Show a friendly hint for adb installation

Signed-off-by: Romain Vimont <rom@rom1v.com>

app/src/command.c

@@ -55,6 +55,28 @@ argv_to_string(const char *const *argv, char *buf, size_t bufsize) {
     return idx;
 }
 
+static void
+show_adb_installation_msg() {
+    static const struct {
+        const char *binary;
+        const char *command;
+    } pkg_managers[] = {
+        {"apt", "apt install adb"},
+        {"apt-get", "apt-get install adb"},
+        {"brew", "brew install android-platform-tools"},
+        {"dnf", "dnf install android-tools"},
+    };
+    for (size_t i = 0; i < ARRAY_LEN(pkg_managers); ++i) {
+        if (cmd_search(pkg_managers[i].binary)) {
+            LOGI("You may install 'adb' by \"%s\"", pkg_managers[i].command);
+            return;
+        }
+    }
+
+    LOGI("You may download and install 'adb' from "
+         "https://developer.android.com/studio/releases/platform-tools");
+}
+
 static void
 show_adb_err_msg(enum process_result err, const char *const argv[]) {
     char buf[512];
@@ -68,6 +90,7 @@ show_adb_err_msg(enum process_result err, const char *const argv[]) {
             LOGE("Command not found: %s", buf);
             LOGE("(make 'adb' accessible from your PATH or define its full"
                  "path in the ADB environment variable)");
+            show_adb_installation_msg();
             break;
         case PROCESS_SUCCESS:
             // do nothing

app/src/command.h

@@ -43,6 +43,9 @@ enum process_result {
     PROCESS_ERROR_MISSING_BINARY,
 };
 
+bool
+cmd_search(const char *file);
+
 enum process_result
 cmd_execute(const char *const argv[], process_t *process);
 

app/src/sys/unix/command.c

@@ -14,6 +14,7 @@
 #include <limits.h>
 #include <signal.h>
 #include <stdlib.h>
+#include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/wait.h>
@@ -21,6 +22,42 @@
 
 #include "util/log.h"
 
+bool
+cmd_search(const char *file) {
+    char *path = getenv("PATH");
+    if (!path)
+        return false;
+    path = strdup(path);
+    if (!path)
+        return false;
+
+    bool ret = false;
+    size_t file_len = strlen(file);
+    char *saveptr;
+    for (char *dir = strtok_r(path, ":", &saveptr); dir;
+            dir = strtok_r(NULL, ":", &saveptr)) {
+        size_t dir_len = strlen(dir);
+        char *fullpath = malloc(dir_len + file_len + 2);
+        if (!fullpath)
+            continue;
+        memcpy(fullpath, dir, dir_len);
+        fullpath[dir_len] = '/';
+        memcpy(fullpath + dir_len + 1, file, file_len + 1);
+
+        struct stat sb;
+        bool fullpath_executable = stat(fullpath, &sb) == 0 &&
+            sb.st_mode & S_IXUSR;
+        free(fullpath);
+        if (fullpath_executable) {
+            ret = true;
+            break;
+        }
+    }
+
+    free(path);
+    return ret;
+}
+
 enum process_result
 cmd_execute(const char *const argv[], pid_t *pid) {
     int fd[2];

app/src/sys/win/command.c

@@ -6,6 +6,12 @@
 #include "util/log.h"
 #include "util/str_util.h"
 
+bool
+cmd_search(const char *file) {
+    // :/
+    return false;
+}
+
 static int
 build_cmd(char *cmd, size_t len, const char *const argv[]) {
     // Windows command-line parsing is WTF: