using System.Windows.Input;
using ytLive.Helpers;
using ytLive.Models;

namespace ytLive.ViewModels;

/// <summary>
/// The creator's own video rate, per tier — the latitude the tier table deliberately does not take
/// away. A creator who knows their upload can set any rate from the tier's YouTube minimum upward;
/// nothing here invents a ceiling, because a wrong guess is what live step-down exists to catch.
///
/// <para><b>Why per tier:</b> a number that is sensible at 1080p60 is wasteful at 720p30, and the
/// creator who tuned one tier has not tuned the other. Unset means "use the shipped default", which
/// is what <see cref="EffectiveQuality"/> substitutes.</para>
///
/// <para><b>Why this matters now:</b> with CBR holding the target (<c>FfmpegArgs.AddRateControl</c>)
/// the number the creator types is the number that goes out, so it is a real quality choice rather
/// than an average to undershoot.</para>
/// </summary>
public partial class MainViewModel
{
    private readonly Dictionary<string, double> _ratedMbpsByTier = new(StringComparer.Ordinal);

    /// <summary>The tier with the creator's rate substituted for the shipped default. Every consumer
    /// that builds encoder options or a step-down policy must use this, never the raw tier.</summary>
    public QualityOption EffectiveQuality(QualityOption tier)
        => RatedFor(tier) is var rated && Math.Abs(rated - tier.Bitrate) > 0.001
            ? tier with { Bitrate = rated }
            : tier;

    private double RatedFor(QualityOption tier)
    {
        if (_ratedMbpsByTier.TryGetValue(tier.Display, out var cached)) return cached;

        // The constructor resolves the default tier before the layout store exists, so the first read
        // must not cache: a cached default would shadow the creator's stored rate for that run.
        var stored = _layoutStore is null ? null : _layoutStore.LoadRatedMbps(tier.Display);
        var value = Math.Max(stored ?? tier.Bitrate, RateLadder.For(tier).Minimum);
        if (_layoutStore is not null) _ratedMbpsByTier[tier.Display] = value;
        return value;
    }

    /// <summary>The rate the selected tier will stream at, in Mbps.</summary>
    public double RatedMbps
    {
        get => RatedFor(SelectedQuality);
        set
        {
            var tier = SelectedQuality;
            var band = RateLadder.For(tier);
            // Below the tier minimum YouTube will not hold the resolution; above ~100 is not a stream.
            var clamped = Math.Clamp(Math.Round(value, 1), band.Minimum, 100.0);
            if (Math.Abs(clamped - RatedFor(tier)) < 0.05)
            {
                OnPropertyChanged(nameof(RatedMbps));
                return;
            }

            _ratedMbpsByTier[tier.Display] = clamped;
            _layoutStore.SaveRatedMbps(tier.Display, clamped);
            ApplyStreamQuality(tier);
            OnPropertyChanged(nameof(RatedMbps));
            OnPropertyChanged(nameof(RateHint));
        }
    }

    /// <summary>What YouTube expects for this tier, shown next to the field.</summary>
    public string RateHint
    {
        get
        {
            var band = RateLadder.For(SelectedQuality);
            return $"YouTube recommends {band.Recommended:0.#} Mbps for {SelectedQuality.Display}; " +
                   $"it will not take less than {band.Minimum:0.#}. Your connection must carry this " +
                   "plus ~20% headroom.";
        }
    }

    /// <summary>Restores the shipped default for the selected tier.</summary>
    public void ResetRatedMbps()
    {
        var tier = SelectedQuality;
        if (!_ratedMbpsByTier.ContainsKey(tier.Display)) return;
        _ratedMbpsByTier.Remove(tier.Display);
        _layoutStore.SaveRatedMbps(tier.Display, null);
        _ratedMbpsByTier[tier.Display] = RatedFor(tier);
        ApplyStreamQuality(tier);
        OnPropertyChanged(nameof(RatedMbps));
        OnPropertyChanged(nameof(RateHint));
    }

    // ─── Between-session suggestion (Models/RateHistory) ───
    //
    // Never applied on its own. The creator is asked once per materially different answer and may say
    // "keep mine"; that refusal is remembered against the proposed value, so the same question is not
    // asked again until the evidence actually moves.

    private RateHistory.Proposal? _rateProposal;

    public bool HasRateProposal => _rateProposal is not null;

    public string? RateProposalText
    {
        get
        {
            if (_rateProposal is not { } proposal) return null;
            var tier = SelectedQuality.Display;
            return proposal.Raise
                ? $"Your last {RateHistory.Window} sessions on {tier} held {proposal.Mbps:0.#} Mbps. " +
                  $"Start the next stream there instead of {RatedMbps:0.#}?"
                : $"Your last {RateHistory.Window} sessions on {tier} had to drop quality. " +
                  $"Start the next stream at {proposal.Mbps:0.#} Mbps instead of {RatedMbps:0.#}?";
        }
    }

    public ICommand AcceptRateProposalCommand { get; private set; } = null!;
    public ICommand DismissRateProposalCommand { get; private set; } = null!;

    private void InitializeRateProposalCommands()
    {
        AcceptRateProposalCommand = new RelayCommand(_ =>
        {
            if (_rateProposal is not { } proposal) return;
            RatedMbps = proposal.Mbps;          // explicit consent is the only path that changes it
            ClearRateProposal();
        });
        DismissRateProposalCommand = new RelayCommand(_ =>
        {
            if (_rateProposal is { } proposal)
                _layoutStore.SaveDismissedRateProposal(SelectedQuality.Display, proposal.Mbps);
            ClearRateProposal();
        });
    }

    /// <summary>Recomputes the suggestion for the selected tier. Called at startup and whenever the tier
    /// or the rate changes; silent unless the evidence warrants a change and the creator has not already
    /// refused this exact number.</summary>
    internal void RefreshRateProposal()
    {
        _rateProposal = null;
        if (_layoutStore is not null)
        {
            var tier = SelectedQuality;
            var history = _layoutStore.LoadRateHistory();
            // Before this run's first stream the encoder is unknown; the last session on this tier is
            // the honest guess, and evidence about a different encoder stays out either way.
            var lastForTier = history.LastOrDefault(entry => entry.Tier == tier.Display);
            var encoder = CurrentHealth.VideoEncoder
                          ?? (string.IsNullOrEmpty(lastForTier.Encoder) ? null : lastForTier.Encoder);

            var suggestion = RateHistory.Suggest(history, tier.Display, encoder, RatedMbps);
            if (suggestion is { } candidate
                && _layoutStore.LoadDismissedRateProposal(tier.Display) != candidate.Mbps)
            {
                _rateProposal = candidate;
            }
        }

        OnPropertyChanged(nameof(HasRateProposal));
        OnPropertyChanged(nameof(RateProposalText));
    }

    private void ClearRateProposal()
    {
        _rateProposal = null;
        OnPropertyChanged(nameof(HasRateProposal));
        OnPropertyChanged(nameof(RateProposalText));
    }
}