using System.Collections.Concurrent;
using System.Text.RegularExpressions;
using Umbraco.Extensions;

namespace Umbraco.Cms.Core.Cache;

/// <summary>
///     Implements a fast <see cref="IAppCache" /> on top of a concurrent dictionary.
/// </summary>
public class FastDictionaryAppCache : IAppCache
{
    /// <summary>
    ///     Gets the internal items dictionary, for tests only!
    /// </summary>
    private readonly ConcurrentDictionary<string, Lazy<object?>> _items = new();

    public IEnumerable<string> Keys => _items.Keys;

    public int Count => _items.Count;

    /// <inheritdoc />
    public object? Get(string cacheKey)
    {
        _items.TryGetValue(cacheKey, out Lazy<object?>? result); // else null
        return result == null ? null : SafeLazy.GetSafeLazyValue(result); // return exceptions as null
    }

    /// <inheritdoc />
    public object? Get(string cacheKey, Func<object?> getCacheItem)
    {
        Lazy<object?>? result = _items.GetOrAdd(cacheKey, k => SafeLazy.GetSafeLazy(getCacheItem));

        var value = result.Value; // will not throw (safe lazy)

        if (value is null)
        {
            // do not cache null values
            _items.TryRemove(cacheKey, out _);
            return null;
        }

        if (!(value is SafeLazy.ExceptionHolder eh))
        {
            return value;
        }

        // and... it's in the cache anyway - so contrary to other cache providers,
        // which would trick with GetSafeLazyValue, we need to remove by ourselves,
        // in order NOT to cache exceptions
        _items.TryRemove(cacheKey, out result);
        eh.Exception.Throw(); // throw once!
        return null; // never reached
    }

    /// <inheritdoc />
    public IEnumerable<object?> SearchByKey(string keyStartsWith) =>
        _items
            .Where(kvp => kvp.Key.InvariantStartsWith(keyStartsWith))
            .Select(kvp => SafeLazy.GetSafeLazyValue(kvp.Value))
            .Where(x => x != null);

    /// <inheritdoc />
    public IEnumerable<object?> SearchByRegex(string regex)
    {
        var compiled = new Regex(regex, RegexOptions.Compiled);
        return _items
            .Where(kvp => compiled.IsMatch(kvp.Key))
            .Select(kvp => SafeLazy.GetSafeLazyValue(kvp.Value))
            .Where(x => x != null);
    }

    /// <inheritdoc />
    public void Clear() => _items.Clear();

    /// <inheritdoc />
    public void Clear(string key) => _items.TryRemove(key, out _);

    /// <inheritdoc />
    public void ClearOfType(Type? type)
    {
        if (type == null)
        {
            return;
        }

        var isInterface = type.IsInterface;

        foreach (KeyValuePair<string, Lazy<object?>> kvp in _items
                     .Where(x =>
                     {
                         // entry.Value is Lazy<object> and not null, its value may be null
                         // remove null values as well, does not hurt
                         // get non-created as NonCreatedValue & exceptions as null
                         var value = SafeLazy.GetSafeLazyValue(x.Value, true);

                         // if T is an interface remove anything that implements that interface
                         // otherwise remove exact types (not inherited types)
                         return value == null || (isInterface ? type.IsInstanceOfType(value) : value.GetType() == type);
                     }))
        {
            _items.TryRemove(kvp.Key, out _);
        }
    }

    /// <inheritdoc />
    public void ClearOfType<T>()
    {
        Type typeOfT = typeof(T);
        var isInterface = typeOfT.IsInterface;

        foreach (KeyValuePair<string, Lazy<object?>> kvp in _items
                     .Where(x =>
                     {
                         // entry.Value is Lazy<object> and not null, its value may be null
                         // remove null values as well, does not hurt
                         // compare on exact type, don't use "is"
                         // get non-created as NonCreatedValue & exceptions as null
                         var value = SafeLazy.GetSafeLazyValue(x.Value, true);

                         // if T is an interface remove anything that implements that interface
                         // otherwise remove exact types (not inherited types)
                         return value == null || (isInterface ? value is T : value.GetType() == typeOfT);
                     }))
        {
            _items.TryRemove(kvp.Key, out _);
        }
    }

    /// <inheritdoc />
    public void ClearOfType<T>(Func<string, T, bool> predicate)
    {
        Type typeOfT = typeof(T);
        var isInterface = typeOfT.IsInterface;

        foreach (KeyValuePair<string, Lazy<object?>> kvp in _items
                     .Where(x =>
                     {
                         // entry.Value is Lazy<object> and not null, its value may be null
                         // remove null values as well, does not hurt
                         // compare on exact type, don't use "is"
                         // get non-created as NonCreatedValue & exceptions as null
                         var value = SafeLazy.GetSafeLazyValue(x.Value, true);
                         if (value == null)
                         {
                             return true;
                         }

                         // if T is an interface remove anything that implements that interface
                         // otherwise remove exact types (not inherited types)
                         return (isInterface ? value is T : value.GetType() == typeOfT)

                                // run predicate on the 'public key' part only, ie without prefix
                                && predicate(x.Key, (T)value);
                     }))
        {
            _items.TryRemove(kvp.Key, out _);
        }
    }

    /// <inheritdoc />
    public void ClearByKey(string keyStartsWith)
    {
        foreach (KeyValuePair<string, Lazy<object?>> ikvp in _items
                     .Where(kvp => kvp.Key.InvariantStartsWith(keyStartsWith)))
        {
            _items.TryRemove(ikvp.Key, out _);
        }
    }

    /// <inheritdoc />
    public void ClearByRegex(string regex)
    {
        var compiled = new Regex(regex, RegexOptions.Compiled);
        foreach (KeyValuePair<string, Lazy<object?>> ikvp in _items
                     .Where(kvp => compiled.IsMatch(kvp.Key)))
        {
            _items.TryRemove(ikvp.Key, out _);
        }
    }
}