// Package config loads verdande's settings from the environment.
//
// Everything is env-driven because verdande ships as a Rune: the panel hands the
// container an environment and a /data volume, and there is nowhere to put a config
// file that the operator would ever see.
package config

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

type Config struct {
	// BaseURL is the address verdande answers on from outside. Invite links,
	// password resets, ICS feeds and OAuth redirects are all built from it, so it
	// has to be the public address, not the listen address.
	BaseURL string
	Addr    string
	DataDir string

	SessionTTL time.Duration
	InviteTTL  time.Duration
	ResetTTL   time.Duration

	SMTP SMTP

	// Gmail is the OAuth client the operator registered in Google Cloud. It
	// belongs to the instance: one registration, any number of users.
	GmailClientID     string
	GmailClientSecret string

	// SecretKey seals the tokens and passwords in the database, 32 bytes of base64.
	// Empty means a key file beside the data — see internal/secret.
	SecretKey string

	// UpdateCheck asks GitHub whether a newer release exists. Off unless asked
	// for: a self-hosted app that reaches out without being told to has broken
	// the deal its operator made by self-hosting.
	UpdateCheck bool

	// The Yggdrasil panel this instance runs under, so it can ask to be restarted
	// from its own interface rather than from another browser tab.
	//
	// A container cannot replace its own image from the inside. Restarting is the
	// panel's job — it recreates the container and pulls `:latest` on the way — so
	// what this needs is a way to ask. All three are required together; any one
	// alone cannot do anything.
	//
	// The token is a panel credential with control over that server. Anybody who
	// can read this environment can restart it, which is true of anybody with the
	// host anyway. It is never sent to a browser: the settings page is told only
	// whether it is set.
	// GmailSyncBudget bounds one "fetch now", well under whatever proxy sits in
	// front of this server. Configurable so a test can prove the budget is applied
	// without spending the real one on every run.
	GmailSyncBudget time.Duration

	// CalendarSyncBudget is the same bound for one calendar refresh, and exists for
	// the same reason: a slow Google held the request open past what Cloudflare is
	// willing to wait, and the browser got Cloudflare's HTML instead of an error
	// this server could explain.
	CalendarSyncBudget time.Duration

	// Where Google is. Empty in production; a test points them at a server it
	// controls, which is the only way to exercise a Google that is slow or refuses.
	// The token endpoint is shared — Gmail and Calendar sign in through the same
	// registration — and the two APIs are not.
	GoogleTokenURL string
	GmailAPIURL    string
	CalendarAPIURL string

	PanelURL      string
	PanelToken    string
	PanelServerID string

	// TrashRetention is how long a soft-deleted task or project stays recoverable.
	TrashRetention time.Duration

	// TrustedProxies are the peers whose forwarded-for header may be believed.
	//
	// The rate limiter and the audit log key on the caller's address, and that
	// address is only as honest as wherever it was read. Read it from a header that
	// anybody can set, and an attacker rotates it to get a fresh guess-bucket for
	// every request and to write someone else's IP into the log. So the header is
	// believed only when the machine that *connected* is one of these — a reverse
	// proxy or tunnel the operator put there — and ignored when the connection came
	// straight off the internet.
	//
	// The default is "the peer is on a private network", which is exactly the shape
	// of a homelab behind Caddy, nginx or a Cloudflare Tunnel: the proxy shares the
	// host or the docker bridge, so its address is loopback or RFC1918. A directly
	// exposed instance sees a public peer, trusts nothing, and keys on the real
	// connection. Override with VERDANDE_TRUSTED_PROXIES (comma-separated CIDRs),
	// or "none" to trust no proxy at all.
	TrustedProxies []netip.Prefix
	// RealIPHeader is where the client address is read from, for a trusted peer.
	RealIPHeader string

	Dev bool
}

type SMTP struct {
	Host     string
	Port     int
	Username string
	Password string
	From     string
	// StartTLS is the common case for a self-hosted Mailcow on 587. Port 465 is
	// implicit TLS instead and sets this false.
	StartTLS bool
	Insecure bool
}

// Configured reports whether outbound mail can be sent. Without a host verdande
// still runs — it just surfaces invite links in the UI instead of mailing them.
func (s SMTP) Configured() bool { return s.Host != "" }

func Load() (*Config, error) {
	c := &Config{
		BaseURL:        env("VERDANDE_BASE_URL", "http://localhost:8080"),
		Addr:           env("VERDANDE_ADDR", ":8080"),
		DataDir:        env("VERDANDE_DATA_DIR", "/data"),
		TrashRetention: 30 * 24 * time.Hour,
		Dev:            envBool("VERDANDE_DEV", false),

		GmailClientID:      env("VERDANDE_GMAIL_CLIENT_ID", ""),
		GmailSyncBudget:    25 * time.Second,
		CalendarSyncBudget: 25 * time.Second,
		PanelURL:           strings.TrimSuffix(env("VERDANDE_PANEL_URL", ""), "/"),
		PanelToken:         env("VERDANDE_PANEL_TOKEN", ""),
		PanelServerID:      env("VERDANDE_PANEL_SERVER_ID", ""),
		GmailClientSecret:  env("VERDANDE_GMAIL_CLIENT_SECRET", ""),
		SecretKey:          env("VERDANDE_SECRET_KEY", ""),
		UpdateCheck:        envBool("VERDANDE_UPDATE_CHECK", false),
	}

	var err error
	if c.SessionTTL, err = envDuration("VERDANDE_SESSION_TTL", 30*24*time.Hour); err != nil {
		return nil, err
	}
	if c.InviteTTL, err = envDuration("VERDANDE_INVITE_TTL", 7*24*time.Hour); err != nil {
		return nil, err
	}
	if c.ResetTTL, err = envDuration("VERDANDE_RESET_TTL", time.Hour); err != nil {
		return nil, err
	}

	port, err := envInt("VERDANDE_SMTP_PORT", 587)
	if err != nil {
		return nil, err
	}
	c.SMTP = SMTP{
		Host:     env("VERDANDE_SMTP_HOST", ""),
		Port:     port,
		Username: env("VERDANDE_SMTP_USER", ""),
		Password: env("VERDANDE_SMTP_PASS", ""),
		From:     env("VERDANDE_SMTP_FROM", "verdande@localhost"),
		// Port 465 is implicit TLS from the first byte; everything else negotiates
		// with STARTTLS. An operator can still override the guess.
		StartTLS: envBool("VERDANDE_SMTP_STARTTLS", port != 465),
		Insecure: envBool("VERDANDE_SMTP_INSECURE", false),
	}

	c.BaseURL = strings.TrimRight(c.BaseURL, "/")
	if c.DataDir, err = filepath.Abs(c.DataDir); err != nil {
		return nil, fmt.Errorf("VERDANDE_DATA_DIR: %w", err)
	}

	c.RealIPHeader = env("VERDANDE_REAL_IP_HEADER", "X-Forwarded-For")
	if c.TrustedProxies, err = parseTrustedProxies(env("VERDANDE_TRUSTED_PROXIES", "")); err != nil {
		return nil, err
	}
	return c, nil
}

// defaultTrustedProxies is "the peer is not on the public internet": loopback,
// the three RFC1918 ranges, Tailscale's CGNAT borrow, IPv6 unique-local and both
// families' link-local. A proxy an operator stands up in front of this server is
// on one of these; a stranger connecting directly is on none.
var defaultTrustedProxies = mustPrefixes(
	"127.0.0.0/8", "::1/128",
	"10.0.0.0/8", "172.16.0.0/12", "192.168.0.0/16",
	"100.64.0.0/10",
	"fc00::/7",
	"169.254.0.0/16", "fe80::/10",
)

// parseTrustedProxies reads the override. Empty keeps the private-network default;
// the literal "none" trusts no proxy at all, for an instance that is exposed
// directly and must never believe a forwarded header.
func parseTrustedProxies(raw string) ([]netip.Prefix, error) {
	raw = strings.TrimSpace(raw)
	if raw == "" {
		return defaultTrustedProxies, nil
	}
	if strings.EqualFold(raw, "none") {
		return nil, nil
	}
	var out []netip.Prefix
	for _, part := range strings.Split(raw, ",") {
		part = strings.TrimSpace(part)
		if part == "" {
			continue
		}
		// A bare address is a host route: 10.0.0.5 means 10.0.0.5/32, so an operator
		// naming one proxy does not have to know CIDR notation to do it.
		if !strings.Contains(part, "/") {
			addr, err := netip.ParseAddr(part)
			if err != nil {
				return nil, fmt.Errorf("VERDANDE_TRUSTED_PROXIES: %q is not an address or CIDR", part)
			}
			out = append(out, netip.PrefixFrom(addr, addr.BitLen()))
			continue
		}
		p, err := netip.ParsePrefix(part)
		if err != nil {
			return nil, fmt.Errorf("VERDANDE_TRUSTED_PROXIES: %q is not a CIDR", part)
		}
		out = append(out, p.Masked())
	}
	return out, nil
}

func mustPrefixes(cidrs ...string) []netip.Prefix {
	out := make([]netip.Prefix, 0, len(cidrs))
	for _, c := range cidrs {
		out = append(out, netip.MustParsePrefix(c))
	}
	return out
}

// DBPath, FilesDir and BackupsDir are the three things that live on the /data volume.
func (c *Config) DBPath() string     { return filepath.Join(c.DataDir, "verdande.db") }
func (c *Config) FilesDir() string   { return filepath.Join(c.DataDir, "files") }
func (c *Config) BackupsDir() string { return filepath.Join(c.DataDir, "backups") }

// GmailRedirectURL has to match what was registered in Google Cloud exactly,
// including the scheme — which is why it is derived from BaseURL rather than
// configured separately and left to drift out of step with it.
func (c *Config) GmailRedirectURL() string { return c.BaseURL + "/oauth/gmail/callback" }

// CalendarRedirectURL is a second registered URI rather than a reuse of Gmail's.
//
// One callback that decided from server-side state which of the two flows had come
// back would save the operator one line in Google Cloud, and would put the choice
// of *which token store to write* behind a lookup. When that goes wrong it goes
// wrong by overwriting a working Gmail connection with calendar tokens — a failure
// nobody would think to look for. Two paths cannot do that.
func (c *Config) CalendarRedirectURL() string { return c.BaseURL + "/oauth/calendar/callback" }

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

func envInt(key string, def int) (int, error) {
	v, ok := os.LookupEnv(key)
	if !ok || v == "" {
		return def, nil
	}
	n, err := strconv.Atoi(v)
	if err != nil {
		return 0, fmt.Errorf("%s: %q is not a number", key, v)
	}
	return n, nil
}

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
}

func envDuration(key string, def time.Duration) (time.Duration, error) {
	v, ok := os.LookupEnv(key)
	if !ok || v == "" {
		return def, nil
	}
	d, err := time.ParseDuration(v)
	if err != nil {
		return 0, fmt.Errorf("%s: %q is not a duration (try 720h)", key, v)
	}
	return d, nil
}