using System;
using System.Diagnostics.CodeAnalysis;
using System.IO;

namespace ADOFAIRenderer.API;

/// <summary>
/// Represents the result and metadata of a completed or canceled render session.
/// </summary>
/// <remarks>
/// Passed to the completion callback registered with <see cref="RenderSession.OnComplete"/>. Immutable.
/// </remarks>
[SuppressMessage("ReSharper", "UnusedType.Global")]
[SuppressMessage("ReSharper", "MemberCanBePrivate.Global")]
public class RenderResult
{
    /// <summary>
    /// Indicates whether the rendering session completed successfully.
    /// </summary>
    public bool Success { get; }

    /// <summary>
    /// The output path of the rendered video file: the path given to <see cref="RenderSession.WithOutputPath"/> as passed
    /// (relative if it was relative), or the path of the time-stamped file in the output directory chosen in the mod
    /// settings (by default &lt;game root&gt;/Render).
    /// Empty string if rendering failed or was cancelled (the unfinished file is deleted).
    /// </summary>
    public string OutputPath { get; }

    /// <summary>
    /// Total number of video frames sent to the encoder.
    /// </summary>
    public long TotalFrames { get; }

    /// <summary>
    /// The calculated video duration in seconds: <see cref="TotalFrames"/> divided by the effective video frame rate
    /// (min of the configured VideoFPS and RenderFPS); 0 when the frame rate is not positive.
    /// </summary>
    public double VideoDuration { get; }

    /// <summary>
    /// Total wall-clock time spent rendering, from the end of the countdown (start of capture) to the end of the render.
    /// </summary>
    public TimeSpan RenderDuration { get; }

    /// <summary>
    /// File size of the output video in bytes (0 if failed or file does not exist).
    /// </summary>
    public long FileSizeBytes { get; }

    /// <summary>
    /// Error message or reason if rendering failed or was canceled; <c>null</c> on success.
    /// A cancelled render has "Rendering was cancelled by user."; a failed render has "Rendering failed: " followed by
    /// the reason. Use <see cref="Success"/> to test the outcome; the texts are meant for display.
    /// </summary>
    public string? ErrorMessage { get; }
    
    /// <summary>
    /// Initializes a new instance of the <see cref="RenderResult"/> class.
    /// </summary>
    /// <param name="success">Whether the render session completed successfully.</param>
    /// <param name="outputPath">The absolute output path of the rendered video file.</param>
    /// <param name="totalFrames">Total number of video frames sent to the encoder.</param>
    /// <param name="videoDuration">Calculated video duration in seconds.</param>
    /// <param name="renderDuration">Total wall-clock time spent rendering.</param>
    /// <param name="fileSizeBytes">File size of the output video in bytes.</param>
    /// <param name="errorMessage">Error message or reason if failed or canceled; otherwise, <c>null</c>.</param>
    public RenderResult(
        bool success,
        string outputPath,
        long totalFrames,
        double videoDuration,
        TimeSpan renderDuration,
        long fileSizeBytes = 0,
        string? errorMessage = null)
    {
        Success = success;
        OutputPath = outputPath;
        TotalFrames = totalFrames;
        VideoDuration = videoDuration;
        RenderDuration = renderDuration;
        FileSizeBytes = fileSizeBytes;
        ErrorMessage = errorMessage;
    }

    /// <summary>
    /// Creates a successful <see cref="RenderResult"/> instance from the specified render metrics.
    /// </summary>
    /// <param name="outputPath">The path to the rendered video file.</param>
    /// <param name="totalFrames">Total number of video frames sent to the encoder.</param>
    /// <param name="fps">The effective frames per second used to compute video duration.</param>
    /// <param name="renderDuration">Total wall-clock time spent rendering.</param>
    /// <returns>A new <see cref="RenderResult"/> representing a successful render session.</returns>
    /// <remarks>The file size is read from disk; it is 0 when the file does not exist or cannot be read.</remarks>
    internal static RenderResult CreateSuccess(string outputPath, long totalFrames, double fps, TimeSpan renderDuration)
    {
        var fileSizeBytes = 0L;
        if (!string.IsNullOrEmpty(outputPath) && File.Exists(outputPath))
        {
            try { fileSizeBytes = new FileInfo(outputPath).Length; }
            catch { /* ignored */ }
        }

        var videoDuration = fps > 0 ? totalFrames / fps : 0.0;
        return new RenderResult(true, outputPath, totalFrames, videoDuration, renderDuration, fileSizeBytes);
    }

    /// <summary>
    /// Creates a failed or cancelled <see cref="RenderResult"/> instance.
    /// </summary>
    /// <param name="errorMessage">Error message or reason for failure/cancellation.</param>
    /// <param name="totalFrames">Total number of video frames sent to the encoder prior to termination.</param>
    /// <param name="fps">The effective frames per second used to compute video duration.</param>
    /// <param name="renderDuration">Total wall-clock time spent rendering prior to termination.</param>
    /// <returns>A new <see cref="RenderResult"/> representing a failed or canceled render session.</returns>
    /// <remarks>OutputPath is empty and FileSizeBytes is 0. A null message is replaced by a generic one.</remarks>
    internal static RenderResult CreateFailure(string? errorMessage, long totalFrames, double fps, TimeSpan renderDuration)
    {
        var videoDuration = fps > 0 ? totalFrames / fps : 0.0;
        return new RenderResult(false, string.Empty, totalFrames, videoDuration, renderDuration, 0, errorMessage ?? "Rendering failed or was cancelled.");
    }

    /// <summary>
    /// Returns a string summarizing the render result metrics or failure reason.
    /// </summary>
    /// <returns>A string representation of the <see cref="RenderResult"/>.</returns>
    public override string ToString()
    {
        return Success
            ? $"[RenderResult: Success, Output={OutputPath}, Frames={TotalFrames}, VideoDuration={VideoDuration:F2}s, Time={RenderDuration.TotalSeconds:F1}s, Size={FileSizeBytes / 1024.0 / 1024.0:F2}MB]"
            : $"[RenderResult: Failed/Cancelled, Error={ErrorMessage ?? "Unknown"}]";
    }
}