Even more CSV support in Jekyll

Gemfile

@@ -2,12 +2,15 @@ source "https://rubygems.org"
 
 gem "jekyll", "~> 4.3.4"
 gem "posix-spawn", "~> 0.3.9"
-gem "ruby-graphviz"
 
 group :jekyll_plugins do
   gem "jekyll-mermaid", "~> 1.0.0"
   gem "jekyll-postfiles", "~> 3.1"
   gem "jekyll-seo-tag", :git => 'https://github.com/numist/jekyll-seo-tag.git', :branch => 'issue/461'
+
+  # Local plugin dependencies
+  gem "ruby-graphviz"
+  gem "dentaku"
 end
 
 group :development do

Gemfile.lock

@@ -23,6 +23,9 @@ GEM
     bigdecimal (3.1.8)
     colorator (1.1.0)
     concurrent-ruby (1.3.4)
+    dentaku (3.5.4)
+      bigdecimal
+      concurrent-ruby
     em-websocket (0.5.3)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0)
@@ -105,6 +108,7 @@ PLATFORMS
   x86_64-linux
 
 DEPENDENCIES
+  dentaku
   jekyll (~> 4.3.4)
   jekyll-mermaid (~> 1.0.0)
   jekyll-postfiles (~> 3.1)

_plugins/csv_block.rb

@@ -1,77 +1,166 @@
+# _plugins/csv_block.rb
+require 'jekyll'
+require 'liquid'
 require 'csv'
-
-# Usage:
-#
-# {% csv %}
-# Name, Age, Occupation
-# Alice, 30, Engineer
-# Bob, 25, Designer
-# Charlie, 35, Teacher
-# {% endcsv %}
-#
-# {% csv header:false %}
-# Alice, 30, Engineer
-# Bob, 25, Designer
-# Charlie, 35, Teacher
-# {% endcsv %}
-#
-# {% csv header:true separator:tab %}
-# Name	Age	Occupation
-# Alice	30	Engineer
-# Bob	25	Designer
-# Charlie	35	Teacher
-# {% endcsv %}
-#
+require 'dentaku'
 
 module Jekyll
-  class CSVBlock < Liquid::Block
+  class CSVBlock < ::Liquid::Block
     def initialize(tag_name, markup, tokens)
       super
-      # Parse options from the markup (e.g., header: false, separator: tab)
       @options = {}
       markup.strip.split.each do |option|
         key, value = option.split(':')
-        if key == 'header'
-          @options[key] = value == 'false' ? false : true
-        elsif key == 'separator'
-          @options[key] = value == 'tab' ? "\t" : ','
-        end
+        @options[key] = (value == 'false' ? false : true) if key == 'header'
+        @options[key] = (value == 'tab' ? "\t" : ',') if key == 'separator'
       end
+      @calculator = Dentaku::Calculator.new
+      @evaluation_cache = {}
     end
 
     def render(context)
-      csv_text = super.strip
-      has_headers = @options.fetch('header', true)
-      separator = @options.fetch('separator', ',')
-
-      # Parse CSV with or without headers and with the specified separator
-      csv_data = CSV.parse(csv_text, headers: has_headers, col_sep: separator)
-
-      # Start generating HTML
-      html = "<table>\n"
-
-      if has_headers
-        # Generate header row
-        html << "<thead>\n<tr>\n"
-        csv_data.headers.each do |header|
-          html << "<th>#{header}</th>"
+      begin
+
+        csv_text = super.strip
+        has_headers = @options.fetch('header', true)
+        separator = @options.fetch('separator', ',')
+
+        csv_data = CSV.parse(csv_text, headers: has_headers, col_sep: separator)
+        if has_headers
+          table_data = [csv_data.headers] + csv_data.map(&:to_hash).map(&:values)
+        else
+          table_data = csv_data
         end
-        html << "</tr>\n</thead>\n"
+
+        html = "<table>\n"
+
+        if has_headers
+          html << "<thead>\n<tr>\n"
+          table_data.first.each_with_index do |header, col_index|
+            html << "<th>#{evaluate_formula_at_index(col_index, 0, table_data)}</th>"
+          end
+          html << "</tr>\n</thead>\n"
+        end
+
+        html << "<tbody>\n"
+        table_data.each_with_index do |row, row_index|
+          next if row_index == 0 and has_headers
+          html << "<tr>"
+          row.each_with_index do |value, col_index|
+            evaluated_value = evaluate_formula_at_index(col_index, row_index, table_data)
+            html << "<td>#{evaluated_value}</td>"
+          end
+          html << "</tr>\n"
+        end
+        html << "</tbody>\n</table>\n"
+
+        return html
+      rescue => e
+        return e.message
+      end
+    end
+
+    private
+
+    #
+    # Conversion functions between spreadsheet style (B3, "val") and zero-based coordinates ([2, 1], "index")
+    #
+
+    def col_index_to_val(col_index)
+      if col_index < 26
+      (col_index + 'A'.ord).chr
+      else
+      quotient, remainder = col_index.divmod(26)
+      col_index_to_val(quotient - 1) + col_index_to_val(remainder)
+      end
+    end
+
+    def col_val_to_index(col_val)
+      if col_val.length == 1
+        col_val.ord - 'A'.ord
+      else
+        base = 'Z'.ord - 'A'.ord + 1
+        col_val.chars.reduce(0) { |result, char| result * base + char.ord - 'A'.ord + 1 } - 1
+      end
+    end
+
+    def row_index_to_val(row_index)
+      row_index + 1
+    end
+
+    def row_val_to_index(row_val)
+      row_val - 1
+    end
+
+    # Convert zero-based coordinates to spreadsheet style
+    def indices_to_val(col_index, row_index)
+      "#{col_index_to_val(col_index)}#{row_index_to_val(row_index)}"
+    end
+
+    # Evaluate a formula at a given cell index
+    # This wrapper function catches exceptions thrown from the actual implementation, converting them into error
+    # messages for display in the rendered HTML. This is necessary because Liquid does not support exceptions in
+    # custom tags, swallowing the error details.
+    def evaluate_formula_at_index(col_index, row_index, table_data)
+      begin
+        evaluate_formula_at_index_internal(col_index, row_index, table_data)
+      rescue => e
+        e.message
+      end
+    end
+
+    # Implementation of formula evaluation.
+    def evaluate_formula_at_index_internal(col_index, row_index, table_data, visiting = Set.new)
+      value = table_data[row_index][col_index].strip
+      return value unless value.is_a?(String) && value.start_with?('=')
+
+      cell_key = [col_index, row_index]
+      return @evaluation_cache[cell_key] if @evaluation_cache.key?(cell_key)
+
+      if visiting.include?(cell_key)
+        raise "Error: circular reference: #{visiting.to_a.map { |key| "#{col_index_to_val(key[0])}#{row_index_to_val(key[1])}" }.sort.join(', ')}"
+      else
+        visiting.add(cell_key)
       end
 
-      # Generate data rows
-      html << "<tbody>\n"
-      csv_data.each do |row|
-        html << "<tr>"
-        row = row.to_hash.values if has_headers
-        row.each do |value|
-          html << "<td>#{value}</td>"
+      formula = value[1..-1].strip # Removes '=' from start of formula
+
+      # Identify cell references and replace with values
+      formula_with_values = formula.gsub(/([A-Z]+)(\d+)(:([A-Z]+)(\d+))?/i) do |match|
+        if $3
+          start_col, start_row, end_col, end_row = $1, $2.to_i, $4, $5.to_i
+          start_col_index = col_val_to_index(start_col)
+          start_row_index = row_val_to_index(start_row)
+          end_col_index = col_val_to_index(end_col)
+          end_row_index = row_val_to_index(end_row)
+
+          if start_col_index.nil? || start_row_index.nil? || end_col_index.nil? || end_row_index.nil? \
+          || start_col_index > end_col_index || start_row_index > end_row_index \
+          || end_col_index >= table_data.first.length || end_row_index >= table_data.length
+            raise "Error: #{col_index_to_val(col_index)}#{row_index_to_val(row_index)} references invalid range #{match}"
+          end
+
+          range_values = []
+          (start_row_index..end_row_index).each do |row_index|
+            (start_col_index..end_col_index).each do |col_index|
+              range_values << evaluate_formula_at_index_internal(col_index, row_index, table_data, visiting)
+            end
+          end
+          range_values.join(',')
+        else
+          ref_row_index = row_val_to_index($2.to_i)
+          ref_col_index = col_val_to_index($1)
+          referenced_value = table_data.dig(ref_row_index, ref_col_index)
+          raise "Error: #{col_index_to_val(col_index)}#{row_index_to_val(row_index)} references invalid cell #{match}" if referenced_value.nil?
+
+          evaluate_formula_at_index_internal(ref_col_index, ref_row_index, table_data, visiting)
         end
-        html << "</tr>\n"
       end
-      html << "</tbody>\n</table>\n"
-
-      html
+
+      evaluated_result = @calculator.evaluate(formula_with_values) or raise "Error: #{col_index_to_val(col_index)}#{row_index_to_val(row_index)} uses invalid formula: #{formula}"
+
+      @evaluation_cache[cell_key] = evaluated_result
+      evaluated_result
     end
   end
 end

_posts/2022-02-17-feedyour.email/2022-02-17-feedyour.email.md

@@ -19,7 +19,7 @@ The next day he had a prototype working[^brooks], and the day after that it was
 
 The next week or two brought more features, like [support for emails bounced into feeds](https://github.com/indirect/feedyour.email/pull/85) using mail rules and [feed-specific favicons](https://github.com/indirect/feedyour.email/issues/23). It's really good.
 
-As a side benefit, this exercise also gave me some exposure to modern web development[^tmbo], which was fun and led indirectly to [this blog](/post/1969/new-blog/).
+As a side benefit, this exercise also gave me some exposure to modern web development[^tmbo], which was fun and led indirectly to this blog.
 
 (P.S. André [wrote something about feedyour.email](https://andre.arko.net/2022/02/17/feedyouremail/) too)