Add --status and --status-interval.

--status prints a status message to stderr at regular intervals.
--status-interval sets the interval for status messages.

Closes: #10

man/epubgrep.1.adoc

@@ -38,6 +38,12 @@ epubgrep -PiC2 '(Apple|Orange)s?' file.epub
 epubgrep -PC0 --raw --no-filename=all '"http[^"]+"' file.epub | tr -d '"'
 --------------------------------------------------------------------------------
 
+.Save the search results to an HTML file and output a status message every 20 seconds
+[source,shell]
+--------------------------------------------------------------------------------
+epubgrep -C2 --status --status-interval=20 --html 'Apples' file.epub > result.html
+--------------------------------------------------------------------------------
+
 == OPTIONS
 
 *-h*, *--help*::
@@ -109,6 +115,12 @@ in an array named `matches`. I will try not to break the API. 😊
 Output HTML instead of plain text. HTML will only be output at the end of the
 program.
 
+*--status*::
+Output status message every *--status-interval* seconds to standard error.
+
+*--status-interval* _NUMBER_::
+Set status message interval to _NUMBER_ seconds.
+
 == USAGE
 
 [source,shellsession]

src/main.cpp

@@ -28,6 +28,7 @@
 #include <fmt/format.h>
 #include <fmt/ostream.h> // For compatibility with fmt 4.
 
+#include <chrono>
 #include <clocale>
 #include <cmath>
 #include <cstdint>
@@ -141,6 +142,7 @@ int main(int argc, char *argv[])
     vector<vector<search::match>> matches_all;
     std::mutex mutex_matches_all;
     vector<std::future<int>> futurepool;
+    std::atomic<size_t> books_searched{0};
 
     auto search_file{
         [&opts, &matches_all, &mutex_matches_all,
@@ -188,7 +190,7 @@ int main(int argc, char *argv[])
         }};
 
     auto futures_cleanup{
-        [&futurepool, &return_code](const bool wait = false)
+        [&futurepool, &return_code, &books_searched](const bool wait = false)
         {
             using namespace std::chrono_literals;
 
@@ -208,6 +210,7 @@ int main(int argc, char *argv[])
                     }
                 }
                 futurepool.erase(it);
+                ++books_searched;
             }
         }};
 
@@ -219,6 +222,26 @@ int main(int argc, char *argv[])
         }()};
     DEBUGLOG << "max_threads = " << max_threads;
 
+    const auto print_status{
+        [&opts, &books_searched, &input_files](std::future<bool> cancel)
+        {
+            if (!opts.status)
+            {
+                return;
+            }
+            while (cancel.wait_for(std::chrono::seconds(opts.status_interval))
+                   != std::future_status::ready)
+            {
+                std::cerr
+                    << format(translate("{0:d} of {1:d} books searched.").str(),
+                              books_searched, input_files.size())
+                    << '\n';
+            }
+            std::cerr << translate("All books searched.") << '\n';
+        }};
+    std::promise<bool> promise_status;
+    std::thread thread_status{print_status, promise_status.get_future()};
+
     for (const auto &filepath : input_files)
     {
         while (futurepool.size() >= max_threads)
@@ -244,6 +267,8 @@ int main(int argc, char *argv[])
     }
     DEBUGLOG << "Waiting for remaining threads to finish";
     futures_cleanup(true);
+    promise_status.set_value(true);
+    thread_status.join();
     if (return_code == EXIT_FATAL)
     {
         return EXIT_FATAL;

src/options.cpp

@@ -88,15 +88,22 @@ options parse_options(int argc, char *argv[])
          .str().data())
         ("dereference-recursive,R",
          translate("Read all files under each directory, recursively, "
-                   "following symlinks.") .str().data())
+                   "following symlinks.").str().data())
         ("ignore-archive-errors",
-         translate("Ignore errors about wrong file formats.") .str().data())
+         translate("Ignore errors about wrong file formats.").str().data())
         ("debug",
-         translate("Enable debug output.") .str().data())
+         translate("Enable debug output.").str().data())
         ("json",
-         translate("Output JSON instead of plain text.") .str().data())
+         translate("Output JSON instead of plain text.").str().data())
         ("html",
-         translate("Output HTML instead of plain text.") .str().data())
+         translate("Output HTML instead of plain text.").str().data())
+        ("status",
+         translate("Output status message every STATUS-INTERVAL seconds")
+         .str().data())
+        ("status-interval", po::value<std::uint64_t>()
+         ->value_name(translate("NUMBER"))->default_value(30),
+         translate("Set status message interval to NUMBER seconds.")
+         .str().data())
     ;
 
     po::options_description options_hidden("Hidden options");
@@ -238,6 +245,8 @@ options parse_again(const po::variables_map &vm)
     opts.debug = vm.count("debug") > 0;
     opts.json = vm.count("json") > 0;
     opts.html = vm.count("html") > 0;
+    opts.status = vm.count("status") > 0;
+    opts.status_interval = vm["status-interval"].as<std::uint64_t>();
 
     if (vm.count("regexp") > 0)
     {

src/options.hpp

@@ -59,6 +59,8 @@ struct options
     bool debug{false};
     bool json{false};
     bool html{false};
+    bool status{false};
+    uint64_t status_interval{0};
 
     //! For the debug output.
     friend std::ostream &operator<<(std::ostream &out, const options &opts);