/*global env: true */

/**
 * Provides access to Markdown-related functions.
 * @module jsdoc/util/markdown
 * @author Michael Mathews <micmath@gmail.com>
 * @author Ben Blank <ben.blank@gmail.com>
 */

/**
 * Enumeration of Markdown parsers that are available.
 * @enum {String}
 */
var parsers = {
    /** The "[markdown-js](https://github.com/evilstreak/markdown-js)" (aka "evilstreak") parser. */
    evilstreak: "markdown",
    /**
     * The "GitHub-flavored Markdown" parser.
     * @deprecated Replaced by "marked."
     */
    gfm: "marked",
    /**
     * The "[Marked](https://github.com/chjj/marked)" parser.
     */
    marked: "marked"
};

/**
 * Escape underscores that occur within {@ ... } in order to protect them
 * from the markdown parser(s).
 * @param {String} source the source text to sanitize.
 * @returns {String} `source` where underscores within {@ ... } have been
 * protected with a preceding backslash (i.e. \_) -- the markdown parsers
 * will strip the backslash and protect the underscore.
 */
function escapeUnderscores(source) {
    return source.replace(/\{@[^}\r\n]+\}/g, function (wholeMatch) {
        return wholeMatch.replace(/(^|[^\\])_/g, '$1\\_');
    });
}

/**
 * Retrieve a function that accepts a single parameter containing Markdown source. The function uses
 * the specified parser to transform the Markdown source to HTML, then returns the HTML as a string.
 *
 * @private
 * @param {String} parser The name of the selected parser.
 * @param {Object} [conf] Configuration for the selected parser, if any.
 * @returns {Function} A function that accepts Markdown source, feeds it to the selected parser, and
 * returns the resulting HTML.
 * @throws {Error} If the name does not correspond to a known parser.
 */
function getParseFunction(parser, conf) {
    conf = conf || {};
    var parse;

    if (parser === parsers.marked) {
        parser = require(parser);
        parser.setOptions({
                gfm: true,
                tables: true,
                breaks: false,
                pedantic: false,
                sanitize: true,
                smartLists: true,
                langPrefix: 'lang-'
            });
        parse = function(source) {
            source = escapeUnderscores(source);
            return parser(source)
                .replace(/\s+$/, '')
                .replace(/&#39;/g, "'");
        };
        parse._parser = parsers.marked;
        return parse;
    } else if (parser === parsers.evilstreak) {
        parser = require(parser).markdown;

        parse = function(source) {
            source = escapeUnderscores(source);
            // evilstreak parser expects line endings to be \n
            source = source.replace(/\r\n|\r/g, '\n');
            return parser.toHTML(source, conf.dialect);
        };
        parse._parser = parsers.evilstreak;
        return parse;
    } else {
        throw new Error("unknown Markdown parser: '" + parser + "'");
    }
}

/**
 * Retrieve a Markdown parsing function based on the value of the `conf.json` file's
 * `env.conf.markdown` property. The parsing function accepts a single parameter containing Markdown
 * source. The function uses the parser specified in `conf.json` to transform the Markdown source to
 * HTML, then returns the HTML as a string.
 * @returns {Function} A function that accepts Markdown source, feeds it to the selected parser, and
 * returns the resulting HTML.
 * @throws {Error} If the value of `env.conf.markdown.parser` does not correspond to a known parser.
 */
exports.getParser = function() {
    var conf = env.conf.markdown;
    if (conf && conf.parser) {
        return getParseFunction(parsers[conf.parser], conf);
    } else if (conf && conf.githubRepoOwner && conf.githubRepoName) {
        // use GitHub-friendly parser if GitHub-specific options are present
        return getParseFunction(parsers.gfm, conf);
    } else {
        // evilstreak is the default parser
        return getParseFunction(parsers.evilstreak, conf);
    }
};