video: add DamusVideoPlayerViewModel

Closes: https://github.com/damus-io/damus/pull/1539
Reviewed-by: William Casarin <jb55@jb55.com>
Signed-off-by: William Casarin <jb55@jb55.com>

damus/Views/Video/DamusVideoPlayerViewModel.swift

@@ -0,0 +1,105 @@
+//
+//  DamusVideoPlayerViewModel.swift
+//  damus
+//
+//  Created by Bryan Montz on 9/5/23.
+//
+
+import AVFoundation
+import Combine
+import Foundation
+import SwiftUI
+
+@MainActor
+final class DamusVideoPlayerViewModel: ObservableObject {
+    
+    private let url: URL
+    private let player_item: AVPlayerItem
+    let player: AVPlayer
+    private let controller: VideoController
+    let id = UUID()
+    
+    @Published var has_audio = false
+    @Binding var video_size: CGSize?
+    @Published var is_muted = true
+    @Published var is_loading = true
+    
+    private var cancellables = Set<AnyCancellable>()
+    
+    private var is_scrolled_into_view = false {
+        didSet {
+            if is_scrolled_into_view && !oldValue {
+                // we have just scrolled from out of view into view
+                controller.focused_model_id = id
+            } else if !is_scrolled_into_view && oldValue {
+                // we have just scrolled from in view to out of view
+                if controller.focused_model_id == id {
+                    controller.focused_model_id = nil
+                }
+            }
+        }
+    }
+    
+    init(url: URL, video_size: Binding<CGSize?>, controller: VideoController) {
+        self.url = url
+        player_item = AVPlayerItem(url: url)
+        player = AVPlayer(playerItem: player_item)
+        self.controller = controller
+        _video_size = video_size
+        
+        Task {
+            await load()
+        }
+        
+        is_muted = controller.should_mute_video(url: url)
+        player.isMuted = is_muted
+        
+        NotificationCenter.default.addObserver(
+            self,
+            selector: #selector(did_play_to_end),
+            name: Notification.Name.AVPlayerItemDidPlayToEndTime,
+            object: player_item
+        )
+        
+        controller.$focused_model_id
+            .sink { [weak self] model_id in
+                model_id == self?.id ? self?.player.play() : self?.player.pause()
+            }
+            .store(in: &cancellables)
+    }
+    
+    private func load() async {
+        if let meta = controller.metadata(for: url) {
+            has_audio = meta.has_audio
+            video_size = meta.size
+        } else {
+            has_audio = await video_has_audio(player: player)
+            if let video_size = await get_video_size(player: player) {
+                self.video_size = video_size
+                let meta = VideoMetadata(has_audio: has_audio, size: video_size)
+                controller.set_metadata(meta, url: url)
+            }
+        }
+        
+        is_loading = false
+    }
+    
+    func did_tap_mute_button() {
+        is_muted.toggle()
+        player.isMuted = is_muted
+        controller.toggle_should_mute_video(url: url)
+    }
+    
+    func set_view_is_visible(_ is_visible: Bool) {
+        is_scrolled_into_view = is_visible
+    }
+    
+    func view_did_disappear() {
+        set_view_is_visible(false)
+    }
+    
+    @objc private func did_play_to_end() {
+        player.seek(to: CMTime.zero)
+        player.play()
+    }
+}