using System;
using System.Collections.Generic;
using System.IO;

partial class Program {

    private static bool ValidateQuery(string query, out string[] queryParameters) {

        while (query.Contains("  ")) { query = query.Replace("  ", " "); }
        queryParameters = query.Split(' ');
        if (queryParameters.Length != 3)
            return false;
        queryParameters[0] = queryParameters[0].ToLower();
        queryParameters[2] = queryParameters[2].ToLower();


        string first = queryParameters[0];
        string second = queryParameters[1];
        string third = queryParameters[2];

        int oper = getIndex(first);
        if (oper == -1)
            return false;

        if (oper < 3) {
            if (!(second == "==" || second == "<>"))
                return false;
        }
        else {
            if (!(second == ">=" || second == "<="))
                return false;
            if (oper == 3 && !(int.TryParse(third, out int number)))
                return false;
            if (oper == 4 && !Double.TryParse(third, out Double number1))
                return false;
        }
        return true;

    }

    private static List<string> ProcessQuery(string[] queryParameters, string pathToDatabase) {
        string[][] data = new string[System.IO.File.ReadAllLines(pathToDatabase).Length][];
        int index = 0;
        try {
            using (StreamReader sr = new StreamReader(pathToDatabase)) {
                string line;
                while ((line = sr.ReadLine()) != null)
                    if (!line.Split(';')[0].ToLower().Equals("first_name"))
                        data[index++] = line.Split(';');
            }
        }
        catch (Exception e) {
            Console.WriteLine(e.Message);
        }
        List<string> currentdata = new List<string>();
        int operation = getIndex(queryParameters[0]);
        //Console.WriteLine(queryParameters[0] + queryParameters[1] + queryParameters[2]);
        if (operation < 3) {
            if (queryParameters[1].Equals("==")) {
                foreach (string[] item in data) {
                    if (item != null && item[operation].ToLower() == queryParameters[2]) {
                        currentdata.Add(join(item));
                    }
                }
            }
            else {
                foreach (string[] item in data)
                    if (item != null && item[operation].ToLower() != queryParameters[2]) {
                        currentdata.Add(join(item));
                    }
            }
        }
        else {
            if (queryParameters[1].Equals("<=")) {
                foreach (string[] item in data) {
                    if (item != null && Double.Parse(item[operation]) <=
                        Double.Parse(queryParameters[2])) {
                        currentdata.Add(join(item));
                    }
                }
            }
            else {
                foreach (string[] item in data) {
                    if (item != null && Double.Parse(item[operation]) >= Double.Parse(queryParameters[2])) {
                        currentdata.Add(join(item));
                    }
                }
            }
        }

        return currentdata;
    }

    private static int getIndex(string param) {
        string[] parametres = { "first_name", "last_name", "group", "rating", "gpa" };
        int ind = -1;
        for (int i = 0; i < parametres.Length; i++)
            if (param == parametres[i]) {
                ind = i;
                return i;
            }
        return -1;

    }
    private static string join(string[] a) {
        string data = "";
        for (int i = 0; i < a.Length - 1; i++)
            data += (a[i] + ";");
        data += a[a.Length - 1];
        return data;
    }
}