// Package config loads he-dydns configuration from a TOML file.
package config

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"github.com/BurntSushi/toml"
)

const DefaultIntervalMinutes = 5

// RecordType identifies which DNS record family an entry updates. Hurricane
// Electric's dynamic DNS API cannot infer this from the submitted address
// alone, so it must be configured explicitly per entry.
type RecordType string

const (
	RecordTypeA    RecordType = "A"
	RecordTypeAAAA RecordType = "AAAA"
)

// Entry describes a single Hurricane Electric dynamic DNS hostname to keep updated.
type Entry struct {
	Hostname string `toml:"hostname"`
	Token    string `toml:"token"`
	// RecordType selects whether this entry updates the A (IPv4) or AAAA
	// (IPv6) record. Defaults to A when omitted.
	RecordType RecordType `toml:"record_type"`
}

// Config is the top-level he-dydns configuration.
type Config struct {
	// Interface, if set, restricts address discovery to this network
	// interface instead of guessing the public IP via an external service.
	Interface string `toml:"interface"`
	// IntervalMinutes controls how often updates run in daemon mode.
	IntervalMinutes int     `toml:"interval_minutes"`
	Entries         []Entry `toml:"entries"`
}

// DefaultPath returns $HOME/.config/he-dydns/config.toml.
func DefaultPath() (string, error) {
	home, err := os.UserHomeDir()
	if err != nil {
		return "", fmt.Errorf("determining home directory: %w", err)
	}
	return filepath.Join(home, ".config", "he-dydns", "config.toml"), nil
}

// Load reads and validates the configuration file at path.
func Load(path string) (*Config, error) {
	var cfg Config
	if _, err := toml.DecodeFile(path, &cfg); err != nil {
		return nil, fmt.Errorf("reading config %s: %w", path, err)
	}

	if len(cfg.Entries) == 0 {
		return nil, fmt.Errorf("config %s: no entries defined", path)
	}
	for i := range cfg.Entries {
		e := &cfg.Entries[i]
		if e.Hostname == "" {
			return nil, fmt.Errorf("config %s: entries[%d] missing hostname", path, i)
		}
		if e.Token == "" {
			return nil, fmt.Errorf("config %s: entries[%d] missing token", path, i)
		}

		switch RecordType(strings.ToUpper(string(e.RecordType))) {
		case "":
			e.RecordType = RecordTypeA
		case RecordTypeA:
			e.RecordType = RecordTypeA
		case RecordTypeAAAA:
			e.RecordType = RecordTypeAAAA
		default:
			return nil, fmt.Errorf("config %s: entries[%d] invalid record_type %q (must be \"A\" or \"AAAA\")", path, i, e.RecordType)
		}
	}

	if cfg.IntervalMinutes <= 0 {
		cfg.IntervalMinutes = DefaultIntervalMinutes
	}

	return &cfg, nil
}