use std::fmt::Debug;

use serde::{de::DeserializeOwned, Serialize};

use transmog::{Format, OwnedDeserializer};

use transmog_pot::Pot;

use crate::{

    document::{BorrowedDocument, CollectionDocument},

    key::Key,

    schema::{

        view::map::{Mappings, ViewMappedValue},

        Collection, CollectionName, Name, SerializedCollection, ViewName,

    },

    AnyError,

};

/// Types for defining a `Map` within a `View`.

pub mod map;

/// Errors that arise when interacting with views.

// TODO add which view name and collection

pub enum Error {

    /// An error occurred while serializing or deserializing keys emitted in a view.

    #[error("error serializing view keys {0}")]

    KeySerialization(Box<dyn AnyError>),

    /// An error unrelated to views.

    #[error("core error: {0}")]

    Core(#[from] crate::Error),

}

impl Error {

    /// Returns a [`Self::KeySerialization`] instance after boxing the error.

}

impl From<pot::Error> for Error {

}

/// A type alias for the result of `ViewSchema::map()`.

pub type ViewMapResult<V> = Result<Mappings<<V as View>::Key, <V as View>::Value>, crate::Error>;

/// A type alias for the result of `ViewSchema::reduce()`.

pub type ReduceResult<V> = Result<<V as View>::Value, crate::Error>;

/// An lazy index of mapped and/or reduced data from a [`Collection`].

///

/// A view provides an efficient way to query data within a collection. BonsaiDb

/// indexes the associated [`View::Collection`] by calling

/// [`CollectionViewSchema::map()`]/[`ViewSchema::map()`] every time a document

/// is created or updated. The result [`Mappings`] form a sorted index that can

/// be efficiently queried using the [`View::Key`] type.

///

/// A View behaves similarly to the standard library's BTreeMap with these

/// types: `BTreeMap<View::Key, Vec<(Header, View::Value)>>`

///

/// For a deeper dive on Views, see [the section in our user's

/// guide](https://dev.bonsaidb.io/main/guide/about/concepts/view.html).

#[doc = "\n"]

#[doc = include_str!("./view-overview.md")]

pub trait View: Send + Sync + Debug + 'static {

    /// The collection this view belongs to

    type Collection: Collection;

    /// The key for this view.

    type Key: for<'a> Key<'a> + 'static;

    /// An associated type that can be stored with each entry in the view.

    type Value: Send + Sync;

    /// The name of the view. Must be unique per collection.

    fn name(&self) -> Name;

    /// The namespaced name of the view.

}

/// The implementation of Map/Reduce for a [`View`].

#[doc = "\n"]

#[doc = include_str!("./view-overview.md")]

pub trait ViewSchema: Send + Sync + Debug + 'static {

    /// The view this schema is defined for.

    type View: SerializedView;

    /// If true, no two documents may emit the same key. Unique views are

    /// updated when the document is saved, allowing for this check to be done

    /// atomically. When a document is updated, all unique views will be

    /// updated, and if any of them fail, the document will not be allowed to

    /// update and an

    /// [`Error::UniqueKeyViolation`](crate::Error::UniqueKeyViolation) will be

    /// returned.

    /// The version of the view. Changing this value will cause indexes to be rebuilt.

    /// The map function for this view. This function is responsible for

    /// emitting entries for any documents that should be contained in this

    /// View. If None is returned, the View will not include the document. See [the user guide's chapter on

    /// views for more information on how map

    /// works](https://dev.bonsaidb.io/main/guide/about/concepts/view.html#map).

    fn map(&self, document: &BorrowedDocument<'_>) -> ViewMapResult<Self::View>;

    /// Returns a value that is produced by reducing a list of `mappings` into a

    /// single value. If `rereduce` is true, the values contained in the

    /// mappings have already been reduced at least one time. If an error of

    /// [`ReduceUnimplemented`](crate::Error::ReduceUnimplemented) is returned,

    /// queries that ask for a reduce operation will return an error. See [the

    /// user guide's chapter on views for more information on how reduce

    /// works](https://dev.bonsaidb.io/main/guide/about/concepts/view.html#reduce).

    #[allow(unused_variables)]

}

/// A [`View`] with additional tyes and logic to handle serializing view values.

pub trait SerializedView: View {

    /// The serialization format for this view.

    type Format: OwnedDeserializer<Self::Value>;

    /// Returns the configured instance of [`Self::Format`].

    // TODO allow configuration to be passed here, such as max allocation bytes.

    fn format() -> Self::Format;

    /// Deserialize `data` as `Self::Value` using this views's format.

    /// Serialize `item` using this views's format.

}

/// A default serialization strategy for views. Uses equivalent settings as

/// [`DefaultSerialization`](crate::schema::DefaultSerialization).

pub trait DefaultViewSerialization: View {}

impl<T> SerializedView for T

where

    T: DefaultViewSerialization,

    T::Value: Serialize + DeserializeOwned,

{

    type Format = Pot;

}

/// A [`View`] for a [`Collection`] that stores Serde-compatible documents. The

/// only difference between implmementing this and [`View`] is that the `map`

/// function receives a [`CollectionDocument`] instead of a [`BorrowedDocument`].

pub trait CollectionViewSchema: Send + Sync + Debug + 'static

where

    <Self::View as View>::Collection: SerializedCollection,

{

    /// The view this schema is an implementation of.

    type View: SerializedView;

    /// If true, no two documents may emit the same key. Unique views are

    /// updated when the document is saved, allowing for this check to be done

    /// atomically. When a document is updated, all unique views will be

    /// updated, and if any of them fail, the document will not be allowed to

    /// update and an

    /// [`Error::UniqueKeyViolation`](crate::Error::UniqueKeyViolation) will be

    /// returned.

    /// The version of the view. Changing this value will cause indexes to be rebuilt.

    /// The map function for this view. This function is responsible for

    /// emitting entries for any documents that should be contained in this

    /// View. If None is returned, the View will not include the document.

    fn map(

        &self,

        document: CollectionDocument<<Self::View as View>::Collection>,

    ) -> ViewMapResult<Self::View>;

    /// The reduce function for this view. If `Err(Error::ReduceUnimplemented)`

    /// is returned, queries that ask for a reduce operation will return an

    /// error. See [`CouchDB`'s Reduce/Rereduce

    /// documentation](https://docs.couchdb.org/en/stable/ddocs/views/intro.html#reduce-rereduce)

    /// for the design this implementation will be inspired by

    #[allow(unused_variables)]

}

impl<T> ViewSchema for T

where

    T: CollectionViewSchema,

    T::View: SerializedView,

    <T::View as View>::Collection: SerializedCollection,

{

    type View = T::View;

}

/// Wraps a [`View`] with serialization to erase the associated types

pub trait Serialized: Send + Sync + Debug {

    /// Wraps returing [`<View::Collection as Collection>::collection_name()`](crate::schema::Collection::collection_name)

    fn collection(&self) -> CollectionName;

    /// Wraps [`ViewSchema::unique`]

    fn unique(&self) -> bool;

    /// Wraps [`ViewSchema::version`]

    fn version(&self) -> u64;

    /// Wraps [`View::view_name`]

    fn view_name(&self) -> ViewName;

    /// Wraps [`ViewSchema::map`]

    fn map(&self, document: &BorrowedDocument<'_>) -> Result<Vec<map::Serialized>, Error>;

    /// Wraps [`ViewSchema::reduce`]

    fn reduce(&self, mappings: &[(&[u8], &[u8])], rereduce: bool) -> Result<Vec<u8>, Error>;

}

/// Defines an unique view named `$view_name` for `$collection` with the

/// mapping provided.

#[macro_export(local_inner_macros)]

macro_rules! define_basic_unique_mapped_view {

    ($view_name:ident, $collection:ty, $version:literal, $name:literal, $key:ty, $mapping:expr $(,)?) => {

        define_mapped_view!(

            $view_name,

            $collection,

            $version,

            $name,

            $key,

            (),

            true,

            $mapping

        );

    };

    ($view_name:ident, $collection:ty, $version:literal, $name:literal, $key:ty, $value:ty, $mapping:expr $(,)?) => {

        define_mapped_view!(

            $view_name,

            $collection,

            $version,

            $name,

            $key,

            $value,

            true,

            $mapping

        );

    };

}

/// Defines a non-unique view named `$view_name` for `$collection` with the

/// mapping provided.

#[macro_export(local_inner_macros)]

macro_rules! define_basic_mapped_view {

    ($view_name:ident, $collection:ty, $version:literal, $name:literal, $key:ty, $mapping:expr $(,)?) => {

        define_mapped_view!(

            $view_name,

            $collection,

            $version,

            $name,

            $key,

            (),

            false,

            $mapping

        );

    };

    ($view_name:ident, $collection:ty, $version:literal, $name:literal, $key:ty, $value:ty, $mapping:expr $(,)?) => {

        define_mapped_view!(

            $view_name,

            $collection,

            $version,

            $name,

            $key,

            $value,

            false,

            $mapping

        );

    };

}

/// Defines a view using the mapping provided.

#[macro_export]

macro_rules! define_mapped_view {

    ($view_name:ident, $collection:ty, $version:literal, $name:literal, $key:ty, $value:ty, $unique:literal, $mapping:expr) => {

        pub struct $view_name;

        impl $crate::schema::View for $view_name {

            type Collection = $collection;

            type Key = $key;

            type Value = $value;

        }

        impl $crate::schema::CollectionViewSchema for $view_name {

            type View = Self;

        }

        impl $crate::schema::view::DefaultViewSerialization for $view_name {}

    };

}