[2/n] Add to_string method to AIConfigRuntime

Allow saving an AIConfigRuntime to a string by creating a `to_string` method that encapsulates the core business logic of the `save` method.

This is needed for VSCode extension (top of stack), which sends the state of the AIConfigRuntime to the editor as a string for management (the IDE is responsible for managing the document, and for saving it to disk).

Test Plan:

Tested out getting started ipynb with:

save JSON:

```
config = AIConfigRuntime.load('travel.aiconfig.json')
config.save('travel2.aiconfig.json')
```

save YAML:
```
config.save('travel2.aiconfig.yaml', mode="yaml")
```

to JSON string:
```
config_str = config.to_string()
print(config_str)
```

to YAML string:
```
config_yaml = config.to_string(mode="yaml")
print(config_yaml)
```

For further sanity made sure that the generated strings could be loaded back as an AIConfig and `config.run` worked:

```
config = config.load_yaml(config_yaml)
config.run(...)
```

python/src/aiconfig/Config.py

@@ -455,17 +455,6 @@ def save(
             config_filepath (str, optional): The file path to the JSON or YAML configuration file.
                 Defaults to "aiconfig.json" or "aiconfig.yaml", depending on the mode.
         """
-        # Decide if we want to serialize as YAML or JSON
-
-        # AIConfig json should only contain the core data fields. These are auxiliary fields that should not be persisted
-        exclude_options = {
-            "prompt_index": True,
-            "file_path": True,
-            "callback_manager": True,
-        }
-
-        if not include_outputs:
-            exclude_options["prompts"] = {"__all__": {"outputs"}}
 
         default_filepath = (
             "aiconfig.yaml" if mode == "yaml" else "aiconfig.json"
@@ -481,30 +470,54 @@ def save(
                 # Default to JSON
                 mode = "json"
 
+        config_string = self.to_string(include_outputs, mode)
+
         with open(config_filepath, "w") as file:
-            # Serialize the AIConfig to JSON
-            json_data = self.model_dump(
-                mode="json",
-                exclude=exclude_options,
-                exclude_none=True,
+            file.write(config_string)
+
+    def to_string(
+        self,
+        include_outputs: bool = True,
+        mode: Literal["json", "yaml"] = "json",
+    ) -> str:
+        """
+        Returns the well-formatted string representing the AIConfig object.
+        Note that this method will return the string that would be saved as a .aiconfig file using the save() method.
+        To get the raw string representation of the AIConfig object, use the __str__() method.
+        """
+        # AIConfig json should only contain the core data fields. These are auxiliary fields that should not be persisted
+        exclude_options = {
+            "prompt_index": True,
+            "file_path": True,
+            "callback_manager": True,
+        }
+
+        if not include_outputs:
+            exclude_options["prompts"] = {"__all__": {"outputs"}}
+
+        # Serialize the AIConfig to JSON
+        json_data = self.model_dump(
+            mode="json",
+            exclude=exclude_options,
+            exclude_none=True,
+        )
+
+        if json_data.get("$schema", None) is None:
+            # Set the schema if it is not set
+            json_data["$schema"] = "https://json.schemastore.org/aiconfig-1.0"
+
+        if mode == "yaml":
+            # Save AIConfig JSON as YAML string
+            return yaml.dump(
+                json_data,
+                indent=2,
+            )
+        else:
+            # Save AIConfig as JSON string, with the schema specified
+            return json.dumps(
+                json_data,
+                indent=2,
             )
-            if mode == "yaml":
-                # Save AIConfig JSON as YAML to the file
-                yaml.dump(
-                    json_data,
-                    file,
-                    indent=2,
-                )
-            else:
-                # Save AIConfig as JSON to the file, with the schema specified
-                json_data[
-                    "$schema"
-                ] = "https://json.schemastore.org/aiconfig-1.0"
-                json.dump(
-                    json_data,
-                    file,
-                    indent=2,
-                )
 
     def get_output_text(
         self, prompt: str | Prompt, output: Optional[dict] = None

typescript/lib/config.ts

@@ -233,12 +233,40 @@ export class AIConfigRuntime implements AIConfig {
    * Saves this AIConfig to a file.
    * @param filePath The path to the file to save to.
    * @param saveOptions Options that determine how to save the AIConfig to the file.
+   * @param mode Whether to save the AIConfig as JSON or YAML. If unspecified, the file extension will be used to determine the mode.
    */
   public save(
     filePath?: string,
     saveOptions?: SaveOptions,
     mode?: "json" | "yaml"
   ) {
+    const defaultFilePath = mode === "yaml" ? "aiconfig.yaml" : "aiconfig.json";
+    if (!filePath) {
+      filePath = this.filePath ?? defaultFilePath;
+    }
+
+    if (mode == null) {
+      if (isYamlExt(filePath)) {
+        mode = "yaml";
+      } else {
+        // Default to JSON
+        mode = "json";
+      }
+    }
+
+    const aiConfigString = this.toString(saveOptions, mode);
+    fs.writeFileSync(filePath, aiConfigString);
+  }
+
+  /**
+   * Returns this AIConfig as a string.
+   *
+   * Note that this doesn't return the full string representation of the AIConfig object,
+   * but rather the string representation of the AIConfig object that can be persisted to a file.
+   * @param saveOptions Options that determine how to serialize the AIConfig to string.
+   * @param mode Whether to save the AIConfig as JSON or YAML. Defaults to JSON.
+   */
+  public toString(saveOptions?: SaveOptions, mode: "json" | "yaml" = "json") {
     const keysToOmit = ["filePath", "callbackManager"] as const;
 
     try {
@@ -254,32 +282,20 @@ export class AIConfigRuntime implements AIConfig {
         aiConfigObj.prompts = prompts;
       }
 
-      const defaultFilePath =
-        mode === "yaml" ? "aiconfig.yaml" : "aiconfig.json";
-      if (!filePath) {
-        filePath = this.filePath ?? defaultFilePath;
-      }
-
-      if (mode == null) {
-        if (isYamlExt(filePath)) {
-          mode = "yaml";
-        } else {
-          // Default to JSON
-          mode = "json";
-        }
+      if (aiConfigObj["$schema"] == null) {
+        // Add the $schema property to the JSON object before saving it. In the future this can respect the version specified in the AIConfig.
+        aiConfigObj["$schema"] = "https://json.schemastore.org/aiconfig-1.0";
       }
 
       // TODO: saqadri - make sure that the object satisfies the AIConfig schema
       let aiConfigString;
       if (mode === "yaml") {
         aiConfigString = yaml.dump(aiConfigObj, { indent: 2 });
       } else {
-        // Add the $schema property to the JSON object before saving it. In the future this can respect the version specified in the AIConfig.
-        aiConfigObj["$schema"] = "https://json.schemastore.org/aiconfig-1.0";
         aiConfigString = JSON.stringify(aiConfigObj, null, 2);
       }
 
-      fs.writeFileSync(filePath, aiConfigString);
+      return aiConfigString;
     } catch (error) {
       console.error(error);
       throw error;