/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed 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 com.pojavdx.dx.util;

import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.StringWriter;
import java.io.Writer;

/**
 * Class that takes a combined output destination and provides two
 * output writers, one of which ends up writing to the left column and
 * one which goes on the right.
 */
public final class TwoColumnOutput {
    /** {@code non-null;} underlying writer for final output */
    private final Writer out;

    /** {@code > 0;} the left column width */
    private final int leftWidth;

    /** {@code non-null;} pending left column output */
    private final StringBuffer leftBuf;

    /** {@code non-null;} pending right column output */
    private final StringBuffer rightBuf;

    /** {@code non-null;} left column writer */
    private final IndentingWriter leftColumn;

    /** {@code non-null;} right column writer */
    private final IndentingWriter rightColumn;

    /**
     * Turns the given two strings (with widths) and spacer into a formatted
     * two-column string.
     *
     * @param s1 {@code non-null;} first string
     * @param width1 {@code > 0;} width of the first column
     * @param spacer {@code non-null;} spacer string
     * @param s2 {@code non-null;} second string
     * @param width2 {@code > 0;} width of the second column
     * @return {@code non-null;} an appropriately-formatted string
     */
    public static String toString(String s1, int width1, String spacer,
                                  String s2, int width2) {
        int len1 = s1.length();
        int len2 = s2.length();

        StringWriter sw = new StringWriter((len1 + len2) * 3);
        TwoColumnOutput twoOut =
            new TwoColumnOutput(sw, width1, width2, spacer);

        try {
            twoOut.getLeft().write(s1);
            twoOut.getRight().write(s2);
        } catch (IOException ex) {
            throw new RuntimeException("shouldn't happen", ex);
        }

        twoOut.flush();
        return sw.toString();
    }

    /**
     * Constructs an instance.
     *
     * @param out {@code non-null;} writer to send final output to
     * @param leftWidth {@code > 0;} width of the left column, in characters
     * @param rightWidth {@code > 0;} width of the right column, in characters
     * @param spacer {@code non-null;} spacer string to sit between the two columns
     */
    public TwoColumnOutput(Writer out, int leftWidth, int rightWidth,
                           String spacer) {
        if (out == null) {
            throw new NullPointerException("out == null");
        }

        if (leftWidth < 1) {
            throw new IllegalArgumentException("leftWidth < 1");
        }

        if (rightWidth < 1) {
            throw new IllegalArgumentException("rightWidth < 1");
        }

        if (spacer == null) {
            throw new NullPointerException("spacer == null");
        }

        StringWriter leftWriter = new StringWriter(1000);
        StringWriter rightWriter = new StringWriter(1000);

        this.out = out;
        this.leftWidth = leftWidth;
        this.leftBuf = leftWriter.getBuffer();
        this.rightBuf = rightWriter.getBuffer();
        this.leftColumn = new IndentingWriter(leftWriter, leftWidth);
        this.rightColumn =
            new IndentingWriter(rightWriter, rightWidth, spacer);
    }

    /**
     * Constructs an instance.
     *
     * @param out {@code non-null;} stream to send final output to
     * @param leftWidth {@code >= 1;} width of the left column, in characters
     * @param rightWidth {@code >= 1;} width of the right column, in characters
     * @param spacer {@code non-null;} spacer string to sit between the two columns
     */
    public TwoColumnOutput(OutputStream out, int leftWidth, int rightWidth,
                           String spacer) {
        this(new OutputStreamWriter(out), leftWidth, rightWidth, spacer);
    }

    /**
     * Gets the writer to use to write to the left column.
     *
     * @return {@code non-null;} the left column writer
     */
    public Writer getLeft() {
        return leftColumn;
    }

    /**
     * Gets the writer to use to write to the right column.
     *
     * @return {@code non-null;} the right column writer
     */
    public Writer getRight() {
        return rightColumn;
    }

    /**
     * Flushes the output. If there are more lines of pending output in one
     * column, then the other column will get filled with blank lines.
     */
    public void flush() {
        try {
            appendNewlineIfNecessary(leftBuf, leftColumn);
            appendNewlineIfNecessary(rightBuf, rightColumn);
            outputFullLines();
            flushLeft();
            flushRight();
        } catch (IOException ex) {
            throw new RuntimeException(ex);
        }
    }

    /**
     * Outputs to the final destination as many full line pairs as
     * there are in the pending output, removing those lines from
     * their respective buffers. This method terminates when at
     * least one of the two column buffers is empty.
     */
    private void outputFullLines() throws IOException {
        for (;;) {
            int leftLen = leftBuf.indexOf("\n");
            if (leftLen < 0) {
                return;
            }

            int rightLen = rightBuf.indexOf("\n");
            if (rightLen < 0) {
                return;
            }

            if (leftLen != 0) {
                out.write(leftBuf.substring(0, leftLen));
            }

            if (rightLen != 0) {
                writeSpaces(out, leftWidth - leftLen);
                out.write(rightBuf.substring(0, rightLen));
            }

            out.write('\n');

            leftBuf.delete(0, leftLen + 1);
            rightBuf.delete(0, rightLen + 1);
        }
    }

    /**
     * Flushes the left column buffer, printing it and clearing the buffer.
     * If the buffer is already empty, this does nothing.
     */
    private void flushLeft() throws IOException {
        appendNewlineIfNecessary(leftBuf, leftColumn);

        while (leftBuf.length() != 0) {
            rightColumn.write('\n');
            outputFullLines();
        }
    }

    /**
     * Flushes the right column buffer, printing it and clearing the buffer.
     * If the buffer is already empty, this does nothing.
     */
    private void flushRight() throws IOException {
        appendNewlineIfNecessary(rightBuf, rightColumn);

        while (rightBuf.length() != 0) {
            leftColumn.write('\n');
            outputFullLines();
        }
    }

    /**
     * Appends a newline to the given buffer via the given writer, but
     * only if it isn't empty and doesn't already end with one.
     *
     * @param buf {@code non-null;} the buffer in question
     * @param out {@code non-null;} the writer to use
     */
    private static void appendNewlineIfNecessary(StringBuffer buf,
                                                 Writer out)
            throws IOException {
        int len = buf.length();

        if ((len != 0) && (buf.charAt(len - 1) != '\n')) {
            out.write('\n');
        }
    }

    /**
     * Writes the given number of spaces to the given writer.
     *
     * @param out {@code non-null;} where to write
     * @param amt {@code >= 0;} the number of spaces to write
     */
    private static void writeSpaces(Writer out, int amt) throws IOException {
        while (amt > 0) {
            out.write(' ');
            amt--;
        }
    }
}
