package main

import (
	"context"
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"io"
	"os"
	"path/filepath"

	"git.ipao.vip/rogee/creator-hub/internal/phasea"
)

const credentialFileVersion byte = 1

type persistentCredentialBridge struct {
	directory     string
	key           [32]byte
	chmod         func(*os.File, os.FileMode) error
	syncDirectory func(string) error
}

func newPersistentCredentialBridge(directory string, key []byte) (*persistentCredentialBridge, error) {
	if !filepath.IsAbs(directory) || len(key) != 32 {
		return nil, errors.New("invalid credential provider configuration")
	}
	if err := os.MkdirAll(directory, 0o700); err != nil || os.Chmod(directory, 0o700) != nil {
		return nil, errors.New("initialize credential provider")
	}
	bridge := &persistentCredentialBridge{
		directory: directory, chmod: (*os.File).Chmod, syncDirectory: syncCredentialDirectory,
	}
	copy(bridge.key[:], key)
	return bridge, nil
}

func (bridge *persistentCredentialBridge) Store(ctx context.Context, reference phasea.CredentialReference, key, value string) error {
	if err := ctx.Err(); err != nil {
		return err
	}
	if !validCredentialReference(reference.Provider, key) || value == "" || len(value) > 64<<10 {
		return errors.New("invalid credential")
	}
	aead, err := bridge.aead()
	if err != nil {
		return err
	}
	nonce := make([]byte, aead.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return errors.New("encrypt credential")
	}
	payload := append([]byte{credentialFileVersion}, nonce...)
	payload = aead.Seal(payload, nonce, []byte(value), credentialAAD(reference.Provider, key))
	temporary, err := os.CreateTemp(bridge.directory, ".credential-*")
	if err != nil {
		return errors.New("store credential")
	}
	temporaryName := temporary.Name()
	defer os.Remove(temporaryName)
	if err = bridge.chmod(temporary, 0o600); err == nil {
		_, err = temporary.Write(payload)
	}
	if err == nil {
		err = temporary.Sync()
	}
	if closeErr := temporary.Close(); err == nil {
		err = closeErr
	}
	if err != nil {
		return errors.New("store credential")
	}
	target := bridge.path(reference.Provider, key)
	if os.Rename(temporaryName, target) != nil {
		return errors.New("store credential")
	}
	if bridge.syncDirectory(bridge.directory) != nil {
		cleanupErr := os.Remove(target)
		if cleanupErr == nil {
			cleanupErr = bridge.syncDirectory(bridge.directory)
		}
		if cleanupErr != nil {
			return errors.Join(errors.New("store credential"), errors.New("delete incomplete credential"))
		}
		return errors.New("store credential")
	}
	return nil
}

func (bridge *persistentCredentialBridge) Delete(ctx context.Context, reference phasea.CredentialReference, key string) error {
	if err := ctx.Err(); err != nil {
		return err
	}
	if !validCredentialReference(reference.Provider, key) {
		return errors.New("invalid credential reference")
	}
	if err := os.Remove(bridge.path(reference.Provider, key)); err != nil && !errors.Is(err, os.ErrNotExist) {
		return errors.New("delete credential")
	}
	if err := bridge.syncDirectory(bridge.directory); err != nil {
		return errors.New("delete credential")
	}
	return nil
}

func (bridge *persistentCredentialBridge) Resolve(ctx context.Context, reference phasea.CredentialReference, key string) ([]byte, error) {
	if err := ctx.Err(); err != nil {
		return nil, err
	}
	if !validCredentialReference(reference.Provider, key) {
		return nil, errors.New("invalid credential reference")
	}
	payload, err := os.ReadFile(bridge.path(reference.Provider, key))
	if err != nil {
		return nil, errors.New("resolve credential")
	}
	aead, err := bridge.aead()
	if err != nil {
		return nil, err
	}
	if len(payload) < 1+aead.NonceSize() || payload[0] != credentialFileVersion {
		return nil, errors.New("invalid credential")
	}
	nonceEnd := 1 + aead.NonceSize()
	value, err := aead.Open(nil, payload[1:nonceEnd], payload[nonceEnd:], credentialAAD(reference.Provider, key))
	if err != nil {
		return nil, errors.New("resolve credential")
	}
	return value, nil
}

func (bridge *persistentCredentialBridge) aead() (cipher.AEAD, error) {
	block, err := aes.NewCipher(bridge.key[:])
	if err != nil {
		return nil, errors.New("initialize credential encryption")
	}
	return cipher.NewGCM(block)
}

func (bridge *persistentCredentialBridge) path(provider, key string) string {
	digest := sha256.Sum256(credentialAAD(provider, key))
	return filepath.Join(bridge.directory, hex.EncodeToString(digest[:])+".credential")
}

func credentialAAD(provider, key string) []byte { return []byte(provider + "\x00" + key) }

func validCredentialReference(provider, key string) bool {
	return (provider == "os_keyring" || provider == "secret_manager") && key != "" && len(key) <= 192
}

func syncCredentialDirectory(path string) error {
	directory, err := os.Open(path)
	if err != nil {
		return err
	}
	defer directory.Close()
	return directory.Sync()
}