Introduce inheritance to the Parameter structure

client/app/services/parameters/NumberParameter.js

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+import { toNumber } from 'lodash';
+import { Parameter } from '.';
+
+class NumberParameter extends Parameter {
+  constructor(parameter, parentQueryId) {
+    super(parameter, parentQueryId);
+    this.setValue(parameter.value);
+  }
+
+  getValue() {
+    const value = toNumber(this.value);
+    return !isNaN(value) ? value : null;
+  }
+}
+
+export default NumberParameter;

client/app/services/parameters/Parameter.js

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+import { isNull, isObject, isFunction, has } from 'lodash';
+import { TextParameter, NumberParameter } from '.';
+
+class Parameter {
+  constructor(parameter, parentQueryId) {
+    this.title = parameter.title;
+    this.name = parameter.name;
+    this.type = parameter.type;
+    this.global = parameter.global; // backward compatibility in Widget service
+    this.parentQueryId = parentQueryId;
+
+    // Used for meta-parameters (i.e. dashboard-level params)
+    this.locals = [];
+
+    // Used for URL serialization
+    Object.defineProperty(this, 'urlPrefix', {
+      configurable: true,
+      enumerable: false, // don't save it
+      writable: true,
+      value: 'p_',
+    });
+  }
+
+  static create(param) {
+    switch (param.type) {
+      case 'text':
+        return new TextParameter(param);
+      case 'number':
+        return new NumberParameter(param);
+      default:
+        return null;
+    }
+  }
+
+  static getValue(param, extra = {}) {
+    if (!isObject(param) || !isFunction(param.getValue)) {
+      return null;
+    }
+
+    return param.getValue(extra);
+  }
+
+  static setValue(param, value) {
+    if (!isObject(param) || !isFunction(param.setValue)) {
+      return null;
+    }
+
+    return param.setValue(value);
+  }
+
+  get isEmpty() {
+    return isNull(this.getValue());
+  }
+
+  clone() {
+    return Parameter.create(this);
+  }
+
+  toUrlParams() {
+    const prefix = this.urlPrefix;
+    return {
+      [`${prefix}${this.name}`]: !this.isEmpty ? this.value : null,
+      [`${prefix}${this.name}.start`]: null,
+      [`${prefix}${this.name}.end`]: null,
+    };
+  }
+
+  fromUrlParams(query) {
+    const prefix = this.urlPrefix;
+    const key = `${prefix}${this.name}`;
+    if (has(query, key)) {
+      this.setValue(query[key]);
+    }
+  }
+}
+
+export default Parameter;

client/app/services/parameters/TextParameter.js

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+import { toString, isEmpty } from 'lodash';
+import { Parameter } from '.';
+
+class TextParameter extends Parameter {
+  constructor(parameter, parentQueryId) {
+    super(parameter, parentQueryId);
+    this.setValue(parameter.value);
+  }
+
+  getValue() {
+    const value = toString(this.value);
+    return !isEmpty(value) ? value : null;
+  }
+}
+
+export default TextParameter;

client/app/services/parameters/index.js

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+export { default as Parameter } from './Parameter';
+export { default as TextParameter } from './TextParameter';
+export { default as NumberParameter } from './NumberParameter';