package org.unicode.cldr.draft;

import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
import java.util.TreeSet;

import com.ibm.icu.impl.Utility;
import com.ibm.icu.lang.UCharacter;
import com.ibm.icu.lang.UScript;
import com.ibm.icu.text.CanonicalIterator;
import com.ibm.icu.text.Normalizer;
import com.ibm.icu.text.UTF16;
import com.ibm.icu.text.UTF16.StringComparator;
import com.ibm.icu.text.UnicodeSet;

public class ShortestCanonicalForm {

    static final UnicodeSet trailing = new UnicodeSet();
    static final UnicodeSet leading = new UnicodeSet();
    static final UnicodeSet leading3 = new UnicodeSet();
    static StringComparator cpCompare = new UTF16.StringComparator(true, false, 0);
    static final Map<Integer, Set<String>> leadToTrail = new TreeMap<Integer, Set<String>>();
    static UnicodeSet skip = new UnicodeSet(
        "[[:hangulsyllabletype=l:][:hangulsyllabletype=v:][:hangulsyllabletype=t:]]");
    static Map<String, String> restoreExclusions = new TreeMap<String, String>();
    static UnicodeSet breakingTrail = new UnicodeSet();

    static {
        for (int i = 0; i <= 0x10FFFF; ++i) {
            final String nfd = Normalizer.normalize(i, Normalizer.NFD);
            if (skip.containsAll(nfd)) {
                continue;
            }

            final String nfc = Normalizer.normalize(i, Normalizer.NFC);
            if (nfc.codePointCount(0, nfc.length()) > 1) {
                restoreExclusions.put(nfc, UTF16.valueOf(i));
                int first = nfc.codePointAt(0);
                final String trailingString = nfc.substring(first > 0xFFFF ? 2 : 1);
                breakingTrail.addAll(trailingString);
            }
            int nfdLen = nfd.codePointCount(0, nfd.length());
            if (nfdLen > 1) {
                int first = nfd.codePointAt(0);
                leading.add(first);
                final String trailingString = nfd.substring(first > 0xFFFF ? 2 : 1);
                trailing.addAll(trailingString);
                Set<String> trails = leadToTrail.get(first);
                if (trails == null) {
                    leadToTrail.put(first, trails = new TreeSet<String>(cpCompare));
                }
                trails.add(trailingString);
                if (UScript.getScript(i) != UScript.HANGUL
                    && trailingString.codePointCount(0, trailingString.length()) > 1) {
                    leading3.add(first);
                }
            }
        }
        leading.freeze();
        trailing.freeze();
        for (int first : leadToTrail.keySet()) {
            if (leading3.contains(first)) {
                for (String trail : leadToTrail.get(first)) {
                    System.out.println(Utility.hex(first, 4) + "," + Utility.hex(trail, 4, ",") + "\t"
                        + UTF16.valueOf(first) + trail);
                }
            }
        }
        System.out.println("Breaking Trail:\t" + breakingTrail);
        System.out.println("Lead-only: " + new UnicodeSet(leading).removeAll(trailing));
        System.out.println("Trail-only: " + new UnicodeSet(trailing).removeAll(leading));
        System.out.println("Lead and trail: " + new UnicodeSet(leading).retainAll(trailing));

        UnicodeSet blockers = new UnicodeSet();

        for (int lead : leadToTrail.keySet()) {
            String leadStr = UTF16.valueOf(lead);
            System.out.println("Testing: " + leadStr);
            Set<String> trails = leadToTrail.get(lead);
            for (String trail1 : trails) {
                for (String trail2 : trails) {
                    if (trail1.length() >= trail2.length()) {
                        continue;
                    }
                    for (Iterator<String> it = new SubstringIterator(trail1); it.hasNext();) {
                        String sub = it.next();
                        String trial = leadStr + sub + trail2;
                        String nfc = shortNFC(trial);
                        String shortest = getShortest(trial, nfc);
                        if (!shortest.equals(nfc)) {
                            final int blocker = nfc.codePointAt(0);
                            if (!blockers.contains(blocker)) {
                                blockers.add(blocker);
                                System.out.println("Adding blocker: " + Utility.hex(blocker, 4) + "\t"
                                    + UTF16.valueOf(blocker));
                                System.out.println("\tNFC: " + Utility.hex(nfc) + "\t" + nfc);
                                System.out.println("\tShort: " + Utility.hex(shortest) + "\t" + shortest);
                            }
                        }
                    }
                }
            }
        }
        System.out.println("Blockers: " + blockers);
    }

    private static String shortNFC(String trial) {
        String result = Normalizer.normalize(trial, Normalizer.NFC);
        result = result.replace("\u0308\u0301", "\u0344");
        for (String exclusion : restoreExclusions.keySet()) {
            // just simple case
            result = result.replace(exclusion, restoreExclusions.get(exclusion));
        }
        return result;
    }

    static class SubstringIterator implements Iterator<String> {
        String string;
        int start;
        int end;

        public SubstringIterator(String s) {
            string = s;
            start = 0;
            end = UCharacter.charCount(string.codePointAt(start));
        }

        public boolean hasNext() {
            return start < string.length();
        }

        public String next() {
            String result = string.substring(start, end);
            if (end < string.length()) {
                end += UCharacter.charCount(string.codePointAt(end));
            } else {
                start += UCharacter.charCount(string.codePointAt(start));
                if (start < string.length()) {
                    end = start + UCharacter.charCount(string.codePointAt(start));
                }
            }
            return result;
        }

        public void remove() {
            throw new UnsupportedOperationException();
        }

        // boolean insideCodePoint(String s, int offset) {
        // if (offset == 0 || offset == s.length()) {
        // return false;
        // }
        // char before = s.charAt(offset - 1);
        // char after = s.charAt(offset);
        // return 0xD800 <= before && before <= 0xDBFF && 0xDC00 <= after && after <= 0xDFFF;
        // }
    }

    private static String getShortest(String trial, String nfc) {
        String best = nfc;
        int bestLength = nfc.codePointCount(0, nfc.length());

        CanonicalIterator ci = new CanonicalIterator(trial);
        for (String s = ci.next(); s != null; s = ci.next()) {
            final int currentLength = s.codePointCount(0, s.length());
            if (currentLength < bestLength) {
                bestLength = currentLength;
                best = s;
            }
        }
        return best;
    }

    CanonicalIterator ci = new CanonicalIterator("");

    public String normalize(String input) {
        // optimize later
        StringBuffer b = new StringBuffer();

        boolean inProblem = false;
        int start = 0;
        final int len = input.length();
        // find chunks of NFD !NFD !NFD... and process them
        int cp;
        for (int i = 0; i < len; i += Character.charCount(cp)) {
            cp = input.codePointAt(i);
            boolean isNFD = trailing.contains(cp);
            if (isNFD) {
                if (inProblem) {
                    // continue;
                } else {// reached end of problem
                    b.append(process(input, start, i));
                    start = i;
                }
            } else { // not NFD
                inProblem = true;
            }
        }
        if (start < len) {
            b.append(process(input, start, len));
        }
        return b.toString();
    }

    // of the form NFD? !NFD !NFD...
    private String process(String input, int start, int end) {
        final String piece = input.substring(start, end);
        String nfc = shortNFC(piece);
        final int nfcLength = nfc.codePointCount(0, nfc.length());
        if (nfcLength == 1) {
            return piece;
        }

        ci.setSource(piece);
        String best = null;
        int bestLength = Integer.MAX_VALUE;
        for (String trial = ci.next(); trial != null; trial = ci.next()) {
            int len = trial.codePointCount(0, trial.length());
            if (len < bestLength) {
                best = trial;
                bestLength = len;
            }
        }
        if (nfcLength <= bestLength) {
            return nfc;
        }
        return best;
    }

    public static void main(String[] args) {
        ShortestCanonicalForm scf = new ShortestCanonicalForm();
        for (int i = 0; i <= 0x10FFFF; ++i) {
            String s = UTF16.valueOf(i);
            final String nfc = shortNFC(s);
            String shortest = scf.normalize(nfc);
            if (!shortest.equals(nfc)) {
                System.out.println("NFC not shortest: " + shortest + ", " + nfc);
            }
        }
    }
}