From f21ae2e502d89acb488232ae4b4f327a33639533 Mon Sep 17 00:00:00 2001
From: Nick Krichevsky <nick@ollien.com>
Date: Thu, 9 Sep 2021 23:19:09 -0400
Subject: [PATCH] Refactor categorization to use a callback instead of
 aggregating the results

This will prepare for taking user input, as we don't want to continue scanning  before we can find out if a user wants to back out
---
 cmd/categorize.go | 69 ++++++++++++++++++++++++++++++-----------------
 cmd/main.go       | 17 +++++++++---
 2 files changed, 58 insertions(+), 28 deletions(-)

diff --git a/cmd/categorize.go b/cmd/categorize.go
index ae3af4b..dd24d5a 100644
--- a/cmd/categorize.go
+++ b/cmd/categorize.go
@@ -16,16 +16,23 @@ type fileLocation struct {
 	location tv.Location
 }
 
+// categorizationResult is the result of an individual categorization; it's effectively what a return value would be
+// for a single operation, but it's returned through a callback
 type categorizationResult struct {
-	locations    []fileLocation
+	// the location of the categorized file.  This should be ignored if the error is non-nil, or "skipped" is true
+	location fileLocation
+	err      error
+}
+
+type categorizationStats struct {
 	filesScanned int
 	filesSkipped int
 }
 
 // Performs the categorization process for the given source (i.e. where the downloaded files are stored)
-// and library (i.e. where they will be sorted into). Errors that halt the program proceeding will be returned. Those
-// that do not will be printed to stderr.
-func categorizeFolder(sourceFolder, libraryFolder string) (categorizationResult, error) {
+// and library (i.e. where they will be sorted into). Errors that halt the program proceeding will be returned. Results
+// and non-fatal errors will be returned via resultCallback. If this callback returns false, categorization stops.
+func categorizeFolder(sourceFolder, libraryFolder string, resultCallback func(categorizationResult) bool) (categorizationStats, error) {
 	sourceFolderContents, err := getDirEntries(sourceFolder, func(entries []os.FileInfo) {
 		// Sort from newest to oldest
 		sort.Slice(entries, func(i, j int) bool {
@@ -37,40 +44,54 @@ func categorizeFolder(sourceFolder, libraryFolder string) (categorizationResult,
 	})
 
 	if err != nil {
-		return categorizationResult{}, fmt.Errorf("failed to read source folder: %w", err)
+		return categorizationStats{}, fmt.Errorf("failed to read source folder: %w", err)
 	}
 
 	categorizer, err := categorize.NewCategorizer(libraryFolder)
 	if err != nil {
-		return categorizationResult{}, fmt.Errorf("failed to make categorizer: %w", err)
+		return categorizationStats{}, fmt.Errorf("failed to make categorizer: %w", err)
 	}
 
-	locations := performCategorization(categorizer, sourceFolderContents)
-	return categorizationResult{
-		locations:    locations,
-		filesScanned: len(locations),
-		filesSkipped: len(sourceFolderContents) - len(locations),
-	}, nil
+	stats := categorizationStats{}
+	performCategorization(categorizer, sourceFolderContents, func(res categorizationResult) bool {
+		stats.filesScanned++
+		if errors.Is(err, match.ErrNoMatches) {
+			stats.filesSkipped++
+			return true
+		} else if res.err != nil {
+			stats.filesSkipped++
+			return true
+		}
+
+		return resultCallback(res)
+	})
+
+	return stats, nil
 }
 
 // performCategorization categorizes the given files through the given categorizer, converting them to a
-// slice of FileLocations, ordered as they were provided in sourceFolderContents.
-// When a file fails to be read, an error will be printed to stderr.
-func performCategorization(categorizer categorize.Categorizer, sourceFolderContents []string) []fileLocation {
-	locations := []fileLocation{}
+// slice of FileLocations, ordered as they were provided in sourceFolderContents.  Results and non-fatal errors will be
+// returned via resultCallback. If this callback returns false, categorization stops.
+func performCategorization(categorizer categorize.Categorizer, sourceFolderContents []string, resultCallback func(categorizationResult) bool) {
 	for _, entry := range sourceFolderContents {
 		location, err := categorizer.CategorizeFile(entry)
-		if errors.Is(err, match.ErrNoMatches) {
-			continue
-		} else if err != nil {
-			fmt.Fprintf(os.Stderr, "Failed to categorize '%s':\n\t%s\n", entry, err)
-			continue
+
+		var wrappedErr error
+		if err != nil {
+			wrappedErr = fmt.Errorf("failed to categorize '%s': %w", entry, err)
 		}
 
-		locations = append(locations, fileLocation{entry, location})
-	}
+		shouldContinue := resultCallback(categorizationResult{
+			location: fileLocation{entry, location},
+			err:      wrappedErr,
+		})
 
-	return locations
+		if shouldContinue {
+			continue
+		} else {
+			break
+		}
+	}
 }
 
 // getDirEntries gets filenames in a directory, ordered by the given sort function.
diff --git a/cmd/main.go b/cmd/main.go
index 03a388e..b291f67 100644
--- a/cmd/main.go
+++ b/cmd/main.go
@@ -17,16 +17,25 @@ func main() {
 
 	sourceFolder, libraryFolder := os.Args[1], os.Args[2]
 
-	categorizationRes, err := categorizeFolder(sourceFolder, libraryFolder)
+	locations := []fileLocation{}
+	categorizationStats, err := categorizeFolder(sourceFolder, libraryFolder, func(res categorizationResult) bool {
+		if res.err != nil {
+			fmt.Fprintln(os.Stderr, res.err)
+		} else {
+			locations = append(locations, res.location)
+		}
+
+		return true
+	})
+
 	if err != nil {
 		panic(err)
 	}
 
-	prettyPrintLocations(categorizationRes.locations)
-	fmt.Fprintf(os.Stderr, "%d items not categorized\n", categorizationRes.filesSkipped)
+	prettyPrintLocations(locations)
+	fmt.Fprintf(os.Stderr, "%d items not categorized\n", categorizationStats.filesSkipped)
 }
 
-
 func prettyPrintLocations(fileLocations []fileLocation) {
 	for _, fl := range fileLocations {
 		filename, location := fl.filename, fl.location