feat: establish Orbit models, migrations and development baseline

internal/config/config.go

@@ -0,0 +1,46 @@
+package config
+
+import (
+	"errors"
+	"fmt"
+	"net"
+	"os"
+	"strconv"
+)
+
+type Config struct {
+	HTTPAddr string
+	MySQLDSN string
+	MaxOpen  int
+	MaxIdle  int
+}
+
+func Load() (Config, error) { return FromEnv(os.Getenv) }
+func FromEnv(get func(string) string) (Config, error) {
+	c := Config{HTTPAddr: get("ORBIT_HTTP_ADDR"), MySQLDSN: get("ORBIT_MYSQL_DSN"), MaxOpen: 20, MaxIdle: 5}
+	if c.HTTPAddr == "" {
+		c.HTTPAddr = "127.0.0.1:8080"
+	}
+	if _, _, err := net.SplitHostPort(c.HTTPAddr); err != nil {
+		return Config{}, errors.New("invalid ORBIT_HTTP_ADDR")
+	}
+	if c.MySQLDSN == "" {
+		return Config{}, errors.New("ORBIT_MYSQL_DSN is required")
+	}
+	for _, field := range []struct {
+		name string
+		dst  *int
+	}{{"ORBIT_DB_MAX_OPEN", &c.MaxOpen}, {"ORBIT_DB_MAX_IDLE", &c.MaxIdle}} {
+		if raw := get(field.name); raw != "" {
+			n, err := strconv.Atoi(raw)
+			if err != nil || n < 0 {
+				return Config{}, fmt.Errorf("%s must be a nonnegative integer", field.name)
+			}
+			*field.dst = n
+		}
+	}
+	if c.MaxOpen <= 0 || c.MaxIdle > c.MaxOpen {
+		return Config{}, errors.New("database pool requires 0 <= max_idle <= max_open and max_open > 0")
+	}
+	return c, nil
+}