SQLite support and some clean-up

.credo.exs

@@ -0,0 +1,217 @@
+# This file contains the configuration for Credo and you are probably reading
+# this after creating it with `mix credo.gen.config`.
+#
+# If you find anything wrong or unclear in this file, please report an
+# issue on GitHub: https://github.com/rrrene/credo/issues
+#
+%{
+  #
+  # You can have as many configs as you like in the `configs:` field.
+  configs: [
+    %{
+      #
+      # Run any config using `mix credo -C <name>`. If no config name is given
+      # "default" is used.
+      #
+      name: "default",
+      #
+      # These are the files included in the analysis:
+      files: %{
+        #
+        # You can give explicit globs or simply directories.
+        # In the latter case `**/*.{ex,exs}` will be used.
+        #
+        included: [
+          "lib/",
+          "src/",
+          "test/",
+          "web/",
+          "apps/*/lib/",
+          "apps/*/src/",
+          "apps/*/test/",
+          "apps/*/web/"
+        ],
+        excluded: [~r"/_build/", ~r"/deps/", ~r"/node_modules/"]
+      },
+      #
+      # Load and configure plugins here:
+      #
+      plugins: [],
+      #
+      # If you create your own checks, you must specify the source files for
+      # them here, so they can be loaded by Credo before running the analysis.
+      #
+      requires: [],
+      #
+      # If you want to enforce a style guide and need a more traditional linting
+      # experience, you can change `strict` to `true` below:
+      #
+      strict: false,
+      #
+      # To modify the timeout for parsing files, change this value:
+      #
+      parse_timeout: 5000,
+      #
+      # If you want to use uncolored output by default, you can change `color`
+      # to `false` below:
+      #
+      color: true,
+      #
+      # You can customize the parameters of any check by adding a second element
+      # to the tuple.
+      #
+      # To disable a check put `false` as second element:
+      #
+      #     {Credo.Check.Design.DuplicatedCode, false}
+      #
+      checks: %{
+        enabled: [
+          #
+          ## Consistency Checks
+          #
+          {Credo.Check.Consistency.ExceptionNames, []},
+          {Credo.Check.Consistency.LineEndings, []},
+          {Credo.Check.Consistency.ParameterPatternMatching, []},
+          {Credo.Check.Consistency.SpaceAroundOperators, []},
+          {Credo.Check.Consistency.SpaceInParentheses, []},
+          {Credo.Check.Consistency.TabsOrSpaces, []},
+
+          #
+          ## Design Checks
+          #
+          # You can customize the priority of any check
+          # Priority values are: `low, normal, high, higher`
+          #
+          {Credo.Check.Design.AliasUsage,
+           [priority: :low, if_nested_deeper_than: 2, if_called_more_often_than: 0]},
+          {Credo.Check.Design.TagFIXME, []},
+          # You can also customize the exit_status of each check.
+          # If you don't want TODO comments to cause `mix credo` to fail, just
+          # set this value to 0 (zero).
+          #
+          {Credo.Check.Design.TagTODO, [exit_status: 2]},
+
+          #
+          ## Readability Checks
+          #
+          {Credo.Check.Readability.AliasOrder, []},
+          {Credo.Check.Readability.FunctionNames, []},
+          # {Credo.Check.Readability.LargeNumbers, []},
+          {Credo.Check.Readability.MaxLineLength, [priority: :low, max_length: 120]},
+          {Credo.Check.Readability.ModuleAttributeNames, []},
+          {Credo.Check.Readability.ModuleDoc, []},
+          {Credo.Check.Readability.ModuleNames, []},
+          {Credo.Check.Readability.ParenthesesInCondition, []},
+          {Credo.Check.Readability.ParenthesesOnZeroArityDefs, []},
+          {Credo.Check.Readability.PipeIntoAnonymousFunctions, []},
+          {Credo.Check.Readability.PredicateFunctionNames, []},
+          {Credo.Check.Readability.PreferImplicitTry, []},
+          {Credo.Check.Readability.RedundantBlankLines, []},
+          {Credo.Check.Readability.Semicolons, []},
+          {Credo.Check.Readability.SpaceAfterCommas, []},
+          {Credo.Check.Readability.StringSigils, []},
+          {Credo.Check.Readability.TrailingBlankLine, []},
+          {Credo.Check.Readability.TrailingWhiteSpace, []},
+          {Credo.Check.Readability.UnnecessaryAliasExpansion, []},
+          {Credo.Check.Readability.VariableNames, []},
+          {Credo.Check.Readability.WithSingleClause, []},
+
+          #
+          ## Refactoring Opportunities
+          #
+          {Credo.Check.Refactor.Apply, []},
+          {Credo.Check.Refactor.CondStatements, []},
+          {Credo.Check.Refactor.CyclomaticComplexity, []},
+          {Credo.Check.Refactor.FilterCount, []},
+          {Credo.Check.Refactor.FilterFilter, []},
+          {Credo.Check.Refactor.FunctionArity, []},
+          {Credo.Check.Refactor.LongQuoteBlocks, []},
+          {Credo.Check.Refactor.MapJoin, []},
+          {Credo.Check.Refactor.MatchInCondition, []},
+          {Credo.Check.Refactor.NegatedConditionsInUnless, []},
+          {Credo.Check.Refactor.NegatedConditionsWithElse, []},
+          {Credo.Check.Refactor.Nesting, []},
+          {Credo.Check.Refactor.RedundantWithClauseResult, []},
+          {Credo.Check.Refactor.RejectReject, []},
+          {Credo.Check.Refactor.UnlessWithElse, []},
+          {Credo.Check.Refactor.WithClauses, []},
+
+          #
+          ## Warnings
+          #
+          {Credo.Check.Warning.ApplicationConfigInModuleAttribute, []},
+          {Credo.Check.Warning.BoolOperationOnSameValues, []},
+          {Credo.Check.Warning.Dbg, []},
+          {Credo.Check.Warning.ExpensiveEmptyEnumCheck, []},
+          {Credo.Check.Warning.IExPry, []},
+          {Credo.Check.Warning.IoInspect, []},
+          {Credo.Check.Warning.MissedMetadataKeyInLoggerConfig, []},
+          {Credo.Check.Warning.OperationOnSameValues, []},
+          {Credo.Check.Warning.OperationWithConstantResult, []},
+          {Credo.Check.Warning.RaiseInsideRescue, []},
+          {Credo.Check.Warning.SpecWithStruct, []},
+          {Credo.Check.Warning.UnsafeExec, []},
+          {Credo.Check.Warning.UnusedEnumOperation, []},
+          {Credo.Check.Warning.UnusedFileOperation, []},
+          {Credo.Check.Warning.UnusedKeywordOperation, []},
+          {Credo.Check.Warning.UnusedListOperation, []},
+          {Credo.Check.Warning.UnusedPathOperation, []},
+          {Credo.Check.Warning.UnusedRegexOperation, []},
+          {Credo.Check.Warning.UnusedStringOperation, []},
+          {Credo.Check.Warning.UnusedTupleOperation, []},
+          {Credo.Check.Warning.WrongTestFileExtension, []}
+        ],
+        disabled: [
+          #
+          # Checks scheduled for next check update (opt-in for now)
+          {Credo.Check.Refactor.UtcNowTruncate, []},
+
+          #
+          # Controversial and experimental checks (opt-in, just move the check to `:enabled`
+          #   and be sure to use `mix credo --strict` to see low priority checks)
+          #
+          {Credo.Check.Consistency.MultiAliasImportRequireUse, []},
+          {Credo.Check.Consistency.UnusedVariableNames, []},
+          {Credo.Check.Design.DuplicatedCode, []},
+          {Credo.Check.Design.SkipTestWithoutComment, []},
+          {Credo.Check.Readability.AliasAs, []},
+          {Credo.Check.Readability.BlockPipe, []},
+          {Credo.Check.Readability.ImplTrue, []},
+          {Credo.Check.Readability.MultiAlias, []},
+          {Credo.Check.Readability.NestedFunctionCalls, []},
+          {Credo.Check.Readability.OneArityFunctionInPipe, []},
+          {Credo.Check.Readability.OnePipePerLine, []},
+          {Credo.Check.Readability.SeparateAliasRequire, []},
+          {Credo.Check.Readability.SingleFunctionToBlockPipe, []},
+          {Credo.Check.Readability.SinglePipe, []},
+          {Credo.Check.Readability.Specs, []},
+          {Credo.Check.Readability.StrictModuleLayout, []},
+          {Credo.Check.Readability.WithCustomTaggedTuple, []},
+          {Credo.Check.Refactor.ABCSize, []},
+          {Credo.Check.Refactor.AppendSingleItem, []},
+          {Credo.Check.Refactor.DoubleBooleanNegation, []},
+          {Credo.Check.Refactor.FilterReject, []},
+          {Credo.Check.Refactor.IoPuts, []},
+          {Credo.Check.Refactor.MapMap, []},
+          {Credo.Check.Refactor.ModuleDependencies, []},
+          {Credo.Check.Refactor.NegatedIsNil, []},
+          {Credo.Check.Refactor.PassAsyncInTestCases, []},
+          {Credo.Check.Refactor.PipeChainStart, []},
+          {Credo.Check.Refactor.RejectFilter, []},
+          {Credo.Check.Refactor.VariableRebinding, []},
+          {Credo.Check.Warning.LazyLogging, []},
+          {Credo.Check.Warning.LeakyEnvironment, []},
+          {Credo.Check.Warning.MapGetUnsafePass, []},
+          {Credo.Check.Warning.MixEnv, []},
+          {Credo.Check.Warning.UnsafeToAtom, []}
+
+          # {Credo.Check.Refactor.MapInto, []},
+
+          #
+          # Custom checks can be created using `mix credo.gen.check`.
+          #
+        ]
+      }
+    }
+  ]
+}

.formatter.exs

@@ -1,4 +1,4 @@
 # Used by "mix format"
 [
-  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test,priv}/**/*.{ex,exs}"]
 ]

.gitignore

@@ -26,3 +26,6 @@ ex_double_entry-*.tar
 /tmp/
 
 mix.lock
+
+# SQLite files
+*.db*

README.md

@@ -10,6 +10,7 @@ An Elixir double-entry library inspired by Ruby's [DoubleEntry](https://github.c
 
 - Postgres 9.4+ (for `JSONB` support)
 - MySQL 8.0+ (for row locking support)
+- SQLite3 (database locking, WAL mode)
 
 ## Installation
 
@@ -20,6 +21,9 @@ def deps do
     # pick one DB package
     {:postgrex, ">= 0.0.0"},
     {:myxql, ">= 0.0.0"},
+    {:exqlite, ">= 0.0.0"},
+    # for SQLite3 also add Ecto SQLite3:
+    {:ecto_sqlite3, ">= 0.0.0"}
   ]
 end
 ```
@@ -71,10 +75,8 @@ config :ex_double_entry,
 ```elixir
 # creates a new account with 0 balance
 ExDoubleEntry.make_account!(
-  # identifier of the account, in atom
-  :savings,
-  # currency can be any arbitrary atom
-  currency: :USD,
+  :savings, # identifier of the account, in atom
+  currency: :USD, # currency can be any arbitrary atom
   # optional, scope can be any arbitrary string
   #
   # due to DB index on `NULL` values, scope value can only be `nil` (stored as
@@ -159,6 +161,10 @@ ExDoubleEntry.lock_accounts([account_a, account_b], fn ->
 end)
 ```
 
+### Locking and SQLite3
+
+SQLite3 is supported but **does not offer row-level locking**. Instead, it uses **database-level locking**, serializing all write operations. When using SQLite3 (configured with `db: :sqlite3`), `lock_accounts/2` and `transfer!/1` rely on Write-Ahead Logging (WAL) mode to ensure atomicity through transaction serialization. This is sufficient for low-concurrency environments (e.g., development, testing, or single-user applications). For high-concurrency production systems, prefer Postgres (9.4+) or MySQL (8.0+).
+
 ## License
 
 Licensed under [MIT](LICENSE.md).

config/dev.exs

@@ -6,3 +6,10 @@ config :ex_double_entry, ExDoubleEntry.Repo,
   database: "ex_double_entry_dev",
   hostname: "localhost",
   pool: Ecto.Adapters.SQL.Sandbox
+
+# When using SQLite
+# config :ex_double_entry, ExDoubleEntry.Repo,
+#   database: Path.expand("../ex_double_entry_dev.db", __DIR__),
+#   pool_size: 5,
+#   stacktrace: true,
+#   show_sensitive_data_on_connection_error: true

config/test_sqlite3.exs

@@ -0,0 +1,17 @@
+import Config
+
+config :ex_double_entry,
+  db: :sqlite3
+
+config :ex_double_entry, ExDoubleEntry.Repo,
+  database: System.get_env("SQLITE_DB_PATH", "ex_double_entry_test.db"),
+  adapter: Ecto.Adapters.SQLite3,
+  journal_mode: :wal,
+  pool_size: 1,
+  pool: Ecto.Adapters.SQL.Sandbox,
+  show_sensitive_data_on_connection_error: true,
+  timeout: :infinity,
+  queue_target: 200,
+  queue_interval: 10
+
+config :logger, level: :info

lib/ex_double_entry.ex

@@ -1,10 +1,19 @@
 defmodule ExDoubleEntry do
-  @db_table_prefix Application.fetch_env!(:ex_double_entry, :db_table_prefix)
-  @repo Application.fetch_env!(:ex_double_entry, :repo)
+  @moduledoc """
+  Contains the main public API, delegating to children modules.
 
-  def db_table_prefix, do: @db_table_prefix
+  # Key functions (delegated)
 
-  def repo, do: @repo
+  - `make_account!/2`: Creates a new account with zero balance.
+  - `lookup_account!/2`: Retrieves an existing account.
+  - `lock_accounts/2`: Locks multiple accounts and executes a function atomically (only on PostgreSQL and MySQL).
+  - `transfer!/1`: Performs a validated, atomic transfer (raising on errors).
+  - `transfer/1`: Non-raising variant of `transfer!/1`.
+  """
+
+  def db_table_prefix, do: Application.get_env(:ex_double_entry, :db_table_prefix, nil)
+
+  def repo, do: Application.fetch_env!(:ex_double_entry, :repo)
 
   @doc """
   ## Examples
@@ -26,22 +35,19 @@ defmodule ExDoubleEntry do
   ## Examples
 
   iex> [ExDoubleEntry.make_account!(:savings)] |> ExDoubleEntry.lock_accounts(fn -> true end)
-  {:ok, true}
+  `{:ok, true}`
   """
   defdelegate lock_accounts(accounts, fun), to: ExDoubleEntry.AccountBalance, as: :lock_multi!
 
   @doc """
   ## Examples
 
   iex> %ExDoubleEntry.Transfer{
-  iex>   money: Money.new(42, :USD),
-  iex>   from: %ExDoubleEntry.Account{identifier: :checking, currency: :USD, balance: Money.new(42, :USD), positive_only?: false},
-  iex>   to: %ExDoubleEntry.Account{identifier: :savings, currency: :USD, balance: Money.new(0, :USD)},
-  iex>   code: :deposit
-  iex> }
-  iex> |> ExDoubleEntry.transfer!()
-  iex> |> Tuple.to_list()
-  iex> |> List.first()
+  ...>   money: Money.new(42, :USD),
+  ...>   from: %ExDoubleEntry.Account{identifier: :checking, currency: :USD, balance: Money.new(42, :USD), positive_only?: false},
+  ...>   to: %ExDoubleEntry.Account{identifier: :savings, currency: :USD, balance: Money.new(0, :USD)},
+  ...>   code: :deposit
+  ...> } |> ExDoubleEntry.transfer!() |> Tuple.to_list() |> List.first()
   :ok
   """
   defdelegate transfer!(transfer), to: ExDoubleEntry.Transfer, as: :perform!

lib/ex_double_entry/application.ex

@@ -1,13 +1,13 @@
 defmodule ExDoubleEntry.Application do
+  @moduledoc false
   use Application
 
   @impl true
   def start(_type, _args) do
     children =
-      with {:ok, repos} <- Application.fetch_env(:ex_double_entry, :ecto_repos) do
+      case Application.fetch_env(:ex_double_entry, :ecto_repos) do
         # ecto_repos are only required for development and test
-        repos
-      else
+        {:ok, repos} -> repos
         _ -> []
       end
 

lib/ex_double_entry/ecto_types/currency.ex

@@ -1,5 +1,6 @@
 if Code.ensure_loaded?(Ecto.Type) do
   defmodule ExDoubleEntry.EctoType.Currency do
+    @moduledoc false
     if macro_exported?(Ecto.Type, :__using__, 1) do
       use Ecto.Type
     else

lib/ex_double_entry/ecto_types/identifier.ex

@@ -1,5 +1,6 @@
 if Code.ensure_loaded?(Ecto.Type) do
   defmodule ExDoubleEntry.EctoType.Identifier do
+    @moduledoc false
     if macro_exported?(Ecto.Type, :__using__, 1) do
       use Ecto.Type
     else

lib/ex_double_entry/ecto_types/scope.ex

@@ -1,5 +1,6 @@
 if Code.ensure_loaded?(Ecto.Type) do
   defmodule ExDoubleEntry.EctoType.Scope do
+    @moduledoc false
     if macro_exported?(Ecto.Type, :__using__, 1) do
       use Ecto.Type
     else