== How to write IoTivity build script ==

IoTivity projects are built with Scons. Scons is a cross-platform build tool,
it's quite similar to 'make'. 'SConstruct' is the entrance of scons build, it's
equivalent to 'Makefile' to 'make'.

This document only a brief reference. Detail about how to write scons script,
please refer to:
	http://www.scons.org/doc/production/HTML/scons-user.html#

== Background: How to control source code compiling ==

Environment is a base conception of Scons. An environment is a collection of
values that can affect how a program is built.

e.g. There is a C file named hello.c, enter the following into a file named
SConstruct:
	env = Environment()
	env.Program('H', 'hello.c')

When run Scons in console, following will be executed:
cc -o hello.o -c hello.c
cc -o H hello.o

If you would like keep debug information in the binary, '-g' flag should be added
when build the source code. To do this, append a C compiler flags as following:
	env = Environment()
	env.AppendUnique(CFLAGS = ['-g'])
	env.Program('H', 'hello.c')

When run Scons, following will be executed:
cc -o hello.o -c -g hello.c
cc -o H hello.o

In above example, 'CFLAGS' is changed. Following list the frequently used keys:

CFLAGS: General options that are passed to the C compiler
CCFLAGS: General options that are passed to the C & C++ compiler
CXXFLAGS: General options that are passed to the C++ compiler
CPPPATH: The directories that the preprocessor will search for include headers.
CPPDEFINES: Platform independent specification of C preprocessor definitions.

Note: CPPPATH and CPPDEFINES is common for all compiler. But others are
compiler specific, when change the key value, it may requried to specify the
target platform(actually the compiler).

e.g.
	env.AppendUnique(CPPPATH = ['.', 'include'])
	env.AppendUnique(CPPDEFINES = ['NDEBUG', 'VER_TEST'])
Above two lines are fine for all target platform. but below line:
	env.AppenUnique(CXXFLAGS = ['-g'])
is only fine for gcc compiler, as '-g' is a gcc flag, other compiler may don't
understand it. so it may should be:
	if target_os not in ['windows', 'winrt']:
		env.AppenUnique(CXXFLAGS = ['-g'])

Still take the hello.c as example. Assume hello.h is in ./include/ directory,
#include "hello.h"
int main(int argc, char** argv)
{
#ifdef LANG_FR
    printf("Bonjour\n");
#else
	printf("Hello\n");
#endif
}

The Scons configure file should as following:
	env = Environment()
	env.AppendUnique(CFLAGS = ['-g'])
	env.AppendUnique(CPPPATH = ['include'])
	env.AppendUnique(CPPDEFINES = ['LANG_FR'])
	env.Program('H', 'hello.c')

When run Scons, following will be executed:
cc -o hello.o -c -g -Iinclude -DLANG_FR hello.c
cc -o H hello.o

=== Get extra information ===

In above example, 'target_os' is used. How to get it?

User can build IoTivity project on Linux / Windows / MAC OSX for various
targets(Linux, Tizen, Android, Arduino, Windows, MAC OSX, IOS ...). Most
platform specific configures have been done in the common scripts which are in
build_common. The common scripts prepare an environment named 'env' with
target platform specific configuration.

When write IoTivity project build script, you can get this environment as
following:
	Import('env')

You can use 'env' directly after import it(it isn't recommended). You can also
clone a new environment and update its keys(recommended).

	new_env1 = Clone('env')
	new_env2 = Clone('env')
	new_env1.AppendUnqiue(xxx = [...])
	new_env2.AppendUnqiue(xxx = [...])

The 'env' environment contains platform specific configuration, besides, there is
some common information. You can get the information with following line:
	env.get('XXX')
or
	env['XXX']

XXX is the information name, below are the extra information added by IoTivity
common scrirpts:
BUILD_DIR: the path of the build directory, all output are in this directory
SRC_DIR: the path of the top directory of the source code
RELEASE: build type, boolean. True - release build, False - debug build
TARGET_OS: the name of the target OS. The possible value depends on the host
	platform. Bellow is the list of host and possible target OS. (darwin means
	MAC OSX)
		linux: linux / android / arduino / tizen (means on Linux, you can build the
			project for Linux/Android/Arduino/Tizen)
		windows: windows / winrt / android / arduino
		darwin: darwin / ios / android / arduino

TARGET_ARCH: the target CPU arch. Its possible value depends on the target OS.
	Bellow list the target OS and allowed CPU architecture.
		linux: x86 / x86_64 / arm / arm64 (means if the target OS is Linux, the CPU
			arch can be x86/x86_64/arm/arm64)
		android: x86 / x86_64 / armeabi / armeabi-v7a / armeabi-v7a-hard / arm64-v8a
		windows: x86 / amd64 / arm
		winrt: arm
		darwin: i386 / x86_64
		ios: i386 / x86_64 / armv7 / armv7s / arm64,
		arduino: avr / arm

=== Extra functions ===

For convenience, in the common scripts, some extra functions are added.

PrintTargets(): print all target names in the help information.
AppendTarget(name, target = None): add a target name into targets list, when use
	PrintTargets, the target name will be print
# @param name - the name of the target(s)(user defined name)
# @param target - Final binary, file(s) etc genereted after build.

InstallTarget(files, name): it takes the same action as AppendTarget, besides,
	it installs the 'files' to BUILD_DIR.

Following functions are only for Arduino:
ImportLib(lib): Arduino IDE includes many libraries. By default, no library is
compiled. If your project use some libraries, you can import the library by
this function. 'lib' is the name of the library to import. The 'include' path
will be auto added to the environment and the library will be built and linked
into the final binary.

CreateBin(bin, src): For Arduino, after build the program, it's required to
be converted into specific format (e.g .hex). This function will genearate the
required .hex (and .eep if target arch is avr) file from 'bin'.

UploadHelp(): For different board, the upload command line is different, this
function print the recommended upload command line. You can see the recommended
upload command line in the help information(the output of command "scons
[options] -h")
Functions for external library management:
PrepareLib(libname, lib = None, path = None, script = None): Check whether a
library exists, if not, notify user to install it or try to download the source
code and build it
# @param libname - the name of the library try to prepare
# @param lib - the lib(.so, .a etc) to check (a library may include more then
#      one lib, e.g. boost, includes boost_thread, boost_system ...
# @param path - the path of the library building script, if it's not set,
#			by default, it's <src_dir>/extlibs/<libname>/
# @param script - the building script, by default, it's 'SConscript'

Download(target, url): Download source code from URL 'url' and save as 'target'.
# @param target - the name of the source code package to be saved as
# @param url - the URL from which to download the source code

Configure(cwd, cmd): Run configure command(such as: boostrap, configure etc.
usually it's done before build a library)
# @param cwd - the work directory, full path or relative path to the directory
		where the library build script in
# @param cmd - the command to run, can be a script or system command

Install_head_file(file): Install header file(s) to <src_dir>/deps/<target_os>/include
# @param file - the head file(s) to install

Install_lib(lib): Install library binaries to <src_dir>/deps/<target_os>/lib/<arch>
# @param lib - the library binary(.so, .a etc) to install

==== Scripts Hierarchy ====

Scons provides a function 'SConscript(scripts, [exports, variant_dir, duplicate])'
It tells scons to execute one or more subsidiary configuration files(A script,
usually named SConscript). Take below project hierarchy as example to show how
to organize the scripts.

		prj
		|-------prj_1
		|		|--------sub_prj_11
		|		|--------sub_prj_..
		|		|--------sub_prj_1n
		|-------prj_2
		|
		| ... ...
		|
		|-------prj_n

As above project hierarchy, in 'SConstruct' file in the 'prj' directory, there
should include some lines like these:

#Please change this part according to the organization of your projects.
#Note: To make the output is in build_dir, the path of the scripts should
#be relevant to build_dir
SConscript(build_dir + 'prj_1/SConscript')
SConscript(build_dir + 'prj_2/SConscript')
... ...
SConscript(build_dir + 'prj_n/SConscript')


It's the same, in the 'prj_1/SConscript', there should include lines like
these:
SConscript('sub_prj_11/SConscript')
... ...
SConscript('sub_prj_1n/SConscript')

The path is relevant to 'prj_1/SConscript'. You can also use the full path
(build_dir + 'prj_1/sub_prj_1x/SConscript'), but it's not recommended.

Above just to show a recommended way to manage subsidiary scripts. You don't
need restrictly follow it.

==== The content of a typical script ====

After run the scripts in build_common (usually it's done at the beginning of
SConstruct), an global environment 'env' is exported, 'env' has include the
default configuration of the target OS and arch. 'env' is used in all projects,
should avoid to change its keys. To avoid change 'env', usually clone 'env' and
update it accroding to the requirement of current sub project. Then specify the
target(usually binary) to build.

Below is an example:
	# import the global environment 'env'
	Import('env')

	# Clone a new environment from 'env'
	new_env = env.Clone()

	# Update the new environment, usually include add header file paths,
	# library path, libs to link and other compiler flags. This part is
	# optional.
	new_env.AppeneUnique(xxx = [ .... ])

	# Specify the target(application, library, object or others) to build
	ts = new_env.Program('progam_name', [source_list])

	# Install the target (optional)
	# If it's an important library or daemon to be published
	new_env.InstallTarget(ts, 'target_name')
or
	# If it's examples or test program or others will not be published
	new_env.AppendTarget('target_name', ts)

==== Tips ====
1. library order: if A lib use B lib, both A and B are linked to target T, when
	specify libraries, A should in front of B, otherwise there may be link
	error. e.g.
		xx_env.AppendUnique(LIBS = ['A', 'B'])

2. On android:
	(1)'pthread' is in libc. So don't use '-lpthread' for android
	(2)By default 'rtti' and 'exception' is disabled, to enable it, you need
	add flags '-frtti' and '-fexceptions'
	(3)If STL is used, need link 'gnustl_shared' library
