package readline

import (
	"bytes"
	"io"
)

type RuneBuffer struct {
	buf         []rune
	idx         int
	prompt      []byte
	w           io.Writer
	lastWritten int
	printPrompt bool
}

func NewRuneBuffer(w io.Writer, prompt string) *RuneBuffer {
	rb := &RuneBuffer{
		prompt:      []byte(prompt),
		w:           w,
		printPrompt: true,
	}
	return rb
}

func (r *RuneBuffer) Runes() []rune {
	return r.buf
}

func (r *RuneBuffer) Pos() int {
	return r.idx
}

func (r *RuneBuffer) Len() int {
	return len(r.buf)
}

func (r *RuneBuffer) MoveToLineStart() {
	if r.idx == 0 {
		return
	}
	r.Refresh(-1, r.SetIdx(0))
}

func (r *RuneBuffer) MoveBackward() {
	if r.idx == 0 {
		return
	}
	r.idx--
	r.Refresh(0, -1)
}

func (rb *RuneBuffer) WriteString(s string) {
	rb.WriteRunes([]rune(s))
}

func (rb *RuneBuffer) WriteRune(r rune) {
	rb.WriteRunes([]rune{r})
}

func (rb *RuneBuffer) WriteRunes(r []rune) {
	tail := append(r, rb.buf[rb.idx:]...)
	rb.buf = append(rb.buf[:rb.idx], tail...)
	rb.idx++
	rb.Refresh(1, 1)
}

func (r *RuneBuffer) MoveForward() {
	if r.idx == len(r.buf) {
		return
	}
	r.idx++
	r.Refresh(0, 1)
}

func (r *RuneBuffer) Delete() {
	if r.idx == len(r.buf) {
		return
	}
	r.buf = append(r.buf[:r.idx], r.buf[r.idx+1:]...)
	r.Refresh(-1, 0)
}

func (r *RuneBuffer) DeleteWord() {
	if r.idx == len(r.buf) {
		return
	}
	for i := r.idx + 1; i < len(r.buf); i++ {
		if r.buf[i] != ' ' && r.buf[i-1] == ' ' {
			r.buf = append(r.buf[:r.idx], r.buf[i-1:]...)
			r.Refresh(r.idx-i+1, 0)
			return
		}
	}
	length := len(r.buf)
	r.buf = r.buf[:r.idx]
	r.Refresh(length-r.idx, 0)
}

func (r *RuneBuffer) MoveToPrevWord() {
	if r.idx == 0 {
		return
	}
	for i := r.idx - 1; i > 0; i-- {
		if r.buf[i] != ' ' && r.buf[i-1] == ' ' {
			r.Refresh(0, r.SetIdx(i))
			return
		}
	}
	r.Refresh(0, r.SetIdx(0))
}

func (r *RuneBuffer) SetIdx(idx int) (change int) {
	i := r.idx
	r.idx = idx
	return r.idx - i
}

func (r *RuneBuffer) MoveToNextWord() {
	for i := r.idx + 1; i < len(r.buf); i++ {
		if r.buf[i] != ' ' && r.buf[i-1] == ' ' {
			r.Refresh(0, r.SetIdx(i))
			return
		}
	}
	r.Refresh(0, r.SetIdx(len(r.buf)))
}

func (r *RuneBuffer) BackEscape() {
	if r.idx == 0 {
		return
	}
	r.idx--
	r.buf = append(r.buf[:r.idx], r.buf[r.idx+1:]...)
	r.Refresh(-1, -1)
}

func (r *RuneBuffer) MoveToLineEnd() {
	if r.idx == len(r.buf) {
		return
	}
	r.Refresh(0, r.SetIdx(len(r.buf)))
}

func (r *RuneBuffer) Refresh(chlen, chidx int) {
	s := r.Output(len(r.buf)-chlen, r.idx-chidx)
	r.w.Write(s)
}

func (r *RuneBuffer) RefreshSet(originLength, originIdx int) {
	r.w.Write(r.Output(originLength, originIdx))
}

func (r *RuneBuffer) Output(originLength, originIdx int) []byte {
	buf := bytes.NewBuffer(nil)
	if r.printPrompt {
		r.printPrompt = false
		buf.Write(r.prompt)
	}

	buf.Write(bytes.Repeat([]byte{'\b'}, originIdx))
	buf.Write([]byte(string(r.buf)))
	if originLength > len(r.buf) {
		buf.Write(bytes.Repeat([]byte{' '}, originLength-len(r.buf)))
		buf.Write(bytes.Repeat([]byte{'\b'}, originLength-len(r.buf)))
	}
	buf.Write(bytes.Repeat([]byte{'\b'}, len(r.buf)-r.idx))
	return buf.Bytes()
}

func (r *RuneBuffer) Clean() {
	moveToFirst := r.idx
	moveToFirst += len(r.prompt)
	r.w.Write(bytes.Repeat([]byte{'\b'}, moveToFirst))
	length := len(r.buf) + len(r.prompt)

	r.w.Write(bytes.Repeat([]byte{' '}, length))
	r.w.Write(bytes.Repeat([]byte{'\b'}, length))
	r.printPrompt = true
}

func (r *RuneBuffer) Reset() []rune {
	ret := r.buf
	r.buf = r.buf[:0]
	r.idx = 0
	r.printPrompt = true
	r.Refresh(-len(ret), r.SetIdx(0))
	return ret
}

func (r *RuneBuffer) Set(buf []rune) {
	length, idx := len(r.buf), r.idx
	r.buf = buf
	r.idx = len(r.buf)
	r.RefreshSet(length, idx)
}