refactoring - migrate to DDDB like approach

Author: TomBlock

core/src/main/java/com/bc/fiduceo/reader/slstr_subset/NcCache.java

@@ -0,0 +1,121 @@
+package com.bc.fiduceo.reader.slstr_subset;
+
+import com.bc.fiduceo.store.Store;
+import org.esa.snap.core.util.StringUtils;
+import org.esa.snap.core.util.io.CsvReader;
+import ucar.nc2.NetcdfFile;
+import ucar.nc2.Variable;
+
+import java.awt.image.Raster;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.TreeSet;
+
+import static ucar.nc2.NetcdfFiles.openInMemory;
+
+class NcCache {
+
+    private final Charset charset = StandardCharsets.UTF_8;
+    private final char[] separators = new char[]{'|'};
+
+    private Store store;
+    private RasterInfo rasterInfo;
+    private HashMap<String, String> dddBMap;
+    private HashMap<String, NetcdfFile> ncFilesMap;
+    private HashMap<String, Variable> variableMap;
+
+    void open(Store store, RasterInfo rasterInfo) throws IOException {
+        this.store = store;
+        this.rasterInfo = rasterInfo;
+
+        parseDDDB();
+
+        ncFilesMap = new HashMap<>();
+        variableMap = new HashMap<>();
+    }
+
+    void close() throws IOException {
+        dddBMap.clear();
+        dddBMap = null;
+
+        variableMap.clear();
+        variableMap = null;
+
+        for (final NetcdfFile ncFile : ncFilesMap.values()) {
+            ncFile.close();
+        }
+        ncFilesMap.clear();
+        ncFilesMap = null;
+
+        if (store != null) {
+            store.close();
+            store = null;
+        }
+    }
+
+    private void parseDDDB() throws IOException {
+        final InputStream inputStream = getClass().getResourceAsStream("slstr_subset_dddb_100.txt");
+        if (inputStream == null) {
+            throw new IllegalStateException("The internal resource file could not be read.");
+        }
+
+        final CsvReader reader = new CsvReader(new InputStreamReader(inputStream, charset), separators, true, "#");
+        final List<String[]> recordList = reader.readStringRecords();
+        dddBMap = new HashMap<>(recordList.size());
+        for (String[] record : recordList) {
+            dddBMap.put(record[0], record[1]);
+        }
+    }
+
+    List<String> getVariableNames() {
+        return new ArrayList<>(dddBMap.keySet());
+    }
+
+    Variable getVariable(String variableName) throws IOException {
+        Variable variable = variableMap.get(variableName);
+        if (variable != null) {
+            return variable;
+        } else {
+            final String fileName = dddBMap.get(variableName);
+            if (StringUtils.isNullOrEmpty(fileName)) {
+                throw new IOException("Invalid variable name requested: " + variableName);
+            }
+
+            final NetcdfFile ncFile = getNetcdfFile(fileName);
+            variable = ncFile.findVariable(variableName);
+            if (variable == null) {
+                throw new IOException("Invalid variable name requested: " + variableName);
+            }
+
+            if (isTiePointVariable(variableName)) {
+                final double subSampling = (double) rasterInfo.tiePointResolution / (double) rasterInfo.rasterResolution;
+                final double offset = rasterInfo.rasterTrackOffset - rasterInfo.tiePointTrackOffset * subSampling;
+                variable = new SlstrSubsetTiePointVariable(variable, rasterInfo.rasterWidth, rasterInfo.rasterHeight, offset, subSampling);
+            }
+            variableMap.put(variableName, variable);
+            return variable;
+        }
+    }
+
+    // package access for testing only tb 2022-08-18
+    static boolean isTiePointVariable(String variableName) {
+        return variableName.endsWith("_tn") || variableName.endsWith("_to");
+    }
+
+    private NetcdfFile getNetcdfFile(String fileName) throws IOException {
+        NetcdfFile ncFile = ncFilesMap.get(fileName);
+        if (ncFile == null) {
+            final TreeSet<String> keys = store.getKeysEndingWith(fileName);
+            final byte[] bytes = store.getBytes(keys.first());
+            ncFile = openInMemory(fileName, bytes);
+            ncFilesMap.put(fileName, ncFile);
+        }
+        return ncFile;
+    }
+}

core/src/main/java/com/bc/fiduceo/reader/slstr_subset/RasterInfo.java

@@ -0,0 +1,10 @@
+package com.bc.fiduceo.reader.slstr_subset;
+
+class RasterInfo {
+    int rasterWidth;
+    int rasterHeight;
+    int rasterResolution;
+    int tiePointResolution;
+    int rasterTrackOffset;
+    int tiePointTrackOffset;
+}