// Copyright 2013 Apcera Inc. All rights reserved.

package term

import (
	"os"
)

// Size is the size of a terminal, expressed in character cells, as Lines and
// Columns.  This might come from environment variables or OS-dependent
// resources.
type Size struct {
	Lines   int
	Columns int
}

// GetSize will return the terminal window size.
//
// We prefer environ $LINES/$COLUMNS, then fall back to tty-held information.
// We do not support use of termcap/terminfo to derive default size information.
func GetSize() (*Size, error) {
	envSize := GetEnvWindowSize()
	if envSize != nil && envSize.Lines != 0 && envSize.Columns != 0 {
		return envSize, nil
	}

	fh, err := os.Open("/dev/tty")
	if err != nil {
		// no tty, no point continuing; we only let the environ
		// avoid an error in this case because if someone has faked
		// up an environ with LINES/COLUMNS _both_ set, we should let
		// them
		return nil, err
	}

	size, err := GetTerminalWindowSize(fh)
	if err != nil {
		if envSize != nil {
			return envSize, nil
		}
		return nil, err
	}
	if envSize == nil {
		return size, err
	}

	if envSize.Lines == 0 {
		envSize.Lines = size.Lines
	}
	if envSize.Columns == 0 {
		envSize.Columns = size.Columns
	}
	return envSize, nil
}