defmodule QueryBuilder.Query.Planner do
  @moduledoc false

  alias QueryBuilder.AssocList

  @barrier_ops [:top_n_per]
  @preload_op :preload

  @join_only_ops [:inner_join, :left_join]

  alias QueryBuilder.Query.{
    Distinct,
    DistinctRoots,
    GroupBy,
    Having,
    LeftJoinLatest,
    LeftJoinTopN,
    Limit,
    Offset,
    OrderBy,
    Select,
    SelectMerge,
    TopNPer,
    Where,
    WhereExistsSubquery,
    WhereNotExistsSubquery
  }

  def compile(%{ecto_query: ecto_query, operations: operations}) when is_list(operations) do
    QueryBuilder.Utils.with_token_cache(fn ->
      root_schema = QueryBuilder.Utils.root_schema(ecto_query)
      operations = Enum.reverse(operations)

      validate_select_operations!(operations)

      {preload_ops, stage_ops} =
        Enum.split_with(operations, &match?({@preload_op, _assocs, _args}, &1))

      {ecto_query, output_assoc_list} = compile_stages(ecto_query, root_schema, stage_ops)

      output_assoc_list = apply_preload_ops(root_schema, output_assoc_list, preload_ops)
      validate_distinct_roots_preload_conflicts!(operations, output_assoc_list)

      ecto_query =
        if preload_ops == [] do
          ecto_query
        else
          QueryBuilder.Query.Preload.preload(ecto_query, output_assoc_list)
        end

      {ecto_query, output_assoc_list}
    end)
  end

  def compile(other) do
    raise ArgumentError,
          "QueryBuilder.Query.Planner.compile/1 expects a %QueryBuilder.Query{}, got: #{inspect(other)}"
  end

  defp validate_distinct_roots_preload_conflicts!(operations, assoc_list) do
    distinct_roots? = Enum.any?(operations, &match?({:distinct_roots, _assocs, _args}, &1))

    if distinct_roots? do
      paths = to_many_through_join_preload_paths(assoc_list)

      if paths != [] do
        raise ArgumentError,
              "distinct_roots/1 cannot be combined with `preload_through_join` on to-many associations, " <>
                "because it collapses join rows and would drop association rows. " <>
                "Use `preload_separate/*` instead. Conflicting preload paths: #{inspect(paths)}"
      end
    end

    :ok
  end

  defp to_many_through_join_preload_paths(%AssocList{} = assoc_list) do
    do_to_many_through_join_preload_paths(assoc_list.roots, [])
  end

  defp do_to_many_through_join_preload_paths(nodes_map, prefix) when is_map(nodes_map) do
    Enum.flat_map(nodes_map, fn {_assoc_field, assoc_data} ->
      current = prefix ++ [assoc_data.assoc_field]

      matches =
        case assoc_data.preload_spec do
          %AssocList.PreloadSpec{strategy: :through_join} when assoc_data.cardinality == :many ->
            [current]

          _ ->
            []
        end

      matches ++ do_to_many_through_join_preload_paths(assoc_data.nested_assocs, current)
    end)
  end

  defp apply_preload_ops(_root_schema, %AssocList{} = assoc_list, []), do: assoc_list

  defp apply_preload_ops(root_schema, %AssocList{} = assoc_list, preload_ops)
       when is_list(preload_ops) do
    Enum.reduce(preload_ops, assoc_list, fn
      {@preload_op, assocs, [%AssocList.PreloadSpec{} = preload_spec]}, assoc_list ->
        AssocList.build(root_schema, assoc_list, assocs,
          join: :none,
          preload_spec: preload_spec
        )

      {@preload_op, _assocs, [other]}, _assoc_list ->
        raise ArgumentError, "invalid preload spec: #{inspect(other)}"

      {@preload_op, _assocs, args}, _assoc_list ->
        raise ArgumentError, "internal error: invalid preload operation args: #{inspect(args)}"

      other, _assoc_list ->
        raise ArgumentError, "internal error: invalid preload operation: #{inspect(other)}"
    end)
  end

  defp compile_stages(ecto_query, root_schema, operations) do
    stages = split_into_stages(operations)

    Enum.reduce(stages, {ecto_query, AssocList.new(root_schema)}, fn stage_ops,
                                                                     {ecto_query,
                                                                      _output_assoc_list} ->
      stage_ends_with_barrier? =
        case List.last(stage_ops) do
          {type, _assocs, _args} when type in @barrier_ops -> true
          _ -> false
        end

      {ecto_query, stage_assoc_list} = compile_stage(ecto_query, root_schema, stage_ops)

      output_assoc_list =
        if stage_ends_with_barrier? do
          AssocList.new(root_schema)
        else
          stage_assoc_list
        end

      {ecto_query, output_assoc_list}
    end)
  end

  defp split_into_stages([]), do: []

  defp split_into_stages(operations) do
    {stages, current_stage_rev} =
      Enum.reduce(operations, {[], []}, fn {type, _assocs, _args} = op,
                                           {stages, current_stage_rev} ->
        current_stage_rev = [op | current_stage_rev]

        if type in @barrier_ops do
          {[Enum.reverse(current_stage_rev) | stages], []}
        else
          {stages, current_stage_rev}
        end
      end)

    stages =
      case current_stage_rev do
        [] -> stages
        current_stage_rev -> [Enum.reverse(current_stage_rev) | stages]
      end

    Enum.reverse(stages)
  end

  defp compile_stage(ecto_query, root_schema, stage_ops) do
    assoc_list =
      Enum.reduce(stage_ops, AssocList.new(root_schema), fn {_type, assocs, _args} = op,
                                                            assoc_list ->
        case List.wrap(assocs) do
          [] ->
            assoc_list

          assoc_fields ->
            AssocList.build(root_schema, assoc_list, assoc_fields, assoc_build_opts(op))
        end
      end)

    ecto_query = QueryBuilder.JoinMaker.make_joins(ecto_query, assoc_list)

    ecto_query =
      Enum.reduce(stage_ops, ecto_query, fn {type, _assocs, _args} = op, ecto_query ->
        if type in @join_only_ops do
          ecto_query
        else
          apply_operation(ecto_query, op, assoc_list)
        end
      end)

    {ecto_query, assoc_list}
  end

  defp assoc_build_opts({:inner_join, _assocs, _args}), do: [join: :inner]

  defp assoc_build_opts({:left_join, _assocs, [left_join_mode, join_filters]})
       when left_join_mode in [:leaf, :path] and is_list(join_filters),
       do: [join: :left, join_filters: join_filters, left_join_mode: left_join_mode]

  defp assoc_build_opts({:left_join, _assocs, args}) do
    raise ArgumentError, "internal error: invalid left_join operation args: #{inspect(args)}"
  end

  defp assoc_build_opts(_operation), do: []

  defp apply_operation(ecto_query, {:where, _assocs, [filters, or_filters]}, assoc_list) do
    Where.where(ecto_query, assoc_list, filters, or_filters)
  end

  defp apply_operation(ecto_query, {:select, _assocs, [selection]}, assoc_list) do
    Select.select(ecto_query, assoc_list, selection)
  end

  defp apply_operation(ecto_query, {:select_merge, _assocs, [selection]}, assoc_list) do
    SelectMerge.select_merge(ecto_query, assoc_list, selection)
  end

  defp apply_operation(ecto_query, {:distinct, _assocs, [value]}, assoc_list) do
    Distinct.distinct(ecto_query, assoc_list, value)
  end

  defp apply_operation(ecto_query, {:distinct_roots, _assocs, []}, assoc_list) do
    DistinctRoots.distinct_roots(ecto_query, assoc_list)
  end

  defp apply_operation(ecto_query, {:group_by, _assocs, [expr]}, assoc_list) do
    GroupBy.group_by(ecto_query, assoc_list, expr)
  end

  defp apply_operation(ecto_query, {:having, _assocs, [filters, or_filters]}, assoc_list) do
    Having.having(ecto_query, assoc_list, filters, or_filters)
  end

  defp apply_operation(ecto_query, {:order_by, _assocs, [value]}, assoc_list) do
    OrderBy.order_by(ecto_query, assoc_list, value)
  end

  defp apply_operation(ecto_query, {:limit, _assocs, [value]}, assoc_list) do
    Limit.limit(ecto_query, assoc_list, value)
  end

  defp apply_operation(ecto_query, {:offset, _assocs, [value]}, assoc_list) do
    Offset.offset(ecto_query, assoc_list, value)
  end

  defp apply_operation(
         ecto_query,
         {:where_exists_subquery, _assocs, [assoc_fields, scope, filters, or_filters]},
         assoc_list
       ) do
    WhereExistsSubquery.where_exists_subquery(
      ecto_query,
      assoc_list,
      assoc_fields,
      scope,
      filters,
      or_filters
    )
  end

  defp apply_operation(
         ecto_query,
         {:where_not_exists_subquery, _assocs, [assoc_fields, scope, filters, or_filters]},
         assoc_list
       ) do
    WhereNotExistsSubquery.where_not_exists_subquery(
      ecto_query,
      assoc_list,
      assoc_fields,
      scope,
      filters,
      or_filters
    )
  end

  defp apply_operation(ecto_query, {:top_n_per, _assocs, [opts]}, assoc_list) do
    TopNPer.top_n_per(ecto_query, assoc_list, opts)
  end

  defp apply_operation(ecto_query, {:left_join_latest, _assocs, [assoc_field, opts]}, assoc_list) do
    LeftJoinLatest.left_join_latest(ecto_query, assoc_list, assoc_field, opts)
  end

  defp apply_operation(ecto_query, {:left_join_top_n, _assocs, [assoc_field, opts]}, assoc_list) do
    LeftJoinTopN.left_join_top_n(ecto_query, assoc_list, assoc_field, opts)
  end

  defp apply_operation(_ecto_query, {type, _assocs, args}, _assoc_list) do
    raise ArgumentError,
          "internal error: unknown query operation #{inspect(type)} with args #{inspect(args)}"
  end

  defp validate_select_operations!(operations) do
    select_indexes =
      operations
      |> Enum.with_index()
      |> Enum.flat_map(fn
        {{type, _assocs, _args}, index}
        when type in [:select, :left_join_latest, :left_join_top_n] ->
          [index]

        {_op, _index} ->
          []
      end)

    case select_indexes do
      [] ->
        :ok

      [select_index] ->
        if Enum.any?(Enum.take(operations, select_index), fn
             {:select_merge, _assocs, _args} -> true
             _ -> false
           end) do
          raise ArgumentError,
                "only one select expression is allowed in query; " <>
                  "calling `select/*` (or `left_join_latest/3` / `left_join_top_n/3`) after `select_merge/*` is not supported (Ecto semantics)"
        end

        :ok

      _many ->
        raise ArgumentError,
              "only one select expression is allowed in query; " <>
                "call `select/*` (or `left_join_latest/3` / `left_join_top_n/3`) at most once and use `select_merge/*` to add fields"
    end
  end
end