using System;

namespace JavaScriptEngineSwitcher.ChakraCore.JsRt
{
	/// <summary>
	/// The Chakra runtime
	/// </summary>
	/// <remarks>
	/// <para>
	/// Each Chakra runtime has its own independent execution engine, JIT compiler, and garbage
	/// collected heap. As such, each runtime is completely isolated from other runtimes.
	/// </para>
	/// <para>
	/// Runtimes can be used on any thread, but only one thread can call into a runtime at any
	/// time.
	/// </para>
	/// <para>
	/// NOTE: A <c>JsRuntime</c>, unlike other objects in the Chakra hosting API, is not
	/// garbage collected since it contains the garbage collected heap itself. A runtime will
	/// continue to exist until <c>Dispose</c> is called.
	/// </para>
	/// </remarks>
	internal struct JsRuntime : IDisposable
	{
		/// <summary>
		/// The handle
		/// </summary>
		private IntPtr _handle;

		/// <summary>
		/// Gets a value indicating whether the runtime is valid
		/// </summary>
		public bool IsValid
		{
			get { return _handle != IntPtr.Zero; }
		}

		/// <summary>
		/// Gets a current memory usage for a runtime
		/// </summary>
		/// <remarks>
		/// Memory usage can be always be retrieved, regardless of whether or not the runtime is active
		/// on another thread.
		/// </remarks>
		public UIntPtr MemoryUsage
		{
			get
			{
				UIntPtr memoryUsage;
				JsErrorHelpers.ThrowIfError(NativeMethods.JsGetRuntimeMemoryUsage(this, out memoryUsage));

				return memoryUsage;
			}
		}

		/// <summary>
		/// Gets or sets a current memory limit for a runtime
		/// </summary>
		/// <remarks>
		/// The memory limit of a runtime can be always be retrieved, regardless of whether or not the
		/// runtime is active on another thread.
		/// </remarks>
		public UIntPtr MemoryLimit
		{
			get
			{
				UIntPtr memoryLimit;
				JsErrorHelpers.ThrowIfError(NativeMethods.JsGetRuntimeMemoryLimit(this, out memoryLimit));

				return memoryLimit;
			}
			set
			{
				JsErrorHelpers.ThrowIfError(NativeMethods.JsSetRuntimeMemoryLimit(this, value));
			}
		}

		/// <summary>
		/// Gets or sets a value indicating whether script execution is disabled in the runtime
		/// </summary>
		public bool Disabled
		{
			get
			{
				bool isDisabled;
				JsErrorHelpers.ThrowIfError(NativeMethods.JsIsRuntimeExecutionDisabled(this, out isDisabled));

				return isDisabled;
			}
			set
			{
				JsErrorHelpers.ThrowIfError(value ?
					NativeMethods.JsDisableRuntimeExecution(this)
					:
					NativeMethods.JsEnableRuntimeExecution(this))
					;
			}
		}


		/// <summary>
		/// Creates a new runtime
		/// </summary>
		/// <returns>The runtime created</returns>
		public static JsRuntime Create()
		{
			return Create(JsRuntimeAttributes.None, null);
		}

		/// <summary>
		/// Creates a new runtime
		/// </summary>
		/// <param name="attributes">The attributes of the runtime to be created</param>
		/// <returns>The runtime created</returns>
		public static JsRuntime Create(JsRuntimeAttributes attributes)
		{
			return Create(attributes, null);
		}

		/// <summary>
		/// Creates a new runtime
		/// </summary>
		/// <param name="attributes">The attributes of the runtime to be created</param>
		/// <param name="threadServiceCallback">The thread service for the runtime. Can be <c>null</c></param>
		/// <returns>The runtime created</returns>
		public static JsRuntime Create(JsRuntimeAttributes attributes, JsThreadServiceCallback threadServiceCallback)
		{
			JsRuntime handle;
			JsErrorHelpers.ThrowIfError(NativeMethods.JsCreateRuntime(attributes, threadServiceCallback, out handle));

			return handle;
		}

		/// <summary>
		/// Performs a full garbage collection
		/// </summary>
		public void CollectGarbage()
		{
			JsErrorHelpers.ThrowIfError(NativeMethods.JsCollectGarbage(this));
		}

		/// <summary>
		/// Sets a memory allocation callback for specified runtime
		/// </summary>
		/// <remarks>
		/// <para>
		/// Registering a memory allocation callback will cause the runtime to call back to the host
		/// whenever it acquires memory from, or releases memory to, the OS. The callback routine is
		/// called before the runtime memory manager allocates a block of memory. The allocation will
		/// be rejected if the callback returns <c>false</c>. The runtime memory manager will also invoke the
		/// callback routine after freeing a block of memory, as well as after allocation failures.
		/// </para>
		/// <para>
		/// The callback is invoked on the current runtime execution thread, therefore execution is
		/// blocked until the callback completes.
		/// </para>
		/// <para>
		/// The return value of the callback is not stored; previously rejected allocations will not
		/// prevent the runtime from invoking the callback again later for new memory allocations.
		/// </para>
		/// </remarks>
		/// <param name="callbackState">
		/// User provided state that will be passed back to the callback.
		/// </param>
		/// <param name="allocationCallback">
		/// Memory allocation callback to be called for memory allocation events.
		/// </param>
		public void SetMemoryAllocationCallback(IntPtr callbackState, JsMemoryAllocationCallback allocationCallback)
		{
			JsErrorHelpers.ThrowIfError(NativeMethods.JsSetRuntimeMemoryAllocationCallback(this, callbackState, allocationCallback));
		}

		/// <summary>
		/// Sets a callback function that is called by the runtime before garbage collection
		/// </summary>
		/// <remarks>
		/// <para>
		/// The callback is invoked on the current runtime execution thread, therefore execution is
		/// blocked until the callback completes.
		/// </para>
		/// <para>
		/// The callback can be used by hosts to prepare for garbage collection. For example, by
		/// releasing unnecessary references on Chakra objects.
		/// </para>
		/// </remarks>
		/// <param name="callbackState">User provided state that will be passed back to the callback</param>
		/// <param name="beforeCollectCallback">The callback function being set</param>
		public void SetBeforeCollectCallback(IntPtr callbackState, JsBeforeCollectCallback beforeCollectCallback)
		{
			JsErrorHelpers.ThrowIfError(NativeMethods.JsSetRuntimeBeforeCollectCallback(this, callbackState, beforeCollectCallback));
		}

		/// <summary>
		/// Creates a script context for running scripts
		/// </summary>
		/// <remarks>
		/// Each script context has its own global object that is isolated from all other script
		/// contexts.
		/// </remarks>
		/// <returns>The created script context</returns>
		public JsContext CreateContext()
		{
			JsContext reference;
			JsErrorHelpers.ThrowIfError(NativeMethods.JsCreateContext(this, out reference));

			return reference;
		}

		/// <summary>
		/// Disposes a runtime
		/// </summary>
		/// <remarks>
		/// Once a runtime has been disposed, all resources owned by it are invalid and cannot be used.
		/// If the runtime is active (i.e. it is set to be current on a particular thread), it cannot
		/// be disposed.
		/// </remarks>
		public void Dispose()
		{
			if (IsValid)
			{
				JsErrorHelpers.ThrowIfError(NativeMethods.JsDisposeRuntime(this));
			}

			_handle = IntPtr.Zero;
		}
	}
}