defmodule Ecto.Adapters.MySQL do
  @moduledoc """
  Adapter module for MySQL.

  It uses `mariaex` for communicating to the database.
  Currently it supports old MySQL versions but upcoming
  Ecto releases will require 5.7+.

  ## Options

  MySQL options split in different categories described
  below. All options can be given via the repository
  configuration:

  ### Connection options

    * `:hostname` - Server hostname
    * `:socket_dir` - Connect to MySQL via UNIX sockets in the given directory
      The socket name is derived based on the port. This is the preferred method
      for configuring sockets and it takes precedence over the hostname. If you are
      connecting to a socket outside of the Postgres convention, use `:socket` instead;
    * `:socket` - Connect to MySQL via UNIX sockets in the given path.
      This option takes precedence over the `:hostname` and `:socket_dir`
    * `:port` - Server port (default: 3306)
    * `:username` - Username
    * `:password` - User password
    * `:database` - the database to connect to
    * `:pool` - The connection pool module, defaults to `DBConnection.ConnectionPool`
    * `:pool_timeout` - The default timeout to use on pool calls, defaults to `5000`
    * `:timeout` - The default timeout to use on queries, defaults to `15000`
    * `:ssl` - Set to true if ssl should be used (default: false)
    * `:ssl_opts` - A list of ssl options, see Erlang's `ssl` docs
    * `:parameters` - Keyword list of connection parameters
    * `:connect_timeout` - The timeout for establishing new connections (default: 5000)
    * `:socket_options` - Specifies socket configuration
    * `:cli_protocol` - The protocol used for the mysql client connection (default: tcp).
      This option is only used for `mix ecto.load` and `mix ecto.dump`,
      via the `mysql` command. For more information, please check
      [MySQL docs](https://dev.mysql.com/doc/en/connecting.html)

  The `:socket_options` are particularly useful when configuring the size
  of both send and receive buffers. For example, when Ecto starts with a
  pool of 20 connections, the memory usage may quickly grow from 20MB to
  50MB based on the operating system default values for TCP buffers. It is
  advised to stick with the operating system defaults but they can be
  tweaked if desired:

      socket_options: [recbuf: 8192, sndbuf: 8192]

  We also recommend developers to consult the
  [Mariaex documentation](https://hexdocs.pm/mariaex/Mariaex.html#start_link/1)
  for a complete listing of all supported options.

  ### Storage options

    * `:charset` - the database encoding (default: "utf8")
    * `:collation` - the collation order
    * `:dump_path` - where to place dumped structures

  ### After connect callback

  If you want to execute a callback as soon as connection is established
  to the database, you can use the `:after_connect` configuration. For
  example, in your repository configuration you can add:

    after_connect: {Mariaex, :query!, ["SET variable = value", []]}

  You can also specify your own module that will receive the Mariaex
  connection as argument.

  ## Limitations

  There are some limitations when using Ecto with MySQL that one
  needs to be aware of.

  ### Engine

  Since Ecto uses transactions, MySQL users running old versions
  (5.1 and before) must ensure their tables use the InnoDB engine
  as the default (MyISAM) does not support transactions.

  Tables created by Ecto are guaranteed to use InnoDB, regardless
  of the MySQL version.

  ### UUIDs

  MySQL does not support UUID types. Ecto emulates them by using
  `binary(16)`.

  ### Read after writes

  Because MySQL does not support RETURNING clauses in INSERT and
  UPDATE, it does not support the `:read_after_writes` option of
  `Ecto.Schema.field/3`.

  ### DDL Transaction

  MySQL does not support migrations inside transactions as it
  automatically commits after some commands like CREATE TABLE.
  Therefore MySQL migrations does not run inside transactions.

  ### usec in datetime

  Old MySQL versions did not support usec in datetime while
  more recent versions would round or truncate the usec value.

  Therefore, in case the user decides to use microseconds in
  datetimes and timestamps with MySQL, be aware of such
  differences and consult the documentation for your MySQL
  version.

  If your version of MySQL supports microsecond precision, you
  will be able to utilize Ecto's usec types.
  """

  # Inherit all behaviour from Ecto.Adapters.SQL
  use Ecto.Adapters.SQL, :mariaex

  # And provide a custom storage implementation
  @behaviour Ecto.Adapter.Storage
  @behaviour Ecto.Adapter.Structure

  ## Custom MySQL types

  # TODO: Remove json encoding/decoding when maps are supported in the adapter

  @impl true
  def loaders({:embed, _} = type, _), do: [&json_decode/1, &Ecto.Adapters.SQL.load_embed(type, &1)]
  def loaders({:map, _}, type),       do: [&json_decode/1, &Ecto.Adapters.SQL.load_embed(type, &1)]
  def loaders(:map, type),            do: [&json_decode/1, type]
  def loaders(:float, type),          do: [&float_decode/1, type]
  def loaders(:boolean, type),        do: [&bool_decode/1, type]
  def loaders(:binary_id, type),      do: [Ecto.UUID, type]
  def loaders(_, type),               do: [type]

  defp bool_decode(<<0>>), do: {:ok, false}
  defp bool_decode(<<1>>), do: {:ok, true}
  defp bool_decode(0), do: {:ok, false}
  defp bool_decode(1), do: {:ok, true}
  defp bool_decode(x), do: {:ok, x}

  defp float_decode(%Decimal{} = decimal), do: {:ok, Decimal.to_float(decimal)}
  defp float_decode(x), do: {:ok, x}

  defp json_decode(x) when is_binary(x),
    do: {:ok, Application.get_env(:mariaex, :json_library, Jason).decode!(x)}
  defp json_decode(x),
    do: {:ok, x}

  ## Storage API

  @impl true
  def storage_up(opts) do
    database = Keyword.fetch!(opts, :database) || raise ":database is nil in repository configuration"
    charset  = opts[:charset] || "utf8"
    opts     = Keyword.put(opts, :skip_database, true)

    command =
      ~s(CREATE DATABASE `#{database}` DEFAULT CHARACTER SET = #{charset})
      |> concat_if(opts[:collation], &"DEFAULT COLLATE = #{&1}")

    case run_query(command, opts) do
      {:ok, _} ->
        :ok
      {:error, %{mariadb: %{code: 1007}}} ->
        {:error, :already_up}
      {:error, error} ->
        {:error, Exception.message(error)}
      {:exit, exit} ->
        {:error, exit_to_exception(exit)}
    end
  end

  defp concat_if(content, nil, _fun),  do: content
  defp concat_if(content, value, fun), do: content <> " " <> fun.(value)

  @impl true
  def storage_down(opts) do
    database = Keyword.fetch!(opts, :database) || raise ":database is nil in repository configuration"
    command = "DROP DATABASE `#{database}`"

    case run_query(command, opts) do
      {:ok, _} ->
        :ok
      {:error, %{mariadb: %{code: 1008}}} ->
        {:error, :already_down}
      {:error, %{mariadb: %{code: 1049}}} ->
        {:error, :already_down}
      {:exit, :killed} ->
        {:error, :already_down}
      {:exit, exit} ->
        {:error, exit_to_exception(exit)}
    end
  end

  @impl true
  def supports_ddl_transaction? do
    false
  end

  @impl true
  def insert(adapter_meta, schema_meta, params, on_conflict, returning, opts) do
    %{source: source, prefix: prefix} = schema_meta
    {_, query_params, _} = on_conflict

    key = primary_key!(schema_meta, returning)
    {fields, values} = :lists.unzip(params)
    sql = @conn.insert(prefix, source, fields, [fields], on_conflict, [])

    case Ecto.Adapters.SQL.query(adapter_meta, sql, values ++ query_params, opts) do
      {:ok, %{num_rows: 1, last_insert_id: last_insert_id}} ->
        {:ok, last_insert_id(key, last_insert_id)}

      {:ok, %{num_rows: 2, last_insert_id: last_insert_id}} ->
        {:ok, last_insert_id(key, last_insert_id)}

      {:error, err} ->
        case @conn.to_constraints(err) do
          []          -> raise err
          constraints -> {:invalid, constraints}
        end
    end
  end

  defp primary_key!(%{autogenerate_id: {_, key, _type}}, [key]), do: key
  defp primary_key!(_, []), do: nil
  defp primary_key!(%{schema: schema}, returning) do
    raise ArgumentError, "MySQL does not support :read_after_writes in schemas for non-primary keys. " <>
                         "The following fields in #{inspect schema} are tagged as such: #{inspect returning}"
  end

  defp last_insert_id(nil, _last_insert_id), do: []
  defp last_insert_id(_key, 0), do: []
  defp last_insert_id(key, last_insert_id), do: [{key, last_insert_id}]

  @impl true
  def structure_dump(default, config) do
    table = config[:migration_source] || "schema_migrations"
    path  = config[:dump_path] || Path.join(default, "structure.sql")

    with {:ok, versions} <- select_versions(table, config),
         {:ok, contents} <- mysql_dump(config),
         {:ok, contents} <- append_versions(table, versions, contents) do
      File.mkdir_p!(Path.dirname(path))
      File.write!(path, contents)
      {:ok, path}
    end
  end

  defp select_versions(table, config) do
    case run_query(~s[SELECT version FROM `#{table}` ORDER BY version], config) do
      {:ok, %{rows: rows}} -> {:ok, Enum.map(rows, &hd/1)}
      {:error, %{mariadb: %{code: 1146}}} -> {:ok, []}
      {:error, _} = error -> error
      {:exit, exit} -> {:error, exit_to_exception(exit)}
    end
  end

  defp mysql_dump(config) do
    case run_with_cmd("mysqldump", config, ["--no-data", "--routines", config[:database]]) do
      {output, 0} -> {:ok, output}
      {output, _} -> {:error, output}
    end
  end

  defp append_versions(_table, [], contents) do
    {:ok, contents}
  end
  defp append_versions(table, versions, contents) do
    {:ok,
      contents <>
      ~s[INSERT INTO `#{table}` (version) VALUES ] <>
      Enum.map_join(versions, ", ", &"(#{&1})") <>
      ~s[;\n\n]}
  end

  @impl true
  def structure_load(default, config) do
    path = config[:dump_path] || Path.join(default, "structure.sql")

    args = [
      "--execute", "SET FOREIGN_KEY_CHECKS = 0; SOURCE #{path}; SET FOREIGN_KEY_CHECKS = 1",
      "--database", config[:database]
    ]

    case run_with_cmd("mysql", config, args) do
      {_output, 0} -> {:ok, path}
      {output, _}  -> {:error, output}
    end
  end

  ## Helpers

  defp run_query(sql, opts) do
    {:ok, _} = Application.ensure_all_started(:mariaex)

    opts =
      opts
      |> Keyword.drop([:name, :log, :pool, :pool_size])
      |> Keyword.put(:backoff_type, :stop)
      |> Keyword.put(:max_restarts, 0)

    {:ok, pid} = Task.Supervisor.start_link

    task = Task.Supervisor.async_nolink(pid, fn ->
      {:ok, conn} = Mariaex.start_link(opts)

      value = Mariaex.query(conn, sql, [], opts)
      GenServer.stop(conn)
      value
    end)

    timeout = Keyword.get(opts, :timeout, 15_000)

    case Task.yield(task, timeout) || Task.shutdown(task) do
      {:ok, {:ok, result}} ->
        {:ok, result}
      {:ok, {:error, error}} ->
        {:error, error}
      {:exit, exit} ->
        {:exit, exit}
      nil ->
        {:error, RuntimeError.exception("command timed out")}
    end
  end

  defp exit_to_exception({%{__struct__: struct} = error, _})
       when struct in [Mariaex.Error, DBConnection.Error],
       do: error

  defp exit_to_exception(reason), do: RuntimeError.exception(Exception.format_exit(reason))

  defp run_with_cmd(cmd, opts, opt_args) do
    unless System.find_executable(cmd) do
      raise "could not find executable `#{cmd}` in path, " <>
            "please guarantee it is available before running ecto commands"
    end

    env =
      if password = opts[:password] do
        [{"MYSQL_PWD", password}]
      else
        []
      end

    host     = opts[:hostname] || System.get_env("MYSQL_HOST") || "localhost"
    port     = opts[:port] || System.get_env("MYSQL_TCP_PORT") || "3306"
    protocol = opts[:cli_protocol] || System.get_env("MYSQL_CLI_PROTOCOL") || "tcp"

    user_args =
      if username = opts[:username] do
        ["--user", username]
      else
        []
      end

    args =
      [
        "--host", host,
        "--port", to_string(port),
        "--protocol", protocol
      ] ++ user_args ++ opt_args

    System.cmd(cmd, args, env: env, stderr_to_stdout: true)
  end
end