gocui: using the Editor interface to implement a custom edition mode

vimeditor.go

package main

import (
	"log"

	"github.com/jroimartin/gocui"
)

type VimEditor struct {
	Insert bool
}

func (ve *VimEditor) Edit(v *gocui.View, key gocui.Key, ch rune, mod gocui.Modifier) {
	if ve.Insert {
		ve.InsertMode(v, key, ch, mod)
	} else {
		ve.NormalMode(v, key, ch, mod)
	}
}

func (ve *VimEditor) InsertMode(v *gocui.View, key gocui.Key, ch rune, mod gocui.Modifier) {
	switch {
	case key == gocui.KeyEsc:
		ve.Insert = false
	case ch != 0 && mod == 0:
		v.EditWrite(ch)
	case key == gocui.KeySpace:
		v.EditWrite(' ')
	case key == gocui.KeyBackspace || key == gocui.KeyBackspace2:
		v.EditDelete(true)
	case key == gocui.KeyDelete:
		v.EditDelete(false)
	case key == gocui.KeyInsert:
		v.Overwrite = !v.Overwrite
	case key == gocui.KeyEnter:
		v.EditNewLine()
	case key == gocui.KeyArrowDown:
		v.MoveCursor(0, 1, false)
	case key == gocui.KeyArrowUp:
		v.MoveCursor(0, -1, false)
	case key == gocui.KeyArrowLeft:
		v.MoveCursor(-1, 0, false)
	case key == gocui.KeyArrowRight:
		v.MoveCursor(1, 0, false)
	}
	// TODO: handle other keybindings...
}

func (ve *VimEditor) NormalMode(v *gocui.View, key gocui.Key, ch rune, mod gocui.Modifier) {
	switch {
	case ch == 'i':
		ve.Insert = true
	case ch == 'j':
		v.MoveCursor(0, 1, false)
	case ch == 'k':
		v.MoveCursor(0, -1, false)
	case ch == 'h':
		v.MoveCursor(-1, 0, false)
	case ch == 'l':
		v.MoveCursor(1, 0, false)
	}
	// TODO: handle other keybindings...
}

func quit(g *gocui.Gui, v *gocui.View) error {
	return gocui.ErrQuit
}

func layout(g *gocui.Gui) error {
	maxX, maxY := g.Size()
	if v, err := g.SetView("main", 0, 0, maxX-1, maxY-1); err != nil {
		if err != gocui.ErrUnknownView {
			return err
		}
		v.Editable = true
		v.Wrap = true
		v.Editor = &VimEditor{}
		if _, err := g.SetCurrentView("main"); err != nil {
			return err
		}
	}
	return nil
}

func main() {
	g, err := gocui.NewGui(gocui.OutputNormal)
	if err != nil {
		log.Fatalln(err)
	}
	defer g.Close()

	g.SetManagerFunc(layout)
	g.InputEsc = true
	g.Cursor = true

	if err := g.SetKeybinding("", gocui.KeyCtrlC, gocui.ModNone, quit); err != nil {
		log.Fatalln(err)
	}

	if err := g.MainLoop(); err != nil && err != gocui.ErrQuit {
		log.Fatalln(err)
	}
}