using CsvHelper;
using CsvHelper.Configuration;
using CsvHelper.Configuration.Attributes;
using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    public class Program
    {
        private static readonly string BASE_DIR = Environment.ExpandEnvironmentVariables(@"%USERPROFILE%\Downloads\deaths\");
        private static readonly string[] SOURCE_FILES = new string[]
        {
            $@"{BASE_DIR}\deces-2018.csv",
            $@"{BASE_DIR}\deces-2019.csv",
            $@"{BASE_DIR}\deces-2020-m01.csv",
            $@"{BASE_DIR}\Deces_2020_M02.csv",
            $@"{BASE_DIR}\Deces_2020_M03.csv",
            $@"{BASE_DIR}\Deces_2020_M04.csv",
            $@"{BASE_DIR}\Deces_2020_M05.csv",
            $@"{BASE_DIR}\Deces_2020_M06.csv",
            $@"{BASE_DIR}\Deces_2020_M07.csv",
            $@"{BASE_DIR}\Deces_2020_M08.csv",
            $@"{BASE_DIR}\Deces_2020_M09.csv",
        };
        private static readonly string DESTINATION_FILE = $@"{BASE_DIR}\deces_out.csv";

        public static async Task Main(string[] args)
        {
            Console.WriteLine("Starting");
            try
            {
                var program = new Program();
                await program.Run();
            }
            catch (Exception ex)
            {
                Console.WriteLine("ERROR");
                Console.WriteLine(ex.ToString());
            }
            Console.WriteLine("Stopping (press enter to exit)");
            Console.ReadLine();
        }

        public Task Run()
        {
            // Initialize empty date/deaths mapping
            var deaths = new Dictionary<DateTime, int>();
            var startPeriod = new DateTime(2018, 01, 01);
            var endPeriod = new DateTime(2020, 09, 21);
            for (DateTime date = startPeriod; date <= endPeriod; date = date.AddDays(1))
            {
                deaths[date] = 0;
            }

            // Compute daily deaths from input CSV files
            Console.WriteLine("Reading input files...");
            foreach (string sourceFile in SOURCE_FILES)
            {
                // Read CSV file
                using var reader = new StreamReader(sourceFile, detectEncodingFromByteOrderMarks: true);
                using var csvReader = new CsvReader(reader, configuration: new CsvConfiguration(CultureInfo.InvariantCulture) { Delimiter = ";", HasHeaderRecord = true });
                IEnumerable<InputEntry> inputEntries = csvReader.GetRecords<InputEntry>();

                // Process all CSV entries
                int index = 0;
                foreach (InputEntry inputEntry in inputEntries)
                {
                    index++;

                    // Parse death date
                    Match match = Regex.Match(inputEntry.DeathDate, @"(\d\d\d\d)(\d\d)(\d\d)");

                    // Ignore & log entries with an invalid date format
                    if (!match.Success)
                    {
                        Console.WriteLine($"Found invalid date format '{inputEntry.DeathDate}' in file '{sourceFile}' at index {index}.");
                        continue;
                    }

                    int year = int.Parse(match.Groups[1].Value);
                    int month = int.Parse(match.Groups[2].Value);
                    int day = int.Parse(match.Groups[3].Value);

                    // Some deaths are dated on the day "0" of the month or on the month "0" of the year, probably because the exact date is uncertain.
                    // Move them to the 1st day of the month / 1st month of the year, the amount is negligible anyway.
                    month = Math.Max(month, 1);
                    day = Math.Max(day, 1);

                    // Ignore & log invalid dates
                    if (!DateTime.TryParse($"{year:0000}-{month:00}-{day:00}", out DateTime deathDate))
                    {
                        Console.WriteLine($"Found invalid date '{inputEntry.DeathDate}' in file '{sourceFile}' at index {index}.");
                        continue;
                    }

                    // Ignore deaths outside of the observed period
                    if (deaths.ContainsKey(deathDate))
                    {
                        deaths[deathDate]++;
                    }
                }
            }

            // Write daily deaths to output CSV file
            Console.WriteLine("Writing ouput file...");
            var outputEntries = deaths
                .OrderBy(x => x.Key)
                .Select(x => new OutputEntry() { Date = x.Key.ToString("yyyy-MM-dd"), Deaths = x.Value })
                .ToList();
            using var writer = new StreamWriter(DESTINATION_FILE, append: false, encoding: Encoding.UTF8);
            using var csvWriter = new CsvWriter(writer, configuration: new CsvConfiguration(CultureInfo.InvariantCulture) { Delimiter = ";", HasHeaderRecord = true });
            csvWriter.WriteRecords(outputEntries);

            return Task.CompletedTask;
        }
    }

    public class InputEntry
    {
        [Name("datedeces")]
        public string DeathDate { get; set; }
    }

    public class OutputEntry
    {
        [Name("date")]
        public string Date { get; set; }
        [Name("deaths")]
        public int Deaths { get; set; }
    }
}