var path = require('path');
var resolve = require('resolve');

var Promise = require('../utils/promise');
var error = require('../utils/error');

var validatePlugin = require('./validatePlugin');

// Return true if an error is a "module not found"
// Wait on https://github.com/substack/node-resolve/pull/81 to be merged
function isModuleNotFound(err) {
    return err.message.indexOf('Cannot find module') >= 0;
}

/**
    Load a plugin in a book

    @param {Book} book
    @param {Plugin} plugin
    @param {String} pkgPath (optional)
    @return {Promise<Plugin>}
*/
function loadPlugin(book, plugin) {
    var logger = book.getLogger();

    var name = plugin.getName();
    var pkgPath = plugin.getPath();


    // Try loading plugins from different location
    var p = Promise()
    .then(function() {
        var packageContent;
        var content;

        // Locate plugin and load pacjage.json
        try {
            var res = resolve.sync('./package.json', { basedir: pkgPath });

            pkgPath = path.dirname(res);
            packageContent = require(res);
        } catch (err) {
            if (!isModuleNotFound(err)) throw err;

            packageContent = undefined;
            content = undefined;

            return;
        }

        // Load plugin JS content
        try {
            content = require(pkgPath);
        } catch(err) {
            // It's no big deal if the plugin doesn't have an "index.js"
            // (For example: themes)
            if (isModuleNotFound(err)) {
                content = {};
            } else {
                throw new error.PluginError(err, {
                    plugin: name
                });
            }
        }

        // Update plugin
        return plugin.merge({
            'package': packageContent,
            'content': content
        });
    })

    .then(validatePlugin)

    // Validate the configuration and update it
    .then(function() {
        var config = that.book.config.get(that.getConfigKey(), {});
        return that.validateConfig(config);
    })
    .then(function(config) {
        that.book.config.set(that.getConfigKey(), config);
    });

    logger.info('loading plugin "' + name + '"... ');
    return logger.info.promise(p);
}


module.exports = loadPlugin;