proof of concept for tabular rules command

Source/swiftlint/Commands/RulesCommand.swift

@@ -10,6 +10,47 @@ import Commandant
 import Result
 import SwiftLintFramework
 
+extension String {
+    private func withPadding(count: Int, character: String = " ") -> String {
+        let length = characters.count
+        if length < count {
+            return self +
+                Repeat(count: count - length, repeatedValue: character).joinWithSeparator("")
+        }
+        return self
+    }
+}
+
+private struct TextTableColumn {
+    let header: String
+    let values: [String]
+
+    var width: Int {
+        return max(header.characters.count, values.reduce(0) { max($0, $1.characters.count) })
+    }
+}
+
+private struct TextTable {
+    let columns: [TextTableColumn]
+
+    func render() -> String {
+        let widths = columns.map({ $0.width })
+        let separator = "+" + widths.map({ width in
+            return Repeat(count: width + 2, repeatedValue: "-").joinWithSeparator("")
+        }).joinWithSeparator("+") + "+"
+        let header = "|" + columns.map({
+            " \($0.header.withPadding($0.width)) "
+        }).joinWithSeparator("|") + "|"
+        let result = separator + "\n\(header)\n" + separator + "\n"
+        let values = (0..<columns.first!.values.count).map({ rowIndex in
+            return "|" + columns.map({ column in
+                return " \(column.values[rowIndex].withPadding(column.width)) "
+            }).joinWithSeparator("|") + "|"
+        }).joinWithSeparator("\n")
+        return result + values + "\n" + separator
+    }
+}
+
 private let violationMarker = "↓"
 
 struct RulesCommand: CommandType {
@@ -26,7 +67,23 @@ struct RulesCommand: CommandType {
             return .Success()
         }
 
-        print(masterRuleList.list.keys.joinWithSeparator("\n"))
+        let sortedRules = masterRuleList.list.sort { $0.0 < $1.0 }
+        let table = TextTable(columns: [
+            TextTableColumn(header: "identifier", values: sortedRules.map({ $0.0 })),
+            TextTableColumn(header: "opt-in", values: sortedRules.map({ _, rule in
+                return (rule.init() is OptInRule) ? "yes" : "no"
+            })),
+            TextTableColumn(header: "description", values: sortedRules.map({ _, rule in
+                let maxLength = 100
+                let description = rule.description.description
+                if description.characters.count < maxLength {
+                    return description
+                }
+                return description
+                    .substringToIndex(description.startIndex.advancedBy(maxLength)) + "..."
+            }))
+        ])
+        print(table.render())
         return .Success()
     }