setup.py: check for third party program requirements

setup.py

@@ -1,6 +1,171 @@
 #!/usr/bin/env python3
 
 from setuptools import setup
+from subprocess import Popen, STDOUT, check_output, CalledProcessError
+from string import Template
+import re
+import sys
+
+
+missing_program = '''
+The program '{program}' could not be executed or was not found on your
+system PATH.
+'''
+
+unknown_version = '''
+OCRmyPDF requires '{program}' {need_version} or higher.  Your system has
+'{program}' but we cannot tell what version is installed.  Contact the
+package maintainer.
+'''
+
+old_version = '''
+OCRmyPDF requires '{program}' {need_version} or higher.  Your system appears
+to have {found_version}.  Please update this program.
+'''
+
+okay_its_optional = '''
+This program is OPTIONAL, so installation of OCRmyPDF can proceed, but
+some functionality may be missing.
+'''
+
+not_okay_its_required = '''
+This program is REQUIRED for OCRmyPDF to work.  Installation will abort.
+'''
+
+osx_install_advice = '''
+If you have homebrew installed, try these command to install the missing
+packages:
+    brew update
+    brew upgrade
+    brew install {package}
+'''
+
+linux_install_advice = '''
+On systems with the aptitude package manager (Debian, Ubuntu), try these
+commands:
+    sudo apt-get update
+    sudo apt-get install {package}
+
+On RPM-based systems (Red Hat, Fedora), search for instructions on
+installing the RPM for {package}.
+'''
+
+
+def _error_trailer(program, package, optional):
+    if program == 'java':
+        return  # You're fucked
+
+    if optional:
+        print(okay_its_optional.format(**locals()), file=sys.stderr)
+    else:
+        print(not_okay_its_required.format(**locals()), file=sys.stderr)
+    if sys.platform.startswith('darwin'):
+        print(osx_install_advice.format(**locals()), file=sys.stderr)
+    elif sys.platform.startswith('linux'):
+        print(linux_install_advice.format(**locals()), file=sys.stderr)
+
+
+def error_missing_program(
+        program,
+        package,
+        optional
+        ):
+    print(missing_program.format(**locals()), file=sys.stderr)
+    _error_trailer(**locals())
+
+
+def error_unknown_version(
+        program,
+        package,
+        optional
+        ):
+    print(unknown_version.format(**locals()), file=sys.stderr)
+    _error_trailer(**locals())
+
+
+def error_old_version(
+        program,
+        package,
+        optional,
+        need_version
+        ):
+    print(old_version.format(**locals()), file=sys.stderr)
+    _error_trailer(**locals())
+
+
+def check_external_program(
+        program,
+        minimum_version,
+        package,
+        version_check_args=['--version'],
+        version_scrape_regex=re.compile(r'(\d+\.\d+(?:\.\d+)?)'),
+        optional=False):
+
+    print('Checking for {program} >= {minimum_version}...'.format(
+            program=program, minimum_version=minimum_version))
+    try:
+        result = check_output(
+                [program] + version_check_args,
+                universal_newlines=True, stderr=STDOUT)
+    except CalledProcessError:
+        error_missing_program(program, package, optional)
+        if not optional:
+            sys.exit(1)
+
+    try:
+        version = version_scrape_regex.search(result).group(1)
+    except AttributeError:
+        error_unknown_version(program, package, optional, minimum_version)
+        if not optional:
+            sys.exit(1)
+
+    if version < minimum_version:
+        error_old_version(program, package, optional, minimum_version)
+
+    print('Found {program} {version}'.format(
+            program=program, version=version))
+
+check_external_program(
+    program='tesseract',
+    minimum_version='3.02.02',
+    package='tesseract'
+)
+
+check_external_program(
+    program='gs',
+    minimum_version='9.14',
+    package='ghostscript'
+)
+
+check_external_program(
+    program='unpaper',
+    minimum_version='6.1',
+    package='unpaper',
+    optional=True
+)
+
+# Deprecated
+check_external_program(
+    program='pdfseparate',
+    minimum_version='0.29.0',
+    package='poppler',
+    version_check_args=['-v']
+)
+
+check_external_program(
+    program='java',
+    minimum_version='1.5.0',
+    package='Java Runtime Environment',
+    version_check_args=['-version']
+)
+
+check_external_program(
+    program='mutool',
+    minimum_version='1.7a',
+    version_check_args=['-v'],
+    version_scrape_regex=re.compile(r'(\d+\.\d+[a-z]+)'),
+    package='mupdf-tools'
+)
 
 setup(
     name='ocrmypdf',
@@ -12,7 +177,7 @@ setup(
     license='Public Domain',
     packages=['ocrmypdf'],
     keywords=['PDF', 'OCR', 'optical character recognition', 'PDF/A', 'scanning'],
-    classifiers = [
+    classifiers=[
         "Programming Language :: Python :: 3",
         "Development Status :: 4 - Beta",
         "Environment :: Console",