Log more when resolving Python (#4185)

* Log more when resolving Python

Users often have problems configuring their Python installations

* Convert if-else ladder to switch statement
* Consolidate Python resolution

Adds additional logging to plugin tasks to
align with the logging that scrapers output.

pkg/python/exec.go

@@ -2,9 +2,12 @@ package python
 
 import (
 	"context"
+	"fmt"
 	"os/exec"
 
 	stashExec "github.com/stashapp/stash/pkg/exec"
+	"github.com/stashapp/stash/pkg/fsutil"
+	"github.com/stashapp/stash/pkg/logger"
 )
 
 type Python string
@@ -22,19 +25,32 @@ func New(path string) *Python {
 // Resolve tries to find the python executable in the system.
 // It first checks for python3, then python.
 // Returns nil and an exec.ErrNotFound error if not found.
-func Resolve() (*Python, error) {
-	_, err := exec.LookPath("python3")
+func Resolve(configuredPythonPath string) (*Python, error) {
+	if configuredPythonPath != "" {
+		isFile, err := fsutil.FileExists(configuredPythonPath)
+		switch {
+		case err == nil && isFile:
+			logger.Tracef("using configured python path: %s", configuredPythonPath)
+			return New(configuredPythonPath), nil
+		case err == nil && !isFile:
+			logger.Warnf("configured python path is not a file: %s", configuredPythonPath)
+		case err != nil:
+			logger.Warnf("unable to use configured python path: %s", err)
+		}
+	}
+
+	python3, err := exec.LookPath("python3")
 
 	if err != nil {
-		_, err = exec.LookPath("python")
+		python, err := exec.LookPath("python")
 		if err != nil {
-			return nil, err
+			return nil, fmt.Errorf("python executable not in PATH: %s", err)
 		}
-		ret := Python("python")
+		ret := Python(python)
 		return &ret, nil
 	}
 
-	ret := Python("python3")
+	ret := Python(python3)
 	return &ret, nil
 }