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+.. _user-guide:
+
+User Guide
+==========
+
+Language Server
+---------------
+
+The language server is responsible for managing the connection with the client as well as sending and receiving messages over
+the `Language Server Protocol <https://microsoft.github.io/language-server-protocol/>`__
+which is based on the `Json RPC protocol <https://www.jsonrpc.org/specification>`__.
+
+Connections
+~~~~~~~~~~~
+
+*pygls* supports :ref:`ls-tcp`, :ref:`ls-stdio` and :ref:`ls-websocket` connections.
+
+.. _ls-tcp:
+
+TCP
+^^^
+
+TCP connections are usually used while developing the language server.
+This way the server can be started in *debug* mode separately and wait
+for the client connection.
+
+.. note:: Server should be started **before** the client.
+
+The code snippet below shows how to start the server in *TCP* mode.
+
+.. code:: python
+
+    from pygls.server import LanguageServer
+
+    server = LanguageServer('example-server', 'v0.1')
+
+    server.start_tcp('127.0.0.1', 8080)
+
+.. _ls-stdio:
+
+STDIO
+^^^^^
+
+STDIO connections are useful when client is starting the server as a child
+process. This is the way to go in production.
+
+The code snippet below shows how to start the server in *STDIO* mode.
+
+.. code:: python
+
+    from pygls.server import LanguageServer
+
+    server = LanguageServer('example-server', 'v0.1')
+
+    server.start_io()
+
+.. _ls-websocket:
+
+WEBSOCKET
+^^^^^^^^^
+
+WEBSOCKET connections are used when you want to expose language server to
+browser based editors.
+
+The code snippet below shows how to start the server in *WEBSOCKET* mode.
+
+.. code:: python
+
+    from pygls.server import LanguageServer
+
+    server = LanguageServer('example-server', 'v0.1')
+
+    server.start_ws('0.0.0.0', 1234)
+
+Logging
+~~~~~~~
+
+Logs are useful for tracing client requests, finding out errors and
+measuring time needed to return results to the client.
+
+*pygls* uses built-in python *logging* module which has to be configured
+before server is started.
+
+Official documentation about logging in python can be found
+`here <https://docs.python.org/3/howto/logging-cookbook.html>`__. Below
+is the minimal setup to setup logging in *pygls*:
+
+.. code:: python
+
+    import logging
+
+    from pygls.server import LanguageServer
+
+    logging.basicConfig(filename='pygls.log', filemode='w', level=logging.DEBUG)
+
+    server = LanguageServer('example-server', 'v0.1')
+
+    server.start_io()
+
+Overriding ``LanguageServerProtocol``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If you have a reason to override the existing ``LanguageServerProtocol`` class,
+you can do that by inheriting the class and passing it to the ``LanguageServer``
+constructor.
+
+Custom Error Reporting
+~~~~~~~~~~~~~~~~~~~~~~
+
+The default :class:`~pygls.server.LanguageServer` will send a :lsp:`window/showMessage` notification to the client to display any uncaught exceptions in the server.
+To override this behaviour define your own :meth:`~pygls.server.LanguageServer.report_server_error` method like so:
+
+.. code:: python
+
+   class CustomLanguageServer(LanguageServer):
+       def report_server_error(self, error: Exception, source: Union[PyglsError, JsonRpcException]):
+           pass
+
+Handling Client Messages
+------------------------
+
+.. admonition:: Requests vs Notifications
+
+   Unlike a *request*, a *notification* message has no ``id`` field and the server *must not* reply to it.
+   This means that, even if you return a result inside a handler function for a notification, the result won't be passed to the client.
+
+   The ``Language Server Protocol``, unlike ``Json RPC``, allows bidirectional communication between the server and the client.
+
+For the majority of the time, a language server will be responding to requests and notifications sent from the client.
+*pygls* refers to the handlers for all of these messages as *features* with one exception.
+
+The Language Server protocol allows a server to define named methods that a client can invoke by sending a :lsp:`workspace/executeCommand` request.
+Unsurprisingly, *pygls* refers to these named methods a *commands*.
+
+*Built-In* Features
+~~~~~~~~~~~~~~~~~~~
+
+*pygls* comes with following predefined set of handlers for the following
+`Language Server Protocol <https://microsoft.github.io/language-server-protocol/>`__
+(LSP) features:
+
+.. note::
+
+    *Built-in* features in most cases should *not* be overridden.
+
+    If you need to do some additional processing of one of the messages listed below, register a feature with the same name and your handler will be called immediately after the corresponding built-in feature.
+
+**Lifecycle Messages**
+
+- The :lsp:`initialize` request is sent as a first request from client to the server to setup their communication.
+  *pygls* automatically computes registered LSP capabilities and sends them as part of the :class:`~lsprotocol.types.InitializeResult` response.
+
+- The :lsp:`shutdown` request is sent from the client to the server to ask the server to shutdown.
+
+- The :lsp:`exit` notification is sent from client to the server to ask the server to exit the process.
+  *pygls* automatically releases all resources and stops the process.
+
+**Text Document Synchronization**
+
+- The :lsp:`textDocument/didOpen` notification will tell *pygls* to create a document in the in-memory workspace which will exist as long as the document is opened in editor.
+
+- The :lsp:`textDocument/didChange` notification will tell *pygls* to update the document text.
+  *pygls* supports *full* and *incremental* document changes.
+
+- The :lsp:`textDocument/didClose` notification will tell *pygls* to remove a document from the in-memory workspace.
+
+**Notebook Document Synchronization**
+
+- The :lsp:`notebookDocument/didOpen` notification will tell *pygls* to create a notebook document in the in-memory workspace which will exist as long as the document is opened in editor.
+
+- The :lsp:`notebookDocument/didChange` notification will tell *pygls* to update the notebook document include its content, metadata, execution results and cell structure.
+
+- The :lsp:`notebookDocument/didClose` notification will tell *pygls* to remove the notebook from the in-memory workspace.
+
+**Miscellanous**
+
+- The :lsp:`workspace/didChangeWorkspaceFolders` notification will tell *pygls* to update in-memory workspace folders.
+
+- The :lsp:`workspace/executeCommand` request will tell *pygls* to execute a custom command.
+
+- The :lsp:`$/setTrace` notification tells *pygls* to update the server's :class:`TraceValue <lsprotocol.types.TraceValues>`.
+
+.. _ls-handlers:
+
+Registering Handlers
+~~~~~~~~~~~~~~~~~~~~
+
+.. seealso::
+
+   It's recommeded that you follow the :ref:`tutorial <tutorial>` before reading this section.
+
+- The :func:`~pygls.server.LanguageServer.feature` decorator is used to register a handler for a given LSP message.
+- The :func:`~pygls.server.LanguageServer.command` decorator is used to register a named command.
+
+The following applies to both feature and command handlers.
+
+Language servers using *pygls* run in an *asyncio event loop*.
+They *asynchronously* listen for incoming messages and, depending on the way handler is registered, apply different execution strategies to process the message.
+
+Depending on the use case, handlers can be registered in three different ways:
+
+- as an :ref:`async <ls-handler-async>` function
+- as a :ref:`synchronous <ls-handler-sync>` function
+- as a :ref:`threaded <ls-handler-thread>` function
+
+.. _ls-handler-async:
+
+*Asynchronous* Functions (*Coroutines*)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+*pygls* supports ``python 3.8+`` which has a keyword ``async`` to
+specify coroutines.
+
+The code snippet below shows how to register a command as a coroutine:
+
+.. code:: python
+
+    @json_server.command(JsonLanguageServer.CMD_COUNT_DOWN_NON_BLOCKING)
+    async def count_down_10_seconds_non_blocking(ls, *args):
+        # Omitted
+
+Registering a *feature* as a coroutine is exactly the same.
+
+Coroutines are functions that are executed as tasks in *pygls*'s *event
+loop*. They should contain at least one *await* expression (see
+`awaitables <https://docs.python.org/3.5/glossary.html#term-awaitable>`__
+for details) which tells event loop to switch to another task while
+waiting. This allows *pygls* to listen for client requests in a
+*non blocking* way, while still only running in the *main* thread.
+
+Tasks can be canceled by the client if they didn't start executing (see
+`Cancellation
+Support <https://microsoft.github.io/language-server-protocol/specification#cancelRequest>`__).
+
+.. warning::
+
+    Using computation intensive operations will *block* the main thread and
+    should be *avoided* inside coroutines. Take a look at
+    `threaded functions <#threaded-functions>`__ for more details.
+
+.. _ls-handler-sync:
+
+*Synchronous* Functions
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Synchronous functions are regular functions which *blocks* the *main*
+thread until they are executed.
+
+`Built-in features <#built-in-features>`__ are registered as regular
+functions to ensure correct state of language server initialization and
+workspace.
+
+The code snippet below shows how to register a command as a regular
+function:
+
+.. code:: python
+
+    @json_server.command(JsonLanguageServer.CMD_COUNT_DOWN_BLOCKING)
+    def count_down_10_seconds_blocking(ls, *args):
+        # Omitted
+
+Registering *feature* as a regular function is exactly the same.
+
+.. warning::
+
+    Using computation intensive operations will *block* the main thread and
+    should be *avoided* inside regular functions. Take a look at
+    `threaded functions <#threaded-functions>`__ for more details.
+
+.. _ls-handler-thread:
+
+*Threaded* Functions
+^^^^^^^^^^^^^^^^^^^^
+
+*Threaded* functions are just regular functions, but marked with
+*pygls*'s ``thread`` decorator:
+
+.. code:: python
+
+    # Decorator order is not important in this case
+    @json_server.thread()
+    @json_server.command(JsonLanguageServer.CMD_COUNT_DOWN_BLOCKING)
+    def count_down_10_seconds_blocking(ls, *args):
+        # Omitted
+
+*pygls* uses its own *thread pool* to execute above function in *daemon*
+thread and it is *lazy* initialized first time when function marked with
+``thread`` decorator is fired.
+
+*Threaded* functions can be used to run blocking operations. If it has been a
+while or you are new to threading in Python, check out Python's
+``multithreading`` and `GIL <https://en.wikipedia.org/wiki/Global_interpreter_lock>`__
+before messing with threads.
+
+.. _passing-instance:
+
+Passing Language Server Instance
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Using language server methods inside registered features and commands are quite
+common. We recommend adding language server as a **first parameter** of a
+registered function.
+
+There are two ways of doing this:
+
+- **ls** (**l**\anguage **s**\erver) naming convention
+
+Add **ls** as first parameter of a function and *pygls* will automatically pass
+the language server instance.
+
+.. code-block:: python
+
+    @json_server.command(JsonLanguageServer.CMD_COUNT_DOWN_BLOCKING)
+    def count_down_10_seconds_blocking(ls, *args):
+        # Omitted
+
+
+- add **type** to first parameter
+
+Add the **LanguageServer** class or any class derived from it as a type to
+first parameter of a function
+
+.. code-block:: python
+
+    @json_server.command(JsonLanguageServer.CMD_COUNT_DOWN_BLOCKING)
+    def count_down_10_seconds_blocking(ser: JsonLanguageServer, *args):
+        # Omitted
+
+
+Using outer ``json_server`` instance inside registered function will make
+writing unit :ref:`tests <testing>` more difficult.
+
+Communicating with the Client
+-----------------------------
+
+.. important::
+
+   Most of the messages listed here cannot be sent until the LSP session has been initialized.
+   See the section on the :lsp:`initiaiize` request in the specification for more details.
+
+In addition to responding to requests, there are a number of additional messages a server can send to the client.
+
+Configuration
+~~~~~~~~~~~~~
+
+The :lsp:`workspace/configuration` request is sent from the server to the client in order to fetch configuration settings from the client.
+Depending on how the handler is registered (see :ref:`here <ls-handlers>`) you can use the :meth:`~pygls.server.LanguageServer.get_configuration` or :meth:`~pygls.server.LanguageServer.get_configuration_async` methods to request configuration from the client:
+
+-  *asynchronous* functions (*coroutines*)
+
+   .. code:: python
+
+      # await keyword tells event loop to switch to another task until notification is received
+      config = await ls.get_configuration(
+          WorkspaceConfigurationParams(
+              items=[
+                  ConfigurationItem(scope_uri='doc_uri_here', section='section')
+              ]
+          )
+      )
+
+-  *synchronous* functions
+
+   .. code:: python
+
+      # callback is called when notification is received
+      def callback(config):
+          # Omitted
+
+      params = WorkspaceConfigurationParams(
+          items=[
+              ConfigurationItem(scope_uri='doc_uri_here', section='section')
+          ]
+      )
+      config = ls.get_configuration(params, callback)
+
+-  *threaded* functions
+
+   .. code:: python
+
+      # .result() will block the thread
+      config = ls.get_configuration(
+          WorkspaceConfigurationParams(
+              items=[
+                  ConfigurationItem(scope_uri='doc_uri_here', section='section')
+              ]
+          )
+      ).result()
+
+Publish Diagnostics
+~~~~~~~~~~~~~~~~~~~
+
+:lsp:`textDocument/publishDiagnostics` notifications are sent from the server to the client to highlight errors or potential issues. e.g. syntax errors or unused variables.
+
+Usually this notification is sent after document is opened, or on document content change:
+
+.. code:: python
+
+   @json_server.feature(TEXT_DOCUMENT_DID_OPEN)
+   async def did_open(ls, params: DidOpenTextDocumentParams):
+       """Text document did open notification."""
+       ls.show_message("Text Document Did Open")
+       ls.show_message_log("Validating json...")
+
+       # Get document from workspace
+       text_doc = ls.workspace.get_text_document(params.text_document.uri)
+
+       diagnostic = Diagnostic(
+          range=Range(
+              start=Position(line-1, col-1),
+              end=Position(line-1, col)
+          ),
+          message="Custom validation message",
+          source="Json Server"
+       )
+
+       # Send diagnostics
+       ls.publish_diagnostics(text_doc.uri, [diagnostic])
+
+Show Message
+~~~~~~~~~~~~
+
+:lsp:`window/showMessage` is a notification that is sent from the server to the client to display a prominant text message. e.g. VSCode will render this as a notification popup
+
+.. code:: python
+
+   @json_server.command(JsonLanguageServer.CMD_COUNT_DOWN_NON_BLOCKING)
+   async def count_down_10_seconds_non_blocking(ls, *args):
+       for i in range(10):
+           # Sends message notification to the client
+           ls.show_message(f"Counting down... {10 - i}")
+           await asyncio.sleep(1)
+
+Show Message Log
+~~~~~~~~~~~~~~~~
+
+:lsp:`window/logMessage` is a notification that is sent from the server to the client to display a discrete text message. e.g. VSCode will display the message in an :guilabel:`Output` channel.
+
+.. code:: python
+
+   @json_server.command(JsonLanguageServer.CMD_COUNT_DOWN_NON_BLOCKING)
+   async def count_down_10_seconds_non_blocking(ls, *args):
+       for i in range(10):
+           # Sends message log notification to the client
+           ls.show_message_log(f"Counting down... {10 - i}")
+           await asyncio.sleep(1)
+
+Workspace Edits
+~~~~~~~~~~~~~~~
+
+The :lsp:`workspace/applyEdit` request allows your language server to ask the client to modify particular documents in the client's workspace.
+
+.. code:: python
+
+   def apply_edit(self, edit: WorkspaceEdit, label: str = None) -> ApplyWorkspaceEditResponse:
+       # Omitted
+
+   def apply_edit_async(self, edit: WorkspaceEdit, label: str = None) -> ApplyWorkspaceEditResponse:
+       # Omitted
+
+Custom Notifications
+~~~~~~~~~~~~~~~~~~~~
+
+.. warning::
+
+   Custom notifications are not part of the LSP specification and dedicated support for your custom notification(s) will have to be added to each language client you intend to support.
+
+A custom notification can be sent to the client using the :meth:`~pygls.server.LanguageServer.send_notification` method
+
+.. code:: python
+
+   server.send_notification('myCustomNotification', 'test data')
+
+
+The Workspace
+-------------
+
+The :class:`~pygls.workspace.Workspace` is a python object that holds information about workspace folders, opened documents and is responsible for synchronising server side document state with that of the client.
+
+**Text Documents**
+
+The :class:`~pygls.workspace.TextDocument` class is how *pygls* represents a text document.
+Given a text document's uri the :meth:`~pygls.workspace.Workspace.get_text_document` method can be used to access the document itself:
+
+.. code:: python
+
+   @json_server.feature(TEXT_DOCUMENT_DID_OPEN)
+   async def did_open(ls, params: DidOpenTextDocumentParams):
+
+       # Get document from workspace
+       text_doc = ls.workspace.get_text_document(params.text_document.uri)
+
+**Notebook Documents**
+
+.. seealso::
+
+   See the section on :lsp:`notebookDocument/synchronization` in the specification for full details on how notebook documents are handled
+
+- A notebook's structure, metadata etc. is represented using the :class:`~lsprotocol.types.NotebookDocument` class from ``lsprotocol``.
+- The contents of a single notebook cell is represented using a standard :class:`~pygls.workspace.TextDocument`
+
+In order to receive notebook documents from the client, your language server must provide an instance of :class:`~lsprotocol.types.NotebookDocumentSyncOptions` which declares the kind of notebooks it is interested in
+
+.. code-block:: python
+
+   server = LanguageServer(
+       name="example-server",
+       version="v0.1",
+       notebook_document_sync=types.NotebookDocumentSyncOptions(
+           notebook_selector=[
+               types.NotebookDocumentSyncOptionsNotebookSelectorType2(
+                   cells=[
+                       types.NotebookDocumentSyncOptionsNotebookSelectorType2CellsType(
+                           language="python"
+                       )
+                   ]
+               )
+           ]
+       ),
+   )
+
+To access the contents of a notebook cell you would call the workspace's :meth:`~pygls.workspace.Workspace.get_text_document` method as normal.
+
+.. code-block:: python
+
+   cell_doc = ls.workspace.get_text_document(cell_uri)
+
+To access the notebook itself call the workspace's :meth:`~pygls.workspace.Workspace.get_notebook_document` method with either the uri of the notebook *or* the uri of any of its cells.
+
+.. code-block:: python
+
+   notebook_doc = ls.workspace.get_notebook_document(notebook_uri=notebook_uri)
+
+   # -- OR --
+
+   notebook_doc = ls.workspace.get_notebook_document(cell_uri=cell_uri)