refactor(platform-browser): move platform-browser/animations to animations/browser (#15130)

Closes: #15130

packages/animations/browser/src/dsl/animation_transition_expr.ts

@@ -0,0 +1,64 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+export const ANY_STATE = '*';
+export declare type TransitionMatcherFn = (fromState: any, toState: any) => boolean;
+
+export function parseTransitionExpr(
+    transitionValue: string | TransitionMatcherFn, errors: string[]): TransitionMatcherFn[] {
+  const expressions: TransitionMatcherFn[] = [];
+  if (typeof transitionValue == 'string') {
+    (<string>transitionValue)
+        .split(/\s*,\s*/)
+        .forEach(str => parseInnerTransitionStr(str, expressions, errors));
+  } else {
+    expressions.push(<TransitionMatcherFn>transitionValue);
+  }
+  return expressions;
+}
+
+function parseInnerTransitionStr(
+    eventStr: string, expressions: TransitionMatcherFn[], errors: string[]) {
+  if (eventStr[0] == ':') {
+    eventStr = parseAnimationAlias(eventStr, errors);
+  }
+  const match = eventStr.match(/^(\*|[-\w]+)\s*(<?[=-]>)\s*(\*|[-\w]+)$/);
+  if (match == null || match.length < 4) {
+    errors.push(`The provided transition expression "${eventStr}" is not supported`);
+    return expressions;
+  }
+
+  const fromState = match[1];
+  const separator = match[2];
+  const toState = match[3];
+  expressions.push(makeLambdaFromStates(fromState, toState));
+
+  const isFullAnyStateExpr = fromState == ANY_STATE && toState == ANY_STATE;
+  if (separator[0] == '<' && !isFullAnyStateExpr) {
+    expressions.push(makeLambdaFromStates(toState, fromState));
+  }
+}
+
+function parseAnimationAlias(alias: string, errors: string[]): string {
+  switch (alias) {
+    case ':enter':
+      return 'void => *';
+    case ':leave':
+      return '* => void';
+    default:
+      errors.push(`The transition alias value "${alias}" is not supported`);
+      return '* => *';
+  }
+}
+
+function makeLambdaFromStates(lhs: string, rhs: string): TransitionMatcherFn {
+  return (fromState: any, toState: any): boolean => {
+    const lhsMatch = lhs == ANY_STATE || lhs == fromState;
+    const rhsMatch = rhs == ANY_STATE || rhs == toState;
+    return lhsMatch && rhsMatch;
+  };
+}