using System;
using System.Reflection;
using StardewModdingAPI.Framework.Reflection;

namespace StardewModdingAPI.Framework.ModHelpers
{
    /// <summary>Provides helper methods for accessing private game code.</summary>
    /// <remarks>This implementation searches up the type hierarchy, and caches the reflected fields and methods with a sliding expiry (to optimise performance without unnecessary memory usage).</remarks>
    internal class ReflectionHelper : BaseHelper, IReflectionHelper
    {
        /*********
        ** Fields
        *********/
        /// <summary>The underlying reflection helper.</summary>
        private readonly Reflector Reflector;

        /// <summary>The mod name for error messages.</summary>
        private readonly string ModName;


        /*********
        ** Public methods
        *********/
        /// <summary>Construct an instance.</summary>
        /// <param name="modID">The unique ID of the relevant mod.</param>
        /// <param name="modName">The mod name for error messages.</param>
        /// <param name="reflector">The underlying reflection helper.</param>
        public ReflectionHelper(string modID, string modName, Reflector reflector)
            : base(modID)
        {
            this.ModName = modName;
            this.Reflector = reflector;
        }

        /// <summary>Get an 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 is not found.</param>
        public IReflectedField<TValue> GetField<TValue>(object obj, string name, bool required = true)
        {
            return this.AssertAccessAllowed(
                this.Reflector.GetField<TValue>(obj, name, required)
            );
        }

        /// <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 is not found.</param>
        public IReflectedField<TValue> GetField<TValue>(Type type, string name, bool required = true)
        {
            return this.AssertAccessAllowed(
                this.Reflector.GetField<TValue>(type, name, required)
            );
        }

        /// <summary>Get an 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 is not found.</param>
        public IReflectedProperty<TValue> GetProperty<TValue>(object obj, string name, bool required = true)
        {
            return this.AssertAccessAllowed(
                this.Reflector.GetProperty<TValue>(obj, name, required)
            );
        }

        /// <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 is not found.</param>
        public IReflectedProperty<TValue> GetProperty<TValue>(Type type, string name, bool required = true)
        {
            return this.AssertAccessAllowed(
                this.Reflector.GetProperty<TValue>(type, name, required)
            );
        }

        /// <summary>Get an instance method.</summary>
        /// <param name="obj">The object which has the method.</param>
        /// <param name="name">The field name.</param>
        /// <param name="required">Whether to throw an exception if the field is not found.</param>
        public IReflectedMethod GetMethod(object obj, string name, bool required = true)
        {
            return this.AssertAccessAllowed(
                this.Reflector.GetMethod(obj, name, required)
            );
        }

        /// <summary>Get a static method.</summary>
        /// <param name="type">The type which has the method.</param>
        /// <param name="name">The field name.</param>
        /// <param name="required">Whether to throw an exception if the field is not found.</param>
        public IReflectedMethod GetMethod(Type type, string name, bool required = true)
        {
            return this.AssertAccessAllowed(
                this.Reflector.GetMethod(type, name, required)
            );
        }


        /*********
        ** Private methods
        *********/
        /// <summary>Assert that mods can use the reflection helper to access the given member.</summary>
        /// <typeparam name="T">The field value type.</typeparam>
        /// <param name="field">The field being accessed.</param>
        /// <returns>Returns the same field instance for convenience.</returns>
        private IReflectedField<T> AssertAccessAllowed<T>(IReflectedField<T> field)
        {
            this.AssertAccessAllowed(field?.FieldInfo);
            return field;
        }

        /// <summary>Assert that mods can use the reflection helper to access the given member.</summary>
        /// <typeparam name="T">The property value type.</typeparam>
        /// <param name="property">The property being accessed.</param>
        /// <returns>Returns the same property instance for convenience.</returns>
        private IReflectedProperty<T> AssertAccessAllowed<T>(IReflectedProperty<T> property)
        {
            this.AssertAccessAllowed(property?.PropertyInfo);
            return property;
        }

        /// <summary>Assert that mods can use the reflection helper to access the given member.</summary>
        /// <param name="method">The method being accessed.</param>
        /// <returns>Returns the same method instance for convenience.</returns>
        private IReflectedMethod AssertAccessAllowed(IReflectedMethod method)
        {
            this.AssertAccessAllowed(method?.MethodInfo);
            return method;
        }

        /// <summary>Assert that mods can use the reflection helper to access the given member.</summary>
        /// <param name="member">The member being accessed.</param>
        private void AssertAccessAllowed(MemberInfo member)
        {
            if (member == null)
                return;

            // get type which defines the member
            Type declaringType = member.DeclaringType;
            if (declaringType == null)
                throw new InvalidOperationException($"Can't validate access to {member.MemberType} {member.Name} because it has no declaring type."); // should never happen

            // validate access
            string rootNamespace = typeof(Program).Namespace;
            if (declaringType.Namespace == rootNamespace || declaringType.Namespace?.StartsWith(rootNamespace + ".") == true)
                throw new InvalidOperationException($"SMAPI blocked access by {this.ModName} to its internals through the reflection API. Accessing the SMAPI internals is strongly discouraged since they're subject to change, which means the mod can break without warning. (Detected access to {declaringType.FullName}.{member.Name}.)");
        }
    }
}