Add watchCommand config option

watchCommand is specified as a list of strings. The first entry is the
application to run. The rest are arguments. Arguments don't need to be
quoted as the shell is not involved in running the command.
"{{vid}}" will be replaced with the Id of the video to watch.

The default command is still to call xdg-open with the YT URL

main.cpp

@@ -3,6 +3,7 @@
 #include "tui.h"
 #include "yt.h"
 #include "db.h"
+#include "subprocess.h"
 
 #include <algorithm>
 #include <cstdlib>
@@ -169,6 +170,17 @@ bool startswith(const std::string &what, const std::string &with)
     return what.substr(0, len) == with;
 }
 
+std::string replace(const std::string &str, const std::string &what, const std::string &with)
+{
+    const size_t replace_length = what.size();
+    std::string out = str;
+    size_t pos = 0;
+    while((pos = out.find(what, pos)) != std::string::npos) {
+        out.replace(pos, replace_length, with);
+    }
+    return out;
+}
+
 void select_channel_by_index(const int index) {
     if(clear_channels_on_change) {
         for(auto &[k, v]: videos) {
@@ -303,18 +315,30 @@ void action_mark_video_watched() {
     ch.load_info(db);
 }
 
+std::vector<std::string> watch_command = {"xdg-open", "https://youtube.com/watch?v={{vid}}"};
+
 void action_watch_video() {
     Channel &ch = channels.at(selected_channel);
     Video &video = videos[ch.id][selected_video];
 
-    const std::string url = "https://youtube.com/watch?v=";
-    const std::string cmd = "xdg-open \"" + url + video.id + "\" > /dev/null";
-    int rc = system(cmd.c_str());
-    if(rc) {
-        message_box("Failed to open browser", ("xdg-open failed with error " + std::to_string(rc)).c_str());
+    const char *cmdline[watch_command.size() + 1];
+    for(size_t i=0; i<watch_command.size(); i++) {
+        const std::string arg = replace(watch_command[i], "{{vid}}", video.id);
+        cmdline[i] = strdup(arg.c_str());
+    }
+    cmdline[watch_command.size()] = nullptr;
+
+    subprocess_s proc;
+    if(int rc = subprocess_create(cmdline, subprocess_option_inherit_environment, &proc); rc != 0) {
+        const std::string message = watch_command.at(0) + " failed with error " + std::to_string(rc);
+        message_box("Failed to run watch command", message);
     } else {
         video.set_flag(db, kWatched);
         ch.load_info(db);
+        subprocess_join(&proc, nullptr);
+        for(size_t i=0; i<watch_command.size(); i++) {
+            free((void*)cmdline[i]);
+        }
     }
 }
 
@@ -451,6 +475,15 @@ int main()
     if(config.count("database") && config["database"].is_string()) {
         database_filename = config["database"];
     }
+    if(config.count("watchCommand") && config["watchCommand"].is_array()) {
+        watch_command.clear();
+        for(const json &elem: config["watchCommand"]) {
+            if(!elem.is_string()) {
+                tui_abort("Configuration error: watchCommand element " + elem.dump() + " is not a string but " + elem.type_name() + ".");
+            }
+            watch_command.push_back(elem);
+        }
+    }
 
     db_init(database_filename);
     make_virtual_unwatched_channel();