history

history.go

@@ -0,0 +1,83 @@
+package app
+
+import "github.com/pkg/errors"
+
+// History is a store that contains URL ordered chronologically.
+type History struct {
+	index   int
+	history []string
+}
+
+// NewHistory creates an history.
+func NewHistory() *History {
+	return &History{
+		index:   -1,
+		history: make([]string, 0, 32),
+	}
+}
+
+// Len returns the number of entries recorded in the history.
+func (h *History) Len() int {
+	return len(h.history)
+}
+
+// Current returns the current entry.
+func (h *History) Current() (url string, err error) {
+	if h.Len() == 0 {
+		err = errors.New("no entry")
+		return
+	}
+
+	url = h.history[h.index]
+	return
+}
+
+// NewEntry adds an entry to the history.
+// Then entry is added after the current one.
+// All the entries that was after the current one are removed.
+func (h *History) NewEntry(url string) {
+	var history []string
+
+	if h.Len() == 0 {
+		history = h.history
+	} else {
+		history = h.history[:h.index+1]
+	}
+
+	h.history = append(history, url)
+	h.index++
+}
+
+// CanPrevious reports whether there is a previous entry.
+func (h *History) CanPrevious() bool {
+	return h.index > 0
+}
+
+// Previous returns the previous entry.
+func (h *History) Previous() (url string, err error) {
+	if !h.CanPrevious() {
+		err = errors.New("no entry to go back")
+		return
+	}
+
+	h.index--
+	url = h.history[h.index]
+	return
+}
+
+// CanNext reports whether there is a next entry.
+func (h *History) CanNext() bool {
+	return h.index < h.Len()-1
+}
+
+// Next returns the next entry.
+func (h *History) Next() (url string, err error) {
+	if !h.CanNext() {
+		err = errors.New("no entry to go next")
+		return
+	}
+
+	h.index++
+	url = h.history[h.index]
+	return
+}