package org.daisy.pipeline.css;
   
   import java.net.URI;
   import java.net.URL;
   import java.text.CharacterIterator;
   import java.text.StringCharacterIterator;
   import java.util.ArrayList;
   import java.util.List;
   import java.util.Map;
  import java.util.NavigableMap;
  import java.util.TreeMap;
  
  import cz.vutbr.web.css.SourceLocator;
  import cz.vutbr.web.csskit.antlr.SourceMap;
  
  import mjson.Json;
  import mjson.Json.MalformedJsonException;
  
  import org.daisy.common.file.URLs;
  
  /**
   * Reads a source map from a JSON object and returns it as a {@link SourceMap} object.
   */
  public final class SourceMapReader {
  
  	private SourceMapReader() {}
  
  	public static SourceMap read(String json, URI base) {
  		NavigableMap<LineColumn,SourceLocator> sourceMap; {
  			try {
  				Json jsonObject = Json.read(json);
  				List<URL> sources; {
  					Json jsonArray = jsonObject.at("sources");
  					if (jsonArray == null)
  						throw new RuntimeException("Missing 'sources'");
  					if (!jsonArray.isArray())
  						throw new RuntimeException("Expected array");
  					sources = new ArrayList<>();
  					for (Json s : jsonArray.asJsonList()) {
  						if (!s.isString())
  							throw new RuntimeException("Expected string");
  						// the source can be either
  						if (s.asString().matches("^\\w+:.*"))
  							// an absolute URL (with encoded path)
  							sources.add(URLs.asURL(URLs.resolve(base, URLs.asURI(s.asString()))));
  						else
  							// or a (unencoded) file path (relative to the current working directory)
  							try {
  								sources.add(URLs.asURL(URLs.resolve(base, new URI(null, null, s.asString(), null)))); }
  							catch (java.net.URISyntaxException e) {
  								throw new RuntimeException(e); } // should not happen
  					}
  				}
  				CharacterIterator mappings; {
  					Json jsonString = jsonObject.at("mappings");
  					if (jsonString == null)
  						throw new RuntimeException("Missing 'mappings'");
  					if (!jsonString.isString())
  						throw new RuntimeException("Expected string");
  					mappings = new StringCharacterIterator(jsonString.asString());
  				}
  				sourceMap = new TreeMap<>();
  				int line = 0;
  				int column = 0;
  				int source = 0;
  				int sourceLine = 0;
  				int sourceColumn = 0;
  				char c = mappings.first();
  				while (c != CharacterIterator.DONE) {
  					if (c != ',' && c != ';') {
  						// first value is the column within the generated file
  						column += Base64VlqDecoder.readInteger(mappings);
  						c = mappings.next();
  						if (c != CharacterIterator.DONE && c != ',' && c != ';') {
  							// second value is the original file
  							source += Base64VlqDecoder.readInteger(mappings);
  							if (source < 0)
  								throw new RuntimeException("Negative index");
  							if (source >= sources.size())
  								throw new RuntimeException("Index exceeds size of sources array");
  							c = mappings.next();
  							if (c == CharacterIterator.DONE || c == ',' || c == ';')
  								throw new RuntimeException("Segment must have of 1, 4 or 5 values");
  							// third value is the line withing the original file
  							sourceLine += Base64VlqDecoder.readInteger(mappings);
  							c = mappings.next();
  							if (c == CharacterIterator.DONE || c == ',' || c == ';')
  								throw new RuntimeException("Segment must have of 1, 4 or 5 values");
  							// fourth value is the column withing the original file
  							sourceColumn += Base64VlqDecoder.readInteger(mappings);
  							c = mappings.next();
  							// ignore fifth value if present
  							if (c != CharacterIterator.DONE && c != ',' && c != ';')
  								c = mappings.next();
  							if (c != CharacterIterator.DONE && c != ',' && c != ';')
  								throw new RuntimeException("Segment must have of 1, 4 or 5 values");
  							LineColumn pos = new LineColumn(line, column);
  							if (!sourceMap.containsKey(pos))
  								sourceMap.put(pos, new SourceLineColumn(sources.get(source), sourceLine, sourceColumn));
 						}
 					}
 					if (c == ',') {
 						c = mappings.next();
 						continue;
 					}
 					if (c == ';') {
 						line++;
 						column = 0;
 						c = mappings.next();
 						continue;
 					}
 					break;
 				}
 			} catch (MalformedJsonException e) {
 				throw new IllegalArgumentException("Source map could not be parsed: " + json, e);
 			} catch (RuntimeException e) {
 				throw new IllegalArgumentException("Source map could not be parsed: " + json, e);
 			}
 		}
 		return new SourceMap() {
 			public SourceLocator get(int line, int column) {
 				return sourceMap.get(new LineColumn(line, column));
 			}
 			public SourceLocator floor(int line, int column) {
 				Map.Entry<LineColumn,SourceLocator> entry = sourceMap.floorEntry(new LineColumn(line, column));
 				return entry == null ? null : entry.getValue();
 			}
 			public SourceLocator ceiling(int line, int column) {
 				Map.Entry<LineColumn,SourceLocator> entry = sourceMap.ceilingEntry(new LineColumn(line, column));
 				return entry == null ? null : entry.getValue();
 			}
 			@Override
 			public String toString() {
 				return sourceMap.toString();
 			}
 		};
 	}
 
 	private static class LineColumn implements Comparable<LineColumn> {
 		private final int line;
 		private final int column;
 		public LineColumn(int line, int column) {
 			this.line = line;
 			this.column = column;
 		}
 		public int compareTo(LineColumn that) {
 			if (this.line < that.line)
 				return -1;
 			else if (this.line > that.line)
 				return 1;
 			else if (this.column < that.column)
 				return -1;
 			else if (this.column > that.column)
 				return 1;
 			else
 				return 0;
 		}
 		public String toString() {
 			return line + ":" + column;
 		}
 	}
 
 	private static class SourceLineColumn implements SourceLocator {
 		private final URL url;
 		private final int line;
 		private final int column;
 		public SourceLineColumn(URL url, int line, int column) {
 			this.url = url;
 			this.line = line;
 			this.column = column;
 		}
 		public URL getURL() {
 			return url;
 		}
 		public int getLineNumber() {
 			return line;
 		}
 		public int getColumnNumber() {
 			return column;
 		}
 		public String toString() {
 			return url + ":" + line + ":" + column;
 		}
 	}
 
 	private static class Base64VlqDecoder {
 
 		private static final String base64Decoder = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
 		private static int readInteger(CharacterIterator base64String) throws IllegalArgumentException {
 			char c = base64String.current();
 			if (c == CharacterIterator.DONE)
 				throw new RuntimeException("End of string");
 			int result = 0;
 			int shift = 0;
 			while (true) {
 				int i = base64Decoder.indexOf(c);
 				if (i < 0)
 					throw new RuntimeException("Unexpected base64 character: " + c);
 				if (i < 32) {
 					result += (i << shift);
 					break;
 				} else {
 					i &= 31;
 					result += (i << shift);
 					shift += 5;
 					c = base64String.next();
 					if (c == CharacterIterator.DONE)
 						throw new RuntimeException("Expected character after continuation character");
 				}
 			}
 			if (result % 2 == 0)
 				return result >> 1;
 			else
 				return - (result >> 1);
 		}
 	}
 }