From 16ad023cfe3a9883bd18766ad94f5c867b244e23 Mon Sep 17 00:00:00 2001
From: Marenz <mathias.baumann@frequenz.com>
Date: Tue, 13 Dec 2022 17:40:00 +0100
Subject: [PATCH] Simple ringbuffer with tests

Signed-off-by: Marenz <mathias.baumann@frequenz.com>
---
 src/frequenz/sdk/util/ringbuffer.py | 111 ++++++++++++++++++++++++++++
 tests/utils/ringbuffer.py           |  44 +++++++++++
 2 files changed, 155 insertions(+)
 create mode 100644 src/frequenz/sdk/util/ringbuffer.py
 create mode 100644 tests/utils/ringbuffer.py

diff --git a/src/frequenz/sdk/util/ringbuffer.py b/src/frequenz/sdk/util/ringbuffer.py
new file mode 100644
index 000000000..95588acc3
--- /dev/null
+++ b/src/frequenz/sdk/util/ringbuffer.py
@@ -0,0 +1,111 @@
+# License: MIT
+# Copyright © 2022 Frequenz Energy-as-a-Service GmbH
+
+"""Ringbuffer implementation with focus on time & memory efficiency"""
+
+from typing import TypeVar, Generic, Sequence
+from abc import ABC, abstractmethod
+
+from collections import deque
+
+from enum import Enum
+
+import numpy as np
+from itertools import chain
+
+
+T = TypeVar('T')
+
+class AbstractRingBufferContainer(Generic[T], ABC):
+    def __init__(self, size):
+        self.size = size
+
+    @abstractmethod
+    def write(self, value: T, index) -> None:
+        """Write to value to the requested index"""
+        pass
+
+    @abstractmethod
+    def __getitem__(self, index):
+        """Returns the value at the requested index"""
+        pass
+
+    def __len__(self):
+        return self.size
+
+class RingBuffer(Generic[T]):
+
+    # class syntax
+    class Overwrite(Enum):
+        GREEN = 2
+        BLUE = 3
+
+    def __init__(self, container: AbstractRingBufferContainer[T]):
+        self.container = container
+        self.write_index = 0
+        self.read_index = 0
+        self.size = 0
+
+    def __len__(self):
+        return self.size
+
+    def push(self, value: T) -> int:
+        """Pushes a new value into the ring buffer, returns the index in the ringbuffer"""
+
+        if self.size == self.container.size:
+            # Move read position one forward, dropping the oldest written value
+            self.read_index = (self.read_index + 1) % self.container.size
+        else:
+            self.size += 1
+
+        self.container.write(value, self.write_index)
+        value_index = self.write_index
+        self.write_index = (self.write_index + 1) % self.container.size
+
+        return value_index
+
+    def pop(self) -> T:
+        """Remove the oldest value from the ring buffer and return it"""
+
+        if self.size == 0:
+            raise
+
+        val = self.container[self.read_index]
+        self.read_index = (self.read_index + 1) % self.container.size
+        self.size -= 1;
+
+        return val
+
+    def __getitem__(self, index_or_slice: int | slice) -> T | Sequence[T]:
+        """Returns the value at the given index or value range at the given slice"""
+        return self.container[index_or_slice]
+
+
+class ListContainer(AbstractRingBufferContainer, ABC):
+    def __init__(self, size: int):
+        AbstractRingBufferContainer.__init__(self, size)
+        self.data = list([T] * size)
+
+
+    def write(self, value: T, index: int) -> None:
+        """"""
+        self.data[index] = value
+
+    def __getitem__(self, index_or_slice: int | slice) -> T | Sequence[T]:
+        return self.data.__getitem__(index_or_slice)
+
+
+class ArrayContainer(AbstractRingBufferContainer, ABC):
+    def __init__(self, size: int):
+        AbstractRingBufferContainer.__init__(self, size)
+        if (T == float):
+            self.data = np.empty(shape=(size,), dtype=np.float64)
+        else:
+            self.data = np.empty(shape=(size,), dtype=object)
+
+    def write(self, value: T, index: int) -> None:
+        """"""
+        self.data[index] = value
+
+    def __getitem__(self, index_or_slice: int | slice) -> T | Sequence[T]:
+        return self.data.__getitem__(index_or_slice)
diff --git a/tests/utils/ringbuffer.py b/tests/utils/ringbuffer.py
new file mode 100644
index 000000000..74e85765e
--- /dev/null
+++ b/tests/utils/ringbuffer.py
@@ -0,0 +1,44 @@
+# License: MIT
+# Copyright © 2022 Frequenz Energy-as-a-Service GmbH
+
+"""
+Tests for the `Ringbuffer` class
+"""
+
+from frequenz.sdk.util.ringbuffer import RingBuffer, ArrayContainer, ListContainer
+
+def _test_simple_push_pop(container):
+    buffer = RingBuffer(container)
+
+    for i in range(len(container)):
+        buffer.push(i)
+
+    assert len(buffer) == len(container)
+
+    for i in range(len(container)):
+        assert i == buffer.pop()
+
+def test_simple_push_pop() -> None:
+    _test_simple_push_pop(ListContainer(50000))
+    _test_simple_push_pop(ArrayContainer(50000))
+
+
+
+def _test_push_pop_over_limit(container):
+    buffer = RingBuffer(container)
+
+    over_limit_pushes = 1000
+
+    for i in range(len(container) + over_limit_pushes):
+        buffer.push(i)
+
+    assert len(buffer) == len(container)
+
+    for i in range(len(container)):
+        assert i + over_limit_pushes == buffer.pop()
+
+    assert len(buffer) == 0
+
+def test_push_pop_over_limit() -> None:
+    _test_push_pop_over_limit(ListContainer(50000))
+    _test_push_pop_over_limit(ArrayContainer(50000))