dbus-top: initial commits

This commit covers the basic functionalities of the dbus-top tool.

The UI is divided into 3 windows as follows:

  +--------------------------+  Window list
  |         Window A         |  A: Summary statistics
  +------------+-------------+  B: Sensor list or detail
  |  Window B  |   Window C  |  C: Detailed statistics
  +------------+-------------+

To navigate the UI:
* Use tab to navigate each window

When a window is highlighted:
  In Window B:
  * Press esc key 3 times to leave the current sensor selection

  In Window C:
  * Press [Enter] to show/hide pop-up menu for column selectio
  * Press [Left]  to move highlight cursor to the left
  * Press [Right] to move highlight cursor to the right
  * Press [A] to sort by the highlighted column in ascending order
  * Press [D] to sort by the highlighted column in descending order

To add recipe to Yocto and build the recipe:
1) Copy and paste the content of the .bb file into a folder that can be
   detected by bitbake, such as meta-phosphor/recipes-phosphor/ipmi.
2) run "devtool modify -n dbus-top (path_to_openbmc_tools)/dbus-top/".

Signed-off-by: Adedeji Adebisi <adedejiadebisi01@gmail.com>
Change-Id: Id58ba30b815cfd9d18f54cf477d749dbdbc4545b
(cherry picked from commit d83c1aa45aa8cc9b61530b4f0fe1d04aa64d2c41)
diff --git a/bargraph.hpp b/bargraph.hpp
new file mode 100644
index 0000000..36f34a1
--- /dev/null
+++ b/bargraph.hpp
@@ -0,0 +1,59 @@
+// Copyright 2021 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#include <stdio.h>
+
+#include <vector>
+
+template <typename ValueType>
+class BarGraph
+{
+  public:
+    std::vector<ValueType> history_; // is actually a ring buffer.
+    int next_;   // index to the slot where the next insertion will go
+    int length_; // total # of data points that have ever been added
+    explicit BarGraph(int capacity) : next_(0), length_(0)
+    {
+        history_.resize(capacity);
+        std::fill(history_.begin(), history_.end(), 0);
+    }
+
+    // The last value is in [0], so on and so forth
+    // Note: if there are not enough data, this function will return as much
+    // as is available
+    std::vector<float> GetLastNValues(int x)
+    {
+        std::vector<float> ret;
+        const int N = static_cast<int>(history_.size());
+        int imax = x;
+        imax = std::min(imax, length_);
+        imax = std::min(imax, N);
+        int idx = (next_ - 1 + N) % N;
+        for (int i = 0; i < imax; i++)
+        {
+            ret.push_back(history_[idx]);
+            idx = (idx - 1 + N) % N;
+        }
+        return ret;
+    }
+
+    void AddValue(ValueType x)
+    {
+        history_[next_] = x;
+        next_ = (next_ + 1) % history_.size();
+        length_++;
+    }
+};