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use std::{fmt::Debug, ops::Deref};

use arc_bytes::serde::{Bytes, CowBytes};

use crate::{
    connection::Connection,
    document::{BorrowedDocument, Header, OwnedDocument},
    schema::SerializedCollection,
    Error,
};

/// A document with serializable contents.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct CollectionDocument<C>
where
    C: SerializedCollection,
{
    /// The header of the document, which contains the id and `Revision`.
    pub header: Header,

    /// The document's contents.
    pub contents: C::Contents,
}

impl<C> AsRef<Header> for CollectionDocument<C>
where
    C: SerializedCollection,
{
    fn as_ref(&self) -> &Header {
        &self.header
    }
}

impl<C> Deref for CollectionDocument<C>
where
    C: SerializedCollection,
{
    type Target = Header;

    fn deref(&self) -> &Self::Target {
        &self.header
    }
}

impl<'a, C> TryFrom<&'a BorrowedDocument<'a>> for CollectionDocument<C>
where
    C: SerializedCollection,
{
    type Error = Error;

    fn try_from(value: &'a BorrowedDocument<'a>) -> Result<Self, Self::Error> {
        Ok(Self {
            contents: C::deserialize(&value.contents)?,
            header: value.header.clone(),
        })
    }
}

impl<'a, C> TryFrom<&'a OwnedDocument> for CollectionDocument<C>
where
    C: SerializedCollection,
{
    type Error = Error;

    fn try_from(value: &'a OwnedDocument) -> Result<Self, Self::Error> {
        Ok(Self {
            contents: C::deserialize(&value.contents)?,
            header: value.header.clone(),
        })
    }
}

impl<'a, 'b, C> TryFrom<&'b CollectionDocument<C>> for BorrowedDocument<'a>
where
    C: SerializedCollection,
{
    type Error = crate::Error;

    fn try_from(value: &'b CollectionDocument<C>) -> Result<Self, Self::Error> {
        Ok(Self {
            contents: CowBytes::from(C::serialize(&value.contents)?),
            header: value.header.clone(),
        })
    }
}

impl<C> CollectionDocument<C>
where
    C: SerializedCollection,
{
    /// Stores the new value of `contents` in the document.
    pub async fn update<Cn: Connection>(&mut self, connection: &Cn) -> Result<(), Error> {
        let mut doc = self.to_document()?;

        connection.update::<C, _>(&mut doc).await?;

        self.header = doc.header;

        Ok(())
    }

    /// Modifies `self`, automatically retrying the modification if the document
    /// has been updated on the server.
    ///
    /// ## Data loss warning
    ///
    /// If you've modified `self` before calling this function and a conflict
    /// occurs, all changes to self will be lost when the current document is
    /// fetched before retrying the process again. When you use this function,
    /// you should limit the edits to the value to within the `modifier`
    /// callback.
    pub async fn modify<Cn: Connection, Modifier: FnMut(&mut Self) + Send + Sync>(
        &mut self,
        connection: &Cn,
        mut modifier: Modifier,
    ) -> Result<(), Error> {
        let mut is_first_loop = true;
        // TODO this should have a retry-limit.
        loop {
            // On the first attempt, we want to try sending the update to the
            // database without fetching new contents. If we receive a conflict,
            // on future iterations we will first re-load the data.
            if is_first_loop {
                is_first_loop = false;
            } else {
                *self = C::get(self.header.id, connection)
                    .await?
                    .ok_or_else(|| Error::DocumentNotFound(C::collection_name(), self.header.id))?;
            }
            modifier(&mut *self);
            match self.update(connection).await {
                Err(Error::DocumentConflict(..)) => {}
                other => return other,
            }
        }
    }

    /// Removes the document from the collection.
    pub async fn delete<Cn: Connection>(&self, connection: &Cn) -> Result<(), Error> {
        connection.collection::<C>().delete(self).await?;

        Ok(())
    }

    /// Converts this value to a serialized `Document`.
    pub fn to_document(&self) -> Result<OwnedDocument, Error> {
        Ok(OwnedDocument {
            contents: Bytes::from(C::serialize(&self.contents)?),
            header: self.header.clone(),
        })
    }
}

/// Helper functions for a slice of [`OwnedDocument`]s.
pub trait OwnedDocuments {
    /// Returns a list of deserialized documents.
    fn collection_documents<C: SerializedCollection>(
        &self,
    ) -> Result<Vec<CollectionDocument<C>>, Error>;
}

impl OwnedDocuments for [OwnedDocument] {
    fn collection_documents<C: SerializedCollection>(
        &self,
    ) -> Result<Vec<CollectionDocument<C>>, Error> {
        self.iter().map(CollectionDocument::try_from).collect()
    }
}