using System;
using NetVips.Internal;

using SMath = System.Math;

namespace NetVips;

/// <summary>
/// This class represents a libvips image which can be modified. See
/// <see cref="Image.Mutate"/>.
/// </summary>
public sealed partial class MutableImage : Image
{
    /// <summary>
    /// The <see cref="Image"/> this <see cref="MutableImage"/> is modifying.
    /// Only use this once you have finished all modifications.
    /// </summary>
    internal Image Image { get; private set; }

    /// <summary>
    /// Make a <see cref="MutableImage"/> from a regular copied <see cref="Image"/>.
    /// </summary>
    /// <remarks>
    /// This is for internal use only. See <see cref="Image.Mutate"/> for the
    /// user-facing interface.
    /// </remarks>
    internal MutableImage(Image copiedImage) : base(copiedImage.ObjectRef())
    {
        Image = copiedImage;
    }

    #region set/remove metadata

    /// <summary>
    /// Set the type and value of an item of metadata.
    /// </summary>
    /// <remarks>
    /// Sets the type and value of an item of metadata. Any old item of the
    /// same name is removed. See <see cref="GValue"/> for types.
    /// </remarks>
    /// <param name="gtype">The GType of the metadata item to create.</param>
    /// <param name="name">The name of the piece of metadata to create.</param>
    /// <param name="value">The value to set as a C# value. It is
    /// converted to the GType, if possible.</param>
    public new void Set(nint gtype, string name, object value)
    {
        using var gv = new GValue();
        gv.SetType(gtype);
        gv.Set(value);
        VipsImage.Set(this, name, in gv.Struct);
    }

    /// <summary>
    /// Set the value of an item of metadata.
    /// </summary>
    /// <remarks>
    /// Sets the value of an item of metadata. The metadata item must already
    /// exist.
    /// </remarks>
    /// <param name="name">The name of the piece of metadata to set the value of.</param>
    /// <param name="value">The value to set as a C# value. It is
    /// converted to the type of the metadata item, if possible.</param>
    /// <exception cref="T:System.ArgumentException">If metadata item <paramref name="name"/> does not exist.</exception>
    public void Set(string name, object value)
    {
        var gtype = GetTypeOf(name);
        if (gtype == IntPtr.Zero)
        {
            throw new ArgumentException(
                $"metadata item {name} does not exist - use the Set(nint, string, object) overload to create and set");
        }

        Set(gtype, name, value);
    }

    /// <summary>
    /// Remove an item of metadata.
    /// </summary>
    /// <remarks>
    /// The named metadata item is removed.
    /// </remarks>
    /// <param name="name">The name of the piece of metadata to remove.</param>
    /// <returns><see langword="true"/> if the metadata is successfully removed;
    /// otherwise, <see langword="false"/>.</returns>
    public bool Remove(string name)
    {
        return VipsImage.Remove(this, name);
    }

    #endregion

    #region overrides

    /// <summary>
    /// Overload `[]`.
    /// </summary>
    /// <remarks>
    /// Use `[]` to set band elements on an image. For example:
    /// <code language="lang-csharp">
    /// using var test = image.Mutate(x => x[1] = green);
    /// </code>
    /// Will change band 1 (the middle band).
    /// </remarks>
    /// <param name="i">The band element to change.</param>
    public new Image this[int i]
    {
        set
        {
            // number of bands to the left and right of value
            var nLeft = SMath.Min(Bands, SMath.Max(0, i));
            var nRight = SMath.Min(Bands, SMath.Max(0, Bands - 1 - i));
            var offset = Bands - nRight;
            using var left = nLeft > 0 ? Image.ExtractBand(0, n: nLeft) : null;
            using var right = nRight > 0 ? Image.ExtractBand(offset, n: nRight) : null;
            if (left == null)
            {
                using (Image)
                {
                    Image = value.Bandjoin(right);
                }
            }
            else if (right == null)
            {
                using (Image)
                {
                    Image = left.Bandjoin(value);
                }
            }
            else
            {
                using (Image)
                {
                    Image = left.Bandjoin(value, right);
                }
            }
        }
    }

    /// <inheritdoc cref="Image"/>
    public override Image Mutate(Action<MutableImage> action)
    {
        action.Invoke(this);
        return Image;
    }

    /// <inheritdoc cref="Image"/>
    public override string ToString()
    {
        return $"<NetVips.MutableImage {Width}x{Height} {Format}, {Bands} bands, {Interpretation}>";
    }

    #endregion
}