Refactor "docker not found" message generation, add Windows message

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>

compose/cli/errors.py

@@ -17,6 +17,7 @@ from .utils import call_silently
 from .utils import is_docker_for_mac_installed
 from .utils import is_mac
 from .utils import is_ubuntu
+from .utils import is_windows
 
 
 log = logging.getLogger(__name__)
@@ -90,11 +91,7 @@ def exit_with_error(msg):
 
 def get_conn_error_message(url):
     if call_silently(['which', 'docker']) != 0:
-        if is_mac():
-            return docker_not_found_mac
-        if is_ubuntu():
-            return docker_not_found_ubuntu
-        return docker_not_found_generic
+        return docker_not_found_msg("Couldn't connect to Docker daemon.")
     if is_docker_for_mac_installed():
         return conn_error_docker_for_mac
     if call_silently(['which', 'docker-machine']) == 0:
@@ -102,25 +99,26 @@ def get_conn_error_message(url):
     return conn_error_generic.format(url=url)
 
 
-docker_not_found_mac = """
-    Couldn't connect to Docker daemon. You might need to install Docker:
-
-    https://docs.docker.com/engine/installation/mac/
-"""
+def docker_not_found_msg(problem):
+    return "{} You might need to install Docker:\n\n{}".format(
+        problem, docker_install_url())
 
 
-docker_not_found_ubuntu = """
-    Couldn't connect to Docker daemon. You might need to install Docker:
-
-    https://docs.docker.com/engine/installation/ubuntulinux/
-"""
+def docker_install_url():
+    if is_mac():
+        return docker_install_url_mac
+    elif is_ubuntu():
+        return docker_install_url_ubuntu
+    elif is_windows():
+        return docker_install_url_windows
+    else:
+        return docker_install_url_generic
 
 
-docker_not_found_generic = """
-    Couldn't connect to Docker daemon. You might need to install Docker:
-
-    https://docs.docker.com/engine/installation/
-"""
+docker_install_url_mac = "https://docs.docker.com/engine/installation/mac/"
+docker_install_url_ubuntu = "https://docs.docker.com/engine/installation/ubuntulinux/"
+docker_install_url_windows = "https://docs.docker.com/engine/installation/windows/"
+docker_install_url_generic = "https://docs.docker.com/engine/installation/"
 
 
 conn_error_docker_machine = """

compose/cli/utils.py

@@ -11,6 +11,7 @@ import sys
 import docker
 
 import compose
+from ..const import IS_WINDOWS_PLATFORM
 
 # WindowsError is not defined on non-win32 platforms. Avoid runtime errors by
 # defining it as OSError (its parent class) if missing.
@@ -73,6 +74,10 @@ def is_ubuntu():
     return platform.system() == 'Linux' and platform.linux_distribution()[0] == 'Ubuntu'
 
 
+def is_windows():
+    return IS_WINDOWS_PLATFORM
+
+
 def get_version_info(scope):
     versioninfo = 'docker-compose version {}, build {}'.format(
         compose.__version__,