Add Kurdish date formatting and custom error types

Introduces KFormat for Kurdish date formatting with Kurdish digits and custom error types for invalid year, month, day, and date. Updates KurdishToGregorian to use new error types. Expands README with usage examples and documents the new formatting method.

Author: rojcode

.gitignore

@@ -17,6 +17,9 @@ coverage.*
 *.coverprofile
 profile.cov
 
+
+
+
 # Dependency directories (remove the comment below to include it)
 # vendor/
 
@@ -30,3 +33,6 @@ go.work.sum
 # Editor/IDE
 # .idea/
 # .vscode/
+
+# Example binaries
+cmd/

README.md

@@ -43,6 +43,22 @@ func main() {
     } else {
         fmt.Printf("Gregorian date: %s\n", g.Format("2006-01-02"))
     }
+
+    // Create a specific Kurdish date and convert to Gregorian
+    // Note: Dialect is optional and not used in conversion, only Epoch matters
+    specificKurdish := kurdical.KurdishDate{
+        Year:    2725,
+        Month:   9,
+        Day:     24,
+        Dialect: kurdical.Sorani, // Optional
+        Epoch:   kurdical.MedianKingdom,
+    }
+    gregorianSpecific, err := kurdical.KurdishToGregorian(specificKurdish)
+    if err != nil {
+        fmt.Println("Error:", err)
+    } else {
+        fmt.Printf("Kurdish 2725-09-24 to Gregorian: %s\n", gregorianSpecific.Format("2006-01-02"))
+    }
 }
 ```
 
@@ -58,6 +74,7 @@ func main() {
 
 - `GregorianToKurdish(t time.Time, dialect Dialect, epoch Epoch) KurdishDate`
 - `KurdishToGregorian(k KurdishDate) (time.Time, error)`
+- `(k KurdishDate) KFormat(layout string) (string, error)`: Formats the Kurdish date using Go time layout strings with Persian digits
 
 ## Kurdish Calendar Details
 

conversions.go

@@ -1,7 +1,6 @@
 package kurdical
 
 import (
-	"fmt"
 	"time"
 )
 
@@ -166,15 +165,6 @@ func mod(a, b int) int {
 	return a % b
 }
 
-// ErrorInvalidYear represents an error for invalid year.
-type ErrorInvalidYear struct {
-	Year int
-}
-
-func (e *ErrorInvalidYear) Error() string {
-	return fmt.Sprintf("invalid year: %d", e.Year)
-}
-
 // isSolarHijriLeap determines if a Solar Hijri year is leap.
 func isSolarHijriLeap(year int) bool {
 	leap, _, _, err := jalCal(year)

errors.go

@@ -0,0 +1,41 @@
+package kurdical
+
+import "fmt"
+
+// ErrorInvalidYear represents an error for invalid year in Jalaali calculations.
+type ErrorInvalidYear struct {
+	Year int
+}
+
+func (e *ErrorInvalidYear) Error() string {
+	return fmt.Sprintf("invalid year: %d", e.Year)
+}
+
+// ErrorInvalidMonth represents an error for invalid month.
+type ErrorInvalidMonth struct {
+	Month int
+}
+
+func (e *ErrorInvalidMonth) Error() string {
+	return fmt.Sprintf("invalid month: %d", e.Month)
+}
+
+// ErrorInvalidDay represents an error for invalid day.
+type ErrorInvalidDay struct {
+	Day int
+}
+
+func (e *ErrorInvalidDay) Error() string {
+	return fmt.Sprintf("invalid day: %d", e.Day)
+}
+
+// ErrorInvalidDate represents an error for invalid date combination.
+type ErrorInvalidDate struct {
+	Year  int
+	Month int
+	Day   int
+}
+
+func (e *ErrorInvalidDate) Error() string {
+	return fmt.Sprintf("invalid date: year=%d, month=%d, day=%d", e.Year, e.Month, e.Day)
+}