Add help screen, currently showing default shortcuts

Hitting '?' brings up a modal with default shortcuts, for quick 
reference.
Also does a little refactoring in the code where default shortcuts are 
declared.

Known issue: anyone that has run SH84 before will have shortcuts loaded 
from config file and the new '?' command will be ignored. Addressing 
this is beyond the scope of this change.

Known issue: custom shortcuts are not displayed in help, only the 
default which may not correspond to the actual user configuration.

config/config.go

@@ -45,6 +45,7 @@ type Config struct {
   Profile             ConfigProfile
 
   Shortcuts           map[string]string
+  ShortcutsReference  string
 
   ArticlesListView    int8
 }
@@ -89,27 +90,49 @@ func LoadConfig() (*Config, error) {
 }
 
 func (cfg *Config) LoadDefaults() (error) {
+
+  shortcutDefaults := []struct{
+    key           tcell.Key
+    command       string
+    keyAltText    string
+  } {
+    {tcell.KeyCtrlQ, "quit", "C-q"},
+    {tcell.KeyCtrlR, "refresh", "C-r"},
+    {tcell.KeyCtrlH, "focus-groups", "C-h"},
+    {tcell.KeyCtrlL, "focus-articles", "C-l"},
+    {tcell.KeyCtrlK, "focus-articles", "C-k"},
+    {tcell.KeyCtrlJ, "focus-preview", "C-j"},
+    {tcell.KeyCtrlA, "article-mark-all-read", "C-a"},
+
+    {tcell.Key('n'), "article-new", ""},
+    {tcell.Key('r'), "article-reply", ""},
+
+    {tcell.Key('h'), "additional-key-left", ""},
+    {tcell.Key('j'), "additional-key-down", ""},
+    {tcell.Key('k'), "additional-key-up", ""},
+    {tcell.Key('l'), "additional-key-right", ""},
+
+    {tcell.Key('g'), "additional-key-home", ""},
+    {tcell.Key('G'), "additional-key-end", ""},
+
+    {tcell.KeyF8, "play", "F8"},
+    {tcell.Key('?'), "help", ""},
+  }
+
+  var sb strings.Builder
+  for _, shortcut := range shortcutDefaults {
+    keyText := string(shortcut.key)
+    if shortcut.keyAltText != "" {
+      keyText = shortcut.keyAltText
+    }
+    sb.WriteString(fmt.Sprintf("%s - %s\n", keyText, shortcut.command))
+  }
+  cfg.ShortcutsReference = sb.String()
+
   if len(cfg.Shortcuts) == 0 {
-    cfg.Shortcuts[strconv.FormatInt(int64(tcell.KeyCtrlQ), 10)] = "quit"
-    cfg.Shortcuts[strconv.FormatInt(int64(tcell.KeyCtrlR), 10)] = "refresh"
-    cfg.Shortcuts[strconv.FormatInt(int64(tcell.KeyCtrlH), 10)] = "focus-groups"
-    cfg.Shortcuts[strconv.FormatInt(int64(tcell.KeyCtrlL), 10)] = "focus-articles"
-    cfg.Shortcuts[strconv.FormatInt(int64(tcell.KeyCtrlK), 10)] = "focus-articles"
-    cfg.Shortcuts[strconv.FormatInt(int64(tcell.KeyCtrlJ), 10)] = "focus-preview"
-
-    cfg.Shortcuts[strconv.FormatInt(int64('n'), 10)]            = "article-new"
-    cfg.Shortcuts[strconv.FormatInt(int64('r'), 10)]            = "article-reply"
-    cfg.Shortcuts[strconv.FormatInt(int64(tcell.KeyCtrlA), 10)] = "article-mark-all-read"
-
-    cfg.Shortcuts[strconv.FormatInt(int64('h'), 10)]            = "additional-key-left"
-    cfg.Shortcuts[strconv.FormatInt(int64('j'), 10)]            = "additional-key-down"
-    cfg.Shortcuts[strconv.FormatInt(int64('k'), 10)]            = "additional-key-up"
-    cfg.Shortcuts[strconv.FormatInt(int64('l'), 10)]            = "additional-key-right"
-
-    cfg.Shortcuts[strconv.FormatInt(int64('g'), 10)]            = "additional-key-home"
-    cfg.Shortcuts[strconv.FormatInt(int64('G'), 10)]            = "additional-key-end"
-
-    cfg.Shortcuts[strconv.FormatInt(int64(tcell.KeyF8), 10)]    = "play"
+    for _, shortcut := range shortcutDefaults {
+      cfg.Shortcuts[strconv.FormatInt(int64(shortcut.key), 10)] = shortcut.command
+    }
   }
 
   return cfg.Persist()

tui/mainscreen.go

@@ -34,6 +34,15 @@ const (
   COLOR_SUBJECT_READ   = "white"
 )
 
+var HELP_TEMPLATE =
+`
+HELP!
+
+Default shortcuts:
+
+%s
+`
+
 type GroupMapEntry struct {
   Index   int
 }
@@ -364,6 +373,8 @@ func (mainscreen *Mainscreen) HandleInput(event *tcell.EventKey) (*tcell.EventKe
     mainscreen.T.App.QueueEvent(tcell.NewEventKey(tcell.KeyHome, 0, tcell.ModNone))
   case "additional-key-end":
     mainscreen.T.App.QueueEvent(tcell.NewEventKey(tcell.KeyEnd, 0, tcell.ModNone))
+  case "help":
+    mainscreen.showHelp()
   }
 
   return event
@@ -548,3 +559,9 @@ func(mainscreen *Mainscreen) replyToArticle(article *models.Article) {
   return
 }
 
+func(mainscreen *Mainscreen) showHelp() {
+  helpMessage := fmt.Sprintf(HELP_TEMPLATE, mainscreen.T.Config.ShortcutsReference)
+  mainscreen.T.ShowHelpModal(helpMessage)
+
+  return
+}

tui/tui.go

@@ -251,6 +251,19 @@ func(t *TUI) ShowErrorModal(text string) {
     })
 }
 
+func(t *TUI) ShowHelpModal(text string) {
+  t.ShowModal(
+    text,
+    map[string]ModalButton{
+      "Press any key to close": {
+        Rune: '*',
+        Callback: func() {
+          return
+        },
+      },
+    })
+}
+
 func (t *TUI) SetInfo(refresh bool) {
   if refresh == true {
     t.Views["mainscreen"].(*Mainscreen).SetInfo(map[string]string{