cv-site/doc/23-DATA-CACHE.md

# Cache Package

## Overview

The `cache` package provides application-level caching for CV and UI data, eliminating per-request file I/O by loading all data once at application startup. This improves performance and reduces latency for all handler operations.

**Key Benefits:**
- Single load at startup, fast reads during request handling
- Thread-safe concurrent access using `sync.RWMutex`
- Language-keyed access ("en", "es")
- Fast-fail strategy: fails at startup if any language data cannot be loaded

## Architecture

### DataCache Structure

```go
type DataCache struct {
    cv map[string]*cvmodel.CV    // CV data indexed by language
    ui map[string]*uimodel.UI    // UI data indexed by language
    mu sync.RWMutex              // Protects concurrent reads
}
```

The cache stores pointer references to CV and UI models, loaded from YAML files. Since reads are frequent and writes never occur, `sync.RWMutex` provides efficient concurrent access.

## Usage

### Initialization

The cache is created once at application startup in `main.go`:

```go
// Initialize data cache (load CV and UI data once at startup)
dataCache, err := cache.New([]string{"en", "es"})
if err != nil {
    log.Fatalf("Failed to initialize data cache: %v", err)
}
```

This loads CV and UI data for English and Spanish. If any language fails to load, the entire startup fails—catch errors early rather than on first request.

### Handler Integration

The cache is injected into handlers via constructor:

```go
cvHandler := handlers.NewCVHandler(templateMgr, serverAddr, emailService, dataCache)
```

Handlers access cached data using language-specific getters:

```go
func (h *CVHandler) renderPage(w http.ResponseWriter, r *http.Request) {
    lang := r.URL.Query().Get("lang")
    cv := h.dataCache.GetCV(lang)
    ui := h.dataCache.GetUI(lang)

    // Use cv and ui data for rendering...
}
```

## API Reference

### `New(languages []string) (*DataCache, error)`

Creates and initializes a new cache with data for the specified languages.

**Parameters:**
- `languages`: List of language codes to load (e.g., `[]string{"en", "es"}`)

**Returns:**
- `*DataCache`: Initialized cache instance
- `error`: Non-nil if any language fails to load

**Behavior:**
- Returns `nil` and error if any language's CV or UI data fails to load
- Empty language list creates empty cache (no error)
- Fails at startup rather than deferring errors to request time

**Example:**
```go
cache, err := cache.New([]string{"en", "es"})
if err != nil {
    log.Fatalf("Failed to initialize cache: %v", err)
}
```

### `GetCV(lang string) *cvmodel.CV`

Retrieves cached CV data for the specified language.

**Parameters:**
- `lang`: Language code (e.g., "en", "es")

**Returns:**
- `*cvmodel.CV`: Pointer to CV data, or `nil` if language not found
- **Note:** Callers must check for `nil` before dereferencing

**Thread Safety:** Safe for concurrent reads

**Example:**
```go
cv := cache.GetCV("en")
if cv == nil {
    // Handle missing language
    return fmt.Errorf("CV not available for language: en")
}
// Use cv...
```

### `GetUI(lang string) *uimodel.UI`

Retrieves cached UI data for the specified language.

**Parameters:**
- `lang`: Language code (e.g., "en", "es")

**Returns:**
- `*uimodel.UI`: Pointer to UI data, or `nil` if language not found

**Thread Safety:** Safe for concurrent reads

**Example:**
```go
ui := cache.GetUI("es")
if ui != nil {
    title := ui.Navigation.Title
}
```

### `Languages() []string`

Returns all language codes currently cached.

**Returns:**
- `[]string`: Slice of available language codes (order not guaranteed)

**Thread Safety:** Safe for concurrent reads

**Example:**
```go
langs := cache.Languages()
for _, lang := range langs {
    cv := cache.GetCV(lang)
    // Process CV for each language...
}
```

## Mutating Cached Data

### Important: Deep Copies for Mutable Fields

Since cache stores pointer references, handlers that modify CV slices must create deep copies before modification:

```go
// In handlers that modify experience/projects:
func prepareTemplateData(cv *cvmodel.CV) *cvmodel.CV {
    // Create copies of mutable slices
    copy := &cvmodel.CV{
        Personal:      cv.Personal,
        Experience:    append([]cvmodel.Experience{}, cv.Experience...), // Deep copy
        Projects:      append([]cvmodel.Project{}, cv.Projects...),      // Deep copy
        Education:     cv.Education,
        Skills:        cv.Skills,
    }

    // Now safe to modify copy.Experience and copy.Projects
    for i := range copy.Experience {
        copy.Experience[i].YearsOfExperience = calculateYears()
    }

    return copy
}
```

This prevents handlers from accidentally mutating cached data during request processing.

## Supported Languages

Currently configured for:
- `"en"` - English
- `"es"` - Spanish

To add a new language, update `main.go`:

```go
dataCache, err := cache.New([]string{"en", "es", "fr"})  // Add "fr"
```

Ensure YAML data files exist in the data directory for the new language, or startup will fail.

## Error Handling

### Startup Failures

The fast-fail strategy ensures all data issues are caught before the server starts:

```go
dataCache, err := cache.New([]string{"en", "es"})
if err != nil {
    // Example error messages:
    // "load CV for 'fr': file not found"
    // "load UI for 'es': invalid YAML"
    log.Fatalf("Failed to initialize data cache: %v", err)
}
```

### Runtime Handling

Handlers should gracefully handle missing languages:

```go
cv := cache.GetCV(lang)
if cv == nil {
    http.Error(w, "Language not supported", http.StatusNotFound)
    return
}
```

## Performance Considerations

### I/O Efficiency
- **Single Load:** CV and UI YAML files are parsed once at startup
- **No Per-Request I/O:** Handler requests never touch disk
- **Memory Trade-off:** Stores decoded objects in memory

### Concurrency
- **RWMutex:** Optimized for high read throughput, zero writes
- **No Contention:** 100+ concurrent reads verified in tests
- **Nil Returns:** Fast path for missing languages (map lookup only)

### Memory Usage
- Minimal overhead: Two maps + one mutex
- Proportional to number of languages loaded
- Shared object references (no duplication per request)

## Testing

Run the comprehensive test suite:

```bash
go test ./internal/cache -v
```

Test coverage includes:
- Cache initialization with valid/invalid languages
- CV and UI data retrieval
- Thread safety with concurrent reads
- Data integrity verification
- Empty language list handling

## Dependencies

- `internal/models/cv` - CV data model
- `internal/models/ui` - UI data model
- Go standard library: `sync`

## Related Files

- **`internal/cache/data_cache.go`** - Cache implementation
- **`internal/cache/data_cache_test.go`** - Comprehensive test suite
- **`main.go`** - Cache initialization at startup
- **`internal/handlers/cv.go`** - Handler injection point