Split meson up to be more modular

This also explicitly constructs reusable library components to make it
easier to extend the project over time. Notably we make less assumptions
about the host system and use pkgconfig where appropriate to give us
system details, such as the systemd system unit directory for packaging.
This can be overriden with the meson option.

Signed-off-by: Ikey Doherty <ikey@solus-project.com>

meson.build

@@ -1,54 +1,49 @@
-project('gamemode', 'c',
-	default_options : ['c_std=c11'],
-	version : '0.2',
-	license : 'BSD' )
+project(
+    'gamemode',
+    'c',
+    default_options : ['c_std=c11'],
+    version: '0.2',
+    license: 'BSD',
+)
+
 cc = meson.get_compiler('c')
 
-libsystemd = cc.find_library('systemd')
-libdl = cc.find_library('dl')
+path_prefix = get_option('prefix')
+path_bindir = join_paths(path_prefix, get_option('bindir'))
+path_datadir = join_paths(path_prefix, get_option('datadir'))
+path_includedir = join_paths(path_prefix, get_option('includedir'))
+path_libdir = join_paths(path_prefix, get_option('libdir'))
 
-executable( 'gamemoded',
-	'daemon/main.c',
-	'daemon/gamemode.c',
-	'daemon/logging.c',
-	'daemon/daemonize.c',
-	'daemon/dbus_messaging.c',
-	'daemon/governors.c',
-	dependencies: libsystemd,
-	install: true )
+# Find systemd via pkgconfig
+dep_systemd = dependency('libsystemd')
 
-# Main client library to message the daemon
-shared_library( 'gamemode',
-	'lib/client_impl.c',
-	dependencies: libsystemd,
-	install : true )
+# On non glibc systems this might be a stub, i.e. for musl
+libdl = cc.find_library('dl', required: false)
 
-# install the service file
-install_data( 'data/gamemoded.service', install_dir: '/etc/systemd/user' )
+# If the path isn't explicitly set, ask systemd for the systemd user unit directory
+path_systemd_unit_dir = get_option('with-systemd-user-unit-dir')
+if path_systemd_unit_dir == ''
+    message('Asking pkg-config for systemd\'s directories')
+    pkgconfig_systemd = dependency('systemd')
+    path_systemd_unit_dir = pkgconfig_systemd.get_pkgconfig_variable('systemduserunitdir')
+endif
 
-# Small target util to get and set cpu governors
-executable( 'cpugovctl',
-	'daemon/cpugovctl.c',
-	'daemon/logging.c',
-	install : true )
+subdir('lib')
+subdir('daemon')
+subdir('example')
+subdir('data')
 
-# Give cpugovctl the permissions it needs
-meson.add_install_script( 'data/cpugovctl_perms.sh',
-	dependencies : 'cpugovctl' )
-
-# Small library to automatically use gamemode
-shared_library( 'gamemodeauto',
-	'lib/client_loader.c',
-	dependencies : libdl,
-	install : true )
-
-# Install the gamemode_client header
-install_headers( 'lib/gamemode_client.h' )
-
-# An example game
-libdir = include_directories('lib')
-executable( 'example',
-	'example/main.c',
-	dependencies : libdl,
-	include_directories : libdir )
+report = [
+    '    Build configuration:',
+    '    ====================',
+    '',
+    '    prefix:                                 @0@'.format(path_prefix),
+    '    bindir:                                 @0@'.format(path_bindir),
+    '    datadir:                                @0@'.format(path_datadir),
+    '    libdir:                                 @0@'.format(path_libdir),
+    '    includedir:                             @0@'.format(path_includedir),
+    '    systemd user unit directory:            @0@'.format(path_systemd_unit_dir),
+]
 
+# Output some stuff to validate the build config
+message('\n\n\n' + '\n'.join(report) + '\n\n')