/* ========================================================================
 * Copyright (c) 2005-2025 The OPC Foundation, Inc. All rights reserved.
 *
 * OPC Foundation MIT License 1.00
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * The complete license agreement can be found here:
 * http://opcfoundation.org/License/MIT/1.00/
 * ======================================================================*/

using System;
using System.Collections.Generic;
using System.IO;
using System.Reflection;
using System.Text;
using SharpFuzz;

namespace Opc.Ua.Fuzzing
{
    public static class FuzzMethods
    {
        /// <summary>
        /// signatures supported by fuzzers
        /// </summary>
        public delegate void AflFuzzStream(Stream stream);
        public delegate void AflFuzzString(string text);
        public delegate void LibFuzzSpan(ReadOnlySpan<byte> bytes);

        public static readonly Type[] Delegates
            = [typeof(AflFuzzStream), typeof(AflFuzzString), typeof(LibFuzzSpan)];

        public static readonly Dictionary<Type, Type> FuzzMethodsToParameterType = new()
        {
            { typeof(AflFuzzStream), typeof(Stream) },
            { typeof(AflFuzzString), typeof(string) },
            { typeof(LibFuzzSpan), typeof(ReadOnlySpan<byte>) }
        };

        /// <summary>
        /// Finds all fuzzing methods for specified delegate.
        /// </summary>
        public static List<Delegate> FindFuzzMethods(Type delegateType)
        {
            var fuzzMethods = new List<Delegate>();
            Type type = typeof(FuzzableCode);
            if (FuzzMethodsToParameterType.TryGetValue(
                delegateType,
                out Type? delegateParameterType))
            {
                foreach (
                    MethodInfo method in type.GetMethods(
                        BindingFlags.Public | BindingFlags.Static))
                {
                    // Determine the target signature
                    ParameterInfo[] parameters = method.GetParameters();
                    if (method.ReturnType == typeof(void) &&
                        !method.ContainsGenericParameters &&
                        parameters.Length == 1 &&
                        parameters[0].ParameterType == delegateParameterType)
                    {
                        fuzzMethods.Add(method.CreateDelegate(delegateType));
                    }
                }
            }
            return fuzzMethods;
        }

        /// <summary>
        /// Finds a fuzzing method by name and returns a delegate to call it.
        /// </summary>
        public static Delegate? FindFuzzMethod(TextWriter errorOutput, string fuzzingFunction)
        {
            // find the function to fuzz based on the first argument using reflection
            Type type = typeof(FuzzableCode);
            MethodInfo method = type.GetMethod(
                fuzzingFunction,
                BindingFlags.Public | BindingFlags.Static)!;
            if (method != null)
            {
                // Determine the target signature
                ParameterInfo[] parameters = method.GetParameters();
                if (method.ReturnType == typeof(void) &&
                    !method.ContainsGenericParameters &&
                    parameters.Length == 1)
                {
                    // afl-fuzz targets
#if NET8_0_OR_GREATER
                    if (parameters[0].ParameterType == typeof(Stream))
                    {
                        return method.CreateDelegate<AflFuzzStream>();
                    }
                    else if (parameters[0].ParameterType == typeof(string))
                    {
                        return method.CreateDelegate<AflFuzzString>();
                    }
                    // libfuzzer span target
                    else if (parameters[0].ParameterType == typeof(ReadOnlySpan<byte>))
                    {
                        return method.CreateDelegate<LibFuzzSpan>();
                    }
#else
                    if (parameters[0].ParameterType == typeof(Stream))
                    {
                        return method.CreateDelegate(typeof(AflFuzzStream));
                    }
                    else if (parameters[0].ParameterType == typeof(string))
                    {
                        return method.CreateDelegate(typeof(AflFuzzString));
                    }
                    // libfuzzer span target
                    else if (parameters[0].ParameterType == typeof(ReadOnlySpan<byte>))
                    {
                        return method.CreateDelegate(typeof(LibFuzzSpan));
                    }
#endif
                }

                errorOutput.WriteLine(
                    "The fuzzing function {0} must be static void with one " +
                    "Stream, string or ReadOnlySpan<byte> parameter.",
                    fuzzingFunction);
            }
            else
            {
                errorOutput.WriteLine("The fuzzing function {0} was not found.", fuzzingFunction);
            }

            return null;
        }

        /// <summary>
        /// Replays one input without starting an instrumentation engine.
        /// </summary>
        public static void Replay(Delegate fuzzingMethod, ReadOnlySpan<byte> input)
        {
            byte[] data = input.ToArray();
            if (fuzzingMethod is LibFuzzSpan spanMethod)
            {
                RunWithOracles(spanMethod.Method.Name, data, () => spanMethod(data));
            }
            else if (fuzzingMethod is AflFuzzStream streamMethod)
            {
                RunWithOracles(streamMethod.Method.Name, data, () =>
                {
                    using var stream = new MemoryStream(data, writable: false);
                    streamMethod(stream);
                });
            }
            else if (fuzzingMethod is AflFuzzString stringMethod)
            {
                string text = Encoding.UTF8.GetString(data);
                RunWithOracles(stringMethod.Method.Name, data, () => stringMethod(text));
            }
            else
            {
                throw new ArgumentException("Unsupported fuzzing delegate.", nameof(fuzzingMethod));
            }
        }

        /// <summary>
        /// Runs one input under the stack and time oracles of <see cref="FuzzOracles"/>.
        /// </summary>
        private static void RunWithOracles(string target, byte[] input, Action run)
        {
            FuzzOracles.RunTarget(target, input.Length, run);
        }

        /// <summary>
        /// Runs the fuzzing method with the given delegate.
        /// </summary>
        public static void RunFuzzMethod(Delegate fuzzingMethod, bool outOfProcess = false)
        {
            // find the function to fuzz method based on the type
            if (fuzzingMethod is AflFuzzStream aflFuzzStreamMethod)
            {
                // Buffered so the oracles can re-run the input and measure its size.
                void RunStream(Stream stream)
                {
                    using var buffer = new MemoryStream();
                    stream.CopyTo(buffer);
                    byte[] data = buffer.ToArray();
                    RunWithOracles(aflFuzzStreamMethod.Method.Name, data, () =>
                    {
                        using var input = new MemoryStream(data, writable: false);
                        aflFuzzStreamMethod(input);
                    });
                }

                if (outOfProcess)
                {
                    Fuzzer.OutOfProcess.Run(RunStream);
                }
                else
                {
                    Fuzzer.Run(RunStream);
                }
            }
            else if (fuzzingMethod is AflFuzzString aflFuzzStringMethod)
            {
                void RunString(string text)
                {
                    RunWithOracles(
                        aflFuzzStringMethod.Method.Name,
                        Encoding.UTF8.GetBytes(text),
                        () => aflFuzzStringMethod(text));
                }

                if (outOfProcess)
                {
                    Fuzzer.OutOfProcess.Run(RunString);
                }
                else
                {
                    Fuzzer.Run(RunString);
                }
                return;
            }
            // libfuzzer span target
            else if (fuzzingMethod is LibFuzzSpan libFuzzSpanMethod)
            {
                Fuzzer.LibFuzzer.Run(bytes =>
                {
                    byte[] data = bytes.ToArray();
                    RunWithOracles(libFuzzSpanMethod.Method.Name, data, () => libFuzzSpanMethod(data));
                });
                return;
            }
            else
            {
                throw new ArgumentException("Unsupported fuzzing delegate.", nameof(fuzzingMethod));
            }
        }
    }
}