defmodule RDF.PrefixMap do
  @moduledoc """
  A mapping a prefix atoms to IRI namespaces.

  `RDF.PrefixMap` implements the `Enumerable` protocol.
  """

  defstruct map: %{}

  alias RDF.IRI

  @doc """
  Creates an empty `RDF.PrefixMap.
  """
  def new(), do: %__MODULE__{}

  @doc """
  Creates a new `RDF.PrefixMap.

  The prefix mappings can be passed as keyword lists or maps.
  The keys for the prefixes can be given as atoms or strings and will be normalized to atoms.
  The namespaces can be given as `RDF.IRI`s or strings and will be normalized to `RDF.IRI`s.
  """
  def new(map)

  def new(map) when is_map(map) do
    %__MODULE__{map: Map.new(map, &normalize/1)}
  end

  def new(map) when is_list(map) do
    map |> Map.new() |> new()
  end

  defp normalize({prefix, %IRI{} = namespace}) when is_atom(prefix),
    do: {prefix, namespace}

  defp normalize({prefix, namespace}) when is_binary(prefix),
    do: normalize({String.to_atom(prefix), namespace})

  defp normalize({prefix, namespace}) when is_binary(namespace),
       do: normalize({prefix, IRI.new(namespace)})

  defp normalize({prefix, _}),
    do: raise("Invalid prefix on PrefixMap: #{inspect(prefix)}}")

  @doc """
  Adds a prefix mapping the given `RDF.PrefixMap`.

  Unless a mapping of the given prefix to a different namespace already exists,
  an ok tuple is returned, other an error tuple.
  """
  def add(prefix_map, prefix, namespace)

  def add(%__MODULE__{map: map}, prefix, %IRI{} = namespace) when is_atom(prefix) do
    if conflicts?(map, prefix, namespace) do
      {:error, "prefix #{inspect(prefix)} is already mapped to another namespace"}
    else
      {:ok, %__MODULE__{map: Map.put(map, prefix, namespace)}}
    end
  end

  def add(%__MODULE__{} = prefix_map, prefix, namespace) do
    with {prefix, namespace} = normalize({prefix, namespace}) do
      add(prefix_map, prefix, namespace)
    end
  end

  @doc """
  Adds a prefix mapping to the given `RDF.PrefixMap` and raises an exception in error cases.
  """
  def add!(prefix_map, prefix, namespace) do
    with {:ok, new_prefix_map} <- add(prefix_map, prefix, namespace) do
      new_prefix_map
    else
      {:error, error} -> raise error
    end
  end

  @doc """
  Merges two `RDF.PrefixMap`s.

  The second prefix map can also be given as any structure which can converted
  to a `RDF.PrefixMap` via `new/1`.

  If there are conflicts between the prefix maps, that is prefixes mapped to
  different namespaces and error tuple is returned, otherwise an ok tuple.
  """
  def merge(prefix_map1, prefix_map2)

  def merge(%__MODULE__{map: map1}, %__MODULE__{map: map2}) do
    with [] <- merge_conflicts(map1, map2) do
      {:ok, %__MODULE__{map: Map.merge(map1, map2)}}
    else
      conflicts ->
        {:error, "conflicting prefix mappings: #{conflicts |> Stream.map(&inspect/1) |> Enum.join(", ")}"}
    end
  end

  def merge(%__MODULE__{} = prefix_map, other_prefixes) do
    merge(prefix_map, new(other_prefixes))
  rescue
    FunctionClauseError ->
      raise ArgumentError, "#{inspect(other_prefixes)} is not convertible to a RDF.PrefixMap"
  end

  defp merge_conflicts(map1, map2) do
    Enum.reduce(map1, [], fn {prefix, namespace}, conflicts ->
      if conflicts?(map2, prefix, namespace) do
        [prefix | conflicts]
      else
        conflicts
      end
    end)
  end

  defp conflicts?(map, prefix, namespace) do
    (existing_namespace = Map.get(map, prefix)) && existing_namespace != namespace
  end

  @doc """
  Deletes a prefix mapping from the given `RDF.PrefixMap`..
  """
  def delete(prefix_map, prefix)

  def delete(%__MODULE__{map: map}, prefix) when is_atom(prefix) do
    %__MODULE__{map: Map.delete(map, prefix)}
  end

  def delete(prefix_map, prefix) when is_binary(prefix) do
    delete(prefix_map, String.to_atom(prefix))
  end

  @doc """
  Returns the namespace for the given prefix in the given `RDF.PrefixMap`.

  Returns `nil`, when the given `prefix` is not present in `prefix_map`.
  """
  def namespace(prefix_map, prefix)

  def namespace(%__MODULE__{map: map}, prefix) when is_atom(prefix) do
    Map.get(map, prefix)
  end

  def namespace(prefix_map, prefix) when is_binary(prefix) do
    namespace(prefix_map, String.to_atom(prefix))
  end

  @doc """
  Returns the prefix for the given namespace in the given `RDF.PrefixMap`.

  Returns `nil`, when the given `namespace` is not present in `prefix_map`.
  """
  def prefix(prefix_map, namespace)

  def prefix(%__MODULE__{map: map}, %IRI{} = namespace) do
    Enum.find_value(map, fn {prefix, ns} -> ns == namespace && prefix end)
  end

  def prefix(prefix_map, namespace) when is_binary(namespace) do
    prefix(prefix_map, IRI.new(namespace))
  end

  @doc """
  Returns whether the given prefix exists in the given `RDF.PrefixMap`.
  """
  def has_prefix?(prefix_map, prefix)

  def has_prefix?(%__MODULE__{map: map}, prefix) when is_atom(prefix) do
    Map.has_key?(map, prefix)
  end

  def has_prefix?(prefix_map, prefix) when is_binary(prefix) do
    has_prefix?(prefix_map, String.to_atom(prefix))
  end

  @doc """
  Returns all prefixes from the given `RDF.PrefixMap`.
  """
  def prefixes(%__MODULE__{map: map}) do
    Map.keys(map)
  end

  @doc """
  Returns all namespaces from the given `RDF.PrefixMap`.
  """
  def namespaces(%__MODULE__{map: map}) do
    Map.values(map)
  end

  defimpl Enumerable do
    def reduce(%RDF.PrefixMap{map: map}, acc, fun), do: Enumerable.reduce(map, acc, fun)

    def member?(%RDF.PrefixMap{map: map}, mapping), do: Enumerable.member?(map, mapping)
    def count(%RDF.PrefixMap{map: map}), do: Enumerable.count(map)
    def slice(_prefix_map), do: {:error, __MODULE__}
  end
end