// Package garage contains helper functions and types which are useful for
// setting up garage configs, processes, and deployments.
package garagesrv

import (
	"crypto/ed25519"
	"crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
)

// DBEngine enumerates the garage db engines which are supported by Isle.
type DBEngine string

// Enumeration of DBEngine values.
const (
	DBEngineLMDB   DBEngine = "lmdb"
	DBEngineSqlite DBEngine = "sqlite"
)

func nodeKeyPath(metaDirPath string) string {
	return filepath.Join(metaDirPath, "node_key")
}

func nodeKeyPubPath(metaDirPath string) string {
	return filepath.Join(metaDirPath, "node_key.pub")
}

// LoadAllocID returns the peer ID (ie the public key) of the node at the given
// meta directory.
func LoadAllocID(metaDirPath string) (string, error) {
	nodeKeyPubPath := nodeKeyPubPath(metaDirPath)

	pubKey, err := os.ReadFile(nodeKeyPubPath)
	if err != nil {
		return "", fmt.Errorf("reading %q: %w", nodeKeyPubPath, err)
	}

	return hex.EncodeToString(pubKey), nil
}

// generatePeerKey generates and returns a public/private key pair for a garage
// instance.
func generatePeerKey() (pubKey, privKey []byte) {
	pubKey, privKey, err := ed25519.GenerateKey(rand.Reader)
	if err != nil {
		panic(err)
	}

	return pubKey, privKey
}

// InitAlloc initializes the meta directory and keys for a particular
// allocation, if it hasn't been done so already. It returns the peer ID (ie the
// public key) in any case.
func InitAlloc(metaDirPath string) (string, error) {

	initDirFor := func(path string) error {
		dir := filepath.Dir(path)
		return os.MkdirAll(dir, 0750)
	}

	var err error
	exists := func(path string) bool {
		if err != nil {
			return false
		} else if _, err = os.Stat(path); errors.Is(err, fs.ErrNotExist) {
			err = nil
			return false
		} else if err != nil {
			err = fmt.Errorf("checking if %q exists: %w", path, err)
			return false
		}
		return true
	}

	var (
		nodeKeyPath    = nodeKeyPath(metaDirPath)
		nodeKeyPubPath = nodeKeyPubPath(metaDirPath)

		nodeKeyPathExists    = exists(nodeKeyPath)
		nodeKeyPubPathExists = exists(nodeKeyPubPath)
	)

	if err != nil {
		return "", err
	} else if nodeKeyPubPathExists != nodeKeyPathExists {
		return "", fmt.Errorf(
			"%q or %q exist without the other existing",
			nodeKeyPath,
			nodeKeyPubPath,
		)
	}

	var pubKeyStr string
	if nodeKeyPathExists {
		if pubKeyStr, err = LoadAllocID(metaDirPath); err != nil {
			return "", fmt.Errorf("reading node public key file: %w", err)
		}

	} else {
		if err := initDirFor(nodeKeyPath); err != nil {
			return "", fmt.Errorf(
				"creating directory for %q: %w", nodeKeyPath, err,
			)
		}

		pubKey, privKey := generatePeerKey()
		if err := os.WriteFile(nodeKeyPath, privKey, 0400); err != nil {
			return "", fmt.Errorf(
				"writing private key to %q: %w", nodeKeyPath, err,
			)

		} else if err := os.WriteFile(nodeKeyPubPath, pubKey, 0440); err != nil {
			return "", fmt.Errorf(
				"writing public key to %q: %w", nodeKeyPubPath, err,
			)
		}

		pubKeyStr = hex.EncodeToString(pubKey)
	}

	return pubKeyStr, nil
}

// GetDBEngine returns the DBEngine currently being used at a particular meta
// data directory, or returns the default if the directory doesn't exist or
// hasn't been fully initialized yet.
func GetDBEngine(
	metaDirPath string, defaultDBEngine DBEngine,
) (
	DBEngine, error,
) {
	search := []struct {
		dbEngine  DBEngine
		path      string
		pathIsDir bool
	}{
		{DBEngineLMDB, filepath.Join(metaDirPath, "db.lmdb"), true},
		{DBEngineSqlite, filepath.Join(metaDirPath, "db.sqlite"), false},
	}

	for _, s := range search {
		stat, err := os.Stat(s.path)
		if errors.Is(err, fs.ErrNotExist) {
			continue
		} else if err != nil {
			return "", fmt.Errorf("checking if %q exists: %w", s.path, err)
		} else if stat.IsDir() != s.pathIsDir {
			continue
		}

		return s.dbEngine, nil
	}

	return defaultDBEngine, nil
}