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javascript/jstest/JSExpressionEngine.java

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+package jstest;
+
+import common.Engine;
+
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.stream.Collectors;
+
+/**
+ * Expression-aware JavaScript engine.
+ *
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+public class JSExpressionEngine implements Engine<Object> {
+    private final JSEngine engine;
+    private final String evaluate;
+    private final String parse;
+    private final String toString;
+
+    public JSExpressionEngine(final Path script, final String evaluate, final String parse, final String toString) {
+        engine = new JSEngine(script);
+        this.evaluate = evaluate;
+        this.parse = parse;
+        this.toString = toString;
+    }
+
+    @Override
+    public Result<Object> prepare(final String expression) {
+        return parse("eval", expression);
+    }
+
+    @Override
+    public Result<Object> parse(final String expression) {
+        return parse(parse, expression);
+    }
+
+    private Result<Object> parse(final String parse, final String expression) {
+        return engine.eval(expression, "%s(\"%s\")".formatted(parse, expression), Object.class);
+    }
+
+    @Override
+    public Result<Number> evaluate(final Result<Object> prepared, final double[] vars) {
+        final String code = "expr%s(%s);".formatted(
+                evaluate,
+                Arrays.stream(vars).mapToObj("%.20f"::formatted).collect(Collectors.joining(","))
+        );
+        return evaluate(prepared, code, Number.class);
+    }
+
+    public Result<String> toString(final Result<Object> prepared) {
+        return evaluate(prepared, "expr." + toString + "()", String.class);
+    }
+
+    protected <T> Engine.Result<T> evaluate(
+            final Engine.Result<Object> prepared,
+            final String code,
+            final Class<T> result
+    ) {
+        engine.set("expr", prepared);
+        return engine.eval(
+                "%n    in %s%n    where expr = %s%n".formatted(code, prepared.context()),
+                code,
+                result
+        );
+    }
+}