feat: Phase 1 - Core API server with authentication

- Added database schema for users, api_keys, sync_state, change_log, and sync_config
- Implemented API key generation and validation with bcrypt hashing
- Created Chi-based REST API server with endpoints for:
  - Task CRUD operations (create, read, update, delete)
  - Task actions (complete, start, stop)
  - Tag management (list, add, remove)
  - Projects listing
  - Health check endpoint
- Added middleware for authentication and CORS
- Implemented change log tracking with triggers (key:value format)
- Added configurable change log retention (default 30 days)
- Created server CLI commands (opal server start, opal server keygen)
- Dependencies added: golang.org/x/crypto/bcrypt, github.com/go-chi/chi/v5

opal-task/internal/api/handlers/sync.go

@@ -0,0 +1,167 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"git.jnss.me/joakim/opal/internal/engine"
+)
+
+// GetChangesRequest represents the request for getting changes
+type GetChangesRequest struct {
+	Since    int64  `json:"since"`
+	ClientID string `json:"client_id"`
+}
+
+// GetChanges returns tasks that have changed since a given timestamp
+func GetChanges(w http.ResponseWriter, r *http.Request) {
+	var req GetChangesRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		errorResponse(w, http.StatusBadRequest, "invalid request body")
+		return
+	}
+
+	// Query change_log for entries since timestamp
+	db := engine.GetDB()
+	if db == nil {
+		errorResponse(w, http.StatusInternalServerError, "database not initialized")
+		return
+	}
+
+	rows, err := db.Query(`
+		SELECT id, task_uuid, change_type, changed_at, data
+		FROM change_log
+		WHERE changed_at > ?
+		ORDER BY id ASC
+	`, req.Since)
+	if err != nil {
+		errorResponse(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	defer rows.Close()
+
+	type Change struct {
+		ID         int64  `json:"id"`
+		TaskUUID   string `json:"task_uuid"`
+		ChangeType string `json:"change_type"`
+		ChangedAt  int64  `json:"changed_at"`
+		Data       string `json:"data"`
+	}
+
+	var changes []Change
+	for rows.Next() {
+		var change Change
+		if err := rows.Scan(&change.ID, &change.TaskUUID, &change.ChangeType, &change.ChangedAt, &change.Data); err != nil {
+			errorResponse(w, http.StatusInternalServerError, err.Error())
+			return
+		}
+		changes = append(changes, change)
+	}
+
+	// Update sync_state for client
+	_, _ = db.Exec(`
+		INSERT OR REPLACE INTO sync_state (client_id, last_sync, last_change_id)
+		VALUES (?, ?, ?)
+	`, req.ClientID, engine.GetCurrentTimestamp(), 0)
+
+	jsonResponse(w, http.StatusOK, changes)
+}
+
+// PushChangesRequest represents the request for pushing changes
+type PushChangesRequest struct {
+	Tasks    []json.RawMessage `json:"tasks"`
+	ClientID string            `json:"client_id"`
+}
+
+// PushChanges accepts task changes from clients
+func PushChanges(w http.ResponseWriter, r *http.Request) {
+	var req PushChangesRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		errorResponse(w, http.StatusBadRequest, "invalid request body")
+		return
+	}
+
+	db := engine.GetDB()
+	if db == nil {
+		errorResponse(w, http.StatusInternalServerError, "database not initialized")
+		return
+	}
+
+	// For each task, parse and apply (last-write-wins for now)
+	var processed int
+	var conflicts int
+
+	for _, taskData := range req.Tasks {
+		var task engine.Task
+		if err := json.Unmarshal(taskData, &task); err != nil {
+			continue
+		}
+
+		// Check if task exists
+		existing, err := engine.GetTask(task.UUID)
+		if err != nil {
+			// Task doesn't exist - create it
+			if err := task.Save(); err != nil {
+				continue
+			}
+			// Add tags
+			for _, tag := range task.Tags {
+				_ = task.AddTag(tag)
+			}
+			processed++
+			continue
+		}
+
+		// Task exists - check timestamps for conflicts
+		if existing.Modified.Unix() > task.Modified.Unix() {
+			// Server version is newer - conflict (but we'll apply last-write-wins)
+			conflicts++
+		}
+
+		// Apply changes (last-write-wins)
+		task.ID = existing.ID // Preserve database ID
+		if err := task.Save(); err != nil {
+			continue
+		}
+
+		// Sync tags
+		existingTags := make(map[string]bool)
+		for _, tag := range existing.Tags {
+			existingTags[tag] = true
+		}
+
+		// Add new tags
+		for _, tag := range task.Tags {
+			if !existingTags[tag] {
+				_ = task.AddTag(tag)
+			}
+		}
+
+		// Remove missing tags
+		for _, tag := range existing.Tags {
+			found := false
+			for _, newTag := range task.Tags {
+				if tag == newTag {
+					found = true
+					break
+				}
+			}
+			if !found {
+				_ = task.RemoveTag(tag)
+			}
+		}
+
+		processed++
+	}
+
+	// Update sync_state
+	_, _ = db.Exec(`
+		INSERT OR REPLACE INTO sync_state (client_id, last_sync, last_change_id)
+		VALUES (?, ?, ?)
+	`, req.ClientID, engine.GetCurrentTimestamp(), 0)
+
+	jsonResponse(w, http.StatusOK, map[string]interface{}{
+		"processed": processed,
+		"conflicts": conflicts,
+	})
+}