var _ = require('lodash');
var path = require('path');
var util = require('util');
var nunjucks = require('nunjucks');
var I18n = require('i18n-t');

var Promise = require('../utils/promise');
var fs = require('../utils/fs');
var defaultFilters = require('../template/filters');
var conrefsLoader = require('./conrefs');
var Output = require('./base');

// Tranform a theme ID into a plugin
function themeID(plugin) {
    return 'theme-' + plugin;
}

// Directory for a theme with the templates
function templatesPath(dir) {
    return path.join(dir, '_layouts');
}

function _WebsiteOutput() {
    Output.apply(this, arguments);

    // Nunjucks environment
    this.env;

    // Plugin instance for the main theme
    this.theme;

    // Plugin instance for the default theme
    this.defaultTheme;

    // Resources loaded from plugins
    this.resources;

    // i18n for themes
    this.i18n = new I18n();
}
util.inherits(_WebsiteOutput, Output);

var WebsiteOutput = conrefsLoader(_WebsiteOutput);

// Name of the generator
// It's being used as a prefix for templates
WebsiteOutput.prototype.name = 'website';

// Load and setup the theme
WebsiteOutput.prototype.prepare = function() {
    var that = this;

    return Promise()
    .then(function() {
        return WebsiteOutput.super_.prototype.prepare.apply(that);
    })

    .then(function() {
        var themeName = that.book.config.get('theme');
        that.theme = that.plugins.get(themeID(themeName));
        that.themeDefault = that.plugins.get(themeID('default'));

        if (!that.theme) {
            throw new Error('Theme "' + themeName + '" is not installed, add "' + themeID(themeName) + '" to your "book.json"');
        }

        if (that.themeDefault.root != that.theme.root) {
            that.log.info.ln('build using theme "' + themeName + '"');
        }

        // This list is ordered to give priority to templates in the book
        var searchPaths = _.chain([
            // The book itself can contains a "_layouts" folder
            that.book.root,

            // Installed plugin (it can be identical to themeDefault.root)
            that.theme.root,

            // Is default theme still installed
            that.themeDefault? that.themeDefault.root : null
        ])
        .compact()
        .uniq()
        .value();

        // Load i18n
        _.each(searchPaths.concat().reverse(), function(searchPath) {
            var i18nRoot = path.resolve(searchPath, '_i18n');

            if (!fs.existsSync(i18nRoot)) return;
            that.i18n.load(i18nRoot);
        });

        that.env = new nunjucks.Environment(new nunjucks.FileSystemLoader(_.map(searchPaths, templatesPath)));

        // Add GitBook default filters
        _.each(defaultFilters, function(fn, filter) {
            that.env.addFilter(filter, fn);
        });

        // Translate using _i18n locales
        that.env.addFilter('t', function(s) {
            return that.i18n.t(that.book.config.get('language'), s);
        });

        // Transform an absolute path into a relative path
        // using this.ctx.page.path
        that.env.addFilter('resolveFile', function(href) {
            return that.resolveForPage(this.ctx.file.path, href);
        });

        // Transform a '.md' into a '.html' (README -> index)
        that.env.addFilter('contentURL', function(s) {
            return that.outputUrl(s);
        });

        // Relase path to an asset
        that.env.addFilter('resolveAsset', function(href) {
            href = path.join('gitbook', href);
            if (!this.ctx.file) return href;

            return that.resolveForPage(this.ctx.file.path, '/' + href);
        });
    })

    // Copy assets from themes before copying files from book
    .then(function() {
        return Promise.serie([
            // Assets from the book are already copied
            // The order is reversed from the template's one

            // Is default theme still installed
            that.themeDefault && that.themeDefault.root != that.theme.root?
                that.themeDefault.root : null,

            // Installed plugin (it can be identical to themeDefault.root)
            that.theme.root
        ], function(folder) {
            if (!folder) return;

            // Copy assets only if exists (don't fail otherwise)
            var assetFolder = path.join(folder, '_assets', that.name);
            if (!fs.existsSync(assetFolder)) return;

            that.log.debug.ln('copy assets from theme', assetFolder);
            return fs.copyDir(
                assetFolder,
                that.resolve('gitbook'),
                {
                    deleteFirst: false, // Delete "to" before
                    overwrite: true,
                    confirm: true
                }
            );
        });
    })

    // Load resources for plugins
    .then(function() {
        return that.plugins.getResources(that.name)
        .then(function(resources) {
            that.resources = resources;
        });
    });
};

// Write a page (parsable file)
WebsiteOutput.prototype.onPage = function(page) {
    var that = this;

    // Parse the page
    return page.toHTML(this)

    // Render the page template with the same context as the json output
    .then(function() {
        return that.render('page', page.getContext());
    })

    // Write the HTML file
    .then(function(html) {
        return that.writeFile(
            that.outputPath(page.path),
            html
        );
    });
};

// Finish generation, create ebook using ebook-convert
WebsiteOutput.prototype.finish = function() {
    var that = this;

    return Promise()
    .then(function() {
        return WebsiteOutput.super_.prototype.finish.apply(that);
    })

    // Copy assets from plugins
    .then(function() {
        return that.plugins.copyResources(that.name, that.resolve('gitbook'));
    });
};

// ----- Utilities ----

// Render a template using nunjucks
// Templates are stored in `_layouts` folders
WebsiteOutput.prototype.render = function(tpl, context) {
    var filename = this.templateName(tpl);

    context = _.extend(context, {
        template: {
            // Same template but in the default theme
            default: this.themeDefault? path.resolve(templatesPath(this.themeDefault.root), filename) : null,

            // Same template but in the theme
            theme: path.resolve(templatesPath(this.theme.root), filename)
        },

        plugins: {
            resources: this.resources
        }
    });

    return Promise.nfcall(this.env.render.bind(this.env), filename, context);
};

// Return a complete name for a template
WebsiteOutput.prototype.templateName = function(name) {
    return path.join(this.name, name+'.html');
};

module.exports = WebsiteOutput;