// Assets/_Project/Scripts/UI/FloatingText.cs
using TMPro;
using UnityEngine;

namespace TD.UI
{
    /// <summary>
    /// One-shot world-space text that floats upward and fades out, then destroys itself.
    /// Spawned by <see cref="FloatingTextSpawner"/> for kill-reward and life-loss feedback.
    /// </summary>
    /// <remarks>
    /// <b>Prefab setup:</b> a GameObject with a <c>TextMeshPro</c> (3D, NOT TextMeshProUGUI)
    /// component as a child or root, this script, and no Canvas required — TMP renders in
    /// world space natively. The text auto-billboards toward the main camera each frame.
    ///
    /// Lifetime, float speed, and fade are tuned on the prefab. The spawner only sets
    /// content + color.
    /// </remarks>
    public class FloatingText : MonoBehaviour
    {
        [Tooltip("The TextMeshPro component that renders the text. Auto-located in children " +
                 "if left empty.")]
        [SerializeField] private TMP_Text text;

        [Tooltip("World units per second the text drifts upward.")]
        [SerializeField] private float floatSpeed = 1.5f;

        [Tooltip("Seconds the text remains visible before the GameObject is destroyed.")]
        [SerializeField] private float lifetime = 1.2f;

        private float elapsed;
        private Color baseColor;

        /// <summary>Sets content and color. Call once immediately after Instantiate.</summary>
        public void Init(string content, Color color)
        {
            if (text == null) text = GetComponentInChildren<TMP_Text>();
            if (text != null)
            {
                text.text  = content;
                text.color = color;
            }
            baseColor = color;
            elapsed   = 0f;
        }

        private void Update()
        {
            elapsed += Time.deltaTime;
            if (elapsed >= lifetime)
            {
                Destroy(gameObject);
                return;
            }

            // Drift upward.
            transform.position += Vector3.up * floatSpeed * Time.deltaTime;

            // Fade alpha linearly from 1 → 0 over the lifetime.
            if (text != null)
            {
                float alpha = 1f - (elapsed / lifetime);
                var c = baseColor;
                c.a = alpha;
                text.color = c;
            }

            // Billboard to the main camera. Using the camera's forward (rather than
            // position-difference) keeps the text upright even when the camera tilts.
            var cam = Camera.main;
            if (cam != null)
                transform.rotation = Quaternion.LookRotation(cam.transform.forward);
        }
    }
}