Add code explanation doc for gwctl

Author: gauravkghildiyal

gwctl/CODE_ORGANIZATION.md

@@ -0,0 +1,80 @@
+## Code Organization
+
+* **cmd/main.go:** 
+    * Entry point for the application.
+    * Uses the widely adopted Cobra: [https://github.com/spf13/cobra](https://github.com/spf13/cobra) library to manage subcommands and flags.
+
+* **pkg/cmd/(describe, get):**
+    * Contain the starting points for individual subcommands.
+    * Tasks:
+        * Parse command-line arguments into internal structures.
+        * Gather necessary data.
+        * Output the data to the console.
+
+* **Conceptual Separation (Model-View):**
+    * **pkg/resourcediscovery:** Handles data model definition and construction.
+    * **pkg/printer:** Manages formatting and printing the data model to the command line (currently the sole view available). 
+
+* **pkg/policymanager:**
+    * Provides logic to work with Policies, Policy CRDs, and facilitates policy merging based on type and hierarchy.
+
+* **pkg/resourcediscovery:**
+    * **ResourceModel (pkg/resourcediscovery/resourcemodel.go):**
+        * Employs a graph-like structure.
+            ```
+                                                                                                          +------------+
+                                                                                                          |   Policy   |
+                                                                                                          +------+-----+
+                                                                                                                 |
+                                                                                                                 |
+                                                                                                                 |
+                +------------+                           +--------------+                               TargetRef is Namespace
+                |   Policy   |                      +----> GatewayClass <-------+                                |
+                +----+-------+                      |    +--------------+       |                                |
+                     |                              |                           |            +---------+         |
+                     |                              |                           |  +-------->|Namespace|<--------+
+                     |                      Parent GatewayClass                 |  |         +---------+
+                     |                              |                           |  |
+                     |                              |                           |  |
+                     |                              |                           |  |
+                     |                        +-----+-----+               +-----+--+--+
+            TargetRef is HTTPRoute    +------->  Gateway  <---+           |  Gateway  <--+
+                     |                |       +-----------+   |           +-----------+  |
+                     |                |                       |                          |
+                     |                |                       |                          |
+                     |           Attached to             Attached to                  Attached to
+                     |                |                       |                          |
+                     |                |                       |                          |
+                     |           +----+------+             +--+--------+            +----+------+
+                     +---------->| HTTPRoute |             | HTTPRoute |            | HTTPRoute |
+                                 +----+------+             +----+------+            +-----+-----+
+                                      |                         |                         |
+                                      |                         |                         |
+                                  Routes to                 Routes to                 Routes to
+                                      |                         |                         |
+                                      |       +---------+       |                    +----v----+
+                                      +-------> Backend <-------+                    | Backend |
+                                              +---------+                            +---------+
+            ```
+        * Nodes: Resources from the Gateway API (Gateways, HTTPRoutes, etc.).
+        * Edges: Connections between resources (e.g., HTTPRoutes linked to Backends).
+    * **Discoverer (pkg/resourcediscovery/discoverer.go):** 
+        * Builds the `ResourceModel`.
+        * **Example (`gwctl describe httproutes -l key1=value1`):** 
+            1. `DiscoverResourcesForHTTPRoute(filter)`:
+                * Identifies HTTPRoutes with the `key1=value1` label.
+                * Inserts them as source nodes into the `ResourceModel`.
+            2. **Graph Traversal:**
+                * Uses a BFS-like algorithm that begins from the source HTTPRoute nodes.
+                * Finds associated Gateways, GatewayClasses, Namespaces, Policies, and Backends
+
+* **pkg/printer:**
+    * Receives the `ResourceModel` as input. 
+    * Extracts relevant information, arranges it into a printable format, and sends it to the command line.
+
+
+### Additional Notes:
+
+* The code partially adheres to the Model-View pattern, with `resourcediscovery` managing data representation and `printer` controlling output.
+* The `Discoverer` constructs the `ResourceModel` graph, performing BFS-like graph traversals to locate connected resources.
+* Future improvements could add alternative output views (e.g., Graphviz visualizations, interactive web interfaces).