package config

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

const (
	HTTPAddressEnvironment  = "CMROUBAO_HTTP_ADDR"
	DatabasePathEnvironment = "CMROUBAO_DATABASE_PATH"

	defaultHTTPAddress  = "127.0.0.1:8080"
	defaultDatabasePath = "var/cmroubao.db"
)

type LookupEnvironment func(string) (string, bool)

type Config struct {
	HTTPAddress       string
	DatabasePath      string
	ReadHeaderTimeout time.Duration
	ReadTimeout       time.Duration
	WriteTimeout      time.Duration
	IdleTimeout       time.Duration
	ShutdownTimeout   time.Duration
	MaxHeaderBytes    int
}

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
	}

	return Config{
		HTTPAddress:       httpAddress,
		DatabasePath:      filepath.Clean(databasePath),
		ReadHeaderTimeout: 5 * time.Second,
		ReadTimeout:       15 * time.Second,
		WriteTimeout:      30 * time.Second,
		IdleTimeout:       60 * time.Second,
		ShutdownTimeout:   10 * time.Second,
		MaxHeaderBytes:    1 << 20,
	}, 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
}