Implement basic ex line input

TODO:
- scrolling
- commit/cancel
- command history (via an external command history provider)
- tab completion (via an external tab completion provider)

4 files changed, 156 insertions, 0 deletions

diff --git a/ui/context.go b/ui/context.go
index ae9e5610..ca3f4522 100644
--- a/ui/context.go
+++ b/ui/context.go
@@ -15,6 +15,14 @@ type Context struct {
 	height int
 }
 
+func (ctx *Context) X() int {
+	return ctx.x
+}
+
+func (ctx *Context) Y() int {
+	return ctx.y
+}
+
 func (ctx *Context) Width() int {
 	return ctx.width
 }
diff --git a/ui/exline.go b/ui/exline.go
new file mode 100644
index 00000000..a377cd71
--- /dev/null
+++ b/ui/exline.go
@@ -0,0 +1,127 @@
+package ui
+
+import (
+	tb "github.com/nsf/termbox-go"
+)
+
+// TODO: history
+// TODO: tab completion
+// TODO: commit
+// TODO: cancel (via esc/ctrl+c)
+// TODO: scrolling
+
+type ExLine struct {
+	command *string
+	commit  func(cmd *string)
+	index   int
+	scroll  int
+
+	onInvalidate func(d Drawable)
+}
+
+func NewExLine() *ExLine {
+	cmd := ""
+	return &ExLine{command: &cmd}
+}
+
+func (ex *ExLine) OnInvalidate(onInvalidate func(d Drawable)) {
+	ex.onInvalidate = onInvalidate
+}
+
+func (ex *ExLine) Invalidate() {
+	if ex.onInvalidate != nil {
+		ex.onInvalidate(ex)
+	}
+}
+
+func (ex *ExLine) Draw(ctx *Context) {
+	cell := tb.Cell{
+		Fg: tb.ColorDefault,
+		Bg: tb.ColorDefault,
+		Ch: ' ',
+	}
+	ctx.Fill(0, 0, ctx.Width(), ctx.Height(), cell)
+	ctx.Printf(0, 0, cell, ":%s", *ex.command)
+	tb.SetCursor(ctx.X()+ex.index-ex.scroll+1, ctx.Y())
+}
+
+func (ex *ExLine) insert(ch rune) {
+	newCmd := (*ex.command)[:ex.index] + string(ch) + (*ex.command)[ex.index:]
+	ex.command = &newCmd
+	ex.index++
+	ex.Invalidate()
+}
+
+func (ex *ExLine) deleteWord() {
+	// TODO: Break on any of / " '
+	if len(*ex.command) == 0 {
+		return
+	}
+	i := ex.index - 1
+	if (*ex.command)[i] == ' ' {
+		i--
+	}
+	for ; i >= 0; i-- {
+		if (*ex.command)[i] == ' ' {
+			break
+		}
+	}
+	newCmd := (*ex.command)[:i+1] + (*ex.command)[ex.index:]
+	ex.command = &newCmd
+	ex.index = i + 1
+	ex.Invalidate()
+}
+
+func (ex *ExLine) deleteChar() {
+	if len(*ex.command) > 0 && ex.index != len(*ex.command) {
+		newCmd := (*ex.command)[:ex.index] + (*ex.command)[ex.index+1:]
+		ex.command = &newCmd
+		ex.Invalidate()
+	}
+}
+
+func (ex *ExLine) backspace() {
+	if len(*ex.command) > 0 && ex.index != 0 {
+		newCmd := (*ex.command)[:ex.index-1] + (*ex.command)[ex.index:]
+		ex.command = &newCmd
+		ex.index--
+		ex.Invalidate()
+	}
+}
+
+func (ex *ExLine) Event(event tb.Event) bool {
+	switch event.Type {
+	case tb.EventKey:
+		switch event.Key {
+		case tb.KeySpace:
+			ex.insert(' ')
+		case tb.KeyBackspace, tb.KeyBackspace2:
+			ex.backspace()
+		case tb.KeyCtrlD, tb.KeyDelete:
+			ex.deleteChar()
+		case tb.KeyCtrlB, tb.KeyArrowLeft:
+			if ex.index > 0 {
+				ex.index--
+				ex.Invalidate()
+			}
+		case tb.KeyCtrlF, tb.KeyArrowRight:
+			if ex.index < len(*ex.command) {
+				ex.index++
+				ex.Invalidate()
+			}
+		case tb.KeyCtrlA, tb.KeyHome:
+			ex.index = 0
+			ex.Invalidate()
+		case tb.KeyCtrlE, tb.KeyEnd:
+			ex.index = len(*ex.command)
+			ex.Invalidate()
+		case tb.KeyCtrlW:
+			ex.deleteWord()
+		default:
+			if event.Ch != 0 {
+				ex.insert(event.Ch)
+			}
+		}
+	}
+	return true
+}
diff --git a/ui/interactive.go b/ui/interactive.go
new file mode 100644
index 00000000..5dd5feff
--- /dev/null
+++ b/ui/interactive.go
@@ -0,0 +1,10 @@
+package ui
+
+import (
+	tb "github.com/nsf/termbox-go"
+)
+
+type Interactive interface {
+	// Returns true if the event was handled by this component
+	Event(event tb.Event) bool
+}
diff --git a/ui/ui.go b/ui/ui.go
index d1d2ca3d..9ea037c3 100644
--- a/ui/ui.go
+++ b/ui/ui.go
@@ -11,6 +11,8 @@ type UI struct {
 	Content Drawable
 	ctx     *Context
 
+	interactive []Interactive
+
 	tbEvents      chan tb.Event
 	invalidations chan interface{}
 }
@@ -58,6 +60,11 @@ func (state *UI) Tick() bool {
 			state.ctx = NewContext(event.Width, event.Height)
 			state.Content.Invalidate()
 		}
+		if state.interactive != nil {
+			for _, i := range state.interactive {
+				i.Event(event)
+			}
+		}
 	case <-state.invalidations:
 		state.Content.Draw(state.ctx)
 		tb.Flush()
@@ -66,3 +73,7 @@ func (state *UI) Tick() bool {
 	}
 	return true
 }
+
+func (state *UI) AddInteractive(i Interactive) {
+	state.interactive = append(state.interactive, i)
+}