// Package config loads and validates server configuration from environment
// variables and optional config files. It provides a single Config struct
// consumed by all other packages at startup.
package config

import (
	"fmt"
	"os"
	"strconv"
)

// Config holds all application-level configuration.
// All environment variables use the PANGOLIN_ prefix (12-factor app style).
type Config struct {
	// HTTPAddr is the public HTTP API listen address.
	// Env: PANGOLIN_HTTP_ADDR  Default: :8080
	HTTPAddr string

	// AdminAddr is the internal admin gRPC listen address.
	// Placeholder for task #5.
	// Env: PANGOLIN_ADMIN_ADDR  Default: :9090
	AdminAddr string

	// GRPCAddr is the data-plane gRPC listen address.
	// Placeholder for task #7.
	// Env: PANGOLIN_GRPC_ADDR  Default: :9091
	GRPCAddr string

	// MySQL connection. Set either MySQLDSN or the individual fields.
	// If MySQLDSN is set the individual fields are ignored.
	MySQLDSN      string // PANGOLIN_MYSQL_DSN
	MySQLHost     string // PANGOLIN_MYSQL_HOST  (required when no DSN)
	MySQLPort     string // PANGOLIN_MYSQL_PORT  Default: 3306
	MySQLUser     string // PANGOLIN_MYSQL_USER  (required when no DSN)
	MySQLPassword string // PANGOLIN_MYSQL_PASSWORD
	MySQLDBName   string // PANGOLIN_MYSQL_DBNAME  (required when no DSN)

	// RedisAddr is the Redis server address.
	// Env: PANGOLIN_REDIS_ADDR  Default: 127.0.0.1:6379
	RedisAddr string

	// AutoMigrate controls whether database migrations run at startup.
	// Env: PANGOLIN_AUTO_MIGRATE=true|false  Default: false
	AutoMigrate bool

	// JWTSecret is the HS256 signing key.
	// Placeholder for task #2 (auth middleware).
	// Env: PANGOLIN_JWT_SECRET
	JWTSecret string

	// WebhookSecret is the HMAC-SHA256 shared secret for card-store webhooks.
	// Env: PANGOLIN_WEBHOOK_SECRET
	WebhookSecret string
}

// Load reads Config from environment variables.
// Returns an error listing any missing required variables.
func Load() (Config, error) {
	c := Config{
		HTTPAddr:      envOr("PANGOLIN_HTTP_ADDR", ":8080"),
		AdminAddr:     envOr("PANGOLIN_ADMIN_ADDR", ":9090"),
		GRPCAddr:      envOr("PANGOLIN_GRPC_ADDR", ":9091"),
		MySQLDSN:      os.Getenv("PANGOLIN_MYSQL_DSN"),
		MySQLHost:     os.Getenv("PANGOLIN_MYSQL_HOST"),
		MySQLPort:     envOr("PANGOLIN_MYSQL_PORT", "3306"),
		MySQLUser:     os.Getenv("PANGOLIN_MYSQL_USER"),
		MySQLPassword: os.Getenv("PANGOLIN_MYSQL_PASSWORD"),
		MySQLDBName:   os.Getenv("PANGOLIN_MYSQL_DBNAME"),
		RedisAddr:     envOr("PANGOLIN_REDIS_ADDR", "127.0.0.1:6379"),
		JWTSecret:     os.Getenv("PANGOLIN_JWT_SECRET"),
		WebhookSecret: os.Getenv("PANGOLIN_WEBHOOK_SECRET"),
	}

	if v := os.Getenv("PANGOLIN_AUTO_MIGRATE"); v != "" {
		b, err := strconv.ParseBool(v)
		if err != nil {
			return Config{}, fmt.Errorf("config: PANGOLIN_AUTO_MIGRATE=%q: %w", v, err)
		}
		c.AutoMigrate = b
	}

	// Validate: either full DSN or individual connection fields must be set.
	if c.MySQLDSN == "" {
		var missing []string
		if c.MySQLHost == "" {
			missing = append(missing, "PANGOLIN_MYSQL_HOST")
		}
		if c.MySQLUser == "" {
			missing = append(missing, "PANGOLIN_MYSQL_USER")
		}
		if c.MySQLDBName == "" {
			missing = append(missing, "PANGOLIN_MYSQL_DBNAME")
		}
		if len(missing) > 0 {
			return Config{}, fmt.Errorf("config: required env vars not set: %v (or set PANGOLIN_MYSQL_DSN)", missing)
		}
	}

	return c, nil
}

func envOr(key, def string) string {
	if v := os.Getenv(key); v != "" {
		return v
	}
	return def
}