package sprig

import (
	"reflect"
)

// dfault checks whether `given` is set, and returns default if not set.
//
// This returns `d` if `given` appears not to be set, and `given` otherwise.
//
// For numeric types 0 is unset.
// For strings, maps, arrays, and slices, len() = 0 is considered unset.
// For bool, false is unset.
// Structs are never considered unset.
//
// For everything else, including pointers, a nil value is unset.
func dfault(d interface{}, given ...interface{}) interface{} {

	if empty(given) || empty(given[0]) {
		return d
	}
	return given[0]
}

// empty returns true if the given value has the zero value for its type.
func empty(given interface{}) bool {
	g := reflect.ValueOf(given)
	if !g.IsValid() {
		return true
	}

	// Basically adapted from text/template.isTrue
	switch g.Kind() {
	default:
		return g.IsNil()
	case reflect.Array, reflect.Slice, reflect.Map, reflect.String:
		return g.Len() == 0
	case reflect.Bool:
		return g.Bool() == false
	case reflect.Complex64, reflect.Complex128:
		return g.Complex() == 0
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return g.Int() == 0
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		return g.Uint() == 0
	case reflect.Float32, reflect.Float64:
		return g.Float() == 0
	case reflect.Struct:
		return false
	}
	return true
}

// coalesce returns the first non-empty value.
func coalesce(v ...interface{}) interface{} {
	for _, val := range v {
		if !empty(val) {
			return val
		}
	}
	return nil
}