// <copyright file="CastleSiegeContext.cs" company="MUnique">
// Licensed under the MIT License. See LICENSE file in the project root for full license information.
// </copyright>

namespace MUnique.OpenMU.GameLogic.CastleSiege;

using MUnique.OpenMU.DataModel.Configuration;

/// <summary>
/// In-memory Castle Siege state machine and battle contention.
/// Time is injected via method parameters so it can be tested deterministically.
/// <para>
/// The cycle uses the original Season 6 <see cref="CastleSiegeState"/> values, which are exactly the values
/// the game client expects (see <c>CASTLESIEGE_STATE</c> in the client's <c>WSclient.h</c>). AdaMu drives only
/// a subset of them, because it registers guilds directly and has no Mark of Lord step:
/// </para>
/// <code>
/// Idle1(0) -> RegisterGuild(1) -> Ready(6) -> Start(7) -> End(8) -> EndCycle(9) -> Idle1(0)
/// </code>
/// <para>
/// The skipped states (<see cref="CastleSiegeState.Idle2"/>, <see cref="CastleSiegeState.RegisterMark"/>,
/// <see cref="CastleSiegeState.Idle3"/>, <see cref="CastleSiegeState.Notify"/>) keep their numbers so the
/// client stays compatible; the server simply never enters them.
/// </para>
/// <para>
/// Guilds are identified by their persistent <see cref="Guid"/>, not by name. A guild rename (or a delete and
/// re-create under the same name) therefore can no longer transfer castle ownership to the wrong guild. Names
/// are carried alongside purely for display and for the packets that send a name to the client.
/// </para>
/// Battle rule: attackers must destroy all castle defenses (gates + guardian statues) and then hold BOTH
/// Crown Switches at the same time — the switches are held by standing on them (evaluated per tick by the
/// plugin), and once both are held by one guild with the defenses down, that guild captures the throne.
/// The throne holder when the siege ends becomes the castle owner.
/// </summary>
public class CastleSiegeContext
{
    /// <summary>The Crown Switch NPC numbers on Valley of Loren; both must be held to take the throne.</summary>
    public static readonly short[] SwitchNumbers = { 217, 218 };

    private readonly Dictionary<Guid, string> _registeredGuilds = new();
    private readonly Dictionary<short, Guid?> _switchHolders = new() { { 217, null }, { 218, null } };
    private DateTime _stateStartedUtc;
    private Guid? _occupier;
    private string? _occupierName;
    private int _defensesRemaining;
    private bool _dirty;
    private Guid? _crownHoldGuild;
    private DateTime? _crownHoldStartUtc;
    private bool _lastShieldDown;

    /// <summary>Initializes a new instance of the <see cref="CastleSiegeContext"/> class.</summary>
    /// <param name="configuration">The cycle timing configuration.</param>
    public CastleSiegeContext(CastleSiegeSettings configuration)
    {
        this.Configuration = configuration;
        this.State = CastleSiegeState.Idle1;
    }

    /// <summary>Raised after the state changes. Argument is the new state.</summary>
    public event Action<CastleSiegeState>? StateChanged;

    /// <summary>Gets the configuration (durations + schedule). Refreshed each tick from the live plugin config
    /// so AdminPanel edits take effect without a restart.</summary>
    public CastleSiegeSettings Configuration { get; private set; }

    /// <summary>Gets the current state.</summary>
    public CastleSiegeState State { get; private set; }

    /// <summary>Gets the UTC time the current state started (used for persistence/restore).</summary>
    public DateTime StateStartedUtc => this._stateStartedUtc;

    /// <summary>Gets the persistent identifier of the owner guild, or <see langword="null"/> if unowned.</summary>
    public Guid? OwnerGuildId { get; private set; }

    /// <summary>Gets the owner guild's name for display and client packets, or null.</summary>
    public string? OwnerGuildName { get; private set; }

    /// <summary>Gets the guild currently holding the throne during the siege, or null.</summary>
    public Guid? OccupierGuildId => this._occupier;

    /// <summary>Gets the throne holder's name for display and client packets, or null.</summary>
    public string? OccupierGuildName => this._occupierName;

    /// <summary>Gets the number of castle defenses (gates + statues) still standing; the throne needs 0.</summary>
    public int DefensesRemaining => this._defensesRemaining;

    /// <summary>Gets the persistent identifiers of the guilds registered for the current cycle.</summary>
    public IReadOnlyCollection<Guid> RegisteredGuildIds => this._registeredGuilds.Keys;

    /// <summary>Gets the names of the guilds registered for the current cycle (display only).</summary>
    public IReadOnlyCollection<string> RegisteredGuildNames => this._registeredGuilds.Values;

    /// <summary>Gets a value indicating whether the siege battle is currently running.</summary>
    public bool IsSiegeRunning => this.State == CastleSiegeState.Start;

    /// <summary>Points the context at the current (possibly AdminPanel-edited) plugin configuration.</summary>
    /// <param name="configuration">The live configuration.</param>
    public void UpdateConfiguration(CastleSiegeSettings configuration) => this.Configuration = configuration;

    /// <summary>Returns whether the given guild is registered for the current cycle.</summary>
    /// <param name="guildId">The persistent guild identifier.</param>
    public bool IsRegistered(Guid guildId) => this._registeredGuilds.ContainsKey(guildId);

    /// <summary>Advances the state machine based on the current time.</summary>
    /// <param name="now">The current UTC time.</param>
    public ValueTask TickAsync(DateTime now)
    {
        switch (this.State)
        {
            case CastleSiegeState.Idle1:
                if (this.Configuration.IsRegistrationOpenTime(now))
                {
                    return this.ForceStartRegistrationAsync(now);
                }

                break;
            case CastleSiegeState.RegisterGuild:
                if (now >= this._stateStartedUtc + this.Configuration.RegistrationDuration)
                {
                    return this.TransitionAsync(CastleSiegeState.Ready, now);
                }

                break;
            case CastleSiegeState.Ready:
                if (now >= this._stateStartedUtc + this.Configuration.PreparationDuration)
                {
                    return this.TransitionAsync(CastleSiegeState.Start, now);
                }

                break;
            case CastleSiegeState.Start:
                if (now >= this._stateStartedUtc + this.Configuration.SiegeDuration)
                {
                    return this.TransitionAsync(CastleSiegeState.End, now);
                }

                break;
            case CastleSiegeState.End:
                // Winner = guild holding the throne at siege end. If none captured, owner unchanged.
                if (this._occupier is { } occupier)
                {
                    this.SetOwner(occupier, this._occupierName);
                }

                this.ClearBattleState();
                return this.TransitionAsync(CastleSiegeState.EndCycle, now);
            case CastleSiegeState.EndCycle:
                return this.TransitionAsync(CastleSiegeState.Idle1, now);
            default:
                break;
        }

        return ValueTask.CompletedTask;
    }

    /// <summary>Admin: forces the cycle into guild registration now (from any state).</summary>
    /// <param name="now">The current UTC time.</param>
    public ValueTask ForceStartRegistrationAsync(DateTime now)
    {
        this._registeredGuilds.Clear();
        this.ClearBattleState();
        return this.TransitionAsync(CastleSiegeState.RegisterGuild, now);
    }

    /// <summary>Admin: forces a specific state now.</summary>
    /// <param name="state">The target state.</param>
    /// <param name="now">The current UTC time.</param>
    public ValueTask ForceStateAsync(CastleSiegeState state, DateTime now)
        => this.TransitionAsync(state, now);

    /// <summary>Admin: resets to the idle (resting) state and clears registrations/battle state.</summary>
    /// <param name="now">The current UTC time.</param>
    public ValueTask ResetAsync(DateTime now)
    {
        this._registeredGuilds.Clear();
        this.ClearBattleState();
        return this.TransitionAsync(CastleSiegeState.Idle1, now);
    }

    /// <summary>Registers a guild for the current cycle. No-op outside the registration state.</summary>
    /// <param name="guildId">The persistent guild identifier.</param>
    /// <param name="guildName">The guild name, for display.</param>
    public void RegisterGuild(Guid guildId, string guildName)
    {
        if (this.State == CastleSiegeState.RegisterGuild
            && this._registeredGuilds.TryAdd(guildId, guildName))
        {
            this._dirty = true;
        }
    }

    /// <summary>Admin: sets (or clears) the current owner guild.</summary>
    /// <param name="guildId">The owner guild identifier, or null to clear.</param>
    /// <param name="guildName">The owner guild name, or null.</param>
    public void SetOwner(Guid? guildId, string? guildName)
    {
        this.OwnerGuildId = guildId;
        this.OwnerGuildName = guildId is null ? null : guildName;
        this._dirty = true;
    }

    /// <summary>
    /// Mirrors the shared castle owner loaded from the database. Used on game servers that do NOT host the
    /// siege, so their hunting-map gate and castle flag still reflect the current owner. Does not mark the
    /// state dirty (these servers never persist).
    /// </summary>
    /// <param name="guildId">The owner guild identifier, or null.</param>
    /// <param name="guildName">The owner guild name, or null.</param>
    public void SyncOwner(Guid? guildId, string? guildName)
    {
        this.OwnerGuildId = guildId;
        this.OwnerGuildName = guildId is null ? null : guildName;
    }

    /// <summary>
    /// Sets the auto-open schedule (days of week + UTC time) into the configuration and marks the state
    /// dirty for persistence. Empty days disables auto-start (manual only). The configuration is the single
    /// source of truth, so this is equivalent to editing the plugin config in the AdminPanel.
    /// </summary>
    /// <param name="days">The days of week registration should auto-open.</param>
    /// <param name="time">The UTC time of day registration should auto-open, or null to disable.</param>
    public void SetSchedule(IEnumerable<DayOfWeek> days, TimeOnly? time)
    {
        var orderedDays = days.Distinct().OrderBy(d => d).ToList();
        this.Configuration.RegistrationOpenDays = orderedDays;
        this.Configuration.RegistrationOpenTimes = orderedDays.Count > 0 && time is { } t
            ? new List<TimeOnly> { t }
            : new List<TimeOnly>();
        this._dirty = true;
    }

    /// <summary>
    /// Returns how much time is left in the running siege battle (the on-map countdown value), or
    /// <see cref="TimeSpan.Zero"/> when the siege is not currently running.
    /// </summary>
    /// <param name="nowUtc">The current UTC time.</param>
    public TimeSpan GetRemainingSiegeTime(DateTime nowUtc)
    {
        if (!this.IsSiegeRunning)
        {
            return TimeSpan.Zero;
        }

        var remaining = (this._stateStartedUtc + this.Configuration.SiegeDuration) - nowUtc;
        return remaining > TimeSpan.Zero ? remaining : TimeSpan.Zero;
    }

    /// <summary>
    /// Returns how much time is left in the current state, or <see cref="TimeSpan.Zero"/> when the state has
    /// no duration (idle states wait for an admin command or the auto-open time).
    /// </summary>
    /// <param name="nowUtc">The current UTC time.</param>
    public TimeSpan GetRemainingStateTime(DateTime nowUtc)
    {
        var duration = this.State switch
        {
            CastleSiegeState.RegisterGuild => this.Configuration.RegistrationDuration,
            CastleSiegeState.Ready => this.Configuration.PreparationDuration,
            CastleSiegeState.Start => this.Configuration.SiegeDuration,
            _ => TimeSpan.Zero,
        };

        if (duration == TimeSpan.Zero)
        {
            return TimeSpan.Zero;
        }

        var remaining = (this._stateStartedUtc + duration) - nowUtc;
        return remaining > TimeSpan.Zero ? remaining : TimeSpan.Zero;
    }

    /// <summary>
    /// Returns the guild that currently holds BOTH crown switches while all castle defenses are down (so the
    /// crown's shield is dropped for them), or null. Only meaningful during the siege.
    /// </summary>
    public Guid? GetShieldEligibleGuild()
    {
        if (!this.IsSiegeRunning || this._defensesRemaining > 0)
        {
            return null;
        }

        var holder = this._switchHolders[217];
        return holder is not null && holder == this._switchHolders[218] ? holder : null;
    }

    /// <summary>
    /// Advances the crown-hold capture. <paramref name="eligibleGuild"/> is the guild with both switches held
    /// and no defenses left (shield down); <paramref name="masterHolding"/> is whether that guild's master is
    /// standing on the crown. Captures the throne for the guild once it has held for <paramref name="holdDuration"/>.
    /// Losing a switch or the master leaving the crown resets the hold (contestable until the siege ends).
    /// </summary>
    /// <param name="eligibleGuild">The guild with both switches and no defenses, or null.</param>
    /// <param name="eligibleGuildName">That guild's name, for display.</param>
    /// <param name="masterHolding">Whether that guild's master is on the crown.</param>
    /// <param name="now">The current UTC time.</param>
    /// <param name="holdDuration">How long the master must hold to capture.</param>
    public CrownTickResult TickCrownHold(Guid? eligibleGuild, string? eligibleGuildName, bool masterHolding, DateTime now, TimeSpan holdDuration)
    {
        var shieldDown = this.IsSiegeRunning && eligibleGuild is not null;
        var shieldChanged = shieldDown != this._lastShieldDown;
        this._lastShieldDown = shieldDown;

        if (!this.IsSiegeRunning)
        {
            this._crownHoldGuild = null;
            this._crownHoldStartUtc = null;
            return new CrownTickResult(false, shieldChanged, CrownEvent.None, null, null);
        }

        var wasHolding = this._crownHoldGuild is not null;

        // The guild that already occupies the throne just holds it — no re-registration (avoids a capture loop).
        // Only a DIFFERENT guild taking both switches can register/capture (contest).
        var canCapture = eligibleGuild is not null && eligibleGuild != this._occupier;

        if (!canCapture || !masterHolding)
        {
            this._crownHoldGuild = null;
            this._crownHoldStartUtc = null;
            return new CrownTickResult(shieldDown, shieldChanged, wasHolding ? CrownEvent.HoldReset : CrownEvent.None, null, null);
        }

        if (this._crownHoldGuild != eligibleGuild || this._crownHoldStartUtc is null)
        {
            this._crownHoldGuild = eligibleGuild;
            this._crownHoldStartUtc = now;
            return new CrownTickResult(shieldDown, shieldChanged, CrownEvent.HoldStarted, eligibleGuild, eligibleGuildName);
        }

        if (now - this._crownHoldStartUtc.Value >= holdDuration)
        {
            this._occupier = eligibleGuild;
            this._occupierName = eligibleGuildName;
            this._crownHoldGuild = null;
            this._crownHoldStartUtc = null;
            this._dirty = true;
            return new CrownTickResult(shieldDown, shieldChanged, CrownEvent.Captured, eligibleGuild, eligibleGuildName);
        }

        return new CrownTickResult(shieldDown, shieldChanged, CrownEvent.None, eligibleGuild, eligibleGuildName);
    }

    /// <summary>
    /// Returns whether the persistable state changed since the last call, resetting the flag.
    /// Called each tick by the plugin to decide whether to write state to the database.
    /// </summary>
    public bool ConsumeDirty()
    {
        var dirty = this._dirty;
        this._dirty = false;
        return dirty;
    }

    /// <summary>
    /// Restores persisted state on startup (owner, state, state-start, registrations) directly, without
    /// firing <see cref="StateChanged"/> or marking the state dirty. Battle state stays cleared.
    /// </summary>
    /// <param name="ownerGuildId">The persisted owner guild identifier, or null.</param>
    /// <param name="ownerGuildName">The persisted owner guild name, or null.</param>
    /// <param name="state">The persisted state.</param>
    /// <param name="stateStartedUtc">When the persisted state started (UTC), or null to keep the default.</param>
    /// <param name="registeredGuilds">The persisted registrations (id to name), or null.</param>
    public void RestoreState(Guid? ownerGuildId, string? ownerGuildName, CastleSiegeState state, DateTime? stateStartedUtc, IEnumerable<KeyValuePair<Guid, string>>? registeredGuilds)
    {
        this.OwnerGuildId = ownerGuildId;
        this.OwnerGuildName = ownerGuildId is null ? null : ownerGuildName;
        this.State = state;
        this._stateStartedUtc = stateStartedUtc ?? this._stateStartedUtc;
        this._registeredGuilds.Clear();
        if (registeredGuilds is not null)
        {
            foreach (var registration in registeredGuilds)
            {
                this._registeredGuilds[registration.Key] = registration.Value;
            }
        }

        this._dirty = false;
    }

    /// <summary>Sets how many castle defenses (gates + guardian statues) exist this siege (when spawned).</summary>
    /// <param name="count">The defense count.</param>
    public void SetDefenseCount(int count) => this._defensesRemaining = count > 0 ? count : 0;

    /// <summary>Notifies that a castle defense (gate/statue) was destroyed. Lowers the remaining count (min 0).</summary>
    public void NotifyDefenseDestroyed()
    {
        if (this._defensesRemaining > 0)
        {
            this._defensesRemaining--;
        }
    }

    /// <summary>
    /// Sets which guild is currently standing on (holding) a Crown Switch. Called every tick by the plugin
    /// based on player positions. Pass <c>null</c> when no registered member stands on it. No-op outside the siege.
    /// </summary>
    /// <param name="switchNumber">The Crown Switch NPC number (217 or 218).</param>
    /// <param name="guildId">The holding guild's persistent identifier, or null.</param>
    public void SetSwitchHolder(short switchNumber, Guid? guildId)
    {
        if (this.IsSiegeRunning && this._switchHolders.ContainsKey(switchNumber))
        {
            this._switchHolders[switchNumber] = guildId;
        }
    }

    /// <summary>
    /// Attempts to capture the throne for a guild (called when a member registers at the Sinior/Crown NPC).
    /// Succeeds only during the siege when the throne is free, all castle defenses are destroyed, and the
    /// guild is currently holding BOTH Crown Switches (a member standing on each).
    /// </summary>
    /// <param name="guildId">The capturing guild's persistent identifier.</param>
    /// <param name="guildName">The capturing guild's name, for display.</param>
    /// <returns>Whether it succeeded and a human-readable reason/result message.</returns>
    public (bool Success, string Reason) TryCaptureThrone(Guid guildId, string guildName)
    {
        if (!this.IsSiegeRunning)
        {
            return (false, "The siege is not running.");
        }

        if (this._occupier is { } occupier)
        {
            return (false, occupier == guildId
                ? "Your guild already holds the throne."
                : $"The throne is already held by '{this._occupierName ?? occupier.ToString()}'.");
        }

        if (this._defensesRemaining > 0)
        {
            return (false, $"Destroy the castle defenses first ({this._defensesRemaining} remaining).");
        }

        if (this._switchHolders[217] != guildId || this._switchHolders[218] != guildId)
        {
            return (false, "Your guild must be holding BOTH Crown Switches at once (stand a member on each).");
        }

        this._occupier = guildId;
        this._occupierName = guildName;
        this._dirty = true;
        return (true, "throne captured");
    }

    /// <summary>Returns a human-readable status summary for admin display.</summary>
    public string GetStatusText()
        => $"CS state={this.State}({(int)this.State}), owner={this.OwnerGuildName ?? "(none)"}, "
           + $"registered={this._registeredGuilds.Count} [{string.Join(", ", this._registeredGuilds.Values)}], "
           + $"defenses={this._defensesRemaining}, throne={this._occupierName ?? "(none)"}, "
           + $"switch217={this.DescribeSwitch(217)}, switch218={this.DescribeSwitch(218)}";

    private string DescribeSwitch(short switchNumber)
        => this._switchHolders[switchNumber] is { } holder
            ? (this._registeredGuilds.TryGetValue(holder, out var name) ? name : holder.ToString())
            : "-";

    private void ClearBattleState()
    {
        this._switchHolders[217] = null;
        this._switchHolders[218] = null;
        this._defensesRemaining = 0;
        this._occupier = null;
        this._occupierName = null;
        this._crownHoldGuild = null;
        this._crownHoldStartUtc = null;
        this._lastShieldDown = false;
    }

    private ValueTask TransitionAsync(CastleSiegeState state, DateTime now)
    {
        this.State = state;
        this._stateStartedUtc = now;
        this._dirty = true;
        this.StateChanged?.Invoke(state);
        return ValueTask.CompletedTask;
    }
}

/// <summary>The event produced by a single <see cref="CastleSiegeContext.TickCrownHold"/> call.</summary>
public enum CrownEvent
{
    /// <summary>Nothing changed this tick.</summary>
    None,

    /// <summary>A guild master just started holding the crown (start the client countdown).</summary>
    HoldStarted,

    /// <summary>The crown was held long enough — the guild captured the throne.</summary>
    Captured,

    /// <summary>An in-progress hold was interrupted (switch lost or master left the crown).</summary>
    HoldReset,
}

/// <summary>The result of a crown-hold tick: the shield state and any event that occurred.</summary>
/// <param name="ShieldDown">Whether the crown shield is currently down (both switches held, defenses cleared).</param>
/// <param name="ShieldChanged">Whether the shield state changed this tick (only then should the client be told).</param>
/// <param name="Event">The event that occurred this tick.</param>
/// <param name="GuildId">The guild the event refers to, if any.</param>
/// <param name="GuildName">That guild's name, for display and client packets.</param>
public readonly record struct CrownTickResult(bool ShieldDown, bool ShieldChanged, CrownEvent Event, Guid? GuildId, string? GuildName);