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+-- Convenience Lua functions that can be used within Python srpm/rpm macros
+
+-- Determine alternate names provided from the given name.
+-- Used in pythonname provides generator, python_provide and py_provides.
+-- If only_3_to_3_X is false/nil/unused there are 2 rules:
+--  python3-foo  -> python-foo, python3.X-foo
+--  python3.X-foo -> python-foo, python3-foo
+-- If only_3_to_3_X is true there is only 1 rule:
+--  python3-foo  -> python3.X-foo
+-- There is no python-foo -> rule, python-foo packages are version agnostic.
+-- Returns a table/array with strings. Empty when no rule matched.
+local function python_altnames(name, only_3_to_3_X)
+  local xy = rpm.expand('%{__default_python3_pkgversion}')
+  local altnames = {}
+  local replaced
+  -- NB: dash needs to be escaped!
+  if name:match('^python3%-') then
+    local prefixes = only_3_to_3_X and {} or {'python-'}
+    for i, prefix in ipairs({'python' .. xy .. '-', table.unpack(prefixes)}) do
+      replaced = name:gsub('^python3%-', prefix)
+      table.insert(altnames, replaced)
+    end
+  elseif name:match('^python' .. xy .. '%-') and not only_3_to_3_X then
+    for i, prefix in ipairs({'python-', 'python3-'}) do
+      replaced = name:gsub('^python' .. xy .. '%-', prefix)
+      table.insert(altnames, replaced)
+    end
+  end
+  return altnames
+end
+
+
+local function __python_alttags(name, evr, tag_type)
+  -- for the "provides" tag_type we want also unversioned provides
+  local only_3_to_3_X = tag_type ~= "provides"
+  local operator = tag_type == "provides" and ' = ' or ' < '
+
+  -- global cache that tells what package NEVRs were already processed for the
+  -- given tag type
+  if __python_alttags_beenthere == nil then
+    __python_alttags_beenthere = {}
+  end
+  if __python_alttags_beenthere[tag_type] == nil then
+    __python_alttags_beenthere[tag_type] = {}
+  end
+  __python_alttags_beenthere[tag_type][name .. ' ' .. evr] = true
+  local alttags = {}
+  for i, altname in ipairs(python_altnames(name, only_3_to_3_X)) do
+    table.insert(alttags, altname .. operator .. evr)
+  end
+  return alttags
+end
+
+-- For any given name and epoch-version-release, return provides except self.
+-- Uses python_altnames under the hood
+-- Returns a table/array with strings.
+local function python_altprovides(name, evr)
+  return __python_alttags(name, evr, "provides")
+end
+
+-- For any given name and epoch-version-release, return versioned obsoletes except self.
+-- Uses python_altnames under the hood
+-- Returns a table/array with strings.
+local function python_altobsoletes(name, evr)
+  return __python_alttags(name, evr, "obsoletes")
+end
+
+
+local function __python_alttags_once(name, evr, tag_type)
+  -- global cache that tells what provides were already processed
+  if __python_alttags_beenthere == nil
+      or __python_alttags_beenthere[tag_type] == nil
+      or __python_alttags_beenthere[tag_type][name .. ' ' .. evr] == nil then
+    return __python_alttags(name, evr, tag_type)
+  else
+    return nil
+  end
+end
+
+-- Like python_altprovides but only return something once.
+-- For each argument can only be used once, returns nil otherwise.
+-- Previous usage of python_altprovides counts as well.
+local function python_altprovides_once(name, evr)
+  return __python_alttags_once(name, evr, "provides")
+end
+
+-- Like python_altobsoletes but only return something once.
+-- For each argument can only be used once, returns nil otherwise.
+-- Previous usage of python_altobsoletes counts as well.
+local function python_altobsoletes_once(name, evr)
+  return __python_alttags_once(name, evr, "obsoletes")
+end
+
+
+return {
+  python_altnames = python_altnames,
+  python_altprovides = python_altprovides,
+  python_altobsoletes = python_altobsoletes,
+  python_altprovides_once = python_altprovides_once,
+  python_altobsoletes_once = python_altobsoletes_once,
+}