-- Helpers for searching and parsing tags

local Tags = {}

-- return [forward,backward] values for a specific tag.
-- e.g. for maxspeed search forward:
--   maxspeed:forward
--   maxspeed
-- and backward:
--   maxspeed:backward
--   maxspeed

function Tags.get_forward_backward_by_key(way,data,key)
  local forward = way:get_value_by_key(key .. ':forward')
  local backward = way:get_value_by_key(key .. ':backward')

  if forward and backward then
    return forward, backward
  end

  local common = way:get_value_by_key(key)
  return forward or common,
         backward or common
end

-- return [forward,backward] values, searching a
-- prioritized sequence of tags
-- e.g. for the sequence [maxspeed,advisory] search forward:
--   maxspeed:forward
--   maxspeed
--   advisory:forward
--   advisory
-- and for backward:
--   maxspeed:backward
--   maxspeed
--   advisory:backward
--   advisory

function Tags.get_forward_backward_by_set(way,data,keys)
  local forward, backward
  for i,key in ipairs(keys) do
    if not forward then
      forward = way:get_value_by_key(key .. ':forward')
    end
    if not backward then
      backward = way:get_value_by_key(key .. ':backward')
    end
    if not forward or not backward then
      local common = way:get_value_by_key(key)
      forward = forward or common
      backward = backward or common
    end
    if forward and backward then
      break
    end
  end

  return forward, backward
end

-- look through a sequence of keys combined with a prefix
-- e.g. for the sequence [motorcar,motor_vehicle,vehicle] and the prefix 'oneway' search for:
-- oneway:motorcar
-- oneway:motor_vehicle
-- oneway:vehicle

function Tags.get_value_by_prefixed_sequence(way,seq,prefix)
  local v
  for i,key in ipairs(seq) do
    v = way:get_value_by_key(prefix .. ':' .. key)
    if v then
      return v
    end
  end
end

-- look through a sequence of keys combined with a postfix
-- e.g. for the sequence [motorcar,motor_vehicle,vehicle] and the postfix 'oneway' search for:
-- motorcar:oneway
-- motor_vehicle:oneway
-- vehicle:oneway

function Tags.get_value_by_postfixed_sequence(way,seq,postfix)
  local v
  for i,key in ipairs(seq) do
    v = way:get_value_by_key(key .. ':' .. postfix)
    if v then
      return v
    end
  end
end

-- check if key-value pairs are set in a way and return a
-- corresponding constant if it is. e.g. for this input:
--
-- local speeds = {
--  highway = {
--    residential = 20,
--    primary = 40
--  },
--  amenity = {
--    parking = 10
--  }
-- }
--
-- we would check whether the following key-value combinations
-- are set, and return the corresponding constant:
--
-- highway = residential      => 20
-- highway = primary          => 40
-- amenity = parking          => 10

function Tags.get_constant_by_key_value(way,lookup)
  for key,set in pairs(lookup) do
    local way_value = way:get_value_by_key(key)
    for value,t in pairs(set) do
      if way_value == value then
        return key,value,t
      end
    end
  end
end

return Tags
