using Disco.Plugins.ServiceTracker.Models;
using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Text;

namespace Disco.Plugins.ServiceTracker.Services
{
    public class GoogleSheetService
    {
        private readonly GoogleSheetConfig _config;
        private readonly string _cachePath;

        public GoogleSheetService(GoogleSheetConfig config, string dataDirectory)
        {
            _config = config;
            _cachePath = Path.Combine(dataDirectory, "sheet_cache.csv");
        }

        public GoogleSheetResult FetchTickets()
        {
            var result = new GoogleSheetResult();
            if (!_config.Enabled || string.IsNullOrEmpty(_config.SpreadsheetId))
            {
                result.Error = "Google Sheet integration is disabled.";
                return result;
            }

            string csvData = null;

            // Check cache
            if (File.Exists(_cachePath))
            {
                var cacheAge = DateTime.Now - File.GetLastWriteTime(_cachePath);
                if (cacheAge.TotalMinutes < _config.RefreshMinutes)
                    csvData = File.ReadAllText(_cachePath);
            }

            if (csvData == null)
            {
                try
                {
                    // Build URL based on ID format
                    string url;
                    var id = _config.SpreadsheetId.Trim();

                    if (id.StartsWith("2PACX", StringComparison.OrdinalIgnoreCase))
                    {
                        // Published key format: /d/e/{publishedKey}/pub?output=csv&gid={gid}
                        url = string.Format(
                            "https://docs.google.com/spreadsheets/d/e/{0}/pub?output=csv&gid={1}",
                            id, _config.GId);
                    }
                    else
                    {
                        // Original spreadsheet ID format: /d/{id}/export?format=csv&gid={gid}
                        url = string.Format(
                            "https://docs.google.com/spreadsheets/d/{0}/export?format=csv&gid={1}",
                            id, _config.GId);
                    }

                    using (var client = new WebClient())
                    {
                        client.Encoding = Encoding.UTF8;
                        // Some Google responses require a user-agent
                        client.Headers.Add("User-Agent", "Mozilla/5.0 DiscoServiceTracker/1.0");
                        csvData = client.DownloadString(url);
                    }

                    // Validate we got actual CSV, not an HTML error page
                    if (csvData != null && csvData.TrimStart().StartsWith("<!DOCTYPE", StringComparison.OrdinalIgnoreCase))
                    {
                        if (File.Exists(_cachePath))
                        {
                            csvData = File.ReadAllText(_cachePath);
                            result.Warning = "Got HTML instead of CSV. Using cached data. Check Publish to Web settings (must publish as CSV).";
                        }
                        else
                        {
                            result.Error = "Google returned HTML instead of CSV. Ensure the sheet is published to web. "
                                + "Go to File > Share > Publish to web > select the tab > choose 'Comma-separated values (.csv)' > Publish.";
                            return result;
                        }
                    }
                    else
                    {
                        File.WriteAllText(_cachePath, csvData);
                    }
                }
                catch (WebException ex)
                {
                    if (File.Exists(_cachePath))
                    {
                        csvData = File.ReadAllText(_cachePath);
                        result.Warning = "Using cached data. Fetch error: " + ex.Message;
                    }
                    else
                    {
                        result.Error = "Could not fetch Google Sheet. Error: " + ex.Message
                            + "\n\nTroubleshooting:"
                            + "\n1. Go to your Google Sheet"
                            + "\n2. File > Share > Publish to web"
                            + "\n3. Select the correct tab"
                            + "\n4. Choose 'Comma-separated values (.csv)'"
                            + "\n5. Click Publish"
                            + "\n6. In Config, set Spreadsheet ID to the published key (starts with 2PACX-...)";
                        return result;
                    }
                }
                catch (Exception ex)
                {
                    result.Error = "Sheet fetch error: " + ex.Message;
                    return result;
                }
            }

            try
            {
                result.Tickets = ParseCsv(csvData);
                if (result.Tickets.Count == 0 && string.IsNullOrEmpty(result.Warning))
                    result.Warning = "Sheet fetched OK but no open tickets found. Check column indices and status values.";
            }
            catch (Exception ex)
            {
                result.Error = "CSV parse error: " + ex.Message;
            }

            return result;
        }

        private List<ExternalTicket> ParseCsv(string csvData)
        {
            var tickets = new List<ExternalTicket>();
            var lines = csvData.Split(new[] { '\n' }, StringSplitOptions.RemoveEmptyEntries);
            int nextId = 100001;

            for (int i = _config.HeaderRows; i < lines.Length; i++)
            {
                var fields = ParseCsvLine(lines[i]);
                if (fields.Count == 0) continue;

                // Skip completely empty rows
                bool allEmpty = true;
                for (int j = 0; j < fields.Count; j++)
                {
                    if (!string.IsNullOrWhiteSpace(fields[j])) { allEmpty = false; break; }
                }
                if (allEmpty) continue;

                var ticket = new ExternalTicket
                {
                    InternalId = nextId++,
                    Source = "ntt",
                    Timestamp = SafeGetDate(fields, _config.ColTimestamp),
                    RequesterEmail = SafeGet(fields, _config.ColEmail),
                    DeviceName = SafeGet(fields, _config.ColDeviceName),
                    Location = SafeGet(fields, _config.ColLocation),
                    IssueDescription = SafeGet(fields, _config.ColIssue),
                    RawPriority = SafeGet(fields, _config.ColPriority),
                    RawStatus = SafeGet(fields, _config.ColStatus),
                    AssignedTo = SafeGet(fields, _config.ColAssignedTo)
                };

                ticket.ExternalId = GenerateStableId(ticket);

                var status = (ticket.RawStatus ?? "").ToLower().Trim();
                ticket.IsOpen = status != "closed" && status != "resolved" && status != "completed" && status != "done";

                // Need at least an issue description or device name to be a valid ticket
                if (ticket.IsOpen && (!string.IsNullOrWhiteSpace(ticket.IssueDescription) || !string.IsNullOrWhiteSpace(ticket.DeviceName)))
                    tickets.Add(ticket);
            }

            return tickets;
        }

        private string GenerateStableId(ExternalTicket t)
        {
            var key = (t.Timestamp.ToString("yyyyMMddHHmm") + "|" + (t.RequesterEmail ?? "") + "|" + (t.DeviceName ?? "")).ToLower();
            int hash = 0;
            for (int i = 0; i < key.Length; i++)
                hash = ((hash << 5) - hash) + key[i];
            return "NTT" + Math.Abs(hash).ToString().PadLeft(6, '0').Substring(0, 6);
        }

        private string SafeGet(List<string> fields, int index)
        {
            if (index < 0 || index >= fields.Count) return null;
            var val = fields[index].Trim();
            return string.IsNullOrEmpty(val) ? null : val;
        }

        private DateTime SafeGetDate(List<string> fields, int index)
        {
            var val = SafeGet(fields, index);
            if (val == null) return DateTime.Now;
            DateTime dt;
            if (DateTime.TryParse(val, out dt)) return dt;
            return DateTime.Now;
        }

        private List<string> ParseCsvLine(string line)
        {
            var fields = new List<string>();
            bool inQuotes = false;
            var current = new StringBuilder();
            for (int i = 0; i < line.Length; i++)
            {
                char c = line[i];
                if (c == '"')
                {
                    if (inQuotes && i + 1 < line.Length && line[i + 1] == '"') { current.Append('"'); i++; }
                    else inQuotes = !inQuotes;
                }
                else if (c == ',' && !inQuotes) { fields.Add(current.ToString()); current.Clear(); }
                else if (c != '\r') current.Append(c);
            }
            fields.Add(current.ToString());
            return fields;
        }
    }

    public class GoogleSheetResult
    {
        public List<ExternalTicket> Tickets { get; set; }
        public string Error { get; set; }
        public string Warning { get; set; }
        public GoogleSheetResult() { Tickets = new List<ExternalTicket>(); }
    }
}