using System;
using System.Collections.Generic;
using System.Linq;
using AcDream.UI.Abstractions.Input;

namespace AcDream.UI.Abstractions.Panels.Settings;

/// <summary>
/// K.3 ViewModel for <see cref="SettingsPanel"/>. Owns a <b>draft</b>
/// copy of the current <see cref="KeyBindings"/>; rebinds modify the
/// draft. <see cref="Save"/> commits draft via the supplied callback
/// (which writes to disk + replaces the live dispatcher's table);
/// <see cref="Cancel"/> reverts the draft to the persisted state.
///
/// <para>
/// Click-to-rebind UX: caller invokes <see cref="BeginRebind"/> with the
/// action being rebound + the binding being replaced. The VM enters
/// modal capture on the dispatcher; when the user presses a chord (or
/// Esc), the dispatcher reports it via <see cref="OnChordCaptured"/>.
/// If the new chord conflicts with another action's binding (same
/// activation type), <see cref="PendingConflict"/> surfaces a prompt
/// the panel renders as Yes / No buttons; <see cref="ResolveConflict"/>
/// dispatches the user's choice.
/// </para>
/// </summary>
public sealed class SettingsVM
{
    private KeyBindings _persisted;
    private KeyBindings _draft;
    private readonly InputDispatcher _dispatcher;
    private readonly Action<KeyBindings> _onSave;

    // L.0 — Display tab. Treated as a single immutable record; mutation
    // through SetDisplay clones via with-expressions on the panel side.
    private DisplaySettings _displayPersisted;
    private DisplaySettings _displayDraft;
    private readonly Action<DisplaySettings> _onSaveDisplay;

    // L.0 — Audio tab. Same shape as Display.
    private AudioSettings _audioPersisted;
    private AudioSettings _audioDraft;
    private readonly Action<AudioSettings> _onSaveAudio;

    // L.0 — Gameplay tab (subset of retail CharacterOption flags).
    private GameplaySettings _gameplayPersisted;
    private GameplaySettings _gameplayDraft;
    private readonly Action<GameplaySettings> _onSaveGameplay;

    // L.0 — Chat tab (CharacterOptions2 channel filters + visual prefs).
    private ChatSettings _chatPersisted;
    private ChatSettings _chatDraft;
    private readonly Action<ChatSettings> _onSaveChat;

    // L.0 — Character tab (per-toon, host-keyed by toon name).
    private CharacterSettings _characterPersisted;
    private CharacterSettings _characterDraft;
    private readonly Action<CharacterSettings> _onSaveCharacter;

    /// <summary>The action currently being rebound, or null when idle.</summary>
    public InputAction? RebindInProgress { get; private set; }

    /// <summary>The original binding being replaced (so we can preserve
    /// activation type on the new chord and roll back on cancel).</summary>
    public Binding? RebindOriginal { get; private set; }

    /// <summary>The action+chord conflict pending confirmation, or null.
    /// Populated when <see cref="OnChordCaptured"/> finds the captured
    /// chord already bound to another action; cleared by
    /// <see cref="ResolveConflict"/>.</summary>
    public ConflictPrompt? PendingConflict { get; private set; }

    /// <summary>The current working draft. Panel renders bindings from
    /// here; mutates via the rebind / reset methods.</summary>
    public KeyBindings Draft => _draft;

    /// <summary>True iff the draft differs structurally from the
    /// persisted snapshot. Used to grey out the Save button when no
    /// rebinds are pending.</summary>
    public bool HasUnsavedChanges
        => !KeyBindingsEqual(_persisted, _draft)
           || _displayPersisted   != _displayDraft
           || _audioPersisted     != _audioDraft
           || _gameplayPersisted  != _gameplayDraft
           || _chatPersisted      != _chatDraft
           || _characterPersisted != _characterDraft;

    /// <summary>The current Display draft. Panel reads from here;
    /// mutation goes through <see cref="SetDisplay"/>.</summary>
    public DisplaySettings DisplayDraft => _displayDraft;

    /// <summary>The current Audio draft. Panel reads from here;
    /// mutation goes through <see cref="SetAudio"/>.</summary>
    public AudioSettings AudioDraft => _audioDraft;

    /// <summary>The current Gameplay draft. Panel reads from here;
    /// mutation goes through <see cref="SetGameplay"/>.</summary>
    public GameplaySettings GameplayDraft => _gameplayDraft;

    /// <summary>The current Chat draft. Panel reads from here;
    /// mutation goes through <see cref="SetChat"/>.</summary>
    public ChatSettings ChatDraft => _chatDraft;

    /// <summary>The current Character draft (per-toon — host owns the
    /// toon-name key). Panel reads from here; mutation goes through
    /// <see cref="SetCharacter"/>.</summary>
    public CharacterSettings CharacterDraft => _characterDraft;

    public SettingsVM(
        KeyBindings persisted,
        InputDispatcher dispatcher,
        Action<KeyBindings> onSave,
        DisplaySettings persistedDisplay,
        Action<DisplaySettings> onSaveDisplay,
        AudioSettings persistedAudio,
        Action<AudioSettings> onSaveAudio,
        GameplaySettings persistedGameplay,
        Action<GameplaySettings> onSaveGameplay,
        ChatSettings persistedChat,
        Action<ChatSettings> onSaveChat,
        CharacterSettings persistedCharacter,
        Action<CharacterSettings> onSaveCharacter)
    {
        _persisted          = persisted          ?? throw new ArgumentNullException(nameof(persisted));
        _dispatcher         = dispatcher         ?? throw new ArgumentNullException(nameof(dispatcher));
        _onSave             = onSave             ?? throw new ArgumentNullException(nameof(onSave));
        _displayPersisted   = persistedDisplay   ?? throw new ArgumentNullException(nameof(persistedDisplay));
        _onSaveDisplay      = onSaveDisplay      ?? throw new ArgumentNullException(nameof(onSaveDisplay));
        _audioPersisted     = persistedAudio     ?? throw new ArgumentNullException(nameof(persistedAudio));
        _onSaveAudio        = onSaveAudio        ?? throw new ArgumentNullException(nameof(onSaveAudio));
        _gameplayPersisted  = persistedGameplay  ?? throw new ArgumentNullException(nameof(persistedGameplay));
        _onSaveGameplay     = onSaveGameplay     ?? throw new ArgumentNullException(nameof(onSaveGameplay));
        _chatPersisted      = persistedChat      ?? throw new ArgumentNullException(nameof(persistedChat));
        _onSaveChat         = onSaveChat         ?? throw new ArgumentNullException(nameof(onSaveChat));
        _characterPersisted = persistedCharacter ?? throw new ArgumentNullException(nameof(persistedCharacter));
        _onSaveCharacter    = onSaveCharacter    ?? throw new ArgumentNullException(nameof(onSaveCharacter));
        _draft              = CloneBindings(persisted);
        _displayDraft       = persistedDisplay;
        _audioDraft         = persistedAudio;
        _gameplayDraft      = persistedGameplay;
        _chatDraft          = persistedChat;
        _characterDraft     = persistedCharacter;
    }

    /// <summary>
    /// Replace the entire Display draft with <paramref name="value"/>.
    /// Panel calls this with a <c>DisplayDraft with { Field = newValue }</c>
    /// so each widget edits exactly one field at a time.
    /// </summary>
    public void SetDisplay(DisplaySettings value)
    {
        _displayDraft = value ?? throw new ArgumentNullException(nameof(value));
    }

    /// <summary>
    /// Replace the entire Audio draft with <paramref name="value"/>.
    /// Live audio preview is achieved at the host layer by pushing
    /// <see cref="AudioDraft"/> into the running OpenAL engine each frame
    /// — this method only mutates VM state. Cancel reverts the draft and
    /// the host's next-frame push restores the pre-edit engine volumes.
    /// </summary>
    public void SetAudio(AudioSettings value)
    {
        _audioDraft = value ?? throw new ArgumentNullException(nameof(value));
    }

    /// <summary>
    /// Replace the entire Gameplay draft with <paramref name="value"/>.
    /// Local-only this phase — values persist on Save but don't yet
    /// flow to the server. When server-sync ships, the host's
    /// <c>onSaveGameplay</c> callback will marshal the draft into the
    /// retail <c>CharacterOption</c> wire bitmask.
    /// </summary>
    public void SetGameplay(GameplaySettings value)
    {
        _gameplayDraft = value ?? throw new ArgumentNullException(nameof(value));
    }

    /// <summary>
    /// Replace the entire Chat draft with <paramref name="value"/>.
    /// Local-only this phase — values persist on Save but the Hear*Chat
    /// flags affect client-side display filtering, not server-side
    /// channel subscriptions.
    /// </summary>
    public void SetChat(ChatSettings value)
    {
        _chatDraft = value ?? throw new ArgumentNullException(nameof(value));
    }

    /// <summary>
    /// Replace the entire Character draft with <paramref name="value"/>.
    /// Per-toon — the host knows which toon's bag we're editing because
    /// it owned the toonKey when constructing the VM.
    /// </summary>
    public void SetCharacter(CharacterSettings value)
    {
        _characterDraft = value ?? throw new ArgumentNullException(nameof(value));
    }

    /// <summary>
    /// Replace BOTH the persisted snapshot and the live draft for the
    /// Character bag. Used when the active toon changes (e.g. on
    /// EnterWorld with a non-default character) — the host loads that
    /// toon's settings from disk and pushes them into the VM here so
    /// <see cref="HasUnsavedChanges"/> doesn't flag the swap as a
    /// pending edit. Differs from <see cref="SetCharacter"/>, which
    /// updates draft only.
    /// </summary>
    public void LoadCharacterContext(CharacterSettings persisted)
    {
        _characterPersisted = persisted ?? throw new ArgumentNullException(nameof(persisted));
        _characterDraft     = persisted;
    }

    /// <summary>
    /// Begin rebinding <paramref name="action"/>. The supplied
    /// <paramref name="original"/> binding will be removed when the new
    /// chord is applied. The dispatcher enters modal capture mode; the
    /// next chord pressed (or Esc) feeds back into
    /// <see cref="OnChordCaptured"/>.
    /// </summary>
    public void BeginRebind(InputAction action, Binding original)
    {
        RebindInProgress = action;
        RebindOriginal   = original;
        _dispatcher.BeginCapture(OnChordCaptured);
    }

    private void OnChordCaptured(KeyChord chord)
    {
        // Sentinel: dispatcher reports default(KeyChord) on Esc cancel.
        if (chord.Equals(default(KeyChord)))
        {
            RebindInProgress = null;
            RebindOriginal   = null;
            return;
        }

        // Conflict check: scan the draft for a binding that matches the
        // captured chord + same activation type, but on a DIFFERENT
        // action. (Same-action bindings are fine — that's already in
        // _draft for this action and gets removed when we apply.)
        var existing = _draft.Find(chord, RebindOriginal!.Value.Activation);
        if (existing is not null && existing.Value.Action != RebindInProgress!.Value)
        {
            PendingConflict = new ConflictPrompt(
                NewAction: RebindInProgress.Value,
                NewChord: chord,
                OriginalBinding: RebindOriginal.Value,
                ConflictingAction: existing.Value.Action,
                ConflictingBinding: existing.Value);
            return;
        }

        ApplyRebind(chord);
    }

    /// <summary>
    /// Resolve a <see cref="PendingConflict"/>: <paramref name="replace"/>=
    /// true removes the conflicting binding and applies the new chord;
    /// false cancels the rebind entirely (original binding intact).
    /// </summary>
    public void ResolveConflict(bool replace)
    {
        if (PendingConflict is null) return;
        var c = PendingConflict.Value;
        if (replace)
        {
            _draft.Remove(c.ConflictingBinding);
            ApplyRebind(c.NewChord);
        }
        else
        {
            RebindInProgress = null;
            RebindOriginal   = null;
        }
        PendingConflict = null;
    }

    private void ApplyRebind(KeyChord chord)
    {
        _draft.Remove(RebindOriginal!.Value);
        _draft.Add(new Binding(chord, RebindInProgress!.Value, RebindOriginal.Value.Activation));
        RebindInProgress = null;
        RebindOriginal   = null;
    }

    /// <summary>
    /// Cancel any in-progress rebind / pending conflict and clear the
    /// dispatcher's capture state. Does NOT revert the draft — for that
    /// see <see cref="Cancel"/>.
    /// </summary>
    public void CancelRebind()
    {
        if (_dispatcher.IsCapturing) _dispatcher.CancelCapture();
        RebindInProgress = null;
        RebindOriginal   = null;
        PendingConflict  = null;
    }

    /// <summary>
    /// Restore the draft's bindings for <paramref name="action"/> to the
    /// retail defaults. Other actions' draft bindings are untouched.
    /// </summary>
    public void ResetActionToDefault(InputAction action)
    {
        var defaults = KeyBindings.RetailDefaults();
        foreach (var b in _draft.ForAction(action).ToList())
            _draft.Remove(b);
        foreach (var b in defaults.ForAction(action))
            _draft.Add(b);
    }

    /// <summary>
    /// Replace the keybinds draft with <see cref="KeyBindings.RetailDefaults"/>
    /// AND the display draft with <see cref="DisplaySettings.Default"/>.
    /// "Reset all" applies to every tab — it's the user's escape hatch
    /// when they've gotten lost.
    /// </summary>
    public void ResetAllToDefaults()
    {
        _draft          = KeyBindings.RetailDefaults();
        _displayDraft   = DisplaySettings.Default;
        _audioDraft     = AudioSettings.Default;
        _gameplayDraft  = GameplaySettings.Default;
        _chatDraft      = ChatSettings.Default;
        _characterDraft = CharacterSettings.Default;
    }

    /// <summary>
    /// Commit both keybinds + display drafts via the onSave callbacks
    /// supplied at construction. After save the drafts become the new
    /// persisted snapshots — <see cref="HasUnsavedChanges"/> resets to
    /// false. Each callback is invoked exactly once per Save; if the
    /// caller wants atomicity across both files it has to handle it
    /// outside the VM.
    /// </summary>
    public void Save()
    {
        _onSave(_draft);
        _onSaveDisplay(_displayDraft);
        _onSaveAudio(_audioDraft);
        _onSaveGameplay(_gameplayDraft);
        _onSaveChat(_chatDraft);
        _onSaveCharacter(_characterDraft);
        _persisted          = CloneBindings(_draft);
        _displayPersisted   = _displayDraft;
        _audioPersisted     = _audioDraft;
        _gameplayPersisted  = _gameplayDraft;
        _chatPersisted      = _chatDraft;
        _characterPersisted = _characterDraft;
    }

    /// <summary>
    /// Revert all drafts to their persisted snapshots and clear any
    /// in-flight rebind state. Used by the panel's "Cancel" button and
    /// when the user closes the settings window without saving.
    /// </summary>
    public void Cancel()
    {
        _draft          = CloneBindings(_persisted);
        _displayDraft   = _displayPersisted;
        _audioDraft     = _audioPersisted;
        _gameplayDraft  = _gameplayPersisted;
        _chatDraft      = _chatPersisted;
        _characterDraft = _characterPersisted;
        CancelRebind();
    }

    // ── helpers ───────────────────────────────────────────────────────

    private static KeyBindings CloneBindings(KeyBindings src)
    {
        var clone = new KeyBindings();
        foreach (var b in src.All) clone.Add(b);
        return clone;
    }

    private static bool KeyBindingsEqual(KeyBindings a, KeyBindings b)
    {
        if (a.All.Count != b.All.Count) return false;
        for (int i = 0; i < a.All.Count; i++)
            if (!a.All[i].Equals(b.All[i])) return false;
        return true;
    }
}

/// <summary>
/// K.3 conflict-prompt payload surfaced when the user binds a chord
/// already in use. The panel renders the <see cref="NewAction"/> +
/// <see cref="ConflictingAction"/> labels in a confirmation prompt;
/// <see cref="SettingsVM.ResolveConflict"/> dispatches the user's
/// answer.
/// </summary>
public readonly record struct ConflictPrompt(
    InputAction NewAction,
    KeyChord NewChord,
    Binding OriginalBinding,
    InputAction ConflictingAction,
    Binding ConflictingBinding);