// substr extracts parts of a string, beginning at the character at the specified
// position, and returns the specified number of characters.
//
// It normally takes two parameters: start and length.
// It can also take one parameter: start, i.e. length is omitted, in which case
// the substring starting from start until the end of the string will be returned.
//
// To extract characters from the end of the string, use a negative start number.
//
// In addition, borrowing from the extended behavior described at http://php.net/substr,
// if length is given and is negative, then that many characters will be omitted from
// the end of string.
func substr(a interface{}, nums ...interface{}) (string, error) {
	aStr, err := cast.ToStringE(a)
	if err != nil {
		return "", err
	}

	var start, length int

	asRunes := []rune(aStr)

	switch len(nums) {
	case 0:
		return "", errors.New("too less arguments")
	case 1:
		if start, err = cast.ToIntE(nums[0]); err != nil {
			return "", errors.New("start argument must be integer")
		}
		length = len(asRunes)
	case 2:
		if start, err = cast.ToIntE(nums[0]); err != nil {
			return "", errors.New("start argument must be integer")
		}
		if length, err = cast.ToIntE(nums[1]); err != nil {
			return "", errors.New("length argument must be integer")
		}
	default:
		return "", errors.New("too many arguments")
	}

	if start < -len(asRunes) {
		start = 0
	}
	if start > len(asRunes) {
		return "", fmt.Errorf("start position out of bounds for %d-byte string", len(aStr))
	}

	var s, e int
	if start >= 0 && length >= 0 {
		s = start
		e = start + length
	} else if start < 0 && length >= 0 {
		s = len(asRunes) + start - length + 1
		e = len(asRunes) + start + 1
	} else if start >= 0 && length < 0 {
		s = start
		e = len(asRunes) + length
	} else {
		s = len(asRunes) + start
		e = len(asRunes) + length
	}

	if s > e {
		return "", fmt.Errorf("calculated start position greater than end position: %d > %d", s, e)
	}
	if e > len(asRunes) {
		e = len(asRunes)
	}

	return string(asRunes[s:e]), nil
}

// After is exposed to templates, to iterate over all the items after N in a
// rangeable list. It's meant to accompany First
func After(index interface{}, seq interface{}) (interface{}, error) {

	if index == nil || seq == nil {
		return nil, errors.New("both limit and seq must be provided")
	}

	indexv, err := cast.ToIntE(index)

	if err != nil {
		return nil, err
	}

	if indexv < 1 {
		return nil, errors.New("can't return negative/empty count of items from sequence")
	}

	seqv := reflect.ValueOf(seq)
	seqv, isNil := indirect(seqv)
	if isNil {
		return nil, errors.New("can't iterate over a nil value")
	}

	switch seqv.Kind() {
	case reflect.Array, reflect.Slice, reflect.String:
		// okay
	default:
		return nil, errors.New("can't iterate over " + reflect.ValueOf(seq).Type().String())
	}
	if indexv >= seqv.Len() {
		return nil, errors.New("no items left")
	}
	return seqv.Slice(indexv, seqv.Len()).Interface(), nil
}

func (self *Options) Int(key string) int {
	value, err := cast.ToIntE(self.Interface(key))
	if err != nil {
		self.log.Printf("%s for key '%s'", err.Error(), key)
	}
	return value
}

// First is exposed to templates, to iterate over the first N items in a
// rangeable list.
func First(limit interface{}, seq interface{}) (interface{}, error) {
	limitv, err := cast.ToIntE(limit)

	if err != nil {
		return nil, err
	}

	if limitv < 1 {
		return nil, errors.New("can't return negative/empty count of items from sequence")
	}

	seqv := reflect.ValueOf(seq)
	seqv, isNil := indirect(seqv)
	if isNil {
		return nil, errors.New("can't iterate over a nil value")
	}

	switch seqv.Kind() {
	case reflect.Array, reflect.Slice, reflect.String:
		// okay
	default:
		return nil, errors.New("can't iterate over " + reflect.ValueOf(seq).Type().String())
	}
	if limitv > seqv.Len() {
		limitv = seqv.Len()
	}
	return seqv.Slice(0, limitv).Interface(), nil
}

func (c *Configr) Int(key string) (int, error) {
	val, err := c.Get(key)
	if err != nil {
		return 0, err
	}
	return cast.ToIntE(val)
}

// First is exposed to templates, to iterate over the first N items in a
// rangeable list.
func First(limit interface{}, seq interface{}) (interface{}, error) {

	limitv, err := cast.ToIntE(limit)

	if err != nil {
		return nil, err
	}

	if limitv < 1 {
		return nil, errors.New("can't return negative/empty count of items from sequence")
	}

	seqv := reflect.ValueOf(seq)
	// this is better than my first pass; ripped from text/template/exec.go indirect():
	for ; seqv.Kind() == reflect.Ptr || seqv.Kind() == reflect.Interface; seqv = seqv.Elem() {
		if seqv.IsNil() {
			return nil, errors.New("can't iterate over a nil value")
		}
		if seqv.Kind() == reflect.Interface && seqv.NumMethod() > 0 {
			break
		}
	}

	switch seqv.Kind() {
	case reflect.Array, reflect.Slice, reflect.String:
		// okay
	default:
		return nil, errors.New("can't iterate over " + reflect.ValueOf(seq).Type().String())
	}
	if limitv > seqv.Len() {
		limitv = seqv.Len()
	}
	return seqv.Slice(0, limitv).Interface(), nil
}

// slicestr slices a string by specifying a half-open range with
// two indices, start and end. 1 and 4 creates a slice including elements 1 through 3.
// The end index can be omitted, it defaults to the string's length.
func slicestr(a interface{}, startEnd ...interface{}) (string, error) {
	aStr, err := cast.ToStringE(a)
	if err != nil {
		return "", err
	}

	var argStart, argEnd int

	argNum := len(startEnd)

	if argNum > 0 {
		if argStart, err = cast.ToIntE(startEnd[0]); err != nil {
			return "", errors.New("start argument must be integer")
		}
	}
	if argNum > 1 {
		if argEnd, err = cast.ToIntE(startEnd[1]); err != nil {
			return "", errors.New("end argument must be integer")
		}
	}

	if argNum > 2 {
		return "", errors.New("too many arguments")
	}

	asRunes := []rune(aStr)

	if argNum > 0 && (argStart < 0 || argStart >= len(asRunes)) {
		return "", errors.New("slice bounds out of range")
	}

	if argNum == 2 {
		if argEnd < 0 || argEnd > len(asRunes) {
			return "", errors.New("slice bounds out of range")
		}
		return string(asRunes[argStart:argEnd]), nil
	} else if argNum == 1 {
		return string(asRunes[argStart:]), nil
	} else {
		return string(asRunes[:]), nil
	}

}

// GetInt takes the name of an argument and returns an integer and an error
func (args Args) GetInt(name string) (int, error) {
	v, ok := args[name]
	if !ok {
		return -1 << 7, ErrNoArg
	}

	i, err := cast.ToIntE(v)
	if err != nil {
		return -1 << 7, err
	}
	return i, nil
}

func resolvePagerSize(options ...interface{}) (int, error) {
	if len(options) == 0 {
		return viper.GetInt("paginate"), nil
	}

	if len(options) > 1 {
		return -1, errors.New("too many arguments, 'pager size' is currently the only option")
	}

	pas, err := cast.ToIntE(options[0])

	if err != nil || pas <= 0 {
		return -1, errors.New(("'pager size' must be a positive integer"))
	}

	return pas, nil
}