Add automatic default selection to challenge/implementation selection

This is triggered in the event there is only 1 challenge/implementation

runtime/main.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"fmt"
-	"github.com/AlecAivazis/survey/v2"
 	"github.com/codemicro/adventOfCode/runtime/challenge"
 	"github.com/codemicro/adventOfCode/runtime/runners"
 	"io/ioutil"
@@ -14,74 +13,22 @@ const (
 	challengeInfoFile = "info.json"
 )
 
-func userSelect(question string, choices []string) (int, error) {
-	var o string
-	prompt := &survey.Select{
-		Message: question,
-		Options: choices,
-	}
-	err := survey.AskOne(prompt, &o)
-	if err != nil {
-		return 0, err
-	}
-
-	for i, x := range choices {
-		if x == o {
-			return i, nil
-		}
-	}
-
-	return -1, nil
-}
-
 func run() error {
 
 	// List and select challenges
 
-	challenges, err := challenge.ListingFromDir(challengeDir)
+	selectedChallenge, err := selectChallenge(challengeDir)
 	if err != nil {
 		return err
 	}
 
-	var selectedChallengeIndex int
-	{
-		var opts []string
-		for _, c := range challenges {
-			opts = append(opts, c.String())
-		}
-
-		chosen, err := userSelect("Which challenge do you want to run?", opts)
-		if err != nil {
-			return err
-		}
-
-		selectedChallengeIndex = chosen
-	}
-	selectedChallenge := challenges[selectedChallengeIndex]
-
 	// List and select implementations
 
-	implementations, err := selectedChallenge.GetImplementations()
+	selectedImplementation, err := selectImplementation(selectedChallenge)
 	if err != nil {
 		return err
 	}
 
-	var selectedImplementationIndex int
-	{
-		var opts []string
-		for _, i := range implementations {
-			opts = append(opts, runners.RunnerNames[i])
-		}
-
-		chosen, err := userSelect("Which implementation do you want to use?", opts)
-		if err != nil {
-			return err
-		}
-
-		selectedImplementationIndex = chosen
-	}
-	selectedImplementation := implementations[selectedImplementationIndex]
-
 	// Load info.json file
 	challengeInfo, err := challenge.LoadChallengeInfo(filepath.Join(selectedChallenge.Dir, challengeInfoFile))
 	if err != nil {

runtime/selections.go

@@ -0,0 +1,90 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"github.com/AlecAivazis/survey/v2"
+	"github.com/codemicro/adventOfCode/runtime/challenge"
+	"github.com/codemicro/adventOfCode/runtime/runners"
+)
+
+func userSelect(question string, choices []string) (int, error) {
+	var o string
+	prompt := &survey.Select{
+		Message: question,
+		Options: choices,
+	}
+	err := survey.AskOne(prompt, &o)
+	if err != nil {
+		return 0, err
+	}
+
+	for i, x := range choices {
+		if x == o {
+			return i, nil
+		}
+	}
+
+	return -1, nil
+}
+
+func selectChallenge(dir string) (*challenge.Challenge, error) {
+
+	challenges, err := challenge.ListingFromDir(dir)
+	if err != nil {
+		return nil, err
+	}
+
+	var selectedChallengeIndex int
+
+	switch len(challenges) {
+	case 0:
+		return nil, errors.New("no challenges to run")
+	case 1:
+		selectedChallengeIndex = 0
+		c := challenges[0]
+		fmt.Printf("Automatically selecting day %d (%s)\n", c.Number, c.Name)
+	default:
+		var opts []string
+		for _, c := range challenges {
+			opts = append(opts, c.String())
+		}
+
+		selectedChallengeIndex, err = userSelect("Which challenge do you want to run?", opts)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return challenges[selectedChallengeIndex], nil
+}
+
+func selectImplementation(ch *challenge.Challenge) (string, error) {
+
+	implementations, err := ch.GetImplementations()
+	if err != nil {
+		return "", err
+	}
+
+	var selectedImplementationIndex int
+
+	switch len(implementations) {
+	case 0:
+		return "", errors.New("no implementations to use")
+	case 1:
+		selectedImplementationIndex = 0
+		fmt.Printf("Automatically selecting implementation %s", runners.RunnerNames[implementations[0]])
+	default:
+		var opts []string
+		for _, i := range implementations {
+			opts = append(opts, runners.RunnerNames[i])
+		}
+
+		selectedImplementationIndex, err = userSelect("Which implementation do you want to use?", opts)
+		if err != nil {
+			return "", err
+		}
+	}
+
+	return implementations[selectedImplementationIndex], nil
+}