// Package config loads the Email Agent runtime configuration from the
// environment.
//
// Values are read from process environment variables. In production those
// variables are provided by the host (for example by
// ~/.config/environment.d/10-secrets.conf) and passed into the container by
// docker-compose. Secret values are never written to disk by this package and
// must never be committed to the repository.
package config

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

// Defaults for the service. Port 8790 is recorded in AGENTS.md §9.
const (
	DefaultPort = 8790
	DefaultEnv  = "development"
	DefaultAddr = ":" + "8790"
	DefaultDB   = "data/email_agent.db"

	// IMAP defaults. Gmail IMAP is implicit TLS on 993. IPv4 is forced in the
	// dialer (AGENTS.md §9): IPv6 to Gmail is broken from .13.
	DefaultIMAPHost         = "imap.gmail.com"
	DefaultIMAPPort         = 993
	DefaultIMAPLookbackDays = 14
	DefaultIMAPMaxMessages  = 100
)

// Config is the fully resolved runtime configuration.
type Config struct {
	// Env is the deployment environment: "development" or "production".
	Env string

	// Addr is the TCP address the HTTP server listens on, e.g. ":8790".
	Addr string

	// Port is the TCP port the HTTP server listens on.
	Port int

	// DBPath is the filesystem path to the SQLite database file.
	DBPath string

	// SessionSecret signs session cookies for the login screen (FR auth).
	// Login itself is implemented in Phase 1.2; the value is loaded here so the
	// service has a single configuration surface.
	SessionSecret string

	// Password is the single-user login password. When it is empty the service
	// falls back to SessionSecret so one configured secret is enough. Secret.
	Password string

	// LogLevel controls slog verbosity: debug, info, warn, error.
	LogLevel string

	// PublicBaseURL is the externally visible base URL of the service.
	PublicBaseURL string

	// Integration settings. These are loaded for later phases so that secret
	// names are defined in one place. Phase 1 does not use them.

	// JEVBaseURL is the base URL of the JEV/TypeSafe HTTP API.
	JEVBaseURL string
	// JEVAPIKey authenticates to JEV. Secret.
	JEVAPIKey string

	// OmniRouteBaseURL is the base URL of the OmniRoute gateway.
	OmniRouteBaseURL string
	// OmniRouteAPIKey authenticates to OmniRoute. Secret.
	OmniRouteAPIKey string

	// GmailUser is the Gmail account that receives the forwarded mail.
	// Secret (half of the app-password pair).
	GmailUser string
	// GmailAppPassword is the Gmail app password used for IMAP and, later, SMTP.
	// Secret. AGENTS.md §9: app password only, no OAuth.
	GmailAppPassword string
	// IMAPHost is the Gmail IMAP host (default imap.gmail.com).
	IMAPHost string
	// IMAPPort is the Gmail IMAP port (default 993, implicit TLS).
	IMAPPort int
	// IMAPLookbackDays bounds the first scan window.
	IMAPLookbackDays int
	// IMAPMaxMessages caps how many messages one scan fetches.
	IMAPMaxMessages int

	// HubToken authenticates the read-only Hub API. Secret.
	HubToken string
}

// Load reads configuration from the environment, applying defaults.
func Load() (*Config, error) {
	c := &Config{
		Env:              getenvDefault("EMAIL_AGENT_ENV", DefaultEnv),
		SessionSecret:    os.Getenv("EMAIL_AGENT_SESSION_SECRET"),
		Password:         os.Getenv("EMAIL_AGENT_PASSWORD"),
		LogLevel:         strings.ToLower(getenvDefault("EMAIL_AGENT_LOG_LEVEL", "info")),
		PublicBaseURL:    strings.TrimRight(getenvDefault("EMAIL_AGENT_PUBLIC_BASE_URL", "http://localhost:8790"), "/"),
		JEVBaseURL:       strings.TrimRight(os.Getenv("JEV_BASE_URL"), "/"),
		JEVAPIKey:        os.Getenv("JEV_API_KEY"),
		OmniRouteBaseURL: strings.TrimRight(os.Getenv("OMNIROUTE_BASE_URL"), "/"),
		OmniRouteAPIKey:  os.Getenv("OMNIROUTE_API_KEY"),
		GmailUser:        os.Getenv("GMAIL_USER"),
		GmailAppPassword: os.Getenv("GMAIL_APP_PASSWORD"),
		HubToken:         os.Getenv("HUB_TOKEN"),
	}

	imapPort, err := resolveIMAPPort()
	if err != nil {
		return nil, err
	}
	c.IMAPHost = getenvDefault("EMAIL_AGENT_IMAP_HOST", DefaultIMAPHost)
	c.IMAPPort = imapPort
	c.IMAPLookbackDays = getenvDefaultInt("EMAIL_AGENT_IMAP_LOOKBACK_DAYS", DefaultIMAPLookbackDays)
	c.IMAPMaxMessages = getenvDefaultInt("EMAIL_AGENT_IMAP_MAX_MESSAGES", DefaultIMAPMaxMessages)

	port, err := resolvePort()
	if err != nil {
		return nil, err
	}
	c.Port = port
	c.Addr = resolveAddr(port)
	c.DBPath = getenvDefault("EMAIL_AGENT_DB_PATH", DefaultDB)

	if err := c.validate(); err != nil {
		return nil, err
	}
	return c, nil
}

// resolveIMAPPort reads EMAIL_AGENT_IMAP_PORT, falling back to DefaultIMAPPort.
func resolveIMAPPort() (int, error) {
	raw := strings.TrimSpace(os.Getenv("EMAIL_AGENT_IMAP_PORT"))
	if raw == "" {
		return DefaultIMAPPort, nil
	}
	p, err := strconv.Atoi(raw)
	if err != nil {
		return 0, fmt.Errorf("EMAIL_AGENT_IMAP_PORT %q is not a number: %w", raw, err)
	}
	return p, nil
}

// getenvDefaultInt reads a positive integer setting, falling back to def when
// unset or malformed.
func getenvDefaultInt(key string, def int) int {
	raw := strings.TrimSpace(os.Getenv(key))
	if raw == "" {
		return def
	}
	n, err := strconv.Atoi(raw)
	if err != nil || n < 1 {
		return def
	}
	return n
}

// resolvePort determines the listening port from EMAIL_AGENT_PORT or the port
// component of EMAIL_AGENT_ADDR, falling back to DefaultPort.
func resolvePort() (int, error) {
	if raw := strings.TrimSpace(os.Getenv("EMAIL_AGENT_PORT")); raw != "" {
		p, err := strconv.Atoi(raw)
		if err != nil {
			return 0, fmt.Errorf("EMAIL_AGENT_PORT %q is not a number: %w", raw, err)
		}
		return p, nil
	}
	if addr := strings.TrimSpace(os.Getenv("EMAIL_AGENT_ADDR")); addr != "" {
		if i := strings.LastIndex(addr, ":"); i >= 0 && i < len(addr)-1 {
			if p, err := strconv.Atoi(addr[i+1:]); err == nil {
				return p, nil
			}
		}
	}
	return DefaultPort, nil
}

// resolveAddr prefers an explicit EMAIL_AGENT_ADDR, otherwise builds one from
// the resolved port.
func resolveAddr(port int) string {
	if addr := strings.TrimSpace(os.Getenv("EMAIL_AGENT_ADDR")); addr != "" {
		return addr
	}
	return fmt.Sprintf(":%d", port)
}

func (c *Config) validate() error {
	if c.Port < 1 || c.Port > 65535 {
		return fmt.Errorf("port %d is out of range", c.Port)
	}
	if strings.TrimSpace(c.DBPath) == "" {
		return fmt.Errorf("EMAIL_AGENT_DB_PATH must not be empty")
	}
	switch c.Env {
	case "development", "production", "test":
	default:
		return fmt.Errorf("EMAIL_AGENT_ENV %q must be development, production, or test", c.Env)
	}
	switch c.LogLevel {
	case "debug", "info", "warn", "error":
	default:
		return fmt.Errorf("EMAIL_AGENT_LOG_LEVEL %q must be debug, info, warn, or error", c.LogLevel)
	}
	if strings.TrimSpace(c.IMAPHost) == "" {
		return fmt.Errorf("EMAIL_AGENT_IMAP_HOST must not be empty")
	}
	if c.IMAPPort < 1 || c.IMAPPort > 65535 {
		return fmt.Errorf("EMAIL_AGENT_IMAP_PORT %d is out of range", c.IMAPPort)
	}
	return nil
}

// GmailConfigured reports whether an IMAP login can be attempted. The service
// still starts without credentials; only mail sync is unavailable.
func (c *Config) GmailConfigured() bool {
	return strings.TrimSpace(c.GmailUser) != "" && strings.TrimSpace(c.GmailAppPassword) != ""
}

// IsProduction reports whether the service runs in the production environment.
func (c *Config) IsProduction() bool { return c.Env == "production" }

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