You've sneaked into another supply closet - this time, it's across from the prototype suit manufacturing lab. You need to sneak inside and fix the issues with the suit, but there's a guard stationed outside the lab, so this is as close as you can safely get.

As you search the closet for anything that might help, you discover that you're not the first person to want to sneak in. Covering the walls, someone has spent an hour starting every midnight for the past few months secretly observing this guard post! They've been writing down the ID of the one guard on duty that night - the Elves seem to have decided that one guard was enough for the overnight shift - as well as when they fall asleep or wake up while at their post (your puzzle input).

Read the full puzzle.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace AdventOfCode.Y2018.Day04;

[ProblemName("Repose Record")]
class Solution : Solver {

    public object PartOne(string input) {
        var foo = from day in Parse(input)
                group day by day.guard into g
                select new { 
                    guard = g.Key, 
                    totalSleeps = g.Select(day => day.totalSleep).Sum(), 
                    sleepByMin = Enumerable.Range(0, 60).Select(minT => g.Sum(day => day.sleep[minT])).ToArray()
                };
        var maxSleep = foo.Max(x => x.totalSleeps);
        var fooT = foo.Single(g => g.totalSleeps == maxSleep);
        var maxSleepByMin = Enumerable.Range(0, 60).Max(minT => fooT.sleepByMin[minT]);
        var min = Enumerable.Range(0, 60).Single(minT => fooT.sleepByMin[minT] == maxSleepByMin);
        return fooT.guard * min;
    }

    public object PartTwo(string input) {
        var foo = from day in Parse(input)
                group day by day.guard into g
                select new { 
                    guard = g.Key, 
                    totalSleeps = g.Select(day => day.totalSleep).Sum(), 
                    sleepByMin = Enumerable.Range(0, 60).Select(minT => g.Sum(day => day.sleep[minT])).ToArray()
                };

        var maxMaxSleep = foo.Max(x => x.sleepByMin.Max());
        var fooT = foo.Single(x => x.sleepByMin.Max() == maxMaxSleep);
        var min = Enumerable.Range(0, 60).Single(minT => fooT.sleepByMin[minT] == maxMaxSleep);

        return fooT.guard * min;
    }

    IEnumerable<Day> Parse(string input) {
        var lines = input.Split("\n").ToList();
        lines.Sort((x, y) => DateTime.Parse(x.Substring(1, "1518-03-25 00:01".Length)).CompareTo(DateTime.Parse(y.Substring(1, "1518-03-25 00:01".Length))));
        var iline = 0;

        while (Int(@"Guard #(\d+) begins shift", out var guard)) {

            var sleep = new int[60];
            while (Date(@"\[(.*)\] falls asleep", out var fallsAsleap)) {
                Date(@"\[(.*)\] wakes up", out var wakesUp);

                var from = fallsAsleap.Hour != 0 ? 0 : fallsAsleap.Minute;
                var to = wakesUp.Hour != 0 ? 0 : wakesUp.Minute;

                for (var min = from; min < to; min++) {
                    sleep[min] = 1;
                }
            }

            yield return new Day() { guard = guard, sleep = sleep };
        }

        if (iline != lines.Count) {
            throw new Exception();
        }
        bool Int(string pattern, out int r) {
            r = 0;
            return String(pattern, out string st) && int.TryParse(st, out r);
        }

        bool Date(string pattern, out DateTime r) {
            r = DateTime.MinValue;
            return String(pattern, out string st) && DateTime.TryParse(st, out r);
        }

        bool String(string pattern, out string st) {
            st = null;
            if (iline >= lines.Count) {
                return false;
            }
            var m = Regex.Match(lines[iline], pattern);
            if (m.Success) {
                iline++;
                st = m.Groups[1].Value;
            }
            return m.Success;
        }

    }
}

class Day {
    public int guard;
    public int[] sleep;
    public int totalSleep => sleep.Sum();
}

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