group.go

package underscore

import (
	"reflect"
)

func (m enumerable) Group(keySelector interface{}) enumerable {
	return enumerable{
		Enumerator: func() IEnumerator {
			groupRVs := make(map[interface{}]reflect.Value)
			iterator := m.GetEnumerator()
			keySelectorRV := reflect.ValueOf(keySelector)
			keyRVs := make([]reflect.Value, 0)
			for ok := iterator.MoveNext(); ok; ok = iterator.MoveNext() {
				keyRV := getReturnValue(keySelectorRV, iterator)
				key := keyRV.Interface()
				groupRV, ok := groupRVs[key]
				if !ok {
					groupRV = reflect.MakeSlice(
						reflect.SliceOf(
							iterator.GetValue().Type(),
						),
						0,
						0,
					)
					keyRVs = append(keyRVs, keyRV)
				}
				groupRVs[key] = reflect.Append(
					groupRV,
					iterator.GetValue(),
				)
			}
			index := 0
			return &enumerator{
				MoveNextFunc: func() (valueRV reflect.Value, keyRV reflect.Value, ok bool) {
					if ok = index < len(keyRVs); ok {
						keyRV = keyRVs[index]
						valueRV = groupRVs[keyRV.Interface()]
						index++
					}
					return
				},
			}
		},
	}
}

func (m enumerable) GroupBy(fieldName string) enumerable {
	getter := FieldValue(fieldName)
	return m.Group(func(value, _ interface{}) facade {
		return facade{
			getter(value),
		}
	})
}