// Package config loads and validates every runtime setting from the
// environment.
//
// Configuration is environment-only on purpose. The Helm chart is the single
// source of truth for how a deployment is configured; letting the binary also
// read a config file would create a second source that operators forget about.
// Every value has a safe default except the secrets and the OIDC issuer, which
// must be supplied explicitly when auth is enabled.
package config

import (
	"crypto/rand"
	"encoding/base64"
	"errors"
	"fmt"
	"net/url"
	"os"
	"strconv"
	"strings"
	"time"
)

// Environment prefixes, tried in order. This lets the Helm chart mount a
// ConfigMap under a distinct prefix without colliding with the pod's own
// environment, which is what makes one image usable across environments.
var envPrefixes = []string{"BANANAS_", "GO_BANANAS_"}

// Config is the fully resolved runtime configuration.
type Config struct {
	// Environment is the deployment name, used in logs and the admin UI.
	Environment string
	// LogLevel is one of debug, info, warn, error.
	LogLevel string
	// LogFormat is json or text.
	LogFormat string

	// HTTPAddr is the listen address, host:port.
	HTTPAddr string
	// PublicBaseURL is the externally reachable origin, without a trailing
	// slash. It is used to build absolute URLs in the runtime manifest and to
	// validate OIDC redirect targets.
	PublicBaseURL string
	// TrustedProxies lists the CIDRs or IPs whose X-Forwarded-For headers may be
	// believed. It is empty by default, which makes the service ignore
	// forwarding headers entirely and log the direct peer.
	TrustedProxies []string
	// ReadTimeout and WriteTimeout bound a single request. WriteTimeout is
	// generous because the runtime CSS endpoint is on the hot path of every page
	// load in every consuming application.
	ReadTimeout  time.Duration
	WriteTimeout time.Duration
	IdleTimeout  time.Duration
	// ShutdownTimeout is how long in-flight requests get to finish on SIGTERM.
	ShutdownTimeout time.Duration

	// CORSAllowedOrigins are the browser origins allowed to call the admin API
	// from a different origin. The runtime API is always public and is not
	// subject to this list.
	CORSAllowedOrigins []string
	// RateLimitPerMinute caps requests per client for the runtime API.
	RateLimitPerMinute int

	// DatabasePath is the SQLite file path. Use ":memory:" for tests.
	DatabasePath string
	// DatabaseBusyTimeout is how long a writer waits for the database lock
	// before failing.
	DatabaseBusyTimeout time.Duration
	// DatabaseMaxConns bounds the connection pool. SQLite serialises writers, so
	// a small pool with WAL is faster than a large one.
	DatabaseMaxConns int

	// AuthMode is oidc, dev, or none.
	AuthMode string
	// OIDCIssuer is the issuer URL, e.g. https://auth.lcl-urpi.be/realms/urpi.
	OIDCIssuer string
	// OIDCClientID is the client identifier registered with the provider.
	OIDCClientID string
	// OIDCClientSecret authenticates the confidential client.
	OIDCClientSecret string
	// OIDCScopes are requested in addition to openid.
	OIDCScopes []string
	// OIDCRedirectURL overrides the computed callback URL. It is only needed
	// when the public URL cannot be derived, for example behind a path-based
	// ingress.
	OIDCRedirectURL string
	// OIDCPostLogoutRedirectURL is where the provider sends the browser after
	// logout. It must be an allowed post-logout target on the provider side.
	OIDCPostLogoutRedirectURL string
	// OIDCAdminGroups are the group names that map to the admin role.
	OIDCAdminGroups []string
	// OIDCEditorGroups are the group names that map to the editor role.
	OIDCEditorGroups []string
	// OIDCViewerGroups are the group names that map to the viewer role.
	OIDCViewerGroups []string
	// OIDCSkipTLSVerify disables provider certificate verification. It exists
	// only so that a self-signed local provider can be used during development
	// and it is refused outside the development environment.
	OIDCSkipTLSVerify bool

	// SessionSecret signs the session cookie. It must be at least 32 bytes and
	// is required whenever auth is enabled.
	SessionSecret string
	// SessionCookieName is the cookie carrying the session.
	SessionCookieName string
	// SessionSecure marks the session cookie Secure.
	SessionSecure bool
	// SessionTTL is the session lifetime.
	SessionTTL time.Duration
	// SessionSameSite is Lax, Strict or None.
	SessionSameSite string

	// RuntimePublic controls whether the runtime API requires a credential. It
	// is enabled by default because a theming service's whole purpose is to be
	// reachable from browsers and CDN caches.
	RuntimePublic bool
	// RuntimeCacheControl is the Cache-Control header sent on runtime assets.
	// It is tuned for aggressive CDN caching with a revalidation window that
	// matches how often themes are published.
	RuntimeCacheControl string
	// RuntimeCDNBaseURL, when set, is used as the absolute base in the manifest
	// so consumers fetch assets from a CDN rather than from this service.
	RuntimeCDNBaseURL string

	// SeedOnStart reconciles the built-in themes at start-up.
	SeedOnStart bool
	// DevFallbackRole is the role granted by the development auth bypass.
	DevFallbackRole string
	// DevUsers maps a development email to a role, overriding DevFallbackRole.
	DevUsers map[string]string

	// EnableMetrics exposes /metrics in Prometheus format.
	EnableMetrics bool
	// EnableProfiler exposes the net/http/pprof handlers under /debug/pprof.
	EnableProfiler bool
	// StaticDir is the directory holding the built admin UI. When empty the UI
	// is not served.
	StaticDir string
	// SDKDir is the directory holding the built runtime SDK bundles.
	SDKDir string
	// BasePath prefixes every route, for deployments behind a path-based ingress.
	BasePath string

	// ephemeralSessionSecret records that the secret was generated rather than
	// supplied. It is not part of the configuration surface; the application reads
	// it only to decide whether to warn.
	ephemeralSessionSecret bool
}

// Auth mode values.
const (
	AuthModeOIDC = "oidc"
	AuthModeDev  = "dev"
	AuthModeNone = "none"
)

// Defaults returns a Config populated with production-safe defaults. Load
// applies the environment on top of this value.
func Defaults() Config {
	return Config{
		Environment: "development",
		LogLevel:    "info",
		LogFormat:   "text",

		HTTPAddr:        ":8080",
		PublicBaseURL:   "http://localhost:8080",
		ReadTimeout:     15 * time.Second,
		WriteTimeout:    30 * time.Second,
		IdleTimeout:     120 * time.Second,
		ShutdownTimeout: 25 * time.Second,

		CORSAllowedOrigins: []string{},
		RateLimitPerMinute: 3000,

		DatabasePath:        "./data/go-bananas.db",
		DatabaseBusyTimeout: 5 * time.Second,
		DatabaseMaxConns:    8,

		AuthMode:            AuthModeDev,
		OIDCScopes:          []string{"profile", "email", "groups"},
		SessionCookieName:   "go-bananas-session",
		SessionSecure:       false,
		SessionTTL:          8 * time.Hour,
		SessionSameSite:     "Lax",
		RuntimePublic:       true,
		RuntimeCacheControl: "public, max-age=60, s-maxage=300, stale-while-revalidate=86400",
		SeedOnStart:         true,
		DevFallbackRole:     "admin",
		DevUsers:            map[string]string{},
		EnableMetrics:       true,
		EnableProfiler:      false,
		StaticDir:           "./web/dist",
		SDKDir:              "./sdk/dist",
	}
}

// Load reads configuration from the environment and validates it.
func Load() (Config, error) {
	return loadFrom(os.LookupEnv)
}

// loadFrom is the testable core of Load.
func loadFrom(lookup func(string) (string, bool)) (Config, error) {
	cfg := Defaults()

	get := func(name string) (string, bool) {
		for _, prefix := range envPrefixes {
			if v, ok := lookup(prefix + name); ok {
				return v, true
			}
		}
		return "", false
	}

	str := func(name string, target *string) {
		if v, ok := get(name); ok {
			*target = strings.TrimSpace(v)
		}
	}

	cfg.Environment = firstNonEmpty(cfg.Environment,
		func() (string, bool) { return get("ENVIRONMENT") },
		func() (string, bool) { return get("ENV") },
	)
	str("LOG_LEVEL", &cfg.LogLevel)
	str("LOG_FORMAT", &cfg.LogFormat)

	str("HTTP_ADDR", &cfg.HTTPAddr)
	str("PUBLIC_BASE_URL", &cfg.PublicBaseURL)
	str("BASE_PATH", &cfg.BasePath)
	str("STATIC_DIR", &cfg.StaticDir)
	str("SDK_DIR", &cfg.SDKDir)

	dur := func(name string, target *time.Duration) error {
		v, ok := get(name)
		if !ok {
			return nil
		}
		parsed, err := time.ParseDuration(strings.TrimSpace(v))
		if err != nil {
			return fmt.Errorf("%s: %w", name, err)
		}
		*target = parsed
		return nil
	}

	num := func(name string, target *int) error {
		v, ok := get(name)
		if !ok {
			return nil
		}
		parsed, err := strconv.Atoi(strings.TrimSpace(v))
		if err != nil {
			return fmt.Errorf("%s: %w", name, err)
		}
		*target = parsed
		return nil
	}

	boolean := func(name string, target *bool) error {
		v, ok := get(name)
		if !ok {
			return nil
		}
		parsed, err := strconv.ParseBool(strings.TrimSpace(v))
		if err != nil {
			return fmt.Errorf("%s: %w", name, err)
		}
		*target = parsed
		return nil
	}

	list := func(name string, target *[]string) {
		if v, ok := get(name); ok {
			*target = splitList(v)
		}
	}

	var err error
	for _, f := range []func() error{
		func() error { return dur("HTTP_READ_TIMEOUT", &cfg.ReadTimeout) },
		func() error { return dur("HTTP_WRITE_TIMEOUT", &cfg.WriteTimeout) },
		func() error { return dur("HTTP_IDLE_TIMEOUT", &cfg.IdleTimeout) },
		func() error { return dur("SHUTDOWN_TIMEOUT", &cfg.ShutdownTimeout) },
		func() error { return dur("SESSION_TTL", &cfg.SessionTTL) },
		func() error { return dur("DB_BUSY_TIMEOUT", &cfg.DatabaseBusyTimeout) },
		func() error { return num("RATE_LIMIT_PER_MINUTE", &cfg.RateLimitPerMinute) },
		func() error { return num("DB_MAX_CONNS", &cfg.DatabaseMaxConns) },
		func() error { return boolean("RUNTIME_PUBLIC", &cfg.RuntimePublic) },
		func() error { return boolean("SEED_ON_START", &cfg.SeedOnStart) },
		func() error { return boolean("ENABLE_METRICS", &cfg.EnableMetrics) },
		func() error { return boolean("ENABLE_PROFILER", &cfg.EnableProfiler) },
		func() error { return boolean("SESSION_SECURE", &cfg.SessionSecure) },
		func() error { return boolean("OIDC_SKIP_TLS_VERIFY", &cfg.OIDCSkipTLSVerify) },
	} {
		if err = f(); err != nil {
			return cfg, err
		}
	}

	list("TRUSTED_PROXIES", &cfg.TrustedProxies)
	list("CORS_ALLOWED_ORIGINS", &cfg.CORSAllowedOrigins)
	list("OIDC_SCOPES", &cfg.OIDCScopes)
	list("OIDC_ADMIN_GROUPS", &cfg.OIDCAdminGroups)
	list("OIDC_EDITOR_GROUPS", &cfg.OIDCEditorGroups)
	list("OIDC_VIEWER_GROUPS", &cfg.OIDCViewerGroups)

	str("AUTH_MODE", &cfg.AuthMode)
	str("OIDC_ISSUER", &cfg.OIDCIssuer)
	str("OIDC_CLIENT_ID", &cfg.OIDCClientID)
	str("OIDC_CLIENT_SECRET", &cfg.OIDCClientSecret)
	str("OIDC_REDIRECT_URL", &cfg.OIDCRedirectURL)
	str("OIDC_POST_LOGOUT_REDIRECT_URL", &cfg.OIDCPostLogoutRedirectURL)
	str("SESSION_SECRET", &cfg.SessionSecret)
	str("SESSION_COOKIE_NAME", &cfg.SessionCookieName)
	str("SESSION_SAMESITE", &cfg.SessionSameSite)
	str("DEV_FALLBACK_ROLE", &cfg.DevFallbackRole)
	str("RUNTIME_CACHE_CONTROL", &cfg.RuntimeCacheControl)
	str("RUNTIME_CDN_BASE_URL", &cfg.RuntimeCDNBaseURL)
	str("DATABASE_PATH", &cfg.DatabasePath)

	if v, ok := get("DEV_USERS"); ok {
		cfg.DevUsers = parseDevUsers(v)
	}

	// A development run should not require the operator to invent a 32-byte
	// secret before the first request. An ephemeral one is generated instead,
	// which is safe because nothing durable is signed with it: sessions simply do
	// not survive a restart, which a local run never notices.
	if cfg.AuthMode != AuthModeNone && cfg.SessionSecret == "" && cfg.IsDevelopment() {
		generated, genErr := randomSecret()
		if genErr != nil {
			return cfg, genErr
		}
		cfg.SessionSecret = generated
		cfg.ephemeralSessionSecret = true
	}

	return cfg, cfg.Validate()
}

// EphemeralSessionSecret reports whether the session secret was generated rather
// than supplied. The caller logs it as a warning, because it means sessions
// survive only until the process restarts.
func (c Config) EphemeralSessionSecret() bool { return c.ephemeralSessionSecret }

// randomSecret returns a 48-byte cryptographically random value, base64 encoded.
func randomSecret() (string, error) {
	buf := make([]byte, 48)
	if _, err := rand.Read(buf); err != nil {
		return "", fmt.Errorf("generate session secret: %w", err)
	}
	return base64.RawURLEncoding.EncodeToString(buf), nil
}

// Validate checks the configuration for internal consistency. It returns every
// problem it finds rather than only the first, because fixing configuration one
// error per deploy is a miserable loop.
func (c Config) Validate() error {
	var problems []string
	add := func(format string, args ...any) {
		problems = append(problems, fmt.Sprintf(format, args...))
	}

	switch c.AuthMode {
	case AuthModeOIDC, AuthModeDev, AuthModeNone:
	default:
		add("AUTH_MODE %q must be one of oidc, dev or none", c.AuthMode)
	}

	if c.AuthMode == AuthModeOIDC {
		if c.OIDCIssuer == "" {
			add("OIDC_ISSUER is required when AUTH_MODE=oidc")
		} else if parsed, err := url.Parse(c.OIDCIssuer); err != nil {
			add("OIDC_ISSUER is not a valid URL: %v", err)
		} else if parsed.Scheme != "https" && !isLocalHost(parsed.Hostname()) {
			add("OIDC_ISSUER must use https outside local development, got %q", parsed.Scheme)
		}
		if c.OIDCClientID == "" {
			add("OIDC_CLIENT_ID is required when AUTH_MODE=oidc")
		}
		if c.OIDCClientSecret == "" {
			add("OIDC_CLIENT_SECRET is required when AUTH_MODE=oidc")
		}
		if c.OIDCSkipTLSVerify && !c.IsDevelopment() {
			add("OIDC_SKIP_TLS_VERIFY is refused outside development; it disables certificate verification on the identity provider connection")
		}
	}

	if c.AuthMode != AuthModeNone {
		if len(c.SessionSecret) < 32 {
			add("SESSION_SECRET must be at least 32 bytes when auth is enabled, got %d", len(c.SessionSecret))
		}
	}

	if c.PublicBaseURL != "" {
		parsed, err := url.Parse(c.PublicBaseURL)
		switch {
		case err != nil:
			add("PUBLIC_BASE_URL is not a valid URL: %v", err)
		case parsed.Scheme == "":
			add("PUBLIC_BASE_URL must include a scheme, got %q", c.PublicBaseURL)
		case parsed.Host == "":
			add("PUBLIC_BASE_URL must include a host, got %q", c.PublicBaseURL)
		}
	}

	if c.BasePath != "" && !strings.HasPrefix(c.BasePath, "/") {
		add("BASE_PATH must start with a slash, got %q", c.BasePath)
	}

	switch strings.ToLower(c.SessionSameSite) {
	case "lax", "strict", "none":
	default:
		add("SESSION_SAMESITE %q must be lax, strict or none", c.SessionSameSite)
	}

	if strings.EqualFold(c.SessionSameSite, "none") && !c.SessionSecure {
		// Browsers reject SameSite=None without Secure, so this combination
		// silently produces a session that never survives a redirect.
		add("SESSION_SAMESITE=none requires SESSION_SECURE=true")
	}

	if !c.SessionSecure && !c.IsDevelopment() && c.PublicBaseURL != "" {
		if strings.HasPrefix(c.PublicBaseURL, "https://") {
			add("SESSION_SECURE must be true when PUBLIC_BASE_URL is https")
		}
	}

	if c.DatabasePath == "" {
		add("DATABASE_PATH must not be empty")
	}
	if c.DatabaseMaxConns < 1 {
		add("DB_MAX_CONNS must be at least 1, got %d", c.DatabaseMaxConns)
	}
	if c.RateLimitPerMinute < 0 {
		add("RATE_LIMIT_PER_MINUTE must not be negative")
	}
	if !c.IsDevelopment() && c.AuthMode == AuthModeDev {
		add("AUTH_MODE=dev is refused outside development; it grants admin to anyone who can reach the service")
	}
	if c.AuthMode == AuthModeNone && !c.IsDevelopment() {
		add("AUTH_MODE=none is refused outside development")
	}

	if len(problems) > 0 {
		return errors.New("invalid configuration:\n  - " + strings.Join(problems, "\n  - "))
	}
	return nil
}

// IsDevelopment reports whether the service is running in development.
func (c Config) IsDevelopment() bool {
	switch strings.ToLower(c.Environment) {
	case "development", "dev", "local", "test", "testing", "ci":
		return true
	default:
		return false
	}
}

// RedirectURL returns the OIDC callback URL, derived from the public base when
// not overridden.
func (c Config) RedirectURL() string {
	if c.OIDCRedirectURL != "" {
		return c.OIDCRedirectURL
	}
	return c.origin() + c.path("/auth/callback")
}

// PostLogoutRedirectURL returns the OIDC end-session target.
func (c Config) PostLogoutRedirectURL() string {
	if c.OIDCPostLogoutRedirectURL != "" {
		return c.OIDCPostLogoutRedirectURL
	}
	return c.origin() + c.path("/")
}

// Origin returns the public origin with no trailing slash.
func (c Config) Origin() string { return c.origin() }

// origin normalises the public base URL.
func (c Config) origin() string {
	return strings.TrimRight(c.PublicBaseURL, "/")
}

// path prefixes a route with the configured base path.
func (c Config) path(route string) string {
	base := strings.TrimRight(c.BasePath, "/")
	if base == "" {
		return route
	}
	return base + route
}

// Path exposes base-path prefixing to the HTTP layer.
func (c Config) Path(route string) string { return c.path(route) }

// CDNBasis returns the absolute base that runtime asset URLs are built from,
// honouring the CDN override.
func (c Config) CDNBasis() string {
	if c.RuntimeCDNBaseURL != "" {
		return strings.TrimRight(c.RuntimeCDNBaseURL, "/")
	}
	return c.origin() + c.path("/rt/v1")
}

// splitList parses a comma or whitespace separated environment list.
func splitList(raw string) []string {
	fields := strings.FieldsFunc(raw, func(r rune) bool {
		return r == ',' || r == '\n' || r == '\t' || r == ' '
	})
	out := make([]string, 0, len(fields))
	for _, f := range fields {
		if trimmed := strings.TrimSpace(f); trimmed != "" {
			out = append(out, trimmed)
		}
	}
	return out
}

// parseDevUsers parses the development role map in "email=role,email=role" form.
func parseDevUsers(raw string) map[string]string {
	out := make(map[string]string)
	for _, pair := range splitList(raw) {
		email, role, ok := strings.Cut(pair, "=")
		if !ok {
			continue
		}
		email = strings.ToLower(strings.TrimSpace(email))
		role = strings.ToLower(strings.TrimSpace(role))
		if email == "" || role == "" {
			continue
		}
		out[email] = role
	}
	return out
}

// firstNonEmpty returns the first non-empty value from a default and a list of
// candidate environment lookups.
func firstNonEmpty(def string, lookups ...func() (string, bool)) string {
	for _, lookup := range lookups {
		if v, ok := lookup(); ok && strings.TrimSpace(v) != "" {
			return strings.TrimSpace(v)
		}
	}
	return def
}

// isLocalHost reports whether host refers to the local machine.
func isLocalHost(host string) bool {
	switch strings.ToLower(host) {
	case "localhost", "127.0.0.1", "::1", "keycloak", "idp", "auth":
		return true
	default:
		return strings.HasSuffix(host, ".local") || strings.HasSuffix(host, ".localhost")
	}
}

// Redacted returns a copy of the configuration with secrets masked, suitable
// for logging or for the diagnostics endpoint.
func (c Config) Redacted() Config {
	mask := func(s string) string {
		if s == "" {
			return ""
		}
		return "***redacted***"
	}
	c.OIDCClientSecret = mask(c.OIDCClientSecret)
	c.SessionSecret = mask(c.SessionSecret)
	return c
}