package coffee.liz.lambda;

import coffee.liz.lambda.parser.ArrowParser;
import coffee.liz.lambda.parser.LambdaParser;
import coffee.liz.lambda.parser.ParseException;
import coffee.liz.lambda.ast.Expression;
import coffee.liz.lambda.ast.LambdaProgram;
import coffee.liz.lambda.ast.Macro;
import coffee.liz.lambda.ast.SourceCode;
import coffee.liz.lambda.bind.ExternalBinding;
import coffee.liz.lambda.eval.Environment;
import coffee.liz.lambda.eval.NormalOrderEvaluator;
import coffee.liz.lambda.eval.Value;

import java.io.StringReader;
import java.util.List;

/**
 * Entry point for parsing and interpreting lambda calculus programs.
 */
public class LambdaDriver {

	/**
	 * Parses source code into an AST.
	 *
	 * @param sourceCode
	 *            the source code (either Lambda or Arrow syntax)
	 * @return the parsed program
	 */
	public static LambdaProgram parse(final SourceCode sourceCode) {
		return switch (sourceCode) {
			case SourceCode.Lambda(String source) -> parseLambda(source);
			case SourceCode.Arrow(String source) -> parseArrow(source);
		};
	}

	private static LambdaProgram parseLambda(final String source) {
		try (final StringReader reader = new StringReader(source)) {
			return new LambdaParser(reader).Program();
		} catch (final ParseException parseException) {
			throw new RuntimeException("Failed to parse program", parseException);
		}
	}

	private static LambdaProgram parseArrow(final String source) {
		try (final StringReader reader = new StringReader(source)) {
			return new ArrowParser(reader).Program();
		} catch (final ParseException parseException) {
			throw new RuntimeException("Failed to parse program", parseException);
		}
	}

	/**
	 * Parses and evaluates lambda calculus programs.
	 *
	 * @param sourceCode
	 *            the source code
	 * @return the evaluated result
	 */
	public static Value interpret(final SourceCode sourceCode) {
		return interpret(sourceCode, List.of());
	}

	/**
	 * Parses and evaluates lambda calculus programs with "FFI"'s.
	 *
	 * @param sourceCode
	 *            the source code
	 * @param bindings
	 *            external Java functions available during evaluation
	 * @return the evaluated result
	 */
	public static Value interpret(final SourceCode sourceCode, final List<ExternalBinding> bindings) {
		final LambdaProgram program = parse(sourceCode);
		final Expression expression = program.expression();
		final List<Macro> macros = program.macros();
		return NormalOrderEvaluator.evaluate(expression, Environment.from(macros, bindings));
	}
}