PlotDirector/PlotLine/Services/CharacterAgeDisplayService.cs

using PlotLine.Models;

namespace PlotLine.Services;

public sealed class CharacterAgeDisplayResult
{
    public bool HasExactAge { get; init; }
    public string? Label { get; init; }
    public string? DisplayText { get; init; }
}

public sealed record CharacterProfileAgeDisplayResult(string DisplayText, string Context, Scene? ReferenceScene);

public static class CharacterAgeDisplayService
{
    public static CharacterProfileAgeDisplayResult GetProfileAge(Character character,
        IReadOnlyList<Scene> orderedScenes, IReadOnlyList<SceneCharacter> appearances)
    {
        var appearanceIds = appearances.Where(x => x.CharacterID == character.CharacterID).Select(x => x.SceneID).ToHashSet();
        var reference = character.AgeReferenceSceneID.HasValue
            ? orderedScenes.FirstOrDefault(x => x.SceneID == character.AgeReferenceSceneID)
            : null;
        if (reference is null || !ResolveEffectiveSceneDate(reference.TimeModeName, reference.StartDateTime).HasValue)
            reference = orderedScenes.FirstOrDefault(x => appearanceIds.Contains(x.SceneID)
                && ResolveEffectiveSceneDate(x.TimeModeName, x.StartDateTime).HasValue
                && (!character.BirthDate.HasValue || x.StartDateTime!.Value.Date >= character.BirthDate.Value.Date));
        var age = GetAgeForScene(character, reference?.TimeModeName, reference?.StartDateTime);
        return new CharacterProfileAgeDisplayResult(age.DisplayText ?? "Unknown",
            age.HasExactAge ? (reference?.SceneID == character.AgeReferenceSceneID ? "At age reference scene" : "At first dated appearance")
                : character.AgeAtSeriesStart.HasValue ? "Approximate age at series start"
                : character.BirthDate.HasValue ? "A dated story scene is needed to calculate age." : "No birth date or approximate age recorded.",
            age.HasExactAge ? reference : null);
    }

    public static CharacterAgeDisplayResult GetAgeForScene(SceneCharacter character, string? sceneTimeModeName, DateTime? sceneStartDateTime)
    {
        var effectiveDate = ResolveEffectiveSceneDate(sceneTimeModeName, sceneStartDateTime);
        if (character.BirthDate.HasValue && effectiveDate.HasValue)
        {
            return new CharacterAgeDisplayResult
            {
                HasExactAge = true,
                Label = "Age in scene",
                DisplayText = FormatExactAge(character.BirthDate.Value.Date, effectiveDate.Value.Date)
            };
        }

        if (character.AgeAtSeriesStart.HasValue)
        {
            return new CharacterAgeDisplayResult
            {
                Label = "Approximate age",
                DisplayText = $"About {character.AgeAtSeriesStart.Value}"
            };
        }

        return new CharacterAgeDisplayResult();
    }

    public static CharacterAgeDisplayResult GetAgeForScene(Character character, string? sceneTimeModeName, DateTime? sceneStartDateTime)
    {
        var effectiveDate = ResolveEffectiveSceneDate(sceneTimeModeName, sceneStartDateTime);
        if (character.BirthDate.HasValue && effectiveDate.HasValue)
        {
            return new CharacterAgeDisplayResult
            {
                HasExactAge = true,
                Label = "Age in scene",
                DisplayText = FormatExactAge(character.BirthDate.Value.Date, effectiveDate.Value.Date)
            };
        }

        if (character.AgeAtSeriesStart.HasValue)
        {
            return new CharacterAgeDisplayResult
            {
                Label = "Approximate age",
                DisplayText = $"About {character.AgeAtSeriesStart.Value}"
            };
        }

        return new CharacterAgeDisplayResult();
    }

    public static DateTime? ResolveEffectiveSceneDate(string? timeModeName, DateTime? startDateTime)
    {
        if (!startDateTime.HasValue)
        {
            return null;
        }

        return string.Equals(timeModeName, "Exact Date", StringComparison.OrdinalIgnoreCase)
            || string.Equals(timeModeName, "Exact DateTime", StringComparison.OrdinalIgnoreCase)
            || string.Equals(timeModeName, "Exact Date and Time", StringComparison.OrdinalIgnoreCase)
                ? startDateTime.Value.Date
                : null;
    }

    public static string FormatExactAge(DateTime birthDate, DateTime sceneDate)
    {
        var (years, months) = CalculateExactAge(birthDate, sceneDate);

        return months == 0
            ? $"{years} year{Pluralise(years)}"
            : $"{years} year{Pluralise(years)}, {months} month{Pluralise(months)}";
    }

    public static (int Years, int Months) CalculateExactAge(DateTime birthDate, DateTime sceneDate)
    {
        var years = sceneDate.Year - birthDate.Year;
        if (sceneDate < birthDate.AddYears(years))
        {
            years--;
        }

        if (years < 0)
        {
            years = 0;
        }

        var lastBirthday = birthDate.AddYears(years);
        var months = ((sceneDate.Year - lastBirthday.Year) * 12) + sceneDate.Month - lastBirthday.Month;
        if (sceneDate.Day < lastBirthday.Day)
        {
            months--;
        }

        if (months < 0)
        {
            months = 0;
        }

        return (years, months);
    }

    private static string Pluralise(int value) => value == 1 ? string.Empty : "s";
}