// Exercise 2: equality, hashing, strings and time (medium)
//
// STEP 1: Make Sku (a class) usable as a dictionary key and in HashSet: two Skus are equal if their Code is
//         equal IGNORING case. Override Equals and GetHashCode consistently (use
//         StringComparer.OrdinalIgnoreCase.GetHashCode(Code)).
// STEP 2: SameEmail(a, b): compare emails ignoring case with an explicit ordinal comparison.
// STEP 3: ToUtcIso(DateTimeOffset local): return the instant in UTC formatted as "yyyy-MM-ddTHH:mm:ssZ".
// STEP 4: CountDistinctQueries(): `query` is a deferred LINQ query with a side effect counter; enumerate it
//         ONCE (materialize with ToList()) and return (count, sum) so the source is evaluated only once.
//
// Run with: dotnet run (inside a console project).

using System;
using System.Collections.Generic;
using System.Linq;

class Sku
{
    public string Code { get; }
    public Sku(string code) { Code = code; }
    // TODO: Equals / GetHashCode
}

class Program
{
    static int Evaluations;

    static bool SameEmail(string a, string b) => a == b; // TODO

    static string ToUtcIso(DateTimeOffset local) => local.ToString("yyyy-MM-ddTHH:mm:ss") + "Z"; // TODO

    static (int count, int sum) CountAndSum()
    {
        IEnumerable<int> query = Enumerable.Range(1, 5).Select(x => { Evaluations++; return x * 10; });
        return (query.Count(), query.Sum()); // TODO: evaluate once
    }

    static void Main()
    {
        int pass = 0, total = 0;
        void Check(string name, bool ok) { total++; if (ok) pass++; Console.WriteLine($"{(ok ? "PASS" : "FAIL")}: {name}"); }

        var set = new HashSet<Sku> { new Sku("ABC-1"), new Sku("abc-1"), new Sku("XYZ") };
        Check("HashSet dedupes case-insensitively", set.Count == 2);
        var stock = new Dictionary<Sku, int> { [new Sku("Bowl")] = 3 };
        Check("dictionary lookup with an equal key", stock.TryGetValue(new Sku("BOWL"), out var n) && n == 3);
        Check("emails ignore case", SameEmail("Ana@Example.com", "ana@example.COM") && !SameEmail("a@x.com", "b@x.com"));
        var tashkent = new DateTimeOffset(2026, 10, 21, 15, 30, 0, TimeSpan.FromHours(5));
        Check("UTC conversion", ToUtcIso(tashkent) == "2026-10-21T10:30:00Z");
        var (count, sum) = CountAndSum();
        Check($"query evaluated once (evaluations {Evaluations})", count == 5 && sum == 150 && Evaluations == 5);

        Console.WriteLine($"--- {pass}/{total} checks passed ---");
    }
}