package cwriter

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"os"

	isatty "github.com/mattn/go-isatty"
	"golang.org/x/crypto/ssh/terminal"
)

// ESC is the ASCII code for escape character
const ESC = 27

var NotATTY = errors.New("not a terminal")

var (
	cursorUp           = fmt.Sprintf("%c[%dA", ESC, 1)
	clearLine          = fmt.Sprintf("%c[2K\r", ESC)
	clearCursorAndLine = cursorUp + clearLine
)

// Writer is a buffered the writer that updates the terminal.
// The contents of writer will be flushed when Flush is called.
type Writer struct {
	out       io.Writer
	buf       bytes.Buffer
	lineCount int
}

// New returns a new Writer with defaults
func New(w io.Writer) *Writer {
	return &Writer{out: w}
}

// Flush flushes the underlying buffer
func (w *Writer) Flush() error {
	err := w.clearLines()
	w.lineCount = bytes.Count(w.buf.Bytes(), []byte("\n"))
	// WriteTo takes care of w.buf.Reset
	if _, e := w.buf.WriteTo(w.out); err == nil {
		err = e
	}
	return err
}

// Write appends the contents of p to the underlying buffer
func (w *Writer) Write(p []byte) (n int, err error) {
	return w.buf.Write(p)
}

// WriteString writes string to the underlying buffer
func (w *Writer) WriteString(s string) (n int, err error) {
	return w.buf.WriteString(s)
}

// ReadFrom reads from the provided io.Reader and writes to the underlying buffer.
func (w *Writer) ReadFrom(r io.Reader) (n int64, err error) {
	return w.buf.ReadFrom(r)
}

func (w *Writer) GetWidth() (int, error) {
	if f, ok := w.out.(*os.File); ok {
		if isatty.IsTerminal(f.Fd()) {
			tw, _, err := terminal.GetSize(int(f.Fd()))
			return tw, err
		}
	}
	return -1, NotATTY
}