/*
 *******************************************************************************
 *
 *   Copyright (C) 1999-2003, International Business Machines
 *   Corporation and others.  All Rights Reserved.
 *
 *******************************************************************************
 */

package sun.font;

/**
 * <code>ScriptRun</code> is used to find runs of characters in
 * the same script, as defined in the <code>Script</code> class.
 * It implements a simple iterator over an array of characters.
 * The iterator will assign <code>COMMON</code> and <code>INHERITED</code>
 * characters to the same script as the preceeding characters. If the
 * COMMON and INHERITED characters are first, they will be assigned to
 * the same script as the following characters.
 *
 * The iterator will try to match paired punctuation. If it sees an
 * opening punctuation character, it will remember the script that
 * was assigned to that character, and assign the same script to the
 * matching closing punctuation.
 *
 * No attempt is made to combine related scripts into a single run. In
 * particular, Hiragana, Katakana, and Han characters will appear in seperate
 * runs.

 * Here is an example of how to iterate over script runs:
 * <pre>
 * void printScriptRuns(char[] text)
 * {
 *     ScriptRun scriptRun = new ScriptRun(text, 0, text.length);
 *
 *     while (scriptRun.next()) {
 *         int start  = scriptRun.getScriptStart();
 *         int limit  = scriptRun.getScriptLimit();
 *         int script = scriptRun.getScriptCode();
 *
 *         System.out.println("Script \"" + Script.getName(script) + "\" from " +
 *                            start + " to " + limit + ".");
 *     }
 *  }
 * </pre>
 *
 */
public final class ScriptRun
{
    private char[] text;   // fixed once set by constructor
    private int textStart;
    private int textLimit;

    private int scriptStart;     // change during iteration
    private int scriptLimit;
    private int scriptCode;

    private int stack[];         // stack used to handle paired punctuation if encountered
    private int parenSP;

    public ScriptRun() {
        // must call init later or we die.
    }

    /**
     * Construct a <code>ScriptRun</code> object which iterates over a subrange
     * of the given characetrs.
     *
     * @param chars the array of characters over which to iterate.
     * @param start the index of the first character over which to iterate
     * @param count the number of characters over which to iterate
     */
    public ScriptRun(char[] chars, int start, int count)
    {
        init(chars, start, count);
    }

    public void init(char[] chars, int start, int count)
    {
        if (chars == null || start < 0 || count < 0 || count > chars.length - start) {
            throw new IllegalArgumentException();
        }

        text = chars;
        textStart = start;
        textLimit = start + count;

        scriptStart = textStart;
        scriptLimit = textStart;
        scriptCode = Script.INVALID_CODE;
        parenSP = 0;
    }

    /**
     * Get the starting index of the current script run.
     *
     * @return the index of the first character in the current script run.
     */
    public final int getScriptStart() {
        return scriptStart;
    }

    /**
     * Get the index of the first character after the current script run.
     *
     * @return the index of the first character after the current script run.
     */
    public final int getScriptLimit() {
        return scriptLimit;
    }

    /**
     * Get the script code for the script of the current script run.
     *
     * @return the script code for the script of the current script run.
     * @see #Script
     */
    public final int getScriptCode() {
        return scriptCode;
    }

    /**
     * Find the next script run. Returns <code>false</code> if there
     * isn't another run, returns <code>true</code> if there is.
     *
     * @return <code>false</code> if there isn't another run, <code>true</code> if there is.
     */
    public final boolean next() {
        int startSP  = parenSP;  // used to find the first new open character

        // if we've fallen off the end of the text, we're done
        if (scriptLimit >= textLimit) {
            return false;
        }
    
        scriptCode  = Script.COMMON;
        scriptStart = scriptLimit;
        
        int ch;
        
        while ((ch = nextCodePoint()) != DONE) {
            int sc = ScriptRunData.getScript(ch);
            int pairIndex = sc == Script.COMMON ? getPairIndex(ch) : -1;

            // Paired character handling:
            //
            // if it's an open character, push it onto the stack.
            // if it's a close character, find the matching open on the
            // stack, and use that script code. Any non-matching open
            // characters above it on the stack will be popped.
            if (pairIndex >= 0) {
                if ((pairIndex & 1) == 0) {
                    if (stack == null) {
                        stack = new int[32];
                    } else if (parenSP == stack.length) {
                        int[] newstack = new int[stack.length + 32];
                        System.arraycopy(stack, 0, newstack, 0, stack.length);
                        stack = newstack;
                    }

                    stack[parenSP++] = pairIndex;
                    stack[parenSP++] = scriptCode;
                } else if (parenSP > 0) {
                    int pi = pairIndex & ~1;

                    while ((parenSP -= 2) >= 0 && stack[parenSP] != pi);

                    if (parenSP >= 0) {
                        sc = stack[parenSP+1];
                    } else {
                      parenSP = 0;
                    }
                    if (parenSP < startSP) {
                        startSP = parenSP;
                    }
               }
            }

            if (sameScript(scriptCode, sc)) {
                if (scriptCode <= Script.INHERITED && sc > Script.INHERITED) {
                    scriptCode = sc;

                    // now that we have a final script code, fix any open
                    // characters we pushed before we knew the script code.
                    while (startSP < parenSP) {
                        stack[startSP+1] = scriptCode;
                        startSP += 2;
                    }
                }

                // if this character is a close paired character,
        // pop it from the stack
                if (pairIndex > 0 && (pairIndex & 1) != 0 && parenSP > 0) {
                    parenSP -= 2;
                }
            } else {
                // We've just seen the first character of
                // the next run. Back over it so we'll see
                // it again the next time.
                pushback(ch);

                // we're outta here
                break; 
            }
        }

        return true;
    }

    static final int SURROGATE_START = 0x10000;
    static final int LEAD_START = 0xd800;
    static final int LEAD_LIMIT = 0xdc00;
    static final int TAIL_START = 0xdc00;
    static final int TAIL_LIMIT = 0xe000;
    static final int LEAD_SURROGATE_SHIFT = 10;
    static final int SURROGATE_OFFSET = SURROGATE_START - (LEAD_START << LEAD_SURROGATE_SHIFT) - TAIL_START;

    static final int DONE = -1;

    private final int nextCodePoint() {
        if (scriptLimit >= textLimit) {
            return DONE;
        }
        int ch = text[scriptLimit++];
        if (ch >= LEAD_START && ch < LEAD_LIMIT && scriptLimit < textLimit) {
            int nch = text[scriptLimit];
            if (nch >= TAIL_START && nch < TAIL_LIMIT) {
                ++scriptLimit;
                ch = (ch << LEAD_SURROGATE_SHIFT) + nch + SURROGATE_OFFSET;
            }
        }
        return ch;
    }

    private final void pushback(int ch) {
        if (ch >= 0) {
            if (ch >= 0x10000) {
                scriptLimit -= 2;
            } else {
                scriptLimit -= 1;
            }
        }
    }

    /**
     * Compare two script codes to see if they are in the same script. If one script is
     * a strong script, and the other is INHERITED or COMMON, it will compare equal.
     *
     * @param scriptOne one of the script codes.
     * @param scriptTwo the other script code.
     * @return <code>true</code> if the two scripts are the same.
     * @see com.ibm.icu.lang.Script
     */
    private static boolean sameScript(int scriptOne, int scriptTwo) {
        return scriptOne == scriptTwo || scriptOne <= Script.INHERITED || scriptTwo <= Script.INHERITED;
    }

    /**
     * Find the highest bit that's set in a word. Uses a binary search through
     * the bits.
     *
     * @param n the word in which to find the highest bit that's set.
     * @return the bit number (counting from the low order bit) of the highest bit.
     */
    private static final byte highBit(int n)
    {
        if (n <= 0) {
            return -32;
        }

        byte bit = 0;

        if (n >= 1 << 16) {
            n >>= 16;
            bit += 16;
        }

        if (n >= 1 << 8) {
            n >>= 8;
            bit += 8;
        }

        if (n >= 1 << 4) {
            n >>= 4;
            bit += 4;
        }

        if (n >= 1 << 2) {
            n >>= 2;
            bit += 2;
        }

        if (n >= 1 << 1) {
            n >>= 1;
            bit += 1;
        }

        return bit;
    }

    /**
     * Search the pairedChars array for the given character.
     *
     * @param ch the character for which to search.
     * @return the index of the character in the table, or -1 if it's not there.
     */
    private static int getPairIndex(int ch)
    {
        int probe = pairedCharPower;
        int index = 0;

        if (ch >= pairedChars[pairedCharExtra]) {
            index = pairedCharExtra;
        }

        while (probe > (1 << 0)) {
            probe >>= 1;

            if (ch >= pairedChars[index + probe]) {
                index += probe;
            }
        }

        if (pairedChars[index] != ch) {
            index = -1;
        }

        return index;
    }

    // all common
    private static int pairedChars[] = {
        0x0028, 0x0029, // ascii paired punctuation  // common
        0x003c, 0x003e, // common
        0x005b, 0x005d, // common
        0x007b, 0x007d, // common
        0x00ab, 0x00bb, // guillemets // common
        0x2018, 0x2019, // general punctuation // common
        0x201c, 0x201d, // common
        0x2039, 0x203a, // common
        0x3008, 0x3009, // chinese paired punctuation // common
        0x300a, 0x300b,
        0x300c, 0x300d,
        0x300e, 0x300f,
        0x3010, 0x3011,
        0x3014, 0x3015,
        0x3016, 0x3017,
        0x3018, 0x3019,
        0x301a, 0x301b
    };

    private static final int pairedCharPower = 1 << highBit(pairedChars.length);
    private static final int pairedCharExtra = pairedChars.length - pairedCharPower;

}