package jsoncommentstrip

import (
	"bufio"
	"io"
)

type readerState int

type reader struct {
	input *bufio.Reader
	err   error
	buff  string
	state readerState
}

func (reader *reader) checkForPreviousError(buff []byte) (count int, err error) {
	if reader.err != nil {
		buffLen := len(buff)
		err = reader.err

		if reader.buff != "" {
			if reader.state == stateOther || reader.state == stateQuotation || reader.state == stateEscape {
				readBuffBytes := []byte(reader.buff)
				readBuffLen := len(readBuffBytes)

				if readBuffLen <= buffLen {
					copy(buff, readBuffBytes)
					reader.buff = ""
					count = readBuffLen
				} else {
					err = io.ErrShortBuffer
				}
				return
			}

			reader.buff = ""
		}
	}

	return
}

func writeStringToBuffer(buff []byte, pos int, value string) (count int) {
	for _, b := range []byte(value) {
		buff[pos+count] = b
		count++
	}

	return
}

func (reader *reader) readRuneAsString() (value string, err error) {
	var char rune
	char, _, err = reader.input.ReadRune()

	if err == nil {
		value = string(char)
	}
	return
}

func (reader *reader) fillBuff() (err error) {
	if reader.buff == "" {
		var buff string
		buff, err = reader.readRuneAsString()
		if err == nil {
			reader.buff = buff
		}
	}
	return
}

func (reader *reader) processOther(next string, buff []byte, pos int) (count int) {
	str := reader.buff + next
	if str == commentMultiStart {
		reader.state = stateMComment
		reader.buff = ""
		return
	}

	if str == commentSingle {
		reader.state = stateSComment
		reader.buff = ""
		return
	}

	if reader.buff == quoteMark {
		reader.state = stateQuotation
	}

	count = writeStringToBuffer(buff, pos, reader.buff)
	reader.buff = next
	return
}

func (reader *reader) processMComment(next string, buff []byte, pos int) (count int) {
	str := reader.buff + next
	if str == commentMultiEnd {
		reader.state = stateOther
		reader.buff = ""
		return
	}
	reader.buff = next
	return
}

func (reader *reader) processSComment(next string, buff []byte, pos int) (count int) {
	if reader.buff == "\n" || reader.buff == "\r" && next == "\n" {
		reader.state = stateOther

		// keep line endings
		count += writeStringToBuffer(buff, pos, reader.buff)
	}
	reader.buff = next
	return
}

func (reader *reader) processQuotation(next string, buff []byte, pos int) (count int) {
	if reader.buff == "\\" {
		reader.state = stateEscape
	} else if reader.buff == quoteMark {
		reader.state = stateOther
	}
	count += writeStringToBuffer(buff, pos, reader.buff)
	reader.buff = next
	return
}

func (reader *reader) processEscape(next string, buff []byte, pos int) (count int) {
	reader.state = stateQuotation
	count += writeStringToBuffer(buff, pos, reader.buff)
	reader.buff = next
	return
}

func (reader *reader) processNextRune(next string, buff []byte, pos int) (count int) {
	switch reader.state {
	case stateOther:
		count = reader.processOther(next, buff, pos)
	case stateMComment:
		count = reader.processMComment(next, buff, pos)
	case stateSComment:
		count = reader.processSComment(next, buff, pos)
	case stateQuotation:
		count = reader.processQuotation(next, buff, pos)
	case stateEscape:
		count = reader.processEscape(next, buff, pos)
	}
	return
}

func (reader *reader) Read(buff []byte) (count int, err error) {
	count, err = reader.checkForPreviousError(buff)

	if err != nil {
		return
	}

	var next string
	buffLen := len(buff)
	for count < buffLen {
		reader.err = reader.fillBuff()
		if reader.err != nil {
			return
		}

		// check buffer free space
		if buffLen-count < len(reader.buff) {
			if count == 0 {
				err = io.ErrShortBuffer
			}
			return
		}

		// read next rune
		next, reader.err = reader.readRuneAsString()
		if reader.err != nil {
			return
		}

		count += reader.processNextRune(next, buff, count)
	}

	return
}

// NewReader creates new Reader instance
func NewReader(input io.Reader) Reader {
	return &reader{
		input: bufio.NewReader(input),
		state: stateOther,
	}
}