cast.go

// Copyright 2014 Steve Francia. All rights reserved.
// Use of this source code is governed by a MIT-style license.

package funcmap

import (
	"encoding/json"
	"fmt"
	"html/template"
	"reflect"
	"strconv"
	"time"
)

// TODO (bradrydzewski) ToString
// TODO (bradrydzewski) ToInt
// TODO (bradrydzewski) ToInt64
// TODO (bradrydzewski) ToTime
// TODO (bradrydzewski) ToDuration
// TODO (bradrydzewski) ToFloat32
// TODO (bradrydzewski) ToFloat64

// From html/template/content.go
// Copyright 2011 The Go Authors. All rights reserved.
// indirect returns the value, after dereferencing as many times
// as necessary to reach the base type (or nil).
func indirect(a interface{}) interface{} {
	if a == nil {
		return nil
	}
	if t := reflect.TypeOf(a); t.Kind() != reflect.Ptr {
		// Avoid creating a reflect.Value if it's not a pointer.
		return a
	}
	v := reflect.ValueOf(a)
	for v.Kind() == reflect.Ptr && !v.IsNil() {
		v = v.Elem()
	}
	return v.Interface()
}

// From html/template/content.go
// Copyright 2011 The Go Authors. All rights reserved.
// indirectToStringerOrError returns the value, after dereferencing as many times
// as necessary to reach the base type (or nil) or an implementation of fmt.Stringer
// or error,
func indirectToStringerOrError(a interface{}) interface{} {
	if a == nil {
		return nil
	}

	var errorType = reflect.TypeOf((*error)(nil)).Elem()
	var fmtStringerType = reflect.TypeOf((*fmt.Stringer)(nil)).Elem()

	v := reflect.ValueOf(a)
	for !v.Type().Implements(fmtStringerType) && !v.Type().Implements(errorType) && v.Kind() == reflect.Ptr && !v.IsNil() {
		v = v.Elem()
	}
	return v.Interface()
}

func toStringE(i interface{}) (string, error) {
	i = indirectToStringerOrError(i)

	switch s := i.(type) {
	case string:
		return s, nil
	case bool:
		return strconv.FormatBool(s), nil
	case float64:
		return strconv.FormatFloat(s, 'f', -1, 64), nil
	case float32:
		return strconv.FormatFloat(float64(s), 'f', -1, 32), nil
	case int:
		return strconv.Itoa(s), nil
	case int64:
		return strconv.FormatInt(s, 10), nil
	case int32:
		return strconv.Itoa(int(s)), nil
	case int16:
		return strconv.FormatInt(int64(s), 10), nil
	case int8:
		return strconv.FormatInt(int64(s), 10), nil
	case uint:
		return strconv.FormatInt(int64(s), 10), nil
	case uint64:
		return strconv.FormatInt(int64(s), 10), nil
	case uint32:
		return strconv.FormatInt(int64(s), 10), nil
	case uint16:
		return strconv.FormatInt(int64(s), 10), nil
	case uint8:
		return strconv.FormatInt(int64(s), 10), nil
	case []byte:
		return string(s), nil
	case template.HTML:
		return string(s), nil
	case template.URL:
		return string(s), nil
	case template.JS:
		return string(s), nil
	case template.CSS:
		return string(s), nil
	case template.HTMLAttr:
		return string(s), nil
	case nil:
		return "", nil
	case fmt.Stringer:
		return s.String(), nil
	case error:
		return s.Error(), nil
	default:
		return "", fmt.Errorf("unable to cast %#v of type %T to string", i, i)
	}
}

func toIntE(i interface{}) (int, error) {
	i = indirect(i)

	intv, ok := toInt(i)
	if ok {
		return intv, nil
	}

	switch s := i.(type) {
	case int64:
		return int(s), nil
	case int32:
		return int(s), nil
	case int16:
		return int(s), nil
	case int8:
		return int(s), nil
	case uint:
		return int(s), nil
	case uint64:
		return int(s), nil
	case uint32:
		return int(s), nil
	case uint16:
		return int(s), nil
	case uint8:
		return int(s), nil
	case float64:
		return int(s), nil
	case float32:
		return int(s), nil
	case string:
		v, err := strconv.ParseInt(trimZeroDecimal(s), 0, 0)
		if err == nil {
			return int(v), nil
		}
		return 0, fmt.Errorf("unable to cast %#v of type %T to int64", i, i)
	case json.Number:
		return toIntE(string(s))
	case bool:
		if s {
			return 1, nil
		}
		return 0, nil
	case nil:
		return 0, nil
	default:
		return 0, fmt.Errorf("unable to cast %#v of type %T to int", i, i)
	}
}

func toTimeE(i interface{}) (tim time.Time, err error) {
	i = indirect(i)

	switch v := i.(type) {
	case time.Time:
		return v, nil
	case string:
		return stringToDate(v)
	case int:
		return time.Unix(int64(v), 0), nil
	case int64:
		return time.Unix(v, 0), nil
	case int32:
		return time.Unix(int64(v), 0), nil
	case uint:
		return time.Unix(int64(v), 0), nil
	case uint64:
		return time.Unix(int64(v), 0), nil
	case uint32:
		return time.Unix(int64(v), 0), nil
	default:
		return time.Time{}, fmt.Errorf("unable to cast %#v of type %T to Time", i, i)
	}
}

func stringToDate(s string) (time.Time, error) {
	return parseDateWith(s, []string{
		time.RFC3339,
		"2006-01-02T15:04:05",
		time.RFC1123Z,
		time.RFC1123,
		time.RFC822Z,
		time.RFC822,
		time.RFC850,
		time.ANSIC,
		time.UnixDate,
		time.RubyDate,
		"2006-01-02 15:04:05.999999999 -0700 MST",
		"2006-01-02",
		"02 Jan 2006",
		"2006-01-02 15:04:05 -07:00",
		"2006-01-02 15:04:05 -0700",
		"2006-01-02 15:04:05Z07:00",
		"2006-01-02 15:04:05",
		time.Kitchen,
		time.Stamp,
		time.StampMilli,
		time.StampMicro,
		time.StampNano,
	})
}

func parseDateWith(s string, dates []string) (d time.Time, e error) {
	for _, dateType := range dates {
		if d, e = time.Parse(dateType, s); e == nil {
			return
		}
	}
	return d, fmt.Errorf("unable to parse date: %s", s)
}

// toInt returns the int value of v if v or v's underlying type
// is an int.
// Note that this will return false for int64 etc. types.
func toInt(v interface{}) (int, bool) {
	switch v := v.(type) {
	case int:
		return v, true
	case time.Weekday:
		return int(v), true
	case time.Month:
		return int(v), true
	default:
		return 0, false
	}
}

func trimZeroDecimal(s string) string {
	var foundZero bool
	for i := len(s); i > 0; i-- {
		switch s[i-1] {
		case '.':
			if foundZero {
				return s[:i-1]
			}
		case '0':
			foundZero = true
		default:
			return s
		}
	}
	return s
}