Add companion application

cmd/companion/config.go

@@ -0,0 +1,92 @@
+package main
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime"
+)
+
+const defaultPort = 17680
+
+type config struct {
+	WikiRoot       string   `json:"wikiRoot"`
+	AllowedOrigins []string `json:"allowedOrigins"`
+	Port           int      `json:"port,omitempty"`
+}
+
+// configPath returns the platform-conventional config path.
+//
+// Windows: %APPDATA%\datascape\companion.json
+// Linux:   $XDG_CONFIG_HOME/datascape/companion.json
+//          (fallback ~/.config/datascape/companion.json)
+func configPath() (string, error) {
+	if runtime.GOOS == "windows" {
+		appData := os.Getenv("APPDATA")
+		if appData == "" {
+			return "", errors.New("APPDATA not set")
+		}
+		return filepath.Join(appData, "datascape", "companion.json"), nil
+	}
+	if x := os.Getenv("XDG_CONFIG_HOME"); x != "" {
+		return filepath.Join(x, "datascape", "companion.json"), nil
+	}
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(home, ".config", "datascape", "companion.json"), nil
+}
+
+// loadOrInitConfig reads the on-disk config, creating a default file if none
+// exists. Returns the resolved config (with port defaulted) and the path.
+func loadOrInitConfig() (*config, string, error) {
+	p, err := configPath()
+	if err != nil {
+		return nil, "", err
+	}
+	data, err := os.ReadFile(p)
+	if errors.Is(err, os.ErrNotExist) {
+		cfg := &config{AllowedOrigins: []string{}, Port: defaultPort}
+		if err := writeConfigFile(p, cfg); err != nil {
+			return nil, p, err
+		}
+		return cfg, p, nil
+	}
+	if err != nil {
+		return nil, p, err
+	}
+	var cfg config
+	if err := json.Unmarshal(data, &cfg); err != nil {
+		return nil, p, fmt.Errorf("parse config: %w", err)
+	}
+	if cfg.Port == 0 {
+		cfg.Port = defaultPort
+	}
+	if cfg.AllowedOrigins == nil {
+		cfg.AllowedOrigins = []string{}
+	}
+	return &cfg, p, nil
+}
+
+// writeConfigFile atomically writes cfg to p (write-temp + rename).
+func writeConfigFile(p string, cfg *config) error {
+	if err := os.MkdirAll(filepath.Dir(p), 0755); err != nil {
+		return err
+	}
+	out := *cfg
+	if out.AllowedOrigins == nil {
+		out.AllowedOrigins = []string{}
+	}
+	data, err := json.MarshalIndent(out, "", "  ")
+	if err != nil {
+		return err
+	}
+	tmp := p + ".tmp"
+	if err := os.WriteFile(tmp, data, 0644); err != nil {
+		return err
+	}
+	return os.Rename(tmp, p)
+}