var Q = require('q');
var _ = require('lodash');
var url = require('url');
var path = require('path');
var cheerio = require('cheerio');
var domSerializer = require('dom-serializer');
var request = require('request');
var crc = require('crc');
var slug = require('github-slugid');

var links = require('./links');
var imgUtils = require('./images');
var fs = require('./fs');
var batch = require('./batch');

var parsableExtensions = require('gitbook-parsers').extensions;

// Map of images that have been converted
var imgConversionCache = {};

// Render a cheerio dom as html
function renderDom($, dom, options) {
    if (!dom && $._root && $._root.children) {
        dom = $._root.children;
    }

    options = options|| dom.options || $._options;
    return domSerializer(dom, options);
}

function replaceText($, el, search, replace, text_only ) {
    return $(el).each(function(){
        var node = this.firstChild,
            val,
            new_val,

            // Elements to be removed at the end.
            remove = [];

        // Only continue if firstChild exists.
        if ( node ) {

            // Loop over all childNodes.
            while (node) {

                // Only process text nodes.
                if ( node.nodeType === 3 ) {

                    // The original node value.
                    val = node.nodeValue;

                    // The new value.
                    new_val = val.replace( search, replace );

                    // Only replace text if the new value is actually different!
                    if ( new_val !== val ) {

                        if ( !text_only && /</.test( new_val ) ) {
                            // The new value contains HTML, set it in a slower but far more
                            // robust way.
                            $(node).before( new_val );

                            // Don't remove the node yet, or the loop will lose its place.
                            remove.push( node );
                        } else {
                            // The new value contains no HTML, so it can be set in this
                            // very fast, simple way.
                            node.nodeValue = new_val;
                        }
                    }
                }

                node = node.nextSibling;
            }
        }

        // Time to remove those elements!
        if (remove.length) $(remove).remove();
    });
}

function pregQuote( str ) {
    return (str+'').replace(/([\\\.\+\*\?\[\^\]\$\(\)\{\}\=\!\<\>\|\:])/g, '\\$1');
}


// Adapt an html snippet to be relative to a base folder
function normalizeHtml(src, options) {
    var $ = cheerio.load(src, {
        // We should parse html without trying to normalize too much
        xmlMode: false,

        // SVG need some attributes to use uppercases
        lowerCaseAttributeNames: false,
        lowerCaseTags: false
    });
    var toConvert = [];
    var svgContent = {};
    var outputRoot = options.book.options.output;

    imgConversionCache[outputRoot] = imgConversionCache[outputRoot] || {};

    // Find svg images to extract and process
    if (options.convertImages) {
        $('svg').each(function() {
            var content = renderDom($, $(this));
            var svgId = _.uniqueId('svg');
            var dest = svgId+'.svg';

            // Generate filename
            dest = '/'+fs.getUniqueFilename(outputRoot, dest);

            svgContent[dest] = '<?xml version="1.0" encoding="UTF-8"?>'+content;
            $(this).replaceWith($('<img>').attr('src', dest));
        });
    }

    // Generate ID for headings
    $('h1,h2,h3,h4,h5,h6').each(function() {
        if ($(this).attr('id')) return;

        $(this).attr('id', slug($(this).text()));
    });

    // Find images to normalize
    $('img').each(function() {
        var origin;
        var src = $(this).attr('src');

        if (!src) return;
        var isExternal = links.isExternal(src);

        // Transform as relative to the bases
        if (links.isRelative(src)) {
            src = links.toAbsolute(src, options.base, options.output);
        }

        // Convert if needed
        if (options.convertImages) {
            // If image is external and ebook, then downlaod the images
            if (isExternal) {
                origin = src;
                src = '/'+crc.crc32(origin).toString(16)+path.extname(url.parse(origin).pathname);
                src = links.toAbsolute(src, options.base, options.output);
                isExternal = false;
            }

            var ext = path.extname(src);
            var srcAbs = links.join('/', options.base, src);

            // Test image extension
            if (_.contains(imgUtils.INVALID, ext)) {
                if (imgConversionCache[outputRoot][srcAbs]) {
                    // Already converted
                    src = imgConversionCache[outputRoot][srcAbs];
                } else {
                    // Not converted yet
                    var dest = '';

                    // Replace extension
                    dest = links.join(path.dirname(srcAbs), path.basename(srcAbs, ext)+'.png');
                    dest = dest[0] == '/'? dest.slice(1) : dest;

                    // Get a name that doesn't exists
                    dest = fs.getUniqueFilename(outputRoot, dest);

                    options.book.log.debug.ln('detect invalid image (will be converted to png):', srcAbs);

                    // Add to cache
                    imgConversionCache[outputRoot][srcAbs] = '/'+dest;

                    // Push to convert
                    toConvert.push({
                        origin: origin,
                        content: svgContent[srcAbs],
                        source: isExternal? srcAbs : path.join('./', srcAbs),
                        dest: path.join('./', dest)
                    });

                    src = links.join('/', dest);
                }

                // Reset as relative to output
                src = links.toAbsolute(src, options.base, options.output);
            }

            else if (origin) {
                // Need to downlaod image
                toConvert.push({
                    origin: origin,
                    source: path.join('./', srcAbs)
                });
            }
        }

        $(this).attr('src', src);
    });

    // Normalize links
    $('a').each(function() {
        var href = $(this).attr('href');
        if (!href) return;

        if (links.isAnchor(href)) {
            // Keep it as it is
        } else if (links.isRelative(href)) {
            var parts = url.parse(href);
            var absolutePath = links.join(options.base, parts.pathname);
            var anchor = parts.hash || '';


            // If is in navigation relative: transform as content
            if (options.navigation[absolutePath]) {
                absolutePath = options.book.contentLink(absolutePath);
            }

            // If md/adoc/rst files is not in summary
            // or for ebook, signal all files that are outside the summary
            else if (_.contains(parsableExtensions, path.extname(absolutePath)) ||
            _.contains(['epub', 'pdf', 'mobi'], options.book.options.generator)) {
                options.book.log.warn.ln('page', options.input, 'contains an hyperlink to resource outside spine \''+href+'\'');
            }

            // Transform as absolute
            href = links.toAbsolute('/'+absolutePath, options.base, options.output)+anchor;
        } else {
            // External links
            $(this).attr('target', '_blank');
        }

        // Transform extension
        $(this).attr('href', href);
    });

    // Highlight code blocks
    $('code').each(function() {
        // Normalize language
        var lang = _.chain(
                ($(this).attr('class') || '').split(' ')
            )
            .map(function(cl) {
                // Markdown
                if (cl.search('lang-') === 0) return cl.slice('lang-'.length);

                // Asciidoc
                if (cl.search('language-') === 0) return cl.slice('language-'.length);

                return null;
            })
            .compact()
            .first()
            .value();

        var source = $(this).text();
        var blk = options.book.template.applyBlock('code', {
            body: source,
            kwargs: {
                language: lang
            }
        });

        if (blk.html === false) $(this).text(blk.body);
        else $(this).html(blk.body);
    });

    // Replace glossary terms
    var glossary = _.sortBy(options.glossary, function(term) {
        return -term.name.length;
    });

    _.each(glossary, function(term) {
        var r =  new RegExp( '\\b(' + pregQuote(term.name.toLowerCase()) + ')\\b' , 'gi' );
        var includedInFiles = false;

        $('*').each(function() {
            // Ignore codeblocks
            if (_.contains(['code', 'pre', 'a'], this.name.toLowerCase())) return;

            replaceText($, this, r, function(match) {
                // Add to files index in glossary
                if (!includedInFiles) {
                    includedInFiles = true;
                    term.files = term.files || [];
                    term.files.push(options.navigation[options.input]);
                }
                return '<a href=\''+links.toAbsolute('/GLOSSARY.html', options.base, options.output) + '#' + term.id+'\' class=\'glossary-term\' title=\''+_.escape(term.description)+'\'>'+match+'</a>';
            });
        });
    });

    return {
        html: renderDom($),
        images: toConvert
    };
}

// Convert svg images to png
function convertImages(images, options) {
    if (!options.convertImages) return Q();

    var downloaded = [];
    options.book.log.debug.ln('convert ', images.length, 'images to png');

    return batch.execEach(images, {
        max: 100,
        fn: function(image) {
            var imgin = path.resolve(options.book.options.output, image.source);

            return Q()

            // Write image if need to be download
            .then(function() {
                if (!image.origin && !_.contains(downloaded, image.origin)) return;
                options.book.log.debug('download image', image.origin, '...');
                downloaded.push(image.origin);
                return options.book.log.debug.promise(fs.writeStream(imgin, request(image.origin)))
                .fail(function(err) {
                    if (!_.isError(err)) err = new Error(err);

                    err.message = 'Fail downloading '+image.origin+': '+err.message;
                    throw err;
                });
            })

            // Write svg if content
            .then(function() {
                if (!image.content) return;
                return fs.writeFile(imgin, image.content);
            })

            // Convert
            .then(function() {
                if (!image.dest) return;
                var imgout = path.resolve(options.book.options.output, image.dest);
                options.book.log.debug('convert image', image.source, 'to', image.dest, '...');
                return options.book.log.debug.promise(imgUtils.convertSVG(imgin, imgout));
            });
        }
    })
    .then(function() {
        options.book.log.debug.ok(images.length+' images converted with success');
    });
}

// Adapt page content to be relative to a base folder
function normalizePage(sections, options) {
    options = _.defaults(options || {}, {
        // Current book
        book: null,

        // Do we need to convert svg?
        convertImages: false,

        // Current file path
        input: '.',

        // Navigation to use to transform path
        navigation: {},

        // Directory parent of the file currently in rendering process
        base: './',

        // Directory parent from the html output
        output: './',

        // Glossary terms
        glossary: []
    });

    // List of images to convert
    var toConvert = [];

    sections = _.map(sections, function(section) {
        if (section.type != 'normal') return section;

        var out = normalizeHtml(section.content, options);

        toConvert = toConvert.concat(out.images);
        section.content = out.html;
        return section;
    });

    return Q()
    .then(function() {
        toConvert = _.uniq(toConvert, 'source');
        return convertImages(toConvert, options);
    })
    .thenResolve(sections);
}


module.exports = {
    normalize: normalizePage
};