From a840d9a60c7afe61f8722ffaa33ba83b20beca76 Mon Sep 17 00:00:00 2001
From: Dongdong Tian <seisman.info@gmail.com>
Date: Fri, 21 Apr 2023 13:53:02 +0800
Subject: [PATCH] clib.Session: Wrap the GMT_Get_Common API function (#2500)

Co-authored-by: Wei Ji <23487320+weiji14@users.noreply.github.com>
---
 doc/api/index.rst     |  1 +
 pygmt/clib/session.py | 91 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 92 insertions(+)

diff --git a/doc/api/index.rst b/doc/api/index.rst
index 29c1ea3bdf1..9ce697b5fbd 100644
--- a/doc/api/index.rst
+++ b/doc/api/index.rst
@@ -302,6 +302,7 @@ Low level access (these are mostly used by the :mod:`pygmt.clib` package):
     clib.Session.__enter__
     clib.Session.__exit__
     clib.Session.get_default
+    clib.Session.get_common
     clib.Session.create_data
     clib.Session.put_matrix
     clib.Session.put_strings
diff --git a/pygmt/clib/session.py b/pygmt/clib/session.py
index d80ac6f1ee9..d7f1b585f8d 100644
--- a/pygmt/clib/session.py
+++ b/pygmt/clib/session.py
@@ -494,6 +494,97 @@ def get_default(self, name):
 
         return value.value.decode()
 
+    def get_common(self, option):
+        """
+        Inquire if a GMT common option has been set and return its current
+        value if possible.
+
+        Parameters
+        ----------
+        option : str
+            The GMT common option to check. Valid options are ``"B"``, ``"I"``,
+            ``"J"``, ``"R"``, ``"U"``, ``"V"``, ``"X"``, ``"Y"``, ``"a"``,
+            ``"b"``, ``"f"``, ``"g"``, ``"h"``, ``"i"``, ``"n"``, ``"o"``,
+            ``"p"``, ``"r"``, ``"s"``, ``"t"``, and ``":"``.
+
+        Returns
+        -------
+        value : bool, int, float, or numpy.ndarray
+            Whether the option was set or its value.
+
+            If the option was not set, return ``False``. Otherwise,
+            the return value depends on the choice of the option.
+
+            - options ``"B"``, ``"J"``, ``"U"``, ``"g"``, ``"n"``, ``"p"``,
+              and ``"s"``: return ``True`` if set, else ``False`` (bool)
+            - ``"I"``: 2-element array for the increments (float)
+            - ``"R"``: 4-element array for the region (float)
+            - ``"V"``: the verbose level (int)
+            - ``"X"``: the xshift (float)
+            - ``"Y"``: the yshift (float)
+            - ``"a"``: geometry of the dataset (int)
+            - ``"b"``: return 0 if `-bi` was set and 1 if `-bo` was set (int)
+            - ``"f"``: return 0 if `-fi` was set and 1 if `-fo` was set (int)
+            - ``"h"``: whether to delete existing header records (int)
+            - ``"i"``: number of input columns (int)
+            - ``"o"``: number of output columns (int)
+            - ``"r"``: registration type (int)
+            - ``"t"``: 2-element array for the transparency (float)
+            - ``":"``: return 0 if `-:i` was set and 1 if `-:o` was set (int)
+
+        Examples
+        --------
+        >>> with Session() as lib:
+        ...     lib.call_module("basemap", "-R0/10/10/15 -JX5i/2.5i -Baf -Ve")
+        ...     region = lib.get_common("R")
+        ...     projection = lib.get_common("J")
+        ...     timestamp = lib.get_common("U")
+        ...     verbose = lib.get_common("V")
+        ...     lib.call_module("plot", "-T -Xw+1i -Yh-1i")
+        ...     xshift = lib.get_common("X")  # xshift/yshift are in inches
+        ...     yshift = lib.get_common("Y")
+        ...
+        >>> print(region, projection, timestamp, verbose, xshift, yshift)
+        [ 0. 10. 10. 15.] True False 3 6.0 1.5
+        >>> with Session() as lib:
+        ...     lib.call_module("basemap", "-R0/10/10/15 -JX5i/2.5i -Baf")
+        ...     lib.get_common("A")
+        ...
+        Traceback (most recent call last):
+        ...
+        pygmt.exceptions.GMTInvalidInput: Unknown GMT common option flag 'A'.
+        """
+        if option not in "BIJRUVXYabfghinoprst:":
+            raise GMTInvalidInput(f"Unknown GMT common option flag '{option}'.")
+
+        c_get_common = self.get_libgmt_func(
+            "GMT_Get_Common",
+            argtypes=[ctp.c_void_p, ctp.c_uint, ctp.POINTER(ctp.c_double)],
+            restype=ctp.c_int,
+        )
+        value = np.empty(6)  # numpy array to store the value of the option
+        status = c_get_common(
+            self.session_pointer,
+            ord(option),
+            value.ctypes.data_as(ctp.POINTER(ctp.c_double)),
+        )
+
+        # GMT_NOTSET (-1) means the option is not set
+        if status == self["GMT_NOTSET"]:
+            return False
+        # option is set and no other value is returned
+        if status == 0:
+            return True
+        # option is set and option values (in double type) are returned via the
+        # 'value' array. 'status' is number of valid values in the array.
+        if option in "IRt":
+            return value[:status]
+        if option in "XY":  # only one valid element in the array
+            return value[0]
+        # option is set and the option value (in integer type) is returned via
+        # the function return value (i.e., 'status')
+        return status
+
     def call_module(self, module, args):
         """
         Call a GMT module with the given arguments.