weaseldb/src/http_handler.hpp

#pragma once

#include <atomic>
#include <memory>
#include <string_view>
#include <thread>
#include <unordered_set>

#include <llhttp.h>

#include "arena_allocator.hpp"
#include "connection.hpp"
#include "connection_handler.hpp"
#include "loop_iterations.hpp"
#include "perfetto_categories.hpp"
#include "pipeline_entry.hpp"
#include "server.hpp"
#include "thread_pipeline.hpp"

// Forward declarations
struct CommitRequest;
struct JsonCommitRequestParser;

/**
 * HTTP routes supported by WeaselDB server.
 * Using enum for efficient switch-based routing.
 */
enum class HttpRoute {
  GET_version,
  POST_commit,
  GET_subscribe,
  GET_status,
  PUT_retention,
  GET_retention,
  DELETE_retention,
  GET_metrics,
  GET_ok,
  NotFound
};

/**
 * HTTP connection state stored in Connection::user_data.
 * Manages llhttp parser state and request data.
 */
struct HttpConnectionState {
  llhttp_t parser;
  llhttp_settings_t settings;

  // Current request data (arena-allocated)
  std::string_view method;
  std::string_view url;

  // Parse state
  bool headers_complete = false;
  bool message_complete = false;
  bool connection_close = false; // Client requested connection close
  HttpRoute route = HttpRoute::NotFound;

  // Status request data
  std::string_view
      status_request_id; // Request ID extracted from /v1/status/{id} URL

  // Header accumulation buffers (arena-allocated)
  using ArenaString =
      std::basic_string<char, std::char_traits<char>, ArenaStlAllocator<char>>;
  ArenaString current_header_field_buf;
  ArenaString current_header_value_buf;
  bool header_field_complete = false;
  int64_t http_request_id =
      0; // X-Request-Id header value (for tracing/logging)

  // Streaming parser for POST requests
  std::unique_ptr<JsonCommitRequestParser> commit_parser;
  std::unique_ptr<CommitRequest> commit_request;
  bool parsing_commit = false;
  bool basic_validation_passed =
      false; // Set to true if basic validation passes

  explicit HttpConnectionState(ArenaAllocator &arena);
};

/**
 * HTTP/1.1 server implementation using llhttp for parsing.
 * Supports the WeaselDB REST API endpoints with enum-based routing.
 */
struct HttpHandler : ConnectionHandler {
  HttpHandler()
      : banned_request_ids(
            ArenaStlAllocator<std::string_view>(&banned_request_arena)) {
    // Stage 0: Sequence assignment thread
    sequenceThread = std::thread{[this]() {
      pthread_setname_np(pthread_self(), "txn-sequence");
      for (;;) {
        auto guard = commitPipeline.acquire<0, 0>();
        if (process_sequence_batch(guard.batch)) {
          return; // Shutdown signal received
        }
      }
    }};

    // Stage 1: Precondition resolution thread
    resolveThread = std::thread{[this]() {
      pthread_setname_np(pthread_self(), "txn-resolve");
      for (;;) {
        auto guard = commitPipeline.acquire<1, 0>();
        if (process_resolve_batch(guard.batch)) {
          return; // Shutdown signal received
        }
      }
    }};

    // Stage 2: Transaction persistence thread
    persistThread = std::thread{[this]() {
      pthread_setname_np(pthread_self(), "txn-persist");
      for (;;) {
        auto guard = commitPipeline.acquire<2, 0>();
        if (process_persist_batch(guard.batch)) {
          return; // Shutdown signal received
        }
      }
    }};

    // Stage 3: Connection return to server thread
    releaseThread = std::thread{[this]() {
      pthread_setname_np(pthread_self(), "txn-release");
      for (;;) {
        auto guard = commitPipeline.acquire<3, 0>();
        if (process_release_batch(guard.batch)) {
          return; // Shutdown signal received
        }
      }
    }};
  }
  ~HttpHandler() {
    // Send single shutdown signal that flows through all pipeline stages
    {
      auto guard = commitPipeline.push(1, true);
      guard.batch[0] =
          ShutdownEntry{}; // Single ShutdownEntry flows through all stages
    }

    // Join all pipeline threads
    sequenceThread.join();
    resolveThread.join();
    persistThread.join();
    releaseThread.join();
  }

  void on_connection_established(Connection &conn) override;
  void on_connection_closed(Connection &conn) override;
  void on_data_arrived(std::string_view data,
                       std::unique_ptr<Connection> &conn_ptr) override;
  void on_write_buffer_drained(std::unique_ptr<Connection> &conn_ptr) override;
  void on_batch_complete(
      std::span<std::unique_ptr<Connection>> /*batch*/) override;

  // Route parsing (public for testing)
  static HttpRoute parseRoute(std::string_view method, std::string_view url);

  // llhttp callbacks (public for HttpConnectionState access)
  static int onUrl(llhttp_t *parser, const char *at, size_t length);
  static int onHeaderField(llhttp_t *parser, const char *at, size_t length);
  static int onHeaderFieldComplete(llhttp_t *parser);
  static int onHeaderValue(llhttp_t *parser, const char *at, size_t length);
  static int onHeaderValueComplete(llhttp_t *parser);
  static int onHeadersComplete(llhttp_t *parser);
  static int onBody(llhttp_t *parser, const char *at, size_t length);
  static int onMessageComplete(llhttp_t *parser);

private:
  static constexpr int lg_size = 16;

  // Pipeline state (sequence thread only)
  int64_t next_version = 1; // Next version to assign (sequence thread only)

  // Pipeline state (persist thread writes, I/O threads read)
  std::atomic<int64_t> committed_version{
      0}; // Highest committed version (persist thread writes, I/O threads read)

  // Arena for banned request IDs and related data structures (sequence thread
  // only)
  ArenaAllocator banned_request_arena;
  using BannedRequestIdSet =
      std::unordered_set<std::string_view, std::hash<std::string_view>,
                         std::equal_to<std::string_view>,
                         ArenaStlAllocator<std::string_view>>;
  BannedRequestIdSet banned_request_ids; // Request IDs that should not commit
                                         // (string_views into arena)

  // Main commit processing pipeline: sequence -> resolve -> persist -> release
  StaticThreadPipeline<PipelineEntry, WaitStrategy::WaitIfUpstreamIdle, 1, 1, 1,
                       1>
      commitPipeline{lg_size};

  // Pipeline stage threads
  std::thread sequenceThread;
  std::thread resolveThread;
  std::thread persistThread;
  std::thread releaseThread;

  // Pipeline stage processing methods (batch-based)
  using BatchType =
      StaticThreadPipeline<PipelineEntry, WaitStrategy::WaitIfUpstreamIdle, 1,
                           1, 1, 1>::Batch;
  bool process_sequence_batch(BatchType &batch);
  bool process_resolve_batch(BatchType &batch);
  bool process_persist_batch(BatchType &batch);
  bool process_release_batch(BatchType &batch);

  // Route handlers
  void handleGetVersion(Connection &conn, const HttpConnectionState &state);
  void handlePostCommit(Connection &conn, const HttpConnectionState &state);
  void handleGetSubscribe(Connection &conn, const HttpConnectionState &state);
  void handleGetStatus(Connection &conn, HttpConnectionState &state);
  void handlePutRetention(Connection &conn, const HttpConnectionState &state);
  void handleGetRetention(Connection &conn, const HttpConnectionState &state);
  void handleDeleteRetention(Connection &conn,
                             const HttpConnectionState &state);
  void handleGetMetrics(Connection &conn, const HttpConnectionState &state);
  void handleGetOk(Connection &conn, const HttpConnectionState &state);
  void handleNotFound(Connection &conn, const HttpConnectionState &state);

  // HTTP utilities
  static void sendResponse(Connection &conn, int status_code,
                           std::string_view content_type, std::string_view body,
                           bool close_connection = false);
  static void send_json_response(Connection &conn, int status_code,
                                 std::string_view json,
                                 bool close_connection = false);
  static void send_error_response(Connection &conn, int status_code,
                                  std::string_view message,
                                  bool close_connection = false);
};