Dynamically resolve extension constants for installed extensions.

Author: fractaledmind

lib/sqlpkg.rb

@@ -1,6 +1,107 @@
 # frozen_string_literal: true
 
 module Sqlpkg
+  DIR = ".sqlpkg"
+  FILE_PATTERN = "*.{dylib,so,dll}"
+
+  # Helper methods
+  module H
+    extend self
+
+    # Don't depend on ActiveSupport just to convert a constant name to a path segment.
+    # Handles acronyms and camelcase constants, e.g. UUID => uuid and SomeName => some_name
+    def constant_to_path(constant_name)
+      constant_name.to_s
+        .gsub("::", "/")
+        .gsub(/([A-Z]+)([A-Z][a-z])/, '\1_\2')
+        .gsub(/([a-z\d])([A-Z])/, '\1_\2')
+        .tr("-", "_")
+        .downcase
+    end
+  end
+
+  # The directory where `sqlpkg` stores installed extensions
+  # => "./.sqlpkg"
+  def self.file_dir
+    File.join(__dir__, DIR)
+  end
+
+  # List of file paths for all installed extensions
+  # => ["./.sqlpkg/asg017/ulid/ulid0.dylib", "./.sqlpkg/nalgeon/uuid/uuid.dylib"]
+  def self.paths
+    Dir.glob File.join(file_dir, "**", FILE_PATTERN)
+  end
+
+  # Dynamically resolve extension constants for installed extensions.
+  # Allows this gem to work with the new sqlite3[https://sparklemotion.github.io/sqlite3-ruby/]
+  # database configuration option `extensions:`, which allows an application to load extensions
+  # when using `sqlite3` >= v2.4.0. The array members may be filesystem paths or the names of
+  # modules that respond to `.to_path`. So, we dynamically build constants that respond to `.to_path`.
+  # Allow either direct access `Sqlpkg::UUID` or owner-scoped access `Sqlpkg::Nalgeon::UUID`.
+  def self.const_missing(const)
+    path_segment = H.constant_to_path(const)
+    is_owner = false
+    path = paths.find do |it|
+      _path, pkg_path = it.split("#{DIR}#{File::SEPARATOR}")
+      owner, name, _file = pkg_path.split(File::SEPARATOR)
+
+      if path_segment == owner
+        is_owner = true
+      else
+        path_segment == name
+      end
+    end
+
+    return super unless path
+
+    if is_owner
+      # Dynamically generated module for the extension owner.
+      # This module has `.file_dir`, `.paths`, and `.const_missing` defined.
+      # Any dynamically generated classes _must be_ installed extensions
+      # for this owner.
+      const_set(const, Module.new do
+        # The directory where `sqlpkg` stores installed extensions for this owner
+        # => "./.sqlpkg/nalgeon"
+        def self.file_dir
+          File.join(__dir__, ".#{H.constant_to_path(self.name)}")
+        end
+
+        # List of file paths for all installed extensions belonging to this owner
+        # => ["./.sqlpkg/nalgeon/uuid/uuid.dylib"]
+        def self.paths
+          Dir.glob File.join(file_dir, "**", FILE_PATTERN)
+        end
+
+        def self.const_missing(const)
+          path_segment = H.constant_to_path(const)
+          path = paths.find do |it|
+            _path, pkg_path = it.split("#{DIR}#{File::SEPARATOR}")
+            _owner, name, _file = pkg_path.split(File::SEPARATOR)
+
+            path_segment == name
+          end
+
+          return super unless path
+
+          # Dynamically generated module for the extension.
+          # This class only has `.to_path` defined.
+          const_set(const, Class.new do
+            define_singleton_method :to_path do
+              path
+            end
+          end)
+        end
+      end)
+    else
+      # Dynamically generated module for the extension.
+      # This class only has `.to_path` defined.
+      const_set(const, Class.new do
+        define_singleton_method :to_path do
+          path
+        end
+      end)
+    end
+  end
 end
 
 require_relative "sqlpkg/version"