using System.Collections;
using UnityEngine;
using UnityEngine.UI;

namespace BaseGames.UI
{
    /// <summary>
    /// UI 协程补间静态库。
    ///
    /// 设计动机：消除 <see cref="BossHPBar"/>、<see cref="ToastNotification"/>、
    /// <see cref="FloatingDamageText"/> 等组件中重复出现的 Lerp + WaitForEndOfFrame 样板，
    /// 集中维护时间步与回调约定。所有协程默认使用 <see cref="Time.unscaledDeltaTime"/>，
    /// 以便 UI 动画在游戏暂停（<see cref="Time.timeScale"/> = 0）时仍能播放。
    ///
    /// 性能特征：
    ///   · 无堆分配（除协程对象本身）；
    ///   · 提前返回保护无效目标；
    ///   · <paramref name="duration"/> &lt;= 0 时立即吸附到终态并退出（一帧 yield 用于保持
    ///     与正常协程一致的栈语义）。
    /// </summary>
    public static class UITween
    {
        // ── 位置 ─────────────────────────────────────────────────────────────

        /// <summary>将 RectTransform 的 anchoredPosition 平滑过渡到目标值。</summary>
        public static IEnumerator MoveAnchored(RectTransform rect,
                                               Vector2 target,
                                               float duration,
                                               bool unscaled = true)
        {
            if (rect == null) yield break;
            if (duration <= 0f)
            {
                rect.anchoredPosition = target;
                yield break;
            }

            Vector2 start = rect.anchoredPosition;
            float t = 0f;
            while (t < duration)
            {
                rect.anchoredPosition = Vector2.Lerp(start, target, t / duration);
                t += unscaled ? Time.unscaledDeltaTime : Time.deltaTime;
                yield return null;
            }
            rect.anchoredPosition = target;
        }

        // ── 透明度 ───────────────────────────────────────────────────────────

        /// <summary>将 CanvasGroup.alpha 平滑过渡到目标值。</summary>
        public static IEnumerator FadeCanvasGroup(CanvasGroup cg,
                                                  float target,
                                                  float duration,
                                                  bool unscaled = true)
        {
            if (cg == null) yield break;
            if (duration <= 0f)
            {
                cg.alpha = target;
                yield break;
            }

            float start = cg.alpha;
            float t = 0f;
            while (t < duration)
            {
                cg.alpha = Mathf.Lerp(start, target, t / duration);
                t += unscaled ? Time.unscaledDeltaTime : Time.deltaTime;
                yield return null;
            }
            cg.alpha = target;
        }

        /// <summary>将 Graphic（Image / TMP_Text 等）的颜色 Alpha 通道平滑过渡到目标值。</summary>
        public static IEnumerator FadeGraphic(Graphic graphic,
                                              float targetAlpha,
                                              float duration,
                                              bool unscaled = true)
        {
            if (graphic == null) yield break;
            if (duration <= 0f)
            {
                var c = graphic.color;
                c.a = targetAlpha;
                graphic.color = c;
                yield break;
            }

            float startAlpha = graphic.color.a;
            float t = 0f;
            while (t < duration)
            {
                var c = graphic.color;
                c.a = Mathf.Lerp(startAlpha, targetAlpha, t / duration);
                graphic.color = c;
                t += unscaled ? Time.unscaledDeltaTime : Time.deltaTime;
                yield return null;
            }
            var fc = graphic.color;
            fc.a = targetAlpha;
            graphic.color = fc;
        }

        // ── 缩放 ─────────────────────────────────────────────────────────────

        /// <summary>将 Transform 的 localScale 等比平滑过渡到目标值。</summary>
        public static IEnumerator Scale(Transform tr,
                                        Vector3 target,
                                        float duration,
                                        bool unscaled = true)
        {
            if (tr == null) yield break;
            if (duration <= 0f)
            {
                tr.localScale = target;
                yield break;
            }

            Vector3 start = tr.localScale;
            float t = 0f;
            while (t < duration)
            {
                tr.localScale = Vector3.Lerp(start, target, t / duration);
                t += unscaled ? Time.unscaledDeltaTime : Time.deltaTime;
                yield return null;
            }
            tr.localScale = target;
        }
    }
}