package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"net/url"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"time"
)

const (
	DefaultBandwidthMB   = 500
	DefaultMaxConcurrent = 2
	DefaultMaxTunnels    = 2
	ConfigDirName        = "devplace-node"
	ConfigFileName       = "config.json"
	UsageFileName        = "usage.json"
	maxConfigBytes       = 64 * 1024
)

var hoursPattern = regexp.MustCompile(`^([01]\d|2[0-3]):[0-5]\d$`)

type Config struct {
	Server         string `json:"server"`
	Secret         string `json:"secret"`
	BandwidthMBDay int    `json:"bandwidth_mb_day"`
	MaxConcurrent  int    `json:"max_concurrent"`
	MaxTunnels     int    `json:"max_tunnels"`
	ActiveFrom     string `json:"active_from"`
	ActiveTo       string `json:"active_to"`
	Timezone       string `json:"timezone"`
}

func DefaultConfig() Config {
	return Config{
		BandwidthMBDay: DefaultBandwidthMB,
		MaxConcurrent:  DefaultMaxConcurrent,
		MaxTunnels:     DefaultMaxTunnels,
	}
}

func DefaultConfigPath() (string, error) {
	base, err := os.UserConfigDir()
	if err != nil {
		return "", fmt.Errorf("cannot find the user config directory: %w", err)
	}
	return filepath.Join(base, ConfigDirName, ConfigFileName), nil
}

func (c Config) Validate() error {
	parsed, err := url.Parse(c.Server)
	if err != nil || (parsed.Scheme != "http" && parsed.Scheme != "https") || parsed.Host == "" {
		return errors.New("server must be an http or https url such as https://devplace.net")
	}
	if !strings.HasPrefix(c.Secret, SecretPrefix) || len(c.Secret) < len(SecretPrefix)+8 {
		return errors.New("secret must be a device secret starting with " + SecretPrefix)
	}
	if c.BandwidthMBDay < 1 || c.BandwidthMBDay > MaxDonorMBPerDay {
		return fmt.Errorf("bandwidth_mb_day must be between 1 and %d", MaxDonorMBPerDay)
	}
	if c.MaxConcurrent < 1 || c.MaxConcurrent > MaxConcurrentCeiling {
		return fmt.Errorf("max_concurrent must be between 1 and %d", MaxConcurrentCeiling)
	}
	if c.MaxTunnels < 1 || c.MaxTunnels > MaxTunnelsCeiling {
		return fmt.Errorf("max_tunnels must be between 1 and %d", MaxTunnelsCeiling)
	}
	for _, value := range []string{c.ActiveFrom, c.ActiveTo} {
		if value != "" && !hoursPattern.MatchString(value) {
			return errors.New("active_from and active_to must be empty or HH:MM")
		}
	}
	if (c.ActiveFrom == "") != (c.ActiveTo == "") {
		return errors.New("active_from and active_to must be set together")
	}
	if _, err := c.Location(); err != nil {
		return err
	}
	return nil
}

func (c Config) Location() (*time.Location, error) {
	if c.Timezone == "" {
		return time.Local, nil
	}
	location, err := time.LoadLocation(c.Timezone)
	if err != nil {
		return nil, fmt.Errorf("timezone %q is not known", c.Timezone)
	}
	return location, nil
}

func (c Config) BaseURL() string {
	return strings.TrimRight(c.Server, "/")
}

func LoadConfig(path string) (Config, error) {
	file, err := os.Open(path)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return Config{}, fmt.Errorf("no config at %s, run: devplace-node login --server URL --secret dpn_...", path)
		}
		return Config{}, err
	}
	defer file.Close()
	config := DefaultConfig()
	decoder := json.NewDecoder(&limitedReader{r: file, left: maxConfigBytes})
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(&config); err != nil {
		return Config{}, fmt.Errorf("config %s is invalid: %w", path, err)
	}
	if err := config.Validate(); err != nil {
		return Config{}, fmt.Errorf("config %s is invalid: %w", path, err)
	}
	return config, nil
}

type limitedReader struct {
	r    *os.File
	left int
}

func (l *limitedReader) Read(p []byte) (int, error) {
	if l.left <= 0 {
		return 0, errors.New("file is too large")
	}
	if len(p) > l.left {
		p = p[:l.left]
	}
	n, err := l.r.Read(p)
	l.left -= n
	return n, err
}

func SaveConfig(path string, config Config) error {
	if err := config.Validate(); err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
		return err
	}
	data, err := json.MarshalIndent(config, "", "  ")
	if err != nil {
		return err
	}
	return writeFileAtomic(path, append(data, '\n'))
}

func writeFileAtomic(path string, data []byte) error {
	temp, err := os.CreateTemp(filepath.Dir(path), ".tmp-*")
	if err != nil {
		return err
	}
	name := temp.Name()
	if err := temp.Chmod(0o600); err != nil {
		temp.Close()
		os.Remove(name)
		return err
	}
	if _, err := temp.Write(data); err != nil {
		temp.Close()
		os.Remove(name)
		return err
	}
	if err := temp.Close(); err != nil {
		os.Remove(name)
		return err
	}
	if err := os.Rename(name, path); err != nil {
		os.Remove(name)
		return err
	}
	return nil
}