Improvements to internal/history

internal/history/history.go

@@ -4,7 +4,7 @@ import "time"
 
 // History stores a stack of items, always keeping the bottom-most one. It must
 // be created using the NewHistory constructor, otherwise it will be invalid.
-type History[T any] struct {
+type History[T comparable] struct {
 	max      int
 	stack    []T
 	topIndex int
@@ -14,7 +14,7 @@ type History[T any] struct {
 // NewHistory creates a new History. The initial item will be on the bottom, and
 // it will remain there until the History overflows and chooses the item after
 // it to be the initial item.
-func NewHistory[T any] (initial T, max int) *History[T] {
+func NewHistory[T comparable] (initial T, max int) *History[T] {
 	return &History[T] {
 		max:   max,
 		stack: []T { initial },
@@ -29,16 +29,30 @@ func (this *History[T]) Top () T {
 // Swap replaces the most recent item with another.
 func (this *History[T]) Swap (item T) {
 	this.topTime = time.Now()
+	this.SwapSilently(item)
+}
+
+// SwapSilently replaces the most recent item with another without updating the
+// time.
+func (this *History[T]) SwapSilently (item T) {
 	this.stack[this.topIndex] = item
 }
 
-// Push pushes a new item onto the stack.
+// Push pushes a new item onto the stack. If the stack overflows (becomes bigger
+// than the specified max value), the initial item is removed and the one on top
+// of it takes its place.
 func (this *History[T]) Push (item T) {
 	this.topTime = time.Now()
+	if this.Top() != item {
 		this.topIndex ++
 		this.stack = append(this.stack[:this.topIndex], item)
 	}
 
+	if len(this.stack) > this.max {
+		this.stack = this.stack[1:]
+	}
+}
+
 // PushWeak replaces the most recent item if it was added recently (sooner than
 // specified by minAge), and will otherwise push the item normally. If the
 // history was popped or cleared beforehand, the item will always be pushed