golang-pault-go-debian-dev 0.5-1 / usr / share / gocode / src / pault.ag / go / debian / control / encode.go

/* {{{ Copyright (c) Paul R. Tagliamonte <paultag@debian.org>, 2015
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE. }}} */

package control

import (
	"fmt"
	"io"
	"reflect"
	"strconv"
	"strings"
)

// Marshallable {{{

// The Marshallable interface defines the interface that Marshal will use
// to do custom dehydration of the Struct back into the Debian 822 format.
type Marshallable interface {
	MarshalControl() (string, error)
}

// }}}

// ConvertToParagraph {{{

// Given a Struct, convert that Struct back into a control.Paragraph.
// This is not exactly useful as part of the external API, but may be
// useful in some funny circumstances where you need to treat a Struct
// you Unmarshaled into as a control.Paragraph again.
//
// In most cases, the Marshal API should be sufficient. Use of this API
// is mildly discouraged.
func ConvertToParagraph(incoming interface{}) (*Paragraph, error) {
	data := reflect.ValueOf(incoming)
	if data.Type().Kind() != reflect.Ptr {
		return nil, fmt.Errorf("Can only Decode a pointer to a Struct")
	}
	return convertToParagraph(data.Elem())
}

// Top-level conversion dispatch {{{

func convertToParagraph(data reflect.Value) (*Paragraph, error) {
	order := []string{}
	values := map[string]string{}

	if data.Type().Kind() != reflect.Struct {
		return nil, fmt.Errorf("Can only Decode a Struct")
	}

	paragraphType := reflect.TypeOf(Paragraph{})
	var foundParagraph Paragraph = Paragraph{}

	for i := 0; i < data.NumField(); i++ {
		field := data.Field(i)
		fieldType := data.Type().Field(i)

		if fieldType.Anonymous {
			if fieldType.Type == paragraphType {
				foundParagraph = field.Interface().(Paragraph)
			}
			continue
		}

		paragraphKey := fieldType.Name
		if it := fieldType.Tag.Get("control"); it != "" {
			paragraphKey = it
		}

		if paragraphKey == "-" {
			/* If the key is "-", lets go ahead and skip it */
			continue
		}

		data, err := marshalStructValue(field, fieldType)
		if err != nil {
			return nil, err
		}

		required := fieldType.Tag.Get("required") == "true"
		if data == "" && !required {
			continue
		}

		if fieldType.Tag.Get("multiline") == "true" {
			data = "\n" + data
		}

		order = append(order, paragraphKey)
		values[paragraphKey] = data
	}
	para := foundParagraph.Update(Paragraph{Order: order, Values: values})
	return &para, nil
}

// }}}

// convert a struct value {{{

func marshalStructValue(field reflect.Value, fieldType reflect.StructField) (string, error) {
	switch field.Type().Kind() {
	case reflect.String:
		return field.String(), nil
	case reflect.Uint:
		return strconv.Itoa(int(field.Uint())), nil
	case reflect.Int:
		return strconv.Itoa(int(field.Int())), nil
	case reflect.Ptr:
		return marshalStructValue(field.Elem(), fieldType)
	case reflect.Slice:
		return marshalStructValueSlice(field, fieldType)
	case reflect.Struct:
		return marshalStructValueStruct(field, fieldType)
	}
	return "", fmt.Errorf("Unknown type: %s", field.Type().Kind())
}

// }}}

// convert a struct value of type struct {{{

func marshalStructValueStruct(field reflect.Value, fieldType reflect.StructField) (string, error) {
	/* Right, so, we've got a type we don't know what to do with. We should
	 * grab the method, or throw a shitfit. */
	if marshal, ok := field.Interface().(Marshallable); ok {
		return marshal.MarshalControl()
	}

	return "", fmt.Errorf(
		"Type '%s' does not implement control.Marshallable",
		field.Type().Name(),
	)
}

// }}}

// convert a struct value of type slice {{{

func marshalStructValueSlice(field reflect.Value, fieldType reflect.StructField) (string, error) {
	var delim = " "
	if it := fieldType.Tag.Get("delim"); it != "" {
		delim = it
	}
	data := []string{}

	for i := 0; i < field.Len(); i++ {
		elem := field.Index(i)
		if stringification, err := marshalStructValue(elem, fieldType); err != nil {
			return "", err
		} else {
			data = append(data, stringification)
		}
	}

	return strings.Join(data, delim), nil
}

// }}}

// }}}

// Marshal {{{

// Marshal is a one-off interface to serialize a single object to a writer.
//
// Most notably, this will *not* separate Paragraphs with a newline as is
// expected upon repeated calls, please use the Encoder streaming interface
// for that.
//
// It's also worth noting that this *will* also write out elements that
// were Unmarshaled into a Struct without a member of that name if (and only
// if) the target Struct contains a `control.Paragraph` anonymous member.
//
// This is handy if the Unmarshaler was given any `X-*` keys that were not
// present on your Struct.
//
// Given a struct (or list of structs), write to the io.Writer stream
// in the RFC822-alike Debian control-file format
//
// This code will attempt to unpack it into the struct based on the
// literal name of the key, This can be overridden by the struct tag
// `control:""`.
//
// If you're dehydrating a list of strings, you have the option of defining
// a string to join the tokens with (`delim:", "`).
//
// In order to Marshal a custom Struct, you are required to implement the
// Marshallable interface. It's highly encouraged to put this interface on
// the struct without a pointer receiver, so that pass-by-value works
// when you call Marshal.
func Marshal(writer io.Writer, data interface{}) error {
	encoder, err := NewEncoder(writer)
	if err != nil {
		return err
	}
	return encoder.Encode(data)
}

// }}}

// Encoder {{{

// Encoder is a struct that allows for the streaming Encoding of data
// back out to an `io.Writer`. Most notably, this will separate
// subsequent `Encode` calls of a Struct with a newline.
//
// It's also worth noting that this *will* also write out elements that
// were Unmarshaled into a Struct without a member of that name if (and only
// if) the target Struct contains a `control.Paragraph` anonymous member.
//
// This is handy if the Unmarshaler was given any `X-*` keys that were not
// present on your Struct.
//
// Given a struct (or list of structs), write to the io.Writer stream
// in the RFC822-alike Debian control-file format
//
// This code will attempt to unpack it into the struct based on the
// literal name of the key, This can be overridden by the struct tag
// `control:""`.
//
// If you're dehydrating a list of strings, you have the option of defining
// a string to join the tokens with (`delim:", "`).
//
// In order to Marshal a custom Struct, you are required to implement the
// Marshallable interface. It's highly encouraged to put this interface on
// the struct without a pointer receiver, so that pass-by-value works
// when you call Marshal.
type Encoder struct {
	writer         io.Writer
	alreadyWritten bool
}

// NewEncoder {{{

// Create a new Encoder, which is configured to write to the given `io.Writer`.
func NewEncoder(writer io.Writer) (*Encoder, error) {
	return &Encoder{
		writer:         writer,
		alreadyWritten: false,
	}, nil
}

// }}}

// Encode {{{

// Take a Struct, Encode it into a Paragraph, and write that out to the
// io.Writer set up when the Encoder was configured.
func (e *Encoder) Encode(incoming interface{}) error {
	data := reflect.ValueOf(incoming)
	return e.encode(data)
}

// Top-level Encode reflect dispatch {{{

func (e *Encoder) encode(data reflect.Value) error {
	if data.Type().Kind() == reflect.Ptr {
		return e.encode(data.Elem())
	}

	switch data.Type().Kind() {
	case reflect.Slice:
		return e.encodeSlice(data)
	case reflect.Struct:
		return e.encodeStruct(data)
	}
	return fmt.Errorf("Unknown type")
}

// }}}

// Encode a Slice {{{

func (e *Encoder) encodeSlice(data reflect.Value) error {
	for i := 0; i < data.Len(); i++ {
		if err := e.encodeStruct(data.Index(i)); err != nil {
			return err
		}
	}
	return nil
}

// }}}

// Encode a Struct {{{

func (e *Encoder) encodeStruct(data reflect.Value) error {
	if e.alreadyWritten {
		_, err := e.writer.Write([]byte("\n"))
		if err != nil {
			return err
		}
	}
	paragraph, err := convertToParagraph(data)
	if err != nil {
		return err
	}
	e.alreadyWritten = true
	return paragraph.WriteTo(e.writer)
}

// }}}

// }}}

// }}}

// vim: foldmethod=marker