initial commit. Cloned timetracker repository

app/utils/mapper/mapper.go

@@ -0,0 +1,74 @@
+package mapper
+
+// Package mapper provides utilities to map fields from one struct to another
+// by matching field names (case-insensitive). Unmatched fields are left as
+// their zero values.
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+// Map copies field values from src into dst by matching field names
+// (case-insensitive). Fields in dst that have no counterpart in src
+// are left at their zero value.
+//
+// Both dst and src must be pointers to structs.
+// Returns an error if the types do not satisfy those constraints.
+func Map(dst, src any) error {
+	dstVal := reflect.ValueOf(dst)
+	srcVal := reflect.ValueOf(src)
+
+	if dstVal.Kind() != reflect.Ptr || dstVal.Elem().Kind() != reflect.Struct {
+		return fmt.Errorf("mapper: dst must be a pointer to a struct, got %T", dst)
+	}
+	if srcVal.Kind() != reflect.Ptr || srcVal.Elem().Kind() != reflect.Struct {
+		return fmt.Errorf("mapper: src must be a pointer to a struct, got %T", src)
+	}
+
+	dstElem := dstVal.Elem()
+	srcElem := srcVal.Elem()
+
+	// Build a lookup map of src fields: lowercase name -> field value
+	srcFields := make(map[string]reflect.Value)
+	for i := 0; i < srcElem.NumField(); i++ {
+		f := srcElem.Type().Field(i)
+		if !f.IsExported() {
+			continue
+		}
+		srcFields[strings.ToLower(f.Name)] = srcElem.Field(i)
+	}
+
+	// Iterate over dst fields and copy matching src values
+	for i := 0; i < dstElem.NumField(); i++ {
+		dstField := dstElem.Field(i)
+		dstType := dstElem.Type().Field(i)
+
+		if !dstType.IsExported() || !dstField.CanSet() {
+			continue
+		}
+
+		srcField, ok := srcFields[strings.ToLower(dstType.Name)]
+		if !ok {
+			// No matching src field – leave zero value in place
+			continue
+		}
+
+		if srcField.Type().AssignableTo(dstField.Type()) {
+			dstField.Set(srcField)
+		} else if srcField.Type().ConvertibleTo(dstField.Type()) {
+			dstField.Set(srcField.Convert(dstField.Type()))
+		}
+		// If neither assignable nor convertible, the dst field keeps its zero value
+	}
+
+	return nil
+}
+
+// MustMap is like Map but panics on error.
+func MustMap(dst, src any) {
+	if err := Map(dst, src); err != nil {
+		panic(err)
+	}
+}