Implement basic shortened URL generation

Makefile

@@ -24,6 +24,9 @@ redirectservice_dev:
 		-ldl \
 		gen/redirectservice.grpc.pb.cc \
 		gen/redirectservice.pb.cc \
+		src/log.cc \
+		src/store.cc \
+		src/urlgen.cc \
 		src/redirectservice.cc \
 		-o build/circlet_redirectservice.dev
 
@@ -39,6 +42,7 @@ redirectservice_release:
 		gen/redirectservice.pb.cc \
 		src/log.cc \
 		src/store.cc \
+		src/urlgen.cc \
 		src/redirectservice.cc \
 		-o build/circlet_redirectservice.dev
 
@@ -54,5 +58,6 @@ redirectservice_dev_mike:
 		gen/redirectservice.pb.cc \
 		src/log.cc \
 		src/store.cc \
+		src/urlgen.cc \
 		src/redirectservice.cc \
 		-o ~/circlet_redirectservice.dev

src/redirectservice.cc

@@ -26,6 +26,7 @@
 
 #include "log.hh"
 #include "store.hh"
+#include "urlgen.hh"
 
 using grpc::Server;
 using grpc::ServerBuilder;
@@ -71,10 +72,13 @@ class RedirectServiceImpl final : public RedirectService::Service {
                 );
             }
 
-            this->get_store()->create_redirect(from_location, "/test");
+            // TODO Make URL generation configurable
+            auto to_location = "/" + encode_url_id(generate_url_id());
+
+            this->get_store()->create_redirect(from_location, to_location);
 
             response->set_from_location(from_location);
-            response->set_to_location("/test");
+            response->set_to_location(to_location);
 
             return Status::OK;
     }

src/urlgen.cc

@@ -0,0 +1,60 @@
+#include <algorithm>
+#include <chrono>
+#include <iostream>
+#include <sstream>
+#include <tuple>
+
+uint64_t generate_url_id() {
+    uint64_t url_id = std::chrono::duration_cast<std::chrono::microseconds>(
+        std::chrono::system_clock::now().time_since_epoch()
+    ).count();
+
+    return url_id;
+}
+
+std::string a = "0123456789befhjmnrstvwyz";
+size_t a_size = 24;
+
+std::string encode_url_id(uint64_t url_id) {
+    std::stringstream s;
+    while (url_id) {
+        s << a[url_id % a_size];
+        url_id /= a_size;
+    }
+    auto str = s.str();
+    std::reverse(str.begin(), str.end());
+    return str;
+}
+
+static uint64_t pow24_cache[14] = {
+    1,
+    24,
+    576,
+    13824,
+    331776,
+    7962624,
+    191102976,
+    4586471424,
+    110075314176,
+    2641807540224,
+    63403380965376,
+    1521681143169024,
+    36520347436056576,
+    876488338465357824,
+};
+
+uint64_t pow24(int n) {
+    if (n > 13) return -1;
+    return pow24_cache[n];
+}
+
+uint64_t decode_url_id(std::string url_id_str) {
+    uint64_t id = 0;
+
+    size_t i = 0;
+    for (auto &l : url_id_str) {
+        id += a.find(l) * pow24(url_id_str.size() - (i + 1));
+        i++;
+    }
+    return id;
+}

src/urlgen.hh

@@ -0,0 +1,5 @@
+#include <string>
+
+uint64_t generate_url_id();
+std::string encode_url_id(uint64_t url_id);
+uint64_t decode_url_id(std::string url_id_str);