expose some interfaces for external usage (from introduction-pods) (#256)

* expose some interfaces for external usage (from introduction-pods)

* add From<MainPod> for OperationArg, add copy op!

Co-authored-by: Eduard S. <eduardsanou@posteo.net>

---------

Co-authored-by: Eduard S. <eduardsanou@posteo.net>

src/frontend/mod.rs

@@ -645,6 +645,22 @@ impl MainPod {
     pub fn id(&self) -> PodId {
         self.pod.id()
     }
+
+    /// Returns the value of a ValueOf statement with self id that defines key if it exists.
+    pub fn get(&self, key: impl Into<Key>) -> Option<Value> {
+        let key: Key = key.into();
+        self.public_statements
+            .iter()
+            .find_map(|st| match st {
+                Statement::ValueOf(ak, value)
+                    if ak.pod_id == self.id() && ak.key.hash() == key.hash() =>
+                {
+                    Some(value)
+                }
+                _ => None,
+            })
+            .cloned()
+    }
 }
 
 struct MainPodCompilerInputs<'a> {
@@ -759,6 +775,9 @@ pub mod build_utils {
         (new_entry, ($key:expr, $value:expr)) => { $crate::frontend::Operation(
             $crate::middleware::OperationType::Native($crate::middleware::NativeOperation::NewEntry),
             $crate::op_args!(($key, $value)), $crate::middleware::OperationAux::None) };
+        (copy, $($arg:expr),+) => { $crate::frontend::Operation(
+            $crate::middleware::OperationType::Native($crate::middleware::NativeOperation::CopyStatement),
+            $crate::op_args!($($arg),*), $crate::middleware::OperationAux::None) };
         (eq, $($arg:expr),+) => { $crate::frontend::Operation(
             $crate::middleware::OperationType::Native($crate::middleware::NativeOperation::EqualFromEntries),
             $crate::op_args!($($arg),*), $crate::middleware::OperationAux::None) };

src/frontend/operation.rs

@@ -1,7 +1,7 @@
 use std::fmt;
 
 use crate::{
-    frontend::SignedPod,
+    frontend::{MainPod, SignedPod},
     middleware::{AnchoredKey, OperationAux, OperationType, Statement, Value},
 };
 
@@ -78,6 +78,18 @@ impl From<(&SignedPod, &str)> for OperationArg {
         ))
     }
 }
+impl From<(&MainPod, &str)> for OperationArg {
+    fn from((pod, key): (&MainPod, &str)) -> Self {
+        // TODO: TryFrom.
+        let value = pod
+            .get(key)
+            .unwrap_or_else(|| panic!("Key {} is not present in POD: {}", key, pod));
+        Self::Statement(Statement::ValueOf(
+            AnchoredKey::from((pod.id(), key)),
+            value,
+        ))
+    }
+}
 
 impl From<Statement> for OperationArg {
     fn from(s: Statement) -> Self {