Add source code.

include/Completer.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <string>
+#include <vector>
+
+#include "CommandSpec.h"
+#include "Completion.h"
+#include "Database.h"
+
+// Works out tab-completion candidates for the text typed so far: command
+// words first, then arguments (task names, account names, statuses, ...).
+class Completer {
+public:
+    Completer(const Database& db, const std::vector<CommandSpec>& specs);
+
+    Completion complete(const std::string& textBeforeCursor) const;
+
+private:
+    std::vector<std::string> valuesFor(ArgKind kind, const std::string& current) const;
+
+    const Database& db_;
+    const std::vector<CommandSpec>& specs_;
+};