1 files changed, 178 insertions, 0 deletions
diff --git a/ext/js/display/display-history.js b/ext/js/display/display-history.js
new file mode 100644
index 00000000..a6335521
--- /dev/null
+++ b/ext/js/display/display-history.js
@@ -0,0 +1,178 @@
+/*
+ * Copyright (C) 2020-2021  Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+class DisplayHistory extends EventDispatcher {
+    constructor({clearable=true, useBrowserHistory=false}) {
+        super();
+        this._clearable = clearable;
+        this._useBrowserHistory = useBrowserHistory;
+        this._historyMap = new Map();
+
+        const historyState = history.state;
+        const {id, state} = isObject(historyState) ? historyState : {id: null, state: null};
+        this._current = this._createHistoryEntry(id, location.href, state, null, null);
+    }
+
+    get state() {
+        return this._current.state;
+    }
+
+    get content() {
+        return this._current.content;
+    }
+
+    get useBrowserHistory() {
+        return this._useBrowserHistory;
+    }
+
+    set useBrowserHistory(value) {
+        this._useBrowserHistory = value;
+    }
+
+    prepare() {
+        window.addEventListener('popstate', this._onPopState.bind(this), false);
+    }
+
+    hasNext() {
+        return this._current.next !== null;
+    }
+
+    hasPrevious() {
+        return this._current.previous !== null;
+    }
+
+    clear() {
+        if (!this._clearable) { return; }
+        this._clear();
+    }
+
+    back() {
+        return this._go(false);
+    }
+
+    forward() {
+        return this._go(true);
+    }
+
+    pushState(state, content, url) {
+        if (typeof url === 'undefined') { url = location.href; }
+
+        const entry = this._createHistoryEntry(null, url, state, content, this._current);
+        this._current.next = entry;
+        this._current = entry;
+        this._updateHistoryFromCurrent(!this._useBrowserHistory);
+    }
+
+    replaceState(state, content, url) {
+        if (typeof url === 'undefined') { url = location.href; }
+
+        this._current.url = url;
+        this._current.state = state;
+        this._current.content = content;
+        this._updateHistoryFromCurrent(true);
+    }
+
+    _onPopState() {
+        this._updateStateFromHistory();
+        this._triggerStateChanged(false);
+    }
+
+    _go(forward) {
+        const target = forward ? this._current.next : this._current.previous;
+        if (target === null) {
+            return false;
+        }
+
+        if (this._useBrowserHistory) {
+            if (forward) {
+                history.forward();
+            } else {
+                history.back();
+            }
+        } else {
+            this._current = target;
+            this._updateHistoryFromCurrent(true);
+        }
+
+        return true;
+    }
+
+    _triggerStateChanged(synthetic) {
+        this.trigger('stateChanged', {history: this, synthetic});
+    }
+
+    _updateHistoryFromCurrent(replace) {
+        const {id, state, url} = this._current;
+        if (replace) {
+            history.replaceState({id, state}, '', url);
+        } else {
+            history.pushState({id, state}, '', url);
+        }
+        this._triggerStateChanged(true);
+    }
+
+    _updateStateFromHistory() {
+        let state = history.state;
+        let id = null;
+        if (isObject(state)) {
+            id = state.id;
+            if (typeof id === 'string') {
+                const entry = this._historyMap.get(id);
+                if (typeof entry !== 'undefined') {
+                    // Valid
+                    this._current = entry;
+                    return;
+                }
+            }
+            // Partial state recovery
+            state = state.state;
+        } else {
+            state = null;
+        }
+
+        // Fallback
+        this._current.id = (typeof id === 'string' ? id : this._generateId());
+        this._current.state = state;
+        this._current.content = null;
+        this._clear();
+    }
+
+    _createHistoryEntry(id, url, state, content, previous) {
+        if (typeof id !== 'string') { id = this._generateId(); }
+        const entry = {
+            id,
+            url,
+            next: null,
+            previous,
+            state,
+            content
+        };
+        this._historyMap.set(id, entry);
+        return entry;
+    }
+
+    _generateId() {
+        return generateId(16);
+    }
+
+    _clear() {
+        this._historyMap.clear();
+        this._historyMap.set(this._current.id, this._current);
+        this._current.next = null;
+        this._current.previous = null;
+    }
+}