using System.Runtime.InteropServices;
using WhiteMagic.Native;

namespace WhiteMagic.Input;

/// <summary>
/// Mouse buttons supported by <see cref="InputSimulator.SendMouseClick"/>.
/// </summary>
public enum MouseButton
{
    /// <summary>The left mouse button.</summary>
    Left,

    /// <summary>The right mouse button.</summary>
    Right,
}

/// <summary>
/// Simulates keyboard and mouse input directed at a target window via window messages.
/// </summary>
public sealed class InputSimulator
{
    /// <summary>
    /// Sends a sequence of character messages to <paramref name="hWnd"/>.
    /// </summary>
    /// <returns><see langword="true"/> if every character was posted successfully.</returns>
    public bool SendKeys(IntPtr hWnd, string text)
    {
        if (text is null)
            throw new ArgumentNullException(nameof(text));

        if (hWnd == IntPtr.Zero)
            return false;

        foreach (char c in text)
        {
            if (!NativeMethods.PostMessageW(hWnd, NativeMethods.WmChar, (nuint)c, 0))
                return false;
        }

        return true;
    }

    /// <summary>
    /// Sends a mouse click at client-area coordinates <paramref name="x"/>,
    /// <paramref name="y"/> to <paramref name="hWnd"/>.
    /// </summary>
    /// <returns><see langword="true"/> if the click was posted successfully.</returns>
    public bool SendMouseClick(IntPtr hWnd, int x, int y, MouseButton button)
    {
        if (hWnd == IntPtr.Zero)
            return false;

        nint lParam = MakeLong(x, y);

        (uint down, uint downWParam) = button switch
        {
            MouseButton.Left => (NativeMethods.WmLButtonDown, NativeMethods.MkLButton),
            MouseButton.Right => (NativeMethods.WmRButtonDown, NativeMethods.MkRButton),
            _ => throw new ArgumentOutOfRangeException(nameof(button)),
        };

        if (!NativeMethods.PostMessageW(hWnd, down, downWParam, lParam))
            return false;

        uint up = button == MouseButton.Left ? NativeMethods.WmLButtonUp : NativeMethods.WmRButtonUp;
        return NativeMethods.PostMessageW(hWnd, up, 0, lParam);
    }

    private static nint MakeLong(int low, int high)
    {
        return (nint)((uint)low | ((uint)high << 16));
    }
}