Add multithreaded logging infrastructure for preparation for future designs (#225)

* Update class diagrams

* Implement BoundedChannel and multithreaded logging infra

* Integrate logging channel system

* Update string concatenations to use std::format

* Add pretty print log

tooling/pipeline/includes/services/enrichment/wikipedia_service.h

@@ -12,13 +12,15 @@
 #include <unordered_map>
 
 #include "enrichment_service.h"
+#include "services/logging/logger.h"
 #include "web_client/web_client.h"
 
 /// @brief Provides Wikipedia summary lookups backed by cached raw extracts.
 class WikipediaEnrichmentService final : public IEnrichmentService {
  public:
   /// @brief Creates a new Wikipedia service with the provided web client.
-  explicit WikipediaEnrichmentService(std::unique_ptr<WebClient> client);
+  explicit WikipediaEnrichmentService(std::unique_ptr<WebClient> client,
+                                      std::shared_ptr<ILogger> logger);
 
   /// @brief Returns the Wikipedia-derived context for a location.
   [[nodiscard]] std::string GetLocationContext(const Location& loc) override;
@@ -26,6 +28,7 @@ class WikipediaEnrichmentService final : public IEnrichmentService {
  private:
   std::string FetchExtract(std::string_view query);
   std::unique_ptr<WebClient> client_;
+  std::shared_ptr<ILogger> logger_;
   /// @brief Canonical cache for raw Wikipedia query extracts.
   std::unordered_map<std::string, std::string> extract_cache_;
 };

tooling/pipeline/includes/services/logging/log_dispatcher.h

@@ -0,0 +1,53 @@
+/**
+ * @file services/logging/log_dispatcher.h
+ * @brief Dedicated log dispatcher for asynchronous pipeline logging.
+ *
+ * The dispatcher drains LogEntry values from a bounded channel and forwards
+ * them to spdlog on a dedicated thread.
+ */
+
+#ifndef BIERGARTEN_PIPELINE_INCLUDES_SERVICES_LOGGING_LOG_DISPATCHER_H_
+#define BIERGARTEN_PIPELINE_INCLUDES_SERVICES_LOGGING_LOG_DISPATCHER_H_
+
+#include <spdlog/spdlog.h>
+
+#include "concurrency/bounded_channel.h"
+#include "services/logging/log_entry.h"
+
+/**
+ * @class LogDispatcher
+ * @brief Consumes log entries from a channel and forwards them to spdlog.
+ *
+ * Non-copyable and non-movable. Intended to run on its own dedicated thread
+ * and exit once the channel has been closed and drained.
+ */
+class LogDispatcher {
+ public:
+  /**
+   * @brief Construct a log dispatcher.
+   *
+   * @param channel Reference to the bounded channel used for log retrieval.
+   */
+  explicit LogDispatcher(BoundedChannel<LogEntry>& channel);
+
+  LogDispatcher(const LogDispatcher&) = delete;
+  LogDispatcher& operator=(const LogDispatcher&) = delete;
+  LogDispatcher(LogDispatcher&&) = delete;
+  LogDispatcher& operator=(LogDispatcher&&) = delete;
+  ~LogDispatcher() = default;
+
+  /**
+   * @brief Drain the channel and forward entries to spdlog.
+   *
+   * Intended to be called once on a dedicated thread. The loop returns after
+   * the channel has been closed and all queued entries have been processed.
+   */
+  void Run();
+
+ private:
+  BoundedChannel<LogEntry>& channel_;
+
+  static spdlog::level::level_enum ToSpdlogLevel(LogLevel level);
+};
+
+#endif  // BIERGARTEN_PIPELINE_INCLUDES_SERVICES_LOGGING_LOG_DISPATCHER_H_

tooling/pipeline/includes/services/logging/log_entry.h

@@ -0,0 +1,88 @@
+/**
+ * @file services/logging/log_entry.h
+ * @brief Structured log record shared by the pipeline logging infra.
+ *
+ * LogEntry is a lightweight value type that can be passed safely between the
+ * logging producer and dispatcher through BoundedChannel<LogEntry>.
+ */
+
+#ifndef BIERGARTEN_PIPELINE_INCLUDES_SERVICES_LOGGING_LOG_ENTRY_H_
+#define BIERGARTEN_PIPELINE_INCLUDES_SERVICES_LOGGING_LOG_ENTRY_H_
+
+#include <chrono>
+#include <source_location>
+#include <string>
+#include <thread>
+#include <vector>
+
+/**
+ * @enum LogLevel
+ * @brief Severity levels supported by the logging infra.
+ */
+enum class LogLevel {
+  Debug,  ///< Development/debugging information.
+  Info,   ///< General informational messages.
+  Warn,   ///< Warning conditions.
+  Error,  ///< Error conditions.
+};
+
+/**
+ * @enum PipelinePhase
+ * @brief Pipeline execution phases used to tag log records.
+ *
+ * The phase tag makes it easier to correlate log output with the part of the
+ * pipeline that emitted it.
+ */
+enum class PipelinePhase {
+  Startup,                   ///< Initialization and validation.
+  UserGeneration,            ///< User profile generation.
+  BreweryAndBeerGeneration,  ///< Brewery and beer data generation.
+  CheckinGeneration,         ///< Checkin (visit) record generation.
+  RatingGeneration,          ///< Rating and review generation.
+  FollowGeneration,          ///< Follow relationship generation.
+  Teardown,                  ///< Finalization and cleanup.
+};
+
+/**
+ * @struct LogDTO
+ * @brief User-provided subset of log fields. Used to capture call-site info transparently.
+ */
+struct LogDTO {
+  LogLevel level;
+  PipelinePhase phase;
+  std::string message;
+};
+
+/**
+ * @struct LogEntry
+ * @brief Single structured log event.
+ *
+ * All fields are value types, which keeps transfer across the bounded channel
+ * simple and avoids shared ownership.
+ *
+ * NOTE: timestamp, thread_id, and origin must be populated by ILogger::Log()
+ * before the entry is dispatched.
+ */
+struct LogEntry {
+  /// @brief Timestamp when the entry was created.
+  std::chrono::system_clock::time_point timestamp{};
+
+  /// @brief Source location where the log call was made.
+  std::source_location origin{};
+
+  /// @brief Thread responsible for emitting the log.
+  std::thread::id thread_id{};
+
+
+  /// @brief Severity level of this entry.
+  LogLevel level;
+
+  /// @brief Pipeline phase associated with the entry.
+  PipelinePhase phase;
+
+  /// @brief Log message text.
+  std::string message;
+
+};
+
+#endif  // BIERGARTEN_PIPELINE_INCLUDES_SERVICES_LOGGING_LOG_ENTRY_H_

tooling/pipeline/includes/services/logging/log_producer.h

@@ -0,0 +1,53 @@
+/**
+ * @file services/logging/log_producer.h
+ * @brief Channel-backed log producer for asynchronous pipeline logging.
+ *
+ * The producer captures log records from application code and forwards them to
+ * a bounded channel for later processing by the dispatcher.
+ */
+
+#ifndef BIERGARTEN_PIPELINE_INCLUDES_SERVICES_LOGGING_CHANNEL_LOGGER_H_
+#define BIERGARTEN_PIPELINE_INCLUDES_SERVICES_LOGGING_CHANNEL_LOGGER_H_
+
+#include <string_view>
+
+#include "concurrency/bounded_channel.h"
+#include "services/logging/log_entry.h"
+#include "services/logging/logger.h"
+
+/**
+ * @class LogProducer
+ * @brief ILogger implementation that forwards entries to a bounded channel.
+ *
+ * Non-copyable and non-movable. The channel reference is non-owning and must
+ * remain valid for the lifetime of the producer.
+ */
+class LogProducer final : public ILogger {
+ public:
+  /**
+   * @brief Construct a channel-backed producer.
+   *
+   * @param channel Reference to the bounded channel used for log transfer.
+   */
+  explicit LogProducer(BoundedChannel<LogEntry>& channel);
+
+  LogProducer(const LogProducer&) = delete;
+  LogProducer& operator=(const LogProducer&) = delete;
+  LogProducer(LogProducer&&) = delete;
+  LogProducer& operator=(LogProducer&&) = delete;
+
+  ~LogProducer() override = default;
+
+  /**
+   * @brief Queue a log message for asynchronous processing.
+   *
+   * Blocks while the channel applies backpressure. This blocking behavior
+   * under heavy load is an accepted trade-off for simplicity.
+   */
+  void DoLog(LogEntry log_entry) override;
+
+ private:
+  BoundedChannel<LogEntry>& channel_;
+};
+
+#endif  // BIERGARTEN_PIPELINE_INCLUDES_SERVICES_LOGGING_CHANNEL_LOGGER_H_

tooling/pipeline/includes/services/logging/logger.h

@@ -0,0 +1,64 @@
+/**
+ * @file services/logging/logger.h
+ * @brief Abstract logging interface used by pipeline components.
+ *
+ * The interface keeps application code independent from the concrete logging
+ * transport, buffering, and formatting implementation.
+ */
+
+#ifndef BIERGARTEN_PIPELINE_INCLUDES_SERVICES_LOGGING_LOGGER_H_
+#define BIERGARTEN_PIPELINE_INCLUDES_SERVICES_LOGGING_LOGGER_H_
+
+#include <source_location>
+#include <string>
+#include <utility>
+
+#include "services/logging/log_entry.h"
+
+/**
+ * @class ILogger
+ * @brief Minimal interface for submitting structured log messages.
+ *
+ * Implementations are non-copyable and non-movable. They are typically owned
+ * by the composition root and injected into services that emit diagnostics.
+ */
+class ILogger {
+ public:
+  ILogger() = default;
+  ILogger(const ILogger&) = delete;
+  ILogger& operator=(const ILogger&) = delete;
+  ILogger(ILogger&&) = delete;
+  ILogger& operator=(ILogger&&) = delete;
+  virtual ~ILogger() = default;
+
+  /**
+   * @brief Submit a log message to the logging subsystem.
+   *
+   * @param payload User-provided log data (level, phase, message).
+   * @param origin Auto-captured source location of the call site.
+   */
+  void Log(LogDTO payload,
+           std::source_location origin = std::source_location::current(),
+           std::chrono::system_clock::time_point timestamp = std::chrono::system_clock::now(),
+           std::thread::id thread_id = std::this_thread::get_id()) {
+    LogEntry entry;
+    entry.timestamp = timestamp;
+    entry.thread_id = thread_id;
+    entry.level = payload.level;
+    entry.phase = payload.phase;
+    entry.message = std::move(payload.message);
+    entry.origin = origin;
+    DoLog(std::move(entry));
+  }
+
+ protected:
+  /**
+   * @brief Underlying implementation to transport the log entry.
+   *
+   * Implementations must be thread-safe as DoLog can be called concurrently
+   * from multiple worker threads.
+   */
+  virtual void DoLog(LogEntry log_entry) = 0;
+};
+
+#endif  // BIERGARTEN_PIPELINE_INCLUDES_SERVICES_LOGGING_LOGGER_H_

tooling/pipeline/includes/services/prompting/prompt_directory.h

@@ -12,11 +12,14 @@
  */
 
 #include <filesystem>
+#include <memory>
 #include <stdexcept>
 #include <string>
 #include <string_view>
 #include <unordered_map>
 
+#include "services/logging/logger.h"
+
 /**
  * @brief Interface for loading named prompt files.
  */
@@ -56,6 +59,8 @@ class PromptDirectory final : public IPromptDirectory {
    *         directory.
    */
   explicit PromptDirectory(const std::filesystem::path& prompt_dir);
+  PromptDirectory(const std::filesystem::path& prompt_dir,
+                  std::shared_ptr<ILogger> logger);
 
   /**
    * @brief Loads the prompt for @p key, caching the result.
@@ -70,6 +75,7 @@ class PromptDirectory final : public IPromptDirectory {
 
  private:
   std::filesystem::path prompt_dir_;
+  std::shared_ptr<ILogger> logger_;
   std::unordered_map<std::string, std::string> cache_;
 };