Implement table formatting in Space Lua (close silverbulletmd#12)

Aligns columns as described in issue silverbulletmd#12. Preserves alignment specifiers
and takes them into consideration for column width (see also silverbulletmd#847, silverbulletmd#1293)

Author: Maarrk

plugs/core/Library/Std/Table.md

@@ -0,0 +1,138 @@
+#meta
+Implements utilities for working with Markdown tables
+
+# Table
+## Commands
+
+```space-lua
+command.define {
+  name = "Table: Format",
+  run = function()
+    position = editor.getCursor()
+    tree = markdown.parseMarkdown(editor.getText())
+    tableNode = nodeParentOfType(tree, position, "Table")
+    if tableNode then
+      formatMarkdownTable(tableNode)
+    else
+      editor.flashNotification("This command must be run with cursor in a table", "error")
+    end
+  end
+}
+```
+
+## Implementation
+
+```space-lua
+-- Find outermost node of given type that contains the position
+-- similar to plug-api/lib/tree.ts nodeAtPos
+function nodeParentOfType(tree, position, nodeType)
+  if position < tree.from or position > tree.to then
+    return nil
+  end
+  if tree.type == nodeType then
+    return tree
+  end
+  if tree.children then
+    for _, child in ipairs(tree.children) do
+      if position >= child.from and position <= child.to then
+        return nodeParentOfType(child, position, nodeType)
+      end
+    end
+  end
+  return nil
+end
+```
+
+```space-lua
+function formatMarkdownTable(tree)
+  -- First find the desired length for each column
+  columnLengths = {}
+  columnAlignments = {}
+  for _, child in ipairs(tree.children) do
+    if child.type == "TableDelimiter" then
+      column = 1
+      for _, spec in ipairs(string.split(child.children[1].text, "|")) do
+        if #spec > 0 then
+          minLength = 1
+          if #spec >= 2 and string.endsWith(spec, ":") then
+            if string.startsWith(spec, ":") then
+              columnAlignments[column] = "center"
+              minLength = 3
+            else
+              columnAlignments[column] = "right"
+              minLength = 2
+            end
+          else
+            columnAlignments[column] = "left"
+          end
+
+          if minLength > (columnLengths[column] or 0) then
+            columnLengths[column] = minLength
+          end
+          column = column + 1
+        end
+      end
+    elseif child.type == "TableHeader" or child.type == "TableRow" then
+      column = 1
+      for i, cell in ipairs(child.children) do
+        if cell.type == "TableDelimiter" then
+          next = child.children[i + 1]
+          if next and next.type == "TableCell" then
+            len = next.to - next.from
+            if len > (columnLengths[column] or 0) then
+              columnLengths[column] = len
+            end
+          end
+          
+          column = column + 1
+        end
+      end
+    end
+  end
+  print(columnAlignments)
+
+  -- Then print the table using these column lengths
+  output = ""
+  for _, child in ipairs(tree.children) do
+    if child.type == "TableDelimiter" then
+      output = output .. "\n|"
+      for column, len in ipairs(columnLengths) do
+        align = columnAlignments[column]
+        if align == "left" then
+          -- This is separate case because could be shorter than 2 characters
+          output = output .. string.rep("-", len)
+        else
+          output = output .. (align == "center" and ":" or "-") .. string.rep("-", len - 2) .. ":"
+        end
+        output = output .. "|"
+      end
+    elseif child.type == "TableHeader" or child.type == "TableRow" then
+      if child.type ~= "TableHeader" then
+        output = output .. "\n"
+      end
+      output = output .. "|"
+      column = 1
+      for i, cell in ipairs(child.children) do
+        if cell.type == "TableDelimiter" then
+          next = child.children[i + 1]
+          if next and next.type == "TableCell" then
+            len = next.to - next.from
+            
+            -- Similar to plugs/index/table.ts:concatChildrenTexts
+            for _, next_child in ipairs(next.children) do
+              output = output .. next_child.text
+            end
+            
+            output = output .. string.rep(" ", columnLengths[column] - len) .. "|"
+          end
+          
+          column = column + 1
+        end
+      end
+    end
+  end
+
+  -- Replace the table node with the formatted content
+  editor.replaceRange(tree.from, tree.to, output)
+end
+```