WriteTracker and DiskWriteTracker (#42)

Author: nedtwigg

python/selfie-lib/selfie_lib/WriteTracker.py

@@ -1,8 +1,12 @@
-from typing import List, Optional
+from typing import List, Optional, Generic, TypeVar, Dict
 from selfie_lib.CommentTracker import SnapshotFileLayout
-import inspect
+from abc import ABC, abstractmethod
+import inspect, threading
 from functools import total_ordering
 
+T = TypeVar("T")
+U = TypeVar("U")
+
 
 @total_ordering
 class CallLocation:
@@ -56,6 +60,17 @@ def ide_link(self, layout: "SnapshotFileLayout") -> str:
         ]
         return "\n".join(links)
 
+    def __eq__(self, other):
+        if not isinstance(other, CallStack):
+            return NotImplemented
+        return (
+            self.location == other.location
+            and self.rest_of_stack == other.rest_of_stack
+        )
+
+    def __hash__(self):
+        return hash((self.location, tuple(self.rest_of_stack)))
+
 
 def recordCall(callerFileOnly: bool = False) -> CallStack:
     stack_frames = inspect.stack()[1:]
@@ -74,3 +89,46 @@ def recordCall(callerFileOnly: bool = False) -> CallStack:
     rest_of_stack = call_locations[1:]
 
     return CallStack(location, rest_of_stack)
+
+
+class FirstWrite(Generic[U]):
+    def __init__(self, snapshot: U, call_stack: CallStack):
+        self.snapshot = snapshot
+        self.call_stack = call_stack
+
+
+class WriteTracker(ABC, Generic[T, U]):
+    def __init__(self):
+        self.lock = threading.Lock()
+        self.writes: Dict[T, FirstWrite[U]] = {}
+
+    @abstractmethod
+    def record(self, key: T, snapshot: U, call: CallStack, layout: SnapshotFileLayout):
+        pass
+
+    def recordInternal(
+        self,
+        key: T,
+        snapshot: U,
+        call: CallStack,
+        layout: SnapshotFileLayout,
+        allow_multiple_equivalent_writes: bool = True,
+    ):
+        with self.lock:
+            this_write = FirstWrite(snapshot, call)
+            if key not in self.writes:
+                self.writes[key] = this_write
+                return
+
+            existing = self.writes[key]
+            if existing.snapshot != snapshot:
+                raise ValueError(
+                    f"Snapshot was set to multiple values!\n  first time: {existing.call_stack.location.ide_link(layout)}\n   this time: {call.location.ide_link(layout)}\n"
+                )
+            elif not allow_multiple_equivalent_writes:
+                raise ValueError("Snapshot was set to the same value multiple times.")
+
+
+class DiskWriteTracker(WriteTracker[T, U]):
+    def record(self, key: T, snapshot: U, call: CallStack, layout: SnapshotFileLayout):
+        super().recordInternal(key, snapshot, call, layout)