/* -*- Mode: java; indent-tabs-mode: nil; c-basic-offset: 2 -*-

 * Copyright (C) 2011 George Yunaev @ Ulduzsoft
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.

  http://www.ulduzsoft.com/2012/01/enumerating-the-fonts-on-android-platform/
 */
 
package org.jwz.xscreensaver;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.HashMap;
 
// The class which loads the TTF file, parses it and returns the TTF font name
class TTFAnalyzer
{
    // This function parses the TTF file and returns the font name specified in the file
    public String getTtfFontName( String fontFilename )
    {
        try
        {
            // Parses the TTF file format.
            // See http://developer.apple.com/fonts/ttrefman/rm06/Chap6.html
            m_file = new RandomAccessFile( fontFilename, "r" );
 
            // Read the version first
            int version = readDword();
 
            // The version must be either 'true' (0x74727565) or 0x00010000 or 'OTTO' (0x4f54544f) for CFF style fonts.
            if ( version != 0x74727565 && version != 0x00010000 && version != 0x4f54544f)
                return null;
 
            // The TTF file consist of several sections called "tables", and we need to know how many of them are there.
            int numTables = readWord();
 
            // Skip the rest in the header
            readWord(); // skip searchRange
            readWord(); // skip entrySelector
            readWord(); // skip rangeShift
 
            // Now we can read the tables
            for ( int i = 0; i < numTables; i++ )
            {
                // Read the table entry
                int tag = readDword();
                readDword(); // skip checksum
                int offset = readDword();
                int length = readDword();
 
                // Now here' the trick. 'name' field actually contains the textual string name.
                // So the 'name' string in characters equals to 0x6E616D65
                if ( tag == 0x6E616D65 )
                {
                    // Here's the name section. Read it completely into the allocated buffer
                    byte[] table = new byte[ length ];
 
                    m_file.seek( offset );
                    read( table );
 
                    // This is also a table. See http://developer.apple.com/fonts/ttrefman/rm06/Chap6name.html
                    // According to Table 36, the total number of table records is stored in the second word, at the offset 2.
                    // Getting the count and string offset - remembering it's big endian.
                    int count = getWord( table, 2 );
                    int string_offset = getWord( table, 4 );
 
                    // Record starts from offset 6
                    for ( int record = 0; record < count; record++ )
                    {
                        // Table 37 tells us that each record is 6 words -> 12 bytes, and that the nameID is 4th word so its offset is 6.
                        // We also need to account for the first 6 bytes of the header above (Table 36), so...
                        int nameid_offset = record * 12 + 6;
                        int platformID = getWord( table, nameid_offset );
                        int nameid_value = getWord( table, nameid_offset + 6 );
 
                        // Table 42 lists the valid name Identifiers. We're interested in 4 but not in Unicode encoding (for simplicity).
                        // The encoding is stored as PlatformID and we're interested in Mac encoding
                        if ( nameid_value == 4 && platformID == 1 )
                        {
                            // We need the string offset and length, which are the word 6 and 5 respectively
                            int name_length = getWord( table, nameid_offset + 8 );
                            int name_offset = getWord( table, nameid_offset + 10 );
 
                            // The real name string offset is calculated by adding the string_offset
                            name_offset = name_offset + string_offset;
 
                            // Make sure it is inside the array
                            if ( name_offset >= 0 && name_offset + name_length < table.length )
                                return new String( table, name_offset, name_length );
                        }
                    }
                }
            }
 
            return null;
        }
        catch (FileNotFoundException e)
        {
            // Permissions?
            return null;
        }
        catch (IOException e)
        {
            // Most likely a corrupted font file
            return null;
        }
    }
 
    // Font file; must be seekable
    private RandomAccessFile m_file = null;
 
    // Helper I/O functions
    private int readByte() throws IOException
    {
        return m_file.read() & 0xFF;
    }
 
    private int readWord() throws IOException
    {
        int b1 = readByte();
        int b2 = readByte();
 
        return b1 << 8 | b2;
    }
 
    private int readDword() throws IOException
    {
        int b1 = readByte();
        int b2 = readByte();
        int b3 = readByte();
        int b4 = readByte();
 
        return b1 << 24 | b2 << 16 | b3 << 8 | b4;
    }
 
    private void read( byte [] array ) throws IOException
    {
        if ( m_file.read( array ) != array.length )
            throw new IOException();
    }
 
    // Helper
    private int getWord( byte [] array, int offset )
    {
        int b1 = array[ offset ] & 0xFF;
        int b2 = array[ offset + 1 ] & 0xFF;
 
        return b1 << 8 | b2;
    }
}