// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.

using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Management.Automation.Language;
using System.Net.NetworkInformation;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Text;
using System.Xml;

namespace System.Management.Automation
{
    /// <summary>
    /// Defines generic utilities and helper methods for PowerShell.
    /// </summary>
    internal static class PsUtils
    {
        /// <summary>
        /// Safely retrieves the MainModule property of a
        /// process. Version 2.0 and below of the .NET Framework are
        /// impacted by a Win32 API usability knot that throws an
        /// exception if API tries to enumerate the process' modules
        /// while it is still loading them. This generates the error
        /// message: Only part of a ReadProcessMemory or
        /// WriteProcessMemory request was completed.
        /// The BCL fix in V3 was to just try more, so we do the same
        /// thing.
        ///
        /// Note: If you attempt to retrieve the MainModule of a 64-bit
        /// process from a WOW64 (32-bit) process, the Win32 API has a fatal
        /// flaw that causes this to return the same error.
        ///
        /// If you need the MainModule of a 64-bit process from a WOW64
        /// process, you will need to write the P/Invoke yourself.
        /// </summary>
        /// <param name="targetProcess">The process from which to
        /// retrieve the MainModule</param>
        /// <exception cref="NotSupportedException">
        /// You are trying to access the MainModule property for a process that is running
        /// on a remote computer. This property is available only for processes that are
        /// running on the local computer.
        /// </exception>
        /// <exception cref="InvalidOperationException">
        /// The process Id is not available (or) The process has exited.
        /// </exception>
        /// <exception cref="System.ComponentModel.Win32Exception">
        /// </exception>
        internal static ProcessModule GetMainModule(Process targetProcess)
        {
            int caughtCount = 0;

            while (true)
            {
                try
                {
                    return targetProcess.MainModule;
                }
                catch (System.ComponentModel.Win32Exception e)
                {
                    // If this is an Access Denied error (which can happen with thread impersonation)
                    // then re-throw immediately.
                    if (e.NativeErrorCode == 5)
                        throw;

                    // Otherwise retry to ensure module is loaded.
                    caughtCount++;
                    System.Threading.Thread.Sleep(100);
                    if (caughtCount == 5)
                        throw;
                }
            }
        }

        // Cache of the current process' parentId
        private static int? s_currentParentProcessId;
        private static readonly int s_currentProcessId = Process.GetCurrentProcess().Id;

        /// <summary>
        /// Retrieve the parent process of a process.
        ///
        /// Previously this code used WMI, but WMI is causing a CPU spike whenever the query gets called as it results in
        /// tzres.dll and tzres.mui.dll being loaded into every process to convert the time information to local format.
        /// For perf reasons, we resort to P/Invoke.
        /// </summary>
        /// <param name="current">The process we want to find the
        /// parent of</param>
        internal static Process GetParentProcess(Process current)
        {
            var processId = current.Id;

            // This is a common query (parent id for the current process)
            // Use cached value if available
            var parentProcessId = processId == s_currentProcessId && s_currentParentProcessId.HasValue ?
                 s_currentParentProcessId.Value :
                 Microsoft.PowerShell.ProcessCodeMethods.GetParentPid(current);

            // cache the current process parent pid if it hasn't been done yet
            if (processId == s_currentProcessId && !s_currentParentProcessId.HasValue)
            {
                s_currentParentProcessId = parentProcessId;
            }

            if (parentProcessId == 0)
                return null;

            try
            {
                Process returnProcess = Process.GetProcessById(parentProcessId);

                // Ensure the process started before the current
                // process, as it could have gone away and had the
                // PID recycled.
                if (returnProcess.StartTime <= current.StartTime)
                    return returnProcess;
                else
                    return null;
            }
            catch (ArgumentException)
            {
                // GetProcessById throws an ArgumentException when
                // you reach the top of the chain -- Explorer.exe
                // has a parent process, but you cannot retrieve it.
                return null;
            }
        }

        /// <summary>
        /// Return true/false to indicate whether the processor architecture is ARM.
        /// </summary>
        /// <returns></returns>
        internal static bool IsRunningOnProcessorArchitectureARM()
        {
            Architecture arch = RuntimeInformation.OSArchitecture;
            return arch == Architecture.Arm || arch == Architecture.Arm64;
        }

        /// <summary>
        /// Get a temporary directory to use, needs to be unique to avoid collision.
        /// </summary>
        internal static string GetTemporaryDirectory()
        {
            string tempDir = string.Empty;
            string tempPath = Path.GetTempPath();
            do
            {
                tempDir = Path.Combine(tempPath, System.Guid.NewGuid().ToString());
            }
            while (Directory.Exists(tempDir));

            try
            {
                Directory.CreateDirectory(tempDir);
            }
            catch (UnauthorizedAccessException)
            {
                tempDir = string.Empty; // will become current working directory
            }

            return tempDir;
        }

        internal static string GetHostName()
        {
            IPGlobalProperties ipProperties = IPGlobalProperties.GetIPGlobalProperties();

            string hostname = ipProperties.HostName;
            string domainName = ipProperties.DomainName;

            // CoreFX on Unix calls GLibc getdomainname()
            // which returns "(none)" if a domain name is not set by setdomainname()
            if (!string.IsNullOrEmpty(domainName) && !domainName.Equals("(none)", StringComparison.Ordinal))
            {
                hostname = hostname + "." + domainName;
            }

            return hostname;
        }

        internal static uint GetNativeThreadId()
        {
#if UNIX
            return Platform.NonWindowsGetThreadId();
#else
            return NativeMethods.GetCurrentThreadId();
#endif
        }

        private static class NativeMethods
        {
            [DllImport(PinvokeDllNames.GetCurrentThreadIdDllName)]
            internal static extern uint GetCurrentThreadId();
        }

        #region ASTUtils

        /// <summary>
        /// This method is to get the unique key for a UsingExpressionAst. The key is a base64
        /// encoded string based on the text of the UsingExpressionAst.
        ///
        /// This method is used when handling a script block that contains $using for Invoke-Command.
        ///
        /// When run Invoke-Command targeting a machine that runs PSv3 or above, we pass a dictionary
        /// to the remote end that contains the key of each UsingExpressionAst and its value. This method
        /// is used to generate the key.
        /// </summary>
        /// <param name="usingAst">A using expression.</param>
        /// <returns>Base64 encoded string as the key of the UsingExpressionAst.</returns>
        internal static string GetUsingExpressionKey(Language.UsingExpressionAst usingAst)
        {
            Diagnostics.Assert(usingAst != null, "Caller makes sure the parameter is not null");

            // We cannot call ToLowerInvariant unconditionally, because usingAst might
            // contain IndexExpressionAst in its SubExpression, such as
            //   $using:bar["AAAA"]
            // and the index "AAAA" might not get us the same value as "aaaa".
            //
            // But we do want a unique key to represent the same UsingExpressionAst's as much
            // as possible, so as to avoid sending redundant key-value's to remote machine.
            // As a workaround, we call ToLowerInvariant when the SubExpression of usingAst
            // is a VariableExpressionAst, because:
            //   (1) Variable name is case insensitive;
            //   (2) People use $using to refer to a variable most of the time.
            string usingAstText = usingAst.ToString();
            if (usingAst.SubExpression is Language.VariableExpressionAst)
            {
                usingAstText = usingAstText.ToLowerInvariant();
            }

            return StringToBase64Converter.StringToBase64String(usingAstText);
        }

        #endregion ASTUtils

        #region EvaluatePowerShellDataFile

        /// <summary>
        /// Evaluate a powershell data file as if it's a module manifest.
        /// </summary>
        /// <param name="parameterName"></param>
        /// <param name="psDataFilePath"></param>
        /// <param name="context"></param>
        /// <param name="skipPathValidation"></param>
        /// <returns></returns>
        internal static Hashtable EvaluatePowerShellDataFileAsModuleManifest(
                                     string parameterName,
                                     string psDataFilePath,
                                     ExecutionContext context,
                                     bool skipPathValidation)
        {
            // Use the same capabilities as the module manifest
            // e.g. allow 'PSScriptRoot' variable
            return EvaluatePowerShellDataFile(
                      parameterName,
                      psDataFilePath,
                      context,
                      Microsoft.PowerShell.Commands.ModuleCmdletBase.PermittedCmdlets,
                      new[] { "PSScriptRoot" },
                      allowEnvironmentVariables: true,
                      skipPathValidation: skipPathValidation);
        }

        /// <summary>
        /// Get a Hashtable object out of a PowerShell data file (.psd1)
        /// </summary>
        /// <param name="parameterName">
        /// Name of the parameter that takes the specified .psd1 file as a value
        /// </param>
        /// <param name="psDataFilePath">
        /// Path to the powershell data file
        /// </param>
        /// <param name="context">
        /// ExecutionContext to use
        /// </param>
        /// <param name="allowedCommands">
        /// Set of command names that are allowed to use in the .psd1 file
        /// </param>
        /// <param name="allowedVariables">
        /// Set of variable names that are allowed to use in the .psd1 file
        /// </param>
        /// <param name="allowEnvironmentVariables">
        /// If true, allow to use environment variables in the .psd1 file
        /// </param>
        /// <param name="skipPathValidation">
        /// If true, caller guarantees the path is valid
        /// </param>
        /// <returns></returns>
        internal static Hashtable EvaluatePowerShellDataFile(
                                     string parameterName,
                                     string psDataFilePath,
                                     ExecutionContext context,
                                     IEnumerable<string> allowedCommands,
                                     IEnumerable<string> allowedVariables,
                                     bool allowEnvironmentVariables,
                                     bool skipPathValidation)
        {
            if (!skipPathValidation && string.IsNullOrEmpty(parameterName)) { throw PSTraceSource.NewArgumentNullException(nameof(parameterName)); }

            if (string.IsNullOrEmpty(psDataFilePath)) { throw PSTraceSource.NewArgumentNullException(nameof(psDataFilePath)); }

            if (context == null) { throw PSTraceSource.NewArgumentNullException(nameof(context)); }

            string resolvedPath;
            if (skipPathValidation)
            {
                resolvedPath = psDataFilePath;
            }
            else
            {
                #region "ValidatePowerShellDataFilePath"

                bool isPathValid = true;

                // File extension needs to be .psd1
                string pathExt = Path.GetExtension(psDataFilePath);
                if (string.IsNullOrEmpty(pathExt) ||
                    !StringLiterals.PowerShellDataFileExtension.Equals(pathExt, StringComparison.OrdinalIgnoreCase))
                {
                    isPathValid = false;
                }

                ProviderInfo provider;
                var resolvedPaths = context.SessionState.Path.GetResolvedProviderPathFromPSPath(psDataFilePath, out provider);

                // ConfigPath should be resolved as FileSystem provider
                if (provider == null || !Microsoft.PowerShell.Commands.FileSystemProvider.ProviderName.Equals(provider.Name, StringComparison.OrdinalIgnoreCase))
                {
                    isPathValid = false;
                }

                // ConfigPath should be resolved to a single path
                if (resolvedPaths.Count != 1)
                {
                    isPathValid = false;
                }

                if (!isPathValid)
                {
                    throw PSTraceSource.NewArgumentException(
                             parameterName,
                             ParserStrings.CannotResolvePowerShellDataFilePath,
                             psDataFilePath);
                }

                resolvedPath = resolvedPaths[0];

                #endregion "ValidatePowerShellDataFilePath"
            }

            #region "LoadAndEvaluatePowerShellDataFile"

            object evaluationResult;
            try
            {
                // Create the scriptInfo for the .psd1 file
                string dataFileName = Path.GetFileName(resolvedPath);
                var dataFileScriptInfo = new ExternalScriptInfo(dataFileName, resolvedPath, context);
                ScriptBlock scriptBlock = dataFileScriptInfo.ScriptBlock;

                // Validate the scriptblock
                scriptBlock.CheckRestrictedLanguage(allowedCommands, allowedVariables, allowEnvironmentVariables);

                // Evaluate the scriptblock
                object oldPsScriptRoot = context.GetVariableValue(SpecialVariables.PSScriptRootVarPath);
                try
                {
                    // Set the $PSScriptRoot before the evaluation
                    context.SetVariable(SpecialVariables.PSScriptRootVarPath, Path.GetDirectoryName(resolvedPath));
                    evaluationResult = PSObject.Base(scriptBlock.InvokeReturnAsIs());
                }
                finally
                {
                    context.SetVariable(SpecialVariables.PSScriptRootVarPath, oldPsScriptRoot);
                }
            }
            catch (RuntimeException ex)
            {
                throw PSTraceSource.NewInvalidOperationException(
                         ex,
                         ParserStrings.CannotLoadPowerShellDataFile,
                         psDataFilePath,
                         ex.Message);
            }

            var retResult = evaluationResult as Hashtable;
            if (retResult == null)
            {
                throw PSTraceSource.NewInvalidOperationException(
                         ParserStrings.InvalidPowerShellDataFile,
                         psDataFilePath);
            }

            #endregion "LoadAndEvaluatePowerShellDataFile"

            return retResult;
        }

        #endregion EvaluatePowerShellDataFile

        internal static readonly string[] ManifestModuleVersionPropertyName = new[] { "ModuleVersion" };
        internal static readonly string[] ManifestGuidPropertyName = new[] { "GUID" };
        internal static readonly string[] ManifestPrivateDataPropertyName = new[] { "PrivateData" };

        internal static readonly string[] FastModuleManifestAnalysisPropertyNames = new[]
        {
            "AliasesToExport",
            "CmdletsToExport",
            "CompatiblePSEditions",
            "FunctionsToExport",
            "NestedModules",
            "RootModule",
            "ModuleToProcess",
            "ModuleVersion"
        };

        internal static Hashtable GetModuleManifestProperties(string psDataFilePath, string[] keys)
        {
            string dataFileContents = ScriptAnalysis.ReadScript(psDataFilePath);
            ParseError[] parseErrors;
            var ast = (new Parser()).Parse(psDataFilePath, dataFileContents, null, out parseErrors, ParseMode.ModuleAnalysis);
            if (parseErrors.Length > 0)
            {
                var pe = new ParseException(parseErrors);
                throw PSTraceSource.NewInvalidOperationException(
                    pe,
                    ParserStrings.CannotLoadPowerShellDataFile,
                    psDataFilePath,
                    pe.Message);
            }

            string unused1;
            string unused2;
            var pipeline = ast.GetSimplePipeline(false, out unused1, out unused2);
            if (pipeline != null)
            {
                var hashtableAst = pipeline.GetPureExpression() as HashtableAst;
                if (hashtableAst != null)
                {
                    var result = new Hashtable(StringComparer.OrdinalIgnoreCase);
                    foreach (var pair in hashtableAst.KeyValuePairs)
                    {
                        var key = pair.Item1 as StringConstantExpressionAst;
                        if (key != null && keys.Contains(key.Value, StringComparer.OrdinalIgnoreCase))
                        {
                            try
                            {
                                var val = pair.Item2.SafeGetValue();
                                result[key.Value] = val;
                            }
                            catch
                            {
                                throw PSTraceSource.NewInvalidOperationException(
                                         ParserStrings.InvalidPowerShellDataFile,
                                         psDataFilePath);
                            }
                        }
                    }

                    return result;
                }
            }

            throw PSTraceSource.NewInvalidOperationException(
                     ParserStrings.InvalidPowerShellDataFile,
                     psDataFilePath);
        }
    }

    /// <summary>
    /// This class provides helper methods for converting to/fro from
    /// string to base64string.
    /// </summary>
    internal static class StringToBase64Converter
    {
        /// <summary>
        /// Converts string to base64 encoded string.
        /// </summary>
        /// <param name="input">String to encode.</param>
        /// <returns>Base64 encoded string.</returns>
        internal static string StringToBase64String(string input)
        {
            // NTRAID#Windows Out Of Band Releases-926471-2005/12/27-JonN
            // shell crashes if you pass an empty script block to a native command
            if (input == null)
            {
                throw PSTraceSource.NewArgumentNullException(nameof(input));
            }

            string base64 = Convert.ToBase64String
                            (
                                Encoding.Unicode.GetBytes(input.ToCharArray())
                            );
            return base64;
        }

        /// <summary>
        /// Decodes base64 encoded string.
        /// </summary>
        /// <param name="base64">Base64 string to decode.</param>
        /// <returns>Decoded string.</returns>
        internal static string Base64ToString(string base64)
        {
            if (string.IsNullOrEmpty(base64))
            {
                throw PSTraceSource.NewArgumentNullException(nameof(base64));
            }

            string output = new string(Encoding.Unicode.GetChars(Convert.FromBase64String(base64)));
            return output;
        }

        /// <summary>
        /// Decodes base64 encoded string in to args array.
        /// </summary>
        /// <param name="base64"></param>
        /// <returns></returns>
        internal static object[] Base64ToArgsConverter(string base64)
        {
            if (string.IsNullOrEmpty(base64))
            {
                throw PSTraceSource.NewArgumentNullException(nameof(base64));
            }

            string decoded = new string(Encoding.Unicode.GetChars(Convert.FromBase64String(base64)));

            // Deserialize string
            XmlReader reader = XmlReader.Create(new StringReader(decoded), InternalDeserializer.XmlReaderSettingsForCliXml);
            object dso;
            Deserializer deserializer = new Deserializer(reader);
            dso = deserializer.Deserialize();
            if (deserializer.Done() == false)
            {
                // This helper function should move to host and it should provide appropriate
                // error message there.
                throw PSTraceSource.NewArgumentException(MinishellParameterBinderController.ArgsParameter);
            }

            PSObject mo = dso as PSObject;
            if (mo == null)
            {
                // This helper function should move the host. Provide appropriate error message.
                // Format of args parameter is not correct.
                throw PSTraceSource.NewArgumentException(MinishellParameterBinderController.ArgsParameter);
            }

            var argsList = mo.BaseObject as ArrayList;
            if (argsList == null)
            {
                // This helper function should move the host. Provide appropriate error message.
                // Format of args parameter is not correct.
                throw PSTraceSource.NewArgumentException(MinishellParameterBinderController.ArgsParameter);
            }

            return argsList.ToArray();
        }
    }

    /// <summary>
    /// A simple implementation of CRC32.
    /// See "CRC-32 algorithm" in https://en.wikipedia.org/wiki/Cyclic_redundancy_check.
    /// </summary>
    internal class CRC32Hash
    {
        // CRC-32C polynomial representations
        private const uint polynomial = 0x1EDC6F41;

        private static uint[] table;

        static CRC32Hash()
        {
            uint temp = 0;
            table = new uint[256];

            for (int i = 0; i < table.Length; i++)
            {
                temp = (uint)i;
                for (int j = 0; j < 8; j++)
                {
                    if ((temp & 1) == 1)
                    {
                        temp = (temp >> 1) ^ polynomial;
                    }
                    else
                    {
                        temp >>= 1;
                    }
                }

                table[i] = temp;
            }
        }

        private static uint Compute(byte[] buffer)
        {
            uint crc = 0xFFFFFFFF;
            for (int i = 0; i < buffer.Length; ++i)
            {
                var index = (byte)(crc ^ buffer[i] & 0xff);
                crc = (crc >> 8) ^ table[index];
            }

            return ~crc;
        }

        internal static byte[] ComputeHash(byte[] buffer)
        {
            uint crcResult = Compute(buffer);
            return BitConverter.GetBytes(crcResult);
        }

        internal static string ComputeHash(string input)
        {
            byte[] hashBytes = ComputeHash(Encoding.UTF8.GetBytes(input));
            return BitConverter.ToString(hashBytes).Replace("-", string.Empty);
        }
    }

    #region ReferenceEqualityComparer

    /// <summary>
    /// Equality comparer based on Object Identity.
    /// </summary>
    internal class ReferenceEqualityComparer : IEqualityComparer
    {
        bool IEqualityComparer.Equals(object x, object y)
        {
            return Object.ReferenceEquals(x, y);
        }

        int IEqualityComparer.GetHashCode(object obj)
        {
            // The Object.GetHashCode and RuntimeHelpers.GetHashCode methods are used in the following scenarios:
            //
            // Object.GetHashCode is useful in scenarios where you care about object value. Two strings with identical
            // contents will return the same value for Object.GetHashCode.
            //
            // RuntimeHelpers.GetHashCode is useful in scenarios where you care about object identity. Two strings with
            // identical contents will return different values for RuntimeHelpers.GetHashCode, because they are different
            // string objects, although their contents are the same.

            return RuntimeHelpers.GetHashCode(obj);
        }
    }

    #endregion
}

