// Package vault owns TreatVault's encrypted source-of-truth file.
package vault

import (
	"bytes"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
	"sync"

	barkfile "cloud.campbellwireless.net/git/barkstack/barkfile-parser/v2"
	"filippo.io/age"
)

const (
	documentVersion  = 1
	maxSecretBytes   = 500 * 1024
	maxDocumentBytes = 16 * 1024 * 1024
)

var ErrSecretNotFound = errors.New("secret not found")

type Record struct {
	Revision string `json:"revision"`
	Value    []byte `json:"value"`
}

type Snapshot struct {
	Version int               `json:"version"`
	VaultID string            `json:"vaultId"`
	Secrets map[string]Record `json:"secrets"`
}

type Metadata struct {
	Name     string
	Revision string
}

type Store struct {
	path      string
	identity  *age.X25519Identity
	recipient age.Recipient
	mu        sync.Mutex
}

func Open(path, identityPath string) (*Store, error) {
	identity, err := ReadIdentity(identityPath)
	if err != nil {
		return nil, err
	}
	store := &Store{path: path, identity: identity, recipient: identity.Recipient()}
	if _, err := store.Load(); err != nil {
		return nil, err
	}
	return store, nil
}

func New(path string, identity *age.X25519Identity) *Store {
	return &Store{path: path, identity: identity, recipient: identity.Recipient()}
}

func ReadIdentity(path string) (*age.X25519Identity, error) {
	contents, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("read age identity: %w", err)
	}
	identity, err := age.ParseX25519Identity(strings.TrimSpace(string(contents)))
	if err != nil {
		return nil, fmt.Errorf("parse age identity: %w", err)
	}
	return identity, nil
}

func GenerateIdentity(path string) (string, error) {
	identity, err := age.GenerateX25519Identity()
	if err != nil {
		return "", fmt.Errorf("generate age identity: %w", err)
	}
	if _, err := os.Stat(path); err == nil {
		return "", fmt.Errorf("identity file %q already exists", path)
	} else if !errors.Is(err, os.ErrNotExist) {
		return "", err
	}
	if err := writeFileAtomic(path, []byte(identity.String()+"\n"), 0o600); err != nil {
		return "", fmt.Errorf("write age identity: %w", err)
	}
	return identity.Recipient().String(), nil
}

func Initialize(path string, identity *age.X25519Identity) error {
	if _, err := os.Stat(path); err == nil {
		return fmt.Errorf("encrypted file %q already exists", path)
	} else if !errors.Is(err, os.ErrNotExist) {
		return err
	}
	store := New(path, identity)
	vaultID, err := randomHex(8)
	if err != nil {
		return err
	}
	return store.save(Snapshot{Version: documentVersion, VaultID: vaultID, Secrets: map[string]Record{}})
}

func (s *Store) Path() string { return s.path }

func (s *Store) Load() (Snapshot, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.load()
}

func (s *Store) Set(name string, value []byte) (Snapshot, error) {
	if !barkfile.ValidSecretReference(name) {
		return Snapshot{}, fmt.Errorf("invalid secret name %q", name)
	}
	if len(value) == 0 {
		return Snapshot{}, errors.New("secret value must not be empty")
	}
	if len(value) > maxSecretBytes {
		return Snapshot{}, fmt.Errorf("secret value exceeds Docker's %d-byte limit", maxSecretBytes)
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	snapshot, err := s.load()
	if err != nil {
		return Snapshot{}, err
	}
	if existing, ok := snapshot.Secrets[name]; ok && bytes.Equal(existing.Value, value) {
		return snapshot, nil
	}
	revision, err := randomHex(16)
	if err != nil {
		return Snapshot{}, err
	}
	snapshot.Secrets[name] = Record{Revision: revision, Value: append([]byte(nil), value...)}
	if err := s.save(snapshot); err != nil {
		return Snapshot{}, err
	}
	return snapshot, nil
}

func (s *Store) Delete(name string) (Snapshot, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	snapshot, err := s.load()
	if err != nil {
		return Snapshot{}, err
	}
	if _, ok := snapshot.Secrets[name]; !ok {
		return Snapshot{}, ErrSecretNotFound
	}
	delete(snapshot.Secrets, name)
	if err := s.save(snapshot); err != nil {
		return Snapshot{}, err
	}
	return snapshot, nil
}

func (s *Store) load() (Snapshot, error) {
	encrypted, err := os.Open(s.path)
	if err != nil {
		return Snapshot{}, fmt.Errorf("open encrypted file: %w", err)
	}
	defer encrypted.Close()
	plaintext, err := age.Decrypt(encrypted, s.identity)
	if err != nil {
		return Snapshot{}, fmt.Errorf("decrypt encrypted file: %w", err)
	}
	decoder := json.NewDecoder(io.LimitReader(plaintext, maxDocumentBytes+1))
	decoder.DisallowUnknownFields()
	var snapshot Snapshot
	if err := decoder.Decode(&snapshot); err != nil {
		return Snapshot{}, fmt.Errorf("decode encrypted file: %w", err)
	}
	if err := validateSnapshot(snapshot); err != nil {
		return Snapshot{}, fmt.Errorf("validate encrypted file: %w", err)
	}
	return cloneSnapshot(snapshot), nil
}

func (s *Store) save(snapshot Snapshot) error {
	if err := validateSnapshot(snapshot); err != nil {
		return err
	}
	var encrypted bytes.Buffer
	writer, err := age.Encrypt(&encrypted, s.recipient)
	if err != nil {
		return fmt.Errorf("initialize encryption: %w", err)
	}
	encoder := json.NewEncoder(writer)
	encoder.SetEscapeHTML(false)
	if err := encoder.Encode(snapshot); err != nil {
		return fmt.Errorf("encode encrypted file: %w", err)
	}
	if err := writer.Close(); err != nil {
		return fmt.Errorf("finish encryption: %w", err)
	}
	if err := writeFileAtomic(s.path, encrypted.Bytes(), 0o600); err != nil {
		return fmt.Errorf("replace encrypted file: %w", err)
	}
	return nil
}

func validateSnapshot(snapshot Snapshot) error {
	if snapshot.Version != documentVersion {
		return fmt.Errorf("unsupported document version %d", snapshot.Version)
	}
	if len(snapshot.VaultID) != 16 {
		return errors.New("vault ID must be 16 hexadecimal characters")
	}
	if _, err := hex.DecodeString(snapshot.VaultID); err != nil {
		return errors.New("vault ID must be hexadecimal")
	}
	if snapshot.Secrets == nil {
		return errors.New("secrets map is required")
	}
	for name, record := range snapshot.Secrets {
		if !barkfile.ValidSecretReference(name) {
			return fmt.Errorf("invalid secret name %q", name)
		}
		if len(record.Value) == 0 || len(record.Value) > maxSecretBytes {
			return fmt.Errorf("secret %q has invalid value length", name)
		}
		if len(record.Revision) != 32 {
			return fmt.Errorf("secret %q has invalid revision", name)
		}
		if _, err := hex.DecodeString(record.Revision); err != nil {
			return fmt.Errorf("secret %q has invalid revision", name)
		}
	}
	return nil
}

func cloneSnapshot(snapshot Snapshot) Snapshot {
	clone := Snapshot{Version: snapshot.Version, VaultID: snapshot.VaultID, Secrets: make(map[string]Record, len(snapshot.Secrets))}
	for name, record := range snapshot.Secrets {
		record.Value = append([]byte(nil), record.Value...)
		clone.Secrets[name] = record
	}
	return clone
}

func randomHex(bytesCount int) (string, error) {
	value := make([]byte, bytesCount)
	if _, err := rand.Read(value); err != nil {
		return "", fmt.Errorf("generate random identifier: %w", err)
	}
	return hex.EncodeToString(value), nil
}

func writeFileAtomic(path string, contents []byte, mode os.FileMode) error {
	directory := filepath.Dir(path)
	if err := os.MkdirAll(directory, 0o700); err != nil {
		return err
	}
	temporary, err := os.CreateTemp(directory, ".treatvault-*")
	if err != nil {
		return err
	}
	temporaryPath := temporary.Name()
	defer os.Remove(temporaryPath)
	if err := temporary.Chmod(mode); err != nil {
		temporary.Close()
		return err
	}
	if _, err := temporary.Write(contents); err != nil {
		temporary.Close()
		return err
	}
	if err := temporary.Sync(); err != nil {
		temporary.Close()
		return err
	}
	if err := temporary.Close(); err != nil {
		return err
	}
	if err := os.Rename(temporaryPath, path); err != nil {
		return err
	}
	directoryHandle, err := os.Open(directory)
	if err != nil {
		return err
	}
	defer directoryHandle.Close()
	return directoryHandle.Sync()
}