using System.Text.RegularExpressions;

namespace w4c_workflows.Services;

/// <summary>
/// Parses human durations like "45s", "30m", "2h", "1d" (also compound forms
/// like "1h30m"). Used by YAML validation and the interval trigger scheduler.
/// </summary>
public static partial class DurationParser
{
    [GeneratedRegex(@"(?<num>\d+(?:\.\d+)?)(?<unit>ms|s|m|h|d)", RegexOptions.Compiled)]
    private static partial Regex PartRegex();

    public static bool TryParse(string? text, out TimeSpan result)
    {
        result = TimeSpan.Zero;
        if (string.IsNullOrWhiteSpace(text))
            return false;

        var matches = PartRegex().Matches(text);
        if (matches.Count == 0)
            return false;

        var total = TimeSpan.Zero;
        foreach (Match match in matches)
        {
            var value = double.Parse(match.Groups["num"].Value, System.Globalization.CultureInfo.InvariantCulture);
            var unit = match.Groups["unit"].Value;
            total += unit switch
            {
                "ms" => TimeSpan.FromMilliseconds(value),
                "s" => TimeSpan.FromSeconds(value),
                "m" => TimeSpan.FromMinutes(value),
                "h" => TimeSpan.FromHours(value),
                "d" => TimeSpan.FromDays(value),
                _ => throw new InvalidOperationException($"Unknown unit {unit}"),
            };
        }

        if (total <= TimeSpan.Zero)
            return false;

        result = total;
        return true;
    }
}