package config

import (
	"errors"
	"net"
	"net/url"
	"path/filepath"
	"strconv"
	"strings"
	"time"
)

const (
	HTTPAddressEnvironment        = "CMROUBAO_HTTP_ADDR"
	DatabasePathEnvironment       = "CMROUBAO_DATABASE_PATH"
	AssetDirectoryEnvironment     = "CMROUBAO_ASSET_DIR"
	TLSCertificateEnvironment     = "CMROUBAO_TLS_CERT_FILE"
	TLSPrivateKeyEnvironment      = "CMROUBAO_TLS_KEY_FILE"
	ClaimLeaseEnvironment         = "CMROUBAO_CLAIM_LEASE"
	RunningLeaseEnvironment       = "CMROUBAO_RUNNING_LEASE"
	ReadinessTTLEnvironment       = "CMROUBAO_READINESS_TTL"
	ShunyunbaoURLEnvironment      = "CMROUBAO_SHUNYUNBAO_URL"
	ShunyunbaoUsernameEnvironment = "CMROUBAO_SHUNYUNBAO_USERNAME"
	ShunyunbaoPasswordEnvironment = "CMROUBAO_SHUNYUNBAO_PASSWORD"
	OCRAPIURLEnvironment          = "CMROUBAO_OCR_API_URL"

	defaultHTTPAddress    = "127.0.0.1:8080"
	defaultDatabasePath   = "var/cmroubao.db"
	defaultAssetDirectory = "var/assets"
	defaultClaimLease     = 10 * time.Minute
	defaultRunningLease   = 30 * time.Minute
	defaultReadinessTTL   = 2 * time.Minute
	defaultShunyunbaoURL  = "https://www.shunyunbaoerp.com"
)

type LookupEnvironment func(string) (string, bool)

type Config struct {
	HTTPAddress        string
	DatabasePath       string
	AssetDirectory     string
	TLSCertificate     string
	TLSPrivateKey      string
	ReadHeaderTimeout  time.Duration
	ReadTimeout        time.Duration
	WriteTimeout       time.Duration
	IdleTimeout        time.Duration
	ShutdownTimeout    time.Duration
	MaxHeaderBytes     int
	ClaimLease         time.Duration
	RunningLease       time.Duration
	ReadinessTTL       time.Duration
	ShunyunbaoURL      string
	ShunyunbaoUsername string
	ShunyunbaoPassword string
	OCRAPIURL          string
	ShunyunbaoTimeout  time.Duration
}

func Load(lookup LookupEnvironment) (Config, error) {
	httpAddress, err := environmentValue(
		lookup,
		HTTPAddressEnvironment,
		defaultHTTPAddress,
	)
	if err != nil {
		return Config{}, err
	}
	if err := validateHTTPAddress(httpAddress); err != nil {
		return Config{}, err
	}

	databasePath, err := environmentValue(
		lookup,
		DatabasePathEnvironment,
		defaultDatabasePath,
	)
	databasePath, err = validatedDatabasePath(databasePath, err)
	if err != nil {
		return Config{}, err
	}

	assetDirectory, err := environmentValue(
		lookup,
		AssetDirectoryEnvironment,
		defaultAssetDirectory,
	)
	if err != nil {
		return Config{}, err
	}
	assetDirectory, err = validatedAssetDirectory(assetDirectory)
	if err != nil {
		return Config{}, err
	}
	tlsCertificate, certificateSet, err := optionalEnvironmentValue(
		lookup,
		TLSCertificateEnvironment,
	)
	if err != nil {
		return Config{}, err
	}
	tlsPrivateKey, privateKeySet, err := optionalEnvironmentValue(
		lookup,
		TLSPrivateKeyEnvironment,
	)
	if err != nil {
		return Config{}, err
	}
	if certificateSet != privateKeySet {
		return Config{}, errors.New(
			TLSCertificateEnvironment + " and " +
				TLSPrivateKeyEnvironment + " must be set together",
		)
	}
	if !certificateSet && !isLoopbackAddress(httpAddress) {
		return Config{}, errors.New(
			HTTPAddressEnvironment +
				" must use loopback unless TLS is configured",
		)
	}
	claimLease, err := durationEnvironment(
		lookup,
		ClaimLeaseEnvironment,
		defaultClaimLease,
		time.Minute,
		30*time.Minute,
	)
	if err != nil {
		return Config{}, err
	}
	runningLease, err := durationEnvironment(
		lookup,
		RunningLeaseEnvironment,
		defaultRunningLease,
		5*time.Minute,
		120*time.Minute,
	)
	if err != nil {
		return Config{}, err
	}
	readinessTTL, err := durationEnvironment(
		lookup,
		ReadinessTTLEnvironment,
		defaultReadinessTTL,
		30*time.Second,
		10*time.Minute,
	)
	if err != nil {
		return Config{}, err
	}
	shunyunbaoURL, err := environmentValue(
		lookup,
		ShunyunbaoURLEnvironment,
		defaultShunyunbaoURL,
	)
	if err != nil {
		return Config{}, err
	}
	if err := validateHTTPSOrigin(shunyunbaoURL, ShunyunbaoURLEnvironment); err != nil {
		return Config{}, err
	}
	shunyunbaoUsername, usernameSet, err := optionalEnvironmentValue(
		lookup,
		ShunyunbaoUsernameEnvironment,
	)
	if err != nil {
		return Config{}, err
	}
	shunyunbaoPassword, passwordSet, err := optionalSecretEnvironmentValue(
		lookup,
		ShunyunbaoPasswordEnvironment,
	)
	if err != nil {
		return Config{}, err
	}
	if usernameSet != passwordSet {
		return Config{}, errors.New(
			ShunyunbaoUsernameEnvironment + " and " +
				ShunyunbaoPasswordEnvironment + " must be set together",
		)
	}
	ocrAPIURL, ocrAPISet, err := optionalEnvironmentValue(lookup, OCRAPIURLEnvironment)
	if err != nil {
		return Config{}, err
	}
	if ocrAPISet && !validOCRAPIURL(ocrAPIURL) {
		return Config{}, errors.New(OCRAPIURLEnvironment + " must be an approved OCR endpoint")
	}

	return Config{
		HTTPAddress:        httpAddress,
		DatabasePath:       filepath.Clean(databasePath),
		AssetDirectory:     assetDirectory,
		TLSCertificate:     cleanOptionalPath(tlsCertificate),
		TLSPrivateKey:      cleanOptionalPath(tlsPrivateKey),
		ReadHeaderTimeout:  5 * time.Second,
		ReadTimeout:        15 * time.Second,
		WriteTimeout:       30 * time.Second,
		IdleTimeout:        60 * time.Second,
		ShutdownTimeout:    10 * time.Second,
		MaxHeaderBytes:     1 << 20,
		ClaimLease:         claimLease,
		RunningLease:       runningLease,
		ReadinessTTL:       readinessTTL,
		ShunyunbaoURL:      strings.TrimRight(shunyunbaoURL, "/"),
		ShunyunbaoUsername: shunyunbaoUsername,
		ShunyunbaoPassword: shunyunbaoPassword,
		OCRAPIURL:          ocrAPIURL,
		ShunyunbaoTimeout:  30 * time.Second,
	}, nil
}

func validOCRAPIURL(value string) bool {
	parsed, err := url.Parse(value)
	if err != nil || parsed.Host == "" || parsed.User != nil ||
		parsed.RawQuery != "" || parsed.Fragment != "" || parsed.Path == "" {
		return false
	}
	if port := parsed.Port(); port != "" {
		parsedPort, portErr := strconv.Atoi(port)
		if portErr != nil || parsedPort < 1 || parsedPort > 65535 {
			return false
		}
	}
	if parsed.Scheme == "https" {
		return true
	}
	if parsed.Scheme != "http" {
		return false
	}
	host := strings.Trim(parsed.Hostname(), "[]")
	return strings.EqualFold(host, "localhost") ||
		(net.ParseIP(host) != nil && net.ParseIP(host).IsLoopback())
}

func validateHTTPSOrigin(value, environment string) error {
	parsed, err := url.Parse(value)
	if err != nil || parsed.Scheme != "https" || parsed.Host == "" ||
		parsed.User != nil || parsed.RawQuery != "" || parsed.Fragment != "" ||
		(parsed.Path != "" && parsed.Path != "/") {
		return errors.New(
			environment + " must be an https origin without credentials or path",
		)
	}
	return nil
}

func durationEnvironment(
	lookup LookupEnvironment,
	name string,
	defaultValue time.Duration,
	minimum time.Duration,
	maximum time.Duration,
) (time.Duration, error) {
	value, exists := lookup(name)
	if !exists {
		return defaultValue, nil
	}
	value = strings.TrimSpace(value)
	duration, err := time.ParseDuration(value)
	if err != nil || duration < minimum || duration > maximum {
		return 0, errors.New(
			name + " must be a duration between " +
				minimum.String() + " and " + maximum.String(),
		)
	}
	return duration, nil
}

func cleanOptionalPath(value string) string {
	if value == "" {
		return ""
	}
	return filepath.Clean(value)
}

func optionalEnvironmentValue(
	lookup LookupEnvironment,
	name string,
) (string, bool, error) {
	value, exists := lookup(name)
	if !exists {
		return "", false, nil
	}
	value = strings.TrimSpace(value)
	if value == "" {
		return "", false, errors.New(name + " must not be blank")
	}
	if strings.ContainsRune(value, '\x00') {
		return "", false, errors.New(name + " contains an invalid character")
	}
	return value, true, nil
}

func optionalSecretEnvironmentValue(
	lookup LookupEnvironment,
	name string,
) (string, bool, error) {
	value, exists := lookup(name)
	if !exists {
		return "", false, nil
	}
	if value == "" || strings.ContainsRune(value, '\x00') {
		return "", false, errors.New(name + " must not be blank")
	}
	return value, true, nil
}

func isLoopbackAddress(address string) bool {
	host, _, err := net.SplitHostPort(address)
	if err != nil {
		return false
	}
	if strings.EqualFold(host, "localhost") {
		return true
	}
	ip := net.ParseIP(host)
	return ip != nil && ip.IsLoopback()
}

func validatedAssetDirectory(path string) (string, error) {
	if strings.ContainsRune(path, '\x00') {
		return "", errors.New(
			AssetDirectoryEnvironment + " contains an invalid character",
		)
	}
	cleanPath := filepath.Clean(path)
	volumeRoot := filepath.VolumeName(cleanPath) + string(filepath.Separator)
	if cleanPath == "." ||
		cleanPath == string(filepath.Separator) ||
		cleanPath == volumeRoot {
		return "", errors.New(
			AssetDirectoryEnvironment + " must be a dedicated directory",
		)
	}
	return cleanPath, nil
}

func LoadDatabasePath(lookup LookupEnvironment) (string, error) {
	databasePath, err := environmentValue(
		lookup,
		DatabasePathEnvironment,
		defaultDatabasePath,
	)
	return validatedDatabasePath(databasePath, err)
}

func environmentValue(
	lookup LookupEnvironment,
	name string,
	defaultValue string,
) (string, error) {
	value, exists := lookup(name)
	if !exists {
		return defaultValue, nil
	}
	value = strings.TrimSpace(value)
	if value == "" {
		return "", errors.New(name + " must not be blank")
	}
	return value, nil
}

func validateHTTPAddress(address string) error {
	host, portValue, err := net.SplitHostPort(address)
	if err != nil || strings.TrimSpace(host) == "" {
		return errors.New(HTTPAddressEnvironment + " must include a host and port")
	}
	port, err := strconv.Atoi(portValue)
	if err != nil || port < 1 || port > 65535 {
		return errors.New(HTTPAddressEnvironment + " port must be between 1 and 65535")
	}
	return nil
}

func validatedDatabasePath(path string, previousError error) (string, error) {
	if previousError != nil {
		return "", previousError
	}
	if strings.ContainsRune(path, '\x00') {
		return "", errors.New(
			DatabasePathEnvironment + " contains an invalid character",
		)
	}
	lowerPath := strings.ToLower(path)
	cleanPath := filepath.Clean(path)
	extension := strings.ToLower(filepath.Ext(cleanPath))
	if cleanPath == "." ||
		cleanPath == string(filepath.Separator) ||
		lowerPath == ":memory:" ||
		strings.HasPrefix(lowerPath, "file:") ||
		(extension != ".db" && extension != ".sqlite" && extension != ".sqlite3") {
		return "", errors.New(
			DatabasePathEnvironment + " must be a SQLite file path",
		)
	}
	return cleanPath, nil
}