// AnimationPlayer.swift
// CADisplayLink-driven playback engine matching Blender's transport controls.

import UIKit
import Observation

@Observable
final class AnimationPlayer {
    var animationSystem: AnimationSystem

    private var displayLink: CADisplayLink?
    private var lastTimestamp: CFTimeInterval = 0

    init(system: AnimationSystem) {
        self.animationSystem = system
    }

    // MARK: - Transport controls (mirror Blender's timeline buttons)

    func play() {
        animationSystem.isPlaying = true
        startDisplayLink()
    }

    func pause() {
        animationSystem.isPlaying = false
        stopDisplayLink()
    }

    func stop() {
        animationSystem.isPlaying = false
        animationSystem.currentFrame = animationSystem.frameStart
        stopDisplayLink()
    }

    func togglePlayback() {
        if animationSystem.isPlaying {
            pause()
        } else {
            play()
        }
    }

    func jumpToStart() {
        animationSystem.currentFrame = animationSystem.frameStart
    }

    func jumpToEnd() {
        animationSystem.currentFrame = animationSystem.frameEnd
    }

    func stepForward() {
        animationSystem.currentFrame = min(
            animationSystem.currentFrame + 1,
            animationSystem.frameEnd
        )
    }

    func stepBackward() {
        animationSystem.currentFrame = max(
            animationSystem.currentFrame - 1,
            animationSystem.frameStart
        )
    }

    func nextKeyframe() {
        guard let action = animationSystem.activeAction else { return }
        let allFrames = action.tracks
            .flatMap { $0.sortedKeyframes }
            .map(\.frame)
            .sorted()
        if let next = allFrames.first(where: { $0 > animationSystem.currentFrame + 0.5 }) {
            animationSystem.currentFrame = next
        }
    }

    func previousKeyframe() {
        guard let action = animationSystem.activeAction else { return }
        let allFrames = action.tracks
            .flatMap { $0.sortedKeyframes }
            .map(\.frame)
            .sorted()
        if let prev = allFrames.last(where: { $0 < animationSystem.currentFrame - 0.5 }) {
            animationSystem.currentFrame = prev
        }
    }

    // MARK: - Display link

    private func startDisplayLink() {
        guard displayLink == nil else { return }
        lastTimestamp = 0
        let link = CADisplayLink(target: self, selector: #selector(tick))
        link.preferredFrameRateRange = CAFrameRateRange(
            minimum: 30, maximum: 120, preferred: 60
        )
        link.add(to: .main, forMode: .common)
        displayLink = link
    }

    private func stopDisplayLink() {
        displayLink?.invalidate()
        displayLink = nil
    }

    @objc private func tick(_ link: CADisplayLink) {
        if lastTimestamp == 0 {
            lastTimestamp = link.timestamp
            return
        }
        let dt = Float(link.timestamp - lastTimestamp)
        lastTimestamp = link.timestamp
        animationSystem.tick(dt: dt)
    }

    deinit {
        stopDisplayLink()
    }
}