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/************************************************************************
 * © 2019-2024 SAP SE or an SAP affiliate company. All rights reserved. *
 ************************************************************************/
package com.sap.cds.generator.util;

import static java.nio.file.StandardCopyOption.REPLACE_EXISTING;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;
import java.nio.file.Files;
import java.nio.file.Path;

import org.apache.commons.io.IOUtils;
import org.slf4j.LoggerFactory;

public class FileSystem implements GeneratedFile.Accessor {

	private final org.slf4j.Logger logger = LoggerFactory.getLogger(FileSystem.class);
	private final Path baseDirectory;
	private final boolean mavenLayout;
	private final boolean overwrite;

	public FileSystem(Path baseDirectory, boolean mavenLayout) {
		this(baseDirectory, mavenLayout, true);
	}

	public FileSystem(Path baseDirectory, boolean mavenLayout, boolean overwrite) {
		this.mavenLayout = mavenLayout;
		this.overwrite = overwrite;
		File dir = baseDirectory.toFile();
		if (dir.exists() && !dir.isDirectory()) {
			String message = "'%s' is not a directory.".formatted(baseDirectory.getFileName());
			throw new IllegalArgumentException(message);
		}
		this.baseDirectory = baseDirectory;
	}

	@Override
	public void accept(GeneratedFile file) throws IOException {
		try {
			Path outputPath = getPath(file);

			if (Files.exists(outputPath)) {
				if (!overwrite) {
					logger.info("Class {} already exists. No new handler is generated.", outputPath.getFileName());
				} else {
					try (ReadableByteChannel rbc = Files.newByteChannel(outputPath);
						 InputStream in = Channels.newInputStream(rbc)) {
						if (!IOUtils.contentEquals(file.getContent(), in)) {
							Files.copy(file.getContent(), outputPath, REPLACE_EXISTING);
						}
					}
				}
			} else {
				Files.createDirectories(outputPath.toFile().getParentFile().toPath());
				Files.copy(file.getContent(), outputPath, REPLACE_EXISTING);
			}
		} catch (IOException e) {
			String message = "Error writing file '%s' to file system.".formatted(file.getUri());
			throw new IOException(message, e);
		}
	}

	private Path getPath(FileLocation location) {
		Path base = getBase(location);
		return base.resolve(location.getUri().getPath());
	}

	private Path getBase(FileLocation location) {
		if (!mavenLayout) {
			return baseDirectory;
		}

		return baseDirectory.resolve(location.isResource() ? "resources" : "java");
	}

	@Override
	public GeneratedFile get(FileLocation location) throws IOException {
		Path path = getPath(location);

		return new GeneratedFile() {
			@Override
			public URI getUri() {
				return location.getUri();
			}

			@Override
			public InputStream getContent() throws IOException {
				if (!path.toFile().exists()) {
					return null;
				}
				return Files.newInputStream(path);
			}
		};
	}
}