using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using ADOFAIRenderer.Data;

namespace ADOFAIRenderer.Util.FFmpeg;

/// <summary>
/// Family of a video encoder. Selects the encoder-specific configuration in <see cref="FFmpegNativeEncoder"/>
/// (input pixel format, hardware device setup, quality option names, speed preset).
/// </summary>
[SuppressMessage("ReSharper", "InconsistentNaming")]
internal enum EncoderKind
{
    /// <summary>CPU encoder library linked into FFmpeg (libx264, libx265, libvpx-vp9, libsvtav1, libaom-av1, libvvenc).</summary>
    Software,

    /// <summary>NVIDIA NVENC hardware encoder (*_nvenc).</summary>
    NVENC,

    /// <summary>AMD Advanced Media Framework hardware encoder (*_amf).</summary>
    AMF,

    /// <summary>Intel Quick Sync Video hardware encoder (*_qsv), driven through a QSV hardware device context.</summary>
    QSV,

    /// <summary>Apple VideoToolbox hardware encoder (*_videotoolbox, macOS).</summary>
    VideoToolbox
}
    
/// <summary>
/// Known FFmpeg video encoder: FFmpeg encoder name, output codec, GPU vendor and encoder family.
///
/// Instances exist only as the static fields below (the constructor is private); compare them with == or
/// <see cref="Equals(VideoEncoder)"/>, which compare <see cref="Name"/> case-insensitively.
/// <see cref="All"/> lists every encoder, and its order is the fallback order used by
/// GPUUtil.GetPrioritizedEncoders after the encoders of the active GPU vendor.
///
/// An entry does not mean that the encoder exists in the loaded FFmpeg build or works on the current machine:
/// FFmpegNativeEncoder.Start looks each one up with avcodec_find_encoder_by_name and opens it, and skips the
/// encoders that are missing or fail to open.
/// Reference: https://ffmpeg.org/ffmpeg-codecs.html (Video Encoders)
/// </summary>
[SuppressMessage("ReSharper", "InconsistentNaming")]
internal sealed class VideoEncoder : IEquatable<VideoEncoder>
{
    // ReSharper disable MemberCanBePrivate.Global

    // Each field: FFmpeg encoder name, output codec, GPU vendor whose hardware runs it
    // (Unknown for CPU encoders), encoder family.

    // ── H.264 ──
    /// <summary>NVIDIA NVENC hardware encoder for H.264 (FFmpeg encoder "h264_nvenc").</summary>
    public static readonly VideoEncoder H264_NVENC = new("h264_nvenc", Codec.H264, GPUVendor.NVIDIA, EncoderKind.NVENC);
    /// <summary>Intel Quick Sync Video hardware encoder for H.264 (FFmpeg encoder "h264_qsv").</summary>
    public static readonly VideoEncoder H264_QSV = new("h264_qsv", Codec.H264, GPUVendor.Intel, EncoderKind.QSV);
    /// <summary>AMD AMF hardware encoder for H.264 (FFmpeg encoder "h264_amf").</summary>
    public static readonly VideoEncoder H264_AMF = new("h264_amf", Codec.H264, GPUVendor.AMD, EncoderKind.AMF);
    /// <summary>Apple VideoToolbox hardware encoder for H.264 (FFmpeg encoder "h264_videotoolbox").</summary>
    public static readonly VideoEncoder H264_VideoToolbox = new("h264_videotoolbox", Codec.H264, GPUVendor.Apple, EncoderKind.VideoToolbox);
    /// <summary>CPU software encoder for H.264 (FFmpeg encoder "libx264").</summary>
    public static readonly VideoEncoder Libx264 = new("libx264", Codec.H264, GPUVendor.Unknown, EncoderKind.Software);

    // ── H.265 (HEVC) ──
    /// <summary>NVIDIA NVENC hardware encoder for H.265 (HEVC) (FFmpeg encoder "hevc_nvenc").</summary>
    public static readonly VideoEncoder HEVC_NVENC = new("hevc_nvenc", Codec.H265, GPUVendor.NVIDIA, EncoderKind.NVENC);
    /// <summary>Intel Quick Sync Video hardware encoder for H.265 (HEVC) (FFmpeg encoder "hevc_qsv").</summary>
    public static readonly VideoEncoder HEVC_QSV = new("hevc_qsv", Codec.H265, GPUVendor.Intel, EncoderKind.QSV);
    /// <summary>AMD AMF hardware encoder for H.265 (HEVC) (FFmpeg encoder "hevc_amf").</summary>
    public static readonly VideoEncoder HEVC_AMF = new("hevc_amf", Codec.H265, GPUVendor.AMD, EncoderKind.AMF);
    /// <summary>Apple VideoToolbox hardware encoder for H.265 (HEVC) (FFmpeg encoder "hevc_videotoolbox").</summary>
    public static readonly VideoEncoder HEVC_VideoToolbox = new("hevc_videotoolbox", Codec.H265, GPUVendor.Apple, EncoderKind.VideoToolbox);
    /// <summary>CPU software encoder for H.265 (HEVC) (FFmpeg encoder "libx265").</summary>
    public static readonly VideoEncoder Libx265 = new("libx265", Codec.H265, GPUVendor.Unknown, EncoderKind.Software);

    // ── VP9 ──
    // libavcodec has no "vp9_nvenc" encoder (NVENC does not encode VP9), so avcodec_find_encoder_by_name returns null
    // for this entry and FFmpegNativeEncoder.Start skips it with a "not found" warning.
    /// <summary>NVIDIA NVENC entry for VP9 (FFmpeg encoder name "vp9_nvenc"); never found in libavcodec, see above.</summary>
    public static readonly VideoEncoder VP9_NVENC = new("vp9_nvenc", Codec.VP9, GPUVendor.NVIDIA, EncoderKind.NVENC);
    /// <summary>Intel Quick Sync Video hardware encoder for VP9 (FFmpeg encoder "vp9_qsv").</summary>
    public static readonly VideoEncoder VP9_QSV = new("vp9_qsv", Codec.VP9, GPUVendor.Intel, EncoderKind.QSV);
    /// <summary>CPU software encoder for VP9 (FFmpeg encoder "libvpx-vp9").</summary>
    public static readonly VideoEncoder LibvpxVP9 = new("libvpx-vp9", Codec.VP9, GPUVendor.Unknown, EncoderKind.Software);

    // ── AV1 ──
    /// <summary>NVIDIA NVENC hardware encoder for AV1 (FFmpeg encoder "av1_nvenc").</summary>
    public static readonly VideoEncoder AV1_NVENC = new("av1_nvenc", Codec.AV1, GPUVendor.NVIDIA, EncoderKind.NVENC);
    /// <summary>Intel Quick Sync Video hardware encoder for AV1 (FFmpeg encoder "av1_qsv").</summary>
    public static readonly VideoEncoder AV1_QSV = new("av1_qsv", Codec.AV1, GPUVendor.Intel, EncoderKind.QSV);
    /// <summary>AMD AMF hardware encoder for AV1 (FFmpeg encoder "av1_amf").</summary>
    public static readonly VideoEncoder AV1_AMF = new("av1_amf", Codec.AV1, GPUVendor.AMD, EncoderKind.AMF);
    /// <summary>CPU software encoder for AV1 (FFmpeg encoder "libsvtav1").</summary>
    public static readonly VideoEncoder LibSvtAv1 = new("libsvtav1", Codec.AV1, GPUVendor.Unknown, EncoderKind.Software);
    /// <summary>CPU software encoder for AV1 (FFmpeg encoder "libaom-av1").</summary>
    public static readonly VideoEncoder LibAomAv1 = new("libaom-av1", Codec.AV1, GPUVendor.Unknown, EncoderKind.Software);

    // ── VVC ──
    /// <summary>CPU software encoder for H.266 (VVC) (FFmpeg encoder "libvvenc").</summary>
    public static readonly VideoEncoder LibVvenc = new("libvvenc", Codec.VVC, GPUVendor.Unknown, EncoderKind.Software);
        
    // ReSharper restore MemberCanBePrivate.Global

    /// <summary>
    /// Every known encoder, grouped by codec. Within a codec the order is NVENC → QSV → AMF → VideoToolbox → software
    /// (for the families the codec has); GPUUtil.GetPrioritizedEncoders keeps this order for the encoders that do not
    /// belong to the active GPU vendor.
    /// </summary>
    public static readonly IReadOnlyList<VideoEncoder> All = new[]
    {
        H264_NVENC, H264_QSV, H264_AMF, H264_VideoToolbox, Libx264,
        HEVC_NVENC, HEVC_QSV, HEVC_AMF, HEVC_VideoToolbox, Libx265,
        VP9_NVENC, VP9_QSV, LibvpxVP9,
        AV1_NVENC, AV1_QSV, AV1_AMF, LibSvtAv1, LibAomAv1,
        LibVvenc
    };

    /// <summary>Lookup table of <see cref="All"/> by <see cref="Name"/> (case-insensitive), used by <see cref="FromName"/>.</summary>
    private static readonly Dictionary<string, VideoEncoder> ByName =
        All.ToDictionary(e => e.Name, StringComparer.OrdinalIgnoreCase);

    /// <summary>FFmpeg encoder name passed to avcodec_find_encoder_by_name (e.g. "h264_nvenc", "libx264").</summary>
    public string Name { get; }

    /// <summary>Video codec of the bitstream the encoder produces.</summary>
    public Codec Codec { get; }

    /// <summary>GPU vendor whose hardware runs the encoder. <see cref="GPUVendor.Unknown"/> for CPU (software) encoders.</summary>
    public GPUVendor Vendor { get; }

    /// <summary>Encoder family (software or hardware API).</summary>
    public EncoderKind Kind { get; }

    /// <summary>True for every family except <see cref="EncoderKind.Software"/>.</summary>
    public bool IsHardware => Kind != EncoderKind.Software;

    /// <summary>Creates an entry. Used only by the static fields of this class.</summary>
    private VideoEncoder(string name, Codec codec, GPUVendor vendor, EncoderKind kind)
    {
        Name = name;
        Codec = codec;
        Vendor = vendor;
        Kind = kind;
    }

    /// <summary>
    /// Returns the known encoder with the given FFmpeg name (case-insensitive),
    /// or null when <paramref name="name"/> is null, empty or not in <see cref="All"/>.
    /// </summary>
    public static VideoEncoder? FromName(string name)
    {
        return string.IsNullOrEmpty(name) ? null : ByName.GetValueOrDefault(name);
    }

    /// <summary>True when <paramref name="other"/> is the same entry or has the same <see cref="Name"/> (case-insensitive).</summary>
    public bool Equals(VideoEncoder other)
    {
        if (ReferenceEquals(null, other)) return false;
        return ReferenceEquals(this, other) || string.Equals(Name, other.Name, StringComparison.OrdinalIgnoreCase);
    }

    /// <summary>True when <paramref name="obj"/> is a <see cref="VideoEncoder"/> equal to this one (see <see cref="Equals(VideoEncoder)"/>).</summary>
    public override bool Equals(object? obj)
    {
        return ReferenceEquals(this, obj) || obj is VideoEncoder other && Equals(other);
    }

    /// <summary>Case-insensitive hash of <see cref="Name"/>, consistent with <see cref="Equals(VideoEncoder)"/>.</summary>
    public override int GetHashCode()
    {
        return StringComparer.OrdinalIgnoreCase.GetHashCode(Name);
    }

    /// <summary>Value equality through <see cref="object.Equals(object, object)"/>; two null operands are equal.</summary>
    public static bool operator ==(VideoEncoder left, VideoEncoder right)
    {
        return Equals(left, right);
    }

    /// <summary>Negation of the <c>==</c> operator.</summary>
    public static bool operator !=(VideoEncoder left, VideoEncoder right)
    {
        return !Equals(left, right);
    }

    /// <summary>Returns the FFmpeg encoder name (<see cref="Name"/>).</summary>
    public override string ToString() => Name;
}