using System;
using System.Reflection;
using System.Runtime.Caching;

namespace StardewModdingAPI.Framework.Reflection
{
    /// <summary>Provides helper methods for accessing inaccessible code.</summary>
    /// <remarks>This implementation searches up the type hierarchy, and caches the reflected fields and methods with a sliding expiry (to optimize performance without unnecessary memory usage).</remarks>
    internal class Reflector
    {
        /*********
        ** Fields
        *********/
        /// <summary>The cached fields and methods found via reflection.</summary>
        private readonly MemoryCache Cache = new(typeof(Reflector).FullName!);

        /// <summary>The sliding cache expiration time.</summary>
        private readonly TimeSpan SlidingCacheExpiry = TimeSpan.FromMinutes(5);


        /*********
        ** Public methods
        *********/
        /****
        ** Fields
        ****/
        /// <summary>Get a instance field.</summary>
        /// <typeparam name="TValue">The field type.</typeparam>
        /// <param name="obj">The object which has the field.</param>
        /// <param name="name">The field name.</param>
        /// <param name="required">Whether to throw an exception if the field isn't found. <strong>Due to limitations with nullable reference types, setting this to <c>false</c> will still mark the value non-nullable.</strong></param>
        /// <returns>Returns the field wrapper, or <c>null</c> if <paramref name="required"/> is <c>false</c> and the field doesn't exist.</returns>
        /// <exception cref="InvalidOperationException">The target field doesn't exist, and <paramref name="required"/> is true.</exception>
        public IReflectedField<TValue> GetField<TValue>(object obj, string name, bool required = true)
        {
            // validate
            if (obj == null)
                throw new ArgumentNullException(nameof(obj), "Can't get a instance field from a null object.");

            // get field from hierarchy
            IReflectedField<TValue>? field = this.GetFieldFromHierarchy<TValue>(obj.GetType(), obj, name, BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);
            if (required && field == null)
                throw new InvalidOperationException($"The {obj.GetType().FullName} object doesn't have a '{name}' instance field.");
            return field!;
        }

        /// <summary>Get a static field.</summary>
        /// <typeparam name="TValue">The field type.</typeparam>
        /// <param name="type">The type which has the field.</param>
        /// <param name="name">The field name.</param>
        /// <param name="required">Whether to throw an exception if the field isn't found. <strong>Due to limitations with nullable reference types, setting this to <c>false</c> will still mark the value non-nullable.</strong></param>
        /// <returns>Returns the field wrapper, or <c>null</c> if <paramref name="required"/> is <c>false</c> and the field doesn't exist.</returns>
        /// <exception cref="InvalidOperationException">The target field doesn't exist, and <paramref name="required"/> is true.</exception>
        public IReflectedField<TValue> GetField<TValue>(Type type, string name, bool required = true)
        {
            // get field from hierarchy
            IReflectedField<TValue>? field = this.GetFieldFromHierarchy<TValue>(type, null, name, BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Public);
            if (required && field == null)
                throw new InvalidOperationException($"The {type.FullName} object doesn't have a '{name}' static field.");
            return field!;
        }

        /****
        ** Properties
        ****/
        /// <summary>Get a instance property.</summary>
        /// <typeparam name="TValue">The property type.</typeparam>
        /// <param name="obj">The object which has the property.</param>
        /// <param name="name">The property name.</param>
        /// <param name="required">Whether to throw an exception if the property isn't found. <strong>Due to limitations with nullable reference types, setting this to <c>false</c> will still mark the value non-nullable.</strong></param>
        /// <returns>Returns the property wrapper, or <c>null</c> if <paramref name="required"/> is <c>false</c> and the property doesn't exist.</returns>
        /// <exception cref="InvalidOperationException">The target property doesn't exist, and <paramref name="required"/> is true.</exception>
        public IReflectedProperty<TValue> GetProperty<TValue>(object obj, string name, bool required = true)
        {
            // validate
            if (obj == null)
                throw new ArgumentNullException(nameof(obj), "Can't get a instance property from a null object.");

            // get property from hierarchy
            IReflectedProperty<TValue>? property = this.GetPropertyFromHierarchy<TValue>(obj.GetType(), obj, name, BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);
            if (required && property == null)
                throw new InvalidOperationException($"The {obj.GetType().FullName} object doesn't have a '{name}' instance property.");
            return property!;
        }

        /// <summary>Get a static property.</summary>
        /// <typeparam name="TValue">The property type.</typeparam>
        /// <param name="type">The type which has the property.</param>
        /// <param name="name">The property name.</param>
        /// <param name="required">Whether to throw an exception if the property isn't found. <strong>Due to limitations with nullable reference types, setting this to <c>false</c> will still mark the value non-nullable.</strong></param>
        /// <returns>Returns the property wrapper, or <c>null</c> if <paramref name="required"/> is <c>false</c> and the property doesn't exist.</returns>
        /// <exception cref="InvalidOperationException">The target property doesn't exist, and <paramref name="required"/> is true.</exception>
        public IReflectedProperty<TValue> GetProperty<TValue>(Type type, string name, bool required = true)
        {
            // get field from hierarchy
            IReflectedProperty<TValue>? property = this.GetPropertyFromHierarchy<TValue>(type, null, name, BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static);
            if (required && property == null)
                throw new InvalidOperationException($"The {type.FullName} object doesn't have a '{name}' static property.");
            return property!;
        }

        /****
        ** Methods
        ****/
        /// <summary>Get a instance method.</summary>
        /// <param name="obj">The object which has the method.</param>
        /// <param name="name">The method name.</param>
        /// <param name="required">Whether to throw an exception if the method isn't found. <strong>Due to limitations with nullable reference types, setting this to <c>false</c> will still mark the value non-nullable.</strong></param>
        /// <returns>Returns the method wrapper, or <c>null</c> if <paramref name="required"/> is <c>false</c> and the method doesn't exist.</returns>
        /// <exception cref="InvalidOperationException">The target method doesn't exist, and <paramref name="required"/> is true.</exception>
        public IReflectedMethod GetMethod(object obj, string name, bool required = true)
        {
            // validate
            if (obj == null)
                throw new ArgumentNullException(nameof(obj), "Can't get a instance method from a null object.");

            // get method from hierarchy
            IReflectedMethod? method = this.GetMethodFromHierarchy(obj.GetType(), obj, name, BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);
            if (required && method == null)
                throw new InvalidOperationException($"The {obj.GetType().FullName} object doesn't have a '{name}' instance method.");
            return method!;
        }

        /// <summary>Get a static method.</summary>
        /// <param name="type">The type which has the method.</param>
        /// <param name="name">The method name.</param>
        /// <param name="required">Whether to throw an exception if the method isn't found. <strong>Due to limitations with nullable reference types, setting this to <c>false</c> will still mark the value non-nullable.</strong></param>
        /// <returns>Returns the method wrapper, or <c>null</c> if <paramref name="required"/> is <c>false</c> and the method doesn't exist.</returns>
        /// <exception cref="InvalidOperationException">The target method doesn't exist, and <paramref name="required"/> is true.</exception>
        public IReflectedMethod GetMethod(Type type, string name, bool required = true)
        {
            // get method from hierarchy
            IReflectedMethod? method = this.GetMethodFromHierarchy(type, null, name, BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static);
            if (required && method == null)
                throw new InvalidOperationException($"The {type.FullName} object doesn't have a '{name}' static method.");
            return method!;
        }


        /*********
        ** Private methods
        *********/
        /// <summary>Get a field from the type hierarchy.</summary>
        /// <typeparam name="TValue">The expected field type.</typeparam>
        /// <param name="type">The type which has the field.</param>
        /// <param name="obj">The object which has the field, or <c>null</c> for a static field.</param>
        /// <param name="name">The field name.</param>
        /// <param name="bindingFlags">The reflection binding which flags which indicates what type of field to find.</param>
        private IReflectedField<TValue>? GetFieldFromHierarchy<TValue>(Type type, object? obj, string name, BindingFlags bindingFlags)
        {
            bool isStatic = bindingFlags.HasFlag(BindingFlags.Static);
            FieldInfo? field = this.GetCached($"field::{isStatic}::{type.FullName}::{name}", () =>
            {
                for (Type? curType = type; curType != null; curType = curType.BaseType)
                {
                    FieldInfo? fieldInfo = curType.GetField(name, bindingFlags);
                    if (fieldInfo != null)
                    {
                        type = curType;
                        return fieldInfo;
                    }
                }

                return null;
            });

            return field != null
                ? new ReflectedField<TValue>(type, obj, field, isStatic)
                : null;
        }

        /// <summary>Get a property from the type hierarchy.</summary>
        /// <typeparam name="TValue">The expected property type.</typeparam>
        /// <param name="type">The type which has the property.</param>
        /// <param name="obj">The object which has the property, or <c>null</c> for a static property.</param>
        /// <param name="name">The property name.</param>
        /// <param name="bindingFlags">The reflection binding which flags which indicates what type of property to find.</param>
        private IReflectedProperty<TValue>? GetPropertyFromHierarchy<TValue>(Type type, object? obj, string name, BindingFlags bindingFlags)
        {
            bool isStatic = bindingFlags.HasFlag(BindingFlags.Static);
            PropertyInfo? property = this.GetCached<PropertyInfo>($"property::{isStatic}::{type.FullName}::{name}", () =>
            {
                for (Type? curType = type; curType != null; curType = curType.BaseType)
                {
                    PropertyInfo? propertyInfo = curType.GetProperty(name, bindingFlags);
                    if (propertyInfo != null)
                    {
                        type = curType;
                        return propertyInfo;
                    }
                }

                return null;
            });

            return property != null
                ? new ReflectedProperty<TValue>(type, obj, property, isStatic)
                : null;
        }

        /// <summary>Get a method from the type hierarchy.</summary>
        /// <param name="type">The type which has the method.</param>
        /// <param name="obj">The object which has the method, or <c>null</c> for a static method.</param>
        /// <param name="name">The method name.</param>
        /// <param name="bindingFlags">The reflection binding which flags which indicates what type of method to find.</param>
        private IReflectedMethod? GetMethodFromHierarchy(Type type, object? obj, string name, BindingFlags bindingFlags)
        {
            bool isStatic = bindingFlags.HasFlag(BindingFlags.Static);
            MethodInfo? method = this.GetCached($"method::{isStatic}::{type.FullName}::{name}", () =>
            {
                for (Type? curType = type; curType != null; curType = curType.BaseType)
                {
                    MethodInfo? methodInfo = curType.GetMethod(name, bindingFlags);
                    if (methodInfo != null)
                    {
                        type = curType;
                        return methodInfo;
                    }
                }

                return null;
            });

            return method != null
                ? new ReflectedMethod(type, obj, method, isStatic: bindingFlags.HasFlag(BindingFlags.Static))
                : null;
        }

        /// <summary>Get a method or field through the cache.</summary>
        /// <typeparam name="TMemberInfo">The expected <see cref="MemberInfo"/> type.</typeparam>
        /// <param name="key">The cache key.</param>
        /// <param name="fetch">Fetches a new value to cache.</param>
        private TMemberInfo? GetCached<TMemberInfo>(string key, Func<TMemberInfo?> fetch)
            where TMemberInfo : MemberInfo
        {
            // get from cache
            if (this.Cache.Contains(key))
            {
                CacheEntry entry = (CacheEntry)this.Cache[key];
                return entry.IsValid
                    ? (TMemberInfo)entry.MemberInfo
                    : default;
            }

            // fetch & cache new value
            TMemberInfo? result = fetch();
            CacheEntry cacheEntry = new(result);
            this.Cache.Add(key, cacheEntry, new CacheItemPolicy { SlidingExpiration = this.SlidingCacheExpiry });
            return result;
        }
    }
}