package tim.prune.function.srtm;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;

public abstract class SrtmSource {
	public abstract String getName();
	public abstract boolean isReadyToUse();
	public abstract boolean downloadTile(SrtmTile inTile)
		throws SrtmSourceException;
	public abstract int getRowSize(SrtmTile inTile);
	protected abstract String getSourceExtension();

	protected int[] slurpTileHeigths(ZipInputStream inStream, int tileSize)
		throws IOException
	{
		int[] heights = new int[tileSize];
		int dataSize = 2 * tileSize;
		byte[] buffer = new byte[dataSize];
		// Read entire file contents into one byte array
		int alreadyRead = 0;
		while (alreadyRead < dataSize)
		{
			alreadyRead += inStream.read(buffer, alreadyRead, dataSize - alreadyRead);
		}
		for (int i = 0; i < tileSize; i++)
		{
			// Bytes are signed. Cast high-order to int with sign
			// extension, and clamp low-order to its unsigned range
			heights[i] = buffer[2 * i] * 256 + (0xff & buffer[2 * i + 1]);
		}
		// Close stream
		inStream.close();
		return heights;
	}

	public int[] getTileHeights(SrtmTile inTile)
		throws SrtmSourceException
	{
		File cacheFileName = getCacheFileName(inTile);
		if (cacheFileName == null)
		{
			throw new SrtmSourceException("Tile "+inTile.getTileName()+" not in cache");
		}
		try
		{
			ZipInputStream inStream = new ZipInputStream(new FileInputStream(cacheFileName));
			ZipEntry entry = inStream.getNextEntry();
			int rowSize = getRowSize(inTile);
			int tileSize = rowSize * rowSize;
			if (entry.getSize() != 2 * tileSize)
			{
				throw new SrtmSourceException("Tile file "+cacheFileName+" does not have the expected size");
			}
			return slurpTileHeigths(inStream, tileSize);
		}
		catch (IOException e)
		{
			throw new SrtmSourceException("Failure opening "+cacheFileName+" for reading:"+e.getMessage());
		}

	}

	protected File getCacheDir()
	{
		return SrtmDiskCache.getCacheDir(getName());
	}

	protected File getCacheFileName(SrtmTile inTile)
	{
		String fileName = inTile.getTileName() + getSourceExtension();
		return new File(getCacheDir(), fileName);
	}

	public boolean isCached(SrtmTile inTile)
	{
		File cachedFileName = getCacheFileName(inTile);
		return cachedFileName != null &&
			getCacheFileName(inTile).exists();
	}
}