using Npgsql;
using NpgsqlTypes;
using System;
using System.Collections.Generic;
using System.Data.Common;
using System.Threading.Tasks;

namespace BirthdayBot.Data
{
    /// <summary>
    /// Represents configuration for a guild user.
    /// </summary>
    class GuildUserConfiguration
    {
        public ulong GuildId { get; }
        public ulong UserId { get; }

        /// <summary>
        /// Month of birth as a numeric value. Range 1-12.
        /// </summary>
        public int BirthMonth { get; private set; }
        /// <summary>
        /// Day of birth as a numeric value. Ranges between 1-31 or lower based on month value.
        /// </summary>
        public int BirthDay { get; private set; }

        public string TimeZone { get; private set; }
        public bool IsKnown { get { return BirthMonth != 0 && BirthDay != 0; } }

        /// <summary>
        /// Creates a new, data-less instance without a corresponding database entry.
        /// Calling <see cref="UpdateAsync(int, int, int)"/> will create a real database enty
        /// </summary>
        private GuildUserConfiguration(ulong guildId, ulong userId)
        {
            GuildId = guildId;
            UserId = userId;
        }

        // Called by GetGuildUsersAsync. Double-check ordinals when changes are made.
        private GuildUserConfiguration(DbDataReader reader)
        {
            GuildId = (ulong)reader.GetInt64(0);
            UserId = (ulong)reader.GetInt64(1);
            BirthMonth = reader.GetInt32(2);
            BirthDay = reader.GetInt32(3);
            if (!reader.IsDBNull(4)) TimeZone = reader.GetString(4);
        }

        /// <summary>
        /// Updates user with given information.
        /// </summary>
        public async Task UpdateAsync(int month, int day, string newtz)
        {
            using (var db = await Database.OpenConnectionAsync())
            {
                using var c = db.CreateCommand();
                c.CommandText = $"insert into {BackingTable} "
                    + "(guild_id, user_id, birth_month, birth_day, time_zone) values "
                    + "(@Gid, @Uid, @Month, @Day, @Tz) "
                    + "on conflict (guild_id, user_id) do update "
                    + "set birth_month = EXCLUDED.birth_month, birth_day = EXCLUDED.birth_day, time_zone = EXCLUDED.time_zone";
                c.Parameters.Add("@Gid", NpgsqlDbType.Bigint).Value = (long)GuildId;
                c.Parameters.Add("@Uid", NpgsqlDbType.Bigint).Value = (long)UserId;
                c.Parameters.Add("@Month", NpgsqlDbType.Numeric).Value = month;
                c.Parameters.Add("@Day", NpgsqlDbType.Numeric).Value = day;
                var tzp = c.Parameters.Add("@Tz", NpgsqlDbType.Text);
                if (newtz != null) tzp.Value = newtz;
                else tzp.Value = DBNull.Value;
                c.Prepare();
                await c.ExecuteNonQueryAsync();
            }

            // Database update succeeded; update instance values
            BirthMonth = month;
            BirthDay = day;
            TimeZone = newtz;
        }

        /// <summary>
        /// Deletes information of this user from the backing database.
        /// The corresponding object reference should ideally be discarded after calling this.
        /// </summary>
        public async Task DeleteAsync()
        {
            using var db = await Database.OpenConnectionAsync();
            using var c = db.CreateCommand();
            c.CommandText = $"delete from {BackingTable} "
                + "where guild_id = @Gid and user_id = @Uid";
            c.Parameters.Add("@Gid", NpgsqlDbType.Bigint).Value = (long)GuildId;
            c.Parameters.Add("@Uid", NpgsqlDbType.Bigint).Value = (long)UserId;
            c.Prepare();
            await c.ExecuteNonQueryAsync();
        }

        #region Database
        public const string BackingTable = "user_birthdays";
        // Take note of ordinals for use in the constructor
        private const string SelectFields = "guild_id, user_id, birth_month, birth_day, time_zone";

        internal static async Task DatabaseSetupAsync(NpgsqlConnection db)
        {
            using var c = db.CreateCommand();
            c.CommandText = $"create table if not exists {BackingTable} ("
                + $"guild_id bigint not null references {GuildConfiguration.BackingTable} ON DELETE CASCADE, "
                + "user_id bigint not null, "
                + "birth_month integer not null, "
                + "birth_day integer not null, "
                + "time_zone text null, "
                + "last_seen timestamptz not null default NOW(), "
                + "PRIMARY KEY (guild_id, user_id)" // index automatically created with this
                + ")";
            await c.ExecuteNonQueryAsync();
        }

        /// <summary>
        /// Attempts to retrieve a user's configuration. Returns a new, updateable instance if none is found.
        /// </summary>
        public static async Task<GuildUserConfiguration> LoadAsync(ulong guildId, ulong userId)
        {
            using var db = await Database.OpenConnectionAsync();
            using var c = db.CreateCommand();
            c.CommandText = $"select {SelectFields} from {BackingTable} where guild_id = @Gid and user_id = @Uid";
            c.Parameters.Add("@Gid", NpgsqlDbType.Bigint).Value = (long)guildId;
            c.Parameters.Add("@Uid", NpgsqlDbType.Bigint).Value = (long)userId;
            c.Prepare();

            using var r = c.ExecuteReader();
            if (await r.ReadAsync()) return new GuildUserConfiguration(r);
            else return new GuildUserConfiguration(guildId, userId);
        }

        /// <summary>
        /// Gets all known user configuration records associated with the specified guild.
        /// </summary>
        public static async Task<IEnumerable<GuildUserConfiguration>> LoadAllAsync(ulong guildId)
        {
            using var db = await Database.OpenConnectionAsync();
            using var c = db.CreateCommand();
            c.CommandText = $"select {SelectFields} from {BackingTable} where guild_id = @Gid";
            c.Parameters.Add("@Gid", NpgsqlDbType.Bigint).Value = (long)guildId;
            c.Prepare();

            using var r = await c.ExecuteReaderAsync();
            var result = new List<GuildUserConfiguration>();
            while (await r.ReadAsync()) result.Add(new GuildUserConfiguration(r));
            return result;
        }
        #endregion
    }
}