Initial commit: monitor-lets-go — automatic monitor layout daemon

internal/hook/hook.go

@@ -0,0 +1,78 @@
+// Package hook runs shell commands after monitor layout changes.
+// Hooks execute asynchronously with a timeout; failures are logged
+// but never interrupt the daemon's operation.
+package hook
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"os"
+	"os/exec"
+	"strings"
+	"time"
+)
+
+const defaultTimeout = 30 * time.Second
+
+// Runner executes shell commands from the hooks configuration.
+type Runner struct {
+	logger *slog.Logger
+}
+
+// NewRunner creates a hook runner with the given logger.
+func NewRunner(logger *slog.Logger) *Runner {
+	return &Runner{logger: logger}
+}
+
+// Run executes a list of shell commands concurrently. Each command gets
+// a separate sub-shell via "sh -c". If a command exceeds defaultTimeout,
+// it is killed. Errors are logged but never returned.
+//
+// Commands undergo basic shell-like expansion for tildes and environment
+// variables before execution.
+func (r *Runner) Run(ctx context.Context, commands []string) {
+	for _, cmdStr := range commands {
+		cmdStr = strings.TrimSpace(cmdStr)
+		if cmdStr == "" {
+			continue
+		}
+
+		go func(cmdStr string) {
+			if err := r.runOne(ctx, cmdStr); err != nil {
+				r.logger.Error("hook failed", "command", cmdStr, "error", err)
+			}
+		}(cmdStr)
+	}
+}
+
+// runOne executes a single command with a timeout.
+func (r *Runner) runOne(ctx context.Context, cmdStr string) error {
+	cmdStr = expandPath(cmdStr)
+
+	cmdCtx, cancel := context.WithTimeout(ctx, defaultTimeout)
+	defer cancel()
+
+	r.logger.Debug("running hook", "command", cmdStr)
+
+	cmd := exec.CommandContext(cmdCtx, "sh", "-c", cmdStr)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("hook: %w", err)
+	}
+	return nil
+}
+
+// expandPath performs basic tilde and $HOME expansion.
+func expandPath(s string) string {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return s
+	}
+	s = strings.ReplaceAll(s, "~", home)
+	s = strings.ReplaceAll(s, "$HOME", home)
+	s = strings.ReplaceAll(s, "${HOME}", home)
+	return s
+}