defmodule Microwaveprop.Radio do
  @moduledoc false

  import Ecto.Query

  alias Microwaveprop.Accounts.User
  alias Microwaveprop.Radio.Contact
  alias Microwaveprop.Radio.ContactEdit
  alias Microwaveprop.Radio.Maidenhead
  alias Microwaveprop.Repo

  @per_page 20
  @sortable_fields ~w(station1 station2 band mode distance_km qso_timestamp inserted_at)a

  @type contact_page :: %{
          entries: [Contact.t()],
          grouped_entries: [{Contact.t(), [Contact.t()]}],
          page: pos_integer(),
          total_pages: pos_integer(),
          total_entries: non_neg_integer()
        }

  @spec list_contacts(keyword()) :: contact_page()
  def list_contacts(opts \\ []) do
    page = max(Keyword.get(opts, :page, 1), 1)
    offset = (page - 1) * @per_page
    search = Keyword.get(opts, :search)

    {sort_field, sort_dir} = sort_opts(opts)

    base_query = maybe_search(Contact, search)

    total_entries = Repo.aggregate(base_query, :count)
    total_pages = max(ceil(total_entries / @per_page), 1)

    entries =
      base_query
      |> order_by([q], [{^sort_dir, field(q, ^sort_field)}, {^sort_dir, q.id}])
      |> limit(^@per_page)
      |> offset(^offset)
      |> Repo.all()
      |> Repo.preload(:user)

    %{
      entries: entries,
      grouped_entries: group_reciprocals(entries),
      page: page,
      total_pages: total_pages,
      total_entries: total_entries
    }
  end

  @doc """
  Groups reciprocal contacts (same station pair swapped, same band, same timestamp).
  Returns a list of `{primary, reciprocals}` tuples where reciprocals is
  a (possibly empty) list of matching contacts.
  """
  @spec group_reciprocals([Contact.t()]) :: [{Contact.t(), [Contact.t()]}]
  def group_reciprocals(contacts) do
    {groups, _seen_ids} =
      Enum.reduce(contacts, {[], MapSet.new()}, fn contact, {groups, seen} ->
        group_contact(contact, contacts, groups, seen)
      end)

    Enum.reverse(groups)
  end

  defp group_contact(contact, contacts, groups, seen) do
    if MapSet.member?(seen, contact.id) do
      {groups, seen}
    else
      reciprocals =
        Enum.filter(contacts, fn other ->
          other.id != contact.id and
            not MapSet.member?(seen, other.id) and
            other.band == contact.band and
            reciprocal_pair?(contact, other)
        end)

      new_seen = Enum.reduce(reciprocals, MapSet.put(seen, contact.id), &MapSet.put(&2, &1.id))
      {[{contact, reciprocals} | groups], new_seen}
    end
  end

  defp reciprocal_pair?(a, b) do
    same_stations =
      (a.station1 == b.station2 and a.station2 == b.station1) or
        (a.station1 == b.station1 and a.station2 == b.station2)

    same_stations and same_hour?(a.qso_timestamp, b.qso_timestamp)
  end

  defp same_hour?(t1, t2) do
    t1 |> NaiveDateTime.truncate(:second) |> Map.take([:year, :month, :day, :hour]) ==
      t2 |> NaiveDateTime.truncate(:second) |> Map.take([:year, :month, :day, :hour])
  end

  defp maybe_search(query, nil), do: query
  defp maybe_search(query, ""), do: query

  defp maybe_search(query, search) do
    terms = search |> String.split() |> Enum.map(&String.trim/1) |> Enum.reject(&(&1 == ""))

    case terms do
      [a, b] ->
        pa = "%" <> String.upcase(a) <> "%"
        pb = "%" <> String.upcase(b) <> "%"

        where(
          query,
          [q],
          (ilike(q.station1, ^pa) and ilike(q.station2, ^pb)) or
            (ilike(q.station1, ^pb) and ilike(q.station2, ^pa))
        )

      _ ->
        pattern = "%" <> String.upcase(search) <> "%"
        where(query, [q], ilike(q.station1, ^pattern) or ilike(q.station2, ^pattern))
    end
  end

  defp sort_opts(opts) do
    sort_by = Keyword.get(opts, :sort_by, :qso_timestamp)
    sort_order = Keyword.get(opts, :sort_order, :desc)

    field = if sort_by in @sortable_fields, do: sort_by, else: :qso_timestamp
    dir = if sort_order in [:asc, :desc], do: sort_order, else: :desc

    {field, dir}
  end

  # ── Enrichment status queries ────────────────────────────────────

  @enrichable_statuses [:pending, :failed]

  @spec contacts_needing_enrichment(
          atom(),
          non_neg_integer(),
          (Ecto.Query.t() -> Ecto.Query.t()) | nil
        ) :: [Contact.t()]
  def contacts_needing_enrichment(field, limit \\ 500, extra_filter \\ nil) do
    query =
      Contact
      |> where([q], field(q, ^field) in ^@enrichable_statuses and not is_nil(q.pos1))
      |> order_by([q], asc: q.qso_timestamp)
      |> limit(^limit)

    query = if extra_filter, do: extra_filter.(query), else: query
    Repo.all(query)
  end

  @spec unprocessed_contacts(non_neg_integer()) :: [Contact.t()]
  def unprocessed_contacts(limit \\ 500), do: contacts_needing_enrichment(:weather_status, limit)

  @spec unprocessed_hrrr_contacts(non_neg_integer()) :: [Contact.t()]
  def unprocessed_hrrr_contacts(limit \\ 500), do: contacts_needing_enrichment(:hrrr_status, limit)

  @spec unprocessed_terrain_contacts(non_neg_integer()) :: [Contact.t()]
  def unprocessed_terrain_contacts(limit \\ 500),
    do: contacts_needing_enrichment(:terrain_status, limit, &where(&1, [q], not is_nil(q.pos2)))

  @spec unprocessed_iemre_contacts(non_neg_integer()) :: [Contact.t()]
  def unprocessed_iemre_contacts(limit \\ 500), do: contacts_needing_enrichment(:iemre_status, limit)

  @spec set_enrichment_status!([Ecto.UUID.t()], atom(), atom()) :: {non_neg_integer(), nil | [any()]}
  def set_enrichment_status!(ids, field, status) do
    Contact
    |> where([q], q.id in ^ids and field(q, ^field) != ^status)
    |> Repo.update_all(set: [{field, status}])
  end

  @spec mark_weather_queued!([Ecto.UUID.t()]) :: {non_neg_integer(), nil | [any()]}
  def mark_weather_queued!(ids), do: set_enrichment_status!(ids, :weather_status, :queued)

  @spec mark_hrrr_queued!([Ecto.UUID.t()]) :: {non_neg_integer(), nil | [any()]}
  def mark_hrrr_queued!(ids), do: set_enrichment_status!(ids, :hrrr_status, :queued)

  @spec mark_terrain_queued!([Ecto.UUID.t()]) :: {non_neg_integer(), nil | [any()]}
  def mark_terrain_queued!(ids), do: set_enrichment_status!(ids, :terrain_status, :queued)

  @spec mark_iemre_queued!([Ecto.UUID.t()]) :: {non_neg_integer(), nil | [any()]}
  def mark_iemre_queued!(ids), do: set_enrichment_status!(ids, :iemre_status, :queued)

  @doc """
  Returns a list of {lat, lon} points along the contact path: pos1, midpoint, pos2.
  Returns [pos1] if pos2 is nil, or [] if pos1 is nil.
  """
  @spec contact_path_points(Contact.t()) :: [{float(), float()}]
  def contact_path_points(%{pos1: nil}), do: []

  def contact_path_points(%{pos1: pos1, pos2: nil}) do
    lat = pos1["lat"]
    lon = pos1["lon"] || pos1["lng"]
    if lat && lon, do: [{lat, lon}], else: []
  end

  def contact_path_points(%{pos1: pos1, pos2: pos2}) do
    build_path_points(extract_latlon(pos1), extract_latlon(pos2))
  end

  defp extract_latlon(%{"lat" => lat} = pos) when is_number(lat) do
    lon = pos["lon"] || pos["lng"]
    if lon, do: {lat, lon}
  end

  defp extract_latlon(_), do: nil

  defp build_path_points({lat1, lon1}, {lat2, lon2}) do
    mid_lat = (lat1 + lat2) / 2
    mid_lon = (lon1 + lon2) / 2
    [{lat1, lon1}, {mid_lat, mid_lon}, {lat2, lon2}]
  end

  defp build_path_points({lat1, lon1}, _), do: [{lat1, lon1}]
  defp build_path_points(_, _), do: []

  @earth_radius_km 6371.0

  @spec haversine_km(number(), number(), number(), number()) :: float()
  def haversine_km(lat1, lon1, lat2, lon2) do
    dlat = deg_to_rad(lat2 - lat1)
    dlon = deg_to_rad(lon2 - lon1)
    rlat1 = deg_to_rad(lat1)
    rlat2 = deg_to_rad(lat2)

    a =
      :math.sin(dlat / 2) ** 2 +
        :math.cos(rlat1) * :math.cos(rlat2) * :math.sin(dlon / 2) ** 2

    2 * @earth_radius_km * :math.asin(:math.sqrt(a))
  end

  @spec backfill_distances([Contact.t()]) :: Postgrex.Result.t() | nil
  def backfill_distances(contacts) do
    updates =
      for contact <- contacts,
          is_nil(contact.distance_km) && contact.pos1 && contact.pos2,
          lat1 = contact.pos1["lat"],
          lon1 = contact.pos1["lon"] || contact.pos1["lng"],
          lat2 = contact.pos2["lat"],
          lon2 = contact.pos2["lon"] || contact.pos2["lng"],
          lat1 && lon1 && lat2 && lon2 do
        dist = lat1 |> haversine_km(lon1, lat2, lon2) |> round()
        {contact.id, dist}
      end

    execute_distance_updates(updates)
  end

  defp execute_distance_updates([]), do: nil

  defp execute_distance_updates(updates) do
    # Build a single UPDATE ... FROM (VALUES ...) statement
    # Ecto.UUID.dump!/1 converts string UUIDs to the 16-byte binary Postgrex expects
    {values_sql, params} =
      updates
      |> Enum.with_index()
      |> Enum.reduce({"", []}, fn {{id, dist}, i}, {sql, params} ->
        frag = "($#{i * 2 + 1}::uuid, $#{i * 2 + 2}::numeric)"
        sep = if sql == "", do: "", else: ", "
        {sql <> sep <> frag, params ++ [Ecto.UUID.dump!(id), dist]}
      end)

    Repo.query!(
      "UPDATE contacts AS c SET distance_km = v.dist FROM (VALUES #{values_sql}) AS v(id, dist) WHERE c.id = v.id",
      params
    )
  end

  defp deg_to_rad(deg), do: deg * :math.pi() / 180

  @spec get_contact!(Ecto.UUID.t()) :: Contact.t()
  def get_contact!(id) do
    Repo.get!(Contact, id)
  end

  @spec toggle_flagged_invalid!(Contact.t()) :: Contact.t()
  def toggle_flagged_invalid!(contact) do
    contact
    |> Ecto.Changeset.change(flagged_invalid: !contact.flagged_invalid)
    |> Repo.update!()
  end

  @spec change_contact(Contact.t(), map()) :: Ecto.Changeset.t()
  def change_contact(contact, attrs \\ %{}) do
    Contact.submission_changeset(contact, attrs)
  end

  @doc """
  Computes pos1/pos2/distance_km from grid squares if missing.
  Returns the updated contact, or the original if already computed or grids are missing.
  """
  @spec ensure_positions!(Contact.t()) :: Contact.t()
  def ensure_positions!(contact) do
    needs_pos1 = is_nil(contact.pos1) && contact.grid1
    needs_pos2 = is_nil(contact.pos2) && contact.grid2

    if needs_pos1 || needs_pos2 do
      do_ensure_positions(contact)
    else
      contact
    end
  end

  defp do_ensure_positions(contact) do
    pos1 = contact.pos1 || latlon_from_grid(contact.grid1)
    pos2 = contact.pos2 || latlon_from_grid(contact.grid2)
    distance = compute_distance(pos1, pos2, contact.distance_km)

    changes = build_position_changes(contact, pos1, pos2, distance)

    apply_position_changes(contact, changes)
  end

  defp compute_distance(pos1, pos2, _existing_distance) when not is_nil(pos1) and not is_nil(pos2) do
    lon1 = pos1["lon"] || pos1["lng"]
    lon2 = pos2["lon"] || pos2["lng"]

    pos1["lat"]
    |> haversine_km(lon1, pos2["lat"], lon2)
    |> round()
    |> Decimal.new()
  end

  defp compute_distance(_pos1, _pos2, existing_distance), do: existing_distance

  defp build_position_changes(contact, pos1, pos2, distance) do
    %{}
    |> then(fn c -> if pos1 && is_nil(contact.pos1), do: Map.put(c, :pos1, pos1), else: c end)
    |> then(fn c -> if pos2 && is_nil(contact.pos2), do: Map.put(c, :pos2, pos2), else: c end)
    |> then(fn c ->
      if distance && is_nil(contact.distance_km), do: Map.put(c, :distance_km, distance), else: c
    end)
  end

  defp apply_position_changes(contact, changes) when changes == %{}, do: contact

  defp apply_position_changes(contact, changes) do
    changes = reset_enrichment_statuses(contact, changes)

    contact
    |> Ecto.Changeset.change(changes)
    |> Repo.update!()
  end

  defp reset_enrichment_statuses(contact, changes) do
    new_pos1 = Map.get(changes, :pos1)
    new_pos2 = Map.get(changes, :pos2)

    changes =
      if new_pos1 do
        changes
        |> maybe_reset_status(:hrrr_status, contact.hrrr_status)
        |> maybe_reset_status(:weather_status, contact.weather_status)
        |> maybe_reset_status(:iemre_status, contact.iemre_status)
      else
        changes
      end

    if new_pos1 && (new_pos2 || contact.pos2) do
      maybe_reset_status(changes, :terrain_status, contact.terrain_status)
    else
      changes
    end
  end

  defp maybe_reset_status(changes, field, :unavailable), do: Map.put(changes, field, :pending)
  defp maybe_reset_status(changes, _field, _status), do: changes

  defp latlon_from_grid(nil), do: nil

  defp latlon_from_grid(grid) do
    case Maidenhead.to_latlon(grid) do
      {:ok, {lat, lon}} ->
        %{"lat" => lat, "lon" => lon}

      _ ->
        # Try truncating to nearest valid even length (e.g. "FN03c" → "FN03")
        truncated = String.slice(grid, 0, div(String.length(grid), 2) * 2)

        case Maidenhead.to_latlon(truncated) do
          {:ok, {lat, lon}} -> %{"lat" => lat, "lon" => lon}
          _ -> nil
        end
    end
  end

  @dedup_window_seconds 3600

  @spec create_contact(map()) ::
          {:ok, Contact.t()} | {:error, Ecto.Changeset.t()} | {:error, :duplicate, Contact.t()}
  def create_contact(attrs) do
    changeset = Contact.submission_changeset(%Contact{}, attrs)

    if changeset.valid? do
      insert_validated_contact(changeset)
    else
      {:error, %{changeset | action: :insert}}
    end
  end

  defp insert_validated_contact(changeset) do
    if existing = find_duplicate_contact(changeset) do
      {:error, :duplicate, existing}
    else
      resolve_grids_and_insert(changeset)
    end
  end

  defp resolve_grids_and_insert(changeset) do
    grid1 = Ecto.Changeset.get_change(changeset, :grid1)
    grid2 = Ecto.Changeset.get_change(changeset, :grid2)

    case {Maidenhead.to_latlon(grid1), Maidenhead.to_latlon(grid2)} do
      {{:ok, {lat1, lon1}}, {:ok, {lat2, lon2}}} ->
        distance = lat1 |> haversine_km(lon1, lat2, lon2) |> round() |> Decimal.new()

        changeset
        |> Ecto.Changeset.put_change(:pos1, %{"lat" => lat1, "lon" => lon1})
        |> Ecto.Changeset.put_change(:pos2, %{"lat" => lat2, "lon" => lon2})
        |> Ecto.Changeset.put_change(:distance_km, distance)
        |> Ecto.Changeset.put_change(:user_submitted, true)
        |> Repo.insert()

      _ ->
        changeset = Ecto.Changeset.add_error(changeset, :grid1, "could not resolve grid to coordinates")
        {:error, %{changeset | action: :insert}}
    end
  end

  defp find_duplicate_contact(changeset) do
    s1 = changeset |> Ecto.Changeset.get_field(:station1) |> to_string() |> String.upcase()
    s2 = changeset |> Ecto.Changeset.get_field(:station2) |> to_string() |> String.upcase()
    g1 = changeset |> Ecto.Changeset.get_field(:grid1) |> to_string() |> String.upcase()
    g2 = changeset |> Ecto.Changeset.get_field(:grid2) |> to_string() |> String.upcase()
    band = Ecto.Changeset.get_field(changeset, :band)
    ts = Ecto.Changeset.get_field(changeset, :qso_timestamp)

    band_decimal = if is_binary(band), do: Decimal.new(band), else: band
    min_ts = DateTime.add(ts, -@dedup_window_seconds, :second)
    max_ts = DateTime.add(ts, @dedup_window_seconds, :second)

    expected_pair = Enum.sort([{s1, g1}, {s2, g2}])

    from(c in Contact,
      where:
        c.band == ^band_decimal and
          c.qso_timestamp >= ^min_ts and
          c.qso_timestamp <= ^max_ts and
          c.flagged_invalid == false
    )
    |> Repo.all()
    |> Enum.find(fn c ->
      pair =
        Enum.sort([
          {String.upcase(c.station1), String.upcase(c.grid1)},
          {String.upcase(c.station2), String.upcase(c.grid2)}
        ])

      pair == expected_pair
    end)
  end

  # ── Contact Edits ───────────────────────────────────────────────

  @doc """
  Create a proposed edit for a contact. Only stores fields that actually
  differ from the contact's current values. Normalizes callsigns and grids
  to uppercase.
  """
  @spec create_contact_edit(Contact.t(), User.t(), map()) ::
          {:ok, ContactEdit.t()} | {:error, Ecto.Changeset.t()}
  def create_contact_edit(%Contact{} = contact, user, proposed_changes) when is_map(proposed_changes) do
    # Normalize and diff against current values
    normalized = normalize_proposed(proposed_changes)
    diffed = diff_against_contact(contact, normalized)

    attrs = %{
      contact_id: contact.id,
      user_id: user.id,
      proposed_changes: diffed
    }

    %ContactEdit{}
    |> ContactEdit.changeset(attrs)
    |> Repo.insert()
  end

  @doc false
  @spec normalize_proposed(map()) :: map()
  def normalize_proposed(changes) do
    changes
    |> normalize_string_field("station1")
    |> normalize_string_field("station2")
    |> normalize_string_field("grid1")
    |> normalize_string_field("grid2")
    |> normalize_string_field("mode")
  end

  defp normalize_string_field(map, key) do
    case Map.get(map, key) do
      nil -> map
      val when is_binary(val) -> Map.put(map, key, val |> String.trim() |> String.upcase())
      val -> Map.put(map, key, val)
    end
  end

  @doc false
  @spec diff_against_contact(Contact.t(), map()) :: map()
  def diff_against_contact(contact, proposed) do
    Enum.reduce(proposed, %{}, fn {key, new_val}, acc ->
      current = current_value(contact, key)

      if values_equal?(current, new_val) do
        acc
      else
        Map.put(acc, key, new_val)
      end
    end)
  end

  defp current_value(contact, "station1"), do: contact.station1
  defp current_value(contact, "station2"), do: contact.station2
  defp current_value(contact, "grid1"), do: contact.grid1
  defp current_value(contact, "grid2"), do: contact.grid2
  defp current_value(contact, "mode"), do: contact.mode

  defp current_value(contact, "band") do
    if contact.band, do: Decimal.to_integer(contact.band)
  end

  defp current_value(contact, "qso_timestamp"), do: contact.qso_timestamp
  defp current_value(_contact, _key), do: nil

  defp values_equal?(a, b) when is_binary(a) and is_binary(b) do
    String.upcase(a) == String.upcase(b)
  end

  defp values_equal?(a, b) when is_integer(a), do: a == to_integer(b)
  defp values_equal?(a, b) when is_integer(b), do: to_integer(a) == b
  defp values_equal?(a, b), do: a == b

  defp to_integer(v) when is_integer(v), do: v
  defp to_integer(v) when is_binary(v), do: String.to_integer(v)
  defp to_integer(%Decimal{} = v), do: Decimal.to_integer(v)
  defp to_integer(v), do: v

  @spec list_pending_edits() :: [ContactEdit.t()]
  def list_pending_edits do
    ContactEdit
    |> where([e], e.status == :pending)
    |> order_by([e], desc: e.inserted_at)
    |> preload([:user, :contact])
    |> Repo.all()
  end

  @spec list_contact_edits(Ecto.UUID.t()) :: [ContactEdit.t()]
  def list_contact_edits(contact_id) do
    ContactEdit
    |> where([e], e.contact_id == ^contact_id)
    |> order_by([e], desc: e.inserted_at)
    |> preload([:user, :reviewed_by])
    |> Repo.all()
  end

  @spec pending_edit_count() :: non_neg_integer()
  def pending_edit_count do
    ContactEdit
    |> where([e], e.status == :pending)
    |> Repo.aggregate(:count)
  end

  @spec pending_edit_for_user(Ecto.UUID.t(), Ecto.UUID.t()) :: ContactEdit.t() | nil
  def pending_edit_for_user(contact_id, user_id) do
    ContactEdit
    |> where([e], e.contact_id == ^contact_id and e.user_id == ^user_id and e.status == :pending)
    |> Repo.one()
  end

  @spec get_contact_edit!(Ecto.UUID.t()) :: ContactEdit.t()
  def get_contact_edit!(id) do
    ContactEdit
    |> preload([:user, :contact, :reviewed_by])
    |> Repo.get!(id)
  end

  @spec approve_edit(ContactEdit.t(), User.t(), String.t() | nil) ::
          {:ok, ContactEdit.t()} | {:error, any()}
  def approve_edit(%ContactEdit{status: :pending} = edit, admin, note) do
    Repo.transaction(fn ->
      # Mark edit as approved
      {:ok, approved} =
        edit
        |> ContactEdit.review_changeset(%{
          status: :approved,
          admin_note: note,
          reviewed_by_id: admin.id,
          reviewed_at: DateTime.truncate(DateTime.utc_now(), :second)
        })
        |> Repo.update()

      # Apply changes to contact
      contact = Repo.get!(Contact, edit.contact_id)
      apply_edit_to_contact(contact, edit.proposed_changes)

      Repo.preload(approved, [:user, :contact, :reviewed_by])
    end)
  end

  @spec reject_edit(ContactEdit.t(), User.t(), String.t() | nil) ::
          {:ok, ContactEdit.t()} | {:error, Ecto.Changeset.t()}
  def reject_edit(%ContactEdit{status: :pending} = edit, admin, note) do
    edit
    |> ContactEdit.review_changeset(%{
      status: :rejected,
      admin_note: note,
      reviewed_by_id: admin.id,
      reviewed_at: DateTime.truncate(DateTime.utc_now(), :second)
    })
    |> Repo.update()
  end

  @doc "Apply proposed changes directly to a contact (admin use)."
  @spec apply_edit_to_contact(Contact.t(), map()) :: Contact.t()
  def apply_edit_to_contact(contact, proposed_changes) do
    changes = build_contact_changes(contact, proposed_changes)
    changes = maybe_recompute_positions(changes, contact, proposed_changes)

    contact
    |> Ecto.Changeset.change(changes)
    |> Repo.update!()
  end

  defp maybe_recompute_positions(changes, contact, proposed) do
    grids_or_band_changed =
      Map.has_key?(proposed, "grid1") or
        Map.has_key?(proposed, "grid2") or
        Map.has_key?(proposed, "band")

    if grids_or_band_changed do
      recompute_positions(changes, contact, proposed)
    else
      changes
    end
  end

  defp recompute_positions(changes, contact, proposed) do
    pos1 = resolve_grid_position(Map.get(proposed, "grid1", contact.grid1)) || contact.pos1
    pos2 = resolve_grid_position(Map.get(proposed, "grid2", contact.grid2)) || contact.pos2
    distance = compute_distance(pos1, pos2)

    changes
    |> Map.put(:pos1, pos1)
    |> Map.put(:pos2, pos2)
    |> Map.put(:distance_km, distance)
    |> Map.put(:hrrr_status, :pending)
    |> Map.put(:weather_status, :pending)
    |> Map.put(:terrain_status, :pending)
    |> Map.put(:iemre_status, :pending)
  end

  defp compute_distance(pos1, pos2) when not is_nil(pos1) and not is_nil(pos2) do
    lon1 = pos1["lon"] || pos1["lng"]
    lon2 = pos2["lon"] || pos2["lng"]
    pos1["lat"] |> haversine_km(lon1, pos2["lat"], lon2) |> round() |> Decimal.new()
  end

  defp compute_distance(_, _), do: nil

  defp build_contact_changes(_contact, proposed) do
    Enum.reduce(proposed, %{}, fn
      {"band", val}, acc ->
        Map.put(acc, :band, Decimal.new(to_string(val)))

      {"qso_timestamp", val}, acc when is_binary(val) ->
        {:ok, dt, _} = DateTime.from_iso8601(val)
        Map.put(acc, :qso_timestamp, dt)

      {"qso_timestamp", %DateTime{} = dt}, acc ->
        Map.put(acc, :qso_timestamp, dt)

      {key, val}, acc ->
        Map.put(acc, String.to_existing_atom(key), val)
    end)
  end

  defp resolve_grid_position(nil), do: nil

  defp resolve_grid_position(grid) do
    case Maidenhead.to_latlon(grid) do
      {:ok, {lat, lon}} -> %{"lat" => lat, "lon" => lon}
      _ -> nil
    end
  end
end