Add scrolling to chat pane

TODO.md

@@ -12,6 +12,10 @@ Bugs:
       through RTM in the selected channel
 - [x] uncovering usernames takes too long, should find a better way
       test without uncovering, if that is the problem
+- [ ] GetMessages for a channel doesn't have to load messages based on height
+      of chat pane (y). Because message will sometimes span more than one
+      line and we're able to scroll. Only figure out how many messages you
+      want to load.
 - [ ] GetMessages for a channel can result in `json: cannot unmarshal number
       into Go value of type string` https://github.com/nlopes/slack/issues/92
 - [ ] docs at exported functions
@@ -20,6 +24,6 @@ Features:
 
 - [x] channel name in chat pane
 - [x] new message indicator
+- [x] scrolling in chat pane
 - [ ] group channels, im channels
-- [ ] scrolling in chat pane
 - [ ] scrolling in channel pane

src/components/channels.go

@@ -140,9 +140,11 @@ func (c *Channels) NewMessage(channelID string) {
 		}
 	}
 
-	// The order of SlackChannels relates to the order of
-	// List.Items, index will be the index of the channel
-	c.List.Items[index] = fmt.Sprintf("* %s", strings.TrimSpace(c.List.Items[index]))
+	if !strings.Contains(c.List.Items[index], "*") {
+		// The order of SlackChannels relates to the order of
+		// List.Items, index will be the index of the channel
+		c.List.Items[index] = fmt.Sprintf("* %s", strings.TrimSpace(c.List.Items[index]))
+	}
 
 	// Play terminal bell sound
 	fmt.Print("\a")

src/components/chat.go

@@ -10,12 +10,14 @@ import (
 type Chat struct {
 	List            *termui.List
 	SelectedChannel string
+	Offset          int
 }
 
 // CreateChat is the constructor for the Chat struct
 func CreateChat(svc *service.SlackService, inputHeight int, selectedChannel SlackChannel) *Chat {
 	chat := &Chat{
-		List: termui.NewList(),
+		List:   termui.NewList(),
+		Offset: 0,
 	}
 
 	chat.List.Height = termui.TermHeight() - inputHeight
@@ -68,14 +70,16 @@ func (c *Chat) Buffer() termui.Buffer {
 	lines = append(lines, line)
 
 	// We will print lines bottom up, it will loop over the lines
-	// backwards and for every line it'll set the cell in that line
+	// backwards and for every line it'll set the cell in that line.
+	// Offset is the number which allows us to begin printing the
+	// line above the last line.
 	buf := c.List.Buffer()
 	linesHeight := len(lines)
 	paneMinY := c.List.InnerBounds().Min.Y
 	paneMaxY := c.List.InnerBounds().Max.Y
 
 	currentY := paneMaxY - 1
-	for i := linesHeight - 1; i >= 0; i-- {
+	for i := (linesHeight - 1) - c.Offset; i >= 0; i-- {
 		if currentY < paneMinY {
 			break
 		}
@@ -152,10 +156,37 @@ func (c *Chat) ClearMessages() {
 	c.List.Items = []string{}
 }
 
+// ScrollUp will render the chat messages based on the Offset of the Chat
+// pane.
+//
+// Offset is 0 when scrolled down. (we loop backwards over the array, so we
+// start with rendering last item in the list at the maximum y of the Chat
+// pane). Increasing the Offset will thus result in substracting the offset
+// from the len(Chat.List.Items).
 func (c *Chat) ScrollUp() {
+	c.Offset = c.Offset + 10
+
+	// Protect overscrolling
+	if c.Offset > len(c.List.Items)-1 {
+		c.Offset = len(c.List.Items) - 1
+	}
 }
 
-func (c *Chat) ScrollDown() {}
+// ScrollDown will render the chat messages based on the Offset of the Chat
+// pane.
+//
+// Offset is 0 when scrolled down. (we loop backwards over the array, so we
+// start with rendering last item in the list at the maximum y of the Chat
+// pane). Increasing the Offset will thus result in substracting the offset
+// from the len(Chat.List.Items).
+func (c *Chat) ScrollDown() {
+	c.Offset = c.Offset - 10
+
+	// Protect overscrolling
+	if c.Offset < 0 {
+		c.Offset = 0
+	}
+}
 
 // SetBorderLabel will set Label of the Chat pane to the specified string
 func (c *Chat) SetBorderLabel(label string) {

src/handlers/event.go

@@ -33,6 +33,10 @@ func anyKeyHandler(ctx *context.AppContext) func(termui.Event) {
 			case "i":
 				actionInsertMode(ctx)
 				return
+			case "<previous>":
+				actionScrollUpChat(ctx)
+			case "<next>":
+				actionScrollDownChat(ctx)
 			}
 		} else if ctx.Mode == context.InsertMode {
 			switch key {
@@ -89,6 +93,8 @@ func incomingMessageHandler(ctx *context.AppContext) {
 					if ev.Channel == ctx.View.Channels.SlackChannels[ctx.View.Channels.SelectedChannel].ID {
 						ctx.View.Chat.AddMessage(m)
 						termui.Render(ctx.View.Chat)
+
+						// TODO: set Chat.Offset to 0?
 					}
 
 					// Set new message indicator for channel
@@ -202,3 +208,13 @@ func actionNewMessage(ctx *context.AppContext, channelID string) {
 	ctx.View.Channels.NewMessage(channelID)
 	termui.Render(ctx.View.Channels)
 }
+
+func actionScrollUpChat(ctx *context.AppContext) {
+	ctx.View.Chat.ScrollUp()
+	termui.Render(ctx.View.Chat)
+}
+
+func actionScrollDownChat(ctx *context.AppContext) {
+	ctx.View.Chat.ScrollDown()
+	termui.Render(ctx.View.Chat)
+}