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// Copyright 2009 The Go Authors. All rights reserved.

// Use of this source code is governed by a BSD-style

// license that can be found in the LICENSE file.

package asn1

import (

        "reflect"

        "strconv"

        "strings"

)

// ASN.1 objects have metadata preceding them:

//   the tag: the type of the object

//   a flag denoting if this object is compound or not

//   the class type: the namespace of the tag

//   the length of the object, in bytes

// Here are some standard tags and classes

const (

        tagBoolean         = 1

        tagInteger         = 2

        tagBitString       = 3

        tagOctetString     = 4

        tagOID             = 6

        tagEnum            = 10

        tagUTF8String      = 12

        tagSequence        = 16

        tagSet             = 17

        tagPrintableString = 19

        tagT61String       = 20

        tagIA5String       = 22

        tagUTCTime         = 23

        tagGeneralizedTime = 24

        tagGeneralString   = 27

)

const (

        classUniversal       = 0

        classApplication     = 1

        classContextSpecific = 2

        classPrivate         = 3

)

type tagAndLength struct {

        class, tag, length int

        isCompound         bool

}

// ASN.1 has IMPLICIT and EXPLICIT tags, which can be translated as "instead

// of" and "in addition to". When not specified, every primitive type has a

// default tag in the UNIVERSAL class.

//

// For example: a BIT STRING is tagged [UNIVERSAL 3] by default (although ASN.1

// doesn't actually have a UNIVERSAL keyword). However, by saying [IMPLICIT

// CONTEXT-SPECIFIC 42], that means that the tag is replaced by another.

//

// On the other hand, if it said [EXPLICIT CONTEXT-SPECIFIC 10], then an

// /additional/ tag would wrap the default tag. This explicit tag will have the

// compound flag set.

//

// (This is used in order to remove ambiguity with optional elements.)

//

// You can layer EXPLICIT and IMPLICIT tags to an arbitrary depth, however we

// don't support that here. We support a single layer of EXPLICIT or IMPLICIT

// tagging with tag strings on the fields of a structure.

// fieldParameters is the parsed representation of tag string from a structure field.

type fieldParameters struct {

        optional     bool   // true iff the field is OPTIONAL

        explicit     bool   // true iff an EXPLICIT tag is in use.

        application  bool   // true iff an APPLICATION tag is in use.

        defaultValue *int64 // a default value for INTEGER typed fields (maybe nil).

        tag          *int   // the EXPLICIT or IMPLICIT tag (maybe nil).

        stringType   int    // the string tag to use when marshaling.

        set          bool   // true iff this should be encoded as a SET

        // Invariants:

        //   if explicit is set, tag is non-nil.

}

// Given a tag string with the format specified in the package comment,

// parseFieldParameters will parse it into a fieldParameters structure,

// ignoring unknown parts of the string.

func parseFieldParameters(str string) (ret fieldParameters) {

        for _, part := range strings.Split(str, ",") {

                switch {

                case part == "optional":

                        ret.optional = true

                case part == "explicit":

                        ret.explicit = true

                        if ret.tag == nil {

                                ret.tag = new(int)

                        }

                case part == "ia5":

                        ret.stringType = tagIA5String

                case part == "printable":

                        ret.stringType = tagPrintableString

                case strings.HasPrefix(part, "default:"):

                        i, err := strconv.ParseInt(part[8:], 10, 64)

                        if err == nil {

                                ret.defaultValue = new(int64)

                                *ret.defaultValue = i

                        }

                case strings.HasPrefix(part, "tag:"):

                        i, err := strconv.Atoi(part[4:])

                        if err == nil {

                                ret.tag = new(int)

                                *ret.tag = i

                        }

                case part == "set":

                        ret.set = true

                case part == "application":

                        ret.application = true

                        if ret.tag == nil {

                                ret.tag = new(int)

                        }

                }

        }

        return

}

// Given a reflected Go type, getUniversalType returns the default tag number

// and expected compound flag.

func getUniversalType(t reflect.Type) (tagNumber int, isCompound, ok bool) {

        switch t {

        case objectIdentifierType:

                return tagOID, false, true

        case bitStringType:

                return tagBitString, false, true

        case timeType:

                return tagUTCTime, false, true

        case enumeratedType:

                return tagEnum, false, true

        case bigIntType:

                return tagInteger, false, true

        }

        switch t.Kind() {

        case reflect.Bool:

                return tagBoolean, false, true

        case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:

                return tagInteger, false, true

        case reflect.Struct:

                return tagSequence, true, true

        case reflect.Slice:

                if t.Elem().Kind() == reflect.Uint8 {

                        return tagOctetString, false, true

                }

                if strings.HasSuffix(t.Name(), "SET") {

                        return tagSet, true, true

                }

                return tagSequence, true, true

        case reflect.String:

                return tagPrintableString, false, true

        }

        return 0, false, false

}