Dynamic property (#749)

* Add DynamicProperty class

* Add tests for DynamicProperty

4 files changed, 275 insertions, 2 deletions

diff --git a/.eslintrc.json b/.eslintrc.json
index 2ff44ead..663e9003 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -108,6 +108,7 @@
                 "deferPromise": "readonly",
                 "clone": "readonly",
                 "generateId": "readonly",
+                "DynamicProperty": "readonly",
                 "EventDispatcher": "readonly",
                 "EventListenerCollection": "readonly"
             }
diff --git a/ext/mixed/js/core.js b/ext/mixed/js/core.js
index 9142a846..5bee4670 100644
--- a/ext/mixed/js/core.js
+++ b/ext/mixed/js/core.js
@@ -260,7 +260,7 @@ function promiseTimeout(delay, resolveValue) {
 
 
 /*
- * Common events
+ * Common classes
  */
 
 class EventDispatcher {
@@ -348,3 +348,106 @@ class EventListenerCollection {
         this._eventListeners = [];
     }
 }
+
+/**
+ * Class representing a generic value with an override stack.
+ * Changes can be observed by listening to the 'change' event.
+ */
+class DynamicProperty extends EventDispatcher {
+    /**
+     * Creates a new instance with the specified value.
+     * @param value The value to assign.
+     */
+    constructor(value) {
+        super();
+        this._value = value;
+        this._defaultValue = value;
+        this._overrides = [];
+    }
+
+    /**
+     * Gets the default value for the property, which is assigned to the
+     * public value property when no overrides are present.
+     */
+    get defaultValue() {
+        return this._defaultValue;
+    }
+
+    /**
+     * Assigns the default value for the property. If no overrides are present
+     * and if the value is different than the current default value,
+     * the 'change' event will be triggered.
+     * @param value The value to assign.
+     */
+    set defaultValue(value) {
+        this._defaultValue = value;
+        if (this._overrides.length === 0) { this._updateValue(); }
+    }
+
+    /**
+     * Gets the current value for the property, taking any overrides into account.
+     */
+    get value() {
+        return this._value;
+    }
+
+    /**
+     * Gets the number of overrides added to the property.
+     */
+    get overrideCount() {
+        return this._overrides.length;
+    }
+
+    /**
+     * Adds an override value with the specified priority to the override stack.
+     * Values with higher priority will take precedence over those with lower.
+     * For tie breaks, the override value added first will take precedence.
+     * If the newly added override has the highest priority of all overrides
+     * and if the override value is different from the current value,
+     * the 'change' event will be fired.
+     * @param value The override value to assign.
+     * @param priority The priority value to use, as a number.
+     * @returns A string token which can be passed to the clearOverride function
+     *  to remove the override.
+     */
+    setOverride(value, priority=0) {
+        const overridesCount = this._overrides.length;
+        let i = 0;
+        for (; i < overridesCount; ++i) {
+            if (priority > this._overrides[i].priority) { break; }
+        }
+        const token = generateId(16);
+        this._overrides.splice(i, 0, {value, priority, token});
+        if (i === 0) { this._updateValue(); }
+        return token;
+    }
+
+    /**
+     * Removes a specific override value. If the removed override
+     * had the highest priority, and the new value is different from
+     * the previous value, the 'change' event will be fired.
+     * @param token The token for the corresponding override which is to be removed.
+     * @returns true if an override was returned, false otherwise.
+     */
+    clearOverride(token) {
+        for (let i = 0, ii = this._overrides.length; i < ii; ++i) {
+            if (this._overrides[i].token === token) {
+                this._overrides.splice(i, 1);
+                if (i === 0) { this._updateValue(); }
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Updates the current value using the current overrides and default value.
+     * If the new value differs from the previous value, the 'change' event will be fired.
+     */
+    _updateValue() {
+        const value = this._overrides.length > 0 ? this._overrides[0].value : this._defaultValue;
+        if (this._value === value) { return; }
+        this._value = value;
+        this.trigger('change', {value});
+    }
+}
diff --git a/package.json b/package.json
index 8bbf883a..d276d701 100644
--- a/package.json
+++ b/package.json
@@ -9,7 +9,7 @@
         "build": "node ./dev/build.js",
         "test": "npm run test-lint && npm run test-code && npm run test-manifest",
         "test-lint": "eslint . && node ./test/lint/global-declarations.js",
-        "test-code": "node ./test/test-schema.js && node ./test/test-dictionary.js && node ./test/test-database.js && node ./test/test-document-util.js && node ./test/test-object-property-accessor.js && node ./test/test-japanese.js && node ./test/test-text-source-map.js && node ./test/test-dom-text-scanner.js && node ./test/test-cache-map.js && node ./test/test-profile-conditions.js",
+        "test-code": "node ./test/test-schema.js && node ./test/test-dictionary.js && node ./test/test-database.js && node ./test/test-document-util.js && node ./test/test-object-property-accessor.js && node ./test/test-japanese.js && node ./test/test-text-source-map.js && node ./test/test-dom-text-scanner.js && node ./test/test-cache-map.js && node ./test/test-profile-conditions.js && node ./test/test-core.js",
         "test-manifest": "node ./test/test-manifest.js"
     },
     "repository": {
diff --git a/test/test-core.js b/test/test-core.js
new file mode 100644
index 00000000..d4a880d1
--- /dev/null
+++ b/test/test-core.js
@@ -0,0 +1,169 @@
+/*
+ * Copyright (C) 2020  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/>.
+ */
+
+const assert = require('assert');
+const crypto = require('crypto');
+const {VM} = require('./yomichan-vm');
+
+const vm = new VM({
+    crypto: {
+        getRandomValues: (array) => {
+            const buffer = crypto.randomBytes(array.byteLength);
+            buffer.copy(array);
+            return array;
+        }
+    }
+});
+vm.execute([
+    'mixed/js/core.js'
+]);
+const [DynamicProperty] = vm.get(['DynamicProperty']);
+
+
+function testDynamicProperty() {
+    const data = [
+        {
+            initialValue: 0,
+            operations: [
+                {
+                    operation: null,
+                    expectedDefaultValue: 0,
+                    expectedValue: 0,
+                    expectedOverrideCount: 0,
+                    expeectedEventOccurred: false
+                },
+                {
+                    operation: 'set.defaultValue',
+                    args: [1],
+                    expectedDefaultValue: 1,
+                    expectedValue: 1,
+                    expectedOverrideCount: 0,
+                    expeectedEventOccurred: true
+                },
+                {
+                    operation: 'set.defaultValue',
+                    args: [1],
+                    expectedDefaultValue: 1,
+                    expectedValue: 1,
+                    expectedOverrideCount: 0,
+                    expeectedEventOccurred: false
+                },
+                {
+                    operation: 'set.defaultValue',
+                    args: [0],
+                    expectedDefaultValue: 0,
+                    expectedValue: 0,
+                    expectedOverrideCount: 0,
+                    expeectedEventOccurred: true
+                },
+                {
+                    operation: 'setOverride',
+                    args: [8],
+                    expectedDefaultValue: 0,
+                    expectedValue: 8,
+                    expectedOverrideCount: 1,
+                    expeectedEventOccurred: true
+                },
+                {
+                    operation: 'setOverride',
+                    args: [16],
+                    expectedDefaultValue: 0,
+                    expectedValue: 8,
+                    expectedOverrideCount: 2,
+                    expeectedEventOccurred: false
+                },
+                {
+                    operation: 'setOverride',
+                    args: [32, 1],
+                    expectedDefaultValue: 0,
+                    expectedValue: 32,
+                    expectedOverrideCount: 3,
+                    expeectedEventOccurred: true
+                },
+                {
+                    operation: 'setOverride',
+                    args: [64, -1],
+                    expectedDefaultValue: 0,
+                    expectedValue: 32,
+                    expectedOverrideCount: 4,
+                    expeectedEventOccurred: false
+                },
+                {
+                    operation: 'clearOverride',
+                    args: [-4],
+                    expectedDefaultValue: 0,
+                    expectedValue: 32,
+                    expectedOverrideCount: 3,
+                    expeectedEventOccurred: false
+                },
+                {
+                    operation: 'clearOverride',
+                    args: [-3],
+                    expectedDefaultValue: 0,
+                    expectedValue: 32,
+                    expectedOverrideCount: 2,
+                    expeectedEventOccurred: false
+                },
+                {
+                    operation: 'clearOverride',
+                    args: [-2],
+                    expectedDefaultValue: 0,
+                    expectedValue: 64,
+                    expectedOverrideCount: 1,
+                    expeectedEventOccurred: true
+                },
+                {
+                    operation: 'clearOverride',
+                    args: [-1],
+                    expectedDefaultValue: 0,
+                    expectedValue: 0,
+                    expectedOverrideCount: 0,
+                    expeectedEventOccurred: true
+                }
+            ]
+        }
+    ];
+
+    for (const {initialValue, operations} of data) {
+        const property = new DynamicProperty(initialValue);
+        const overrideTokens = [];
+        let eventOccurred = false;
+        const onChange = () => { eventOccurred = true; };
+        property.on('change', onChange);
+        for (const {operation, args, expectedDefaultValue, expectedValue, expectedOverrideCount, expeectedEventOccurred} of operations) {
+            eventOccurred = false;
+            switch (operation) {
+                case 'set.defaultValue': property.defaultValue = args[0]; break;
+                case 'setOverride': overrideTokens.push(property.setOverride(...args)); break;
+                case 'clearOverride': property.clearOverride(overrideTokens[overrideTokens.length + args[0]]); break;
+            }
+            assert.strictEqual(eventOccurred, expeectedEventOccurred);
+            assert.strictEqual(property.defaultValue, expectedDefaultValue);
+            assert.strictEqual(property.value, expectedValue);
+            assert.strictEqual(property.overrideCount, expectedOverrideCount);
+        }
+        property.off('change', onChange);
+    }
+}
+
+
+function main() {
+    testDynamicProperty();
+}
+
+
+if (require.main === module) { main(); }