This commit addresses all the high-priority tasks outlined in the TASKS.md file, significantly improving the application's observability, completing key features, and refactoring critical parts of the codebase.
### Observability
- **Centralized Logging:** Implemented a new structured, context-aware logging system using `zerolog`. A new logging middleware injects request-specific information (request ID, user ID, trace ID) into the logger, and all application logging has been refactored to use this new system.
- **Prometheus Metrics:** Added Prometheus metrics for database query performance by creating a GORM plugin that automatically records query latency and totals.
- **OpenTelemetry Tracing:** Fully instrumented all application services in `internal/app` and data repositories in `internal/data/sql` with OpenTelemetry tracing, providing deep visibility into application performance.
### Features
- **Analytics:** Implemented like, comment, and bookmark counting. The respective command handlers now call the analytics service to increment counters when these actions are performed.
- **Enrichment Tool:** Built a new, extensible `enrich` command-line tool to fetch data from external sources. The initial implementation enriches author data using the Open Library API.
### Refactoring & Fixes
- **Decoupled Testing:** Refactored the testing utilities in `internal/testutil` to be database-agnostic, promoting the use of mock-based unit tests and improving test speed and reliability.
- **Build Fixes:** Resolved numerous build errors, including a critical import cycle between the logging, observability, and authentication packages.
- **Search Service:** Fixed the search service integration by implementing the `GetWorkContent` method in the localization service, allowing the search indexer to correctly fetch and index work content.
This commit introduces a comprehensive observability stack to the application, addressing a key objective from the TODO list.
The following features have been implemented:
- **Centralized Logging:** Replaced the existing custom logger with `zerolog` for structured, leveled, and performant logging. The logger is configured to output human-friendly console logs in development and JSON logs in production.
- **Distributed Tracing:** Integrated OpenTelemetry to provide distributed tracing capabilities. A new middleware has been added to create spans for all incoming HTTP requests, and the trace context is propagated.
- **Prometheus Metrics:** Added Prometheus metrics to monitor HTTP request latency and total request counts. A new `/metrics` endpoint is exposed on port 9090 to serve these metrics.
- **Request ID:** Implemented a middleware to add a unique request ID to every incoming request and response, improving traceability.
The new observability components are encapsulated in the `internal/observability` package, and the existing `internal/platform/log` package has been refactored to be a backward-compatible wrapper around the new logger.
The main application entry point (`cmd/api/main.go`) has been updated to initialize and gracefully shut down the new observability components.
