POC: Expression builder class.

src/legacy/ui/public/visualize/loader/pipeline_helpers/expression_builder.ts

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+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/**
+ * Simple chainable class for building expression strings. Handles the overhead of
+ * checking for undefined args, escaping strings & JSON, and adding spaces & pipes.
+ *
+ * @example
+ *
+ * const exp = new ExpressionBuilder();
+ * exp.addFn('kibana');
+ *
+ * exp.addFn('tagcloud')
+ *   .addArg('metric', '{ vis_dimension 1 }') // works when given a subexpression as a string
+ *   .addArg('visConfig', { foo: 'bar' }); // will handle stringifying & escaping objects
+ *
+ * exp.printFn('tagcloud'); // "tagcloud metric={ vis_dimension 1 } visConfig='{ foo: \'bar\' }'"
+ *
+ * exp.addFn('render')
+ *   addArg('baz', '"hello"');
+ *
+ * exp.print(); // "kibana | tagcloud metric={ vis_dimension 1 } visConfig='{ foo: \'bar\' }' | render baz='\"hello\""'"
+ */
+export class ExpressionBuilder {
+  private fns: Map<string, { [key: string]: string }> = new Map();
+  private currFn: string | null = null;
+
+  public selectFn(name: string) {
+    this.currFn = name;
+    return this;
+  }
+
+  public addFn(name: string) {
+    this.fns.set(name, {});
+    this.selectFn(name);
+    return this;
+  }
+
+  public removeFn(name: string) {
+    if (this.fns.has(name)) {
+      this.fns.delete(name);
+    }
+    return this;
+  }
+
+  public addArg(name: string, data: string | object | undefined) {
+    if (this.currFn && data) {
+      const fn = this.fns.get(this.currFn);
+      if (fn) {
+        fn[name] = this.prepareData(data);
+      }
+    }
+    return this;
+  }
+
+  public removeArg(name: string) {
+    if (this.currFn) {
+      const fn = this.fns.get(this.currFn);
+      if (fn) {
+        delete fn[name];
+      }
+    }
+    return this;
+  }
+
+  public printFn(fnName: string): string {
+    const fn = this.fns.get(fnName);
+    let str = '';
+    if (fn) {
+      str += fnName;
+      Object.keys(fn).forEach(argName => {
+        str += ` ${this.printFnArg(fnName, argName)}`;
+      });
+    }
+    return str;
+  }
+
+  public print() {
+    let str = '';
+    Array.from(this.fns.keys()).forEach((fn, i) => {
+      if (i !== 0) {
+        str += ` | `;
+      }
+      str += this.printFn(fn);
+    });
+    return str;
+  }
+
+  public clear() {
+    this.fns.clear();
+    this.currFn = null;
+    return this;
+  }
+
+  private printFnArg(fnName: string, argName: string) {
+    const fn = this.fns.get(fnName);
+    if (!fn || !fn[argName]) {
+      return;
+    }
+    return `${argName}=${fn[argName]}`;
+  }
+
+  private prepareData(data: string | object) {
+    if (typeof data === 'object') {
+      return this.escapeString(JSON.stringify(data));
+    }
+    return this.escapeString(data);
+  }
+
+  private escapeString(data: string) {
+    return `'${data.replace(/\\/g, `\\\\`).replace(/'/g, `\\'`)}'`;
+  }
+}