Fixes #8 - Allow breaking out of the UI to run external commands (eg vim)

This isn't perfect, but it does work acceptably. By turning off event handlers
(using empty func() as the handler for an event) and by readding echo and opost to the
tty, we get a functional terminal.

(NB: the stty isn't strictly necessary for vim, but does cause a problem if you enter vim
and then get to a shell from inside it. So screw it, make it work for interactive shell too via
:shell command.)

Author: Mike Pountney

command_bar_fragment.go

@@ -70,6 +70,8 @@ func handleCommand(command string) {
 		if len(command) > 10 {
 			handleCommentCommand(string(command[9:]))
 		}
+	case action == "shell":
+		runShell()
 	case action == "search" || action == "search-open" || action == "so":
 		handleSearchOpen(args)
 	case action == "search-all" || action == "sa":

run.go

@@ -233,7 +233,7 @@ Query Options:
 	}
 	defer ui.Close()
 
-	registerKeyboardHandlers()
+	registerEventHandlers()
 
 	helpPage = new(HelpPage)
 	commandBar = new(CommandBar)

ui_controls.go

@@ -6,7 +6,7 @@ import (
 	ui "github.com/gizak/termui"
 )
 
-func registerKeyboardHandlers() {
+func registerEventHandlers() {
 	ui.Handle("/sys/kbd/", func(ev ui.Event) {
 		handleAnyKey(ev)
 	})
@@ -18,6 +18,12 @@ func registerKeyboardHandlers() {
 	})
 }
 
+func deregisterEventHandlers() {
+	ui.Handle("/sys/kbd/", func(ev ui.Event) {})
+	ui.Handle("/sys/kbd/C-c", func(ev ui.Event) {})
+	ui.Handle("/sys/wnd/resize", func(ev ui.Event) {})
+}
+
 func handleLabelViewKey() {
 	switch page := currentPage.(type) {
 	case *TicketListPage:

utils.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"os"
+	"os/exec"
 	"regexp"
 	"strings"
 
@@ -38,13 +39,43 @@ func countLabelsFromQueryData(data interface{}) map[string]int {
 	return counts
 }
 
+func RunExternalCommand(fn func() error) error {
+	log.Debugf("ShellOut() called with %q", fn)
+	deregisterEventHandlers()
+	ui.Clear()
+	stty := exec.Command("stty", "-f", "/dev/tty", "echo", "opost")
+	_ = stty.Run()
+	err := fn() // magic happens
+	stty = exec.Command("stty", "-f", "/dev/tty", "-echo", "-opost")
+	_ = stty.Run()
+	registerEventHandlers()
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func runShell() {
+	_ = RunExternalCommand(
+		func() error {
+			cmd := exec.Command("bash")
+			cmd.Stdout, cmd.Stderr, cmd.Stdin = os.Stdout, os.Stderr, os.Stdin
+			return cmd.Run()
+		})
+}
+
 func runJiraCmdEdit(ticketId string) {
-	opts := getJiraOpts()
-	c := jira.New(opts)
-	ui.Close()
-	c.CmdEdit(ticketId)
-	log.Notice("Regrettably, need to exit after edit. See https://github.com/mikepea/go-jira-ui/issues/8")
-	os.Exit(0)
+	_ = RunExternalCommand(
+		func() error {
+			opts := getJiraOpts()
+			c := jira.New(opts)
+			return c.CmdEdit(ticketId)
+		})
+	switch c := currentPage.(type) {
+	case Refresher:
+		c.Refresh()
+	}
+	changePage()
 }
 
 func runJiraCmdCommentNoEditor(ticketId string, comment string) {