// Package config holds Nurse's settings: where to listen, where notes live and how to reach
// Authentik. The notes themselves are not in here.
package config

import (
	"crypto/rand"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"net/url"
	"os"
	"path/filepath"
	"strings"
	"sync"
)

// OIDC is the OAuth client Authentik gives you for Nurse.
type OIDC struct {
	Issuer       string `json:"issuer"`
	ClientID     string `json:"client_id"`
	ClientSecret string `json:"client_secret"`
}

type Config struct {
	Listen  string `json:"listen"`
	DataDir string `json:"data_dir"`

	// PublicURL is the address you open Nurse at, such as https://notes.example.com. The sign-in
	// redirect is PublicURL + /auth/callback.
	PublicURL string `json:"public_url"`
	OIDC      OIDC   `json:"oidc"`

	// Allowed limits who may sign in, by email, username or Authentik id. Empty means anyone Authentik
	// lets into the application, each with a notebook of their own.
	Allowed []string `json:"allowed,omitempty"`

	// Secret signs session cookies, so a restart does not sign you out. It is made on first run.
	Secret string `json:"secret,omitempty"`
}

// Defaults fills in what is missing.
func (c *Config) Defaults() {
	if c.Listen == "" {
		c.Listen = "127.0.0.1:8490"
	}
	if c.DataDir == "" {
		c.DataDir = "data"
	}
	if c.Secret == "" {
		b := make([]byte, 32)
		rand.Read(b)
		c.Secret = base64.RawURLEncoding.EncodeToString(b)
	}
	c.PublicURL = strings.TrimRight(strings.TrimSpace(c.PublicURL), "/")
	c.OIDC.Issuer = strings.TrimSpace(c.OIDC.Issuer)
	c.OIDC.ClientID = strings.TrimSpace(c.OIDC.ClientID)
	c.OIDC.ClientSecret = strings.TrimSpace(c.OIDC.ClientSecret)
}

// RedirectURL is the address to enter in Authentik as the redirect URI.
func (c Config) RedirectURL() string { return c.PublicURL + "/auth/callback" }

// Secure says whether Nurse is reached over HTTPS, which decides whether cookies are Secure.
func (c Config) Secure() bool { return strings.HasPrefix(c.PublicURL, "https://") }

// IsLocal reports whether a URL points at this machine, where plain http is fine.
func IsLocal(u *url.URL) bool {
	h := u.Hostname()
	return h == "localhost" || h == "127.0.0.1" || h == "::1" || strings.HasSuffix(h, ".localhost")
}

func checkURL(name, raw string) error {
	u, err := url.Parse(raw)
	if err != nil || u.Host == "" || (u.Scheme != "https" && u.Scheme != "http") {
		return fmt.Errorf("%s must be a full address such as https://notes.example.com (got %q)", name, raw)
	}
	if u.Scheme == "http" && !IsLocal(u) {
		return fmt.Errorf("%s must use https unless it points at this machine (got %q)", name, raw)
	}
	return nil
}

// Check says what is still missing before Nurse can sign anyone in, in words a person can act on.
func (c Config) Check() error {
	var missing []string
	if c.PublicURL == "" {
		missing = append(missing, "  public_url           (NURSE_PUBLIC_URL)          where you open Nurse, such as https://notes.example.com")
	}
	if c.OIDC.Issuer == "" {
		missing = append(missing, "  oidc.issuer          (NURSE_OIDC_ISSUER)         from Authentik, such as https://auth.example.com/application/o/nurse/")
	}
	if c.OIDC.ClientID == "" {
		missing = append(missing, "  oidc.client_id       (NURSE_OIDC_CLIENT_ID)      the Client ID of the Authentik provider")
	}
	if c.OIDC.ClientSecret == "" {
		missing = append(missing, "  oidc.client_secret   (NURSE_OIDC_CLIENT_SECRET)  the Client Secret of the Authentik provider")
	}
	if len(missing) > 0 {
		return fmt.Errorf("Nurse signs in with Authentik, and these settings are still empty:\n%s\n\nIn Authentik, make an OAuth2/OpenID provider with the redirect URI %s/auth/callback.\nSee the README for the steps", strings.Join(missing, "\n"), orPlaceholder(c.PublicURL))
	}
	if err := checkURL("public_url", c.PublicURL); err != nil {
		return err
	}
	if u, _ := url.Parse(c.PublicURL); u.Path != "" {
		return fmt.Errorf("public_url must not have a path (got %q)", c.PublicURL)
	}
	return checkURL("oidc.issuer", c.OIDC.Issuer)
}

func orPlaceholder(s string) string {
	if s == "" {
		return "https://your-address"
	}
	return s
}

// Holder keeps the settings file. Environment variables override what is in the file, but are
// never written back to it.
type Holder struct {
	path string
	mu   sync.RWMutex
	file Config
}

// Load reads the file. A missing file gives the defaults (and is created by the first Update).
func Load(path string) (*Holder, error) {
	h := &Holder{path: path}
	b, err := os.ReadFile(path)
	switch {
	case errors.Is(err, os.ErrNotExist):
	case err != nil:
		return nil, err
	default:
		if err := json.Unmarshal(b, &h.file); err != nil {
			return nil, fmt.Errorf("%s: %w", path, err)
		}
	}
	h.file.Defaults()
	return h, nil
}

func (h *Holder) Path() string { return h.path }

// Exists says whether the file is on disk yet.
func (h *Holder) Exists() bool { _, err := os.Stat(h.path); return err == nil }

// Get returns the settings with the environment applied.
func (h *Holder) Get() Config {
	h.mu.RLock()
	c := h.file
	c.Allowed = append([]string{}, c.Allowed...)
	h.mu.RUnlock()
	env := func(name string, to *string) {
		if v := strings.TrimSpace(os.Getenv(name)); v != "" {
			*to = v
		}
	}
	env("NURSE_LISTEN", &c.Listen)
	env("NURSE_DATA", &c.DataDir)
	env("NURSE_PUBLIC_URL", &c.PublicURL)
	env("NURSE_OIDC_ISSUER", &c.OIDC.Issuer)
	env("NURSE_OIDC_CLIENT_ID", &c.OIDC.ClientID)
	env("NURSE_OIDC_CLIENT_SECRET", &c.OIDC.ClientSecret)
	if v := os.Getenv("NURSE_ALLOWED"); strings.TrimSpace(v) != "" {
		c.Allowed = nil
		for _, a := range strings.FieldsFunc(v, func(r rune) bool { return r == ',' || r == ';' || r == '\n' }) {
			if a = strings.TrimSpace(a); a != "" {
				c.Allowed = append(c.Allowed, a)
			}
		}
	}
	c.Defaults()
	return c
}

// Save writes the file as it is now, which is what makes the generated secret stick.
func (h *Holder) Save() error {
	h.mu.Lock()
	defer h.mu.Unlock()
	b, err := json.MarshalIndent(h.file, "", "  ")
	if err != nil {
		return err
	}
	if dir := filepath.Dir(h.path); dir != "." {
		os.MkdirAll(dir, 0o755)
	}
	tmp := h.path + ".tmp"
	if err := os.WriteFile(tmp, append(b, '\n'), 0o600); err != nil {
		return err
	}
	return os.Rename(tmp, h.path)
}