-- This script receives four parameters, all encoded with
-- MessagePack. The decoded values are used for saving a model
-- instance in Redis, creating or updating a hash as needed and
-- updating zero or more sets (indices) and zero or more hashes
-- (unique indices).
--
-- # model
--
-- Table with one or two attributes:
--    name (model name)
--    id (model instance id, optional)
--
-- If the id is not provided, it is treated as a new record.
--
-- # attrs
--
-- Array with attribute/value pairs.
--
-- # indices
--
-- Fields and values to be indexed. Each key in the indices
-- table is mapped to an array of values. One index is created
-- for each field/value pair.
--
-- # uniques
--
-- Fields and values to be indexed as unique. Unlike indices,
-- values are not enumerable. If a field/value pair is not unique
-- (i.e., if there was already a hash entry for that field and
-- value), an error is returned with the UniqueIndexViolation
-- message and the field that triggered the error.
--
local model   = cmsgpack.unpack(ARGV[1])
local attrs   = cmsgpack.unpack(ARGV[2])
local indices = cmsgpack.unpack(ARGV[3])
local uniques = cmsgpack.unpack(ARGV[4])

local function save(model, attrs)
  if model.id == nil then
    model.id = redis.call("INCR", model.name .. ":id")
  end

  model.key = model.name .. ":" .. model.id

  redis.call("SADD", model.name .. ":all", model.id)
  redis.call("DEL", model.key)

  if math.mod(#attrs, 2) == 1 then
    error("Wrong number of attribute/value pairs")
  end

  if #attrs > 0 then
    redis.call("HMSET", model.key, unpack(attrs))
  end
end

local function index(model, indices)
  for field, enum in pairs(indices) do
    for _, val in ipairs(enum) do
      local key = model.name .. ":indices:" .. field .. ":" .. tostring(val)

      redis.call("SADD", model.key .. ":_indices", key)
      redis.call("SADD", key, model.id)
    end
  end
end

local function remove_indices(model)
  local memo = model.key .. ":_indices"
  local existing = redis.call("SMEMBERS", memo)

  for _, key in ipairs(existing) do
    redis.call("SREM", key, model.id)
    redis.call("SREM", memo, key)
  end
end

local function unique(model, uniques)
  for field, value in pairs(uniques) do
    local key = model.name .. ":uniques:" .. field

    redis.call("HSET", model.key .. ":_uniques", key, value)
    redis.call("HSET", key, value, model.id)
  end
end

local function remove_uniques(model)
  local memo = model.key .. ":_uniques"

  for _, key in pairs(redis.call("HKEYS", memo)) do
    redis.call("HDEL", key, redis.call("HGET", memo, key))
    redis.call("HDEL", memo, key)
  end
end

local function verify(model, uniques)
  local duplicates = {}

  for field, value in pairs(uniques) do
    local key = model.name .. ":uniques:" .. field
    local id = redis.call("HGET", key, tostring(value))

    if id and id ~= tostring(model.id) then
      duplicates[#duplicates + 1] = field
    end
  end

  return duplicates, #duplicates ~= 0
end

local duplicates, err = verify(model, uniques)

if err then
  error("UniqueIndexViolation: " .. duplicates[1])
end

save(model, attrs)

remove_indices(model)
index(model, indices)

remove_uniques(model, uniques)
unique(model, uniques)

return tostring(model.id)