defmodule MapSorter.Cond do
@moduledoc """
Generates `cond/1` clauses as a heredoc from a list of sort specs.
"""
import MapSorter.SortSpec, only: [brackets: 1]
alias MapSorter.{SortSpec, SortSpecs}
@doc ~S'''
Generates `cond/1` clauses as a heredoc from a list of sort specs.
## Examples
iex> alias MapSorter.Cond
iex> sort_specs = [:name, {:desc, :dob}]
iex> Cond.clauses(sort_specs)
"""
&1[:name] < &2[:name] -> true
&1[:name] > &2[:name] -> false
&1[:dob] > &2[:dob] -> true
&1[:dob] < &2[:dob] -> false
"""
iex> alias MapSorter.Cond
iex> sort_specs = [:name, {:desc, {:dob, Date}}]
iex> Cond.clauses(sort_specs)
"""
&1[:name] < &2[:name] -> true
&1[:name] > &2[:name] -> false
&1[:dob] != nil and Date.compare(&1[:dob], &2[:dob]) == :gt -> true
&1[:dob] != nil and Date.compare(&1[:dob], &2[:dob]) == :lt -> false
"""
iex> alias MapSorter.Cond
iex> sort_specs = [:name, {:desc, {:dob, String}}]
iex> Cond.clauses(sort_specs)
"""
&1[:name] < &2[:name] -> true
&1[:name] > &2[:name] -> false
&1[{:dob, String}] > &2[{:dob, String}] -> true
&1[{:dob, String}] < &2[{:dob, String}] -> false
"""
'''
@spec clauses(SortSpecs.t()) :: String.t()
def clauses(sort_specs) when is_list(sort_specs) do
Enum.map_join(sort_specs, &do_clauses/1)
end
## Private functions
# Use short-circuit 'and' to prevent compare if key not in map...
@spec cond(SortSpec.key(), String.t(), atom) :: String.t()
defp cond(key, module, op) when op in [:lt, :gt] do
# brackets(:dob) => "[:dob]"
# brackets('dob') => "['dob']"
# brackets("dob") => ~s/["dob"]/
brk = brackets(key)
"""
&1#{brk} != nil and #{module}.compare(&1#{brk}, &2#{brk}) == #{inspect(op)}
"""
|> String.trim_trailing()
end
@spec do_clauses(SortSpec.t()) :: String.t()
defp do_clauses({:asc, {key, module}}) when is_atom(module) do
with {:module, module} <- Code.ensure_loaded(module),
true <- function_exported?(module, :compare, 2) do
module = "#{inspect(module)}"
"""
#{cond(key, module, :lt)} -> true
#{cond(key, module, :gt)} -> false
"""
else
_not_a_loaded_module_or_no_compare_function ->
# Then sort spec key is a 2-element tuple...
key = {key, module}
"""
&1#{brackets(key)} < &2#{brackets(key)} -> true
&1#{brackets(key)} > &2#{brackets(key)} -> false
"""
end
end
defp do_clauses({:desc, {key, module}}) when is_atom(module) do
with {:module, module} <- Code.ensure_loaded(module),
true <- function_exported?(module, :compare, 2) do
module = "#{inspect(module)}"
"""
#{cond(key, module, :gt)} -> true
#{cond(key, module, :lt)} -> false
"""
else
_not_a_loaded_module_or_no_compare_function ->
# Then sort spec key is a 2-element tuple...
key = {key, module}
"""
&1#{brackets(key)} > &2#{brackets(key)} -> true
&1#{brackets(key)} < &2#{brackets(key)} -> false
"""
end
end
defp do_clauses({:asc, key}) do
"""
&1#{brackets(key)} < &2#{brackets(key)} -> true
&1#{brackets(key)} > &2#{brackets(key)} -> false
"""
end
defp do_clauses({:desc, key}) do
"""
&1#{brackets(key)} > &2#{brackets(key)} -> true
&1#{brackets(key)} < &2#{brackets(key)} -> false
"""
end
defp do_clauses(key) do
do_clauses({:asc, key})
end
end