feat: add picker to pick value from record

pkg/picker/config.go

@@ -0,0 +1,93 @@
+package picker
+
+import "fmt"
+
+// Config is the configuration to build Picker
+// The priority is as follows:
+//		ConcatItems > Indices
+// 		Nullable
+// 		DefaultValue
+//    NullValue, if set to null, subsequent conversions will be skipped.
+// 		Type
+// 		Function
+type Config struct {
+	ConcatItems  ConcatItems       // Concat index column, constant, or mixed.
+	Indices      []int             // Set index columns, the first non-null.
+	Nullable     func(string) bool // Determine whether it is null. Optional.
+	NullValue    string            // Set null value when it is null. Optional.
+	DefaultValue *string           // Set default value when it is null. Optional.
+	Type         string            // Set the type of value.
+	Function     *string           // Set the conversion function of value.
+}
+
+func (c *Config) Build() (Picker, error) {
+	var retPicker Picker
+	var nullHandled bool
+	switch {
+	case c.ConcatItems.Len() > 0:
+		retPicker = ConcatPicker{
+			items: c.ConcatItems,
+		}
+	case len(c.Indices) == 1:
+		retPicker = IndexPicker(c.Indices[0])
+	case len(c.Indices) > 1:
+		if c.Nullable == nil {
+			// the first must be picked
+			retPicker = IndexPicker(c.Indices[0])
+		} else {
+			pickers := make(NullablePickers, 0, len(c.Indices))
+			for _, index := range c.Indices {
+				pickers = append(pickers, ConverterPicker{
+					picker: IndexPicker(index),
+					converter: NullableConverters{
+						NullableConverter{
+							Nullable: c.Nullable,
+						},
+					},
+				})
+			}
+			retPicker = pickers
+		}
+		nullHandled = true
+	default:
+		return nil, fmt.Errorf("no indices or concat items")
+	}
+
+	var converters []Converter
+
+	if !nullHandled && c.Nullable != nil {
+		converters = append(converters, NullableConverter{
+			Nullable: c.Nullable,
+		})
+	}
+
+	if c.Nullable != nil {
+		if c.DefaultValue != nil {
+			converters = append(converters, DefaultConverter{
+				Value: *c.DefaultValue,
+			})
+		} else {
+			converters = append(converters, NullConverter{
+				Value: c.NullValue,
+			})
+		}
+	}
+
+	converters = append(converters, NewTypeConverter(c.Type))
+
+	if c.Function != nil {
+		converters = append(converters, FuncConverter{
+			Name: *c.Function,
+		})
+	}
+
+	var converter Converter = Converters(converters)
+	if c.Nullable != nil {
+		converter = NullableConverters(converters)
+	}
+
+	return ConverterPicker{
+		picker:    retPicker,
+		converter: converter,
+	}, nil
+}