/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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.
 */
package org.apache.maven.doxia.macro.snippet;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Pattern;

/**
 * Utility class for reading snippets.
 */
public class SnippetReader {
    /** System-dependent EOL. */
    private static final String EOL = System.getProperty("line.separator");

    /** The source. */
    private URL source;

    /** The encoding of the source. */
    private String encoding;

    /**
     * Constructor.
     *
     * @param src The source
     * @param encoding The file encoding
     */
    public SnippetReader(URL src, String encoding) {
        this.source = src;
        this.encoding = encoding;
    }

    /**
     * Constructor.
     *
     * @param src The source
     */
    public SnippetReader(URL src) {
        this(src, null);
    }

    /**
     * Reads the snippet with given id.
     *
     * @param snippetId The id of the snippet.
     * @return The snippet.
     * @throws java.io.IOException if something goes wrong.
     */
    public StringBuffer readSnippet(String snippetId) throws IOException {
        List<String> lines = readLines(snippetId);
        int minIndent = minIndent(lines);
        StringBuffer result = new StringBuffer();
        for (String line : lines) {
            result.append(line.substring(minIndent));
            result.append(EOL);
        }
        return result;
    }

    /**
     * Returns the minimal indent of all the lines in the given List.
     *
     * @param lines A List of lines.
     * @return the minimal indent.
     */
    int minIndent(List<String> lines) {
        int minIndent = Integer.MAX_VALUE;
        for (String line : lines) {
            minIndent = Math.min(minIndent, indent(line));
        }
        return minIndent;
    }

    /**
     * Returns the indent of the given line.
     *
     * @param line A line.
     * @return the indent.
     */
    int indent(String line) {
        char[] chars = line.toCharArray();
        int indent = 0;
        for (; indent < chars.length; indent++) {
            if (chars[indent] != ' ') {
                break;
            }
        }
        return indent;
    }

    /**
     * Reads the snippet and returns the lines in a List.
     *
     * @param snippetId The id of the snippet.
     * @return A List of lines.
     * @throws IOException if something goes wrong.
     */
    private List<String> readLines(String snippetId) throws IOException {
        BufferedReader reader;
        if (encoding == null || "".equals(encoding)) {
            reader = new BufferedReader(new InputStreamReader(source.openStream()));
        } else {
            reader = new BufferedReader(new InputStreamReader(source.openStream(), encoding));
        }

        List<String> lines = new ArrayList<>();
        try (BufferedReader withReader = reader) {
            boolean capture = false;
            String line;
            boolean foundStart = false;
            boolean foundEnd = false;
            boolean hasSnippetId = snippetId != null && !snippetId.isEmpty();
            while ((line = withReader.readLine()) != null) {
                if (!hasSnippetId) {
                    lines.add(line);
                } else {
                    if (isStart(snippetId, line)) {
                        capture = true;
                        foundStart = true;
                    } else if (isEnd(snippetId, line)) {
                        foundEnd = true;
                        break;
                    } else if (capture) {
                        lines.add(line);
                    }
                }
            }

            if (hasSnippetId && !foundStart) {
                throw new IOException("Failed to find START of snippet " + snippetId + " in file at URL: " + source);
            }
            if (hasSnippetId && !foundEnd) {
                throw new IOException("Failed to find END of snippet " + snippetId + " in file at URL: " + source);
            }
        }
        return lines;
    }

    /**
     * Determines if the given line is a start demarcator.
     *
     * @param snippetId the id of the snippet.
     * @param line the line.
     * @return True, if the line is a start demarcator.
     */
    protected boolean isStart(String snippetId, String line) {
        return isDemarcator(snippetId, "START", line);
    }

    /**
     * Determines if the given line is a demarcator.
     *
     * @param snippetId the id of the snippet.
     * @param what Identifier for the demarcator.
     * @param line the line.
     * @return True, if the line is a start demarcator.
     */
    protected static boolean isDemarcator(String snippetId, String what, String line) {
        // SNIPPET and what are case insensitive
        // SNIPPET and what can switch order
        String snippetRegExp = "(^|\\W)(?i:SNIPPET)($|\\W)";
        String snippetIdRegExp = "(^|\\W)" + snippetId + "($|\\W)";
        String whatRegExp = "(^|\\W)(?i:" + what + ")($|\\W)";

        return Pattern.compile(snippetRegExp).matcher(line).find()
                && Pattern.compile(whatRegExp).matcher(line).find()
                && Pattern.compile(snippetIdRegExp).matcher(line).find();
    }

    /**
     * Determines if the given line is an end demarcator.
     *
     * @param snippetId the id of the snippet.
     * @param line the line.
     * @return True, if the line is an end demarcator.
     */
    protected boolean isEnd(String snippetId, String line) {
        return isDemarcator(snippetId, "END", line);
    }
}