using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using Microsoft.SharePoint.Client;
using System.Security;

namespace SharepointEDMSSample
{
    // 
    // Class to read the input data without presuming where that data comes from; it could be a csv file,
    // a database, or something else.  The code for this class should be replaced by code to read the data from your source.
    //
    // The code for this instance of this class calls Sharepoint or Sharepoint Online to get the contents of a Document Library
    //
    // This code relies on Sharepoint's Document Id Service being activated in order to get a link to the document.
    //
    class DataReader
    {
        private const bool USE_SHAREPOINT_ONLINE = false;
        private const string SHAREPOINT_URL = "http://companyweb/SoftwareEngineering";
        private const string SHAREPOINT_ONLINE_URL = "https://digmap.sharepoint.com";
        private const string ONLINE_USER = "jjwilson@digmap.onmicrosoft.com";
        private const string ONLINE_PASSWORD = "jjw#ADF$61";
        private const string DOCUMENT_LIBRARY_TITLE = "Test EDMS Library";

        // The current page of the Sharepoint Document Library
        private ListItemCollection _docsList = null;

        // If there are more than 2000 documents in the document library then the documents will be fetched in
        // pages of 2000.  The next two variables contain the current document within the current page and the
        // position of that page within the whole Sharepoint list.

        private int _localPosition = -1;  // The current position within this page of the document list
        private ListItemCollectionPosition _globalPosition = null; // the current position within the 

        //
        // FetchMoreData gets one more page worth of documents from Sharepoint.
        //
        private bool FetchMoreData(bool firstTime)
        {
            string contextUrl;
            if (USE_SHAREPOINT_ONLINE)
                contextUrl = SHAREPOINT_ONLINE_URL;
            else
                contextUrl = SHAREPOINT_URL;
            using (ClientContext SharePointcontext = new ClientContext(contextUrl))
            {
                if (!firstTime && _globalPosition == null)
                    return false;

                if (USE_SHAREPOINT_ONLINE)
                {
                    SecureString passWord = new SecureString();
                    foreach (char c in ONLINE_PASSWORD.ToCharArray()) passWord.AppendChar(c);
                    SharePointcontext.Credentials = new SharePointOnlineCredentials(ONLINE_USER, passWord);
                }

                List docs = SharePointcontext.Web.Lists.GetByTitle(DOCUMENT_LIBRARY_TITLE);
                CamlQuery query = new CamlQuery();
                query.ListItemCollectionPosition = _globalPosition;
                query.ViewXml = "<View><RowLimit>2000</RowLimit></View>";
                _docsList = docs.GetItems(query);
                SharePointcontext.Load(_docsList);
                SharePointcontext.ExecuteQuery();
                _globalPosition = _docsList.ListItemCollectionPosition;
                return true;
            }
        }

        public DataReader()
        {
            FetchMoreData(true);
        }

        public bool ReadNext()
        {
            _localPosition++;
            if (_localPosition < _docsList.Count)
                return true;
            else
            {
                if (FetchMoreData(false))
                {
                    _localPosition = 0;
                    return true;
                }
                else
                    return false;
            }
        }

        public string GetField(string FieldName)
        {
            if (FieldName == "_dlc_DocIdUrl")
            {
                FieldUrlValue link = (FieldUrlValue) _docsList[_localPosition][FieldName];
                return link.Url;
            }
            else
                return (string) _docsList[_localPosition][FieldName];
        }

        public string this[string FieldName]
        {
            get { return GetField(FieldName); }
        }
    }
}