using Elwig.Helpers;
using Elwig.Helpers.Export;
using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Threading.Tasks;

namespace Elwig.Services {
    public static class BackupService {

        public static bool IsAnyBackupUpToDate {
            get {
                var lastDbWrite = File.GetLastWriteTime(App.Config.DatabaseFile);
                lastDbWrite += new TimeSpan(0, 0, -1);
                return Directory.GetFiles(App.Config.BackupPath, "????-??-??_??-??-??.*.zip")
                    .Any(n => DateTime.ParseExact(Path.GetFileName(n)[..19], "yyyy-MM-dd_HH-mm-ss", CultureInfo.InvariantCulture, DateTimeStyles.None) >= lastDbWrite);
            }
        }

        public static async Task TryDatabaseBackup() {
            if (IsAnyBackupUpToDate) return;
            await BackupDatabase();
            PruneBackups();
        }

        public static async Task BackupDatabase() {
            await Database.ExportSql(Path.Combine(App.Config.BackupPath, $"{File.GetLastWriteTime(App.Config.DatabaseFile):yyyy-MM-dd_HH-mm-ss}.sql.zip"), true);
        }

        public static void PruneBackups() {
            var retain = new HashSet<string>();
            var backups = Directory.GetFiles(App.Config.BackupPath, "????-??-??_??-??-??.*.zip")
                .Select(n => (FileName: n, Timestamp: DateTime.ParseExact(Path.GetFileName(n)[..19], "yyyy-MM-dd_HH-mm-ss", CultureInfo.InvariantCulture, DateTimeStyles.None)))
                .OrderByDescending(t => t.Timestamp).ToArray();

            DateTime now;

            // retain hourly backups
            now = DateTime.Now;
            for (int i = 0; i < App.Config.BackupRetainHours; i++, now = now.AddHours(-1)) {
                foreach (var b in backups) {
                    if (b.Timestamp.Date == now.Date && b.Timestamp.Hour == now.Hour) {
                        retain.Add(b.FileName);
                        break;
                    }
                }
            }

            // retain daily backups
            now = DateTime.Now;
            for (int i = 0; i < App.Config.BackupRetainDays; i++, now = now.AddDays(-1)) {
                foreach (var b in backups) {
                    if (b.Timestamp.Date == now.Date) {
                        retain.Add(b.FileName);
                        break;
                    }
                }
            }

            // retain weekly backups
            now = DateTime.Now;
            for (int i = 0; i < App.Config.BackupRetainWeeks; i++, now = now.AddDays(-7)) {
                foreach (var b in backups) {
                    if (b.Timestamp.GetYearAndWeek() == now.GetYearAndWeek()) {
                        retain.Add(b.FileName);
                        break;
                    }
                }
            }

            // retain monthly backups
            now = DateTime.Now;
            for (int i = 0; i < App.Config.BackupRetainMonths; i++, now = now.AddMonths(-1)) {
                foreach (var b in backups) {
                    if (b.Timestamp.Year == now.Year && b.Timestamp.Month == now.Month) {
                        retain.Add(b.FileName);
                        break;
                    }
                }
            }

            // retain tertial backups
            now = new DateTime(DateTime.Now.Year + 1, 3, 1);
            for (int i = 0; i < 600; i++, now = now.AddMonths(-4)) {
                foreach (var b in backups) {
                    if (b.Timestamp.GetYearAndTertial() == now.GetYearAndTertial()) {
                        retain.Add(b.FileName);
                        break;
                    }
                }
            }

            // delete non-retained files
            foreach (var b in backups) {
                if (retain.Contains(b.FileName)) continue;
                try {
                    File.Delete(b.FileName);
                } catch { }
            }
            // delete temp files
            foreach (var f in Directory.GetFiles(App.Config.BackupPath, "*.tmp")) {
                try {
                    File.Delete(f);
                } catch { }
            }
        }
    }
}