Factor out jpeg list image dataset loading for use in calibration.

Change-Id: Ie546a9458699fd80cb4359c703b8cacc32e2e52a
diff --git a/aos/vision/image/image_dataset.cc b/aos/vision/image/image_dataset.cc
new file mode 100644
index 0000000..cd3ec46
--- /dev/null
+++ b/aos/vision/image/image_dataset.cc
@@ -0,0 +1,84 @@
+#include "aos/vision/image/image_dataset.h"
+
+#include <fstream>
+
+#include "aos/vision/image/image_types.h"
+
+namespace aos {
+namespace vision {
+
+namespace {
+std::string GetFileContents(const std::string &filename) {
+  std::ifstream in(filename, std::ios::in | std::ios::binary);
+  if (in) {
+    std::string contents;
+    in.seekg(0, std::ios::end);
+    contents.resize(in.tellg());
+    in.seekg(0, std::ios::beg);
+    in.read(&contents[0], contents.size());
+    in.close();
+    return (contents);
+  }
+  fprintf(stderr, "Could not read file: %s\n", filename.c_str());
+  exit(-1);
+}
+
+std::vector<std::string> Split(DataRef inp, char delim) {
+  size_t i = 0;
+  std::vector<size_t> pos;
+  while (i < inp.size()) {
+    i = inp.find(delim, i);
+    if (i == std::string::npos) break;
+    // fprintf(stderr, "k=%d, i=%d\n", k, (int)i);
+    pos.emplace_back(i);
+    i = i + 1;
+  }
+  std::vector<std::string> res;
+  res.reserve(pos.size() + 1);
+  i = 0;
+  for (auto p : pos) {
+    res.emplace_back(inp.substr(i, p - i).to_string());
+    i = p + 1;
+  }
+  res.emplace_back(inp.substr(i).to_string());
+  return res;
+}
+}  // namespace
+
+std::vector<DatasetFrame> LoadDataset(const std::string &jpeg_list_filename) {
+  std::vector<DatasetFrame> images;
+  auto contents = GetFileContents(jpeg_list_filename);
+
+  std::string basename;
+  auto it = jpeg_list_filename.find_last_of('/');
+  if (it != std::string::npos) {
+    basename = jpeg_list_filename.substr(0, it + 1);
+  }
+
+  for (const auto &jpeg_filename : Split(contents, '\n')) {
+    [&]() {
+      if (jpeg_filename.empty()) return;
+      for (std::size_t i = 0; i < jpeg_filename.size(); ++i) {
+        if (jpeg_filename[i] == '#') return;
+        if (jpeg_filename[i] != ' ') break;
+      }
+      bool is_jpeg = true;
+      size_t l = jpeg_filename.size();
+      if (l > 4 && jpeg_filename[l - 1] == 'v') {
+        is_jpeg = false;
+      }
+      if (jpeg_filename[0] == '/') {
+        images.emplace_back(
+            DatasetFrame{is_jpeg, GetFileContents(jpeg_filename)});
+      } else {
+        images.emplace_back(
+            DatasetFrame{is_jpeg, GetFileContents(basename + jpeg_filename)});
+      }
+    }();
+  }
+
+  return images;
+}
+
+}  // namespace vision
+}  // namespace aos