using adas_core.Application.Services.Interfaces;
using adas_core.Domain.Models.GroupedObservations;
using MongoDB.Bson;
using System.Collections.Concurrent;

namespace adas_core.Application.Services.Caching
{
    /// <summary>
    /// Implementación de caché en memoria con soporte de locking seguro
    /// mediante LockManagerService + InMemoryLockProvider.
    /// Compatible con la interfaz ICacheService incluyendo GetOrSet.
    /// </summary>
    /// <!-- aidoc:v1 sig=53daded -->
    public class CacheService(LockManagerService lockManager) : ICacheService
    {
        private readonly ConcurrentDictionary<string, object> _mem = new();

        // HELPERS
        /// <summary>
        /// Builds a composite key for a grouped observation field, scoped to a specific patient.
        /// </summary>
        /// <param name="gf">The grouped field whose name is included in the key.</param>
        /// <param name="patientId">The identifier of the patient the key is scoped to.</param>
        /// <returns>A formatted key string in the form <c>GroupedObs:{patientId}:{gf.Name}</c>.</returns>
        /// <!-- aidoc:v1 sig=72c65a6 -->
        private static string BuildGroupedKey(GroupedField gf, ObjectId patientId)
                    => $"GroupedObs:{patientId}:{gf.Name}";

        
        // GET OR SET (string key)
        /// <summary>
        /// Retrieves an object from the in-memory cache by key, or creates and stores it using the provided factory if absent. Uses a fast path for cache hits and a lock-based path with a double-check to prevent duplicate creation across concurrent callers.
        /// </summary>
        /// <param name="key">The cache key used to look up and store the object.</param>
        /// <param name="factory">The asynchronous factory function invoked to produce the object when it is not found in the cache.</param>
        /// <param name="ttl">Optional time-to-live associated with the cached object.</param>
        /// <param name="cancellationToken">A token to observe for cancellation requests.</param>
        /// <returns>The cached or newly created object of type <typeparamref name="T"/>.</returns>
        /// <!-- aidoc-review:v1 severity=high kind=mentions_removed_behavior
        ///      "The `ttl` parameter is documented as 'Optional time-to-live associated with the cached object', but the method body never uses `ttl`—the cache assignment `_mem[key] = created;` has no TTL/expiration handling, so readers will be misled into believing the TTL is honored." -->
        public async Task<T> GetOrSetObjectAsync<T>(
                    string key,
                    Func<Task<T>> factory,
                    TimeSpan? ttl = null,
                    CancellationToken cancellationToken = default)
                {
                    // FAST PATH
                    if (_mem.TryGetValue(key, out var existing))
                        return (T)existing;
        
                    // LOCKED PATH
                    return await lockManager.WithLockAsync(
                        $"getorset:{key}",
                        TimeSpan.FromSeconds(5),
                        async () =>
                        {
                            if (_mem.TryGetValue(key, out var again))
                                return (T)again;
        
                            var created = await factory();
        
                            if (created != null!)
                                _mem[key] = created;
        
                            return created!;
                        },
                        cancellationToken);
                }

        /// <summary>
        /// Asynchronously retrieves the cached string value associated with the specified key, or loads and stores it using the provided loader function if absent.
        /// Delegates to <see cref="GetOrSetObjectAsync"/> to handle caching, honoring the optional TTL override for the cache entry.
        /// </summary>
        /// <param name="key">The cache key used to identify the stored string value.</param>
        /// <param name="loader">The asynchronous function invoked to load the value when no cached entry exists for the key.</param>
        /// <param name="ttlOverride">An optional time span that overrides the default time-to-live for the cached value.</param>
        /// <returns>The cached or newly loaded string value, or <c>null</c> when the underlying cache entry is absent or cannot be cast to a string.</returns>
        /// <!-- aidoc-review:v1 severity=low kind=wrong_returns
        ///      "The <returns> text claims the method returns null 'when the underlying cache entry ... cannot be cast to a string', but the explicit cast (string?)result would throw InvalidCastException rather than yield null in that case." -->
        public async Task<string?> GetOrSetValueAsync(
                    string key,
                    Func<Task<string>> loader,
                    TimeSpan? ttlOverride = null)
                {
                    
                    var result = await GetOrSetObjectAsync(key, loader, ttlOverride);
                    return (string?)result;
        
                }

        
        // GET OR SET (GroupedField + patientId)
        /// <summary>
        /// Asynchronously retrieves a cached object associated with the given grouped field and patient, or creates and caches a new one using the supplied factory when no cached value exists.
        /// The factory is only invoked when the cache does not contain a value for the key, and the produced value is stored in the cache only when it is not null.
        /// </summary>
        /// <param name="groupedField">The grouped field that contributes to the cache key.</param>
        /// <param name="patientId">The patient identifier that contributes to the cache key.</param>
        /// <param name="factory">The asynchronous factory used to build the object when no cached value is available.</param>
        /// <param name="ttl">Optional time-to-live for the cached entry.</param>
        /// <param name="cancellationToken">Token used to cancel the asynchronous operation.</param>
        /// <returns>A task containing the cached or newly created object.</returns>
        /// <!-- aidoc-review:v1 severity=medium kind=wrong_param_role
        ///      "The `ttl` parameter is documented as 'Optional time-to-live for the cached entry', but it is never referenced in the method body — no TTL is applied to the stored entry, and the lock timeout is hardcoded to 5 seconds. A reader would expect their TTL value to be honored, but it is effectively ignored." -->
        public async Task<T> GetOrSetObjectAsync<T>(
                    GroupedField groupedField,
                    ObjectId patientId,
                    Func<Task<T>> factory,
                    TimeSpan? ttl = null,
                    CancellationToken cancellationToken = default)
                {
                    var key = BuildGroupedKey(groupedField, patientId);
        
                    if (_mem.TryGetValue(key, out var existing))
                        return (T)existing;
        
                    return await lockManager.WithLockAsync(
                        $"getorset:{key}",
                        TimeSpan.FromSeconds(5),
                        async () =>
                        {
                            if (_mem.TryGetValue(key, out var again))
                                return (T)again;
        
                            var created = await factory();
        
                            if (created != null!)
                                _mem[key] = created;
        
                            return created!;
                        },
                        cancellationToken);
                }

        
        // GET / SET
        /// <summary>
        /// Stores the specified value in the in-memory collection under the given key, overwriting any existing entry.
        /// </summary>
        /// <param name="key">The key that identifies where the value will be stored.</param>
        /// <param name="value">The value to associate with the specified key.</param>
        /// <!-- aidoc:v1 sig=f3491fe -->
        public void SetValue(string key, string value)
                    => _mem[key] = value;

        /// <summary>
        /// Retrieves the string representation of the value associated with the specified key from the in-memory store.
        /// Returns the value converted via <see cref="object.ToString"/> when the key is found, or <c>null</c> when the key is not present.
        /// </summary>
        /// <param name="key">The key used to look up the value in the underlying store.</param>
        /// <returns>The string representation of the stored value if the key exists; otherwise, <c>null</c>.</returns>
        /// <!-- aidoc:v1 sig=7a34703 -->
        public string? GetValue(string key)
                    => _mem.TryGetValue(key, out var v) ? v.ToString() : null;

        /// <summary>
        /// Asynchronously retrieves an object of type <typeparamref name="T"/> from the in-memory cache using the specified key.
        /// Returns the stored value cast to <typeparamref name="T"/> if the key exists, or <c>default</c> (null for reference types) if the key is not found.
        /// </summary>
        /// <param name="key">The cache key used to look up the stored object.</param>
        /// <param name="updateExpiration">Indicates whether the entry's expiration should be refreshed on access. Not currently used by this implementation.</param>
        /// <returns>A <see cref="Task{T}"/> containing the cached value cast to <typeparamref name="T"/>, or <c>null</c> if no entry exists for the given key.</returns>
        /// <!-- aidoc:v1 sig=5046896 body=6902631 -->
        public Task<T?> GetObjectAsync<T>(string key, bool updateExpiration = true)
                {
                    return Task.FromResult(
                        _mem.TryGetValue(key, out var v) ? (T?)v : default
                    );
                }

        /// <summary>
        /// Asynchronously stores the specified object in the in-memory cache using the given key.
        /// </summary>
        /// <param name="key">The cache key under which the object will be stored.</param>
        /// <param name="obj">The object to store in the cache.</param>
        /// <param name="updateExpiration">Indicates whether the cache entry's expiration should be refreshed.</param>
        /// <!-- aidoc-review:v1 severity=medium kind=mentions_removed_behavior
        ///      "The updateExpiration parameter is documented as indicating whether the cache entry's expiration should be refreshed, but the method body never references this parameter, so the documented behavior does not occur." -->
        public Task SetObjectAsync<T>(string key, T obj, bool updateExpiration = true)
                {
                    _mem[key] = obj!;
                    return Task.CompletedTask;
                }

        /// <summary>
        /// Retrieves an object of type <typeparamref name="T"/> associated with the specified key by delegating to an overload that supports an update flag. The <paramref name="ttlOverride"/> parameter is accepted by this overload but is not forwarded to the underlying call.
        /// </summary>
        /// <param name="key">The identifier of the object to retrieve.</param>
        /// <param name="ttlOverride">An optional time-to-live override accepted by this overload but ignored when delegating to the underlying retrieval call.</param>
        /// <param name="upd">A flag indicating whether the retrieval should trigger an update on the stored object.</param>
        /// <returns>A task that represents the asynchronous operation, containing the retrieved object of type <typeparamref name="T"/> or <c>null</c> if no object is found for the given key.</returns>
        /// <!-- aidoc:v1 sig=773648d -->
        public Task<T?> GetObjectAsync<T>(string key, TimeSpan? ttlOverride, bool upd)
                    => GetObjectAsync<T>(key, upd);

        /// <summary>
        /// Asynchronously stores an object associated with the specified key, with an option to override its time-to-live. The <paramref name="ttlOverride"/> parameter is accepted but is not forwarded to the underlying storage call, so the effective time-to-live is determined elsewhere.
        /// </summary>
        /// <param name="key">The identifier used to store and later retrieve the object.</param>
        /// <param name="obj">The object to store in the underlying store.</param>
        /// <param name="ttlOverride">An optional time-to-live override for the stored entry; not applied by this overload.</param>
        /// <param name="upd">A flag indicating whether the operation should update an existing entry.</param>
        /// <returns>A task that represents the asynchronous set operation.</returns>
        /// <!-- aidoc:v1 sig=874b6ce -->
        public Task SetObjectAsync<T>(string key, T obj, TimeSpan? ttlOverride, bool upd)
                    => SetObjectAsync(key, obj, upd);

        
        // DELETE / CLEAN
        /// <summary>
        /// Asynchronously removes the object associated with the specified key from the in-memory store. The operation succeeds silently whether or not the key exists.
        /// </summary>
        /// <param name="key">The identifier of the object to delete.</param>
        /// <!-- aidoc:v1 sig=93555f0 body=00affc5 -->
        public Task DeleteObjectAsync(string key)
                {
                    _mem.TryRemove(key, out _);
                    return Task.CompletedTask;
                }

        /// <summary>
        /// Asynchronously deletes cache entries whose keys contain the specified pattern, where asterisk (*) characters in the pattern are treated as wildcards (stripped and matched as substrings). Returns the number of entries successfully removed.
        /// </summary>
        /// <param name="pattern">The pattern to match against cache keys. Asterisk (*) characters are removed and the remaining text is used as a substring match.</param>
        /// <returns>A task that represents the asynchronous operation, containing the count of entries that were removed.</returns>
        /// <!-- aidoc:v1 sig=a8cca2e body=81413d3 -->
        public Task<long> DeleteByPatternAsync(string pattern)
                {
                    var p = pattern.Replace("*", "");
                    var keys = _mem.Keys.Where(k => k.Contains(p)).ToList();
        
                    long removed = 0;
                    foreach (var k in keys)
                        if (_mem.TryRemove(k, out _))
                            removed++;
        
                    return Task.FromResult(removed);
                }

        /// <summary>
        /// Clears all entries from the in-memory cache, removing any previously stored data.
        /// </summary>
        /// <!-- aidoc:v1 sig=8762842 -->
        public void CleanCache() => _mem.Clear();
    }
}