[fp-enhancer] Apply functional programming and immutability improvements

pkg/sliceutil/sliceutil.go

@@ -27,3 +27,36 @@ func ContainsAny(s string, substrings ...string) bool {
 func ContainsIgnoreCase(s, substr string) bool {
 	return strings.Contains(strings.ToLower(s), strings.ToLower(substr))
 }
+
+// Filter returns a new slice containing only elements that match the predicate.
+// This is a pure function that does not modify the input slice.
+func Filter[T any](slice []T, predicate func(T) bool) []T {
+	result := make([]T, 0, len(slice))
+	for _, item := range slice {
+		if predicate(item) {
+			result = append(result, item)
+		}
+	}
+	return result
+}
+
+// Map transforms each element in a slice using the provided function.
+// This is a pure function that does not modify the input slice.
+func Map[T, U any](slice []T, transform func(T) U) []U {
+	result := make([]U, len(slice))
+	for i, item := range slice {
+		result[i] = transform(item)
+	}
+	return result
+}
+
+// MapToSlice converts a map's keys to a slice.
+// The order of elements is not guaranteed as map iteration order is undefined.
+// This is a pure function that does not modify the input map.
+func MapToSlice[K comparable, V any](m map[K]V) []K {
+	result := make([]K, 0, len(m))
+	for key := range m {
+		result = append(result, key)
+	}
+	return result
+}

pkg/workflow/action_pins.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/githubnext/gh-aw/pkg/console"
 	"github.com/githubnext/gh-aw/pkg/logger"
+	"github.com/githubnext/gh-aw/pkg/sliceutil"
 )
 
 var actionPinsLog = logger.New("workflow:action_pins")
@@ -85,7 +86,7 @@ func getActionPins() []ActionPin {
 			actionPinsLog.Printf("Found %d key/version mismatches in action_pins.json", mismatchCount)
 		}
 
-		// Convert map to sorted slice
+		// Convert map values to slice - immutable initialization
 		pins := make([]ActionPin, 0, len(data.Entries))
 		for _, pin := range data.Entries {
 			pins = append(pins, pin)
@@ -109,16 +110,23 @@ func getActionPins() []ActionPin {
 	return cachedActionPins
 }
 
-// sortPinsByVersion sorts action pins by version in descending order (highest first)
-// Uses Go's standard library sort with custom comparison function
-func sortPinsByVersion(pins []ActionPin) {
-	sort.Slice(pins, func(i, j int) bool {
+// sortPinsByVersion sorts action pins by version in descending order (highest first).
+// This function returns a new sorted slice without modifying the input.
+// This is an immutable operation for better safety and clarity.
+func sortPinsByVersion(pins []ActionPin) []ActionPin {
+	// Create a copy to avoid mutating the input
+	result := make([]ActionPin, len(pins))
+	copy(result, pins)
+
+	sort.Slice(result, func(i, j int) bool {
 		// Strip 'v' prefix for comparison
-		v1 := strings.TrimPrefix(pins[i].Version, "v")
-		v2 := strings.TrimPrefix(pins[j].Version, "v")
+		v1 := strings.TrimPrefix(result[i].Version, "v")
+		v2 := strings.TrimPrefix(result[j].Version, "v")
 		// Return true if v1 > v2 to get descending order
 		return compareVersions(v1, v2) > 0
 	})
+
+	return result
 }
 
 // GetActionPin returns the pinned action reference for a given action repository
@@ -128,24 +136,21 @@ func sortPinsByVersion(pins []ActionPin) {
 func GetActionPin(actionRepo string) string {
 	actionPins := getActionPins()
 
-	// Find all pins matching the repo
-	var matchingPins []ActionPin
-	for _, pin := range actionPins {
-		if pin.Repo == actionRepo {
-			matchingPins = append(matchingPins, pin)
-		}
-	}
+	// Find all pins matching the repo - using functional filter
+	matchingPins := sliceutil.Filter(actionPins, func(pin ActionPin) bool {
+		return pin.Repo == actionRepo
+	})
 
 	if len(matchingPins) == 0 {
 		// If no pin exists, return empty string to signal that this action is not pinned
 		return ""
 	}
 
-	// Sort matching pins by version (descending - latest first)
-	sortPinsByVersion(matchingPins)
+	// Sort matching pins by version (descending - latest first) - immutable operation
+	sortedPins := sortPinsByVersion(matchingPins)
 
 	// Return the latest version (first after sorting)
-	latestPin := matchingPins[0]
+	latestPin := sortedPins[0]
 	return formatActionReference(actionRepo, latestPin.SHA, latestPin.Version)
 }
 
@@ -185,22 +190,19 @@ func GetActionPinWithData(actionRepo, version string, data *WorkflowData) (strin
 	actionPinsLog.Printf("Falling back to hardcoded pins for %s@%s", actionRepo, version)
 	actionPins := getActionPins()
 
-	// Find all pins matching the repo
-	var matchingPins []ActionPin
-	for _, pin := range actionPins {
-		if pin.Repo == actionRepo {
-			matchingPins = append(matchingPins, pin)
-		}
-	}
+	// Find all pins matching the repo - using functional filter
+	matchingPins := sliceutil.Filter(actionPins, func(pin ActionPin) bool {
+		return pin.Repo == actionRepo
+	})
 
 	if len(matchingPins) == 0 {
 		// No pins found for this repo, will handle below
 		actionPinsLog.Printf("No hardcoded pins found for %s", actionRepo)
 	} else {
 		actionPinsLog.Printf("Found %d hardcoded pin(s) for %s", len(matchingPins), actionRepo)
 
-		// Sort matching pins by version (descending - highest first)
-		sortPinsByVersion(matchingPins)
+		// Sort matching pins by version (descending - highest first) - immutable operation
+		matchingPins = sortPinsByVersion(matchingPins)
 
 		// First, try to find an exact version match (for version tags)
 		for _, pin := range matchingPins {
@@ -228,13 +230,10 @@ func GetActionPinWithData(actionRepo, version string, data *WorkflowData) (strin
 		// Semver compatibility means respecting major version boundaries
 		// (e.g., v5 -> highest v5.x.x, not v6.x.x)
 		if !data.StrictMode && len(matchingPins) > 0 {
-			// Filter for semver-compatible pins (matching major version)
-			var compatiblePins []ActionPin
-			for _, pin := range matchingPins {
-				if isSemverCompatible(pin.Version, version) {
-					compatiblePins = append(compatiblePins, pin)
-				}
-			}
+			// Filter for semver-compatible pins (matching major version) - using functional filter
+			compatiblePins := sliceutil.Filter(matchingPins, func(pin ActionPin) bool {
+				return isSemverCompatible(pin.Version, version)
+			})
 
 			// If we found compatible pins, use the highest one (first after sorting)
 			// Otherwise fall back to the highest overall pin
@@ -417,21 +416,18 @@ func ApplyActionPinsToTypedSteps(steps []*WorkflowStep, data *WorkflowData) []*W
 func GetActionPinByRepo(repo string) (ActionPin, bool) {
 	actionPins := getActionPins()
 
-	// Find all pins matching the repo
-	var matchingPins []ActionPin
-	for _, pin := range actionPins {
-		if pin.Repo == repo {
-			matchingPins = append(matchingPins, pin)
-		}
-	}
+	// Find all pins matching the repo - using functional filter
+	matchingPins := sliceutil.Filter(actionPins, func(pin ActionPin) bool {
+		return pin.Repo == repo
+	})
 
 	if len(matchingPins) == 0 {
 		return ActionPin{}, false
 	}
 
-	// Sort matching pins by version (descending - latest first)
-	sortPinsByVersion(matchingPins)
+	// Sort matching pins by version (descending - latest first) - immutable operation
+	sortedPins := sortPinsByVersion(matchingPins)
 
 	// Return the latest version (first after sorting)
-	return matchingPins[0], true
+	return sortedPins[0], true
 }

pkg/workflow/action_pins_test.go

@@ -831,11 +831,8 @@ func TestSortPinsByVersion(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			// Make a copy to avoid modifying the test case
-			result := make([]ActionPin, len(tt.input))
-			copy(result, tt.input)
-
-			sortPinsByVersion(result)
+			// sortPinsByVersion now returns a new sorted slice (immutable operation)
+			result := sortPinsByVersion(tt.input)
 
 			if len(result) != len(tt.expected) {
 				t.Errorf("sortPinsByVersion() length = %d, want %d", len(result), len(tt.expected))

pkg/workflow/env.go

@@ -6,6 +6,7 @@ import (
 	"strings"
 
 	"github.com/githubnext/gh-aw/pkg/logger"
+	"github.com/githubnext/gh-aw/pkg/sliceutil"
 )
 
 var envLog = logger.New("workflow:env")
@@ -20,11 +21,8 @@ func writeHeadersToYAML(yaml *strings.Builder, headers map[string]string, indent
 
 	envLog.Printf("Writing %d headers to YAML", len(headers))
 
-	// Sort keys for deterministic output
-	keys := make([]string, 0, len(headers))
-	for key := range headers {
-		keys = append(keys, key)
-	}
+	// Sort keys for deterministic output - using functional helper
+	keys := sliceutil.MapToSlice(headers)
 	sort.Strings(keys)
 
 	// Write each header with proper comma placement

pkg/workflow/mcp_config_custom.go

@@ -9,6 +9,7 @@ import (
 	"github.com/githubnext/gh-aw/pkg/console"
 	"github.com/githubnext/gh-aw/pkg/logger"
 	"github.com/githubnext/gh-aw/pkg/parser"
+	"github.com/githubnext/gh-aw/pkg/sliceutil"
 	"github.com/githubnext/gh-aw/pkg/types"
 )
 
@@ -316,10 +317,8 @@ func renderSharedMCPConfig(yaml *strings.Builder, toolName string, toolConfig ma
 		case "env":
 			if renderer.Format == "toml" {
 				fmt.Fprintf(yaml, "%senv = { ", renderer.IndentLevel)
-				envKeys := make([]string, 0, len(mcpConfig.Env))
-				for key := range mcpConfig.Env {
-					envKeys = append(envKeys, key)
-				}
+				// Using functional helper to extract map keys
+				envKeys := sliceutil.MapToSlice(mcpConfig.Env)
 				sort.Strings(envKeys)
 				for i, envKey := range envKeys {
 					if i > 0 {
@@ -390,10 +389,8 @@ func renderSharedMCPConfig(yaml *strings.Builder, toolName string, toolConfig ma
 			// TOML format for HTTP headers (Codex style)
 			if len(mcpConfig.Headers) > 0 {
 				fmt.Fprintf(yaml, "%shttp_headers = { ", renderer.IndentLevel)
-				headerKeys := make([]string, 0, len(mcpConfig.Headers))
-				for key := range mcpConfig.Headers {
-					headerKeys = append(headerKeys, key)
-				}
+				// Using functional helper to extract map keys
+				headerKeys := sliceutil.MapToSlice(mcpConfig.Headers)
 				sort.Strings(headerKeys)
 				for i, headerKey := range headerKeys {
 					if i > 0 {
@@ -409,10 +406,8 @@ func renderSharedMCPConfig(yaml *strings.Builder, toolName string, toolConfig ma
 				comma = ""
 			}
 			fmt.Fprintf(yaml, "%s\"headers\": {\n", renderer.IndentLevel)
-			headerKeys := make([]string, 0, len(mcpConfig.Headers))
-			for key := range mcpConfig.Headers {
-				headerKeys = append(headerKeys, key)
-			}
+			// Using functional helper to extract map keys
+			headerKeys := sliceutil.MapToSlice(mcpConfig.Headers)
 			sort.Strings(headerKeys)
 			for headerIndex, headerKey := range headerKeys {
 				headerComma := ","

pkg/workflow/mcp_setup_generator.go

@@ -67,6 +67,7 @@ import (
 
 	"github.com/githubnext/gh-aw/pkg/constants"
 	"github.com/githubnext/gh-aw/pkg/logger"
+	"github.com/githubnext/gh-aw/pkg/sliceutil"
 )
 
 var mcpSetupGeneratorLog = logger.New("workflow:mcp_setup_generator")
@@ -329,10 +330,7 @@ func (c *Compiler) generateMCPSetup(yaml *strings.Builder, tools map[string]any,
 		yaml.WriteString("        run: |\n")
 
 		// Generate individual tool files (sorted by name for stable code generation)
-		safeInputToolNames := make([]string, 0, len(workflowData.SafeInputs.Tools))
-		for toolName := range workflowData.SafeInputs.Tools {
-			safeInputToolNames = append(safeInputToolNames, toolName)
-		}
+		safeInputToolNames := sliceutil.MapToSlice(workflowData.SafeInputs.Tools)
 		sort.Strings(safeInputToolNames)
 
 		for _, toolName := range safeInputToolNames {
@@ -408,11 +406,8 @@ func (c *Compiler) generateMCPSetup(yaml *strings.Builder, tools map[string]any,
 
 		safeInputsSecrets := collectSafeInputsSecrets(workflowData.SafeInputs)
 		if len(safeInputsSecrets) > 0 {
-			// Sort env var names for consistent output
-			envVarNames := make([]string, 0, len(safeInputsSecrets))
-			for envVarName := range safeInputsSecrets {
-				envVarNames = append(envVarNames, envVarName)
-			}
+			// Sort env var names for consistent output - using functional helper
+			envVarNames := sliceutil.MapToSlice(safeInputsSecrets)
 			sort.Strings(envVarNames)
 
 			for _, envVarName := range envVarNames {
@@ -452,10 +447,8 @@ func (c *Compiler) generateMCPSetup(yaml *strings.Builder, tools map[string]any,
 			yaml.WriteString("        env:\n")
 
 			// Sort environment variable names for consistent output
-			envVarNames := make([]string, 0, len(mcpEnvVars))
-			for envVarName := range mcpEnvVars {
-				envVarNames = append(envVarNames, envVarName)
-			}
+			// Using functional helper to extract map keys
+			envVarNames := sliceutil.MapToSlice(mcpEnvVars)
 			sort.Strings(envVarNames)
 
 			// Write environment variables in sorted order
@@ -522,10 +515,8 @@ func (c *Compiler) generateMCPSetup(yaml *strings.Builder, tools map[string]any,
 
 		// Add user-configured environment variables
 		if len(gatewayConfig.Env) > 0 {
-			envVarNames := make([]string, 0, len(gatewayConfig.Env))
-			for envVarName := range gatewayConfig.Env {
-				envVarNames = append(envVarNames, envVarName)
-			}
+			// Using functional helper to extract map keys
+			envVarNames := sliceutil.MapToSlice(gatewayConfig.Env)
 			sort.Strings(envVarNames)
 
 			for _, envVarName := range envVarNames {
@@ -612,10 +603,8 @@ func (c *Compiler) generateMCPSetup(yaml *strings.Builder, tools map[string]any,
 			containerCmd += " -e GH_AW_SAFE_OUTPUTS_API_KEY"
 		}
 		if len(gatewayConfig.Env) > 0 {
-			envVarNames := make([]string, 0, len(gatewayConfig.Env))
-			for envVarName := range gatewayConfig.Env {
-				envVarNames = append(envVarNames, envVarName)
-			}
+			// Using functional helper to extract map keys
+			envVarNames := sliceutil.MapToSlice(gatewayConfig.Env)
 			sort.Strings(envVarNames)
 			for _, envVarName := range envVarNames {
 				containerCmd += " -e " + envVarName

pkg/workflow/sandbox.go

@@ -18,6 +18,7 @@ import (
 	"fmt"
 
 	"github.com/githubnext/gh-aw/pkg/logger"
+	"github.com/githubnext/gh-aw/pkg/sliceutil"
 )
 
 var sandboxLog = logger.New("workflow:sandbox")
@@ -166,11 +167,8 @@ func generateSRTConfigJSON(workflowData *WorkflowData) (string, error) {
 		}
 	}
 
-	// Convert to slice
-	allowedDomains := make([]string, 0, len(domainMap))
-	for domain := range domainMap {
-		allowedDomains = append(allowedDomains, domain)
-	}
+	// Convert map keys to slice - using functional helper
+	allowedDomains := sliceutil.MapToSlice(domainMap)
 	SortStrings(allowedDomains)
 
 	srtConfig := &SandboxRuntimeConfig{