namespace Uwaa.PNG;

/// <summary>
/// A PNG image. Call <see cref="Open(byte[])"/> to open from file or bytes.
/// </summary>
public class Png
{
    readonly RawPngData data;
    readonly bool hasTransparencyChunk;

    /// <summary>
    /// The header data from the PNG image.
    /// </summary>
    public ImageHeader Header { get; }

    /// <summary>
    /// The width of the image in pixels.
    /// </summary>
    public int Width => Header.Width;

    /// <summary>
    /// The height of the image in pixels.
    /// </summary>
    public int Height => Header.Height;

    /// <summary>
    /// Whether the image has an alpha (transparency) layer.
    /// </summary>
    public bool HasAlphaChannel => (Header.ColorType & ColorType.AlphaChannelUsed) != 0 || hasTransparencyChunk;

    internal Png(ImageHeader header, RawPngData data, bool hasTransparencyChunk)
    {
        Header = header;
        this.data = data ?? throw new ArgumentNullException(nameof(data));
        this.hasTransparencyChunk = hasTransparencyChunk;
    }

    /// <summary>
    /// Get the pixel at the given column and row (x, y).
    /// </summary>
    /// <remarks>
    /// Pixel values are generated on demand from the underlying data to prevent holding many items in memory at once, so consumers
    /// should cache values if they're going to be looped over many time.
    /// </remarks>
    /// <param name="x">The x coordinate (column).</param>
    /// <param name="y">The y coordinate (row).</param>
    /// <returns>The pixel at the coordinate.</returns>
    public Pixel GetPixel(int x, int y) => data.GetPixel(x, y);

    /// <summary>
    /// Read the PNG image from the stream.
    /// </summary>
    /// <param name="stream">The stream containing PNG data to be read.</param>
    /// <returns>The <see cref="Png"/> data from the stream.</returns>
    public static Png Open(Stream stream)
        => PngOpener.Open(stream);

    /// <summary>
    /// Read the PNG image from the bytes.
    /// </summary>
    /// <param name="bytes">The bytes of the PNG data to be read.</param>
    /// <returns>The <see cref="Png"/> data from the bytes.</returns>
    public static Png Open(byte[] bytes)
    {
        using var memoryStream = new MemoryStream(bytes);
        return PngOpener.Open(memoryStream);
    }

    /// <summary>
    /// Read the PNG from the file path.
    /// </summary>
    /// <param name="path">The path to the PNG file to open.</param>
    /// <remarks>This will open the file to obtain a <see cref="FileStream"/> so will lock the file during reading.</remarks>
    /// <returns>The <see cref="Png"/> data from the file.</returns>
    public static Png Open(string path)
    {
        using var fileStream = File.OpenRead(path);
        return Open(fileStream);
    }
}