/*
 *******************************************************************************
 * Copyright (C) 2004, International Business Machines Corporation and         *
 * others. All Rights Reserved.                                                *
 *******************************************************************************
 */
package com.ibm.icu.impl;

import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

import com.ibm.icu.util.VersionInfo;


/**
 * This class reads the *.res resource bundle format
 * 
 * File format for .res resource bundle files (formatVersion=1.1)
 *
 * An ICU4C resource bundle file (.res) is a binary, memory-mappable file
 * with nested, hierarchical data structures.
 * It physically contains the following:
 *
 *   Resource root; -- 32-bit Resource item, root item for this bundle's tree;
 *                     currently, the root item must be a table or table32 resource item
 *   int32_t indexes[indexes[0]]; -- array of indexes for friendly
 *                                   reading and swapping; see URES_INDEX_* above
 *                                   new in formatVersion 1.1
 *   char keys[]; -- characters for key strings
 *                   (formatVersion 1.0: up to 65k of characters; 1.1: <2G)
 *                   (minus the space for root and indexes[]),
 *                   which consist of invariant characters (ASCII/EBCDIC) and are NUL-terminated;
 *                   padded to multiple of 4 bytes for 4-alignment of the following data
 *   data; -- data directly and indirectly indexed by the root item;
 *            the structure is determined by walking the tree
 *
 * Each resource bundle item has a 32-bit Resource handle (see typedef above)
 * which contains the item type number in its upper 4 bits (31..28) and either
 * an offset or a direct value in its lower 28 bits (27..0).
 * The order of items is undefined and only determined by walking the tree.
 * Leaves of the tree may be stored first or last or anywhere in between,
 * and it is in theory possible to have unreferenced holes in the file.
 *
 * Direct values:
 * - Empty Unicode strings have an offset value of 0 in the Resource handle itself.
 * - Integer values are 28-bit values stored in the Resource handle itself;
 *   the interpretation of unsigned vs. signed integers is up to the application.
 *
 * All other types and values use 28-bit offsets to point to the item's data.
 * The offset is an index to the first 32-bit word of the value, relative to the
 * start of the resource data (i.e., the root item handle is at offset 0).
 * To get byte offsets, the offset is multiplied by 4 (or shifted left by 2 bits).
 * All resource item values are 4-aligned.
 *
 * The structures (memory layouts) for the values for each item type are listed
 * in the table above.
 *
 * Nested, hierarchical structures: -------------
 *
 * Table items contain key-value pairs where the keys are 16-bit offsets to char * key strings.
 * Key string offsets are also relative to the start of the resource data (of the root handle),
 * i.e., the first string has an offset of 4 (after the 4-byte root handle).
 *
 * The values of these pairs are Resource handles.
 *
 * Array items are simple vectors of Resource handles.
 *
 * An alias item is special (and new in ICU 2.4): --------------
 *
 * Its memory layout is just like for a UnicodeString, but at runtime it resolves to
 * another resource bundle's item according to the path in the string.
 * This is used to share items across bundles that are in different lookup/fallback
 * chains (e.g., large collation data among zh_TW and zh_HK).
 * This saves space (for large items) and maintenance effort (less duplication of data).
 *
 * --------------------------------------------------------------------------
 *
 * Resource types:
 *
 * Most resources have their values stored at four-byte offsets from the start
 * of the resource data. These values are at least 4-aligned.
 * Some resource values are stored directly in the offset field of the Resource itself.
 * See UResType in unicode/ures.h for enumeration constants for Resource types.
 *
 * Type Name            Memory layout of values
 *                      (in parentheses: scalar, non-offset values)
 *
 * 0  Unicode String:   int32_t length, UChar[length], (UChar)0, (padding)
 *                  or  (empty string ("") if offset==0)
 * 1  Binary:           int32_t length, uint8_t[length], (padding)
 *                      - this value should be 32-aligned -
 * 2  Table:            uint16_t count, uint16_t keyStringOffsets[count], (uint16_t padding), Resource[count]
 * 3  Alias:            (physically same value layout as string, new in ICU 2.4)
 * 4  Table32:          int32_t count, int32_t keyStringOffsets[count], Resource[count]
 *                      (new in formatVersion 1.1/ICU 2.8)
 *
 * 7  Integer:          (28-bit offset is integer value)
 * 8  Array:            int32_t count, Resource[count]
 *
 * 14 Integer Vector:   int32_t length, int32_t[length]
 * 15 Reserved:         This value denotes special purpose resources and is for internal use.
 *
 * Note that there are 3 types with data vector values:
 * - Vectors of 8-bit bytes stored as type Binary.
 * - Vectors of 16-bit words stored as type Unicode String
 *                     (no value restrictions, all values 0..ffff allowed!).
 * - Vectors of 32-bit words stored as type Integer Vector.
 *
 *
 */
public final class ICUResourceBundleReader implements ICUBinary.Authenticate{

    /**
     * File format version that this class understands.
     * "ResB"
     */
    private static final byte DATA_FORMAT_ID[] = {(byte)0x52, (byte)0x65, 
                                                     (byte)0x73, (byte)0x42};
    private static final byte DATA_FORMAT_VERSION[] = {(byte)0x1, (byte)0x1, 
                                                         (byte)0x0, (byte)0x0};
    private byte[] version;
    private static final String ICU_RESOURCE_SUFFIX = ".res";
    
    private static final int    URES_INDEX_LENGTH           = 0;        /* [0] contains URES_INDEX_TOP==the length of indexes[] */
    private static final int    URES_INDEX_STRINGS_TOP      = 1;        /* [1] contains the top of the strings, */
                                                                        /*     same as the bottom of resources, rounded up */
    private static final int    URES_INDEX_RESOURCES_TOP    = 2;        /* [2] contains the top of all resources */
    private static final int    URES_INDEX_BUNDLE_TOP       = 3;        /* [3] contains the top of the bundle, */
                                                                        /*     in case it were ever different from [2] */
    private static final int    URES_INDEX_MAX_TABLE_LENGTH = 4;        /* [4] max. length of any table */
    private static final int    URES_INDEX_TOP              = 5;
    //private static final int    URES_STRINGS_BOTTOM=(1+URES_INDEX_TOP)*4;
    private static final boolean DEBUG = false;
    
    private byte[] data;
    
    private ICUResourceBundleReader(InputStream stream, String resolvedName){

        BufferedInputStream bs = new BufferedInputStream(stream);
        try{
            if(DEBUG) System.out.println("The InputStream class is: " + stream.getClass().getName());
            if(DEBUG) System.out.println("The BufferedInputStream class is: " + bs.getClass().getName());
            if(DEBUG) System.out.println("The bytes avialable in stream before reading the header: " + bs.available());
            
            version = ICUBinary.readHeader(bs,DATA_FORMAT_ID,this);

            if(DEBUG) System.out.println("The bytes avialable in stream after reading the header: " + bs.available());
                 
            data = readData(bs);

            stream.close();
        }catch(IOException ex){
            throw new RuntimeException("Data file "+ resolvedName+ " is corrupt.", ex);   
        }
    }
    public static ICUResourceBundleReader getReader(String baseName, String localeName, ClassLoader root){
        String resolvedName = getFullName(baseName, localeName);
        InputStream stream = ICUData.getStream(root,resolvedName);
        
        if(stream==null){
            return null;
        }
        ICUResourceBundleReader reader = new ICUResourceBundleReader(stream, resolvedName);
        return reader;
    }
    /* indexes[] value names; indexes are generally 32-bit (Resource) indexes */
        
    private static byte[] readData(InputStream stream)
            throws IOException{
        
        DataInputStream ds = new DataInputStream(stream);

        if(DEBUG) System.out.println("The DataInputStream class is: " + ds.getClass().getName());
        if(DEBUG) System.out.println("The available bytes in the stream before reading the data: "+ds.available());
        
        ds.mark((1+URES_INDEX_TOP)*4);
        int[] indexes = new int[URES_INDEX_TOP];
        ds.readInt(); // ignore the root resource
        
        for(int i=1; i< URES_INDEX_TOP; i++){
            indexes[i] = ds.readInt();   
        }
        ds.reset();
        
        int length = indexes[URES_INDEX_BUNDLE_TOP]*4;
        if(DEBUG) System.out.println("The number of bytes in the bundle: "+length);
    
        byte[] data = new byte[length];
        ds.readFully(data);
        return data;
       
    }
    /**
     * Gets the full name of the resource with suffix.
     * If the 
     * @param baseName
     * @param localeName
     * @return
     */
    public static String getFullName(String baseName, String localeName){
        if(baseName.indexOf('.')==-1){
            if(baseName.charAt(baseName.length()-1)!= '/'){
                return baseName+"/"+localeName+ICU_RESOURCE_SUFFIX;
            }else{
                return baseName+localeName+ICU_RESOURCE_SUFFIX;   
            }
        }else{
            baseName = baseName.replace('.','/');
            if(localeName.length()==0){
                return baseName+ICU_RESOURCE_SUFFIX;   
            }else{
                return baseName+"_"+localeName+ICU_RESOURCE_SUFFIX;
            }
        }
    }
    
    public VersionInfo getVersion(){
        return VersionInfo.getInstance(version[0],version[1],version[2],version[3]);   
    }
    public boolean isDataVersionAcceptable(byte version[]){
        return version[0] == DATA_FORMAT_VERSION[0] 
               && version[1] == DATA_FORMAT_VERSION[1]
               && version[2] == DATA_FORMAT_VERSION[2] 
               && version[3] == DATA_FORMAT_VERSION[3];
    }
    
    public byte[] getData(){
        return data;   
    }
    
}