using BirthdayBot.Data;
using System.Text;

namespace BirthdayBot.UserInterface;

/// <summary>
/// Commands for listing upcoming and all birthdays.
/// </summary>
internal class ListingCommands : CommandsCommon {
    public ListingCommands(Configuration db) : base(db) { }

    public override IEnumerable<(string, CommandHandler)> Commands
        => new List<(string, CommandHandler)>()
        {
                ("list", CmdList),
                ("upcoming", CmdUpcoming),
                ("recent", CmdUpcoming),
                ("when", CmdWhen)
        };

    #region Documentation
    public static readonly CommandDocumentation DocList =
        new(new string[] { "list" }, "Exports all birthdays to a file."
            + " Accepts `csv` as an optional parameter.", null);
    public static readonly CommandDocumentation DocUpcoming =
        new(new string[] { "recent", "upcoming" }, "Lists recent and upcoming birthdays.", null);
    public static readonly CommandDocumentation DocWhen =
        new(new string[] { "when" }, "Displays the given user's birthday information.", null);
    #endregion

    private async Task CmdWhen(ShardInstance instance, GuildConfiguration gconf,
                               string[] param, SocketTextChannel reqChannel, SocketGuildUser reqUser) {
        if (!await HasMemberCacheAsync(reqChannel.Guild)) {
            await reqChannel.SendMessageAsync(MemberCacheEmptyError);
            return;
        }

        // Requires a parameter
        if (param.Length == 1) {
            await reqChannel.SendMessageAsync(ParameterError, embed: DocWhen.UsageEmbed).ConfigureAwait(false);
            return;
        }

        var search = param[1];
        if (param.Length == 3) {
            // param maxes out at 3 values. param[2] might contain part of the search string (if name has a space)
            search += " " + param[2];
        }

        SocketGuildUser? searchTarget = null;

        if (!TryGetUserId(search, out ulong searchId)) // ID lookup
        {
            // name lookup without discriminator
            foreach (var searchuser in reqChannel.Guild.Users) {
                if (string.Equals(search, searchuser.Username, StringComparison.OrdinalIgnoreCase)) {
                    searchTarget = searchuser;
                    break;
                }
            }
        } else {
            searchTarget = reqChannel.Guild.GetUser(searchId);
        }
        if (searchTarget == null) {
            await reqChannel.SendMessageAsync(BadUserError, embed: DocWhen.UsageEmbed).ConfigureAwait(false);
            return;
        }

        var searchTargetData = await GuildUserConfiguration.LoadAsync(reqChannel.Guild.Id, searchId).ConfigureAwait(false);
        if (!searchTargetData.IsKnown) {
            await reqChannel.SendMessageAsync("I do not have birthday information for that user.").ConfigureAwait(false);
            return;
        }

        string result = Common.FormatName(searchTarget, false);
        result += ": ";
        result += $"`{searchTargetData.BirthDay:00}-{Common.MonthNames[searchTargetData.BirthMonth]}`";
        result += searchTargetData.TimeZone == null ? "" : $" - `{searchTargetData.TimeZone}`";

        await reqChannel.SendMessageAsync(result).ConfigureAwait(false);
    }

    // Creates a file with all birthdays.
    private async Task CmdList(ShardInstance instance, GuildConfiguration gconf,
                               string[] param, SocketTextChannel reqChannel, SocketGuildUser reqUser) {
        // For now, we're restricting this command to moderators only. This may turn into an option later.
        if (!gconf.IsBotModerator(reqUser)) {
            // Do not add detailed usage information to this error message.
            await reqChannel.SendMessageAsync(":x: Only bot moderators may use this command.").ConfigureAwait(false);
            return;
        }

        if (!await HasMemberCacheAsync(reqChannel.Guild)) {
            await reqChannel.SendMessageAsync(MemberCacheEmptyError);
            return;
        }

        bool useCsv = false;
        // Check for CSV option
        if (param.Length == 2) {
            if (param[1].ToLower() == "csv") useCsv = true;
            else {
                await reqChannel.SendMessageAsync(":x: That is not available as an export format.", embed: DocList.UsageEmbed)
                    .ConfigureAwait(false);
                return;
            }
        } else if (param.Length > 2) {
            await reqChannel.SendMessageAsync(ParameterError, embed: DocList.UsageEmbed).ConfigureAwait(false);
            return;
        }

        var bdlist = await GetSortedUsersAsync(reqChannel.Guild).ConfigureAwait(false);

        var filepath = Path.GetTempPath() + "birthdaybot-" + reqChannel.Guild.Id;
        string fileoutput;
        if (useCsv) {
            fileoutput = ListExportCsv(reqChannel, bdlist);
            filepath += ".csv";
        } else {
            fileoutput = ListExportNormal(reqChannel, bdlist);
            filepath += ".txt.";
        }
        await File.WriteAllTextAsync(filepath, fileoutput, Encoding.UTF8).ConfigureAwait(false);

        try {
            await reqChannel.SendFileAsync(filepath, $"Exported {bdlist.Count} birthdays to file.").ConfigureAwait(false);
        } catch (Discord.Net.HttpException) {
            reqChannel.SendMessageAsync(":x: Unable to send list due to a permissions issue. Check the 'Attach Files' permission.").Wait();
        } catch (Exception ex) {
            Program.Log("Listing", ex.ToString());
            reqChannel.SendMessageAsync(InternalError).Wait();
            // TODO webhook report
        } finally {
            File.Delete(filepath);
        }
    }

    // "Recent and upcoming birthdays"
    // The 'recent' bit removes time zone ambiguity and spares us from extra time zone processing here
    private async Task CmdUpcoming(ShardInstance instance, GuildConfiguration gconf,
                                   string[] param, SocketTextChannel reqChannel, SocketGuildUser reqUser) {
        if (!await HasMemberCacheAsync(reqChannel.Guild)) {
            await reqChannel.SendMessageAsync(MemberCacheEmptyError);
            return;
        }

        var now = DateTimeOffset.UtcNow;
        var search = DateIndex(now.Month, now.Day) - 8; // begin search 8 days prior to current date UTC
        if (search <= 0) search = 366 - Math.Abs(search);

        var query = await GetSortedUsersAsync(reqChannel.Guild).ConfigureAwait(false);

        var output = new StringBuilder();
        var resultCount = 0;
        output.AppendLine("Recent and upcoming birthdays:");
        for (int count = 0; count <= 21; count++) // cover 21 days total (7 prior, current day, 14 upcoming)
        {
            var results = from item in query
                          where item.DateIndex == search
                          select item;

            // push up search by 1 now, in case we back out early
            search += 1;
            if (search > 366) search = 1; // wrap to beginning of year

            if (!results.Any()) continue; // back out early
            resultCount += results.Count();

            // Build sorted name list
            var names = new List<string>();
            foreach (var item in results) {
                names.Add(item.DisplayName);
            }
            names.Sort(StringComparer.OrdinalIgnoreCase);

            var first = true;
            output.AppendLine();
            output.Append($"● `{Common.MonthNames[results.First().BirthMonth]}-{results.First().BirthDay:00}`: ");
            foreach (var item in names) {
                // If the output is starting to fill up, send out this message and prepare a new one.
                if (output.Length > 800) {
                    await reqChannel.SendMessageAsync(output.ToString()).ConfigureAwait(false);
                    output.Clear();
                    first = true;
                    output.Append($"● `{Common.MonthNames[results.First().BirthMonth]}-{results.First().BirthDay:00}`: ");
                }

                if (first) first = false;
                else output.Append(", ");
                output.Append(item);
            }
        }

        if (resultCount == 0)
            await reqChannel.SendMessageAsync(
                "There are no recent or upcoming birthdays (within the last 7 days and/or next 21 days).")
                .ConfigureAwait(false);
        else
            await reqChannel.SendMessageAsync(output.ToString()).ConfigureAwait(false);
    }

    /// <summary>
    /// Fetches all guild birthdays and places them into an easily usable structure.
    /// Users currently not in the guild are not included in the result.
    /// </summary>
    private static async Task<List<ListItem>> GetSortedUsersAsync(SocketGuild guild) {
        using var db = await Database.OpenConnectionAsync();
        using var c = db.CreateCommand();
        c.CommandText = "select user_id, birth_month, birth_day from " + GuildUserConfiguration.BackingTable
            + " where guild_id = @Gid order by birth_month, birth_day";
        c.Parameters.Add("@Gid", NpgsqlTypes.NpgsqlDbType.Bigint).Value = (long)guild.Id;
        c.Prepare();
        using var r = await c.ExecuteReaderAsync();
        var result = new List<ListItem>();
        while (await r.ReadAsync()) {
            var id = (ulong)r.GetInt64(0);
            var month = r.GetInt32(1);
            var day = r.GetInt32(2);

            var guildUser = guild.GetUser(id);
            if (guildUser == null) continue; // Skip user not in guild

            result.Add(new ListItem() {
                BirthMonth = month,
                BirthDay = day,
                DateIndex = DateIndex(month, day),
                UserId = guildUser.Id,
                DisplayName = Common.FormatName(guildUser, false)
            });
        }
        return result;
    }

    private string ListExportNormal(SocketGuildChannel channel, IEnumerable<ListItem> list) {
        // Output: "● Mon-dd: (user ID) Username [ - Nickname: (nickname)]"
        var result = new StringBuilder();
        result.AppendLine("Birthdays in " + channel.Guild.Name);
        result.AppendLine();
        foreach (var item in list) {
            var user = channel.Guild.GetUser(item.UserId);
            if (user == null) continue; // User disappeared in the instant between getting list and processing
            result.Append($"● {Common.MonthNames[item.BirthMonth]}-{item.BirthDay:00}: ");
            result.Append(item.UserId);
            result.Append(" " + user.Username + "#" + user.Discriminator);
            if (user.Nickname != null) result.Append(" - Nickname: " + user.Nickname);
            result.AppendLine();
        }
        return result.ToString();
    }

    private string ListExportCsv(SocketGuildChannel channel, IEnumerable<ListItem> list) {
        // Output: User ID, Username, Nickname, Month-Day, Month, Day
        var result = new StringBuilder();

        // Conforming to RFC 4180; with header
        result.Append("UserId,Username,Nickname,MonthDayDisp,Month,Day");
        result.Append("\r\n"); // crlf line break is specified by the standard
        foreach (var item in list) {
            var user = channel.Guild.GetUser(item.UserId);
            if (user == null) continue; // User disappeared in the instant between getting list and processing
            result.Append(item.UserId);
            result.Append(',');
            result.Append(CsvEscape(user.Username + "#" + user.Discriminator));
            result.Append(',');
            if (user.Nickname != null) result.Append(user.Nickname);
            result.Append(',');
            result.Append($"{Common.MonthNames[item.BirthMonth]}-{item.BirthDay:00}");
            result.Append(',');
            result.Append(item.BirthMonth);
            result.Append(',');
            result.Append(item.BirthDay);
            result.Append("\r\n");
        }
        return result.ToString();
    }

    private static string CsvEscape(string input) {
        var result = new StringBuilder();
        result.Append('"');
        foreach (var ch in input) {
            if (ch == '"') result.Append('"');
            result.Append(ch);
        }
        result.Append('"');
        return result.ToString();
    }

    private static int DateIndex(int month, int day) {
        var dateindex = 0;
        // Add month offsets
        if (month > 1) dateindex += 31; // Offset January
        if (month > 2) dateindex += 29; // Offset February (incl. leap day)
        if (month > 3) dateindex += 31; // etc
        if (month > 4) dateindex += 30;
        if (month > 5) dateindex += 31;
        if (month > 6) dateindex += 30;
        if (month > 7) dateindex += 31;
        if (month > 8) dateindex += 31;
        if (month > 9) dateindex += 30;
        if (month > 10) dateindex += 31;
        if (month > 11) dateindex += 30;
        dateindex += day;
        return dateindex;
    }

    private struct ListItem {
        public int DateIndex;
        public int BirthMonth;
        public int BirthDay;
        public ulong UserId;
        public string DisplayName;
    }
}