Fix off by one with default value in pagination

lib/tty/prompt/paginator.rb

@@ -21,7 +21,7 @@ class Paginator
       #
       # @api private
       def initialize(**options)
-        @last_index  = Array(options[:default]).flatten.first || 0
+        @last_index  = Array(options[:default]).flatten.first
         @per_page    = options[:per_page]
         @start_index = Array(options[:default]).flatten.first
       end
@@ -75,15 +75,23 @@ def paginate(list, active, per_page = nil, &block)
           end
         end
 
-        step = (current_index - @last_index).abs
-        if current_index > @last_index # going up
-          if current_index >= @end_index && current_index < list.size - 1
-            last_page = list.size - @per_page
-            @start_index = [@start_index + step, last_page].min
+        if @last_index.nil?
+          if current_index == @start_index && current_index > 0
+            @start_index -= 1
+          elsif current_index == @end_index && current_index < list.size - 1
+            @start_index += 1
           end
-        elsif current_index < @last_index # going down
-          if current_index <= @start_index && current_index > 0
-            @start_index = [@start_index - step, 0].max
+        else
+          step = (current_index - @last_index).abs
+          if current_index > @last_index # going up
+            if current_index >= @end_index && current_index < list.size - 1
+              last_page = list.size - @per_page
+              @start_index = [@start_index + step, last_page].min
+            end
+          elsif current_index < @last_index # going down
+            if current_index <= @start_index && current_index > 0
+              @start_index = [@start_index - step, 0].max
+            end
           end
         end
 

spec/unit/multi_select_spec.rb

@@ -380,7 +380,7 @@ def exit_message(prompt, choices)
       expect(answer).to eq(["D"])
 
       expected_output =
-        output_helper("What letter?", choices[3..5], "D", %w[D], init: true,
+        output_helper("What letter?", choices[2..4], "D", %w[D], init: true,
           hint: "Press #{up_down}/#{left_right} arrow to move, Space/Ctrl+A|R to select (all|rev) and Enter to finish") +
         exit_message("What letter?", %w[D])
 
@@ -396,7 +396,7 @@ def exit_message(prompt, choices)
       expect(answer).to eq([4])
 
       expected_output =
-        output_helper("What letter?", choices.keys[3..5], :D, [:D], init: true,
+        output_helper("What letter?", choices.keys[2..4], :D, [:D], init: true,
           hint: "Press #{up_down}/#{left_right} arrow to move, Space/Ctrl+A|R to select (all|rev) and Enter to finish") +
         exit_message("What letter?", %w[D])
 
@@ -416,7 +416,7 @@ def exit_message(prompt, choices)
       expect(answer).to eq(["D"])
 
       expected_output =
-        output_helper("What letter?", choices[3..5], "D", %w[D], init: true,
+        output_helper("What letter?", choices[2..4], "D", %w[D], init: true,
           hint: "Press #{up_down}/#{left_right} arrow to move, Space/Ctrl+A|R to select (all|rev) and Enter to finish") +
         exit_message("What letter?", %w[D])
 
@@ -472,7 +472,7 @@ def exit_message(prompt, choices)
       expect(answer).to eq(%w[4 10])
 
       expected_output =
-        output_helper("What number?", choices[3..6], "4", ["4"], init: true,
+        output_helper("What number?", choices[1..4], "4", ["4"], init: true,
           hint: "Press #{up_down}/#{left_right} arrow to move, Space/Ctrl+A|R to select (all|rev) and Enter to finish") +
         output_helper("What number?", choices[4..7], "8", ["4"]) +
         output_helper("What number?", choices[8..9], "10", ["4"]) +

spec/unit/paginator_spec.rb

@@ -75,6 +75,15 @@
     expect(paginator.end_index).to eq(6)
   end
 
+  it "always returns a page that includes the current selection" do
+    list = (1..100).to_a
+    list.each do |one_based_index|
+      zero_based_page_indexes = described_class.new.paginate(list, one_based_index, 5).map(&:last)
+      zero_based_index = one_based_index - 1
+      expect(zero_based_page_indexes).to include(zero_based_index)
+    end
+  end
+
   it "starts with default selection" do
     list = %w[a b c d e f g]
     paginator = described_class.new(per_page: 3, default: 3)

spec/unit/select_spec.rb

@@ -394,9 +394,9 @@ def exit_message(prompt, choice)
       expect(answer).to eq("D")
       expected_output = [
         "\e[?25lWhat letter? \e[90m(Press #{up_down}/#{left_right} arrow to move and Enter to select)\e[0m\n",
+        "  C\n",
         "\e[32m#{symbols[:marker]} D\e[0m\n",
-        "  E\n",
-        "  F",
+        "  E",
         "\e[2K\e[1G\e[1A" * 3,
         "\e[2K\e[1G",
         "What letter? \e[32mD\e[0m\n\e[?25h"
@@ -416,9 +416,9 @@ def exit_message(prompt, choice)
       expect(answer).to eq(4)
       expected_output = [
         "\e[?25lWhat letter? \e[90m(Press #{up_down}/#{left_right} arrow to move and Enter to select)\e[0m\n",
+        "  C\n",
         "\e[32m#{symbols[:marker]} D\e[0m\n",
-        "  E\n",
-        "  F",
+        "  E",
         "\e[2K\e[1G\e[1A" * 3,
         "\e[2K\e[1G",
         "What letter? \e[32mD\e[0m\n\e[?25h"
@@ -441,9 +441,9 @@ def exit_message(prompt, choice)
 
       expected_output = [
         "\e[?25lWhat letter? \e[90m(Press #{up_down}/#{left_right} arrow to move and Enter to select)\e[0m\n",
+        "  C\n",
         "\e[32m#{symbols[:marker]} D\e[0m\n",
-        "  E\n",
-        "  F",
+        "  E",
         "\e[2K\e[1G\e[1A" * 3,
         "\e[2K\e[1G",
         "What letter? \e[32mD\e[0m\n\e[?25h"
@@ -484,7 +484,7 @@ def exit_message(prompt, choice)
       expect(answer).to eq("10")
 
       expected_output = [
-        output_helper("What number?", choices[3..6], "4", init: true,
+        output_helper("What number?", choices[1..4], "4", init: true,
           hint: "Press #{up_down}/#{left_right} arrow to move and Enter to select"),
         output_helper("What number?", choices[4..7], "8"),
         output_helper("What number?", choices[8..9], "10"),