using UnityEngine;

namespace CreatureControl {

    /// <summary>
    /// A target rig or skeleton for a creature
    /// </summary>
    public class TargetRig : MonoBehaviour {
        /// <summary>
        /// Pose the target rig using the IK targets
        /// </summary>
        public virtual void Pose() {
        }
        
        /// <summary>
        /// Align the target rig with a creature
        /// </summary>
        /// <param name="creature">The creature to align to</param>
        public void MatchTo(Creature creature) {
            bool anythingChangedDummy = false;
            MatchTo(creature, ref anythingChangedDummy);
        }

        /// <summary>
        /// Align the target rig with a creature
        /// </summary>
        /// <param name="creature">The creature to align to</param>
        /// <param name="anythingChanged">True when any property of the creature has changed</param>
        public virtual void MatchTo(Creature creature, ref bool anythingChanged) {
            Vector3 targetToModelTranslation = creature.model.position - this.transform.position;
            bool changed = targetToModelTranslation != creature.targetToModelTranslation;
            if (changed) {
                anythingChanged = true;
                creature.targetToModelTranslation = targetToModelTranslation;
            }

            Quaternion targetToModelRotation = Quaternion.Inverse(this.transform.rotation) * creature.model.rotation;
            changed = targetToModelRotation != creature.targetToModelRotation;
            if (changed) {
                anythingChanged = true;
                creature.targetToModelRotation = targetToModelRotation;
            }
        }

        /// <summary>
        /// Compute the rotation from the target bone to a creature's bone
        /// </summary>
        /// <param name="bone">The creature's bone for this target bone</param>
        /// <param name="nextBone">The next bone in the creature's hierarchy</param>
        /// <returns>The rotation from the target bone rotation to the creature bone rotation</returns>
        /// The next bone is used to compute the direction of the bone.
        /// The 'up'-direction of the bone is currently fixed to (world) up.
        public static Quaternion TargetToBoneRotation(Transform bone, Transform nextBone) {
            if (bone == null || nextBone == null)
                return Quaternion.identity;

            Vector3 direction = nextBone.position - bone.position;
            Quaternion targetRotation = Quaternion.LookRotation(direction, Vector3.up);
            Quaternion toBoneRotation = Quaternion.Inverse(targetRotation) * bone.rotation;
            return toBoneRotation;
        }
    }

}