package main

import (
    "fmt"
    "os"

    "github.com/gdamore/tcell/v2"
    "github.com/gdamore/tcell/v2/encoding"

    "github.com/mattn/go-runewidth"
)

func emitStr(s tcell.Screen, x, y int, style tcell.Style, str string) {
    for _, c := range str {
        var comb []rune
        w := runewidth.RuneWidth(c)
        if w == 0 {
            comb = []rune{c}
            c = ' '
            w = 1
        }
        s.SetContent(x, y, c, comb, style)
        x += w
    }
}

func displayHelloWorld(s tcell.Screen) {
    w, h := s.Size()
    s.Clear()
    style := tcell.StyleDefault.Foreground(tcell.ColorCadetBlue.TrueColor()).Background(tcell.ColorWhite)
    emitStr(s, w/2-7, h/2, style, "Hello, World!")
    emitStr(s, w/2-9, h/2+1, tcell.StyleDefault, "Press ESC to exit.")
    s.Show()
}

// This program just prints "Hello, World!".  Press ESC to exit.
func main() {
    encoding.Register()

    s, e := tcell.NewScreen()
    if e != nil {
        fmt.Fprintf(os.Stderr, "%v\n", e)
        os.Exit(1)
    }
    if e := s.Init(); e != nil {
        fmt.Fprintf(os.Stderr, "%v\n", e)
        os.Exit(1)
    }

    defStyle := tcell.StyleDefault.
    Background(tcell.ColorBlack).
    Foreground(tcell.ColorWhite)
    s.SetStyle(defStyle)

    displayHelloWorld(s)

    for {
        switch ev := s.PollEvent().(type) {
        case *tcell.EventResize:
            s.Sync()
            displayHelloWorld(s)
        case *tcell.EventKey:
            if ev.Key() == tcell.KeyEscape {
                s.Fini()
                os.Exit(0)
            }
        }
    }
}