package coffee.liz.ecs.animation

import coffee.liz.ecs.System
import coffee.liz.ecs.World

/**
 * System that updates animation playback state for all entities with an Animator component.
 *
 * This system:
 * - Updates elapsed time for playing animations
 * - Advances frame indices based on frame duration
 * - Handles loop modes (ONCE, LOOP, PING_PONG)
 * - Stops animations when they complete (for ONCE mode)
 */
class AnimationSystem : System {
    override fun update(world: World, deltaTime: Float) {
        // Query all entities that have both Animator and SpriteSheet
        world.query(Animator::class, SpriteSheet::class).forEach { entity ->
            val animator = entity.get(Animator::class) ?: return@forEach

            // Skip if animation is not playing
            if (!animator.playing) return@forEach

            // Get the current animation clip
            val clip = animator.clips[animator.currentClip] ?: return@forEach

            // Accumulate elapsed time
            animator.elapsed += deltaTime

            // Advance frames while we have enough elapsed time
            while (animator.elapsed >= clip.frameDuration) {
                animator.elapsed -= clip.frameDuration
                advanceFrame(animator, clip)
            }
        }
    }

    /**
     * Advances the animation to the next frame based on loop mode.
     */
    private fun advanceFrame(animator: Animator, clip: AnimationClip) {
        animator.frameIndex += animator.direction

        when (clip.loopMode) {
            LoopMode.ONCE -> {
                // Play once and stop on last frame
                if (animator.frameIndex >= clip.frameNames.size) {
                    animator.frameIndex = clip.frameNames.size - 1
                    animator.playing = false
                }
            }

            LoopMode.LOOP -> {
                // Loop back to beginning
                if (animator.frameIndex >= clip.frameNames.size) {
                    animator.frameIndex = 0
                } else if (animator.frameIndex < 0) {
                    // Handle negative wrap (shouldn't happen in LOOP but be safe)
                    animator.frameIndex = clip.frameNames.size - 1
                }
            }

            LoopMode.PING_PONG -> {
                // Bounce back and forth
                if (animator.frameIndex >= clip.frameNames.size) {
                    // Hit the end, reverse direction
                    animator.frameIndex = (clip.frameNames.size - 2).coerceAtLeast(0)
                    animator.direction = -1
                } else if (animator.frameIndex < 0) {
                    // Hit the beginning, reverse direction
                    animator.frameIndex = 1.coerceAtMost(clip.frameNames.size - 1)
                    animator.direction = 1
                }
            }
        }
    }
}