using UnityEditor;
using UnityEditor.SceneManagement;
using UnityEngine;

namespace Ashwild.EditorTools
{
    /// <summary>
    /// Toggleable editor option that forces play mode to always start from the first build scene
    /// (index 0, the boot/menu scene), no matter which scene is open. When enabled, pressing the
    /// normal Play button boots from scene 0 and Unity automatically returns to the scene you were
    /// editing once you stop — so you never have to manually open the menu scene to test.
    /// The toggle shows a checkmark in the menu and its state persists across sessions.
    /// </summary>
    [InitializeOnLoad]
    public static class PlayFromFirstScene
    {
        #region Constants

        private const string MenuPath = "Tools/Ashwild/Play From Scene 0";

        /// <summary>
        /// EditorPrefs key persisting whether the "boot from scene 0" override is enabled.
        /// </summary>
        private const string EnabledKey = "Ashwild.PlayFromFirstScene.Enabled";

        #endregion

        #region Initialization

        /// <summary>
        /// Re-applies the saved toggle state after every domain reload so the play-mode start scene
        /// stays bound even after a recompile.
        /// </summary>
        static PlayFromFirstScene()
        {
            EditorApplication.delayCall += () => ApplyStartScene(IsEnabled);
        }

        #endregion

        #region Menu

        /// <summary>
        /// Flips the override on or off and immediately (un)binds the play-mode start scene.
        /// </summary>
        [MenuItem(MenuPath, priority = -100)]
        public static void Toggle()
        {
            bool enabled = !IsEnabled;
            EditorPrefs.SetBool(EnabledKey, enabled);
            ApplyStartScene(enabled);
        }

        /// <summary>
        /// Draws the checkmark next to the menu entry to reflect the current state.
        /// </summary>
        [MenuItem(MenuPath, validate = true)]
        public static bool ToggleValidate()
        {
            Menu.SetChecked(MenuPath, IsEnabled);
            return true;
        }

        #endregion

        #region Internal Helpers

        /// <summary>
        /// Whether the override is currently enabled, read from persisted EditorPrefs.
        /// </summary>
        private static bool IsEnabled => EditorPrefs.GetBool(EnabledKey, false);

        /// <summary>
        /// Binds (or clears) Unity's playModeStartScene to build scene 0. While bound, every play
        /// session starts there and returns to the open scene on stop; clearing restores the default
        /// behaviour of playing the currently open scene. Logs and self-disables if scene 0 is missing.
        /// </summary>
        private static void ApplyStartScene(bool enabled)
        {
            if (!enabled)
            {
                EditorSceneManager.playModeStartScene = null;
                return;
            }

            if (EditorBuildSettings.scenes.Length == 0 ||
                string.IsNullOrEmpty(EditorBuildSettings.scenes[0].path))
            {
                Debug.LogError("[PlayFromFirstScene] No scene at Build Settings index 0 — add the menu scene there.");
                EditorPrefs.SetBool(EnabledKey, false);
                EditorSceneManager.playModeStartScene = null;
                return;
            }

            SceneAsset firstScene =
                AssetDatabase.LoadAssetAtPath<SceneAsset>(EditorBuildSettings.scenes[0].path);
            EditorSceneManager.playModeStartScene = firstScene;
        }

        #endregion
    }
}