// Copyright 2023 wanderer <a_mirre at utb dot cz>
// SPDX-License-Identifier: AGPL-3.0-only

package config

import (
	"context"
	"fmt"
	"os"
	"os/exec"
	"time"

	"git.dotya.ml/mirre-mt/pcmt/slogging"
	"github.com/philandstuff/dhall-golang/v6"
	"golang.org/x/exp/slog"
)

type session struct {
	CookieName string
	// CookieAuthSecret is the key used for signing and authentication.
	CookieAuthSecret string
	// CookieEncrSecret is the key used for encrypting.
	CookieEncrSecret string
	MaxAge           int
}

type httpRec struct {
	// Secure denotes whether the HTTP should use TLS (i.e. HTTPS).
	Secure                bool
	Domain                string
	AutoTLS               bool
	TLSCertKeyPath        string
	TLSKeyPath            string
	ContentSecurityPolicy string
	// HSTSMaxAge sets the strict transport security duration, zero mean it's not set.
	HSTSMaxAge int
	// Gzip is the level of gzip compression, 0 means do not enable gzip.
	Gzip int
	// RateLimit controls the number of requests per second, 0 means no limit.
	RateLimit int
	// Timount controls connection timeout in seconds, 0 means no limit.
	Timeout int
}

type mailer struct {
	Enabled              bool
	EnableHELO           bool
	ForceTrustServerCert bool
	Protocol             string
	SMTPPort             int
	SendPlainText        bool
	SubjectPrefix        string
}

type initialiser struct {
	AdminPassword string
	CreateAdmin   bool
}

// Config represents the Dhall configuration schema,
// https://git.dotya.ml/mirre-mt/pcmt-config-schema/ for reference.
type Config struct {
	AppPath      string
	Host         string
	Port         int
	HTTP         httpRec
	LiveMode     bool
	DevelMode    bool
	Session      session
	Registration struct{ Allowed bool }
	Logger       struct {
		JSON bool
		Fmt  string
	}
	Init initialiser
	// Mailer is currently a noop.
	Mailer mailer
}

const (
	schemaCompatibility = "0.0.1-rc.2"

	// authKeySize is the session cookie auth key length in bytes.
	authKeySize = 64
	// encrKeySize is the session cookie encryption key length in bytes.
	encrKeySize = 32
)

var (
	log slogging.Slogger

	errSessionAuthSecretWrongSize = fmt.Errorf("session cookie authentication secret should be *exactly* 64 bytes long, both raw and hex-encoded strings are accepted; make sure to generate the key with sufficient entropy e.g. using openssl")
	errSessionEncrSecretWrongSize = fmt.Errorf("session cookie encryption secret should be *exactly* 32 bytes (for 256 bit AES), both raw and hex-encoded strings are accepted; make sure to generate the key with sufficient entropy e.g. using openssl")
	errSessionSecretZeros         = fmt.Errorf("session cookie secrets cannot be all zeros")
	errInitAdminPasswdEmpty       = fmt.Errorf("requested initial admin creation and the initial admin password is empty")

	// authSecretIsHex is used to recall whether the authentication secret was
	// determined to be pure hex.
	authSecretIsHex bool
	// authSecretIsHex is used to recall whether the encryption secret was
	// determined to be pure hex.
	encrSecretIsHex bool
	quiet           bool
)

func Load(conf string, isPath bool) (*Config, error) {
	var config Config

	var err error

	slogger := slogging.Logger()
	// initialise if not already initialised.
	if slogger == nil {
		/// this should never happen, as the logger is initialised in run.go.
		slogger = slogging.Init(true)
	}

	// have a local copy.
	log = *slogger
	// add attr to all statements made with the local copy.
	log.Logger = log.Logger.With(
		slog.Group("pcmt extra", slog.String("module", "config")),
	)

	log.Debugf("schema compatibility: '%s'", schemaCompatibility)

	switch {
	case isPath:
		log.Debug("config from file")

		err = dhall.UnmarshalFile(conf, &config)
	case !isPath:
		log.Debug("config raw from cmdline")

		err = dhall.Unmarshal([]byte(conf), &config)
	}

	if !config.Logger.JSON {
		slogger = slogging.Init(false)
		log.Logger = slogger.Logger.With(
			slog.Group("pcmt extra", slog.String("module", "config")),
		)
	}

	if config.DevelMode && os.Getenv("PCMT_DEVEL") != "False" && !quiet {
		log.Debug("set DEBUG level based on config value")

		slogger = slogging.SetLevel(slogging.LevelDebug)
		log.Logger = slogger.Logger.With(
			slog.Group("pcmt extra", slog.String("module", "config")),
		)

		log.Debugf("parsed config: %+v", config)

		if dhallCmdExists() {
			_ = prettyPrintConfig(conf, isPath)
		}
	}

	// only return now (if err), after we've had the chance to print the loaded
	// config, as would be the case if the config *did* adhere to the schema imported
	// but app's Config type definition above didn't - "don't know how to
	// decode <nil> into ..." is the most likely outcome in that case and it
	// could be the product of (at least) three things:
	// * completely wrong config not following the schema
	// * config is following a newer schema than the app supports
	// * config is following an older schema than the app supports
	//
	// NOTE: for the most part the only thing checked above would be adherence
	// to config schema (apart from *some* value validation).
	if err != nil {
		return nil, err
	}

	// make sure the secrets meet *basic* requirements for consumption.
	// NOTE: this func does not prevent the user from using dumb but correctly
	// sized keys (such as 32 bytes of 0x01...). secrets are checked if they
	// are not all zero bytes, though.
	if err = checkSessionSecretsLen(&config); err != nil {
		return nil, err
	}

	if config.Init.CreateAdmin && config.Init.AdminPassword == "" {
		return nil, errInitAdminPasswdEmpty
	}

	return &config, nil
}

func (c *Config) SessionSecretsAreHex() (bool, bool) {
	return authSecretIsHex, encrSecretIsHex
}

func checkSessionSecretsLen(conf *Config) error {
	auth := conf.Session.CookieAuthSecret
	encr := conf.Session.CookieEncrSecret

	log.Debugf("auth len bytes: %d", len([]byte(auth)))
	log.Debugf("encr len bytes: %d", len([]byte(encr)))

	switch {
	case (len([]byte(auth)) != authKeySize) && (isHex(auth) && len([]byte(auth)) != 2*authKeySize):
		return errSessionAuthSecretWrongSize

	case (len([]byte(encr)) != encrKeySize) && (isHex(encr) && len([]byte(encr)) != 2*encrKeySize):
		return errSessionEncrSecretWrongSize

	case isAllZeros([]byte(auth)) || isAllZeros([]byte(encr)):
		return errSessionSecretZeros

	case isHex(auth):
		authSecretIsHex = true
		fallthrough

	case isHex(encr):
		encrSecretIsHex = true
	}

	return nil
}

func isAllZeros(b []byte) bool {
	for _, v := range b {
		if v != 0 {
			return false
		}
	}

	return true
}

// isHex checks if the string is a hex string with even number of bytes.
func isHex(s string) bool {
	bs := []byte(s)

	for _, b := range bs {
		if !(b >= '0' && b <= '9' || b >= 'a' && b <= 'f' || b >= 'A' && b <= 'F') {
			return false
		}
	}

	return true
}

func prettyPrintConfig(conf string, isPath bool) error {
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()

	var cmd *exec.Cmd
	if isPath {
		cmd = exec.CommandContext(ctx, "/bin/sh", "-c", "dhall --file "+conf) //nolint:gosec
	} else {
		cmd = exec.CommandContext(ctx, "/bin/sh", "-c", "dhall <<< \""+conf+"\"") //nolint:gosec
	}

	output, err := cmd.CombinedOutput()
	if err != nil {
		log.Debug("could not pretty-print config", "error", err)
		return err
	}

	if isPath {
		fmt.Fprintln(os.Stderr, "\n"+conf+":\n"+string(output))
	} else {
		fmt.Fprintln(os.Stderr, "\nconfig:\n"+string(output))
	}

	return nil
}

func dhallCmdExists() bool {
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()

	if err := exec.CommandContext(ctx, "/bin/sh", "-c", "command -v dhall").Run(); err != nil {
		log.Debug("no command dhall")
		return false
	}

	return true
}

// BeQuiet instruct this package to be more frugal with logging/printing info.
func BeQuiet() {
	quiet = true
}