var npm = require('npm');
var semver = require('semver');
var Immutable = require('immutable');

var Promise = require('../utils/promise');
var Plugin = require('../models/plugin');
var gitbook = require('../gitbook');

var npmIsReady;

/**
    Initialize and prepare NPM

    @return {Promise}
*/
function initNPM() {
    if (npmIsReady) return npmIsReady;

    npmIsReady = Promise.nfcall(npm.load, {
        silent: true,
        loglevel: 'silent'
    });

    return npmIsReady;
}

/**
    Resolve a plugin dependency to a version

    @param {PluginDependency} plugin
    @return {Promise<String>}
*/
function resolveVersion(plugin) {
    var npmId = Plugin.nameToNpmID(plugin.getName());
    var requiredVersion = plugin.getVersion();

    if (plugin.isGitDependency()) {
        return Promise.resolve(requiredVersion);
    }

    return initNPM()
    .then(function() {
        return Promise.nfcall(npm.commands.view, [npmId + '@' + requiredVersion, 'engines'], true);
    })
    .then(function(versions) {
        versions = Immutable.Map(versions).entrySeq();

        var result = versions
            .map(function(entry) {
                return {
                    version: entry[0],
                    gitbook: (entry[1].engines || {}).gitbook
                };
            })
            .filter(function(v) {
                return v.gitbook && gitbook.satisfies(v.gitbook);
            })
            .sort(function(v1, v2) {
                return semver.lt(v1.version, v2.version)? 1 : -1;
            })
            .get(0);

        if (!result) {
            return undefined;
        } else {
            return result.version;
        }
    });
}

module.exports = resolveVersion;