first commit

internal/config/config.go

@@ -0,0 +1,143 @@
+// Package config reads and writes data/settings.conf, a plain key=value
+// file holding non-secret app settings plus the AES key (app_secret) used
+// to encrypt exchange credentials stored in the database.
+package config
+
+import (
+	"bufio"
+	"crypto/rand"
+	"encoding/hex"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"sync"
+)
+
+type Config struct {
+	Port                  int
+	PollIntervalSeconds   int
+	HistoryRefreshSeconds int
+	DBPath                string
+	AppSecret             []byte // 32 bytes, AES-256 key
+	path                  string
+
+	mu           sync.RWMutex
+	baseCurrency string // guarded by mu: changeable at runtime via the settings page
+}
+
+func defaults() *Config {
+	return &Config{
+		Port:                  8080,
+		PollIntervalSeconds:   60,
+		HistoryRefreshSeconds: 300,
+		DBPath:                "data/app.db",
+		baseCurrency:          "GBP",
+	}
+}
+
+// Load reads path, creating it with defaults (and a fresh random app_secret)
+// if it doesn't exist yet.
+func Load(path string) (*Config, error) {
+	cfg := defaults()
+	cfg.path = path
+
+	f, err := os.Open(path)
+	if os.IsNotExist(err) {
+		secret := make([]byte, 32)
+		if _, err := rand.Read(secret); err != nil {
+			return nil, fmt.Errorf("generate app_secret: %w", err)
+		}
+		cfg.AppSecret = secret
+		if err := cfg.save(); err != nil {
+			return nil, err
+		}
+		return cfg, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	values := map[string]string{}
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue
+		}
+		k, v, ok := strings.Cut(line, "=")
+		if !ok {
+			continue
+		}
+		values[strings.TrimSpace(k)] = strings.TrimSpace(v)
+	}
+	if err := scanner.Err(); err != nil {
+		return nil, err
+	}
+
+	if v, ok := values["port"]; ok {
+		if n, err := strconv.Atoi(v); err == nil {
+			cfg.Port = n
+		}
+	}
+	if v, ok := values["poll_interval_seconds"]; ok {
+		if n, err := strconv.Atoi(v); err == nil {
+			cfg.PollIntervalSeconds = n
+		}
+	}
+	if v, ok := values["history_refresh_seconds"]; ok {
+		if n, err := strconv.Atoi(v); err == nil {
+			cfg.HistoryRefreshSeconds = n
+		}
+	}
+	if v, ok := values["db_path"]; ok && v != "" {
+		cfg.DBPath = v
+	}
+	if v, ok := values["base_currency"]; ok && v != "" {
+		cfg.baseCurrency = strings.ToUpper(v)
+	}
+	secretHex, ok := values["app_secret"]
+	if !ok || secretHex == "" {
+		return nil, fmt.Errorf("settings.conf missing app_secret")
+	}
+	secret, err := hex.DecodeString(secretHex)
+	if err != nil || len(secret) != 32 {
+		return nil, fmt.Errorf("settings.conf app_secret must be 32 random bytes hex-encoded")
+	}
+	cfg.AppSecret = secret
+
+	return cfg, nil
+}
+
+// BaseCurrency is the fiat currency (e.g. "GBP") all values are shown in.
+func (c *Config) BaseCurrency() string {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return c.baseCurrency
+}
+
+// SetBaseCurrency updates and persists the base currency.
+func (c *Config) SetBaseCurrency(v string) error {
+	v = strings.ToUpper(strings.TrimSpace(v))
+	if v == "" {
+		return fmt.Errorf("base currency required")
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.baseCurrency = v
+	return c.save()
+}
+
+// save must be called with mu held (directly or via the zero-value path
+// during Load, before the Config is shared across goroutines).
+func (c *Config) save() error {
+	var b strings.Builder
+	fmt.Fprintf(&b, "port=%d\n", c.Port)
+	fmt.Fprintf(&b, "poll_interval_seconds=%d\n", c.PollIntervalSeconds)
+	fmt.Fprintf(&b, "history_refresh_seconds=%d\n", c.HistoryRefreshSeconds)
+	fmt.Fprintf(&b, "db_path=%s\n", c.DBPath)
+	fmt.Fprintf(&b, "base_currency=%s\n", c.baseCurrency)
+	fmt.Fprintf(&b, "app_secret=%s\n", hex.EncodeToString(c.AppSecret))
+	return os.WriteFile(c.path, []byte(b.String()), 0600)
+}