refactor: extract base exporter, add sentinel errors, document unused fields

internal/services/app.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"fmt"
 
+	"github.com/kjanat/articulate-parser/internal/apperrors"
 	"github.com/kjanat/articulate-parser/internal/interfaces"
 	"github.com/kjanat/articulate-parser/internal/models"
 )
@@ -37,7 +38,7 @@ func NewApp(parser interfaces.CourseParser, exporterFactory interfaces.ExporterF
 func (a *App) ProcessCourseFromFile(ctx context.Context, filePath, format, outputPath string) error {
 	// Check for cancellation before loading
 	if err := ctx.Err(); err != nil {
-		return fmt.Errorf("operation canceled: %w", err)
+		return fmt.Errorf("%w: %w", apperrors.ErrOperationCanceled, err)
 	}
 
 	course, err := a.parser.LoadCourseFromFile(filePath)
@@ -68,7 +69,7 @@ func (a *App) ProcessCourseFromURI(ctx context.Context, uri, format, outputPath
 func (a *App) exportCourse(ctx context.Context, course *models.Course, format, outputPath string) error {
 	// Check for cancellation before export
 	if err := ctx.Err(); err != nil {
-		return fmt.Errorf("operation canceled: %w", err)
+		return fmt.Errorf("%w: %w", apperrors.ErrOperationCanceled, err)
 	}
 
 	exporter, err := a.exporterFactory.CreateExporter(format)

internal/services/parser.go

@@ -10,6 +10,7 @@ import (
 	"os"
 	"regexp"
 
+	"github.com/kjanat/articulate-parser/internal/apperrors"
 	"github.com/kjanat/articulate-parser/internal/config"
 	"github.com/kjanat/articulate-parser/internal/interfaces"
 	"github.com/kjanat/articulate-parser/internal/models"
@@ -127,17 +128,17 @@ func (p *ArticulateParser) extractShareID(uri string) (string, error) {
 	// Parse the URL to validate the domain
 	parsedURL, err := url.Parse(uri)
 	if err != nil {
-		return "", fmt.Errorf("invalid URI: %s", uri)
+		return "", fmt.Errorf("%w: %s", apperrors.ErrInvalidURI, uri)
 	}
 
 	// Validate that it's an Articulate Rise domain
 	if parsedURL.Host != riseHost {
-		return "", fmt.Errorf("invalid domain for Articulate Rise URI: %s", parsedURL.Host)
+		return "", fmt.Errorf("%w: %s", apperrors.ErrInvalidDomain, parsedURL.Host)
 	}
 
 	matches := shareIDRegex.FindStringSubmatch(uri)
 	if len(matches) < 2 {
-		return "", fmt.Errorf("could not extract share ID from URI: %s", uri)
+		return "", fmt.Errorf("%w: %s", apperrors.ErrNoShareID, uri)
 	}
 	return matches[1], nil
 }