using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using BepInEx.Logging;
using Mono.Cecil;
using Mono.Cecil.Cil;

namespace SPT.PrePatch
{
    public static class SPTPrePatcher
    {
        public static IEnumerable<string> TargetDLLs { get; } = new[] { "Assembly-CSharp.dll" };
        private const string _sptPluginFolder = "plugins/spt";

        public static void Patch(ref AssemblyDefinition assembly)
        {
            PerformPreValidation();
            ChangeAppDataPath(assembly);
        }

        private static void ChangeAppDataPath(AssemblyDefinition assembly)
        {
            // Change icon cache folder path to be local to SPT
            // find the type that contains a method called ClearIconCache, there is currently only one
            var typeToEdit = assembly.MainModule.GetTypes().FirstOrDefault(x => x.Methods.Any(m => m.Name == "ClearIconCache"));

            // find the .cctor and change the instructions to use our path instead
            var methodToEdit = typeToEdit.Methods.FirstOrDefault(x => x.Name == ".cctor");
            var ilProc = methodToEdit.Body.GetILProcessor();
            var instructions = GetCacheInstructions(assembly);

            // all this constructor does is set this static field up
            methodToEdit.Body.Instructions.Clear();
            
            foreach (var ins in instructions)
            {
                ilProc.Append(ins);
            }
        }

        private static List<Instruction> GetCacheInstructions(AssemblyDefinition assembly)
        {
            return new List<Instruction>
            {
                Instruction.Create(OpCodes.Call, assembly.MainModule.ImportReference(typeof(Environment).GetMethod("get_CurrentDirectory"))),
                Instruction.Create(OpCodes.Ldstr, "user"),
                Instruction.Create(OpCodes.Ldstr, "sptappdata"),
                Instruction.Create(OpCodes.Call, assembly.MainModule.ImportReference(typeof(Path).GetMethod("Combine", new []{ typeof(string), typeof(string), typeof(string) }))),
                Instruction.Create(OpCodes.Stsfld, assembly.MainModule.GetTypes().FirstOrDefault(x => x.Methods.Any(m => m.Name == "ClearIconCache")).Fields.FirstOrDefault(f => f.Name == "Path")),
                Instruction.Create(OpCodes.Ret)
            };
        }

        private static void PerformPreValidation()
        {
            // Check if the launcher was used
            bool launcherUsed = ValidateLauncherUse(out string launcherError);

            // Check that all the expected plugins are in the BepInEx/Plugins/spt/ folder
            string assemblyFolder = Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location);
            string sptPluginPath = Path.GetFullPath(Path.Combine(assemblyFolder, "..", _sptPluginFolder));
            bool pluginsValidated = ValidateSptPlugins(sptPluginPath, out string pluginErrorMessage);

            // If either the launcher wasn't used, or the plugins weren't found, exit
            if (!launcherUsed || !pluginsValidated)
            {
                string errorTitle = (!launcherUsed) ? "Startup Error" : "Missing Core Files";
                string errorMessage = (!launcherUsed) ? launcherError : pluginErrorMessage;
                MessageBoxHelper.Show(errorMessage, $"[SPT] {errorTitle}", MessageBoxHelper.MessageBoxType.OK);
                Environment.Exit(0);
            }
        }

        private static bool ValidateLauncherUse(out string message)
        {
            // Validate that parameters were passed to EscapeFromTarkov.exe, to verify the
            // player used the SPT Launcher to start the process
            string[] args = Environment.GetCommandLineArgs();
            if (args.Length > 1)
            {
                message = "";
                return true; 
            }

            message = "Please start SPT using SPT.Launcher.exe. Exiting.";
            return false;
        }

        private static bool ValidateSptPlugins(string sptPluginPath, out string message)
        {
            string exitMessage = "\n\nPlease re-install SPT. Exiting.";
            ManualLogSource logger = Logger.CreateLogSource(nameof(SPTPrePatcher));

            // Validate that the SPT plugin path exists
            if (!Directory.Exists(sptPluginPath))
            {
                message = $"'{sptPluginPath}' directory not found{exitMessage}";
                logger.LogError(message);
                return false;
            }

            // Validate that the folder exists, and contains our plugins
            string[] sptPlugins = new string[] { "spt-common.dll", "spt-reflection.dll", "spt-core.dll", "spt-custom.dll", "spt-singleplayer.dll" };
            string[] foundPlugins = Directory.GetFiles(sptPluginPath).Select(x => Path.GetFileName(x)).ToArray();

            foreach (string pluginNameAndSuffix in sptPlugins)
            {
                if (!foundPlugins.Contains(pluginNameAndSuffix))
                {
                    message = $"Required SPT plugin: {pluginNameAndSuffix} missing from '{sptPluginPath}' {exitMessage}";
                    logger.LogError(message);
                    return false;
                }
            }

            message = "";
            return true;
        }
    }
}