defmodule MvWeb.MemberLive.Index.FieldVisibility do
  @moduledoc """
  Manages field visibility by merging user-specific selection with global settings.

  This module handles:
  - Getting all available fields (member fields + custom fields)
  - Merging user selection with global settings (user selection takes priority)
  - Falling back to global settings when no user selection exists
  - Converting between different field name formats (atoms vs strings)

  ## Field Naming Convention

  - **Member Fields**: Atoms (e.g., `:first_name`, `:email`)
  - **Custom Fields**: Strings with format `"custom_field_<id>"` (e.g., `"custom_field_abc-123"`)

  ## Priority Order

  1. User-specific selection (from URL/Session/Cookie)
  2. Global settings (from database)
  3. Default (all fields visible)

  ## Pseudo Member Fields

  Overview-only fields that are not in `Mv.Constants.member_fields()` (e.g. computed/UI-only).
  They appear in the field dropdown and in `member_fields_visible` but are not domain attributes.
  """

  alias Mv.Membership.Helpers.VisibilityConfig

  # Single UI key for "Membership Fee Status"; only this appears in the dropdown.
  # Groups and membership_fee_type are also pseudo fields (not in member_fields(), displayed in the table).
  # :name and :address are composite display-only columns (Name = name + email,
  # Address = street/house number over postal code/city).
  # Order mirrors the overview table / export column order (fee type before fee
  # status), so the Columns dropdown and the table agree.
  @pseudo_member_fields [:membership_fee_type, :membership_fee_status, :groups, :name, :address]

  # The composite display columns and the constituent columns they replace. The
  # column manager offers exactly one variant per group, selected by the view
  # settings: the composite when the matching "compact" setting is on, otherwise
  # the constituents (see `offered_member_fields/2`).
  @name_composite :name
  @name_constituents [:first_name, :last_name, :email]
  @address_composite :address
  @address_constituents [:street, :house_number, :postal_code, :city]

  # Export/API may accept this as alias; must not appear in the UI options list.
  @export_only_alias :payment_status

  # Curated default-visible column set (§1.2): the columns shown on first visit
  # when there is no persisted selection and no global override. Everything else
  # (the individual name/address sub-fields, notes, dates other than join date)
  # defaults to hidden so the table fits common desktop widths.
  @default_visible_fields MapSet.new([
                            :name,
                            :address,
                            :membership_fee_type,
                            :membership_fee_status,
                            :groups,
                            :join_date
                          ])

  # The curated default-visible column set for the given view settings. In
  # compact mode the composite `:name` / `:address` columns are default; when a
  # composite is switched off, its constituent columns take over as the defaults
  # instead (§7b). While the Member composite is compact, `include_email` decides
  # where the email lives: folded into the Member cell (`true`, no separate
  # column) or as a default-visible `:email` column (`false`).
  defp default_visible_set(compact_member, include_email, compact_address) do
    @default_visible_fields
    |> apply_name_default(compact_member, include_email)
    |> apply_group_default(compact_address, @address_composite, @address_constituents)
  end

  # Compact Member cell with email folded in: only the composite is default.
  defp apply_name_default(set, true = _compact, true = _include_email), do: set

  # Compact Member cell without folded email: the composite plus a separate
  # default-visible email column.
  defp apply_name_default(set, true = _compact, false = _include_email),
    do: MapSet.put(set, :email)

  # Non-compact: drop the composite and make first/last name and email default.
  defp apply_name_default(set, false = _compact, _include_email) do
    set
    |> MapSet.delete(@name_composite)
    |> MapSet.union(MapSet.new(@name_constituents))
  end

  # Compact: the composite stays the default. Non-compact: drop the composite and
  # make the constituents default-visible.
  defp apply_group_default(set, true, _composite, _constituents), do: set

  defp apply_group_default(set, false, composite, constituents) do
    set
    |> MapSet.delete(composite)
    |> MapSet.union(MapSet.new(constituents))
  end

  @doc """
  Member-field atoms the column manager offers for the given view settings, in
  dropdown/table order.

  The identity block always leads, regardless of whether each group is compact:

  1. the name group — the composite `:name` when compact, otherwise its
     constituents `:first_name`, `:last_name`;
  2. the `:email` column, when offered as a separate column (it is folded into
     the Member cell only while the composite is compact and `include_email` is
     on);
  3. the address group — the composite `:address` when compact, otherwise its
     constituents `:street`, `:house_number`, `:postal_code`, `:city`.

  Everything else follows in the configured data-fields order. This keeps the
  name group ahead of the address group even when the name group is expanded
  into `:first_name`/`:last_name` while the address stays compact.
  """
  @spec offered_member_fields(boolean(), boolean(), boolean()) :: [atom()]
  def offered_member_fields(compact_member, include_email, compact_address) do
    name_group = if compact_member, do: [@name_composite], else: [:first_name, :last_name]
    email_group = if email_offered?(compact_member, include_email), do: [:email], else: []

    address_group =
      if compact_address, do: [@address_composite], else: @address_constituents

    leading = name_group ++ email_group ++ address_group

    rest =
      Enum.reject(overview_member_fields(), fn field ->
        field == @export_only_alias or
          hidden_variant?(field, compact_member, include_email, compact_address) or
          field in leading
      end)

    leading ++ rest
  end

  @doc """
  The DB constituent columns the composite `:name` cell stands in for, in
  canonical order. `:email` is a constituent only while it is folded into the
  compact Member cell (`include_email?` true); otherwise it is its own column.
  """
  @spec name_constituents(boolean()) :: [atom()]
  def name_constituents(include_email?) do
    if include_email?, do: @name_constituents, else: @name_constituents -- [:email]
  end

  @doc "The DB constituent columns the composite `:address` cell stands in for, in canonical order."
  @spec address_constituents() :: [:street | :house_number | :postal_code | :city, ...]
  def address_constituents, do: @address_constituents

  # The email is a separate offered column except when it is folded into the
  # compact Member cell (compact + include_email).
  defp email_offered?(compact_member, include_email), do: not (compact_member and include_email)

  # The variant of a composite group that is not offered in the current mode.
  defp hidden_variant?(field, compact_member, include_email, compact_address) do
    name_variant_hidden?(field, compact_member, include_email) or
      address_variant_hidden?(field, compact_address)
  end

  # Compact hides first-name/last-name (folded into the composite). The email is
  # hidden only when it is folded into the cell (compact + include_email); with
  # include_email off it stays offered as a separate column. Non-compact hides the
  # composite in favour of the constituents.
  defp name_variant_hidden?(@name_composite, compact_member, _include_email),
    do: not compact_member

  defp name_variant_hidden?(:email, compact_member, include_email),
    do: compact_member and include_email

  defp name_variant_hidden?(field, compact_member, _include_email)
       when field in [:first_name, :last_name],
       do: compact_member

  defp name_variant_hidden?(_field, _compact_member, _include_email), do: false

  defp address_variant_hidden?(@address_composite, compact_address),
    do: not compact_address

  defp address_variant_hidden?(field, compact_address)
       when field in [:street, :house_number, :postal_code, :city],
       do: compact_address

  defp address_variant_hidden?(_field, _compact_address), do: false

  @doc """
  All fields the column manager offers for the given view settings: the offered
  member fields (see `offered_member_fields/3`) followed by the custom fields.
  """
  @spec get_offered_fields([struct()], boolean(), boolean(), boolean()) :: [
          atom() | String.t()
        ]
  def get_offered_fields(custom_fields, compact_member, include_email, compact_address) do
    custom_field_names = Enum.map(custom_fields, &"custom_field_#{&1.id}")
    offered_member_fields(compact_member, include_email, compact_address) ++ custom_field_names
  end

  defp overview_member_fields do
    Mv.Constants.member_fields() ++ @pseudo_member_fields
  end

  @doc """
  Builds field selection from URL, scoped to the columns offered for the given
  view settings (`:compact_member` / `:member_include_email` / `:compact_address`
  in `opts`): fields in `url_selection` are visible, all others false.

  Use when `?fields=...` is in the URL so column visibility is not merged with
  global settings.
  """
  @spec selection_from_url_only(%{String.t() => boolean()}, [struct()], keyword()) :: %{
          String.t() => boolean()
        }
  def selection_from_url_only(url_selection, custom_fields, opts)
      when is_map(url_selection) and is_list(opts) do
    {cm, ie, ca} = view_opts(opts)
    do_selection_from_url_only(url_selection, get_offered_fields(custom_fields, cm, ie, ca))
  end

  def selection_from_url_only(_, _, _), do: %{}

  defp do_selection_from_url_only(url_selection, all_fields) do
    Enum.reduce(all_fields, %{}, fn field, acc ->
      field_string = field_to_string(field)
      visible = Map.get(url_selection, field_string, false)
      Map.put(acc, field_string, visible)
    end)
  end

  defp view_opts(opts) do
    {
      Keyword.get(opts, :compact_member, true),
      Keyword.get(opts, :member_include_email, false),
      Keyword.get(opts, :compact_address, true)
    }
  end

  @doc """
  Merges user field selection with global settings, scoped to the columns offered
  for the given view settings (`:compact_member` / `:member_include_email` /
  `:compact_address` in `opts`).

  User selection takes priority over global settings. If a field is not in the
  user selection, the global setting is used; if a field is not in global
  settings, it defaults to visible. Only offered columns appear in the result, so
  a column that is not applicable in the current mode (e.g. `:first_name` while
  the composite "Name" is on) never leaks into the visible set. Defaults follow
  the mode via `default_visible_set/3`.
  """
  @spec merge_with_global_settings(%{String.t() => boolean()}, map(), [struct()], keyword()) ::
          %{String.t() => boolean()}
  def merge_with_global_settings(user_selection, global_settings, custom_fields, opts)
      when is_list(opts) do
    {cm, ie, ca} = view_opts(opts)
    all_fields = get_offered_fields(custom_fields, cm, ie, ca)
    default_set = default_visible_set(cm, ie, ca)
    do_merge(user_selection, global_settings, custom_fields, all_fields, default_set)
  end

  defp do_merge(user_selection, global_settings, custom_fields, all_fields, default_set) do
    global_visibility = get_global_visibility_map(global_settings, custom_fields, default_set)

    Enum.reduce(all_fields, %{}, fn field, acc ->
      field_string = field_to_string(field)

      visibility =
        case Map.get(user_selection, field_string) do
          nil -> Map.get(global_visibility, field_string, true)
          user_value -> user_value
        end

      Map.put(acc, field_string, visibility)
    end)
  end

  @doc """
  Gets visible member fields from field selection.

  Returns only member fields (atoms) that are visible.

  ## Examples

      iex> selection = %{"first_name" => true, "email" => true, "custom_field_123" => true}
      iex> get_visible_member_fields(selection)
      [:first_name, :email]
  """
  @spec get_visible_member_fields(%{String.t() => boolean()}) :: [atom()]
  def get_visible_member_fields(field_selection) when is_map(field_selection) do
    member_fields = overview_member_fields()

    field_selection
    |> Enum.filter(fn {field_string, visible} ->
      field_atom = to_field_identifier(field_string)
      visible && field_atom in member_fields
    end)
    |> Enum.map(fn {field_string, _visible} -> to_field_identifier(field_string) end)
    |> Enum.uniq()
  end

  def get_visible_member_fields(_), do: []

  @doc """
  Returns the list of computed (UI-only) member field atoms.

  These fields are not in the database; they must not be used for Ash query
  select/sort. Use this to filter sort options and validate sort_field.
  """
  @spec computed_member_fields() :: [:membership_fee_status | :membership_fee_type | :groups, ...]
  def computed_member_fields, do: @pseudo_member_fields

  @doc """
  Visible member fields that are real DB attributes (from `Mv.Constants.member_fields()`).

  Use for query select/sort. Not for rendering column visibility (use
  `get_visible_member_fields/1` for that).
  """
  @spec get_visible_member_fields_db(%{String.t() => boolean()}) :: [atom()]
  def get_visible_member_fields_db(field_selection) when is_map(field_selection) do
    db_fields = MapSet.new(Mv.Constants.member_fields())

    field_selection
    |> Enum.filter(fn {field_string, visible} ->
      field_atom = to_field_identifier(field_string)
      visible && field_atom in db_fields
    end)
    |> Enum.map(fn {field_string, _visible} -> to_field_identifier(field_string) end)
    |> Enum.uniq()
  end

  def get_visible_member_fields_db(_), do: []

  @doc """
  Visible member fields that are computed/UI-only (e.g. membership_fee_status).

  Use for rendering; do not use for query select or sort.
  """
  @spec get_visible_member_fields_computed(%{String.t() => boolean()}) :: [atom()]
  def get_visible_member_fields_computed(field_selection) when is_map(field_selection) do
    computed_set = MapSet.new([:membership_fee_status])

    field_selection
    |> Enum.filter(fn {field_string, visible} ->
      field_atom = to_field_identifier(field_string)
      visible && field_atom in computed_set
    end)
    |> Enum.map(fn {field_string, _visible} -> to_field_identifier(field_string) end)
    |> Enum.uniq()
  end

  def get_visible_member_fields_computed(_), do: []

  @doc """
  Gets visible custom fields from field selection.

  Returns only custom field identifiers (strings) that are visible.

  ## Examples

      iex> selection = %{"first_name" => true, "custom_field_123" => true, "custom_field_456" => false}
      iex> get_visible_custom_fields(selection)
      ["custom_field_123"]
  """
  @spec get_visible_custom_fields(%{String.t() => boolean()}) :: [String.t()]
  def get_visible_custom_fields(field_selection) when is_map(field_selection) do
    prefix = Mv.Constants.custom_field_prefix()

    field_selection
    |> Enum.filter(fn {field_string, visible} ->
      visible && String.starts_with?(field_string, prefix)
    end)
    |> Enum.map(fn {field_string, _visible} -> field_string end)
  end

  def get_visible_custom_fields(_), do: []

  # Gets global visibility map from settings
  defp get_global_visibility_map(settings, custom_fields, default_set) do
    member_visibility = get_member_field_visibility_from_settings(settings, default_set)
    custom_field_visibility = get_custom_field_visibility(custom_fields)

    Map.merge(member_visibility, custom_field_visibility)
  end

  # Gets member field visibility from settings (domain fields from settings, pseudo fields default true)
  defp get_member_field_visibility_from_settings(settings, default_set) do
    visibility_config =
      VisibilityConfig.normalize(Map.get(settings, :member_field_visibility, %{}))

    domain_fields = Mv.Constants.member_fields()

    domain_map =
      Enum.reduce(domain_fields, %{}, fn field, acc ->
        field_string = Atom.to_string(field)
        default_visibility = MapSet.member?(default_set, field)
        show_in_overview = Map.get(visibility_config, field, default_visibility)
        Map.put(acc, field_string, show_in_overview)
      end)

    Enum.reduce(@pseudo_member_fields, domain_map, fn field, acc ->
      Map.put(acc, Atom.to_string(field), MapSet.member?(default_set, field))
    end)
  end

  # Gets custom field visibility (all custom fields with show_in_overview=true are visible)
  defp get_custom_field_visibility(custom_fields) do
    prefix = Mv.Constants.custom_field_prefix()

    Enum.reduce(custom_fields, %{}, fn custom_field, acc ->
      field_string = "#{prefix}#{custom_field.id}"
      visible = Map.get(custom_field, :show_in_overview, true)
      Map.put(acc, field_string, visible)
    end)
  end

  # Converts field string to atom (for member fields) or keeps as string (for custom fields).
  # Maps export-only alias to canonical UI key so only one option controls the column.
  defp to_field_identifier(field_string) when is_binary(field_string) do
    if String.starts_with?(field_string, Mv.Constants.custom_field_prefix()) do
      field_string
    else
      atom =
        try do
          String.to_existing_atom(field_string)
        rescue
          ArgumentError -> field_string
        end

      if atom == @export_only_alias, do: :membership_fee_status, else: atom
    end
  end

  # Converts field identifier to string
  defp field_to_string(field) when is_atom(field), do: Atom.to_string(field)
  defp field_to_string(field) when is_binary(field), do: field
end