// Package config holds the server's runtime options and the flag plumbing that
// populates them.
package config

import (
	"fmt"
	"net"
	"net/url"
	"strconv"
	"strings"
	"time"
)

// Config is the fully-resolved server configuration.
type Config struct {
	Listen    string
	Port      int // overrides the port in Listen when set
	DataDir   string
	BasePath  string // normalised: always "/" or "/prefix/"
	PublicURL string // absolute origin+path for generated links; "" => relative

	// SourceURL is linked in the footer. It defaults to where this program is
	// developed, and a fork should point it at its own; setting it empty drops
	// the footer entirely, for an instance that would rather not advertise.
	SourceURL string

	MaxSize       int64         // per-upload cap; Unlimited means no cap
	MaxExpiry     time.Duration // longest lifetime a caller may request
	DefaultExpiry time.Duration // lifetime when the caller does not ask
	MaxTotalBytes int64         // whole-store quota
	MinFreeBytes  int64         // refuse uploads below this much free disk

	TokensPath    string
	TrustedProxy  string // comma-separated CIDRs allowed to set X-Forwarded-For
	SweepInterval time.Duration

	UploadRate       int // uploads per hour per client
	UploadBurst      int
	MaxConcurrent    int
	trustedProxyNets []*net.IPNet
}

const EnvPrefix = "UNCENSORED_SEND_"

// defaultSourceURL is where this program is developed. Anyone running a
// modified copy should say so with --source-url, and anyone who would rather
// not mention it at all can pass an empty one.
const defaultSourceURL = "https://git.uncensored.hu/thayol/uncensored-send"

// Register wires every option onto s. Short forms exist only for the options
// reached often; everything else is long-only, by design.
func (c *Config) Register(s *Set) {
	s.String(&c.Listen, "listen", "l", "127.0.0.1:8080", "ADDR",
		"address to listen on; keep it on loopback behind a reverse proxy")
	s.Int(&c.Port, "port", "p", 0,
		"port to listen on, replacing the one in --listen")
	s.String(&c.DataDir, "data", "d", "./data", "DIR",
		"directory holding uploaded objects and their metadata")
	s.String(&c.BasePath, "base-url", "b", "/", "PATH",
		"path prefix this service is mounted under")
	s.String(&c.PublicURL, "public-url", "u", "", "URL",
		"absolute base URL used in generated links; relative links when empty")
	s.String(&c.SourceURL, "source-url", "", defaultSourceURL, "URL",
		"where the footer's source link points; empty hides the footer")

	s.Size(&c.MaxSize, "max-size", "s", "2GiB",
		"largest upload accepted from an anonymous caller")
	s.Duration(&c.MaxExpiry, "max-expiry", "e", "3d",
		"longest lifetime an anonymous caller may request")
	s.Duration(&c.DefaultExpiry, "default-expiry", "", "3d",
		"lifetime applied when the caller does not ask for one")

	s.Size(&c.MaxTotalBytes, "max-total-bytes", "", "unlimited",
		"refuse uploads once stored data exceeds this total")
	s.Size(&c.MinFreeBytes, "min-free-bytes", "", "10GiB",
		"refuse uploads when the filesystem has less free space than this")
	s.String(&c.TokensPath, "tokens", "", "", "FILE",
		"token file location (default <data>/tokens.json)")
	s.String(&c.TrustedProxy, "trusted-proxy", "", "", "CIDRS",
		"comma-separated networks whose X-Forwarded-For header is believed")
	s.Duration(&c.SweepInterval, "sweep-interval", "", "1m",
		"how often expired objects are swept from disk")

	s.Int(&c.UploadRate, "upload-rate", "", 60,
		"uploads permitted per hour per client address")
	s.Int(&c.UploadBurst, "upload-burst", "", 10,
		"uploads permitted back-to-back before the rate applies")
	s.Int(&c.MaxConcurrent, "max-concurrent", "", 8,
		"uploads allowed to be in flight at once")
}

// Normalise validates interdependent options and canonicalises the derived
// ones. It must be called after parsing and before the config is used.
func (c *Config) Normalise() error {
	c.BasePath = NormalisePath(c.BasePath)

	// --port is a convenience over --listen: it replaces only the port, so the
	// host stays wherever --listen (or its default) put it.
	if c.Port != 0 {
		if c.Port < 1 || c.Port > 65535 {
			return fmt.Errorf("--port: %d is not a port number", c.Port)
		}
		host, _, err := net.SplitHostPort(c.Listen)
		if err != nil {
			// --listen held a bare host, which is fine once a port is supplied.
			host = strings.TrimSpace(c.Listen)
		}
		c.Listen = net.JoinHostPort(host, strconv.Itoa(c.Port))
	}
	if _, _, err := net.SplitHostPort(c.Listen); err != nil {
		return fmt.Errorf("--listen: %q is not an address:port (use --port to set just the port)", c.Listen)
	}

	if c.PublicURL != "" {
		u, err := url.Parse(c.PublicURL)
		if err != nil {
			return fmt.Errorf("--public-url: %w", err)
		}
		if !u.IsAbs() {
			return fmt.Errorf("--public-url: %q is not absolute", c.PublicURL)
		}
		c.PublicURL = strings.TrimSuffix(u.String(), "/")
	}

	if c.SourceURL != "" {
		u, err := url.Parse(c.SourceURL)
		if err != nil {
			return fmt.Errorf("--source-url: %w", err)
		}
		if !u.IsAbs() {
			return fmt.Errorf("--source-url: %q is not absolute", c.SourceURL)
		}
		c.SourceURL = u.String()
	}

	if c.TokensPath == "" {
		c.TokensPath = c.DataDir + "/tokens.json"
	}
	if c.MaxExpiry != Unlimited && (c.DefaultExpiry == Unlimited || c.DefaultExpiry > c.MaxExpiry) {
		return fmt.Errorf("--default-expiry (%s) exceeds --max-expiry (%s)",
			FormatDuration(c.DefaultExpiry), FormatDuration(c.MaxExpiry))
	}
	if c.SweepInterval <= 0 {
		return fmt.Errorf("--sweep-interval must be positive")
	}
	if c.MaxConcurrent < 1 {
		return fmt.Errorf("--max-concurrent must be at least 1")
	}

	for _, cidr := range strings.Split(c.TrustedProxy, ",") {
		cidr = strings.TrimSpace(cidr)
		if cidr == "" {
			continue
		}
		// Accept both a bare address and a network.
		if ip := net.ParseIP(cidr); ip != nil {
			bits := 32
			if ip.To4() == nil {
				bits = 128
			}
			c.trustedProxyNets = append(c.trustedProxyNets,
				&net.IPNet{IP: ip, Mask: net.CIDRMask(bits, bits)})
			continue
		}
		_, n, err := net.ParseCIDR(cidr)
		if err != nil {
			return fmt.Errorf("--trusted-proxy: %w", err)
		}
		c.trustedProxyNets = append(c.trustedProxyNets, n)
	}
	return nil
}

// TrustsProxy reports whether X-Forwarded-For from ip should be believed.
func (c *Config) TrustsProxy(ip net.IP) bool {
	for _, n := range c.trustedProxyNets {
		if n.Contains(ip) {
			return true
		}
	}
	return false
}

// NormalisePath canonicalises a mount prefix to "/" or "/prefix/".
func NormalisePath(p string) string {
	p = strings.Trim(strings.TrimSpace(p), "/")
	if p == "" {
		return "/"
	}
	return "/" + p + "/"
}