using System.Security.Cryptography;

namespace Kvdb
{
    public class Kvdb
    {
        private const string DefaultDbLocation = "database/db";
        private const string DefaultDirName = "database/";
        public static void InitializeDataBase() // function to create all the necessary folders and files
        {
            if(!Directory.Exists("database")){
                Directory.CreateDirectory("database");
            }
        }

        public static string Hash(string text) // function to get name of a database file
        {
            if (String.IsNullOrEmpty(text))
                return String.Empty;

            var sha = new SHA256Managed(); // hash algorithm
            {
                byte[] textData = System.Text.Encoding.UTF8.GetBytes(text);
                byte[] hash = sha.ComputeHash(textData);
                return BitConverter.ToString(hash).Replace("-", String.Empty);
            }
        }

        private static string GetDbLocation(string? dbName) // function to get the location of a database
        {
            string currentDbLocation = "";
            if (dbName != null)
            {
                currentDbLocation = DefaultDirName + Hash(dbName);
            }
            else
            {
                currentDbLocation = DefaultDbLocation;
            }

            return currentDbLocation;
        }

        public static void Put(string? dbName, string key, string value) // put command
        {
            string currentDbLocation = GetDbLocation(dbName);
            Remove(dbName, key); // removes the key (because put always overrides current value). It also prints the value stored there before.
            string line = key + " " + value; // new line that is going to be placed under the key
            var streamWriter = new StreamWriter(currentDbLocation, true);
            streamWriter.WriteLine(line); // writing the new line to db
            streamWriter.Close();
        }

        private static void Get(string? dbName, string key) // get command
        {
            string currentDbLocation = GetDbLocation(dbName);

            var foundLine = ""; // initially the found string is empty
            foreach (string line in File.ReadLines(currentDbLocation)) // reading all lines
            {
                var arr = line.Split(" ");
                if (arr[0] == key)
                {
                    foundLine = line.Substring(arr[0].Length + 1);
                }
            }
            Console.WriteLine(foundLine);
        }

        private static void Remove(string? dbName, string key) // remove command
        {
            string currentDbLocation = GetDbLocation(dbName);

            var lineToRemove = "";
            var tempFile = Path.GetTempFileName(); // creating a temporary file to store all the lines except for the one to remove
            var streamWriter = new StreamWriter(tempFile);
            if(File.Exists(currentDbLocation)){
                foreach (var line in File.ReadLines(currentDbLocation))
                {
                    var arr = line.Split(" ");
                    if (arr[0] != key)
                    {
                        streamWriter.WriteLine(line); // if it is any other line except for the one to remove
                    }
                    else
                    {
                        lineToRemove = line.Substring(arr[0].Length + 1); // if it is the line to remove
                    }
                }

                Console.WriteLine(lineToRemove); // printing what was there before we remove it
                streamWriter.Close();
                File.Delete(currentDbLocation); // deleting the previous db file
                File.Move(tempFile, currentDbLocation); // moving contents of temporary file to the new database
            }
        }

        public static void Main(string[] args)
        {
            if (args.Length == 0)
            {
                Console.WriteLine("You didn't provide any arguments. That's sad. I'm quitting.");
            }
            switch (args[0])
            {
                case "put":
                    if (args.Length == 3) // if db is not specicfied
                    {
                        Put(null, args[1], args[2]);
                    }
                    else if (args.Length == 4) // if db is specified
                    {
                        Put(args[1], args[2], args[3]);
                    }
                    else
                    {
                        Console.WriteLine("Wrong command format. Correct format is: put [dbname?] [key] [value]");
                    }
                    break;

                case "get":
                    if (args.Length == 2)
                    {
                        Get(null, args[1]);
                    }
                    else if (args.Length == 3)
                    {
                        Get(args[1], args[2]);
                    }
                    else
                    {
                        Console.WriteLine("Wrong command format. Correct format is: get [dbname?] [key]");
                    }
                    break;

                case "remove":
                    if (args.Length == 2)
                    {
                        Remove(null, args[1]);
                    }
                    else if (args.Length == 3)
                    {
                        Remove(args[1], args[2]);
                    }
                    else
                    {
                        Console.WriteLine("Wrong command format. Correct format is: remove [dbname?] [key]");
                    }
                    break;

                default:
                    Console.WriteLine("I don't know this command. I suggest you read the documentation. That might help actually.");
                    break;
            }
        }
    }
}