using Backend.MarketDataRequest;
using System.Globalization;

namespace Backend.DatabaseHandler
{
	public static class HistoricalRequestParser
	{
		public static HistoricalRequestWindow BuildWindow(
			string endDateTimeIsoUtc,
			string duration,
			HistoricalBarSize barSize)
		{
			DateTime endUtc = ParseRequestEndDateTimeUtc(endDateTimeIsoUtc);
			TimeSpan durationSpan = ParseDuration(duration);
			DateTime startUtc = endUtc - durationSpan;

			int expectedBarsMin = EstimateExpectedBars(durationSpan, barSize);

			return new HistoricalRequestWindow
			{
				StartUtc = startUtc,
				EndUtc = endUtc,
				ExpectedBarCountMin = expectedBarsMin
			};
		}

		public static DateTime ParseRequestEndDateTimeUtc(string raw)
		{
			if (string.IsNullOrWhiteSpace(raw))
				throw new FormatException("endDateTime is empty.");

			raw = raw.Trim();

Console.WriteLine(raw);
			if (!DateTimeOffset.TryParseExact(
					raw,
					new[]
					{
						"yyyy-MM-dd'T'HH:mm:ss'Z'",
						"yyyy-MM-dd'T'HH:mm:ss.FFF'Z'",
						"O"
					},
					CultureInfo.InvariantCulture,
					DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal,
					out var dto))
			{
				throw new FormatException(
					$"endDateTime must be ISO 8601 UTC, e.g. 2026-03-17T20:00:00Z. Received: '{raw}'");
			}

			return dto.UtcDateTime;
		}

		private static TimeSpan ParseDuration(string duration)
		{
			if (string.IsNullOrWhiteSpace(duration))
				throw new ArgumentException("Duration is empty.");

			string normalized = duration.Trim().Replace("+", " ");
			var parts = normalized.Split(' ', StringSplitOptions.RemoveEmptyEntries);

			if (parts.Length != 2)
				throw new ArgumentException($"Invalid duration format: '{duration}'");

			int value = int.Parse(parts[0], CultureInfo.InvariantCulture);
			string unit = parts[1].ToUpperInvariant();

			return unit switch
			{
				"S" => TimeSpan.FromSeconds(value),
				"D" => TimeSpan.FromDays(value),
				"W" => TimeSpan.FromDays(value * 7),
				"M" => TimeSpan.FromDays(value * 30),
				"Y" => TimeSpan.FromDays(value * 365),
				_ => throw new ArgumentException($"Unsupported duration unit: '{unit}'")
			};
		}

		private static int EstimateExpectedBars(TimeSpan duration, HistoricalBarSize barSize)
		{
			double secondsPerBar = barSize switch
			{
				HistoricalBarSize.OneMin => 60,
				HistoricalBarSize.FiveMins => 300,
				HistoricalBarSize.FifteenMins => 900,
				HistoricalBarSize.OneHour => 3600,
				HistoricalBarSize.TwoHours => 7200,
				HistoricalBarSize.ThreeHours => 10800,
				HistoricalBarSize.FourHours => 14400,
				HistoricalBarSize.EightHours => 28800,
				HistoricalBarSize.OneDay => 86400,
				HistoricalBarSize.FiveDays => 432000,
				HistoricalBarSize.OneWeek => 604800,
				HistoricalBarSize.OneMonth => 2592000,
				_ => throw new ArgumentOutOfRangeException(nameof(barSize))
			};

			// Markets trade ~6.5 hours/day, 5 days/week — not 24/7 calendar time.
			// NYSE averages ~252 trading days/year, but holiday-heavy windows
			// (e.g. Nov-Jan with Thanksgiving, Christmas, New Year's, MLK Day)
			// can have significantly fewer. Using 240/365 gives a conservative
			// floor that prevents false cache misses during these periods.
			double marketFraction = barSize switch
			{
				HistoricalBarSize.OneMonth => 1.0,
				HistoricalBarSize.OneDay or HistoricalBarSize.FiveDays or HistoricalBarSize.OneWeek => 240.0 / 365.0,
				_ => (6.5 * 240.0) / (24.0 * 365.0)
			};

			return Math.Max(1, (int)Math.Floor(duration.TotalSeconds * marketFraction / secondsPerBar));
		}
	}
}