Signal-iOS/SignalUI/Views/VideoEditor/VideoAttachmentPrepViewController.swift

//
// Copyright 2022 Signal Messenger, LLC
// SPDX-License-Identifier: AGPL-3.0-only
//

import AVFoundation
import UIKit

protocol VideoPlaybackState {
    var isPlaying: Bool { get }
    var currentTimeSeconds: TimeInterval { get }
}

protocol VideoEditorDataSource: AnyObject {
    var untrimmedDurationSeconds: TimeInterval { get }
    var trimmedStartSeconds: TimeInterval { get }
    var trimmedEndSeconds: TimeInterval { get }
    var canBeTrimmed: Bool { get }
    var isTrimmed: Bool { get }
}

/**
 * Coordinate data transfer between VideoEditorView and VideoTimelineView
 */
class VideoAttachmentPrepViewController: AttachmentPrepViewController {

    private let model: VideoEditorModel

    private lazy var editorView = VideoEditorView(model: model, delegate: self, dataSource: self, viewControllerProvider: self)

    private lazy var timelineView: VideoTimelineView = {
        let timelineView = VideoTimelineView()
        timelineView.dataSource = self
        timelineView.delegate = self
        return timelineView
    }()

    required init?(attachmentApprovalItem: AttachmentApprovalItem) {
        guard let videoEditorModel = attachmentApprovalItem.videoEditorModel else {
            owsFailDebug("videoEditorModel is empty.")
            return nil
        }

        self.model = videoEditorModel

        super.init(attachmentApprovalItem: attachmentApprovalItem)

        model.add(observer: self)
    }

    override var contentView: AttachmentPrepContentView {
        editorView
    }

    override var toolbarSupplementaryView: UIView? {
        timelineView
    }

    override func prepareContentView() {
        editorView.configureSubviews()
        generateThumbnailsAsync()
    }

    override func prepareToMoveOffscreen() {
        editorView.pauseIfPlaying()
    }

    override public var canSaveMedia: Bool {
        if model.needsRender {
            return true
        }
        return super.canSaveMedia
    }

    private(set) var videoThumbnails: [UIImage]?
    private var shouldResumeVideoPlaybackOnScrubbingEnd = false
}

extension VideoAttachmentPrepViewController: VideoEditorViewDelegate {

    func videoEditorViewPlaybackTimeDidChange(_ videoEditorView: VideoEditorView) {
        timelineView.updateCursorPosition()
        timelineView.updateTimeBubble()
    }
}

extension VideoAttachmentPrepViewController: VideoEditorDataSource {

    var untrimmedDurationSeconds: TimeInterval {
        return model.untrimmedDurationSeconds
    }

    var trimmedStartSeconds: TimeInterval {
        return model.trimmedStartSeconds
    }

    var trimmedEndSeconds: TimeInterval {
        return model.trimmedEndSeconds
    }

    var canBeTrimmed: Bool {
        return model.canBeTrimmed
    }

    var isTrimmed: Bool {
        return model.isTrimmed
    }
}

extension VideoAttachmentPrepViewController: VideoPlaybackState {

    var isPlaying: Bool {
        return editorView.isPlaying
    }

    var currentTimeSeconds: TimeInterval {
        return editorView.currentTimeSeconds
    }
}

extension VideoAttachmentPrepViewController: VideoTimelineViewDataSource {

    var videoAspectRatio: CGSize {
        return model.displaySize
    }

    private func generateThumbnailsAsync() {
        let model = self.model
        let videoAspectRatio = videoAspectRatio
        let untrimmedDurationSeconds = self.untrimmedDurationSeconds

        firstly {
            VideoAttachmentPrepViewController.thumbnails(forVideoAtPath: model.srcVideoPath,
                                                         aspectRatio: videoAspectRatio,
                                                         thumbnailHeight: VideoTimelineView.preferredHeight,
                                                         untrimmedDurationSeconds: untrimmedDurationSeconds)
        }.done(on: .main) { [weak self] (thumbnails: [UIImage]) -> Void in
            guard let self = self else {
                return
            }
            self.videoThumbnails = thumbnails
            self.timelineView.updateThumbnailView()
        }.catch { error in
            owsFailDebug("Error: \(error)")
        }
    }

    private class func thumbnails(forVideoAtPath videoPath: String,
                                  aspectRatio: CGSize,
                                  thumbnailHeight: CGFloat,
                                  untrimmedDurationSeconds: TimeInterval) -> Promise<[UIImage]> {
        AssertIsOnMainThread()

        let contextSize = CurrentAppContext().frame.size
        let screenScale = UIScreen.main.scale

        return DispatchQueue.global().async(.promise) {
            // We generate enough thumbnails for the worst case (full-screen landscape)
            // to avoid the complexity of regeneration.
            let contextMaxDimension = max(contextSize.width, contextSize.height)
            let thumbnailWidth = floor(thumbnailHeight * aspectRatio.width / aspectRatio.height)
            let thumbnailCount = UInt(ceil(contextMaxDimension / thumbnailWidth))

            let maxThumbnailSize = max(thumbnailWidth, thumbnailHeight) * screenScale

            let url = URL(fileURLWithPath: videoPath)
            let asset = AVURLAsset(url: url, options: nil)
            let generator = AVAssetImageGenerator(asset: asset)
            generator.maximumSize = CGSize(square: maxThumbnailSize)
            generator.appliesPreferredTrackTransform = true
            var thumbnails = [UIImage]()
            for index in 0..<thumbnailCount {
                let thumbnailAlpha = Double(index) / Double(thumbnailCount - 1)
                let thumbnailTimeSeconds = thumbnailAlpha * untrimmedDurationSeconds
                let thumbnailCMTime = CMTime(seconds: thumbnailTimeSeconds, preferredTimescale: 1000)
                let cgImage = try generator.copyCGImage(at: thumbnailCMTime, actualTime: nil)
                let thumbnail = UIImage(cgImage: cgImage, scale: 1, orientation: .up)
                thumbnails.append(thumbnail)
            }
            return thumbnails
        }
    }
}

extension VideoAttachmentPrepViewController: VideoTimelineViewDelegate {

    func videoTimelineViewDidBeginTrimming(_ view: VideoTimelineView) {
        editorView.pauseIfPlaying()
        editorView.isTrimmingVideo = true
    }

    func videoTimelineView(_ view: VideoTimelineView, didTrimBeginningTo seconds: TimeInterval) {
        model.trimToStartSeconds(seconds)
        editorView.seek(toSeconds: seconds)
    }

    func videoTimelineView(_ view: VideoTimelineView, didTrimEndTo seconds: TimeInterval) {
        model.trimToEndSeconds(seconds)
        editorView.seek(toSeconds: seconds)
    }

    func videoTimelineViewDidEndTrimming(_ view: VideoTimelineView) {
        editorView.isTrimmingVideo = false
        editorView.ensureSeekReflectsTrimming()

        if model.needsRender {
            _ = model.ensureCurrentRender()
        }
    }

    func videoTimelineViewWillBeginScrubbing(_ view: VideoTimelineView) {
        // Pause playback during scrubbing.
        shouldResumeVideoPlaybackOnScrubbingEnd = editorView.pauseIfPlaying()
    }

    func videoTimelineView(_ view: VideoTimelineView, didScrubTo seconds: TimeInterval) {
        editorView.seek(toSeconds: seconds)
    }

    func videoTimelineViewDidEndScrubbing(_ view: VideoTimelineView) {
        if shouldResumeVideoPlaybackOnScrubbingEnd {
            editorView.playVideo()
        }
    }
}

extension VideoAttachmentPrepViewController: VideoEditorModelObserver {

    func videoEditorModelDidChange(_ model: VideoEditorModel) {
        timelineView.updateContents()
    }
}

extension VideoAttachmentPrepViewController: VideoEditorViewControllerProviding {

    func viewController(forVideoEditorView videoEditorView: VideoEditorView) -> UIViewController {
        return self
    }
}