// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;

namespace System.Reflection.Context.Projection
{
    internal abstract class Projector
    {
        [return: NotNullIfNotNull(nameof(values))]
        public IList<T>? Project<T>(IList<T>? values, Func<T, T> project)
        {
            if (values == null || values.Count == 0)
                return values;

            T[] projected = ProjectAll(values, project);

            return Array.AsReadOnly(projected);
        }

        [return: NotNullIfNotNull(nameof(values))]
        public T[]? Project<T>(T[]? values, Func<T, T> project)
        {
            if (values == null || values.Length == 0)
                return values;

            return ProjectAll(values, project);
        }

        public T Project<T>(T value, Func<T, T> project)
        {
            if (NeedsProjection(value))
            {
                // NeedsProjection should guarantee this.
                Debug.Assert(!(value is IProjectable) || ((IProjectable)value).Projector != this);

                return project(value);
            }

            return value;
        }

        [return: NotNullIfNotNull(nameof(value))]
        public abstract TypeInfo? ProjectType(Type? value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract Assembly? ProjectAssembly(Assembly? value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract Module? ProjectModule(Module? value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract FieldInfo? ProjectField(FieldInfo? value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract EventInfo? ProjectEvent(EventInfo? value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract ConstructorInfo? ProjectConstructor(ConstructorInfo? value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract MethodInfo? ProjectMethod(MethodInfo? value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract MethodBase? ProjectMethodBase(MethodBase? value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract PropertyInfo? ProjectProperty(PropertyInfo? value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract ParameterInfo? ProjectParameter(ParameterInfo? value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract MethodBody? ProjectMethodBody(MethodBody? value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract LocalVariableInfo? ProjectLocalVariable(LocalVariableInfo? value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract ExceptionHandlingClause? ProjectExceptionHandlingClause(ExceptionHandlingClause? value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract CustomAttributeData? ProjectCustomAttributeData(CustomAttributeData? value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract ManifestResourceInfo? ProjectManifestResource(ManifestResourceInfo? value);
        public abstract CustomAttributeTypedArgument ProjectTypedArgument(CustomAttributeTypedArgument value);
        public abstract CustomAttributeNamedArgument ProjectNamedArgument(CustomAttributeNamedArgument value);
        public abstract InterfaceMapping ProjectInterfaceMapping(InterfaceMapping value);
        [return: NotNullIfNotNull(nameof(value))]
        public abstract MemberInfo? ProjectMember(MemberInfo? value);

        [return: NotNullIfNotNull(nameof(values))]
        public static Type[]? Unproject(Type[]? values)
        {
            if (values == null)
                return null;

            Type[] newTypes = new Type[values.Length];
            for (int i = 0; i < values.Length; i++)
            {
                newTypes[i] = Unproject(values[i]);
            }

            return newTypes;
        }

        [return: NotNullIfNotNull(nameof(value))]
        public static Type? Unproject(Type? value)
        {
            if (value is ProjectingType projectingType)
                return projectingType.UnderlyingType;
            else
                return value;
        }

        public bool NeedsProjection([NotNullWhen(true)] object? value)
        {
            Debug.Assert(value != null);

            if (value == null)
                return false;

            if (value is IProjectable projector && projector == this)
                return false;   // Already projected

            // Different context, so we need to project it
            return true;
        }

        //protected abstract object ExecuteProjection<T>(object value);

        //protected abstract IProjection GetProjector(Type t);

        private T[] ProjectAll<T>(IList<T> values, Func<T, T> project)
        {
            Debug.Assert(null != project);
            Debug.Assert(values != null && values.Count > 0);

            var projected = new T[values.Count];

            for (int i = 0; i < projected.Length; i++)
            {
                T value = values[i];

                Debug.Assert(NeedsProjection(value));
                projected[i] = project(value);
            }

            return projected;
        }
    }
}