namespace Uwaa.PNG;

/// <summary>
/// The header for a data chunk in a PNG file.
/// </summary>
public readonly struct ChunkHeader
{
    /// <summary>
    /// The position/start of the chunk header within the stream.
    /// </summary>
    public long Position { get; }

    /// <summary>
    /// The length of the chunk in bytes.
    /// </summary>
    public int Length { get; }

    /// <summary>
    /// The name of the chunk, uppercase first letter means the chunk is critical (vs. ancillary).
    /// </summary>
    public string Name { get; }

    /// <summary>
    /// Whether the chunk is critical (must be read by all readers) or ancillary (may be ignored).
    /// </summary>
    public bool IsCritical => char.IsUpper(Name[0]);

    /// <summary>
    /// A public chunk is one that is defined in the International Standard or is registered in the list of public chunk types maintained by the Registration Authority. 
    /// Applications can also define private (unregistered) chunk types for their own purposes.
    /// </summary>
    public bool IsPublic => char.IsUpper(Name[1]);

    /// <summary>
    /// Whether the (if unrecognized) chunk is safe to copy.
    /// </summary>
    public bool IsSafeToCopy => char.IsUpper(Name[3]);

    /// <summary>
    /// Create a new <see cref="ChunkHeader"/>.
    /// </summary>
    public ChunkHeader(long position, int length, string name)
    {
        if (length < 0)
        {
            throw new ArgumentException($"Length less than zero ({length}) encountered when reading chunk at position {position}.");
        }

        Position = position;
        Length = length;
        Name = name;
    }

    public override string ToString()
    {
        return $"{Name} at {Position} (length: {Length}).";
    }
}