package core

import (
	"fmt"
	"net"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"time"
)

// Config is the complete runtime configuration, loaded from the environment.
// Every field has a working default so the binary runs with no configuration
// at all — important for "podman run" first-run experience.
type Config struct {
	// Listen is the address the HTTP server binds, e.g. ":7788".
	Listen string
	// DataDir holds the SQLite database and persistent state.
	DataDir string
	// ConfigDir holds derived, regenerable artifacts (thumbnails, page cache).
	ConfigDir string
	// MediaDirs are read-only library roots. Vellum never writes here.
	MediaDirs []string

	DBPath string

	LogLevel  string
	LogFormat string

	// AdminUser / AdminPassword create the first administrator, but only when
	// the users table is empty. Ignored on any established database.
	AdminUser     string
	AdminPassword string

	// ComicVineAPIKey enables comic metadata. ComicVine has no keyless tier, so
	// the provider is simply absent when this is empty.
	ComicVineAPIKey string

	// IGDBClientID / IGDBClientSecret enable game metadata via Twitch's
	// client-credentials flow. Both must be set for the provider to appear.
	IGDBClientID     string
	IGDBClientSecret string

	CookieName   string
	CookieSecure bool

	// PublicURL is the external origin Vellum is reached at, e.g.
	// "https://media.example.com". Empty means "not published", which is the
	// case for plain-HTTP LAN use. It is the signal that the deployment sits
	// behind a TLS-terminating proxy, so it also drives the CookieSecure default.
	PublicURL string
	// TrustedProxies are the networks allowed to speak for a client in
	// X-Forwarded-For. Empty means trust nobody: only RemoteAddr is used.
	TrustedProxies []*net.IPNet

	// Discovery advertises the server on the LAN over mDNS so clients find it
	// without a typed URL.
	Discovery bool

	SessionTTL    time.Duration
	ReadTimeout   time.Duration
	WriteTimeout  time.Duration
	IdleTimeout   time.Duration
	ShutdownGrace time.Duration
}

// LoadConfig reads configuration from the environment and fills in defaults.
// It does not create directories; call Validate for that.
func LoadConfig() (Config, error) {
	publicURL := env("VELLUM_PUBLIC_URL", "")
	c := Config{
		Listen:        env("VELLUM_LISTEN", ":7788"),
		DataDir:       env("VELLUM_DATA_DIR", "./data"),
		ConfigDir:     env("VELLUM_CONFIG_DIR", "./config"),
		MediaDirs:     envList("VELLUM_MEDIA_DIRS", nil),
		LogLevel:      env("VELLUM_LOG_LEVEL", "info"),
		LogFormat:     env("VELLUM_LOG_FORMAT", "text"), // text|json
		AdminUser:     env("VELLUM_ADMIN_USER", ""),
		AdminPassword: env("VELLUM_ADMIN_PASSWORD", ""),

		ComicVineAPIKey: env("VELLUM_COMICVINE_API_KEY", ""),

		IGDBClientID:     env("VELLUM_IGDB_CLIENT_ID", ""),
		IGDBClientSecret: env("VELLUM_IGDB_CLIENT_SECRET", ""),
		CookieName:       env("VELLUM_COOKIE_NAME", "vellum_session"),
		// Secure defaults to true for an https:// PublicURL — a published origin
		// is TLS-terminated, so plain-HTTP dev still gets false with it unset.
		// VELLUM_COOKIE_SECURE overrides both ways; boot logs a warning when off.
		CookieSecure:  envBool("VELLUM_COOKIE_SECURE", strings.HasPrefix(publicURL, "https://")),
		PublicURL:     publicURL,
		SessionTTL:    envDuration("VELLUM_SESSION_TTL", 30*24*time.Hour),
		ReadTimeout:   envDuration("VELLUM_READ_TIMEOUT", 15*time.Second),
		WriteTimeout:  envDuration("VELLUM_WRITE_TIMEOUT", 0), // 0 = no limit; streaming needs this
		IdleTimeout:   envDuration("VELLUM_IDLE_TIMEOUT", 120*time.Second),
		ShutdownGrace: envDuration("VELLUM_SHUTDOWN_GRACE", 15*time.Second),

		Discovery: !envOff("VELLUM_DISCOVERY"),
	}

	proxies, err := envCIDRs("VELLUM_TRUSTED_PROXIES")
	if err != nil {
		return Config{}, err
	}
	c.TrustedProxies = proxies

	abs, err := filepath.Abs(c.DataDir)
	if err != nil {
		return Config{}, fmt.Errorf("resolve data dir: %w", err)
	}
	c.DataDir = abs
	c.DBPath = filepath.Join(abs, "vellum.db")

	if abs, err := filepath.Abs(c.ConfigDir); err == nil {
		c.ConfigDir = abs
	}

	return c, nil
}

// EnsureDirs creates the data and config directories if missing.
//
// Separate from Validate because the CLI needs the directories but has no
// interest in the media roots: `vellum user add` must work on a fresh install,
// and must not fail because a library happens to be unmounted.
func (c Config) EnsureDirs() error {
	for _, dir := range []string{c.DataDir, c.ConfigDir} {
		if err := os.MkdirAll(dir, 0o750); err != nil {
			return fmt.Errorf("create %s: %w", dir, err)
		}
	}
	return nil
}

// Validate creates the data and config directories if missing and checks that
// the configured media roots exist. A missing media root is an error, not a
// warning: silently scanning nothing is worse than failing loudly at boot.
func (c Config) Validate() error {
	if err := c.EnsureDirs(); err != nil {
		return err
	}
	for _, dir := range c.MediaDirs {
		info, err := os.Stat(dir)
		if err != nil {
			return fmt.Errorf("media dir %s: %w", dir, err)
		}
		if !info.IsDir() {
			return fmt.Errorf("media dir %s: not a directory", dir)
		}
	}
	return nil
}

func env(key, def string) string {
	if v, ok := os.LookupEnv(key); ok && v != "" {
		return v
	}
	return def
}

// envList parses a colon-separated list, the same separator as $PATH.
func envList(key string, def []string) []string {
	v, ok := os.LookupEnv(key)
	if !ok || strings.TrimSpace(v) == "" {
		return def
	}
	var out []string
	for _, part := range strings.Split(v, ":") {
		if part = strings.TrimSpace(part); part != "" {
			out = append(out, part)
		}
	}
	return out
}

// envCIDRs parses a comma-separated CIDR list, e.g.
// "172.16.0.0/12,127.0.0.1/32". A malformed entry is an error rather than a
// silent skip: dropping a proxy network quietly widens the trust boundary,
// which is exactly the failure this setting exists to prevent.
func envCIDRs(key string) ([]*net.IPNet, error) {
	var out []*net.IPNet
	for _, part := range strings.Split(env(key, ""), ",") {
		if part = strings.TrimSpace(part); part == "" {
			continue
		}
		_, n, err := net.ParseCIDR(part)
		if err != nil {
			return nil, fmt.Errorf("%s: %w", key, err)
		}
		out = append(out, n)
	}
	return out, nil
}

func envDuration(key string, def time.Duration) time.Duration {
	v, ok := os.LookupEnv(key)
	if !ok || v == "" {
		return def
	}
	d, err := time.ParseDuration(v)
	if err != nil {
		return def
	}
	return d
}

func envBool(key string, def bool) bool {
	v, ok := os.LookupEnv(key)
	if !ok || v == "" {
		return def
	}
	b, err := strconv.ParseBool(v)
	if err != nil {
		return def
	}
	return b
}

// envOff reads a switch that is ON unless it is explicitly turned off. Unlike
// envBool it accepts the on/off spellings operators actually type, because
// strconv.ParseBool rejects "off" and would silently leave the feature on.
func envOff(key string) bool {
	switch strings.ToLower(strings.TrimSpace(os.Getenv(key))) {
	case "off", "no", "false", "0":
		return true
	}
	return false
}