::Text, DB> for String
where
    DB: Backend,
    str: ToSql<sql_types::Text, DB>,
{
    fn to_sql<W: Write>(&self, out: &mut Output<W, DB>) -> serialize::Result {
        (self as &str).to_sql(out)
    }
}

impl<ST, DB> FromSql<ST, DB> for Vec<u8>
where
    DB: Backend,
    *const [u8]: FromSql<ST, DB>,
{
    fn from_sql(bytes: backend::RawValue<DB>) -> deserialize::Result<Self> {
        let slice_ptr = <*const [u8] as FromSql<ST, DB>>::from_sql(bytes)?;
        // We know that the pointer impl will never return null
        let bytes = unsafe { &*slice_ptr };
        Ok(bytes.to_owned())
    }
}

/// The returned pointer is *only* valid for the lifetime to the argument of
/// `from_sql`. This impl is intended for uses where you want to write a new
/// impl in terms of `Vec<u8>`, but don't want to allocate. We have to return a
/// raw pointer instead of a reference with a lifetime due to the structure of
/// `FromSql`
impl<DB> FromSql<sql_types::Binary, DB> for *const [u8]
where
    DB: Backend + for<'a> BinaryRawValue<'a>,
{
    fn from_sql(bytes: backend::RawValue<DB>) -> deserialize::Result<Self> {
        Ok(DB::as_bytes(bytes) as *const _)
    }
}

impl<DB> ToSql<sql_types::Binary, DB> for Vec<u8>
where
    DB: Backend,
    [u8]: ToSql<sql_types::Binary, DB>,
{
    fn to_sql<W: Write>(&self, out: &mut Output<W, DB>) -> serialize::Result {
        (self as &[u8]).to_sql(out)
    }
}

impl<DB: Backend> ToSql<sql_types::Binary, DB> for [u8] {
    fn to_sql<W: Write>(&self, out: &mut Output<W, DB>) -> serialize::Result {
        out.write_all(self)
            .map(|_| IsNull::No)
            .map_err(|e| Box::new(e) as Box<dyn Error + Send + Sync>)
    }
}

use std::borrow::{Cow, ToOwned};
use std::fmt;
impl<'a, T: ?Sized, ST, DB> ToSql<ST, DB> for Cow<'a, T>
where
    T: 'a + ToOwned + ToSql<ST, DB>,
    DB: Backend,
    Self: fmt::Debug,
{
    fn to_sql<W: Write>(&self, out: &mut Output<W, DB>) -> serialize::Result {
        ToSql::<ST, DB>::to_sql(&**self, out)
    }
}

impl<'a, T: ?Sized, ST, DB> FromSql<ST, DB> for Cow<'a, T>
where
    T: 'a + ToOwned,
    DB: Backend,
    T::Owned: FromSql<ST, DB>,
{
    fn from_sql(bytes: backend::RawValue<DB>) -> deserialize::Result<Self> {
        T::Owned::from_sql(bytes).map(Cow::Owned)
    }
}

impl<'a, T: ?Sized, ST, DB> Queryable<ST, DB> for Cow<'a, T>
where
    T: 'a + ToOwned,
    ST: SingleValue,
    DB: Backend,
    Self: FromSql<ST, DB>,
{
    type Row = Self;

    fn build(row: Self::Row) -> Self {
        row
    }
}

use crate::expression::bound::Bound;
use crate::expression::{AsExpression, Expression, TypedExpressionType};
use sql_types::SqlType;

impl<'a, T: ?Sized, ST> AsExpression<ST> for Cow<'a, T>
where
    T: 'a + ToOwned,
    Bound<ST, Cow<'a, T>>: Expression<SqlType = ST>,
    ST: SqlType + TypedExpressionType,
{
    type Expression = Bound<ST, Self>;

    fn as_expression(self) -> Self::Expression {
        Bound::new(self)
    }
}

impl<'a, 'b, T: ?Sized, ST> AsExpression<ST> for &'b Cow<'a, T>
where
    T: 'a + ToOwned,
    Bound<ST, &'b T>: Expression<SqlType = ST>,
    ST: SqlType + TypedExpressionType,
{
    type Expression = Bound<ST, &'b T>;

    fn as_expression(self) -> Self::Expression {
        Bound::new(&**self)
    }
}