docs/plans/2026-07-19-scanner-engine-fuzzy-diff.md

@@ -55,11 +55,11 @@
 > Note: the library exposes `fuzzy.RankMatch` (subsequence-ranked Levenshtein distance: 0=exact, -1=no match) rather than a `fuzzy.Ratio` 0-100 function assumed in the plan. Task 3 will normalize this into a 0.0-1.0 similarity score.
 
 ### Task 2: Extract normalization into `internal/normalize`
-- [ ] create `internal/normalize/normalize.go` with `NormalizeString(s string) string` and `NormalizeArtistName(s string) string`, moving the regexes + logic from `internal/musicbrainz/api.go:132-165`
-- [ ] refactor `internal/musicbrainz/api.go` to call `normalize.NormalizeString` / `normalize.NormalizeArtistName` instead of its local copies (remove duplicated regexes/functions)
-- [ ] write tests `internal/normalize/normalize_test.go` (table-driven): lowercase, bracket/paren strip, year strip `(20xx)`, special-char strip, space collapse, `NormalizeArtistName` prefix strip (`the `/`a `/`an `)
-- [ ] update existing `internal/musicbrainz/api_test.go` if it referenced the moved functions, ensuring it still passes
-- [ ] run tests — must pass before task 3
+- [x] create `internal/normalize/normalize.go` with `NormalizeString(s string) string` and `NormalizeArtistName(s string) string`, moving the regexes + logic from `internal/musicbrainz/api.go:132-165`
+- [x] refactor `internal/musicbrainz/api.go` to call `normalize.NormalizeString` / `normalize.NormalizeArtistName` instead of its local copies (remove duplicated regexes/functions)
+- [x] write tests `internal/normalize/normalize_test.go` (table-driven): lowercase, bracket/paren strip, year strip `(20xx)`, special-char strip, space collapse, `NormalizeArtistName` prefix strip (`the `/`a `/`an `)
+- [x] update existing `internal/musicbrainz/api_test.go` if it referenced the moved functions, ensuring it still passes
+- [x] run tests — must pass before task 3
 
 ### Task 3: Implement similarity scoring in `internal/scanner`
 - [ ] create `internal/scanner/scanner.go` with `Similarity(a, b string) float64` using `normalize.NormalizeString` + `fuzzy.Ratio` (normalized to 0.0–1.0); define `IsMatch(a, b string, threshold float64) bool`

internal/musicbrainz/api.go

@@ -4,11 +4,9 @@ import (
 	"context"
 	"fmt"
 	"net/url"
-	"regexp"
-	"strings"
-	"unicode"
 
 	"naviwatcher/internal/database"
+	"naviwatcher/internal/normalize"
 )
 
 // excludedStatuses contains release-group statuses that should be filtered out.
@@ -26,14 +24,6 @@ var includedTypes = map[string]bool{
 	"Compilation": true,
 }
 
-// Precompiled regexes for NormalizeString — compiled once at package init.
-var (
-	bracketRe = regexp.MustCompile(`\[[^\]]*\]`)
-	parenRe   = regexp.MustCompile(`\([^)]*\)`)
-	yearRe    = regexp.MustCompile(`\b(1[0-9]{3}|2[0-9]{3})\b`)
-	spaceRe   = regexp.MustCompile(`\s+`)
-)
-
 // GetArtistReleaseGroups fetches all release groups for a given artist from MusicBrainz.
 // It queries the artist's release groups via the MusicBrainz Web Service API,
 // parses the XML response, and applies status and type filtering.
@@ -122,63 +112,18 @@ func IsTypeIncluded(releaseType string) bool {
 	return includedTypes[releaseType]
 }
 
-// NormalizeString normalizes a string for fuzzy matching by:
-//   - Converting to lowercase
-//   - Removing special characters (keeping only letters, digits, and spaces)
-//   - Removing years (4-digit numbers that look like years)
-//   - Removing bracketed keywords (e.g., [Deluxe], [Remastered])
-//   - Collapsing multiple spaces into one
-//   - Trimming leading/trailing whitespace
+// NormalizeString normalizes a string for fuzzy matching.
+// It delegates to the shared normalize package; see normalize.NormalizeString
+// for the full normalization contract.
 func NormalizeString(s string) string {
-	// Convert to lowercase
-	s = strings.ToLower(s)
-
-	// Remove bracketed content first (e.g., [Deluxe Edition], [Remastered 2020])
-	s = bracketRe.ReplaceAllString(s, "")
-
-	// Remove parenthesized content (e.g., (Deluxe), (Remastered))
-	s = parenRe.ReplaceAllString(s, "")
-
-	// Remove years (4-digit numbers between 1000-2999)
-	s = yearRe.ReplaceAllString(s, "")
-
-	// Replace common separators with spaces before stripping other special chars
-	s = strings.ReplaceAll(s, "-", " ")
-	s = strings.ReplaceAll(s, "_", " ")
-
-	// Keep only letters, digits, and spaces
-	var b strings.Builder
-	for _, r := range s {
-		if unicode.IsLetter(r) || unicode.IsDigit(r) || unicode.IsSpace(r) {
-			b.WriteRune(r)
-		}
-	}
-	s = b.String()
-
-	// Collapse multiple spaces
-	s = spaceRe.ReplaceAllString(s, " ")
-
-	// Trim
-	s = strings.TrimSpace(s)
-
-	return s
+	return normalize.NormalizeString(s)
 }
 
 // NormalizeArtistName normalizes an artist name for comparison.
-// It applies NormalizeString and additionally handles common prefixes.
+// It delegates to the shared normalize package; see
+// normalize.NormalizeArtistName for the full normalization contract.
 func NormalizeArtistName(name string) string {
-	name = NormalizeString(name)
-
-	// Remove common leading articles for better matching
-	prefixes := []string{"the ", "a ", "an "}
-	for _, prefix := range prefixes {
-		if strings.HasPrefix(name, prefix) {
-			name = strings.TrimPrefix(name, prefix)
-			break
-		}
-	}
-
-	return strings.TrimSpace(name)
+	return normalize.NormalizeArtistName(name)
 }
 
 // ToExternalRelease converts a ReleaseGroup to an ExternalRelease

internal/normalize/normalize.go

@@ -0,0 +1,80 @@
+// Package normalize provides string normalization helpers used for
+// fuzzy matching across NaviWatcher (artist names, album titles, etc.).
+//
+// It is the single shared home for normalization logic; previously this
+// lived inside the musicbrainz package but is needed by the scanner engine
+// and any other consumer that compares strings.
+package normalize
+
+import (
+	"regexp"
+	"strings"
+	"unicode"
+)
+
+// Precompiled regexes — compiled once at package init.
+var (
+	bracketRe = regexp.MustCompile(`\[[^\]]*\]`)
+	parenRe   = regexp.MustCompile(`\([^)]*\)`)
+	yearRe    = regexp.MustCompile(`\b(1[0-9]{3}|2[0-9]{3})\b`)
+	spaceRe   = regexp.MustCompile(`\s+`)
+)
+
+// NormalizeString normalizes a string for fuzzy matching by:
+//   - Converting to lowercase
+//   - Removing special characters (keeping only letters, digits, and spaces)
+//   - Removing years (4-digit numbers that look like years)
+//   - Removing bracketed keywords (e.g., [Deluxe], [Remastered])
+//   - Collapsing multiple spaces into one
+//   - Trimming leading/trailing whitespace
+func NormalizeString(s string) string {
+	// Convert to lowercase
+	s = strings.ToLower(s)
+
+	// Remove bracketed content first (e.g., [Deluxe Edition], [Remastered 2020])
+	s = bracketRe.ReplaceAllString(s, "")
+
+	// Remove parenthesized content (e.g., (Deluxe), (Remastered))
+	s = parenRe.ReplaceAllString(s, "")
+
+	// Remove years (4-digit numbers between 1000-2999)
+	s = yearRe.ReplaceAllString(s, "")
+
+	// Replace common separators with spaces before stripping other special chars
+	s = strings.ReplaceAll(s, "-", " ")
+	s = strings.ReplaceAll(s, "_", " ")
+
+	// Keep only letters, digits, and spaces
+	var b strings.Builder
+	for _, r := range s {
+		if unicode.IsLetter(r) || unicode.IsDigit(r) || unicode.IsSpace(r) {
+			b.WriteRune(r)
+		}
+	}
+	s = b.String()
+
+	// Collapse multiple spaces
+	s = spaceRe.ReplaceAllString(s, " ")
+
+	// Trim
+	s = strings.TrimSpace(s)
+
+	return s
+}
+
+// NormalizeArtistName normalizes an artist name for comparison.
+// It applies NormalizeString and additionally handles common prefixes.
+func NormalizeArtistName(name string) string {
+	name = NormalizeString(name)
+
+	// Remove common leading articles for better matching
+	prefixes := []string{"the ", "a ", "an "}
+	for _, prefix := range prefixes {
+		if strings.HasPrefix(name, prefix) {
+			name = strings.TrimPrefix(name, prefix)
+			break
+		}
+	}
+
+	return strings.TrimSpace(name)
+}

internal/normalize/normalize_test.go

@@ -0,0 +1,76 @@
+package normalize
+
+import "testing"
+
+func TestNormalizeString_Basic(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		// Lowercase conversion
+		{"DARK SIDE OF THE MOON", "dark side of the moon"},
+		// Special character removal
+		{"Dark Side of the Moon!", "dark side of the moon"},
+		{"Dark-Side-of-the-Moon", "dark side of the moon"},
+		{"Dark_Side_of_the_Moon", "dark side of the moon"},
+		// Bracket removal
+		{"Dark Side of the Moon [Deluxe Edition]", "dark side of the moon"},
+		{"Dark Side of the Moon [Remastered 2020]", "dark side of the moon"},
+		{"Album [2023 Remix]", "album"},
+		// Parenthesis removal
+		{"Dark Side of the Moon (Deluxe)", "dark side of the moon"},
+		{"Album (Remastered)", "album"},
+		// Year removal
+		{"Dark Side of the Moon 1973", "dark side of the moon"},
+		{"Album 2020 Remastered", "album remastered"},
+		// Space collapsing
+		{"Dark   Side   of   the   Moon", "dark side of the moon"},
+		// Trim
+		{"  Dark Side of the Moon  ", "dark side of the moon"},
+		// Combined
+		{"The Dark Side of the Moon [2011 Remaster] (Deluxe Edition)", "the dark side of the moon"},
+		// Empty
+		{"", ""},
+		// Only special chars
+		{"!@#$%^&*()", ""},
+		// Digits that are not years should stay
+		{"30 Seconds to Mars", "30 seconds to mars"},
+		{"1941 - The Greatest Hits", "the greatest hits"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			got := NormalizeString(tt.input)
+			if got != tt.expected {
+				t.Errorf("NormalizeString(%q) = %q, want %q", tt.input, got, tt.expected)
+			}
+		})
+	}
+}
+
+func TestNormalizeArtistName(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{"Pink Floyd", "pink floyd"},
+		{"The Beatles", "beatles"},
+		{"A Perfect Circle", "perfect circle"},
+		{"An Orchestra", "orchestra"},
+		{"  The  Who  ", "who"},
+		{"THE WHO", "who"},
+		// No stripping needed
+		{"Radiohead", "radiohead"},
+		// Already stripped
+		{"Beatles", "beatles"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			got := NormalizeArtistName(tt.input)
+			if got != tt.expected {
+				t.Errorf("NormalizeArtistName(%q) = %q, want %q", tt.input, got, tt.expected)
+			}
+		})
+	}
+}