diff --git a/src/org/jetbrains/js/compiler/SourceMapBuilder.java b/src/org/jetbrains/js/compiler/SourceMapBuilder.java
index 1723a407ecc..72b6c36f59c 100644
--- a/src/org/jetbrains/js/compiler/SourceMapBuilder.java
+++ b/src/org/jetbrains/js/compiler/SourceMapBuilder.java
@@ -1,166 +1,17 @@
 package org.jetbrains.js.compiler;
 
-import com.google.dart.compiler.common.SourceInfo;
-import com.google.dart.compiler.util.TextOutput;
-import com.intellij.util.PairConsumer;
-import gnu.trove.TObjectIntHashMap;
+import java.io.File;
 
-import java.util.ArrayList;
-import java.util.List;
+public interface SourceMapBuilder {
+    void newLine();
 
-public class SourceMapBuilder {
-    private final StringBuilder out = new StringBuilder();
-    private final String generatedFilename;
-    private final TextOutput textOutput;
-    private final PairConsumer<SourceMapBuilder, Object> sourceInfoConsumer;
+    void addMapping(String source, int sourceLine, int sourceColumn);
 
-    private String lastSource;
-    private int lastSourceIndex;
+    void processSourceInfo(Object info);
 
-    private final TObjectIntHashMap<String> sources = new TObjectIntHashMap<String>() {
-        @Override
-        public int get(String key) {
-            int index = index(key);
-            return index < 0 ? -1 : _values[index];
-        }
-    };
+    void addLink();
 
-    private final List<String> orderedSources = new ArrayList<String>();
+    File getOutFile();
 
-    private int previousGeneratedColumn;
-    private int previousSourceIndex;
-    private int previousSourceLine;
-    private int previousSourceColumn;
-
-    public SourceMapBuilder(String generatedFilename, TextOutput textOutput, PairConsumer<SourceMapBuilder, Object> sourceInfoConsumer) {
-        this.generatedFilename = generatedFilename;
-        this.textOutput = textOutput;
-        this.sourceInfoConsumer = sourceInfoConsumer;
-    }
-
-    public String getOutFilename() {
-        return generatedFilename + ".map";
-    }
-
-    public String build() {
-        StringBuilder sb = new StringBuilder();
-        sb.append("{\"version\":3,\"file\":\"").append(generatedFilename).append('"').append(',');
-        appendSources(sb);
-        sb.append(",\"names\":[");
-        sb.append("],\"mappings\":\"");
-        sb.append(out);
-        sb.append("\"}");
-        return sb.toString();
-    }
-
-    private void appendSources(StringBuilder sb) {
-        boolean isNotFirst = false;
-        sb.append('"').append("sources").append("\":[");
-        for (String source : orderedSources) {
-            if (isNotFirst) {
-                sb.append(',');
-            }
-            else {
-                isNotFirst = true;
-            }
-            sb.append('"').append(source).append('"');
-        }
-        sb.append(']');
-    }
-
-    public void newLine() {
-        out.append(';');
-        previousGeneratedColumn = 0;
-    }
-
-    public void processSourceInfo(Object sourceInfo) {
-        if (sourceInfo instanceof SourceInfo) {
-            throw new UnsupportedOperationException("SourceInfo is not yet supported");
-        }
-        sourceInfoConsumer.consume(this, sourceInfo);
-    }
-
-    private int getSourceIndex(String source) {
-        if (source.equals(lastSource)) {
-            return lastSourceIndex;
-        }
-
-        int sourceIndex = sources.get(source);
-        if (sourceIndex == -1) {
-            sourceIndex = sources.put(source, orderedSources.size());
-            orderedSources.add(source);
-        }
-
-        lastSource = source;
-        lastSourceIndex = sourceIndex;
-
-        return sourceIndex;
-    }
-
-    public void addMapping(String source, int sourceLine, int sourceColumn) {
-        if (previousGeneratedColumn != 0) {
-            out.append(',');
-        }
-
-        Base64VLQ.encode(out, textOutput.getColumn() - previousGeneratedColumn);
-        previousGeneratedColumn = textOutput.getColumn();
-
-        int sourceIndex = getSourceIndex(source);
-        Base64VLQ.encode(out, sourceIndex - previousSourceIndex);
-        previousSourceIndex = sourceIndex;
-
-        Base64VLQ.encode(out, sourceLine - previousSourceLine);
-        previousSourceLine = sourceLine;
-
-        Base64VLQ.encode(out, sourceColumn - previousSourceColumn);
-        previousSourceColumn = sourceColumn;
-    }
-
-    private static int toVLQSigned(int value) {
-        return value < 0 ? ((-value) << 1) + 1 : value << 1;
-    }
-
-    public void addLink() {
-        textOutput.print("\n//@ sourceMappingURL=");
-        textOutput.print(getOutFilename());
-    }
-
-    private static final class Base64VLQ {
-        // A Base64 VLQ digit can represent 5 bits, so it is base-32.
-        private static final int VLQ_BASE_SHIFT = 5;
-        private static final int VLQ_BASE = 1 << VLQ_BASE_SHIFT;
-
-        // A mask of bits for a VLQ digit (11111), 31 decimal.
-        private static final int VLQ_BASE_MASK = VLQ_BASE - 1;
-
-        // The continuation bit is the 6th bit.
-        private static final int VLQ_CONTINUATION_BIT = VLQ_BASE;
-
-        /**
-         * A map used to convert integer values in the range 0-63 to their base64
-         * values.
-         */
-        private static final String BASE64_MAP =
-                "ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
-                "abcdefghijklmnopqrstuvwxyz" +
-                "0123456789+/";
-
-        public static void encode(StringBuilder out, int value) {
-            value = toVLQSigned(value);
-            do {
-                int digit = value & VLQ_BASE_MASK;
-                value >>>= VLQ_BASE_SHIFT;
-                if (value > 0) {
-                    digit |= VLQ_CONTINUATION_BIT;
-                }
-                out.append(toBase64(digit));
-            }
-            while (value > 0);
-        }
-
-        public static char toBase64(int value) {
-            assert (value <= 63 && value >= 0) : "value out of range:" + value;
-            return BASE64_MAP.charAt(value);
-        }
-    }
+    String build();
 }