From f2a44ec128aa30ab44c8a067ef049d07130ef997 Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <prudiger@anaconda.com>
Date: Thu, 24 Mar 2022 14:43:01 +0100
Subject: [PATCH] Allow Variables to reference each other

---
 lumen/dashboard.py      |  3 +-
 lumen/state.py          |  6 +++-
 lumen/ui/dashboard.py   |  2 +-
 lumen/variables/base.py | 61 ++++++++++++++++++++++++++++-------------
 4 files changed, 49 insertions(+), 23 deletions(-)

diff --git a/lumen/dashboard.py b/lumen/dashboard.py
index 93fa4712f..fca6d0b08 100644
--- a/lumen/dashboard.py
+++ b/lumen/dashboard.py
@@ -224,8 +224,7 @@ def __init__(self, specification=None, **params):
         self.auth = Auth.from_spec(state.spec.get('auth', {}))
         self.config = Config.from_spec(state.spec.get('config', {}))
         self.defaults = Defaults.from_spec(state.spec.get('defaults', {}))
-        vars = Variables.from_spec(state.spec.get('variables', {}))
-        self.variables = state._variables[pn.state.curdoc] = vars
+        self.variables = Variables.from_spec(state.spec.get('variables', {}))
         self.defaults.apply()
 
         # Load and populate template
diff --git a/lumen/state.py b/lumen/state.py
index 15516d1a2..11a8f82d5 100644
--- a/lumen/state.py
+++ b/lumen/state.py
@@ -166,10 +166,14 @@ def _resolve_source_ref(self, refs):
     def resolve_reference(self, reference, variables=None):
         if not is_ref(reference):
             raise ValueError('References should be prefixed by $ symbol.')
+        from .variables import Variable
         refs = reference[1:].split('.')
         vars = variables or self.variables
         if refs[0] == 'variables':
-            return vars[refs[1]]
+            value = vars[refs[1]]
+            if isinstance(value, Variable):
+                value = value.value
+            return value
         return self._resolve_source_ref(refs)
 
 
diff --git a/lumen/ui/dashboard.py b/lumen/ui/dashboard.py
index b6179d2f0..f05446753 100644
--- a/lumen/ui/dashboard.py
+++ b/lumen/ui/dashboard.py
@@ -140,7 +140,7 @@ def _yaml_upload(self, event):
         return
 
     def _create_new(self, event):
-        self.spec = {'config': {}, 'sources': {}, 'targets': []}
+        self.spec = {'config': {}, 'sources': {}, 'targets': [], 'variables': {}}
 
     def _selected(self, event):
         self.spec = event.obj.spec
diff --git a/lumen/variables/base.py b/lumen/variables/base.py
index 126525887..c5657f18a 100644
--- a/lumen/variables/base.py
+++ b/lumen/variables/base.py
@@ -20,34 +20,48 @@
 
 
 class Variables(param.Parameterized):
+    """
+    The Variables component stores a number Variable types and mirrors
+    their values onto dynamically created parameters allowing other
+    components to easily watch changes in a variable.
+    """
 
-    def __init__(self, **vars):
-        super().__init__()
-        for p, var in vars.items():
-            vtype = type(var.value)
-            ptype = _PARAM_MAP.get(vtype, param.Parameter)
-            self.param.add_parameter(p, ptype())
-            var.param.watch(partial(self._update_value, p), 'value')
-            var.param.trigger('value')
-        self._vars = vars
-
-    def _update_value(self, p, event):
-        self.param.update({p: event.new})
-
-    def __getitem__(self, key):
-        return getattr(self, key)
+    def __init__(self, **params):
+        super().__init__(**params)
+        self._vars = {}
 
     @classmethod
     def from_spec(cls, spec):
-        vars = {}
+        variables = cls()
+        if pn.state.curdoc:
+            state._variables[pn.state.curdoc] = variables
         for name, var_spec in spec.items():
             if not isinstance(var_spec, dict):
                 var_spec = {
                     'type': 'constant',
                     'default': var_spec
                 }
-            vars[name] = Variable.from_spec(dict(var_spec, name=name), vars)
-        return cls(**vars)
+            var = Variable.from_spec(dict(var_spec, name=name), variables)
+            variables.add_variable(var)
+        return variables
+
+    def add_variable(self, var):
+        """
+        Adds a new variable to the Variables instance and sets up
+        a parameter that can be watched.
+        """
+        self._vars[var.name] = var
+        self.param.add_parameter(var.name, param.Parameter(default=var.value))
+        var.param.watch(partial(self._update_value, var.name), 'value')
+
+    def _update_value(self, name, event):
+        self.param.update({name: event.new})
+
+    def __getitem__(self, key):
+        if key in self.param:
+            return getattr(self, key)
+        else:
+            raise KeyError(f'No variable named {key!r} has been defined.')
 
     @property
     def panel(self):
@@ -60,6 +74,14 @@ def panel(self):
 
 
 class Variable(Component):
+    """
+    A Variable may declare a static or dynamic value that can be
+    referenced from other components. The source of the Variable value
+    can be anything from an environment variable to a widget or URL
+    parameter. Variable components allow a concise way to configure
+    other components and make it possible to orchestrate actions across
+    multiple components.
+    """
 
     default = param.Parameter(doc="""
        Default value to use if no other value is defined""")
@@ -74,7 +96,8 @@ class Variable(Component):
     secure = param.Boolean(default=False, constant=True, doc="""
        Whether the variable should be treated as secure.""")
 
-    value = param.Parameter()
+    value = param.Parameter(doc="""
+       The materialized value of the variable.""")
 
     variable_type = None