using System;
using System.Collections.Concurrent;
using System.IO;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;

namespace MarketAlly.AIPlugin.DevOps.Performance
{
    public class AnalysisCache
    {
        private readonly ConcurrentDictionary<string, CacheEntry> _cache;
        private readonly ILogger<AnalysisCache> _logger;
        private readonly TimeSpan _defaultExpiry;

        public AnalysisCache(ILogger<AnalysisCache> logger = null, TimeSpan? defaultExpiry = null)
        {
            _cache = new ConcurrentDictionary<string, CacheEntry>();
            _logger = logger;
            _defaultExpiry = defaultExpiry ?? TimeSpan.FromHours(1);
        }

        public async Task<T> GetOrSetAsync<T>(string key, Func<Task<T>> factory, TimeSpan? expiry = null) where T : class
        {
            var cacheKey = GenerateCacheKey(key);
            var expiryTime = expiry ?? _defaultExpiry;

            if (_cache.TryGetValue(cacheKey, out var existingEntry))
            {
                if (existingEntry.ExpiresAt > DateTime.UtcNow)
                {
                    try
                    {
                        var cachedResult = JsonSerializer.Deserialize<T>(existingEntry.Data);
                        _logger?.LogDebug("Cache hit for key: {CacheKey}", cacheKey);
                        return cachedResult;
                    }
                    catch (JsonException ex)
                    {
                        _logger?.LogWarning(ex, "Failed to deserialize cached data for key: {CacheKey}", cacheKey);
                        _cache.TryRemove(cacheKey, out _);
                    }
                }
                else
                {
                    _cache.TryRemove(cacheKey, out _);
                    _logger?.LogDebug("Cache entry expired for key: {CacheKey}", cacheKey);
                }
            }

            _logger?.LogDebug("Cache miss for key: {CacheKey}, executing factory", cacheKey);
            var result = await factory();
            
            if (result != null)
            {
                await SetAsync(cacheKey, result, expiryTime);
            }

            return result;
        }

        public async Task<T> GetAsync<T>(string key) where T : class
        {
            var cacheKey = GenerateCacheKey(key);

            if (_cache.TryGetValue(cacheKey, out var entry))
            {
                if (entry.ExpiresAt > DateTime.UtcNow)
                {
                    try
                    {
                        var result = JsonSerializer.Deserialize<T>(entry.Data);
                        _logger?.LogDebug("Retrieved from cache: {CacheKey}", cacheKey);
                        return result;
                    }
                    catch (JsonException ex)
                    {
                        _logger?.LogWarning(ex, "Failed to deserialize cached data for key: {CacheKey}", cacheKey);
                        _cache.TryRemove(cacheKey, out _);
                    }
                }
                else
                {
                    _cache.TryRemove(cacheKey, out _);
                }
            }

            return null;
        }

        public async Task SetAsync<T>(string key, T value, TimeSpan? expiry = null)
        {
            var cacheKey = GenerateCacheKey(key);
            var expiryTime = expiry ?? _defaultExpiry;

            try
            {
                var jsonData = JsonSerializer.Serialize(value, new JsonSerializerOptions
                {
                    WriteIndented = false,
                    PropertyNamingPolicy = JsonNamingPolicy.CamelCase
                });

                var entry = new CacheEntry
                {
                    Data = jsonData,
                    CreatedAt = DateTime.UtcNow,
                    ExpiresAt = DateTime.UtcNow.Add(expiryTime)
                };

                _cache.AddOrUpdate(cacheKey, entry, (k, v) => entry);
                _logger?.LogDebug("Cached data for key: {CacheKey}, expires at: {ExpiresAt}", cacheKey, entry.ExpiresAt);

                await Task.CompletedTask;
            }
            catch (Exception ex)
            {
                _logger?.LogError(ex, "Failed to cache data for key: {CacheKey}", cacheKey);
            }
        }

        public async Task<string> GenerateFileBasedCacheKeyAsync(string filePath, string operation)
        {
            if (!File.Exists(filePath))
            {
                return $"{operation}:{filePath}:notfound";
            }

            try
            {
                var fileInfo = new FileInfo(filePath);
                var lastWriteTime = fileInfo.LastWriteTimeUtc.Ticks;
                var fileSize = fileInfo.Length;
                
                // Create a hash of file metadata for cache key
                var keyData = $"{operation}:{filePath}:{lastWriteTime}:{fileSize}";
                
                using var sha256 = SHA256.Create();
                var hashBytes = sha256.ComputeHash(Encoding.UTF8.GetBytes(keyData));
                var hashString = Convert.ToHexString(hashBytes)[..16]; // Use first 16 characters
                
                return $"{operation}:{hashString}";
            }
            catch (Exception ex)
            {
                _logger?.LogWarning(ex, "Failed to generate file-based cache key for: {FilePath}", filePath);
                return $"{operation}:{filePath}:error";
            }
        }

        public void InvalidateByPattern(string pattern)
        {
            var keysToRemove = new List<string>();

            foreach (var kvp in _cache)
            {
                if (kvp.Key.Contains(pattern, StringComparison.OrdinalIgnoreCase))
                {
                    keysToRemove.Add(kvp.Key);
                }
            }

            foreach (var key in keysToRemove)
            {
                _cache.TryRemove(key, out _);
                _logger?.LogDebug("Invalidated cache entry: {CacheKey}", key);
            }

            _logger?.LogInformation("Invalidated {Count} cache entries matching pattern: {Pattern}", 
                keysToRemove.Count, pattern);
        }

        public void Clear()
        {
            var count = _cache.Count;
            _cache.Clear();
            _logger?.LogInformation("Cleared {Count} cache entries", count);
        }

        public void CleanupExpired()
        {
            var now = DateTime.UtcNow;
            var expiredKeys = new List<string>();

            foreach (var kvp in _cache)
            {
                if (kvp.Value.ExpiresAt <= now)
                {
                    expiredKeys.Add(kvp.Key);
                }
            }

            foreach (var key in expiredKeys)
            {
                _cache.TryRemove(key, out _);
            }

            if (expiredKeys.Count > 0)
            {
                _logger?.LogDebug("Cleaned up {Count} expired cache entries", expiredKeys.Count);
            }
        }

        public CacheStatistics GetStatistics()
        {
            var now = DateTime.UtcNow;
            var validEntries = 0;
            var expiredEntries = 0;

            foreach (var kvp in _cache)
            {
                if (kvp.Value.ExpiresAt > now)
                {
                    validEntries++;
                }
                else
                {
                    expiredEntries++;
                }
            }

            return new CacheStatistics
            {
                TotalEntries = _cache.Count,
                ValidEntries = validEntries,
                ExpiredEntries = expiredEntries,
                HitRate = 0 // Would need to track hits/misses for actual hit rate
            };
        }

        private string GenerateCacheKey(string key)
        {
            using var sha256 = SHA256.Create();
            var hashBytes = sha256.ComputeHash(Encoding.UTF8.GetBytes(key));
            return Convert.ToHexString(hashBytes)[..16]; // Use first 16 characters for shorter keys
        }

        private class CacheEntry
        {
            public string Data { get; set; }
            public DateTime CreatedAt { get; set; }
            public DateTime ExpiresAt { get; set; }
        }
    }

    public class CacheStatistics
    {
        public int TotalEntries { get; set; }
        public int ValidEntries { get; set; }
        public int ExpiredEntries { get; set; }
        public double HitRate { get; set; }
    }
}