//
// Copyright 2025 New Vector Ltd.
//
// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
// Please see LICENSE files in the repository root for full details.
//

@testable import ElementX
import QuickLook
import XCTest

@MainActor
class TimelineMediaPreviewDataSourceTests: XCTestCase {
    var initialMediaItems: [EventBasedMessageTimelineItemProtocol]!
    var initialMediaViewStates: [RoomTimelineItemViewState]!
    let initialItemIndex = 2
    
    var initialPadding = 100
    let previewController = QLPreviewController()
    
    override func setUp() {
        initialMediaItems = newChunk()
        initialMediaViewStates = initialMediaItems.map { RoomTimelineItemViewState(item: $0, groupStyle: .single) }
    }
    
    func testInitialItems() throws -> TimelineMediaPreviewDataSource {
        // Given a data source built with the initial items.
        let dataSource = TimelineMediaPreviewDataSource(itemViewStates: initialMediaViewStates,
                                                        initialItem: initialMediaItems[initialItemIndex],
                                                        initialPadding: initialPadding,
                                                        paginationState: .initial)
        
        // When the preview controller displays the data.
        let previewItemCount = dataSource.numberOfPreviewItems(in: previewController)
        let displayedItem = try XCTUnwrap(dataSource.previewController(previewController, previewItemAt: dataSource.initialItemIndex) as? TimelineMediaPreviewItem.Media,
                                          "A preview item should be found.")
        
        // Then the preview controller should be showing the initial item and the data source should reflect this.
        XCTAssertEqual(dataSource.initialItemIndex, initialItemIndex + initialPadding, "The initial item index should be padded for the preview controller.")
        XCTAssertEqual(displayedItem.id, initialMediaItems[initialItemIndex].id.eventOrTransactionID, "The displayed item should be the initial item.")
        XCTAssertEqual(dataSource.currentMediaItemID, initialMediaItems[initialItemIndex].id.eventOrTransactionID, "The current item should also be the initial item.")
        
        XCTAssertEqual(dataSource.previewItems.count, initialMediaViewStates.count, "The initial count of preview items should be correct.")
        XCTAssertEqual(previewItemCount, initialMediaViewStates.count + (2 * initialPadding), "The initial item count should be padded for the preview controller.")
        
        return dataSource
    }
    
    func testCurrentUpdateItem() throws {
        // Given a data source built with the initial items.
        let dataSource = TimelineMediaPreviewDataSource(itemViewStates: initialMediaViewStates,
                                                        initialItem: initialMediaItems[initialItemIndex],
                                                        paginationState: .initial)
        
        // When a different item is displayed.
        let previewItem = try XCTUnwrap(dataSource.previewController(previewController, previewItemAt: 1 + initialPadding) as? TimelineMediaPreviewItem.Media,
                                        "A preview item should be found.")
        dataSource.updateCurrentItem(.media(previewItem))
        
        // Then the data source should reflect the change of item.
        XCTAssertEqual(dataSource.currentMediaItemID, previewItem.id, "The displayed item should be the initial item.")
        
        // When a loading item is displayed.
        guard let loadingItem = dataSource.previewController(previewController, previewItemAt: initialPadding - 1) as? TimelineMediaPreviewItem.Loading else {
            XCTFail("A loading item should be be returned.")
            return
        }
        dataSource.updateCurrentItem(.loading(loadingItem))
        
        // Then the data source should show a loading item
        XCTAssertEqual(dataSource.currentItem, .loading(loadingItem), "The displayed item should be the loading item.")
    }
    
    func testUpdatedItems() async throws {
        // Given a data source built with the initial items.
        let dataSource = try testInitialItems()
        
        // When one of the items changes but no pagination has occurred.
        let deferred = deferFailure(dataSource.previewItemsPaginationPublisher, timeout: 1) { _ in true }
        dataSource.updatePreviewItems(itemViewStates: initialMediaViewStates)
        
        // Then no pagination should be detected and none of the data should have changed.
        try await deferred.fulfill()
        
        let previewItemCount = dataSource.numberOfPreviewItems(in: previewController)
        let displayedItem = try XCTUnwrap(dataSource.previewController(previewController, previewItemAt: dataSource.initialItemIndex) as? TimelineMediaPreviewItem.Media)
        XCTAssertEqual(displayedItem.id, initialMediaItems[initialItemIndex].id.eventOrTransactionID, "The displayed item should not change.")
        XCTAssertEqual(dataSource.currentMediaItemID, initialMediaItems[initialItemIndex].id.eventOrTransactionID, "The current item should not change.")
        
        XCTAssertEqual(dataSource.previewItems.count, initialMediaViewStates.count, "The number of items should not change.")
        XCTAssertEqual(previewItemCount, initialMediaViewStates.count + (2 * initialPadding), "The padded number of items should not change.")
    }
    
    func testPagination() async throws {
        // Given a data source built with the initial items.
        let dataSource = try testInitialItems()
        
        // When more items are loaded in a back pagination.
        var deferred = deferFulfillment(dataSource.previewItemsPaginationPublisher) { _ in true }
        let backPaginationChunk = newChunk().map { RoomTimelineItemViewState(item: $0, groupStyle: .single) }
        var newViewStates = backPaginationChunk + initialMediaViewStates
        dataSource.updatePreviewItems(itemViewStates: newViewStates)
        
        // Then the new items should be added but the displayed item should not change or move in the array.
        try await deferred.fulfill()
        XCTAssertEqual(dataSource.previewItems.count, newViewStates.count, "The new items should be added.")
        
        var previewItemCount = dataSource.numberOfPreviewItems(in: previewController)
        var displayedItem = try XCTUnwrap(dataSource.previewController(previewController, previewItemAt: dataSource.initialItemIndex) as? TimelineMediaPreviewItem.Media)
        XCTAssertEqual(displayedItem.id, initialMediaItems[initialItemIndex].id.eventOrTransactionID, "The displayed item should not change.")
        XCTAssertEqual(dataSource.currentMediaItemID, initialMediaItems[initialItemIndex].id.eventOrTransactionID, "The current item should not change.")
        XCTAssertEqual(previewItemCount, initialMediaViewStates.count + (2 * initialPadding), "The number of items should not change")
        
        // When more items are loaded in a forward pagination or sync.
        deferred = deferFulfillment(dataSource.previewItemsPaginationPublisher) { _ in true }
        let forwardPaginationChunk = newChunk().map { RoomTimelineItemViewState(item: $0, groupStyle: .single) }
        newViewStates += forwardPaginationChunk
        dataSource.updatePreviewItems(itemViewStates: newViewStates)
        
        // Then the new items should be added but the displayed item should not change or move in the array.
        try await deferred.fulfill()
        XCTAssertEqual(dataSource.previewItems.count, newViewStates.count, "The new items should be added.")
        
        previewItemCount = dataSource.numberOfPreviewItems(in: previewController)
        displayedItem = try XCTUnwrap(dataSource.previewController(previewController, previewItemAt: dataSource.initialItemIndex) as? TimelineMediaPreviewItem.Media)
        XCTAssertEqual(displayedItem.id, initialMediaItems[initialItemIndex].id.eventOrTransactionID, "The displayed item should not change.")
        XCTAssertEqual(dataSource.currentMediaItemID, initialMediaItems[initialItemIndex].id.eventOrTransactionID, "The current item should not change.")
        XCTAssertEqual(previewItemCount, initialMediaViewStates.count + (2 * initialPadding), "The number of items should not change")
    }
    
    func testPaginationLimits() async throws {
        // Given a data source with a small amount of padding remaining.
        initialPadding = 2
        let dataSource = try testInitialItems()
        
        // When paginating backwards by more than the available padding.
        var deferred = deferFulfillment(dataSource.previewItemsPaginationPublisher) { _ in true }
        let backPaginationChunk = newChunk().map { RoomTimelineItemViewState(item: $0, groupStyle: .single) }
        var newViewStates = backPaginationChunk + initialMediaViewStates
        XCTAssertTrue(newViewStates.count > initialPadding)
        dataSource.updatePreviewItems(itemViewStates: newViewStates)
        
        // Then all the items should be added but the preview-able count shouldn't grow and displayed item should not change or move.
        try await deferred.fulfill()
        XCTAssertEqual(dataSource.previewItems.count, newViewStates.count, "The new items should be added.")
        
        var previewItemCount = dataSource.numberOfPreviewItems(in: previewController)
        var displayedItem = try XCTUnwrap(dataSource.previewController(previewController, previewItemAt: dataSource.initialItemIndex) as? TimelineMediaPreviewItem.Media)
        XCTAssertEqual(displayedItem.id, initialMediaItems[initialItemIndex].id.eventOrTransactionID, "The displayed item should not change.")
        XCTAssertEqual(dataSource.currentMediaItemID, initialMediaItems[initialItemIndex].id.eventOrTransactionID, "The current item should not change.")
        XCTAssertEqual(previewItemCount, initialMediaViewStates.count + (2 * initialPadding), "The number of items should not change")
        
        // When paginating forwards by more than the available padding.
        deferred = deferFulfillment(dataSource.previewItemsPaginationPublisher) { _ in true }
        let forwardPaginationChunk = newChunk().map { RoomTimelineItemViewState(item: $0, groupStyle: .single) }
        newViewStates += forwardPaginationChunk
        dataSource.updatePreviewItems(itemViewStates: newViewStates)
        
        // Then all the items should be added but the preview-able count shouldn't grow and displayed item should not change or move.
        try await deferred.fulfill()
        XCTAssertEqual(dataSource.previewItems.count, newViewStates.count, "The new items should be added.")
        
        previewItemCount = dataSource.numberOfPreviewItems(in: previewController)
        displayedItem = try XCTUnwrap(dataSource.previewController(previewController, previewItemAt: dataSource.initialItemIndex) as? TimelineMediaPreviewItem.Media)
        XCTAssertEqual(displayedItem.id, initialMediaItems[initialItemIndex].id.eventOrTransactionID, "The displayed item should not change.")
        XCTAssertEqual(dataSource.currentMediaItemID, initialMediaItems[initialItemIndex].id.eventOrTransactionID, "The current item should not change.")
        XCTAssertEqual(previewItemCount, initialMediaViewStates.count + (2 * initialPadding), "The number of items should not change")
    }
    
    func testEmptyTimeline() async throws {
        // Given a data source built with no timeline items loaded.
        let initialItem = initialMediaItems[initialItemIndex]
        let dataSource = TimelineMediaPreviewDataSource(itemViewStates: [],
                                                        initialItem: initialItem,
                                                        initialPadding: initialPadding,
                                                        paginationState: .initial)
        
        // When the preview controller displays the data.
        var previewItemCount = dataSource.numberOfPreviewItems(in: previewController)
        var displayedItem = try XCTUnwrap(dataSource.previewController(previewController, previewItemAt: dataSource.initialItemIndex) as? TimelineMediaPreviewItem.Media,
                                          "A preview item should be found.")
        
        // Then the preview controller should always show the initial item.
        XCTAssertEqual(dataSource.previewItems.count, 1, "The initial item should be in the preview items array.")
        XCTAssertEqual(previewItemCount, 1 + (2 * initialPadding), "The initial item count should be padded for the preview controller.")
        XCTAssertEqual(dataSource.initialItemIndex, initialPadding, "The initial item index should be padded for the preview controller.")
        
        XCTAssertEqual(displayedItem.id, initialItem.id.eventOrTransactionID, "The displayed item should be the initial item.")
        XCTAssertEqual(dataSource.currentMediaItemID, initialItem.id.eventOrTransactionID, "The current item should also be the initial item.")
        
        // When the timeline loads the initial items.
        let deferred = deferFulfillment(dataSource.previewItemsPaginationPublisher) { _ in true }
        let loadedItems = initialMediaItems.map { RoomTimelineItemViewState(item: $0, groupStyle: .single) }
        dataSource.updatePreviewItems(itemViewStates: loadedItems)
        try await deferred.fulfill()
        
        // Then the preview controller should still show the initial item with the other items loaded around it.
        previewItemCount = dataSource.numberOfPreviewItems(in: previewController)
        displayedItem = try XCTUnwrap(dataSource.previewController(previewController, previewItemAt: dataSource.initialItemIndex) as? TimelineMediaPreviewItem.Media,
                                      "A preview item should be found.")
        
        XCTAssertEqual(dataSource.previewItems.count, initialMediaViewStates.count, "The preview items should now be loaded.")
        XCTAssertEqual(previewItemCount, 1 + (2 * initialPadding), "The item count should not change as the padding will be reduced.")
        XCTAssertEqual(dataSource.initialItemIndex, initialPadding, "The item index should not change.")
        
        XCTAssertEqual(displayedItem.id, initialMediaItems[initialItemIndex].id.eventOrTransactionID, "The displayed item should not change.")
        XCTAssertEqual(dataSource.currentMediaItemID, initialMediaItems[initialItemIndex].id.eventOrTransactionID, "The current item should not change.")
    }
    
    func testTimelineUpdateWithoutInitialItem() async throws {
        // Given a data source built with no timeline items loaded.
        let initialItem = initialMediaItems[initialItemIndex]
        let dataSource = TimelineMediaPreviewDataSource(itemViewStates: [],
                                                        initialItem: initialItem,
                                                        initialPadding: initialPadding,
                                                        paginationState: .initial)
        
        // When the preview controller displays the data.
        var previewItemCount = dataSource.numberOfPreviewItems(in: previewController)
        var displayedItem = try XCTUnwrap(dataSource.previewController(previewController, previewItemAt: dataSource.initialItemIndex) as? TimelineMediaPreviewItem.Media,
                                          "A preview item should be found.")
        
        // Then the preview controller should always show the initial item.
        XCTAssertEqual(dataSource.previewItems.count, 1, "The initial item should be in the preview items array.")
        XCTAssertEqual(previewItemCount, 1 + (2 * initialPadding), "The initial item count should be padded for the preview controller.")
        XCTAssertEqual(dataSource.initialItemIndex, initialPadding, "The initial item index should be padded for the preview controller.")
        
        XCTAssertEqual(displayedItem.id, initialItem.id.eventOrTransactionID, "The displayed item should be the initial item.")
        XCTAssertEqual(dataSource.currentMediaItemID, initialItem.id.eventOrTransactionID, "The current item should also be the initial item.")
        
        // When the timeline loads more items but still doesn't include the initial item.
        let failure = deferFailure(dataSource.previewItemsPaginationPublisher, timeout: 1) { _ in true }
        let loadedItems = newChunk().map { RoomTimelineItemViewState(item: $0, groupStyle: .single) }
        dataSource.updatePreviewItems(itemViewStates: loadedItems)
        try await failure.fulfill()
        
        // Then the preview controller shouldn't update the available preview items.
        previewItemCount = dataSource.numberOfPreviewItems(in: previewController)
        displayedItem = try XCTUnwrap(dataSource.previewController(previewController, previewItemAt: dataSource.initialItemIndex) as? TimelineMediaPreviewItem.Media,
                                      "A preview item should be found.")
        
        XCTAssertEqual(dataSource.previewItems.count, 1, "No new items should have been added to the array.")
        XCTAssertEqual(previewItemCount, 1 + (2 * initialPadding), "The initial item count should not change.")
        XCTAssertEqual(dataSource.initialItemIndex, initialPadding, "The initial item index should not change.")
        
        XCTAssertEqual(displayedItem.id, initialItem.id.eventOrTransactionID, "The displayed item should not change.")
        XCTAssertEqual(dataSource.currentMediaItemID, initialItem.id.eventOrTransactionID, "The current item not change.")
    }
    
    // MARK: Helpers
    
    func newChunk() -> [EventBasedMessageTimelineItemProtocol] {
        RoomTimelineItemFixtures.mediaChunk
            .compactMap { $0 as? EventBasedMessageTimelineItemProtocol }
            .filter(\.supportsMediaCaption) // Voice messages can't be previewed (and don't support captions).
    }
}

private extension TimelineMediaPreviewDataSource {
    var currentMediaItemID: TimelineItemIdentifier.EventOrTransactionID? {
        switch currentItem {
        case .media(let mediaItem): mediaItem.id
        case .loading: nil
        }
    }
}