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// Copyright 2023-2024 Hugo Osvaldo Barrera
//
// SPDX-License-Identifier: EUPL-1.2

//! Types for specifying rules for a synchronisation.
use std::sync::Arc;

use crate::{
    base::{Item, Storage},
    CollectionId, Href,
};

/// A collection declared either via its `href` or `collection_id`.
#[derive(Debug, Clone)]
pub enum CollectionDescription {
    Id { id: CollectionId },
    Href { href: Href },
}

impl CollectionDescription {
    pub(crate) fn alias(&self) -> String {
        match self {
            CollectionDescription::Id { id } => id.to_string(),
            CollectionDescription::Href { href } => format!("href:{href}"),
        }
    }
}

/// A mapping between of a pair of collections across storages.
///
/// This is an unresolved mapping which may be lacking information on one side.
#[derive(Debug, Clone)]
pub enum DeclaredMapping {
    /// Copy between two collections with the same definition on both sides.
    ///
    /// Usage of [`CollectionDescription::Href`] between different storage implementations is
    /// discouraged.
    Direct { description: CollectionDescription },
    /// Copy between two collections with explicit definitions on both sides.
    Mapped {
        /// A descriptive name used for logging and display.
        alias: String,
        a: CollectionDescription,
        b: CollectionDescription,
    },
}

impl DeclaredMapping {
    /// Create a direct mapping.
    ///
    /// This creates the simplest kind of mapping: it maps two collections with the same
    /// [`CollectionId`].
    #[must_use]
    pub fn direct(id: CollectionId) -> Self {
        DeclaredMapping::Direct {
            description: CollectionDescription::Id { id },
        }
    }
}

/// A pair of storage that are to be synchronised.
///
/// This type merely wraps around the declaration of what shall be synchronised. It can be
/// constructed offline and is the entry point to create a [`Plan`] and then execute it.
///
/// New pairs can be created via [`StoragePair::new`].
///
/// [`Plan`]: crate::sync::plan::Plan
pub struct StoragePair<I: Item> {
    pub(super) storage_a: Arc<dyn Storage<I>>,
    pub(super) storage_b: Arc<dyn Storage<I>>,
    pub(super) mappings: Vec<DeclaredMapping>,
    pub(super) all_from_a: bool,
    pub(super) all_from_b: bool,
    pub(super) on_empty: OnEmpty,
}

impl<I: Item> StoragePair<I> {
    /// Create a new instance.
    ///
    /// By default, no collections are to be synchronised. See other associated functions for
    /// details con configuring additional collections.
    #[must_use]
    pub fn new(storage_a: Arc<dyn Storage<I>>, storage_b: Arc<dyn Storage<I>>) -> StoragePair<I> {
        StoragePair {
            storage_a,
            storage_b,
            mappings: Vec::new(),
            all_from_a: false,
            all_from_b: false,
            on_empty: OnEmpty::Skip,
        }
    }

    /// Include the specified mapping when synchronising.
    #[must_use]
    pub fn with_mapping(mut self, mapping: DeclaredMapping) -> Self {
        self.mappings.push(mapping);
        self
    }

    /// Include all collections from storage A when synchronising.
    ///
    /// By default, only explicitly included collections are synchronised.
    #[must_use]
    pub fn with_all_from_a(mut self) -> Self {
        self.all_from_a = true;
        self
    }

    /// Include all collections from storage B when synchronising.
    ///
    /// By default, only explicitly included collections are synchronised.
    #[must_use]
    pub fn with_all_from_b(mut self) -> Self {
        self.all_from_b = true;
        self
    }

    /// Returns a reference to storage a.
    #[must_use]
    pub fn storage_a(&self) -> &dyn Storage<I> {
        self.storage_a.as_ref()
    }

    /// Returns a reference to storage a.
    #[must_use]
    pub fn storage_b(&self) -> &dyn Storage<I> {
        self.storage_b.as_ref()
    }

    /// Action to take when a collection is completely emptied.
    #[must_use]
    pub fn on_empty(mut self, action: OnEmpty) -> Self {
        self.on_empty = action;
        self
    }
}

#[derive(Debug, PartialEq, Default)]
pub enum OnEmpty {
    #[default]
    Skip,
    Sync,
}