using System;
using System.Runtime.InteropServices;
using System.Text;

namespace NetVips;

/// <summary>
/// An input connection.
/// </summary>
public partial class Source : Connection
{
    /// <summary>
    /// Secret ref for <see cref="NewFromMemory(byte[])"/>.
    /// </summary>
    private GCHandle _dataHandle;

    /// <inheritdoc cref="Connection"/>
    internal Source(nint pointer) : base(pointer)
    {
    }

    /// <summary>
    /// Make a new source from a file descriptor (a small integer).
    /// </summary>
    /// <remarks>
    /// Make a new source that is attached to the descriptor. For example:
    /// <code language="lang-csharp">
    /// using var source = Source.NewFromDescriptor(0);
    /// </code>
    /// Makes a descriptor attached to stdin.
    ///
    /// You can pass this source to (for example) <see cref="Image.NewFromSource"/>.
    /// </remarks>
    /// <param name="descriptor">Read from this file descriptor.</param>
    /// <returns>A new <see cref="Source"/>.</returns>
    /// <exception cref="VipsException">If unable to create a new <see cref="Source"/> from <paramref name="descriptor"/>.</exception>
    public static Source NewFromDescriptor(int descriptor)
    {
        var pointer = Internal.VipsSource.NewFromDescriptor(descriptor);
        if (pointer == IntPtr.Zero)
        {
            throw new VipsException($"can't create source from descriptor {descriptor}");
        }

        return new Source(pointer);
    }

    /// <summary>
    /// Make a new source from a filename.
    /// </summary>
    /// <remarks>
    /// Make a new source that is attached to the named file. For example:
    /// <code language="lang-csharp">
    /// using var source = Source.NewFromFile("myfile.jpg");
    /// </code>
    /// You can pass this source to (for example) <see cref="Image.NewFromSource"/>.
    /// </remarks>
    /// <param name="filename">Read from this filename.</param>
    /// <returns>A new <see cref="Source"/>.</returns>
    /// <exception cref="VipsException">If unable to create a new <see cref="Source"/> from <paramref name="filename"/>.</exception>
    public static Source NewFromFile(string filename)
    {
        var bytes = Encoding.UTF8.GetBytes(filename + char.MinValue); // Ensure null-terminated string
        var pointer = Internal.VipsSource.NewFromFile(bytes);
        if (pointer == IntPtr.Zero)
        {
            throw new VipsException($"can't create source from filename {filename}");
        }

        return new Source(pointer);
    }

    /// <summary>
    /// Make a new source from a memory object.
    /// </summary>
    /// <remarks>
    /// Make a new source that is attached to the memory object. For example:
    /// <code language="lang-csharp">
    /// using var source = Source.NewFromMemory(data);
    /// </code>
    /// You can pass this source to (for example) <see cref="Image.NewFromSource"/>.
    /// </remarks>
    /// <param name="data">The memory object.</param>
    /// <returns>A new <see cref="Source"/>.</returns>
    /// <exception cref="VipsException">If unable to create a new <see cref="Source"/> from <paramref name="data"/>.</exception>
    public static Source NewFromMemory(byte[] data)
    {
        var handle = GCHandle.Alloc(data, GCHandleType.Pinned);
        var pointer = Internal.VipsSource.NewFromMemory(handle.AddrOfPinnedObject(), (nuint)data.Length);
        if (pointer == IntPtr.Zero)
        {
            if (handle.IsAllocated)
            {
                handle.Free();
            }

            throw new VipsException("can't create input source from memory");
        }

        return new Source(pointer) { _dataHandle = handle };
    }

    /// <summary>
    /// Make a new source from a memory object.
    /// </summary>
    /// <remarks>
    /// Make a new source that is attached to the memory object. For example:
    /// <code language="lang-csharp">
    /// using var source = Source.NewFromMemory(data);
    /// </code>
    /// You can pass this source to (for example) <see cref="Image.NewFromSource"/>.
    /// </remarks>
    /// <param name="data">The memory object.</param>
    /// <returns>A new <see cref="Source"/>.</returns>
    /// <exception cref="VipsException">If unable to create a new <see cref="Source"/> from <paramref name="data"/>.</exception>
    public static Source NewFromMemory(string data) => NewFromMemory(Encoding.UTF8.GetBytes(data));

    /// <summary>
    /// Make a new source from a memory object.
    /// </summary>
    /// <remarks>
    /// Make a new source that is attached to the memory object. For example:
    /// <code language="lang-csharp">
    /// using var source = Source.NewFromMemory(data);
    /// </code>
    /// You can pass this source to (for example) <see cref="Image.NewFromSource"/>.
    /// </remarks>
    /// <param name="data">The memory object.</param>
    /// <returns>A new <see cref="Source"/>.</returns>
    /// <exception cref="VipsException">If unable to create a new <see cref="Source"/> from <paramref name="data"/>.</exception>
    public static Source NewFromMemory(char[] data) => NewFromMemory(Encoding.UTF8.GetBytes(data));

    /// <inheritdoc cref="GObject"/>
    protected override void Dispose(bool disposing)
    {
        // release reference to our secret ref
        if (_dataHandle.IsAllocated)
        {
            _dataHandle.Free();
        }

        // Call our base Dispose method
        base.Dispose(disposing);
    }
}