cli:run: add more error checking to running single files, add dry-run…

… option, small fixes

src/pymcnp/cli/run.py

@@ -6,15 +6,19 @@
     -p --parallel=<threads>       Run files in parallel on <threads> threads.
     -c --command=<command>        Command to run.
     -P --path=<path>              Path to use.
+    -n --dry-run                  Don't run or create directories, just print what would happen
 """
 
 import os
 import inspect
+from pathlib import Path
+import shutil
+import subprocess
 import sys
 from typing import Final
-from pathlib import Path
 
 from docopt import docopt
+from rich import print
 
 from ..files.inp import Inp, read_input
 from . import _io
@@ -41,18 +45,20 @@ class Run:
     def __init__(
         self,
         inp: Inp,
-        path: str | Path = '.',
+        path: str | Path = Path('.'),
         command: str = 'mcnp6',
+        dry_run: bool = False,
     ):
         """
         Parameters:
             path: Path to directory to store run inputs and outputs.
             command: Terminal command to execute.
         """
 
-        self.path: Final[str] = Path(path)
+        self.path: Final[Path] = Path(path)
         self.command: Final[str] = command
         self.inp: Final[Inp] = inp
+        self.dry_run: bool = dry_run
 
     @staticmethod
     def prehook():
@@ -70,9 +76,14 @@ def parallel_prehook():
     def parallel_posthook():
         pass
 
+    def check_prog(self, name: str) -> None:
+        if shutil.which(name) is None:
+            print(f'[red]ERROR[/] Cannot find {name} program.')
+            sys.exit(3)
+
     def run_single(self) -> Path:
         """
-        Runs MCNP INP files.
+        Runs a MCNP INP files.
 
         ``run_single`` creates a directory to store a copy of the input file
         passed to MCNP and the outputfiles generated by MCNP.
@@ -83,14 +94,27 @@ def run_single(self) -> Path:
 
         timestamp = _io.get_timestamp()
 
-        directory_path = self.path / f'pymcnp-run-{timestamp}'
-        directory_path.mkdir(exist_ok=False, parents=True)
+        self.check_prog(self.command)
 
+        directory_path = self.path / f'pymcnp-run-{timestamp}'
         inp_path = directory_path / f'pymcnp-inp-{timestamp}.inp'
+
+        command_to_run = f'{self.command} i={inp_path.name}'
+
+        if self.dry_run:
+            print('[yellow]INFO[/] Would run:')
+            print(f'   create {directory_path}')
+            print(f'   save {inp_path}')
+            print('   executing prehook')
+            print(f'   {command_to_run}')
+            print('   executing posthook')
+            return directory_path
+
+        directory_path.mkdir(exist_ok=False, parents=True)
         self.inp.to_mcnp_file(inp_path)
 
         self.prehook()
-        os.system(f'{self.command} i={inp_path}')
+        subprocess.run(command_to_run, cwd=directory_path, shell=True)
         self.posthook()
 
         return directory_path
@@ -114,6 +138,9 @@ def run_parallel(self, count: int) -> Path:
         if count <= 0:
             _io.error('Invalid Count.')
 
+        self.check_prog(self.command)
+        self.check_prog('parallel')
+
         timestamp = _io.get_timestamp()
 
         directory_path = self.path / f'pymcnp-runs-{timestamp}'
@@ -177,8 +204,9 @@ def main() -> None:
     inp = read_input(args['<file>'])
     command = args['--command'] if args['--command'] else 'mcnp6'
     path = args['--path'] if args['--path'] else Path.cwd()
+    dry_run = args['--dry-run']
 
-    run = Run(inp, path=path, command=command)
+    run = Run(inp, path=path, command=command, dry_run=dry_run)
 
     if args['--parallel'] is not None:
         run.run_parallel(int(args['--parallel']))