// Assets/_Project/Scripts/VFX/FallFromSkyVisual.cs
using System.Collections;
using UnityEngine;

namespace TD.VFX
{
    /// <summary>
    /// Animates this object falling from the sky down to its own spawn position. Intended for
    /// a one-shot placeholder VFX prefab (e.g. <c>FireballSpellDefinition.impactVfxPrefab</c>)
    /// that gets instantiated already at the correct landing point — on <c>Start</c>, it snaps
    /// itself up by <see cref="dropHeight"/> and animates back down over
    /// <see cref="duration"/> seconds.
    /// </summary>
    /// <remarks>
    /// Mirrors <see cref="TD.Combat.TowerLandingVisual"/>'s fall coroutine, minus the
    /// <c>TowerInstance</c> coupling — this is a plain local one-shot visual, not tied to any
    /// networked gameplay state, so it can run from <c>Start()</c> instead of waiting on a
    /// spawn event.
    /// </remarks>
    public class FallFromSkyVisual : MonoBehaviour
    {
        [Tooltip("How high above the landing point this object starts.")]
        [SerializeField] private float dropHeight = 20f;

        [Tooltip("Seconds for the fall animation to complete.")]
        [Min(0.01f)]
        [SerializeField] private float duration = 0.5f;

        [Tooltip("Eases the fall over Duration. X = normalized time, Y = normalized fraction " +
                 "of DropHeight already descended (0 = still at drop height, 1 = landed).")]
        [SerializeField] private AnimationCurve fallCurve = AnimationCurve.EaseInOut(0f, 0f, 1f, 1f);

        [Header("Angle (optional — 0 = straight down)")]
        [Tooltip("Angle from vertical, in degrees. 0 = falls straight down. Higher values = " +
                 "a shallower, more meteor-like diagonal approach. Capped below 90 — at 90 the " +
                 "object would never actually descend.")]
        [Range(0f, 80f)]
        [SerializeField] private float fallAngleDegrees = 0f;

        [Tooltip("Horizontal direction the object travels as it falls (only used when " +
                 "FallAngleDegrees > 0). Magnitude is ignored — normalized automatically.")]
        [SerializeField] private Vector3 fallDirection = Vector3.forward;

        private void Start()
        {
            StartCoroutine(AnimateDrop());
        }

        private IEnumerator AnimateDrop()
        {
            Vector3 landedPosition = transform.position; // already correct — spawned at the target point

            // Split dropHeight into a vertical component (unchanged from the straight-down case)
            // plus a horizontal component derived from the angle via basic trig: at angle θ from
            // vertical, horizontal distance = dropHeight * tan(θ). At θ = 0 this is 0, so the
            // whole angle path collapses back to the original straight-down offset.
            float angleRad = fallAngleDegrees * Mathf.Deg2Rad;
            float horizontalDistance = dropHeight * Mathf.Tan(angleRad);

            // Only the horizontal (XZ) part of fallDirection matters — a Y component would just
            // be double-counting dropHeight, so it's dropped before normalizing.
            Vector3 flatDirection = new Vector3(fallDirection.x, 0f, fallDirection.z);
            Vector3 horizontalDir = flatDirection.sqrMagnitude > 0.0001f
                ? flatDirection.normalized
                : Vector3.zero;

            Vector3 startOffset = Vector3.up * dropHeight - horizontalDir * horizontalDistance;
            transform.position = landedPosition + startOffset;

            float t = 0f;
            while (t < duration)
            {
                t += Time.deltaTime;
                float u = fallCurve.Evaluate(Mathf.Clamp01(t / duration));
                transform.position = landedPosition + startOffset * (1f - u);
                yield return null;
            }

            transform.position = landedPosition; // snap exactly, avoid float drift
        }
    }
}