using System;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using UnityEngine.Rendering;
using UnityEngine.Rendering.HighDefinition;

namespace UnityEditor.Rendering.HighDefinition
{
    internal abstract class VolumeComponentWithQualityEditor : VolumeComponentEditor
    {
        // Quality settings
        SerializedDataParameter m_QualitySetting;

        /// <summary>
        /// An opaque blob storing preset settings (used to remember what were the last custom settings that were used).
        /// </summary>
        internal class QualitySettingsBlob
        {
            private struct QualitySetting
            {
                public bool state;
                public object value;
            }

            Dictionary<int, QualitySetting> settings = new Dictionary<int, QualitySetting>();

            public static bool IsEqual(QualitySettingsBlob left, QualitySettingsBlob right)
            {
                if (right == null && left == null)
                {
                    return true;
                }

                if ((right == null && left != null) || (right != null && left == null))
                {
                    return false;
                }

                if (left.settings.Count != right.settings.Count)
                {
                    return false;
                }

                foreach (var key in left.settings.Keys)
                {
                    if (!left.settings[key].Equals(right.settings[key]))
                    {
                        return false;
                    }
                }

                return true;
            }

            // TODO: Should be an override of GetHashCode (in core)?
            int Hash(SerializedDataParameter setting)
            {
                int hash = setting.GetHashCode();

                unchecked
                {
                    hash = 23 * setting.value.GetHashCode();
                    hash = 23 * setting.overrideState.GetHashCode();
                }

                return hash;
            }

            // Save a setting to the quality blob.
            public void Save<T>(SerializedDataParameter setting) where T : struct
            {
                QualitySetting s;
                s.state = setting.overrideState.boolValue;
                s.value = setting.value.GetInline<T>();

                int key = Hash(setting);

                if (settings.ContainsKey(key))
                {
                    // If the setting exists, overwrite the value
                    settings[key] = s;
                }
                else
                {
                    // Otherwise, cache a new setting
                    settings.Add(key, s);
                }
            }

            // Attempts to fill a quality setting with its custom value and override state.
            public void TryLoad<T>(ref SerializedDataParameter setting) where T : struct
            {
                if (settings.TryGetValue(Hash(setting), out QualitySetting s))
                {
                    setting.value.SetInline((T)s.value);
                    setting.overrideState.boolValue = s.state;
                }
            }
        }

        /// <summary>
        /// Scoped quality setting change checker.
        /// </summary>
        public struct QualityScope : IDisposable
        {
            VolumeComponentWithQualityEditor m_QualityComponent;
            QualitySettingsBlob m_Settings;

            // Cache the quality setting
            public QualityScope(VolumeComponentWithQualityEditor component)
            {
                m_QualityComponent = component;
                m_Settings = m_QualityComponent.SaveCustomQualitySettingsAsObject();
                EditorGUI.BeginChangeCheck();
            }

            public void Dispose()
            {
                if (EditorGUI.EndChangeCheck())
                {
                    QualitySettingsBlob newSettings = m_QualityComponent?.SaveCustomQualitySettingsAsObject();

                    if (!QualitySettingsBlob.IsEqual(m_Settings, newSettings))
                        m_QualityComponent?.QualitySettingsWereChanged();
                }
            }
        }

        // Note: Editors are refreshed on gui changes by the volume system, so any state that we want to store here needs to be a static (or in a serialized variable)
        // We use ConditionalWeakTable instead of a Dictionary of InstanceIDs to get automatic clean-up of dead entries in the table
        static ConditionalWeakTable<UnityEngine.Object, QualitySettingsBlob> s_CustomSettingsHistory = new ConditionalWeakTable<UnityEngine.Object, QualitySettingsBlob>();

        static readonly int k_CustomQuality = ScalableSettingLevelParameter.LevelCount;

        public override void OnEnable()
        {
            var o = new PropertyFetcher<VolumeComponentWithQuality>(serializedObject);
            m_QualitySetting = Unpack(o.Find(x => x.quality));

            // Ensure we reflect presets in the pipeline asset, not the hardcoded defaults.
            // Warning: base.OnEnable must be called after VolumeComponentWithQuality has unpacked SerializedData.
            if (RenderPipelineManager.currentPipeline is HDRenderPipeline pipeline)
            {
                serializedObject.Update();

                if (m_QualitySetting.value.intValue < k_CustomQuality && QualityEnabled())
                    LoadSettingsFromQualityPreset(pipeline.currentPlatformRenderPipelineSettings, m_QualitySetting.value.intValue);

                serializedObject.ApplyModifiedProperties();
            }
        }

        public override void OnInspectorGUI()
        {
            int prevQualityLevel = m_QualitySetting.value.intValue;

            EditorGUI.BeginChangeCheck();
            PropertyField(m_QualitySetting);

            // When a quality preset changes, we want to detect and reflect the settings in the UI. PropertyFields mirror the contents of one memory loccation, so
            // the idea is that we copy the presets to that location. This logic is optional, if volume components don't override the helper functions at the end,
            // they will continue to work, but the preset settings will not be reflected in the UI.
            if (EditorGUI.EndChangeCheck() && QualityEnabled())
            {
                int newQualityLevel = m_QualitySetting.value.intValue;

                if (newQualityLevel == k_CustomQuality)
                {
                    // If we have switched to custom quality from a preset, then load the last custom quality settings the user has used in this volume
                    if (prevQualityLevel != k_CustomQuality)
                    {
                        QualitySettingsBlob history = null;
                        s_CustomSettingsHistory.TryGetValue(serializedObject.targetObject, out history);
                        if (history != null)
                        {
                            LoadSettingsFromObject(history);
                        }
                    }
                }
                else
                {
                    // If we are going to use a quality preset, then load the preset values so they are reflected in the UI
                    var pipeline = (HDRenderPipeline)RenderPipelineManager.currentPipeline;
                    if (pipeline != null)
                    {
                        // If we switch from a custom quality level, then save these values so we can re-use them if teh user switches back
                        if (prevQualityLevel == k_CustomQuality)
                        {
                            QualitySettingsBlob history = null;
                            s_CustomSettingsHistory.TryGetValue(serializedObject.targetObject, out history);
                            if (history != null)
                            {
                                SaveCustomQualitySettingsAsObject(history);
                            }
                            else
                            {
                                // Only keep track of custom settings for components that implement the new interface (and return not null)
                                history = SaveCustomQualitySettingsAsObject();
                                if (history != null)
                                {
                                    s_CustomSettingsHistory.Add(serializedObject.targetObject, history);
                                }
                            }
                        }
                        LoadSettingsFromQualityPreset(pipeline.currentPlatformRenderPipelineSettings, newQualityLevel);
                    }
                }
            }
        }

        protected bool useCustomValue => m_QualitySetting.value.intValue == k_CustomQuality;
        protected bool overrideState => m_QualitySetting.overrideState.boolValue;

        /// <summary>
        /// This utility can be used to copy a value into a volume component setting visible in the inspector.
        /// </summary>
        protected void CopySetting<T>(ref SerializedDataParameter setting, T value) where T : struct
        {
            setting.value.SetInline(value);

            // Force enable the override state to match the state of the quality setting.
            setting.overrideState.boolValue = m_QualitySetting.overrideState.boolValue;
        }

        /// <summary>
        /// This should be called after the user manually edits a quality setting that appears in a preset. After calling this function, the quality preset will change to Custom.
        /// </summary>
        public void QualitySettingsWereChanged() { m_QualitySetting.value.intValue = k_CustomQuality; }

        /// <summary>
        /// This function should be overriden by a volume component to load preset settings from RenderPipelineSettings
        /// </summary>
        public virtual void LoadSettingsFromQualityPreset(RenderPipelineSettings settings, int level) { }

        /// <summary>
        /// This function should be overriden by a volume component to return an opaque object (binary blob) with the custom quality settings currently in use.
        /// </summary>
        public virtual QualitySettingsBlob SaveCustomQualitySettingsAsObject(QualitySettingsBlob history = null) { return null; }

        /// <summary>
        /// This function should be overriden by a volume component to load a custom preset setting from an opaque binary blob (as returned from SaveCustomQualitySettingsAsObject)
        /// </summary>
        public virtual void LoadSettingsFromObject(QualitySettingsBlob settings) { }

        /// <summary>
        /// This function should be overriden by a volume component to enable the quality setting functionality only in certain cases.
        /// </summary>
        /// <returns></returns>
        public virtual bool QualityEnabled() => true;
    }
}