thread.go

package raweml

import (
	"bytes"
	"encoding/base64"
	"encoding/binary"
	"errors"
	"io"
	"math/rand"
	"time"

	"github.com/google/uuid"
	// "github.com/pborman/uuid"
)

// Thread represents an email thread (conversation group)
type Thread struct {
	DateUnixNano int64        // Thread Date in Unix Nanoseconds
	guid         uuid.UUID    // created based on the "topic" NOTE: Once the thread is created guid is saved and cannot be changed
	topic        string       // usually a normalized subject (subject without prefixes "RE:", "FW:")
	ChildBlocks  []ChildBlock // Sub-Thread
}

// ChildBlock represents a sub thread of the email thread
//
// - TimeFlag: 1 bit
//		0 when TimeDiff < 0.02s && TimeDiff > 2 years;
//		1 when TimeDiff < 1s && TimeDiff > 56 years)
// - TimeDifference: time difference between the child block create time and the time in the header block expressed in FILETIME units
// 		if TimeFlag = 0 : discard high 15 bits and low 18 bits
// 		if TimeFlag = 1 : discard high 10 bits and low 32 bits
// - RandomNum: random number gernerated by calling GetTickCount()
// - SequenceCount: default set to 0 (Four bits containing a sequence count that is taken from part of the random number.)
type ChildBlock struct {
	TimeFlag       bool
	TimeDifference int64 // Unix NanoSecond
	RandomNum      byte
	SequenceCount  byte
}

// NewThread creates a new Thread struct based on the provided `topic` argument
func NewThread(topic string) Thread {
	guid := uuid.NewSHA1(nameSpaceAppID, []byte(topic))
	return Thread{
		time.Now().UTC().UnixNano(),
		guid,
		topic,
		nil,
	}
}

// NewEmailThreadFromParams creates a new Thread struct from arguments
func NewEmailThreadFromParams(dateUnixNanoSec int64, guid uuid.UUID, topic string, childBlocks []ChildBlock) (r Thread) {
	return Thread{
		dateUnixNanoSec,
		guid,
		topic,
		childBlocks,
	}
}

// ParseEmailThread creates thread based on the idx and topic
func ParseEmailThread(idx string, topic string) (r Thread, err error) {
	// Thread-Index is composed of 22 bytes total + 0 or more child blocks of 5 bytes
	//  1 byte	- reserved (value 1) (used with next 5 bytes as 6 bytes structure holding the FILETIME value)
	//  5 bytes	- (plus the first byte) current system time converted to the FILETIME structure format
	// 16 bytes - holiding GUID
	// -------------------------------------------------------------------------------------------------
	// ref: https://docs.microsoft.com/en-us/office/client-developer/outlook/mapi/tracking-conversations
	// -------------------------------------------------------------------------------------------------

	if len(idx) < 22 {
		return r, errors.New("Inavlid Thread-Index. Expected minimum 22 bytes.")
	}

	// decode Base64
	bytes, errD := base64.StdEncoding.DecodeString(idx)
	if errD != nil {
		return r, errD
	}

	// get TimeStamp (first 6 bytes)
	bTS := [8]byte{0, 0, 0, 0, 0, 0, 0, 0}
	copy(bTS[:6], bytes[:6])

	// convert TimeStamp to Unix nanoseconds
	uxNs := timeStampToUnix(binary.BigEndian.Uint64(bTS[:]))

	// Unix Time in nanoseconds
	threadTimeUnixNano := time.Unix(0, int64(uxNs)).UTC().UnixNano()

	// GUID portion
	threadGUID, errG := uuid.FromBytes(bytes[6:22])
	if errG != nil {
		return r, errG
	}

	// child blocks
	var childBlocks []ChildBlock
	for i := 22; i < len(bytes) && i < (22+500*5); i += 5 {
		block, err := ParseChildBlock(string(bytes[i : i+5]))
		if err != nil {
			return r, err
		}
		childBlocks = append(childBlocks, block)
	}

	return Thread{
		threadTimeUnixNano,
		threadGUID,
		topic,
		childBlocks,
	}, nil

}

// AddChildBlock ads a child block to the emails thread
func (thread *Thread) AddChildBlock() {
	deltaTime := time.Since(time.Unix(0, thread.DateUnixNano))
	thread.ChildBlocks = append(thread.ChildBlocks, NewChildBlock(deltaTime.Nanoseconds()))
}

// String returns thread data as Base64 encoded string
func (thread Thread) String() string {
	return string(thread.Bytes())
}

// Bytes returns thread bytes data encoded in Base64
func (thread Thread) Bytes() (r []byte) {

	// get Unix nanoseconds
	tn := thread.DateUnixNano

	// conver to timestamp
	tn = unixToTimeStamp64(tn)
	tsBytes := int64ToBytes(tn)

	// compose Thread Index
	bufIdx := new(bytes.Buffer)
	encoder := base64.NewEncoder(base64.StdEncoding, bufIdx)
	defer encoder.Close()
	encoder.Write(tsBytes[:6])                     // 6  - TIME_STAMP
	encoder.Write(thread.GUIDBytes())              // 16 - GUID
	for i := 0; i < len(thread.ChildBlocks); i++ { // 5  - per Child block
		encoder.Write(thread.ChildBlocks[i].Bytes())
	}

	encoder.Close()
	return bufIdx.Bytes()
}

// GUIDBytes returns bytes of the thread GUID
func (thread Thread) GUIDBytes() []byte {
	bytes, _ := thread.guid.MarshalBinary() // this will never return error
	return bytes
}
func (thread Thread) write(w io.Writer) {
	w.Write(thread.Bytes())
}

// Index is an alias for String() function that returns the thread as Base64 encoded string
func (thread Thread) Index() string {
	return thread.String()
}

// Reference returns a hashed version of the Thread GUID that is created based on nameSpaceAppID and Topic
func (thread *Thread) Reference() string {
	return hexToBase64(thread.GUIDBytes())
}

// GetGUID returns thread GUID
func (thread Thread) GetGUID() uuid.UUID {
	return thread.guid
}

// GetTopic returns thread topic
func (thread Thread) GetTopic() string {
	return thread.topic
}

// NewChildBlock creates a child header block
func NewChildBlock(deltaTimeUxNs int64) (r ChildBlock) {
	// child block is composed of 5 bytes total as follows:
	// 1 bit 	- One  bit containing a code representing the difference between the current time and the time stored in the header block.
	//				This bit will be: 0 if the difference is less than .02 second and greater than two years and
	//								  1 if the difference is less than one second and greater than 56 years.
	// 				   default value: 0 although MS doesn't specify what value should be set between 1s and 2y
	// 31 bits 	- containing the difference between the current time and the time in the header block expressed in FILETIME units.
	//			  This part of the child block is produced using one of two strategies, depending on the value of the first bit.
	//			  * If this bit is zero, ScCreateConversationIndex discards the high 15 bits and the low 18 bits.
	//			  * If this bit is one, the function discards the high 10 bits and the low 23 bits.
	// 4 bits 	- containing a random number generated by calling the Win32 function GetTickCount.
	// 4 bits 	- containing a sequence count that is taken from part of the random number.
	// -------------------------------------------------------------------------------------------------
	// ref: https://docs.microsoft.com/en-us/office/client-developer/outlook/mapi/tracking-conversations
	// -------------------------------------------------------------------------------------------------
	timeFlag := false
	deltaDuration := time.Duration(deltaTimeUxNs) * time.Nanosecond
	deltaYears := deltaDuration.Hours() / 24 / 365
	if deltaDuration.Seconds() <= 0.02 || deltaYears > 2 {
		timeFlag = false
	} else if deltaDuration.Seconds() <= 1 || deltaYears > 56 {
		timeFlag = true
	}

	// random num (last 1 Byte)
	rand.Seed(time.Now().UnixNano())
	randomNum := byte(rand.Intn(15))

	// sequence count
	sequenceCount := byte(0)

	return ChildBlock{
		timeFlag,
		deltaTimeUxNs,
		randomNum,
		sequenceCount,
	}
}

// ParseChildBlock converts string to a ChildBlock struct
func ParseChildBlock(blockString string) (block ChildBlock, err error) {
	if len(blockString) < 0 || len(blockString) > 5 {
		return ChildBlock{}, errors.New("Block string is too short/long!")
	}

	bytes := []byte(blockString)

	//  1 bit - flag
	timeFlag := byte(bytes[0]&0x80) > 0

	// 31 bit - time - containing the difference between the current time and the time in the header block expressed in FILETIME units.This part of the child block is produced using one of two strategies, depending on the value of the first bit.
	//		If first bit is 1, the function discards the high 10 bits and the low 23 bits.
	//		If first bit is 0, ScCreateConversationIndex discards the high 15 bits and the low 18 bits.

	// add prefix + suffix
	dWord := binary.BigEndian.Uint32(bytes[:4])
	dWord = dWord & 0x7fffffff // remove first bit (timeFlag)
	qWord := uint64(dWord)
	if timeFlag {
		qWord = qWord << 23
	} else {
		qWord = qWord << 18
	}
	tsDiff := time.Duration(qWord*100) * time.Nanosecond

	//  4 bit - Random num
	rnd := bytes[4] & 0xF0 >> 4

	//  4 bit - sequence count
	seq := bytes[4] & 0x0F

	return ChildBlock{
		timeFlag,
		tsDiff.Nanoseconds(),
		rnd,
		seq,
	}, nil

}

// Bytes returns bits representing the Child block :
// 40 bits: 1 flag, 31 time diff, 4 random, 4 seq
func (block ChildBlock) Bytes() []byte {

	if block.TimeDifference == 0 {
		return nil
	}
	cbBytes := []byte{0, 0, 0, 0, 0}
	const FirstBitUp = uint64(0x80000000)

	// get first 4 bytes as follows:
	//  1  bit - time flag
	// 31 bits - containing the difference between the current time and the time in the header block expressed in FILETIME units.This part of the child block is produced using one of two strategies, depending on the value of the first bit.
	//		If first bit is 1, the function discards the high 10 bits and the low 23 bits.
	//		If first bit is 0, ScCreateConversationIndex discards the high 15 bits and the low 18 bits.
	tsDiff := uint64(block.TimeDifference / 100)

	// componse (first 4 bytes)
	if block.TimeFlag {
		tsDiff = tsDiff << 10
		tsDiff = tsDiff >> (10 + 23)
	} else {
		tsDiff = tsDiff << 15
		tsDiff = tsDiff >> (15 + 18)
	}
	// componse first bit
	if block.TimeFlag {
		tsDiff = tsDiff | FirstBitUp
	}
	binary.BigEndian.PutUint32(cbBytes, uint32(tsDiff))

	// get last 1 byte
	cbBytes[4] = (block.RandomNum << 4) | block.SequenceCount

	return cbBytes
}

// String returns the base64 encoded string of the header child block
func (block ChildBlock) String() string {
	return string(block.Bytes())
}

// Helping types -----------------------

// Filetime represents the date and time for a file.
// It is a 64-bit value representing the number of 100-nanosecond intervals since January 1, 1601 (UTC)
// This is different from Unix time which is the number of nanoseconds elapsed since January 1, 1970, 00:00:00 (UTC)
type Filetime struct {
	// --------------------------
	// 	Generic file time stamp :
	// --------------------------
	// 	31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 	15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
	//  |<------ year ------>|<- month ->|<---- day --->|	|<--- hour --->|<---- minute --->|<- second/2 ->|
	//
	//    Offset   Length   Contents
	// 	   0       7 bits   year     years since 1980
	// 	   7       4 bits   month    [1..12]
	//    11       5 bits   day      [1..31]
	//    16       5 bits   hour     [0..23]
	//    21       6 bits   minite   [0..59]
	//    27       5 bits   second/2 [0..29]
	// --------------------------
	// ref: https://golang.org/src/syscall/types_windows.go
	LowDateTime  uint32
	HighDateTime uint32
}

// UnixNanoseconds returns Filetime in nanoseconds since Epoch (00:00:00 UTC, January 1, 1970).
func (ft *Filetime) UnixNanoseconds() int64 {

	// 100-nanosecond intervals since January 1, 1601
	nsec := int64(ft.HighDateTime)<<32 + int64(ft.LowDateTime)

	// change starting time to the Epoch (00:00:00 UTC, January 1, 1970)
	nsec -= 116444736000000000

	// convert into nanoseconds
	nsec *= 100
	return nsec
}

// UnixNanoToFiletime converts nano seconds to Filetime
func UnixNanoToFiletime(nsec int64) (ft Filetime) {
	// convert into 100-nanosecond
	nsec /= 100

	// change starting time to January 1, 1601
	nsec += 116444736000000000

	// split into high / low
	ft.LowDateTime = uint32(nsec & 0xffffffff)
	ft.HighDateTime = uint32(nsec >> 32 & 0xffffffff)
	return ft
}

// Helping functions

// hexToBase64 converts bytes to base64 string
func hexToBase64(bites []byte) string {
	return base64.StdEncoding.EncodeToString(bites)
}

// timeStampToUnix converts time stamp to unix time
func timeStampToUnix(timeStampTicks uint64) (unixNano uint64) {
	// 	timeStampTicks - a 64-bit value representing the number of 100-nanosecond intervals since January 1, 1601 (UTC)
	//	 	  UnixNano - the number of nanoseconds elapsed since January 1, 1970, 00:00:00 (UTC)
	return (timeStampTicks - 116444736000000000) * 100
}

// unixToTimeStamp64 converts unix time to time stamp int64
func unixToTimeStamp64(unixNanosecond int64) int64 {
	return unixNanosecond/100 + 116444736000000000
}

// Helping functions (private)

func int64ToBytes(num int64) []byte {
	b := make([]byte, 8)
	binary.BigEndian.PutUint64(b, uint64(num))
	return b
}

func bytesToInt64(b []byte) int64 {
	return int64(binary.BigEndian.Uint64(b))
}