PluralKit/PluralKit.Core/Stores.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using App.Metrics.Logging;
using Dapper;
using NodaTime;
using Npgsql;

using Serilog;

namespace PluralKit {
    public class FullMessage
    {
        public PKMessage Message;
        public PKMember Member;
        public PKSystem System;
    }
    
    public struct PKMessage
    {
        public ulong Mid;
        public ulong Channel;
        public ulong Sender;
        public ulong? OriginalMid;
    }

    public struct ImportedSwitch
    {
        public Instant Timestamp;
        public IReadOnlyCollection<PKMember> Members;
    }

    public struct SwitchListEntry
    {
        public ICollection<PKMember> Members;
        public Instant TimespanStart;
        public Instant TimespanEnd;
    }

    public struct MemberMessageCount
    {
        public int Member;
        public int MessageCount;
    }
    
    public struct FrontBreakdown
    {
        public Dictionary<PKMember, Duration> MemberSwitchDurations;
        public Duration NoFronterDuration;
        public Instant RangeStart;
        public Instant RangeEnd;
    }
    
    public struct SwitchMembersListEntry
    {
        public int Member;
        public Instant Timestamp;
    }

    public struct GuildConfig
    {
        public ulong Id { get; set; }
        public ulong? LogChannel { get; set; }
    }

    public interface IDataStore
    {
        /// <summary>
        /// Gets a system by its internal system ID.
        /// </summary>
        /// <returns>The <see cref="PKSystem"/> with the given internal ID, or null if no system was found.</returns>
        Task<PKSystem> GetSystemById(int systemId);
        
        /// <summary>
        /// Gets a system by its user-facing human ID.
        /// </summary>
        /// <returns>The <see cref="PKSystem"/> with the given human ID, or null if no system was found.</returns>
        Task<PKSystem> GetSystemByHid(string systemHid);
        
        /// <summary>
        /// Gets a system by one of its linked Discord account IDs. Multiple IDs can return the same system.
        /// </summary>
        /// <returns>The <see cref="PKSystem"/> with the given linked account, or null if no system was found.</returns>
        Task<PKSystem> GetSystemByAccount(ulong linkedAccount);
        
        /// <summary>
        /// Gets a system by its API token. 
        /// </summary>
        /// <returns>The <see cref="PKSystem"/> with the given API token, or null if no corresponding system was found.</returns> 
        Task<PKSystem> GetSystemByToken(string apiToken);
        
        /// <summary>
        /// Gets the Discord account IDs linked to a system.
        /// </summary>
        /// <returns>An enumerable of Discord account IDs linked to this system.</returns>
        Task<IEnumerable<ulong>> GetSystemAccounts(PKSystem system);

        /// <summary>
        /// Gets the member count of a system.
        /// </summary>
        Task<int> GetSystemMemberCount(PKSystem system);
        
        /// <summary>
        /// Creates a system, auto-generating its corresponding IDs.
        /// </summary>
        /// <param name="systemName">An optional system name to set. If `null`, will not set a system name.</param>
        /// <returns>The created system model.</returns>
        Task<PKSystem> CreateSystem(string systemName);
        // TODO: throw exception if account is present (when adding) or account isn't present (when removing)
        
        /// <summary>
        /// Links a Discord account to a system.
        /// </summary>
        /// <exception>Throws an exception (TODO: which?) if the given account is already linked to a system.</exception>
        Task AddAccount(PKSystem system, ulong accountToAdd);
        
        /// <summary>
        /// Unlinks a Discord account from a system.
        ///
        /// Will *not* throw if this results in an orphaned system - this is the caller's responsibility to ensure.
        /// </summary>
        /// <exception>Throws an exception (TODO: which?) if the given account is not linked to the given system.</exception>
        Task RemoveAccount(PKSystem system, ulong accountToRemove);
        
        /// <summary>
        /// Saves the information within the given <see cref="PKSystem"/> struct to the data store.
        /// </summary>
        Task SaveSystem(PKSystem system);
        
        /// <summary>
        /// Deletes the given system from the database.
        /// </summary>
        /// <para>
        /// This will also delete all the system's members, all system switches, and every message that has been proxied
        /// by members in the system.
        /// </para>
        Task DeleteSystem(PKSystem system);

        /// <summary>
        /// Gets a system by its internal member ID.
        /// </summary>
        /// <returns>The <see cref="PKMember"/> with the given internal ID, or null if no member was found.</returns>
        Task<PKMember> GetMemberById(int memberId);
        
        /// <summary>
        /// Gets a member by its user-facing human ID.
        /// </summary>
        /// <returns>The <see cref="PKMember"/> with the given human ID, or null if no member was found.</returns>
        Task<PKMember> GetMemberByHid(string memberHid);
        
        /// <summary>
        /// Gets a member by its member name within one system.
        /// </summary>
        /// <para>
        /// Member names are *usually* unique within a system (but not always), whereas member names
        /// are almost certainly *not* unique globally - therefore only intra-system lookup is
        /// allowed.
        /// </para> 
        /// <returns>The <see cref="PKMember"/> with the given name, or null if no member was found.</returns>
        Task<PKMember> GetMemberByName(PKSystem system, string name);
        
        /// <summary>
        /// Gets all members inside a given system.
        /// </summary>
        /// <returns>An enumerable of <see cref="PKMember"/> structs representing each member in the system, in no particular order.</returns>
        Task<IEnumerable<PKMember>> GetSystemMembers(PKSystem system);
        /// <summary>
        /// Gets the amount of messages proxied by a given member. 
        /// </summary>
        /// <returns>The message count of the given member.</returns>
        Task<ulong> GetMemberMessageCount(PKMember member);
        
        /// <summary>
        /// Collects a breakdown of each member in a system's message count.
        /// </summary>
        /// <returns>An enumerable of members along with their message counts.</returns>
        Task<IEnumerable<MemberMessageCount>> GetMemberMessageCountBulk(PKSystem system);
        
        /// <summary>
        /// Creates a member, auto-generating its corresponding IDs.
        /// </summary>
        /// <param name="system">The system in which to create the member.</param>
        /// <param name="name">The name of the member to create.</param>
        /// <returns>The created system model.</returns>
        Task<PKMember> CreateMember(PKSystem system, string name);
        
        /// <summary>
        /// Creates multiple members, auto-generating each corresponding ID.
        /// </summary>
        /// <param name="system">The system to create the member in.</param>
        /// <param name="memberNames">A dictionary containing a mapping from an arbitrary key to the member's name.</param>
        /// <returns>A dictionary containing the resulting member structs, each mapped to the key given in the argument dictionary.</returns>
        Task<Dictionary<string, PKMember>> CreateMembersBulk(PKSystem system, Dictionary<string, string> memberNames);
        
        /// <summary>
        /// Saves the information within the given <see cref="PKMember"/> struct to the data store.
        /// </summary>
        Task SaveMember(PKMember member);
        
        /// <summary>
        /// Deletes the given member from the database.
        /// </summary>
        /// <para>
        /// This will remove this member from any switches it's involved in, as well as all the messages
        /// proxied by this member.
        /// </para>
        Task DeleteMember(PKMember member);
        
        /// <summary>
        /// Gets a message and its information by its ID.
        /// </summary>
        /// <param name="id">The message ID to look up. This can be either the ID of the trigger message containing the proxy tags or the resulting proxied webhook message.</param>
        /// <returns>An extended message object, containing not only the message data itself but the associated system and member structs.</returns>
        Task<FullMessage> GetMessage(ulong id); // id is both original and trigger, also add return type struct

        /// <summary>
        /// Saves a posted message to the database.
        /// </summary>
        /// <param name="senderAccount">The ID of the account that sent the original trigger message.</param>
        /// <param name="channelId">The ID of the channel the message was posted to.</param>
        /// <param name="postedMessageId">The ID of the message posted by the webhook.</param>
        /// <param name="triggerMessageId">The ID of the original trigger message containing the proxy tags.</param>
        /// <param name="proxiedMember">The member (and by extension system) that was proxied.</param>
        /// <returns></returns>
        Task AddMessage(ulong senderAccount, ulong channelId, ulong postedMessageId, ulong triggerMessageId, PKMember proxiedMember);
        
        /// <summary>
        /// Deletes a message from the data store.
        /// </summary>
        /// <param name="postedMessageId">The ID of the webhook message to delete.</param>
        Task DeleteMessage(ulong postedMessageId);

        /// <summary>
        /// Deletes messages from the data store in bulk.
        /// </summary>
        /// <param name="postedMessageIds">The IDs of the webhook messages to delete.</param>
        Task DeleteMessagesBulk(IEnumerable<ulong> postedMessageIds);
        
        /// <summary>
        /// Gets switches from a system.
        /// </summary>
        /// <returns>An enumerable of the *count* latest switches in the system, in latest-first order. May contain fewer elements than requested.</returns>
        Task<IEnumerable<PKSwitch>> GetSwitches(PKSystem system, int count);

        /// <summary>
        /// Gets the latest (temporally; closest to now) switch of a given system.
        /// </summary>
        Task<PKSwitch> GetLatestSwitch(PKSystem system);

        /// <summary>
        /// Gets the members a given switch consists of.
        /// </summary>
        Task<IEnumerable<PKMember>> GetSwitchMembers(PKSwitch sw);

        /// <summary>
        /// Gets a list of fronters over a given period of time.
        /// </summary>
        /// <para>
        /// This list is returned as an enumerable of "switch members", each containing a timestamp
        /// and a member ID. <seealso cref="GetMemberById"/>
        ///
        /// Switches containing multiple members will be returned as multiple switch members each with the same
        /// timestamp, and a change in timestamp should be interpreted as the start of a new switch.
        /// </para>
        /// <returns>An enumerable of the aforementioned "switch members".</returns>
        Task<IEnumerable<SwitchListEntry>> GetPeriodFronters(PKSystem system, Instant periodStart, Instant periodEnd);

        /// <summary>
        /// Calculates a breakdown of a system's fronters over a given period, including how long each member has
        /// been fronting, and how long *no* member has been fronting. 
        /// </summary>
        /// <para>
        /// Switches containing multiple members will count the full switch duration for all members, meaning
        /// the total duration may add up to longer than the breakdown period.
        /// </para>
        /// <param name="system"></param>
        /// <param name="periodStart"></param>
        /// <param name="periodEnd"></param>
        /// <returns></returns>
        Task<FrontBreakdown> GetFrontBreakdown(PKSystem system, Instant periodStart, Instant periodEnd);
        
        /// <summary>
        /// Registers a switch with the given members in the given system.
        /// </summary>
        /// <exception>Throws an exception (TODO: which?) if any of the members are not in the given system.</exception>
        Task AddSwitch(PKSystem system, IEnumerable<PKMember> switchMembers);
        
        /// <summary>
        /// Registers switches in bulk.
        /// </summary>
        /// <param name="switches">A list of switch structs, each containing a timestamp and a list of members.</param>
        /// <exception>Throws an exception (TODO: which?) if any of the given members are not in the given system.</exception>
        Task AddSwitchesBulk(PKSystem system, IEnumerable<ImportedSwitch> switches);
        
        /// <summary>
        /// Updates the timestamp of a given switch. 
        /// </summary>
        Task MoveSwitch(PKSwitch sw, Instant time);
        
        /// <summary>
        /// Deletes a given switch from the data store.
        /// </summary>
        Task DeleteSwitch(PKSwitch sw);

        /// <summary>
        /// Deletes all switches in a given system from the data store.
        /// </summary>
        Task DeleteAllSwitches(PKSystem system);

        /// <summary>
        /// Gets the total amount of systems in the data store.
        /// </summary>
        Task<ulong> GetTotalSystems();
        
        /// <summary>
        /// Gets the total amount of members in the data store.
        /// </summary>
        Task<ulong> GetTotalMembers();
        
        /// <summary>
        /// Gets the total amount of switches in the data store.
        /// </summary>
        Task<ulong> GetTotalSwitches();
        
        /// <summary>
        /// Gets the total amount of messages in the data store.
        /// </summary>
        Task<ulong> GetTotalMessages();

        /// <summary>
        /// Gets the guild configuration struct for a given guild.
        /// </summary>
        /// <returns>The guild's configuration struct, or a default struct if no guild was found in the data store.</returns>
        Task<GuildConfig> GetGuildConfig(ulong guild);
        
        /// <summary>
        /// Saves the given guild configuration struct to the data store.
        /// </summary>
        Task SaveGuildConfig(GuildConfig cfg);
    }
    
    public class PostgresDataStore: IDataStore {
        private DbConnectionFactory _conn;
        private ILogger _logger;

        public PostgresDataStore(DbConnectionFactory conn, ILogger logger)
        {
            _conn = conn;
            _logger = logger;
        }

        public async Task<PKSystem> CreateSystem(string systemName = null) {
            string hid;
            do
            {
                hid = Utils.GenerateHid();
            } while (await GetSystemByHid(hid) != null);

            PKSystem system;
            using (var conn = await _conn.Obtain())
                system = await conn.QuerySingleAsync<PKSystem>("insert into systems (hid, name) values (@Hid, @Name) returning *", new { Hid = hid, Name = systemName });

            _logger.Information("Created system {System}", system.Id);
            return system;
        }

        public async Task AddAccount(PKSystem system, ulong accountId) {
            // We have "on conflict do nothing" since linking an account when it's already linked to the same system is idempotent
            // This is used in import/export, although the pk;link command checks for this case beforehand
            using (var conn = await _conn.Obtain())
                await conn.ExecuteAsync("insert into accounts (uid, system) values (@Id, @SystemId) on conflict do nothing", new { Id = accountId, SystemId = system.Id });

            _logger.Information("Linked system {System} to account {Account}", system.Id, accountId);
        }

        public async Task RemoveAccount(PKSystem system, ulong accountId) {
            using (var conn = await _conn.Obtain())
                await conn.ExecuteAsync("delete from accounts where uid = @Id and system = @SystemId", new { Id = accountId, SystemId = system.Id });

            _logger.Information("Unlinked system {System} from account {Account}", system.Id, accountId);
        }

        public async Task<PKSystem> GetSystemByAccount(ulong accountId) {
            using (var conn = await _conn.Obtain())
                return await conn.QuerySingleOrDefaultAsync<PKSystem>("select systems.* from systems, accounts where accounts.system = systems.id and accounts.uid = @Id", new { Id = accountId });
        }

        public async Task<PKSystem> GetSystemByHid(string hid) {
            using (var conn = await _conn.Obtain())
                return await conn.QuerySingleOrDefaultAsync<PKSystem>("select * from systems where systems.hid = @Hid", new { Hid = hid.ToLower() });
        }

        public async Task<PKSystem> GetSystemByToken(string token) {
            using (var conn = await _conn.Obtain())
                return await conn.QuerySingleOrDefaultAsync<PKSystem>("select * from systems where token = @Token", new { Token = token });
        }

        public async Task<PKSystem> GetSystemById(int id)
        {
            using (var conn = await _conn.Obtain())
                return await conn.QuerySingleOrDefaultAsync<PKSystem>("select * from systems where id = @Id", new { Id = id });
        }

        public async Task SaveSystem(PKSystem system) {
            using (var conn = await _conn.Obtain())
                await conn.ExecuteAsync("update systems set name = @Name, description = @Description, tag = @Tag, avatar_url = @AvatarUrl, token = @Token, ui_tz = @UiTz where id = @Id", system);

            _logger.Information("Updated system {@System}", system);
        }

        public async Task DeleteSystem(PKSystem system) {
            using (var conn = await _conn.Obtain())
                await conn.ExecuteAsync("delete from systems where id = @Id", system);
            _logger.Information("Deleted system {System}", system.Id);
        }

        public async Task<IEnumerable<ulong>> GetSystemAccounts(PKSystem system)
        {
            using (var conn = await _conn.Obtain())
                return await conn.QueryAsync<ulong>("select uid from accounts where system = @Id", new { Id = system.Id });
        }

        public async Task DeleteAllSwitches(PKSystem system)
        {
            using (var conn = await _conn.Obtain())
                await conn.ExecuteAsync("delete from switches where system = @Id", system);
        }

        public async Task<ulong> GetTotalSystems()
        {
            using (var conn = await _conn.Obtain())
                return await conn.ExecuteScalarAsync<ulong>("select count(id) from systems");
        }

        public async Task<PKMember> CreateMember(PKSystem system, string name) {
            string hid;
            do
            {
                hid = Utils.GenerateHid();
            } while (await GetMemberByHid(hid) != null);

            PKMember member;
            using (var conn = await _conn.Obtain())
                member = await conn.QuerySingleAsync<PKMember>("insert into members (hid, system, name) values (@Hid, @SystemId, @Name) returning *", new {
                    Hid = hid,
                    SystemID = system.Id,
                    Name = name
                });

            _logger.Information("Created member {Member}", member.Id);
            return member;
        }

        public async Task<Dictionary<string,PKMember>> CreateMembersBulk(PKSystem system, Dictionary<string,string> names)
        {
            using (var conn = await _conn.Obtain())
            using (var tx = conn.BeginTransaction())
            {
                var results = new Dictionary<string, PKMember>();
                foreach (var name in names)
                {
                    string hid;
                    do
                    {
                        hid = await conn.QuerySingleOrDefaultAsync<string>("SELECT @Hid WHERE NOT EXISTS (SELECT id FROM members WHERE hid = @Hid LIMIT 1)", new
                        {
                            Hid = Utils.GenerateHid()
                        });
                    } while (hid == null);
                    var member = await conn.QuerySingleAsync<PKMember>("INSERT INTO members (hid, system, name) VALUES (@Hid, @SystemId, @Name) RETURNING *", new
                    {
                        Hid = hid,
                        SystemID = system.Id,
                        Name = name.Value
                    });
                    results.Add(name.Key, member);
                }

                tx.Commit();
                _logger.Information("Created {MemberCount} members for system {SystemID}", names.Count(), system.Hid);
                return results;
            }
        }

        public async Task<PKMember> GetMemberById(int id) {
            using (var conn = await _conn.Obtain())
                return await conn.QuerySingleOrDefaultAsync<PKMember>("select * from members where id = @Id", new { Id = id });
        }
        
        public async Task<PKMember> GetMemberByHid(string hid) {
            using (var conn = await _conn.Obtain())
                return await conn.QuerySingleOrDefaultAsync<PKMember>("select * from members where hid = @Hid", new { Hid = hid.ToLower() });
        }

        public async Task<PKMember> GetMemberByName(PKSystem system, string name) {
            // QueryFirst, since members can (in rare cases) share names
            using (var conn = await _conn.Obtain())
                return await conn.QueryFirstOrDefaultAsync<PKMember>("select * from members where lower(name) = lower(@Name) and system = @SystemID", new { Name = name, SystemID = system.Id });
        }

        public async Task<IEnumerable<PKMember>> GetSystemMembers(PKSystem system) {
            using (var conn = await _conn.Obtain())
                return await conn.QueryAsync<PKMember>("select * from members where system = @SystemID", new { SystemID = system.Id });
        }

        public async Task SaveMember(PKMember member) {
            using (var conn = await _conn.Obtain())
                await conn.ExecuteAsync("update members set name = @Name, display_name = @DisplayName, description = @Description, color = @Color, avatar_url = @AvatarUrl, birthday = @Birthday, pronouns = @Pronouns, proxy_tags = @ProxyTags, keep_proxy = @KeepProxy where id = @Id", member);

            _logger.Information("Updated member {@Member}", member);
        }

        public async Task DeleteMember(PKMember member) {
            using (var conn = await _conn.Obtain())
                await conn.ExecuteAsync("delete from members where id = @Id", member);

            _logger.Information("Deleted member {@Member}", member);
        }

        public async Task<ulong> GetMemberMessageCount(PKMember member)
        {
            using (var conn = await _conn.Obtain())
                return await conn.QuerySingleAsync<ulong>("select count(*) from messages where member = @Id", member);
        }

        public async Task<IEnumerable<MemberMessageCount>> GetMemberMessageCountBulk(PKSystem system)
        {
            using (var conn = await _conn.Obtain())
                return await conn.QueryAsync<MemberMessageCount>(
                    @"SELECT messages.member, COUNT(messages.member) messagecount
                        FROM members
                        JOIN messages
                        ON members.id = messages.member
                        WHERE members.system = @System
                        GROUP BY messages.member",
                    new { System = system.Id });
        }

        public async Task<int> GetSystemMemberCount(PKSystem system)
        {
            using (var conn = await _conn.Obtain())
                return await conn.ExecuteScalarAsync<int>("select count(*) from members where system = @Id", system);
        }

        public async Task<ulong> GetTotalMembers()
        {
            using (var conn = await _conn.Obtain())
                return await conn.ExecuteScalarAsync<ulong>("select count(id) from members");
        }
        public async Task AddMessage(ulong senderId, ulong messageId, ulong channelId, ulong originalMessage, PKMember member) {
            using (var conn = await _conn.Obtain())
                await conn.ExecuteAsync("insert into messages(mid, channel, member, sender, original_mid) values(@MessageId, @ChannelId, @MemberId, @SenderId, @OriginalMid)", new {
                    MessageId = messageId,
                    ChannelId = channelId,
                    MemberId = member.Id,
                    SenderId = senderId,
                    OriginalMid = originalMessage
                });

            _logger.Information("Stored message {Message} in channel {Channel}", messageId, channelId);
        }

        public async Task<FullMessage> GetMessage(ulong id)
        {
            using (var conn = await _conn.Obtain())
                return (await conn.QueryAsync<PKMessage, PKMember, PKSystem, FullMessage>("select messages.*, members.*, systems.* from messages, members, systems where (mid = @Id or original_mid = @Id) and messages.member = members.id and systems.id = members.system", (msg, member, system) => new FullMessage
                {
                    Message = msg,
                    System = system,
                    Member = member
                }, new { Id = id })).FirstOrDefault();
        }

        public async Task DeleteMessage(ulong id) {
            using (var conn = await _conn.Obtain())
                if (await conn.ExecuteAsync("delete from messages where mid = @Id", new { Id = id }) > 0)
                    _logger.Information("Deleted message {Message}", id);
        }

        public async Task DeleteMessagesBulk(IEnumerable<ulong> ids)
        {
            using (var conn = await _conn.Obtain())
            {
                // Npgsql doesn't support ulongs in general - we hacked around it for plain ulongs but tbh not worth it for collections of ulong
                // Hence we map them to single longs, which *are* supported (this is ok since they're Technically (tm) stored as signed longs in the db anyway)
                var foundCount = await conn.ExecuteAsync("delete from messages where mid = any(@Ids)", new {Ids = ids.Select(id => (long) id).ToArray()});
                if (foundCount > 0)
                    _logger.Information("Bulk deleted messages {Messages}, {FoundCount} found", ids, foundCount);
            }
        }

        public async Task<ulong> GetTotalMessages()
        {
            using (var conn = await _conn.Obtain())
                return await conn.ExecuteScalarAsync<ulong>("select count(mid) from messages");
        }

        public async Task<GuildConfig> GetGuildConfig(ulong guild)
        {
            using (var conn = await _conn.Obtain())
            {
                var cfg = await conn.QuerySingleOrDefaultAsync<GuildConfig>("select * from servers where id = @Id",
                    new {Id = guild});

                if (cfg.Id == 0)
                    // No entry was found in the db, this is the default entry returned
                    cfg.Id = guild;
                
                return cfg;
            }
        }

        public async Task SaveGuildConfig(GuildConfig cfg)
        {
            using (var conn = await _conn.Obtain())
                await conn.ExecuteAsync("insert into servers (id, log_channel) values (@Id, @LogChannel) on conflict (id) do update set log_channel = @LogChannel", cfg);
            _logger.Information("Updated guild configuration {@GuildCfg}", cfg);
        }

        public async Task AddSwitch(PKSystem system, IEnumerable<PKMember> members)
        {
            // Use a transaction here since we're doing multiple executed commands in one
            using (var conn = await _conn.Obtain())
            using (var tx = conn.BeginTransaction())
            {
                // First, we insert the switch itself
                var sw = await conn.QuerySingleAsync<PKSwitch>("insert into switches(system) values (@System) returning *",
                    new {System = system.Id});

                // Then we insert each member in the switch in the switch_members table
                // TODO: can we parallelize this or send it in bulk somehow?
                foreach (var member in members)
                {
                    await conn.ExecuteAsync(
                        "insert into switch_members(switch, member) values(@Switch, @Member)",
                        new {Switch = sw.Id, Member = member.Id});
                }

                // Finally we commit the tx, since the using block will otherwise rollback it
                tx.Commit();

                _logger.Information("Registered switch {Switch} in system {System} with members {@Members}", sw.Id, system.Id, members.Select(m => m.Id));
            }
        }

        public async Task AddSwitchesBulk(PKSystem system, IEnumerable<ImportedSwitch> switches)
        {
            // Read existing switches to enforce unique timestamps
            var priorSwitches = await GetSwitches(system);
            var lastSwitchId = priorSwitches.Any()
                ? priorSwitches.Max(x => x.Id)
                : 0;
            
            using (var conn = (PerformanceTrackingConnection) await _conn.Obtain())
            {
                using (var tx = conn.BeginTransaction())
                {
                    // Import switches in bulk
                    using (var importer = conn.BeginBinaryImport("COPY switches (system, timestamp) FROM STDIN (FORMAT BINARY)"))
                    {
                        foreach (var sw in switches)
                        {
                            // If there's already a switch at this time, move on
                            if (priorSwitches.Any(x => x.Timestamp.Equals(sw.Timestamp)))
                                continue;

                            // Otherwise, add it to the importer
                            importer.StartRow();
                            importer.Write(system.Id, NpgsqlTypes.NpgsqlDbType.Integer);
                            importer.Write(sw.Timestamp, NpgsqlTypes.NpgsqlDbType.Timestamp);
                        }
                        importer.Complete(); // Commits the copy operation so dispose won't roll it back
                    }

                    // Get all switches that were created above and don't have members for ID lookup
                    var switchesWithoutMembers =
                        await conn.QueryAsync<PKSwitch>(@"
                        SELECT switches.*
                        FROM switches
                        LEFT JOIN switch_members
                        ON switch_members.switch = switches.id
                        WHERE switches.id > @LastSwitchId
                        AND switches.system = @System
                        AND switch_members.id IS NULL", new { LastSwitchId = lastSwitchId, System = system.Id });

                    // Import switch_members in bulk
                    using (var importer = conn.BeginBinaryImport("COPY switch_members (switch, member) FROM STDIN (FORMAT BINARY)"))
                    {
                        // Iterate over the switches we created above and set their members
                        foreach (var pkSwitch in switchesWithoutMembers)
                        {
                            // If this isn't in our import set, move on
                            var sw = switches.Select(x => (ImportedSwitch?) x).FirstOrDefault(x => x.Value.Timestamp.Equals(pkSwitch.Timestamp));
                            if (sw == null)
                                continue;

                            // Loop through associated members to add each to the switch
                            foreach (var m in sw.Value.Members)
                            {
                                // Skip switch-outs - these don't have switch_members
                                if (m == null)
                                    continue;
                                importer.StartRow();
                                importer.Write(pkSwitch.Id, NpgsqlTypes.NpgsqlDbType.Integer);
                                importer.Write(m.Id, NpgsqlTypes.NpgsqlDbType.Integer);
                            }
                        }
                        importer.Complete(); // Commits the copy operation so dispose won't roll it back
                    }
                    tx.Commit();
                }
            }

            _logger.Information("Completed bulk import of switches for system {0}", system.Hid);
        }
        
        public async Task<IEnumerable<PKSwitch>> GetSwitches(PKSystem system, int count = 9999999)
        {
            // TODO: refactor the PKSwitch data structure to somehow include a hydrated member list
            // (maybe when we get caching in?)
            using (var conn = await _conn.Obtain())
                return await conn.QueryAsync<PKSwitch>("select * from switches where system = @System order by timestamp desc limit @Count", new {System = system.Id, Count = count});
        }

        public async Task<IEnumerable<SwitchMembersListEntry>> GetSwitchMembersList(PKSystem system, Instant start, Instant end)
        {
            // Wrap multiple commands in a single transaction for performance
            using (var conn = await _conn.Obtain())
            using (var tx = conn.BeginTransaction())
            {
                // Find the time of the last switch outside the range as it overlaps the range
                // If no prior switch exists, the lower bound of the range remains the start time
                var lastSwitch = await conn.QuerySingleOrDefaultAsync<Instant>(
                    @"SELECT COALESCE(MAX(timestamp), @Start)
                        FROM switches
                        WHERE switches.system = @System
                        AND switches.timestamp < @Start",
                    new { System = system.Id, Start = start });

                // Then collect the time and members of all switches that overlap the range
                var switchMembersEntries = await conn.QueryAsync<SwitchMembersListEntry>(
                    @"SELECT switch_members.member, switches.timestamp
                        FROM switches
                        LEFT JOIN switch_members
                        ON switches.id = switch_members.switch
                        WHERE switches.system = @System
                        AND (
	                        switches.timestamp >= @Start
	                        OR switches.timestamp = @LastSwitch
                        )
                        AND switches.timestamp < @End
                        ORDER BY switches.timestamp DESC",
                    new { System = system.Id, Start = start, End = end, LastSwitch = lastSwitch });

                // Commit and return the list
                tx.Commit();
                return switchMembersEntries;
            }
        }

        public async Task<IEnumerable<PKMember>> GetSwitchMembers(PKSwitch sw)
        {
            using (var conn = await _conn.Obtain())
                return await conn.QueryAsync<PKMember>(
                    "select * from switch_members, members where switch_members.member = members.id and switch_members.switch = @Switch order by switch_members.id",
                    new {Switch = sw.Id});
        }

        public async Task<PKSwitch> GetLatestSwitch(PKSystem system) => (await GetSwitches(system, 1)).FirstOrDefault();

        public async Task MoveSwitch(PKSwitch sw, Instant time)
        {
            using (var conn = await _conn.Obtain())
                await conn.ExecuteAsync("update switches set timestamp = @Time where id = @Id",
                    new {Time = time, Id = sw.Id});

            _logger.Information("Moved switch {Switch} to {Time}", sw.Id, time);
        }

        public async Task DeleteSwitch(PKSwitch sw)
        {
            using (var conn = await _conn.Obtain())
                await conn.ExecuteAsync("delete from switches where id = @Id", new {Id = sw.Id});

            _logger.Information("Deleted switch {Switch}");
        }

        public async Task<ulong> GetTotalSwitches()
        {
            using (var conn = await _conn.Obtain())
                return await conn.ExecuteScalarAsync<ulong>("select count(id) from switches");
        }

        public async Task<IEnumerable<SwitchListEntry>> GetPeriodFronters(PKSystem system, Instant periodStart, Instant periodEnd)
        {
            // Returns the timestamps and member IDs of switches overlapping the range, in chronological (newest first) order
            var switchMembers = await GetSwitchMembersList(system, periodStart, periodEnd);

            // query DB for all members involved in any of the switches above and collect into a dictionary for future use
            // this makes sure the return list has the same instances of PKMember throughout, which is important for the dictionary
            // key used in GetPerMemberSwitchDuration below
            Dictionary<int, PKMember> memberObjects;
            using (var conn = await _conn.Obtain())
            {
                memberObjects = (
                    await conn.QueryAsync<PKMember>(
                        "select * from members where id = any(@Switches)", // lol postgres specific `= any()` syntax
                        new { Switches = switchMembers.Select(m => m.Member).Distinct().ToList() })
                    ).ToDictionary(m => m.Id);
            }

            // Initialize entries - still need to loop to determine the TimespanEnd below
            var entries =
                from item in switchMembers
                group item by item.Timestamp into g
                select new SwitchListEntry
                {
                    TimespanStart = g.Key,
                    Members = g.Where(x => x.Member != 0).Select(x => memberObjects[x.Member]).ToList()
                };

            // Loop through every switch that overlaps the range and add it to the output list
            // end time is the *FOLLOWING* switch's timestamp - we cheat by working backwards from the range end, so no dates need to be compared
            var endTime = periodEnd;
            var outList = new List<SwitchListEntry>();
            foreach (var e in entries)
            {
                // Override the start time of the switch if it's outside the range (only true for the "out of range" switch we included above)
                var switchStartClamped = e.TimespanStart < periodStart
                    ? periodStart
                    : e.TimespanStart;

                outList.Add(new SwitchListEntry
                {
                    Members = e.Members,
                    TimespanStart = switchStartClamped,
                    TimespanEnd = endTime
                });

                // next switch's end is this switch's start (we're working backward in time)
                endTime = e.TimespanStart;
            }

            return outList;
        }
        public async Task<FrontBreakdown> GetFrontBreakdown(PKSystem system, Instant periodStart, Instant periodEnd)
        {
            var dict = new Dictionary<PKMember, Duration>();

            var noFronterDuration = Duration.Zero;

            // Sum up all switch durations for each member
            // switches with multiple members will result in the duration to add up to more than the actual period range

            var actualStart = periodEnd; // will be "pulled" down
            var actualEnd = periodStart; // will be "pulled" up

            foreach (var sw in await GetPeriodFronters(system, periodStart, periodEnd))
            {
                var span = sw.TimespanEnd - sw.TimespanStart;
                foreach (var member in sw.Members)
                {
                    if (!dict.ContainsKey(member)) dict.Add(member, span);
                    else dict[member] += span;
                }

                if (sw.Members.Count == 0) noFronterDuration += span;

                if (sw.TimespanStart < actualStart) actualStart = sw.TimespanStart;
                if (sw.TimespanEnd > actualEnd) actualEnd = sw.TimespanEnd;
            }

            return new FrontBreakdown
            {
                MemberSwitchDurations = dict,
                NoFronterDuration = noFronterDuration,
                RangeStart = actualStart,
                RangeEnd = actualEnd
            };
        }
    }
}