/*global cull, dome*/
this.gts = this.gts || {};

/**
 * Utilities for working with syntax highligted blobs. Assumes the markup for
 * blobs generated by Dolt. Exports three functions:
 * 
 * * trackFocus
 *   Sets up events to highlight lines on mouseover, and allows the user to
 *   highlight regions
 * * regionFromUrl
 *   Parses the URL and finds line number or region to highlight
 * * highlightRegion
 *   Highlights a region
 *
 * The following functions all assume that a blob is contained in some root
 * element that represents each line in the file as an li element.
 * 
 * A "region" is an array of two numbers, denoting the first and last line of
 * a consecutive region. Both boundaries are inclusive. Regions start at 1 (not
 * 0).
 *     [1, 2] - The region consisting of the first and second line, inclusive
 *     [1, 1] - The first line 
 *     [10, 14] - The region of lines 10, 11, 12, 13 and 14
 */
this.gts.blob = (function () {
    /**
     * Accepts the root element of a blob and a region, and adds the "region"
     * class name to all li elements in the region.
     */
    function highlightRegion(element, region) {
        // Line numbers are 1-based, but ElementLists are 0-indexed,
        // offset region accordingly
        var start = region[0] - 1;
        var end = region[1] - 1;
        var lines = element.getElementsByTagName("li");

        cull.doall(function (li, num) {
            var inRegion = start <= num && num <= end;
            dome.cn[inRegion ? "add" : "rm"]("region", li);
        }, element.getElementsByTagName("li"));
    }

    /**
     * Given an li element representing a line, return which line number it
     * represents.
     */
    function getLineNum(element) {
        while (element && element.tagName !== "LI") {
            element = element.parentNode;
        }
        var lineNum = element && element.className.match(/L(\d+)/)[1];
        if (!lineNum) { return; }
        return parseInt(lineNum, 10);
    }

    /**
     * Set the active region. Marks the region and updates the URL with the
     * new region as an anchor ("#L<start>-<end>").
     */
    function setRegion(element, region, redirect) {
        var regionStr = region[0];
        regionStr += region[1] !== region[0] ? "-" + region[1] : "";
        redirect("#L" + regionStr);
        highlightRegion(element, region);
    }

    /**
     * Given two numbers, return a region where the lowest number is the start
     * and the highest number is the end. The end is optional, in which case
     * the [start, start] region is returned.
     */
    function orderedRegion(start, end) {
        end = typeof end === "number" ? end : start;
        return [Math.min(start, end), Math.max(start, end)];
    }

    /**
     * Track selected region through clicks on lines.
     * 
     * Clicking a line highlights it by setting the region to that line
     * (e.g [n, n]).
     * 
     * Holding shift while clicking a line makes a region starting at the
     * previously clicked line and ending at the line being clicked. Example:
     * 
     * Click on line 4. Press shift, click line 9. Lines 4, 5, 6, 7, 8 and 9
     * will be highlighted. While holding shift, click line 1. Lines 1, 2, 3 and
     * 4 will be highlighted. Release shift, click line 5, line 5 (and no
     * others) will be highlighted.
     */
    function trackSelectedRegion(element, redirect) {
        var shift = false, anchor;
        var events = [];

        dome.on(document.body, "keydown", function (e) {
            shift = e.which === 16;
        });
        dome.on(document.body, "keyup", function (e) {
            shift = e.which !== 16;
        });

        dome.on(element, "click", function (e) {
            var region, currLine = getLineNum(e.target);
            if (!shift || !anchor) { anchor = e.target; }

            if (anchor && shift) {
                region = orderedRegion(getLineNum(anchor), currLine);
                e.preventDefault();
            } else {
                region = [currLine, currLine];
            }

            setRegion(element, region, redirect);
        });
    }

    /**
     * Track focus on lines by highlighting lines as the cursor hovers them, and
     * by highlighting (and selecting) regions as lines are clicked (see the
     * above function)
     */
    function trackFocus(element, redirect) {
        var highlight = function () { dome.cn.add("focus", this); };
        var dim = function () { dome.cn.rm("focus", this); };

        cull.doall(function (li) {
            dome.on(li, "mouseenter", highlight);
            dome.on(li, "mouseleave", dim);
        }, element.getElementsByTagName("li"));

        trackSelectedRegion(element, redirect);
    }

    /**
     * Regions can be specified over the URL by using the #L<start>[-<end>]
     * syntax. This function extracts it. Examples:
     * 
     * /some/url#L1    - [1, 1]
     * /some/url#L1-2  - [1, 2]
     * /some/url#l12-2 - [2, 12] (ordered)
     */
    function regionFromUrl(url) {
        var matches = url.match(/\#l(\d+)(?:-(\d+))?/i);
        if (!matches) { return; }
        return orderedRegion(matches[1], matches[2] && Number(matches[2]));
    }

    return {
        trackFocus: trackFocus,
        regionFromUrl: regionFromUrl,
        highlightRegion: highlightRegion
    };
}());