78 lines
2.1 KiB
Go
78 lines
2.1 KiB
Go
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package history
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import "time"
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// History stores a stack of items, always keeping the bottom-most one. It must
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// be created using the NewHistory constructor, otherwise it will be invalid.
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type History[T any] struct {
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max int
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stack []T
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topIndex int
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topTime time.Time
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}
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// NewHistory creates a new History. The initial item will be on the bottom, and
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// it will remain there until the History overflows and chooses the item after
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// it to be the initial item.
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func NewHistory[T any] (initial T, max int) *History[T] {
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return &History[T] {
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max: max,
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stack: []T { initial },
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}
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}
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// Top returns the most recent item.
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func (this *History[T]) Top () T {
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return this.stack[this.topIndex]
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}
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// Swap replaces the most recent item with another.
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func (this *History[T]) Swap (item T) {
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this.topTime = time.Now()
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this.stack[this.topIndex] = item
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}
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// Push pushes a new item onto the stack.
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func (this *History[T]) Push (item T) {
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this.topTime = time.Now()
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this.topIndex ++
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this.stack = append(this.stack[:this.topIndex], item)
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}
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// PushWeak replaces the most recent item if it was added recently (sooner than
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// specified by minAge), and will otherwise push the item normally. If the
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// history was popped or cleared beforehand, the item will always be pushed
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// normally. This is intended to be used for things such as keystrokes.
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func (this *History[T]) PushWeak (item T, minAge time.Duration) {
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if time.Since(this.topTime) > minAge {
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this.Push(item)
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} else {
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this.Swap(item)
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}
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}
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// Redo undoes an Undo operation and returns the resulting top of the stack.
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func (this *History[T]) Redo () T {
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if this.topIndex < len(this.stack) - 1 {
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this.topIndex ++
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}
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return this.Top()
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}
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// Undo removes the most recent item and returns what was under it. If there is
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// only one item (the initial item), it will kept and returned.
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func (this *History[T]) Undo () T {
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this.topTime = time.Time { }
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if this.topIndex > 0 {
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this.topIndex --
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}
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return this.Top()
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}
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// Clear removes all items except for the initial one.
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func (this *History[T]) Clear () {
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this.topTime = time.Time { }
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this.stack = this.stack[:1]
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this.topIndex = 0
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}
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