using System;
using System.IO;
using System.Linq;
using GeViSetEditor.Core.Models;

namespace GeViSetEditor.Core.Writers
{
    /// <summary>
    /// Safe writer that preserves binary integrity
    /// Only modifies action mappings, keeps everything else intact
    /// </summary>
    public class SafeSetFileWriter
    {
        /// <summary>
        /// Write SafeSetFile back to binary format
        /// Returns byte array that can be sent to GeViServer
        /// </summary>
        public byte[] Write(SafeSetFile setFile)
        {
            if (setFile.OriginalData == null || setFile.OriginalData.Length == 0)
            {
                throw new InvalidOperationException("Cannot write: OriginalData is missing");
            }

            Console.WriteLine($"Writing .set file: {setFile.FileSize} bytes");
            Console.WriteLine($"Action mappings: {setFile.ActionMappings.Count}");

            // Start with exact copy of original data
            byte[] output = setFile.GetDataForWriting();
            Console.WriteLine($"  Output data created: {output.Length} bytes");

            // Verify header is intact
            if (VerifyHeader(output))
            {
                Console.WriteLine("  Header verification: PASSED");
            }
            else
            {
                Console.WriteLine("  Header verification: FAILED (proceeding anyway for round-trip test)");
                // Don't throw - allow round-trip test to see byte comparison
            }

            // TODO: If action mappings were modified, update them here
            // For now, we just preserve everything as-is for safe round-trip

            Console.WriteLine($"Write complete: {output.Length} bytes");
            return output;
        }

        /// <summary>
        /// Write to file
        /// </summary>
        public void WriteToFile(SafeSetFile setFile, string filePath)
        {
            byte[] data = Write(setFile);

            // Create backup if file exists
            if (File.Exists(filePath))
            {
                string backupPath = filePath + ".backup";
                File.Copy(filePath, backupPath, true);
                Console.WriteLine($"Created backup: {backupPath}");
            }

            File.WriteAllBytes(filePath, data);
            Console.WriteLine($"Wrote {data.Length} bytes to {filePath}");
        }

        /// <summary>
        /// Verify the output file is valid before writing to server
        /// </summary>
        public bool Verify(byte[] data)
        {
            if (data == null || data.Length < 100)
            {
                Console.WriteLine("Verification failed: File too small");
                return false;
            }

            if (!VerifyHeader(data))
            {
                Console.WriteLine("Verification failed: Invalid header");
                return false;
            }

            // Additional checks
            if (data.Length > 10 * 1024 * 1024) // 10MB max
            {
                Console.WriteLine("Verification failed: File too large");
                return false;
            }

            Console.WriteLine("Verification passed");
            return true;
        }

        private bool VerifyHeader(byte[] data)
        {
            // Check for "GeViSoft Parameters" header
            string expectedHeader = "GeViSoft Parameters";

            int offset = (data[0] == 0x00) ? 1 : 0;

            if (offset + 2 + expectedHeader.Length > data.Length)
                return false;

            if (data[offset] != 0x07) // Pascal string marker
                return false;

            byte headerLen = data[offset + 1];
            if (headerLen < 10 || headerLen > 50)
                return false;

            string actualHeader = System.Text.Encoding.UTF8.GetString(data, offset + 2, Math.Min(headerLen, expectedHeader.Length));

            return actualHeader.StartsWith("GeViSoft");
        }

        /// <summary>
        /// Compare two .set files for differences
        /// Useful for testing round-trip conversion
        /// </summary>
        public ComparisonResult Compare(byte[] original, byte[] modified)
        {
            var result = new ComparisonResult
            {
                OriginalSize = original.Length,
                ModifiedSize = modified.Length
            };

            if (original.Length != modified.Length)
            {
                result.IsIdentical = false;
                result.Differences.Add($"Size mismatch: {original.Length} vs {modified.Length}");
                return result;
            }

            for (int i = 0; i < original.Length; i++)
            {
                if (original[i] != modified[i])
                {
                    result.DifferentBytes++;
                    if (result.Differences.Count < 10) // Limit to first 10 differences
                    {
                        result.Differences.Add($"Byte {i} (0x{i:X}): {original[i]:X2} != {modified[i]:X2}");
                    }
                }
            }

            result.IsIdentical = (result.DifferentBytes == 0);

            if (result.IsIdentical)
            {
                Console.WriteLine("Files are identical!");
            }
            else
            {
                Console.WriteLine($"Files differ in {result.DifferentBytes} bytes");
            }

            return result;
        }
    }

    public class ComparisonResult
    {
        public bool IsIdentical { get; set; }
        public int OriginalSize { get; set; }
        public int ModifiedSize { get; set; }
        public int DifferentBytes { get; set; }
        public List<string> Differences { get; set; } = new();
    }
}