// Copyright 2023, Command Line Inc.
// SPDX-License-Identifier: Apache-2.0

package statediff

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"strings"
)

const LineDiffVersion_0 = 0
const LineDiffVersion = 1

type SingleLineEntry struct {
	LineVal int
	Run     int
}

type LineDiffType struct {
	Version     int
	SplitString string // added in version 1
	Lines       []SingleLineEntry
	NewData     []string
}

func (diff *LineDiffType) Clear() {
	diff.Version = LineDiffVersion
	diff.SplitString = ""
	diff.Lines = nil
	diff.NewData = nil
}

func (diff LineDiffType) Dump() {
	fmt.Printf("DIFF: v%d\n", diff.Version)
	pos := 1
	for _, entry := range diff.Lines {
		fmt.Printf("  %d-%d: %d\n", pos, pos+entry.Run, entry.LineVal)
		pos += entry.Run
	}
	for idx, str := range diff.NewData {
		fmt.Printf("  n%d: %s\n", idx+1, str)
	}
}

// simple encoding
// a 0 means read a line from NewData
// a non-zero number means read the 1-indexed line from OldData
func (diff LineDiffType) applyDiff(oldData []string) ([]string, error) {
	rtn := make([]string, 0, len(diff.Lines))
	newDataPos := 0
	for _, entry := range diff.Lines {
		if entry.LineVal == 0 {
			for i := 0; i < entry.Run; i++ {
				if newDataPos >= len(diff.NewData) {
					return nil, fmt.Errorf("not enough newdata for diff")
				}
				rtn = append(rtn, diff.NewData[newDataPos])
				newDataPos++
			}
		} else {
			oldDataPos := entry.LineVal - 1 // 1-indexed
			for i := 0; i < entry.Run; i++ {
				realPos := oldDataPos + i
				if realPos < 0 || realPos >= len(oldData) {
					return nil, fmt.Errorf("diff index out of bounds %d old-data-len:%d", realPos, len(oldData))
				}
				rtn = append(rtn, oldData[realPos])
			}
		}
	}
	return rtn, nil
}

func putUVarint(buf *bytes.Buffer, viBuf []byte, ival int) {
	l := binary.PutUvarint(viBuf, uint64(ival))
	buf.Write(viBuf[0:l])
}

// run length encoding, writes a uvarint for length, and then that many bytes of data
func putEncodedString(buf *bytes.Buffer, viBuf []byte, str string) {
	l := binary.PutUvarint(viBuf, uint64(len(str)))
	buf.Write(viBuf[0:l])
	buf.WriteString(str)
}

func readEncodedString(buf *bytes.Buffer) (string, error) {
	strLen64, err := binary.ReadUvarint(buf)
	if err != nil {
		return "", fmt.Errorf("invalid diff, cannot read string length: %v", err)
	}
	strLen := int(strLen64)
	if strLen == 0 {
		return "", nil
	}
	strBytes := buf.Next(strLen)
	if len(strBytes) != strLen {
		return "", fmt.Errorf("invalid diff, partial read, expected %d, got %d", strLen, len(strBytes))
	}
	return string(strBytes), nil
}

// version 0 is no longer used, but kept here as a reference for decoding
// simple encoding
// write varints.  first version, then then len, then len-number-of-varints, then fill the rest with newdata
// [version] [len-varint] [varint]xlen... newdata (bytes)
func (diff LineDiffType) Encode_v0() []byte {
	var buf bytes.Buffer
	viBuf := make([]byte, binary.MaxVarintLen64)
	putUVarint(&buf, viBuf, LineDiffVersion_0)
	putUVarint(&buf, viBuf, len(diff.Lines))
	for _, entry := range diff.Lines {
		putUVarint(&buf, viBuf, entry.LineVal)
		putUVarint(&buf, viBuf, entry.Run)
	}
	for idx, str := range diff.NewData {
		buf.WriteString(str)
		if idx != len(diff.NewData)-1 {
			buf.WriteString(diff.SplitString)
		}
	}
	return buf.Bytes()
}

// version 1 updates the diff to include the split-string
// it also encodes all the strings with run-length encoding
func (diff LineDiffType) Encode() []byte {
	var buf bytes.Buffer
	viBuf := make([]byte, binary.MaxVarintLen64)
	putUVarint(&buf, viBuf, LineDiffVersion)
	putEncodedString(&buf, viBuf, diff.SplitString)
	putUVarint(&buf, viBuf, len(diff.Lines))
	for _, entry := range diff.Lines {
		putUVarint(&buf, viBuf, entry.LineVal)
		putUVarint(&buf, viBuf, entry.Run)
	}
	writeEncodedStringArray(&buf, viBuf, diff.NewData)
	return buf.Bytes()
}

func (rtn *LineDiffType) readEncodedLines(buf *bytes.Buffer) error {
	linesLen64, err := binary.ReadUvarint(buf)
	if err != nil {
		return fmt.Errorf("invalid diff, cannot read lines length: %v", err)
	}
	linesLen := int(linesLen64)
	rtn.Lines = make([]SingleLineEntry, linesLen)
	for idx := 0; idx < linesLen; idx++ {
		lineVal64, err := binary.ReadUvarint(buf)
		if err != nil {
			return fmt.Errorf("invalid diff, cannot read line %d: %v", idx, err)
		}
		lineRun64, err := binary.ReadUvarint(buf)
		if err != nil {
			return fmt.Errorf("invalid diff, cannot read line-run %d: %v", idx, err)
		}
		rtn.Lines[idx] = SingleLineEntry{LineVal: int(lineVal64), Run: int(lineRun64)}
	}
	return nil
}

func writeEncodedStringArray(buf *bytes.Buffer, viBuf []byte, strArr []string) {
	putUVarint(buf, viBuf, len(strArr))
	for _, str := range strArr {
		putEncodedString(buf, viBuf, str)
	}
}

func readEncodedStringArray(buf *bytes.Buffer) ([]string, error) {
	strArrLen64, err := binary.ReadUvarint(buf)
	if err != nil {
		return nil, fmt.Errorf("invalid diff, cannot read string-array length: %v", err)
	}
	strArrLen := int(strArrLen64)
	rtn := make([]string, strArrLen)
	for idx := 0; idx < strArrLen; idx++ {
		str, err := readEncodedString(buf)
		if err != nil {
			return nil, err
		}
		rtn[idx] = str
	}
	return rtn, nil
}

func (rtn *LineDiffType) Decode(diffBytes []byte) error {
	rtn.Clear()
	if len(diffBytes) == 0 {
		return nil
	}
	r := bytes.NewBuffer(diffBytes)
	version, err := binary.ReadUvarint(r)
	if err != nil {
		return fmt.Errorf("invalid diff, cannot read version: %v", err)
	}
	if version == LineDiffVersion_0 {
		return rtn.Decode_v0(diffBytes)
	}
	if version != LineDiffVersion {
		return fmt.Errorf("invalid diff, bad version: %d", version)
	}
	rtn.Version = int(version)
	splitString, err := readEncodedString(r)
	if err != nil {
		return fmt.Errorf("invalid diff, cannot read split-string: %v", err)
	}
	rtn.SplitString = splitString
	err = rtn.readEncodedLines(r)
	if err != nil {
		return err
	}
	rtn.NewData, err = readEncodedStringArray(r)
	if err != nil {
		return err
	}
	return nil
}

func (rtn *LineDiffType) Decode_v0(diffBytes []byte) error {
	r := bytes.NewBuffer(diffBytes)
	version, err := binary.ReadUvarint(r)
	if err != nil {
		return fmt.Errorf("invalid diff, cannot read version: %v", err)
	}
	if version != LineDiffVersion_0 {
		return fmt.Errorf("invalid diff, bad version: %d", version)
	}
	rtn.Version = int(version)
	rtn.SplitString = "\n" // added when we added version 1
	err = rtn.readEncodedLines(r)
	if err != nil {
		return err
	}
	restOfInput := string(r.Bytes())
	if len(restOfInput) > 0 {
		rtn.NewData = strings.Split(restOfInput, "\n")
	}
	return nil
}

func makeLineDiff(oldData []string, newData []string, splitString string) LineDiffType {
	var rtn LineDiffType
	rtn.Version = LineDiffVersion
	rtn.SplitString = splitString
	oldDataMap := make(map[string]int) // 1-indexed
	for idx, str := range oldData {
		if _, found := oldDataMap[str]; found {
			continue
		}
		oldDataMap[str] = idx + 1
	}
	var cur *SingleLineEntry
	rtn.Lines = make([]SingleLineEntry, 0)
	for _, str := range newData {
		oldIdx, found := oldDataMap[str]
		if cur != nil && cur.LineVal != 0 {
			checkLine := cur.LineVal + cur.Run - 1
			if checkLine < len(oldData) && oldData[checkLine] == str {
				cur.Run++
				continue
			}
		} else if cur != nil && cur.LineVal == 0 && !found {
			cur.Run++
			rtn.NewData = append(rtn.NewData, str)
			continue
		}
		if cur != nil {
			rtn.Lines = append(rtn.Lines, *cur)
		}
		cur = &SingleLineEntry{Run: 1}
		if found {
			cur.LineVal = oldIdx
		} else {
			cur.LineVal = 0
			rtn.NewData = append(rtn.NewData, str)
		}
	}
	if cur != nil {
		rtn.Lines = append(rtn.Lines, *cur)
	}
	return rtn
}

func MakeLineDiff(str1 string, str2 string, splitString string) []byte {
	if str1 == str2 {
		return nil
	}
	str1Arr := strings.Split(str1, splitString)
	str2Arr := strings.Split(str2, splitString)
	diff := makeLineDiff(str1Arr, str2Arr, splitString)
	return diff.Encode()
}

func ApplyLineDiff(str1 string, diffBytes []byte) (string, error) {
	if len(diffBytes) == 0 {
		return str1, nil
	}
	var diff LineDiffType
	err := diff.Decode(diffBytes)
	if err != nil {
		return "", err
	}
	str1Arr := strings.Split(str1, diff.SplitString)
	str2Arr, err := diff.applyDiff(str1Arr)
	if err != nil {
		return "", err
	}
	return strings.Join(str2Arr, diff.SplitString), nil
}