using System;
using ADOFAIRenderer.Localization;
using TMPro;
using UnityEngine;

namespace ADOFAIRenderer.UI;

/// <summary>
/// Component that binds a TextMeshProUGUI component to a localization key or dynamic string provider,
/// automatically updating the displayed text whenever the active language changes.
/// <para>
/// The text is set when the binding is made (<see cref="Bind(TextMeshProUGUI, string)"/>), when the component is enabled,
/// and on every <see cref="LocalizationManager.OnLanguageChanged"/> event. A key and a dynamic provider are mutually
/// exclusive: setting one clears the other. With neither set, <see cref="Refresh"/> leaves the text unchanged.
/// Runs on the Unity main thread.
/// </para>
/// </summary>
internal class LocalizedText : MonoBehaviour
{
    /// <summary>Text component that receives the string; looked up on the same GameObject if not assigned by Bind.</summary>
    private TextMeshProUGUI? _textComponent;
    /// <summary>Localization key resolved through <see cref="LocalizationManager.Get(string)"/>; <c>null</c> when a provider is used.</summary>
    private string? _key;
    /// <summary>Function that returns the full text (already localized/formatted); <c>null</c> when a key is used.</summary>
    private Func<string>? _dynamicProvider;

    /// <summary>
    /// Gets or sets the localization key. Setting this will clear any dynamic provider and refresh the text immediately.
    /// A null or empty key leaves the current text as it is.
    /// </summary>
    public string? Key
    {
        get => _key;
        set
        {
            _key = value;
            _dynamicProvider = null;
            Refresh();
        }
    }

    /// <summary>
    /// Sets a dynamic string provider function, clears the key and refreshes the text immediately.
    /// The provider is called on every refresh (enable and language change), so it can combine several keys or
    /// runtime values, e.g. a label that depends on UI state.
    /// </summary>
    /// <param name="provider">Function returning the text to display; called on the Unity main thread.</param>
    public void SetDynamic(Func<string> provider)
    {
        _dynamicProvider = provider;
        _key = null;
        Refresh();
    }

    /// <summary>
    /// Finds the text component and subscribes to language changes. The subscription lasts until <see cref="OnDestroy"/>,
    /// also while the component is disabled (a refresh of a disabled object only changes its text).
    /// </summary>
    private void Awake()
    {
        EnsureComponent();
        LocalizationManager.OnLanguageChanged += HandleLanguageChanged;
    }

    /// <summary>Refreshes the text each time the component is enabled.</summary>
    private void OnEnable()
    {
        Refresh();
    }

    /// <summary>Unsubscribes from <see cref="LocalizationManager.OnLanguageChanged"/>.</summary>
    private void OnDestroy()
    {
        LocalizationManager.OnLanguageChanged -= HandleLanguageChanged;
    }

    /// <summary>Language change handler; the new language is read by <see cref="LocalizationManager.Get(string)"/>.</summary>
    private void HandleLanguageChanged(SystemLanguage language)
    {
        Refresh();
    }

    /// <summary>Assigns <see cref="_textComponent"/> from the same GameObject if it is not set yet.</summary>
    private void EnsureComponent()
    {
        if (_textComponent == null)
        {
            _textComponent = GetComponent<TextMeshProUGUI>();
        }
    }

    /// <summary>
    /// Refreshes the text using either the dynamic provider or the static localization key.
    /// The provider takes precedence; with neither set, or without a text component, nothing changes.
    /// A key that is missing in every locale is displayed as the key itself (see <see cref="LocalizationManager.Get(string)"/>).
    /// </summary>
    public void Refresh()
    {
        EnsureComponent();
        if (_textComponent == null) return;

        if (_dynamicProvider != null)
        {
            _textComponent.text = _dynamicProvider();
        }
        else if (!string.IsNullOrEmpty(_key))
        {
            _textComponent.text = LocalizationManager.Get(_key);
        }
    }

    /// <summary>
    /// Binds a TextMeshProUGUI component to a localization key.
    /// Reuses the <see cref="LocalizedText"/> already on the target's GameObject or adds one, then sets the key,
    /// which replaces any earlier binding and updates the text immediately.
    /// </summary>
    /// <param name="target">Text to localize.</param>
    /// <param name="key">Localization key, e.g. <c>"ui.render_config.codec"</c>.</param>
    /// <returns>The binding component.</returns>
    /// <exception cref="ArgumentNullException"><paramref name="target"/> is null.</exception>
    public static LocalizedText Bind(TextMeshProUGUI target, string key)
    {
        if (target == null) throw new ArgumentNullException(nameof(target));
        var component = target.GetComponent<LocalizedText>() ?? target.gameObject.AddComponent<LocalizedText>();
        component._textComponent = target;
        component.Key = key;
        return component;
    }

    /// <summary>
    /// Binds a TextMeshProUGUI component to a dynamic string provider function.
    /// Reuses or adds the component like <see cref="Bind(TextMeshProUGUI, string)"/> and updates the text immediately.
    /// </summary>
    /// <param name="target">Text to localize.</param>
    /// <param name="provider">Function returning the text; called on every refresh.</param>
    /// <returns>The binding component.</returns>
    /// <exception cref="ArgumentNullException"><paramref name="target"/> is null.</exception>
    public static LocalizedText Bind(TextMeshProUGUI target, Func<string> provider)
    {
        if (target == null) throw new ArgumentNullException(nameof(target));
        var component = target.GetComponent<LocalizedText>() ?? target.gameObject.AddComponent<LocalizedText>();
        component._textComponent = target;
        component.SetDynamic(provider);
        return component;
    }
}