Add C++ implementation

cpp/statement.cpp

@@ -0,0 +1,95 @@
+#include "statement.h"
+
+#include <iostream>
+#include <sstream>
+#include <iomanip>
+
+// https://stackoverflow.com/a/7277333/104370
+class comma_numpunct : public std::numpunct<char>
+{
+  protected:
+    virtual char do_thousands_sep() const override
+    {
+        return ',';
+    }
+
+    virtual std::string do_grouping() const override
+    {
+        return "\03";
+    }
+};
+
+std::string format_as_dollars(float amount)
+{
+    // this creates a new locale based on the current application default
+    // (which is either the one given on startup, but can be overriden with
+    // std::locale::global) - then extends it with an extra facet that 
+    // controls numeric output.
+    const std::locale comma_locale(std::locale(), new comma_numpunct());
+
+    std::ostringstream out;
+    // tell stream to use our new locale.
+    out.imbue(comma_locale);
+    out.precision(2);
+    out << "$" << std::fixed << amount;
+    return out.str();
+}
+
+std::string statement(
+    const nlohmann::json& invoice,
+    const nlohmann::json& plays)
+{
+    float total_amount = 0;
+    int volume_credits = 0;
+
+    std::stringstream result;
+    result << "Statement for " << invoice["customer"].get<std::string>() << '\n';
+
+    for( const auto& perf : invoice["performances"])
+    {
+        float this_amount = 0;
+        auto play = plays[perf["playID"].get<std::string>()];
+        if (play["type"] == "tragedy")
+        {
+            this_amount = 40000;
+            if (perf["audience"] > 30)
+            {
+                this_amount += 1000 * (perf["audience"].get<int>() - 30);
+            }
+        }
+
+        else if (play["type"] == "comedy")
+        {
+            this_amount = 30000;
+            if (perf["audience"] > 20)
+            {
+                this_amount += 10000 + 500 * (perf["audience"].get<int>() - 20);
+            }
+
+            this_amount += 300 * perf["audience"].get<int>();
+        }
+
+        else
+        {
+            throw std::domain_error("unknown type: " + play["type"].get<std::string>());
+        }
+
+        // add volume credits
+        volume_credits += std::max(perf["audience"].get<int>() - 30, 0);
+
+        // add extra credit for every ten comedy attendees
+        if ("comedy" == play["type"])
+        {
+            volume_credits += perf["audience"].get<int>() / 5;
+        }
+
+        // print line for this order
+        result << " " << play["name"].get<std::string>() << ": " << format_as_dollars(this_amount/100) << 
+            " (" << perf["audience"] << " seats)\n";
+        total_amount += this_amount;
+    }
+
+    result << "Amount owed is " << format_as_dollars(total_amount/100.0f) << "\n";
+    result << "You earned " << volume_credits << " credits";
+    return result.str();
+}