def populate_packages_updatealternatives(d):
    if not update_alternatives_enabled(d):
        return

    # Do actual update alternatives processing
    for pkg in (d.getVar('PACKAGES') or "").split():
        # Create post install/removal scripts
        alt_setup_links = ""
        alt_remove_links = ""
        updates = update_alternatives_alt_targets(d, pkg)
        for alt_name, alt_link, alt_target, alt_priority in updates:
            alt_setup_links  += '\tupdate-alternatives --install %s %s %s %s\n' % (alt_link, alt_name, alt_target, alt_priority)
            alt_remove_links += '\tupdate-alternatives --remove  %s %s\n' % (alt_name, alt_target)

        if alt_setup_links:
            # RDEPENDS setup
            provider = d.getVar('VIRTUAL-RUNTIME_update-alternatives')
            if provider:
                #bb.note('adding runtime requirement for update-alternatives for %s' % pkg)
                d.appendVar('RDEPENDS:%s' % pkg, ' ' + d.getVar('MLPREFIX', False) + provider)

            bb.note('adding update-alternatives calls to postinst/prerm for %s' % pkg)
            bb.note('%s' % alt_setup_links)
            postinst = d.getVar('pkg_postinst:%s' % pkg)
            if postinst:
                postinst = alt_setup_links + postinst
            else:
                postinst = '#!/bin/sh\n' + alt_setup_links
            d.setVar('pkg_postinst:%s' % pkg, postinst)

            bb.note('%s' % alt_remove_links)
            prerm = d.getVar('pkg_prerm:%s' % pkg) or '#!/bin/sh\n'
            prerm += alt_remove_links
            d.setVar('pkg_prerm:%s' % pkg, prerm)

populate_packages_updatealternatives(d)

def update_alternatives_enabled(d):
    # Update Alternatives only works on target packages...
    if bb.data.inherits_class('native', d) or \
       bb.data.inherits_class('cross', d) or bb.data.inherits_class('crosssdk', d) or \
       bb.data.inherits_class('cross-canadian', d):
        return False

    # Disable when targeting mingw32 (no target support)
    if d.getVar("TARGET_OS") == "mingw32":
        return False

    return True

def update_alternatives_alt_targets(d, pkg):
    """
    Returns the update-alternatives metadata for a package.

    The returned format is a list of tuples where the tuple contains:
    alt_name:     The binary name
    alt_link:     The path for the binary (Shared by different packages)
    alt_target:   The path for the renamed binary (Unique per package)
    alt_priority: The priority of the alt_target

    All the alt_targets will be installed into the sysroot. The alt_link is
    a symlink pointing to the alt_target with the highest priority.
    """

    pn = d.getVar('BPN')
    pkgdest = d.getVar('PKGD')
    updates = list()
    for alt_name in (d.getVar('ALTERNATIVE:%s' % pkg) or "").split():
        alt_link     = d.getVarFlag('ALTERNATIVE_LINK_NAME', alt_name)
        alt_target   = d.getVarFlag('ALTERNATIVE_TARGET_%s' % pkg, alt_name) or \
                       d.getVarFlag('ALTERNATIVE_TARGET', alt_name) or \
                       d.getVar('ALTERNATIVE_TARGET_%s' % pkg) or \
                       d.getVar('ALTERNATIVE_TARGET') or \
                       alt_link
        alt_priority = d.getVarFlag('ALTERNATIVE_PRIORITY_%s' % pkg,  alt_name) or \
                       d.getVarFlag('ALTERNATIVE_PRIORITY',  alt_name) or \
                       d.getVar('ALTERNATIVE_PRIORITY_%s' % pkg) or  \
                       d.getVar('ALTERNATIVE_PRIORITY')

        # This shouldn't trigger, as it should have been resolved earlier!
        if alt_link == alt_target:
            bb.note('alt_link == alt_target: %s == %s -- correcting, this should not happen!' % (alt_link, alt_target))
            alt_target = '%s.%s' % (alt_target, pn)

        if not os.path.lexists('%s/%s' % (pkgdest, alt_target)):
            bb.warn('%s: NOT adding alternative provide %s: %s does not exist' % (pn, alt_link, alt_target))
            continue

        alt_target = os.path.normpath(alt_target)
        updates.append( (alt_name, alt_link, alt_target, alt_priority) )

    return updates