using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Runtime.Serialization.Json;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using System.Web.Services.Protocols;
using System.Security.Cryptography;
using System.Text;
using System.Web.SessionState;
using System.Data;
using System.Drawing.Imaging;
using System.Drawing;
using System.IO;
using System.Data.SqlClient;
using System.Configuration;

/// <summary>
/// FacebookHelper 的摘要描述
/// </summary>
public class FacebookHelper
{
    private string _appId;
    private string _appSecret;
    private string _accessToken;

    public string AccessToken
    {
        get
        {
            if (_accessToken == null)
                GetAccessToken();

            return _accessToken;
        }
        set { _accessToken = value; }
    }

    public FacebookHelper(string appId, string appSecret)
    {
        this._appId = appId;
        this._appSecret = appSecret;
    }

    public string GetAccessToken()
    {
        var facebookCookie = HttpContext.Current.Request.Cookies["fbsr_" + _appId];
        if (facebookCookie != null && facebookCookie.Value != null)
        {
            string jsoncode = System.Text.ASCIIEncoding.ASCII.GetString(FromBase64ForUrlString(facebookCookie.Value.Split(new char[] { '.' })[1]));
            var tokenParams = HttpUtility.ParseQueryString(GetAccessToken((string)JObject.Parse(jsoncode)["code"]));
            _accessToken = tokenParams["access_token"];
            return _accessToken;
        }
        else
            return null;

        // return DBLoginCall(username, passwordHash, cookieToken, cookieTokenExpires, args.LoginType == LoginType.Logout, null);
    }

    private string GetAccessToken(string code)
    {
        //Notice the empty redirect_uri! And the replace on the code we get from the cookie.
        string url = string.Format("https://graph.facebook.com/oauth/access_token?client_id={0}&redirect_uri={1}&client_secret={2}&code={3}", _appId, "", _appSecret, code.Replace("\"", ""));

        System.Net.HttpWebRequest request = System.Net.WebRequest.Create(url) as System.Net.HttpWebRequest;
        System.Net.HttpWebResponse response = null;

        try
        {
            using (response = request.GetResponse() as System.Net.HttpWebResponse)
            {
                System.IO.StreamReader reader = new System.IO.StreamReader(response.GetResponseStream());

                string retVal = reader.ReadToEnd();
                return retVal;
            }
        }
        catch
        {
            return null;
        }
    }

    private byte[] FromBase64ForUrlString(string base64ForUrlInput)
    {
        int padChars = (base64ForUrlInput.Length % 4) == 0 ? 0 : (4 - (base64ForUrlInput.Length % 4));
        StringBuilder result = new StringBuilder(base64ForUrlInput, base64ForUrlInput.Length + padChars);
        result.Append(String.Empty.PadRight(padChars, '='));
        result.Replace('-', '+');
        result.Replace('_', '/');
        return Convert.FromBase64String(result.ToString());
    }
}