Refactor BiergartenDataGenerator to use dependency injection container

pipeline/src/services/wikipedia/fetch_extract.cpp

@@ -0,0 +1,51 @@
+/**
+ * @file wikipedia/fetch_extract.cpp
+ * @brief WikipediaService::FetchExtract() implementation.
+ */
+
+#include <spdlog/spdlog.h>
+
+#include <boost/json.hpp>
+#include <string>
+#include <string_view>
+
+#include "services/wikipedia_service.h"
+
+auto WikipediaService::FetchExtract(std::string_view query) const
+    -> std::string {
+   const std::string encoded = client_->UrlEncode(std::string(query));
+   const std::string url =
+       "https://en.wikipedia.org/w/api.php?action=query&titles=" + encoded +
+       "&prop=extracts&explaintext=1&format=json";
+
+   const std::string body = client_->Get(url);
+
+   boost::system::error_code ec;
+   boost::json::value doc = boost::json::parse(body, ec);
+
+   if (!ec && doc.is_object()) {
+      try {
+         auto& pages = doc.at("query").at("pages").get_object();
+         if (!pages.empty()) {
+            auto& page = pages.begin()->value().get_object();
+            if (page.contains("extract") && page.at("extract").is_string()) {
+               std::string extract(page.at("extract").as_string().c_str());
+               spdlog::debug("WikipediaService fetched {} chars for '{}'",
+                             extract.size(), query);
+               return extract;
+            }
+         }
+      } catch (const std::exception& e) {
+         spdlog::warn(
+             "WikipediaService: failed to parse response structure for '{}': "
+             "{}",
+             query, e.what());
+         return {};
+      }
+   } else if (ec) {
+      spdlog::warn("WikipediaService: JSON parse error for '{}': {}", query,
+                   ec.message());
+   }
+
+   return {};
+}