/**
 * Data transmission over HTTP(S)
 *
 *  Copyright (C) 2014, 2015 R-T Specialty, LLC.
 *
 *  This file is part of the Liza Data Collection Framework
 *
 *  Liza is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

var Class    = require( 'easejs' ).Class,
    DataApi  = require( '../DataApi' ),
    HttpImpl = require( './HttpImpl' ),

    // RFC 2616 methods
    rfcmethods = {
        DELETE:  true,
        GET:     true,
        HEAD:    true,
        OPTIONS: true,
        POST:    true,
        PUT:     true,
        TRACE:   true
    };


/**
 * HTTP request abstraction. Does minor validation, but delegates to a specific
 * HTTP implementation for the actual request.
 */
module.exports = Class( 'HttpDataApi' )
    .implement( DataApi )
    .extend(
{
    /**
     * Request URL
     * @type {string}
     */
    'private _url': '',

    /**
     * HTTP method
     * @type {string}
     */
    'private _method': '',

    /**
     * HTTP implementation to perfom request
     * @type {HttpImpl}
     */
    'private _impl': null,


    /**
     * Initialize Data API with destination and HTTP implementation
     *
     * The supplied HTTP implementation will be used to perform the HTTP
     * requests, which permits the user to use whatever implementation works
     * well with their existing system.
     *
     * TODO: Accept URI encoder.
     *
     * @param {string}   url    destination URL
     * @param {string}   method RFC-2616-compliant HTTP method
     * @param {HttpImpl} impl   HTTP implementation
     *
     * @throws {TypeError} when non-HttpImpl is provided
     */
    __construct: function( url, method, impl )
    {
        if ( !( Class.isA( HttpImpl, impl ) ) )
        {
            throw TypeError( "Expected HttpImpl" );
        }

        this._url    = ''+url;
        this._method = this._validateMethod( method );
        this._impl   = impl;
    },


    /**
     * Perform an asynchronous request and invoke the callback with the reply
     *
     * DATA must be either a string or an object; the latter is treated as a
     * key-value parameter list, which will have each key and value
     * individually URI-encoded and converted into a string, delimited by
     * ampersands.  `null` may be used to indicate that no data should be
     * sent.
     *
     * In the event of an error, the first parameter is the error; otherwise, it
     * is null. The return data shall not be used in the event of an error.
     *
     * The return value shall be a raw string; conversion to other formats must
     * be handled by a wrapper.
     *
     * @param {?Object<string,string>|string} data request params or post data
     *
     * @param {function(?Error,*):string} callback continuation upon reply
     *
     * @return {DataApi} self
     *
     * @throws {TypeError} on validation failure
     */
    'virtual public request': function( data, callback )
    {
        // null is a good indicator of "I have no intent to send any data";
        // empty strings and objects are not, since those are valid data
        if ( data === null )
        {
            data = "";
        }

        this._validateDataType( data );

        this._impl.requestData(
            this._url,
            this._method,
            this._encodeData( data ),
            callback
        );

        return this;
    },


    /**
     * Ensures that the provided method conforms to RFC 2616
     *
     * @param {string} method HTTP method
     * @return {string} provided method
     *
     * @throws {Error} on non-conforming method
     */
    'private _validateMethod': function( method )
    {
        if ( !( rfcmethods[ method ] ) )
        {
            throw Error( "Invalid RFC 2616 method: " + method );
        }

        return method;
    },


    /**
     * Validates that the provided data type is accepted by the Data API
     *
     * @param {*} data data to validate
     * @return {undefined}
     *
     * @throws {TypeError} on validation failure
     */
    'private _validateDataType': function( data )
    {
        var type = typeof data;

        if( !( ( type === 'string' ) || ( type === 'object' ) ) )
        {
            throw TypeError(
                "Data must be a string of raw data or object containing " +
                "key-value params"
            );
        }
    },


    /**
     * If the data are an object, it's converted to an encoded key-value
     * URI; otherwise, the original string datum is returned.
     *
     * @param {?Object<string,string>|string=} data raw data or key-value
     *
     * @return {string} encoded data
     */
    'private _encodeData': function( data )
    {
        if ( typeof data !== 'object' )
        {
            return ''+data;
        }

        return this._encodeKeys( data );
    },


    /**
     * Generate params for URI from key-value DATA
     *
     * @param {Object<string,string>} data key-value request params
     *
     * @return {string} generated URI, or empty if no keys
     */
    'private _encodeKeys': function( obj )
    {
        var uri = '';

        // ES3 support
        for ( var key in obj )
        {
            if ( !Object.prototype.hasOwnProperty.call( obj, key ) )
            {
                continue;
            }

            uri += ( uri )
                ? '&'
                : '';

            uri += encodeURIComponent( key ) + '=' +
                encodeURIComponent( obj[ key ] );
        }

        return uri;
    }
} );