Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System/compmod/system/configuration/appsettingsreader.cs

@@ -0,0 +1,91 @@
+//------------------------------------------------------------------------------
+// <copyright file="AppSettingsReader.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//------------------------------------------------------------------------------
+
+using System;
+using System.Reflection;
+using System.Configuration;
+using System.Collections.Specialized;
+using System.Globalization;
+
+namespace System.Configuration {
+
+    /// <devdoc>
+    ///     The AppSettingsReader class provides a wrapper for System.Configuration.ConfigurationManager.AppSettings
+    ///     which provides a single method for reading values from the config file of a particular type.
+    /// </devdoc>
+    public class AppSettingsReader {
+        private NameValueCollection map;
+        static Type stringType = typeof(string);
+        static Type[] paramsArray = new Type[] { stringType };
+        static string NullString = "None";
+
+        /// <devdoc>
+        ///     Constructor
+        /// </devdoc>
+        public AppSettingsReader() {
+            map = System.Configuration.ConfigurationManager.AppSettings;
+        }
+
+        /// <devdoc>
+        ///     Gets the value for specified key from ConfigurationManager.AppSettings, and returns
+        ///     an object of the specified type containing the value from the config file.  If the key
+        ///     isn't in the config file, or if it is not a valid value for the given type, it will 
+        ///     throw an exception with a descriptive message so the user can make the appropriate
+        ///     change
+        /// </devdoc>
+        public object GetValue(string key, Type type) {
+            if (key == null) throw new ArgumentNullException("key");
+            if (type == null) throw new ArgumentNullException("type");
+
+            string val = map[key];
+
+            if (val == null) throw new InvalidOperationException(SR.GetString(SR.AppSettingsReaderNoKey, key));
+
+            if (type == stringType) {
+                // It's a string, so we can ALMOST just return the value.  The only
+                // tricky point is that if it's the string "(None)", then we want to
+                // return null.  And of course we need a way to represent the string
+                // (None), so we use ((None)), and so on... so it's a little complicated.
+                int NoneNesting = GetNoneNesting(val);
+                if (NoneNesting == 0) {
+                    // val is not of the form ((..((None))..))
+                    return val;
+                }
+                else if (NoneNesting == 1) {
+                    // val is (None)
+                    return null;
+                }
+                else {
+                    // val is of the form ((..((None))..))
+                    return val.Substring(1, val.Length - 2);
+                }
+            }
+            else {
+                try {
+                    return Convert.ChangeType(val, type, CultureInfo.InvariantCulture);
+                } catch (Exception) {
+                    string displayString = (val.Length == 0) ? SR.AppSettingsReaderEmptyString : val;
+                    throw new InvalidOperationException(SR.GetString(SR.AppSettingsReaderCantParse, displayString, key, type.ToString()));
+                }               
+            }  
+        }
+
+        private int GetNoneNesting(string val) {
+            int count = 0;
+            int len = val.Length;
+            if (len > 1) {
+                while (val[count] == '(' && val[len - count - 1] == ')') {
+                    count++;
+                }
+                if (count > 0 && string.Compare(NullString, 0, val, count, len - 2 * count, StringComparison.Ordinal) != 0) {
+                    // the stuff between the parens is not "None"
+                    count = 0;
+                }
+            }
+            return count;
+        }
+    }
+}