Add reading values from config root

source/poodinis/config/dictionary.d

@@ -1,5 +1,31 @@
+/**
+ * Authors:
+ *  Mike Bierlee, m.bierlee@lostmoment.com
+ * Copyright: 2022 Mike Bierlee
+ * License:
+ *  This software is licensed under the terms of the MIT license.
+ *  The full terms of the license can be found in the LICENSE file.
+ */
+
 module poodinis.config.dictionary;
 
+import std.exception : enforce;
+import std.string : split, startsWith, endsWith;
+import std.conv : to, ConvException;
+
+class ConfigReadException : Exception {
+    this(string msg, string file = __FILE__, size_t line = __LINE__) {
+        super(msg, file, line);
+    }
+}
+
+class PathParseException : Exception {
+    this(string msg, string path, string file = __FILE__, size_t line = __LINE__) {
+        string fullMsg = msg ~ " (Path: " ~ path ~ ")";
+        super(fullMsg, file, line);
+    }
+}
+
 interface ConfigNode {
 }
 
@@ -34,13 +60,108 @@ class NodeArray : ConfigNode {
     this(ConfigNode[] children...) {
         this.children = children;
     }
+
+    this(string[] values...) {
+        foreach (string value; values) {
+            children ~= new NodeValue(value);
+        }
+    }
+}
+
+class PathSegment {
+}
+
+class ArrayPathSegment : PathSegment {
+    const size_t index;
+
+    this(const size_t index) {
+        this.index = index;
+    }
+}
+
+class ConfigPath {
+    private const string path;
+    private string[] segments;
+
+    this(const string path) {
+        this.path = path;
+        this.segments = path.split(".");
+    }
+
+    PathSegment getNextSegment() {
+        if (segments.length == 0) {
+            return null;
+        }
+
+        PathSegment ret(PathSegment segment) {
+            segments = segments.length > 1 ? segments[1 .. $] : [];
+            return segment;
+        }
+
+        string segment = segments[0];
+
+        if (segment.startsWith("[") && segment.endsWith("]")) {
+            if (segment.length <= 2) {
+                throw new PathParseException("Path has array accessor but no index specified", path);
+            }
+
+            auto indexString = segment[1 .. $ - 1];
+            try {
+                auto index = indexString.to!size_t;
+                return ret(new ArrayPathSegment(index));
+            } catch (ConvException e) {
+                throw new PathParseException("Array index '" ~ indexString ~ "' is not acceptable as an array number", path);
+            }
+        }
+
+        throw new Exception("Not yet implemented");
+    }
 }
 
 class ConfigDictionary {
     ConfigNode rootNode;
+
+    string get(string configPath) {
+        enforce!ConfigReadException(rootNode !is null, "The config is empty");
+        enforce!ConfigReadException(configPath.length > 0, "Supplied config path is empty");
+
+        if (configPath == ".") {
+            auto rootValue = cast(NodeValue) rootNode;
+            if (rootValue) {
+                return rootValue.value;
+            } else {
+                throw new ConfigReadException("The root of the config is not a value type");
+            }
+        }
+
+        auto path = new ConfigPath(configPath);
+        auto currentNode = rootNode;
+        PathSegment currentPathSegment = path.getNextSegment();
+        while (currentPathSegment !is null) {
+            auto arrayPath = cast(ArrayPathSegment) currentPathSegment;
+            if (arrayPath) {
+                auto arrayNode = cast(NodeArray) currentNode;
+                if (arrayNode) {
+                    currentNode = arrayNode.children[arrayPath.index];
+                }
+            }
+
+            currentPathSegment = path.getNextSegment();
+        }
+
+        auto value = cast(NodeValue) currentNode;
+        if (value) {
+            return value.value;
+        } else {
+            throw new ConfigReadException(
+                "The configuration at the given path is not a value: " ~ configPath);
+        }
+    }
 }
 
 version (unittest) {
+    import std.exception : assertThrown;
+
     @("Dictionary creation")
     unittest {
         auto root = new NodeObject([
@@ -51,4 +172,45 @@ version (unittest) {
         auto dictionary = new ConfigDictionary();
         dictionary.rootNode = root;
     }
+
+    @("Get value in dictionary with empty root fails")
+    unittest {
+        auto dictionary = new ConfigDictionary();
+
+        assertThrown!ConfigReadException(dictionary.get("."));
+    }
+
+    @("Get value in dictionary with empty path fails")
+    unittest {
+        auto dictionary = new ConfigDictionary();
+        dictionary.rootNode = new NodeValue("hehehe");
+
+        assertThrown!ConfigReadException(dictionary.get(""));
+    }
+
+    @("Get value in root")
+    unittest {
+        auto dictionary = new ConfigDictionary();
+        dictionary.rootNode = new NodeValue("yup");
+
+        assert(dictionary.get(".") == "yup");
+    }
+
+    @("Get value in root fails when root is not a value")
+    unittest {
+        auto dictionary = new ConfigDictionary();
+        dictionary.rootNode = new NodeArray();
+
+        assertThrown!ConfigReadException(dictionary.get("."));
+    }
+
+    @("Get array value from root")
+    unittest {
+        auto dictionary = new ConfigDictionary();
+        dictionary.rootNode = new NodeArray("aap", "noot", "mies");
+
+        assert(dictionary.get("[0]") == "aap");
+        assert(dictionary.get("[1]") == "noot");
+        assert(dictionary.get("[2]") == "mies");
+    }
 }