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

namespace ytLive.Models;

/// <summary>One Super Chat or Super Sticker event, as YouTube reports it.</summary>
public sealed record SuperChatEvent(
    string Id,
    ChatEventKind Kind,
    long AmountMicros,
    string Currency,
    string? DisplayAmount,
    DateTime PublishedAt);

/// <summary>
/// TASK 3·20: what this session's rewards added up to — <b>in memory only</b>.
/// <para>Derived on demand from <c>superChatEvents.list</c> rather than persisted: YouTube is the system
/// of record for money, and keeping a local ledger would contradict the published promise that no
/// viewer, member or donor information is retained after the session ends.</para>
/// <para>Totals are kept <b>per currency</b> and never summed across currencies — a $5 and a €5 are not
/// $10, and a single blended number would be a lie.</para>
/// </summary>
public sealed record SessionRewardSummary(
    int SuperChatCount,
    int SuperStickerCount,
    IReadOnlyDictionary<string, long> MicrosByCurrency,
    DateTime? FirstEventAt,
    DateTime? LastEventAt)
{
    public static readonly SessionRewardSummary Empty = new(
        0, 0, new Dictionary<string, long>(), null, null);

    public int TotalEvents => SuperChatCount + SuperStickerCount;

    public bool HasEvents => TotalEvents > 0;

    /// <summary>Filters to a session window and rolls the events up. Events outside
    /// [<paramref name="sinceUtc"/>, <paramref name="untilUtc"/>] are ignored, which is what makes a
    /// report "this session" rather than "this channel".</summary>
    public static SessionRewardSummary From(
        IEnumerable<SuperChatEvent> events, DateTime sinceUtc, DateTime? untilUtc = null)
    {
        var until = untilUtc ?? DateTime.MaxValue;
        var inWindow = events
            .Where(e => e.PublishedAt >= sinceUtc && e.PublishedAt <= until)
            .OrderBy(e => e.PublishedAt)
            .ToList();

        if (inWindow.Count == 0) return Empty;

        var byCurrency = new Dictionary<string, long>(StringComparer.OrdinalIgnoreCase);
        foreach (var e in inWindow)
        {
            var currency = string.IsNullOrWhiteSpace(e.Currency) ? "?" : e.Currency.ToUpperInvariant();
            byCurrency.TryGetValue(currency, out var total);
            byCurrency[currency] = total + Math.Max(0, e.AmountMicros);
        }

        return new SessionRewardSummary(
            inWindow.Count(e => e.Kind == ChatEventKind.SuperChat),
            inWindow.Count(e => e.Kind == ChatEventKind.SuperSticker),
            byCurrency,
            inWindow[0].PublishedAt,
            inWindow[^1].PublishedAt);
    }

    /// <summary>Money lines for display, e.g. "USD $12.34 · EUR €4.00". Empty when there is nothing to
    /// show — a creator who never monetized must never be shown a zero.</summary>
    public IReadOnlyList<string> MoneyLines()
        => MicrosByCurrency
            .Where(pair => pair.Value > 0)
            .OrderByDescending(pair => pair.Value)
            .Select(pair => $"{pair.Key} {Format(pair.Key, pair.Value)}")
            .ToList();

    private static string Format(string currency, long micros)
    {
        var amount = micros / 1_000_000m;
        var symbol = currency switch
        {
            "USD" => "$",
            "EUR" => "€",
            "GBP" => "£",
            "CAD" => "CA$",
            "AUD" => "A$",
            _ => string.Empty,
        };
        return symbol.Length > 0
            ? symbol + amount.ToString("0.00", CultureInfo.InvariantCulture)
            : amount.ToString("0.00", CultureInfo.InvariantCulture) + " " + currency;
    }
}