define([
           'dojo/_base/declare',
           'dojo/_base/array',
           'JBrowse/Util',
           'JBrowse/Util/TextIterator',
           'JBrowse/Store/LRUCache',
           'JBrowse/Errors',
           'JBrowse/Model/XHRBlob',
           'JBrowse/Model/BGZip/BGZBlob',
           'JBrowse/Model/TabixIndex'
       ],
       function(
           declare,
           array,
           Util,
           TextIterator,
           LRUCache,
           Errors,
           XHRBlob,
           BGZBlob,
           TabixIndex
       ) {

return declare( null, {

    constructor: function( args ) {
        this.browser = args.browser;
        this.index = new TabixIndex({ blob: new BGZBlob( args.tbi ), browser: args.browser } );
        this.data  = new BGZBlob( args.file );
        this.indexLoaded = this.index.load();

        this.chunkSizeLimit = args.chunkSizeLimit || 2000000;
    },

    getLines: function( ref, min, max, itemCallback, finishCallback, errorCallback ) {
        var thisB = this;
        var args = Array.prototype.slice.call(arguments);
        this.indexLoaded.then(function() {
            thisB._fetch.apply( thisB, args );
        }, errorCallback);
    },

    _fetch: function( ref, min, max, itemCallback, finishCallback, errorCallback ) {
        errorCallback = errorCallback || function(e) { console.error(e, e.stack); };

        var chunks = this.index.blocksForRange( ref, min, max);
        if ( ! chunks ) {
            errorCallback('Error in index fetch ('+[ref,min,max].join(',')+')');
            return;
        }

        // toString function is used by the cache for making cache keys
        chunks.toString = chunks.toUniqueString = function() {
            return this.join(', ');
        };

        // check the chunks for any that are over the size limit.  if
        // any are, don't fetch any of them
        for( var i = 0; i<chunks.length; i++ ) {
            var size = chunks[i].fetchedSize();
            if( size > this.chunkSizeLimit ) {
                errorCallback( new Errors.DataOverflow('Too much data. Chunk size '+Util.commifyNumber(size)+' bytes exceeds chunkSizeLimit of '+Util.commifyNumber(this.chunkSizeLimit)+'.' ) );
                return;
            }
        }

        var fetchError;
        try {
            this._fetchChunkData(
                chunks,
                ref,
                min,
                max,
                itemCallback,
                finishCallback,
                errorCallback
            );
        } catch( e ) {
            errorCallback( e );
        }
    },

    _fetchChunkData: function( chunks, ref, min, max, itemCallback, endCallback, errorCallback ) {
        var thisB = this;

        if( ! chunks.length ) {
            endCallback();
            return;
        }

        var allItems = [];
        var chunksProcessed = 0;

        var cache = this.chunkCache = this.chunkCache || new LRUCache({
            name: 'TabixIndexedFileChunkedCache',
            fillCallback: dojo.hitch( this, '_readChunkItems' ),
            sizeFunction: function( chunkItems ) {
                return chunkItems.length;
            },
            maxSize: 100000 // cache up to 100,000 items
        });

        var regRef = this.browser.regularizeReferenceName( ref );

        var haveError;
        array.forEach( chunks, function( c ) {
            cache.get( c, function( chunkItems, e ) {
                if( e && !haveError )
                    errorCallback( e );
                if(( haveError = haveError || e )) {
                    return;
                }

                for( var i = 0; i< chunkItems.length; i++ ) {
                    var item = chunkItems[i];
                    if( item._regularizedRef == regRef ) {
                        // on the right ref seq
                        if( item.start > max ) // past end of range, can stop iterating
                            break;
                        else if( item.end >= min ) // must be in range
                            itemCallback( item );
                    }
                }
                if( ++chunksProcessed == chunks.length ) {
                    endCallback();
                }
            });
        });
    },

    _readChunkItems: function( chunk, callback ) {
        var thisB = this;
        var items = [];

        thisB.data.read(chunk.minv.block, chunk.maxv.block - chunk.minv.block + 1, function( data ) {
            data = new Uint8Array(data);

            // throw away the first (probably incomplete) line
            var parseStart = chunk.minv.block ? array.indexOf( data, thisB._newlineCode, 0 ) + 1 : 0;
            var lineIterator = new TextIterator.FromBytes({ bytes: data, offset: parseStart });

            try {
                thisB._parseItems(
                    lineIterator,
                    function(i) { items.push(i); },
                    function() { callback(items); }
                );
            } catch( e ) {
                callback( null, e );
            }
        },
        function(e) {
            callback( null, e );
        });
    },

    _parseItems: function( lineIterator, itemCallback, finishCallback ) {
        var that = this;
        var itemCount = 0;

        var maxItemsWithoutYielding = 300;
        while ( true ) {
            // if we've read no more than a certain number of items this cycle, read another one
            if( itemCount <= maxItemsWithoutYielding ) {
                var item = this.parseItem( lineIterator );
                if( item ) {
                    itemCallback( item );
                    itemCount++;
                }
                else {
                    finishCallback();
                    return;
                }
            }
            // if we're not done but we've read a good chunk of
            // items, schedule the rest of our work in a timeout to continue
            // later, avoiding blocking any UI stuff that needs to be done
            else {
                window.setTimeout( function() {
                    that._parseItems( lineIterator, itemCallback, finishCallback );
                }, 1);
                return;
            }
        }
    },

    parseItem: function( iterator ) {
        var metaChar = this.index.metaChar;
        var line, item;
        do {
            line = iterator.getline();
        } while( line && (    line.charAt(0) == metaChar // meta line, skip
                           || line.charAt( line.length - 1 ) != "\n" // no newline at the end, incomplete
                           || ! ( item = this.tryParseLine( line ) )   // line could not be parsed
                         )
               );

        if( line && item )
            return item;

        return null;
    },

    tryParseLine: function( line ) {
        try {
            return this.parseLine( line );
        } catch(e) {
            console.warn('parse failed: "'+line+'"');
            return null;
        }
    },

    parseLine: function( line ) {
        var fields = line.split( "\t" );
        fields[fields.length-1] = fields[fields.length-1].replace(/\n$/,''); // trim off the newline
        var item = { // note: index column numbers are 1-based
            ref:   fields[this.index.columnNumbers.ref-1],
            _regularizedRef: this.browser.regularizeReferenceName( fields[this.index.columnNumbers.ref-1] ),
            start: parseInt(fields[this.index.columnNumbers.start-1]),
            end:   parseInt(fields[this.index.columnNumbers.end-1]),
            fields: fields
        };
        return item;
    }

});
});

@@ -4489,17 +4489,16 @@
 (data);%0A
-%0A
         
@@ -4507,93 +4507,76 @@
   //
- throw away the first (probably incomplete) line%0A            var parseStart =
+console.log( 'reading chunk %25d compressed, %25d uncompressed',
  chunk.m
 inv.
@@ -4575,72 +4575,55 @@
 nk.m
-in
+ax
 v.block
- ? array.indexOf( data, thisB._newlineCode, 0 ) + 1 : 0
+-chunk.minv.block+65536, data.length )
 ;%0A  
@@ -4705,24 +4705,14 @@
 et: 
-parseStart
+0
  %7D);%0A
-%0A
     
@@ -6868,24 +6868,26 @@
             
+//
 console.warn

stop warning about parse errors in tabix-indexed files, don't cut off the first line of a tabix chunk, just let it have a parse error if it is going to.