GUI: initialize support for vars prompts

... for now only when updating a machine (not when installing)

Whenever the user clicks on the update button in the machine view, and only if user input is needed for some missing vars, the user will be forwarded to a vars page.

pkgs/clan-cli/clan_cli/vars/generate.py

@@ -294,10 +294,28 @@ def _ask_prompts(
     return prompt_values
 
 
+def _get_previous_value(
+    machine: "Machine",
+    generator: Generator,
+    prompt: Prompt,
+) -> str | None:
+    if not prompt.persist:
+        return None
+
+    pub_store = machine.public_vars_store
+    if pub_store.exists(generator, prompt.name):
+        return pub_store.get(generator, prompt.name).decode()
+    sec_store = machine.secret_vars_store
+    if sec_store.exists(generator, prompt.name):
+        return sec_store.get(generator, prompt.name).decode()
+    return None
+
+
 def get_closure(
     machine: "Machine",
     generator_name: str | None,
     regenerate: bool,
+    include_previous_values: bool = False,
 ) -> list[Generator]:
     from .graph import all_missing_closure, full_closure
 
@@ -310,14 +328,24 @@ def get_closure(
     for generator in vars_generators:
         generator.machine(machine)
 
+    result_closure = []
     if generator_name is None:  # all generators selected
         if regenerate:
-            return full_closure(generators)
-        return all_missing_closure(generators)
+            result_closure = full_closure(generators)
+        else:
+            result_closure = all_missing_closure(generators)
     # specific generator selected
-    if regenerate:
-        return requested_closure([generator_name], generators)
-    return minimal_closure([generator_name], generators)
+    elif regenerate:
+        result_closure = requested_closure([generator_name], generators)
+    else:
+        result_closure = minimal_closure([generator_name], generators)
+
+    if include_previous_values:
+        for generator in result_closure:
+            for prompt in generator.prompts:
+                prompt.previous_value = _get_previous_value(machine, generator, prompt)
+
+    return result_closure
 
 
 @API.register
@@ -325,6 +353,7 @@ def get_generators_closure(
     machine_name: str,
     base_dir: Path,
     regenerate: bool = False,
+    include_previous_values: bool = False,
 ) -> list[Generator]:
     from clan_cli.machines.machines import Machine
 
@@ -332,13 +361,14 @@ def get_generators_closure(
         machine=Machine(name=machine_name, flake=Flake(str(base_dir))),
         generator_name=None,
         regenerate=regenerate,
+        include_previous_values=include_previous_values,
     )
 
 
 def _generate_vars_for_machine(
     machine: "Machine",
     generators: list[Generator],
-    all_prompt_values: dict[str, dict],
+    all_prompt_values: dict[str, dict[str, str]],
     no_sandbox: bool = False,
 ) -> bool:
     for generator in generators:
@@ -350,7 +380,7 @@ def _generate_vars_for_machine(
                 generator=generator,
                 secret_vars_store=machine.secret_vars_store,
                 public_vars_store=machine.public_vars_store,
-                prompt_values=all_prompt_values[generator.name],
+                prompt_values=all_prompt_values.get(generator.name, {}),
                 no_sandbox=no_sandbox,
             )
     return True