1 files changed, 135 insertions, 0 deletions
diff --git a/examples/go-dashboard/src/github.com/mum4k/termdash/private/button/button.go b/examples/go-dashboard/src/github.com/mum4k/termdash/private/button/button.go
new file mode 100644
index 000000000..d4e0601b8
--- /dev/null
+++ b/examples/go-dashboard/src/github.com/mum4k/termdash/private/button/button.go
@@ -0,0 +1,135 @@
+// Copyright 2019 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package button implements a state machine that tracks mouse button clicks.
+package button
+
+import (
+	"image"
+
+	"github.com/mum4k/termdash/mouse"
+	"github.com/mum4k/termdash/terminal/terminalapi"
+)
+
+// State represents the state of the mouse button.
+type State int
+
+// String implements fmt.Stringer()
+func (s State) String() string {
+	if n, ok := stateNames[s]; ok {
+		return n
+	}
+	return "StateUnknown"
+}
+
+// stateNames maps State values to human readable names.
+var stateNames = map[State]string{
+	Up:   "StateUp",
+	Down: "StateDown",
+}
+
+const (
+	// Up is the default idle state of the mouse button.
+	Up State = iota
+
+	// Down is a state where the mouse button is pressed down and held.
+	Down
+)
+
+// FSM implements a finite-state machine that tracks mouse clicks within an
+// area.
+//
+// Simplifies tracking of mouse button clicks, i.e. when the caller wants to
+// perform an action only if both the button press and release happen within
+// the specified area.
+//
+// This object is not thread-safe.
+type FSM struct {
+	// button is the mouse button whose state this FSM tracks.
+	button mouse.Button
+
+	// area is the area provided to NewFSM.
+	area image.Rectangle
+
+	// state is the current state of the FSM.
+	state stateFn
+}
+
+// NewFSM creates a new FSM instance that tracks the state of the specified
+// mouse button through button events that fall within the provided area.
+func NewFSM(button mouse.Button, area image.Rectangle) *FSM {
+	return &FSM{
+		button: button,
+		area:   area,
+		state:  wantPress,
+	}
+}
+
+// Event is used to forward mouse events to the state machine.
+// Only events related to the button specified on a call to NewFSM are
+// processed.
+//
+// Returns a bool indicating if an action guarded by the button should be
+// performed and the state of the button after the provided event.
+// The bool is true if the button click should take an effect, i.e. if the
+// FSM saw both the button click and its release.
+func (fsm *FSM) Event(m *terminalapi.Mouse) (bool, State) {
+	clicked, bs, next := fsm.state(fsm, m)
+	fsm.state = next
+	return clicked, bs
+}
+
+// UpdateArea informs FSM of an area change.
+// This method is idempotent.
+func (fsm *FSM) UpdateArea(area image.Rectangle) {
+	fsm.area = area
+}
+
+// stateFn is a single state in the state machine.
+// Returns bool indicating if a click happened, the state of the button and the
+// next state of the FSM.
+type stateFn func(fsm *FSM, m *terminalapi.Mouse) (bool, State, stateFn)
+
+// wantPress is the initial state, expecting a button press inside the area.
+func wantPress(fsm *FSM, m *terminalapi.Mouse) (bool, State, stateFn) {
+	if m.Button != fsm.button || !m.Position.In(fsm.area) {
+		return false, Up, wantPress
+	}
+	return false, Down, wantRelease
+}
+
+// wantRelease waits for a mouse button release in the same area as
+// the press.
+func wantRelease(fsm *FSM, m *terminalapi.Mouse) (bool, State, stateFn) {
+	switch m.Button {
+	case fsm.button:
+		if m.Position.In(fsm.area) {
+			// Remain in the same state, since termbox reports move of mouse with
+			// button held down as a series of clicks, one per position.
+			return false, Down, wantRelease
+		}
+		return false, Up, wantPress
+
+	case mouse.ButtonRelease:
+		if m.Position.In(fsm.area) {
+			// Seen both press and release, report a click.
+			return true, Up, wantPress
+		}
+		// Release the button even if the release event happened outside of the area.
+		return false, Up, wantPress
+
+	default:
+		return false, Up, wantPress
+	}
+}