Sankey Diagram (#2269)

* Enhance cash flow dashboard with new cash flow period handling and improved Sankey diagram rendering. Update D3 and related dependencies for better performance and features.

* Fix Rubocop offenses

* Refactor Sankey chart controller to use Number.parseFloat for value formatting and improve code readability by restructuring conditional logic for node shapes.

app/controllers/pages_controller.rb

@@ -6,6 +6,23 @@ class PagesController < ApplicationController
     @balance_sheet = Current.family.balance_sheet
     @accounts = Current.family.accounts.active.with_attached_logo
 
+    period_param = params[:cashflow_period]
+    @cashflow_period = if period_param.present?
+      begin
+        Period.from_key(period_param)
+      rescue Period::InvalidKeyError
+        Period.last_30_days
+      end
+    else
+      Period.last_30_days
+    end
+
+    family_currency = Current.family.currency
+    income_totals = Current.family.income_statement.income_totals(period: @cashflow_period)
+    expense_totals = Current.family.income_statement.expense_totals(period: @cashflow_period)
+
+    @cashflow_sankey_data = build_cashflow_sankey_data(income_totals, expense_totals, family_currency)
+
     @breadcrumbs = [ [ "Home", root_path ], [ "Dashboard", nil ] ]
   end
 
@@ -31,4 +48,98 @@ class PagesController < ApplicationController
     def github_provider
       Provider::Registry.get_provider(:github)
     end
+
+    def build_cashflow_sankey_data(income_totals, expense_totals, currency_symbol)
+      nodes = []
+      links = []
+      node_indices = {} # Memoize node indices by a unique key: "type_categoryid"
+
+      # Helper to add/find node and return its index
+      add_node = ->(unique_key, display_name, value, percentage, color) {
+        node_indices[unique_key] ||= begin
+          nodes << { name: display_name, value: value.to_f.round(2), percentage: percentage.to_f.round(1), color: color }
+          nodes.size - 1
+        end
+      }
+
+      total_income_val = income_totals.total.to_f.round(2)
+      total_expense_val = expense_totals.total.to_f.round(2)
+
+      # --- Create Central Cash Flow Node ---
+      cash_flow_idx = add_node.call("cash_flow_node", "Cash Flow", total_income_val, 0, "var(--color-success)")
+
+      # --- Process Income Side ---
+      income_category_values = Hash.new(0.0)
+      income_totals.category_totals.each do |ct|
+        val = ct.total.to_f.round(2)
+        next if val.zero? || !ct.category.parent_id
+        income_category_values[ct.category.parent_id] += val
+      end
+
+      income_totals.category_totals.each do |ct|
+        val = ct.total.to_f.round(2)
+        percentage_of_total_income = total_income_val.zero? ? 0 : (val / total_income_val * 100).round(1)
+        next if val.zero?
+
+        node_display_name = ct.category.name
+        node_value_for_label = val + income_category_values[ct.category.id] # This sum is for parent node display
+        node_percentage_for_label = total_income_val.zero? ? 0 : (node_value_for_label / total_income_val * 100).round(1)
+
+        node_color = ct.category.color.presence || Category::COLORS.sample
+        current_cat_idx = add_node.call("income_#{ct.category.id}", node_display_name, node_value_for_label, node_percentage_for_label, node_color)
+
+        if ct.category.parent_id
+          parent_cat_idx = node_indices["income_#{ct.category.parent_id}"]
+          parent_cat_idx ||= add_node.call("income_#{ct.category.parent.id}", ct.category.parent.name, income_category_values[ct.category.parent.id], 0, ct.category.parent.color || Category::COLORS.sample) # Parent percentage will be recalc based on its total flow
+          links << { source: current_cat_idx, target: parent_cat_idx, value: val, color: node_color, percentage: percentage_of_total_income }
+        else
+          links << { source: current_cat_idx, target: cash_flow_idx, value: val, color: node_color, percentage: percentage_of_total_income }
+        end
+      end
+
+      # --- Process Expense Side ---
+      expense_category_values = Hash.new(0.0)
+      expense_totals.category_totals.each do |ct|
+        val = ct.total.to_f.round(2)
+        next if val.zero? || !ct.category.parent_id
+        expense_category_values[ct.category.parent_id] += val
+      end
+
+      expense_totals.category_totals.each do |ct|
+        val = ct.total.to_f.round(2)
+        percentage_of_total_expense = total_expense_val.zero? ? 0 : (val / total_expense_val * 100).round(1)
+        next if val.zero?
+
+        node_display_name = ct.category.name
+        node_value_for_label = val + expense_category_values[ct.category.id]
+        node_percentage_for_label = total_expense_val.zero? ? 0 : (node_value_for_label / total_expense_val * 100).round(1) # Percentage relative to total expenses for expense nodes
+
+        node_color = ct.category.color.presence || Category::UNCATEGORIZED_COLOR
+        current_cat_idx = add_node.call("expense_#{ct.category.id}", node_display_name, node_value_for_label, node_percentage_for_label, node_color)
+
+        if ct.category.parent_id
+          parent_cat_idx = node_indices["expense_#{ct.category.parent_id}"]
+          parent_cat_idx ||= add_node.call("expense_#{ct.category.parent.id}", ct.category.parent.name, expense_category_values[ct.category.parent.id], 0, ct.category.parent.color || Category::UNCATEGORIZED_COLOR)
+          links << { source: parent_cat_idx, target: current_cat_idx, value: val, color: nodes[parent_cat_idx][:color], percentage: percentage_of_total_expense }
+        else
+          links << { source: cash_flow_idx, target: current_cat_idx, value: val, color: node_color, percentage: percentage_of_total_expense }
+        end
+      end
+
+      # --- Process Surplus ---
+      leftover = (total_income_val - total_expense_val).round(2)
+      if leftover.positive?
+        percentage_of_total_income_for_surplus = total_income_val.zero? ? 0 : (leftover / total_income_val * 100).round(1)
+        surplus_idx = add_node.call("surplus_node", "Surplus", leftover, percentage_of_total_income_for_surplus, "var(--color-success)")
+        links << { source: cash_flow_idx, target: surplus_idx, value: leftover, color: "var(--color-success)", percentage: percentage_of_total_income_for_surplus }
+      end
+
+      # Update Cash Flow and Income node percentages (relative to total income)
+      if node_indices["cash_flow_node"]
+        nodes[node_indices["cash_flow_node"]][:percentage] = 100.0
+      end
+      # No primary income node anymore, percentages are on individual income cats relative to total_income_val
+
+      { nodes: nodes, links: links, currency_symbol: Money::Currency.new(currency_symbol).symbol }
+    end
 end