feat(orm): implement Prism and Orm

lib/prism/orm/pagination.rb

@@ -0,0 +1,69 @@
+module Prism
+  module Orm
+    # Kaminari/will_paginate-lite: `.page(n).per(size)` on any Relation,
+    # staying immutable and chainable like the rest of the query engine.
+    # `total_count`/`total_pages` re-run the same condition without the
+    # page's own limit/offset rather than caching a count that could go
+    # stale across calls on a different relation.
+    module Pagination
+      DefaultPerPage = 25
+
+      def page(number)
+        paginate(page: number, per_page: @per_page_value || DefaultPerPage)
+      end
+
+      def per(size)
+        paginate(page: @page_value || 1, per_page: size)
+      end
+
+      def current_page
+        @page_value || 1
+      end
+
+      def per_page
+        @per_page_value || DefaultPerPage
+      end
+
+      def total_count
+        @total_count ||= unpaginated.count
+      end
+
+      def total_pages
+        return 0 if total_count.zero?
+        (total_count.to_f / per_page).ceil
+      end
+
+      def out_of_range?
+        total_pages.positive? && current_page > total_pages
+      end
+
+      def first_page?
+        current_page <= 1
+      end
+
+      def last_page?
+        current_page >= total_pages
+      end
+
+      def prev_page
+        first_page? ? nil : current_page - 1
+      end
+
+      def next_page
+        last_page? ? nil : current_page + 1
+      end
+
+      private
+
+      def paginate(page:, per_page:)
+        page = [page.to_i, 1].max
+        per_page = [per_page.to_i, 1].max
+        spawn(page_value: page, per_page_value: per_page, limit_value: per_page, offset_value: (page - 1) * per_page)
+      end
+
+      def unpaginated
+        spawn(page_value: nil, per_page_value: nil, limit_value: nil, offset_value: nil)
+      end
+    end
+  end
+end