more tests and standardize struct field casing

client/client.go

@@ -12,7 +12,16 @@ var (
 	defaultAPI = "https://openlibrary.org/api/books"
 )
 
-// Client
+var (
+	// FormatError marks errors with provided book identifers
+	FormatError = fmt.Errorf("identifier in wrong format")
+	// NetworkError marks errors with the connection to the OpenLibrary API
+	NetworkError = fmt.Errorf("network error")
+	// NotFoundError marks an empty response from the OpenLibrary API
+	NotFoundError = fmt.Errorf("book not found")
+)
+
+// Client provides OpenLibrary Books API query methods
 type Client struct {
 	httpClient http.Client
 	apipath    string
@@ -33,9 +42,9 @@ func (c *Client) SetAPIPath(p string) {
 // GetByISBN fetches details for a book based on its ISBN10 or ISBN13.
 func (c *Client) GetByISBN(k string) (*BookDetails, error) {
 	if k == "" {
-		return nil, fmt.Errorf("ISBN cannot be empty")
+		return nil, fmt.Errorf("%w: ISBN cannot be empty", FormatError)
 	} else if len(k) != 10 && len(k) != 13 {
-		return nil, fmt.Errorf("ISBN must be either 10 or 13 digits")
+		return nil, fmt.Errorf("%w: ISBN must be either 10 or 13 digits", FormatError)
 	}
 	key := "ISBN:" + k
 	return c.fetch(key)
@@ -44,7 +53,7 @@ func (c *Client) GetByISBN(k string) (*BookDetails, error) {
 // GetByOCLC fetches details for a book based on its WorldCat OCLC number.
 func (c *Client) GetByOCLC(k string) (*BookDetails, error) {
 	if k == "" {
-		return nil, fmt.Errorf("OCLC cannot be empty")
+		return nil, fmt.Errorf("%w: OCLC cannot be empty", FormatError)
 	}
 	key := "OCLC:" + k
 	return c.fetch(key)
@@ -53,7 +62,7 @@ func (c *Client) GetByOCLC(k string) (*BookDetails, error) {
 // GetByLCCN fetches details for a book based on its Library of Congress Control Number.
 func (c *Client) GetByLCCN(k string) (*BookDetails, error) {
 	if k == "" {
-		return nil, fmt.Errorf("LCCN cannot be empty")
+		return nil, fmt.Errorf("%w: LCCN cannot be empty", FormatError)
 	}
 	key := "LCCN:" + k
 	return c.fetch(key)
@@ -62,7 +71,7 @@ func (c *Client) GetByLCCN(k string) (*BookDetails, error) {
 // GetByOLID fetches details for a book based on its OpenLibrary ID number.
 func (c *Client) GetByOLID(k string) (*BookDetails, error) {
 	if k == "" {
-		return nil, fmt.Errorf("OLID cannot be empty")
+		return nil, fmt.Errorf("%w: OLID cannot be empty", FormatError)
 	}
 	key := "OLID:" + k
 	return c.fetch(key)
@@ -82,7 +91,7 @@ func (c *Client) fetch(key string) (*BookDetails, error) {
 	}
 	u, err := url.Parse(h)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("%w: %v", NetworkError, err)
 	}
 	u.RawQuery = url.Values{
 		"bibkeys": []string{key},
@@ -92,26 +101,26 @@ func (c *Client) fetch(key string) (*BookDetails, error) {
 
 	resp, err := c.httpClient.Get(u.String())
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("%w: %v", NetworkError, err)
 	}
 	defer resp.Body.Close()
 
 	if resp.StatusCode != http.StatusOK {
-		return nil, fmt.Errorf("received non-200 status code: %d", resp.StatusCode)
+		return nil, fmt.Errorf("%w: received non-200 status code: %d", NetworkError, resp.StatusCode)
 	}
 
 	var result response
 	b, err := io.ReadAll(resp.Body)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("%w: %v", NetworkError, err)
 	}
 	if err = json.Unmarshal(b, &result); err != nil {
-		return nil, err
+		return nil, fmt.Errorf("%w: %v", NetworkError, err)
 	}
 
 	details, ok := result[key]
 	if !ok {
-		return nil, fmt.Errorf("book not found")
+		return nil, NotFoundError
 	}
 
 	return &details, nil