Implement Web Push API Go library with VAPID support and pluggable storage

Co-authored-by: imjasonh <210737+imjasonh@users.noreply.github.com>

storage/storage.go

@@ -0,0 +1,46 @@
+// Package storage provides interfaces and implementations for storing
+// web push subscriptions.
+package storage
+
+import (
+	"context"
+	"time"
+
+	"github.com/imjasonh/webpush"
+)
+
+// Record represents a stored subscription with metadata.
+type Record struct {
+	ID           string                `json:"id"`
+	UserID       string                `json:"user_id,omitempty"`
+	Subscription *webpush.Subscription `json:"subscription"`
+	CreatedAt    time.Time             `json:"created_at"`
+	UpdatedAt    time.Time             `json:"updated_at"`
+}
+
+// Storage defines the interface for storing web push subscriptions.
+type Storage interface {
+	// Save stores or updates a subscription.
+	Save(ctx context.Context, record *Record) error
+
+	// Get retrieves a subscription by ID.
+	Get(ctx context.Context, id string) (*Record, error)
+
+	// GetByEndpoint retrieves a subscription by its endpoint URL.
+	GetByEndpoint(ctx context.Context, endpoint string) (*Record, error)
+
+	// GetByUserID retrieves all subscriptions for a user.
+	GetByUserID(ctx context.Context, userID string) ([]*Record, error)
+
+	// Delete removes a subscription by ID.
+	Delete(ctx context.Context, id string) error
+
+	// DeleteByEndpoint removes a subscription by its endpoint URL.
+	DeleteByEndpoint(ctx context.Context, endpoint string) error
+
+	// List returns all subscriptions with pagination.
+	List(ctx context.Context, limit, offset int) ([]*Record, error)
+
+	// Close closes the storage connection.
+	Close() error
+}