john-okeefe
0f8db2ab07
Enhance NormalizeISBN to validate and convert ISBNs: - Validate length (10 or 13 digits), return error if invalid - Convert ISBN-10 to ISBN-13 by prefixing '978' and recalculating checksum - Add NormalizeISBNSafe for backward compatibility in scanners This ensures all ISBNs stored in database are valid ISBN-13 format.
68 lines
1.7 KiB
Go
68 lines
1.7 KiB
Go
package utils
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import (
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"errors"
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"regexp"
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)
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var (
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ErrInvalidISBN = errors.New("ISBN must be 10 or 13 digits")
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)
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// NormalizeISBN removes hyphens and spaces from ISBN to standardize format
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// Handles ISBN-10 and ISBN-13 formats
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// Returns error if ISBN is not 10 or 13 digits after normalization
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// Converts ISBN-10 to ISBN-13 by prefixing with "978" and recalculating checksum
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func NormalizeISBN(isbn string) (string, error) {
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if isbn == "" {
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return "", nil
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}
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// Remove hyphens and spaces, return only digits and X (for ISBN-10)
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normalized := regexp.MustCompile(`[-\s]`).ReplaceAllString(isbn, "")
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// Check length: must be 10 or 13 digits
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length := len(normalized)
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if length == 10 {
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// Convert ISBN-10 to ISBN-13
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return convertISBN10To13(normalized)
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}
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if length == 13 {
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return normalized, nil
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}
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return "", ErrInvalidISBN
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}
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// NormalizeISBNSafe removes hyphens and spaces from ISBN without validation
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// Used by scanners where metadata may be incomplete or malformed
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func NormalizeISBNSafe(isbn string) string {
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if isbn == "" {
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return ""
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}
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// Remove hyphens and spaces, return only digits and X (for ISBN-10)
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return regexp.MustCompile(`[-\s]`).ReplaceAllString(isbn, "")
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}
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// convertISBN10To13 converts ISBN-10 to ISBN-13 by prefixing "978" and recalculating checksum
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func convertISBN10To13(isbn10 string) (string, error) {
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// ISBN-10 to ISBN-13: prefix "978" and recalculate checksum
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// Replace last digit (X becomes 0 for calculation purposes)
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isbn12 := "978" + isbn10[:9]
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// Calculate ISBN-13 checksum
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sum := 0
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for i := 0; i < 12; i++ {
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digit := int(isbn12[i] - '0')
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if i%2 == 0 {
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sum += digit * 1
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} else {
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sum += digit * 3
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}
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}
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checksum := (10 - (sum % 10)) % 10
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return isbn12 + string(rune('0'+checksum)), nil
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}
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