Implement interface for using web plotter from C++

It's not actually usable yet due to ODR violations created by
abseil being compiled into libwebrtc_full.a, but it does work based
on testing I've done with using websockets for data transfer.

Change-Id: I574570c7b5c85df9e53321bfb971a608d20b9803
diff --git a/frc971/analysis/in_process_plotter.cc b/frc971/analysis/in_process_plotter.cc
new file mode 100644
index 0000000..e82cb2f
--- /dev/null
+++ b/frc971/analysis/in_process_plotter.cc
@@ -0,0 +1,131 @@
+#include "frc971/analysis/in_process_plotter.h"
+
+#include "aos/configuration.h"
+
+namespace frc971 {
+namespace analysis {
+
+namespace {
+const char *kDataPath = "frc971/analysis";
+const char *kConfigPath = "frc971/analysis/plotter.json";
+}  // namespace
+
+Plotter::Plotter()
+    : config_(aos::configuration::ReadConfig(kConfigPath)),
+      event_loop_factory_(&config_.message()),
+      event_loop_(event_loop_factory_.MakeEventLoop("plotter")),
+      plot_sender_(event_loop_->MakeSender<Plot>("/analysis")),
+      web_proxy_(event_loop_.get(), -1),
+      builder_(plot_sender_.MakeBuilder()) {
+  web_proxy_.SetDataPath(kDataPath);
+  event_loop_->SkipTimingReport();
+  color_wheel_.push_back(Color(1, 0, 0));
+  color_wheel_.push_back(Color(0, 1, 0));
+  color_wheel_.push_back(Color(0, 0, 1));
+  color_wheel_.push_back(Color(1, 1, 0));
+  color_wheel_.push_back(Color(0, 1, 1));
+  color_wheel_.push_back(Color(1, 0, 1));
+}
+
+void Plotter::Spin() { event_loop_factory_.Run(); }
+
+void Plotter::Title(std::string_view title) {
+  title_ = builder_.fbb()->CreateString(title);
+}
+
+void Plotter::AddFigure(std::string_view title, double width, double height) {
+  MaybeFinishFigure();
+
+  if (!title.empty()) {
+    figure_title_ = builder_.fbb()->CreateString(title);
+  }
+
+  // For positioning, just stack figures vertically.
+  auto position_builder = builder_.MakeBuilder<Position>();
+  position_builder.add_top(next_top_);
+  position_builder.add_left(0);
+  position_builder.add_width(width);
+  position_builder.add_height(height);
+  position_ = position_builder.Finish();
+
+  next_top_ += height;
+}
+
+void Plotter::XLabel(std::string_view label) {
+  xlabel_ = builder_.fbb()->CreateString(label);
+}
+
+void Plotter::YLabel(std::string_view label) {
+  ylabel_ = builder_.fbb()->CreateString(label);
+}
+
+void Plotter::AddLine(const std::vector<double> &x,
+                      const std::vector<double> &y, std::string_view label) {
+  CHECK_EQ(x.size(), y.size());
+  CHECK(!position_.IsNull())
+      << "You must call AddFigure() before calling AddLine().";
+
+  flatbuffers::Offset<flatbuffers::String> label_offset;
+  if (!label.empty()) {
+    label_offset = builder_.fbb()->CreateString(label);
+  }
+
+  std::vector<Point> points;
+  for (size_t ii = 0; ii < x.size(); ++ii) {
+    points.emplace_back(x[ii], y[ii]);
+  }
+  const flatbuffers::Offset<flatbuffers::Vector<const Point*>>
+      points_offset = builder_.fbb()->CreateVectorOfStructs(points);
+
+  const Color *color = &color_wheel_.at(color_wheel_position_);
+  color_wheel_position_ = (color_wheel_position_ + 1) % color_wheel_.size();
+
+  auto line_builder = builder_.MakeBuilder<Line>();
+  line_builder.add_label(label_offset);
+  line_builder.add_points(points_offset);
+  line_builder.add_color(color);
+  lines_.push_back(line_builder.Finish());
+}
+
+void Plotter::MaybeFinishFigure() {
+  if (!lines_.empty()) {
+    const flatbuffers::Offset<flatbuffers::Vector<flatbuffers::Offset<Line>>>
+        lines_offset = builder_.fbb()->CreateVector(lines_);
+    auto figure_builder = builder_.MakeBuilder<Figure>();
+    figure_builder.add_title(figure_title_);
+    figure_builder.add_position(position_);
+    figure_builder.add_lines(lines_offset);
+    figure_builder.add_xlabel(xlabel_);
+    figure_builder.add_share_x_axis(share_x_axis_);
+    figure_builder.add_ylabel(ylabel_);
+    figures_.push_back(figure_builder.Finish());
+  }
+  lines_.clear();
+  figure_title_.o = 0;
+  xlabel_.o = 0;
+  ylabel_.o = 0;
+  position_.o = 0;
+  share_x_axis_ = false;
+  color_wheel_position_ = 0;
+}
+
+void Plotter::Publish() {
+  MaybeFinishFigure();
+  const flatbuffers::Offset<flatbuffers::Vector<flatbuffers::Offset<Figure>>>
+      figures_offset = builder_.fbb()->CreateVector(figures_);
+
+  auto plot_builder = builder_.MakeBuilder<Plot>();
+  plot_builder.add_title(title_);
+  plot_builder.add_figures(figures_offset);
+
+  builder_.Send(plot_builder.Finish());
+
+  builder_ = plot_sender_.MakeBuilder();
+
+  title_.o = 0;
+  figures_.clear();
+  next_top_ = 0;
+}
+
+}  // namespace analysis
+}  // namespace frc971