feat!: rewrote the GUI and model for better testability

The Model was getting unmaintanable mess. This is an attempt to refactor/rewrite the Model so that data of certain type is exposed in standardized way, offering certain standard manipulations for that data type, and on the GUI side, certain standard widgets to tied to that data.

This rewrite closes #72, #106 and #120.

tracker/alert.go

@@ -0,0 +1,110 @@
+package tracker
+
+import (
+	"container/heap"
+	"time"
+)
+
+const alertSpeed = 10 // units: fadeLevels per second
+const defaultAlertDuration = time.Second * 3
+
+type (
+	Alert struct {
+		Name      string
+		Priority  AlertPriority
+		Message   string
+		Duration  time.Duration
+		FadeLevel float64
+	}
+
+	AlertPriority  int
+	AlertYieldFunc func(alert Alert)
+	Alerts         Model
+)
+
+const (
+	None AlertPriority = iota
+	Info
+	Warning
+	Error
+)
+
+// Model methods
+
+func (m *Model) Alerts() *Alerts { return (*Alerts)(m) }
+
+// Alerts methods
+
+func (m *Alerts) Iterate(yield AlertYieldFunc) {
+	for _, a := range m.alerts {
+		yield(a)
+	}
+}
+
+func (m *Alerts) Update(d time.Duration) (animating bool) {
+	for i := len(m.alerts) - 1; i >= 0; i-- {
+		if m.alerts[i].Duration >= d {
+			m.alerts[i].Duration -= d
+			if m.alerts[i].FadeLevel < 1 {
+				animating = true
+				m.alerts[i].FadeLevel += float64(alertSpeed*d) / float64(time.Second)
+				if m.alerts[i].FadeLevel > 1 {
+					m.alerts[i].FadeLevel = 1
+				}
+			}
+		} else {
+			m.alerts[i].Duration = 0
+			m.alerts[i].FadeLevel -= float64(alertSpeed*d) / float64(time.Second)
+			animating = true
+			if m.alerts[i].FadeLevel < 0 {
+				heap.Remove(m, i)
+			}
+		}
+	}
+	return
+}
+
+func (m *Alerts) Add(message string, priority AlertPriority) {
+	m.AddAlert(Alert{
+		Priority: priority,
+		Message:  message,
+		Duration: defaultAlertDuration,
+	})
+}
+
+func (m *Alerts) AddNamed(name, message string, priority AlertPriority) {
+	m.AddAlert(Alert{
+		Name:     name,
+		Priority: priority,
+		Message:  message,
+		Duration: defaultAlertDuration,
+	})
+}
+
+func (m *Alerts) AddAlert(a Alert) {
+	for i := range m.alerts {
+		if n := m.alerts[i].Name; n != "" && n == a.Name {
+			a.FadeLevel = m.alerts[i].FadeLevel
+			m.alerts[i] = a
+			heap.Fix(m, i)
+			return
+		}
+	}
+	heap.Push(m, a)
+}
+
+func (m *Alerts) Push(x any) {
+	m.alerts = append(m.alerts, x.(Alert))
+}
+
+func (m *Alerts) Pop() any {
+	old := m.alerts
+	n := len(old)
+	x := old[n-1]
+	m.alerts = old[0 : n-1]
+	return x
+}
+
+func (m Alerts) Len() int           { return len(m.alerts) }
+func (m Alerts) Less(i, j int) bool { return m.alerts[i].Priority < m.alerts[j].Priority }
+func (m Alerts) Swap(i, j int)      { m.alerts[i], m.alerts[j] = m.alerts[j], m.alerts[i] }