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//! Types related to managing bind parameters during query construction.

use crate::backend::Backend;
use crate::result::Error::SerializationError;
use crate::result::QueryResult;
use crate::serialize::{IsNull, Output, ToSql};
use crate::sql_types::{HasSqlType, TypeMetadata};

#[doc(inline)]
#[diesel_derives::__diesel_public_if(
    feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"
)]
pub(crate) use self::private::ByteWrapper;

/// A type which manages serializing bind parameters during query construction.
///
/// The only reason you would ever need to interact with this trait is if you
/// are adding support for a new backend to Diesel. Plugins which are extending
/// the query builder will use [`AstPass::push_bind_param`] instead.
///
/// [`AstPass::push_bind_param`]: crate::query_builder::AstPass::push_bind_param()
pub trait BindCollector<'a, DB: TypeMetadata>: Sized {
    /// The internal buffer type used by this bind collector
    type Buffer;

    /// Serializes the given bind value, and collects the result.
    fn push_bound_value<T, U>(
        &mut self,
        bind: &'a U,
        metadata_lookup: &mut DB::MetadataLookup,
    ) -> QueryResult<()>
    where
        DB: Backend + HasSqlType<T>,
        U: ToSql<T, DB> + 'a;
}

#[derive(Debug)]
/// A bind collector used by backends which transmit bind parameters as an
/// opaque blob of bytes.
///
/// For most backends, this is the concrete implementation of `BindCollector`
/// that should be used.
#[non_exhaustive]
pub struct RawBytesBindCollector<DB: Backend + TypeMetadata> {
    /// The metadata associated with each bind parameter.
    ///
    /// This vec is guaranteed to be the same length as `binds`.
    #[cfg(feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes")]
    pub metadata: Vec<DB::TypeMetadata>,
    #[cfg(not(feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"))]
    pub(crate) metadata: Vec<DB::TypeMetadata>,
    /// The serialized bytes for each bind parameter.
    ///
    /// This vec is guaranteed to be the same length as `metadata`.
    #[cfg(feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes")]
    pub binds: Vec<Option<Vec<u8>>>,
    #[cfg(not(feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"))]
    pub(crate) binds: Vec<Option<Vec<u8>>>,
}

#[allow(clippy::new_without_default)]
impl<DB: Backend + TypeMetadata> RawBytesBindCollector<DB> {
    /// Construct an empty `RawBytesBindCollector`
    pub fn new() -> Self {
        RawBytesBindCollector {
            metadata: Vec::new(),
            binds: Vec::new(),
        }
    }

    pub(crate) fn reborrow_buffer<'a: 'b, 'b>(b: &'b mut ByteWrapper<'a>) -> ByteWrapper<'b> {
        ByteWrapper(b.0)
    }
}

impl<'a, DB> BindCollector<'a, DB> for RawBytesBindCollector<DB>
where
    DB: Backend<BindCollector = Self> + TypeMetadata,
{
    type Buffer = ByteWrapper<'a>;

    fn push_bound_value<T, U>(
        &mut self,
        bind: &U,
        metadata_lookup: &mut DB::MetadataLookup,
    ) -> QueryResult<()>
    where
        DB: HasSqlType<T>,
        U: ToSql<T, DB>,
    {
        let mut bytes = Vec::new();
        let is_null = {
            let mut to_sql_output = Output::new(ByteWrapper(&mut bytes), metadata_lookup);
            bind.to_sql(&mut to_sql_output)
                .map_err(SerializationError)?
        };
        let metadata = <DB as HasSqlType<T>>::metadata(metadata_lookup);
        match is_null {
            IsNull::No => self.binds.push(Some(bytes)),
            IsNull::Yes => self.binds.push(None),
        }
        self.metadata.push(metadata);
        Ok(())
    }
}

// This is private for now as we may want to add `Into` impls for the wrapper type
// later on
mod private {
    /// A type wrapper for raw bytes
    #[derive(Debug)]
    pub struct ByteWrapper<'a>(pub(crate) &'a mut Vec<u8>);
}