use std::fmt::Debug;

use serde::de::DeserializeOwned;

use serde::{Deserialize, Serialize};

use transmog::{Format, OwnedDeserializer};

use transmog_pot::Pot;

use crate::connection::{self, AsyncConnection, Connection};

use crate::document::{BorrowedDocument, CollectionDocument};

use crate::key::{ByteSource, Key, KeyDescription};

use crate::schema::view::map::{MappedValue, Mappings, ViewMappedValue};

use crate::schema::{Collection, CollectionName, Name, SerializedCollection, ViewName};

use crate::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<'doc, V> = Result<

    Mappings<<V as ViewSchema>::MappedKey<'doc>, <<V as ViewSchema>::View 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

/// [`CollectionMapReduce::map()`]/[`MapReduce::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)>>`

///

/// This trait only defines the types and functionality required to interact

/// with the view's query system. The [`MapReduce`]/[`CollectionMapReduce`]

/// traits define the map/reduce behavior, and the [`ViewSchema`] trait defines

/// additional metadata such as the [`ViewUpdatePolicy`] and view version.

///

/// 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: Sized + Send + Sync + 'static {

    /// The collection this view belongs to

    type Collection: Collection;

    /// The key for this view.

    type Key: for<'k> Key<'k> + PartialEq + '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.

}

/// Schema information for a [`View`].

///

/// This trait controls several behaviors for a view:

///

/// - [`MappedKey<'doc>`](Self::MappedKey): A [`Key`] type that is compatible

///   with the associated [`View::Key`] type, but can borrow from the document

///   by using the `'doc` generic associated lifetime.

/// - [`update_policy()`](Self::update_policy): Controls when the view's data is

///   updated and any restrictions on the data contained in the view. The

///   default policy for views is [`ViewUpdatePolicy`]

/// - [`version()`](Self::version): An integer representing the view's version.

///   Changing this number will cause the view to be re-indexed. This is useful

///   when there are fundamental changes in how the view is implemented.

///

/// ## Where is this trait used?

///

/// This trait is currently only used by `bonsaidb-local`, but is provided in

/// `bonsaidb-core` to allow it to be used anywhere. It may be desireable to

/// keep the implementation of `ViewSchema` in the "server" binary, while only

/// exposing the `View` implementation to the "client".

///

/// ## Deriving this Trait

///

/// This trait can be derived, and all attributes are optional. The available

/// options are:

///

/// - `view`: Sets the associated [`View`](Self::View) type. If not provided,

///   `Self` will be used.

/// - `version`: Sets the [version number](Self::version) of the view. If not

///   provided, `0` will be used.

/// - `mapped_key`: Sets the [`MappedKey<'doc>`](Self::MappedKey) type to the

///   provided type. The `'doc` lifetime can be utilized to borrow data during

///   the [`MapReduce::map()`] function.

///

///   If not provided, the `ViewSchema` implementation uses [`View::Key`].

/// - `policy`: Sets the [`ViewUpdatePolicy`]. The accepted policies are:

///   - [`Lazy`](ViewUpdatePolicy::Lazy)

///   - [`Eager`](ViewUpdatePolicy::Eager)

///   - [`Unique`](ViewUpdatePolicy::Unique)

///

///   If not provided, the [`Lazy`](ViewUpdatePolicy::Lazy) policy will be used.

///

/// Here is an example that showcases most of the options:

/// ```rust

/// # mod collection {

/// # bonsaidb_core::__doctest_prelude!();

/// # }

/// # use collection::MyCollection;

/// use std::borrow::Cow;

///

/// use bonsaidb_core::document::{BorrowedDocument, Emit};

/// use bonsaidb_core::schema::view::{ReduceResult, ViewMapResult};

/// use bonsaidb_core::schema::{MapReduce, View, ViewMappedValue, ViewSchema};

///

/// #[derive(View, ViewSchema)]

/// #[view(collection = MyCollection, key = String, value = u32)]

/// #[view_schema(mapped_key = Cow<'doc, str>, policy = Unique)]

/// # #[view(core = bonsaidb_core)]

/// # #[view_schema(core = bonsaidb_core)]

/// struct UniqueByName;

///

/// impl MapReduce for UniqueByName {

///     fn map<'doc>(&self, document: &'doc BorrowedDocument<'_>) -> ViewMapResult<'doc, Self> {

///         let contents_as_str = std::str::from_utf8(&document.contents).expect("invalid utf-8");

///         document

///             .header

///             .emit_key_and_value(Cow::Borrowed(contents_as_str), 1)

///     }

///

///     fn reduce(

///         &self,

///         mappings: &[ViewMappedValue<'_, Self::View>],

///         _rereduce: bool,

///     ) -> ReduceResult<Self::View> {

///         Ok(mappings.iter().map(|mapping| mapping.value).sum())

///     }

/// }

/// ```

#[doc = "\n"]

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

pub trait ViewSchema: Send + Sync + 'static {

    /// The view this schema is defined for.

    type View: SerializedView;

    /// The key type used during the map/reduce operation.

    ///

    /// This can typically be specified as `<Self::View as View>::Key`. However,

    /// if the view can take advantage of utilizing borrowed data from the

    /// document in the `map()` and/or `reduce()` function calls, this type can

    /// utilize the generic associated lifetime `'doc`. For example, `Cow<'doc,

    /// str>` can be used when the related [`View::Key`] type is `String`, and

    /// the `map()` function would be able to return a string slice that

    /// borrowed from the document.

    type MappedKey<'doc>: Key<'doc>;

    /// Returns the update policy for this view, which controls when and how the

    /// view's data is updated. The provided implementation returns

    /// [`ViewUpdatePolicy::Lazy`].

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

    /// rebuilt.

}

/// The policy under which a [`View`] is updated when documents are saved.

pub enum ViewUpdatePolicy {

    /// The view is updated when a query is made. If a document is updated

    /// multiple times between queries, the view will only be updated when the

    /// query is executed.

    #[default]

    Lazy,

    /// The view is updated during the transaction where documents are being

    /// inserted, updated, or removed.

    Eager,

    /// 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.

    Unique,

}

impl ViewUpdatePolicy {

    /// Returns true if the view should be updated eagerly.

    ///

    /// This returns true if the policy is either [`Eager`](Self::Eager) or

    /// [`Unique`](Self::Unique).

    #[must_use]

}

impl std::fmt::Display for ViewUpdatePolicy {

}

/// The Map/Reduce functionality for a [`ViewSchema`].

///

/// This trait implementation provides the behavior for mapping data from

/// documents into their key/value pairs for this view, as well as reducing

/// multiple values into a single value.

pub trait MapReduce: ViewSchema {

    /// 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<'doc>(&self, document: &'doc BorrowedDocument<'_>) -> ViewMapResult<'doc, Self>;

    /// 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.

    /// Returns a builder for a view query or view reduce.

    /// Returns a builder for a view query or view reduce.

}

/// 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 [`MapReduce`] implementation that automatically serializes/deserializes

/// using [`CollectionDocument`] and [`SerializedCollection`].

///

/// Implementing this trait automatically implements [`ViewSchema`] for the same

/// type.

pub trait CollectionMapReduce: ViewSchema

where

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

{

    /// 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<'doc>(

        &self,

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

    ) -> ViewMapResult<'doc, Self>

    where

        CollectionDocument<<Self::View as View>::Collection>: 'doc;

    /// 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> MapReduce for T

where

    T: CollectionMapReduce,

    T::View: SerializedView,

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

{

}

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

pub trait Serialized: Send + Sync {

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

    fn collection(&self) -> CollectionName;

    /// Returns the description of the view's `Key`.

    fn key_description(&self) -> KeyDescription;

    /// Wraps [`ViewSchema::update_policy`]

    fn update_policy(&self) -> ViewUpdatePolicy;

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

    fn version(&self) -> u64;

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

    fn view_name(&self) -> ViewName;

    /// Wraps [`MapReduce::map`]

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

    /// Wraps [`MapReduce::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::ViewSchema for $view_name {

            type MappedKey<'doc> = <Self as $crate::schema::View>::Key;

            type View = Self;

                if $unique {

                } else {

                }

        }

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

        }

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

    };

}