// Package vaultgpg is a thin client for Ben's Vault GPG secrets engine
// (vault-plugin-secrets-gpg), used two ways:
//
//   - the service reads the ARMORED PUBLIC key (GET <mount>/keys/<name>) to
//     encrypt objects locally; and
//   - the CLI decrypts a wrapped DEK (POST <mount>/decrypt/<name>) to retrieve
//     objects. The engine does whole-payload decrypt only, but logarchiver only
//     ever sends it the tiny wrapped-DEK blob, so that is a non-issue.
//
// Auth mirrors passv: ambient VAULT_* env (token or ~/.vault-token) for humans,
// or the kubernetes auth method for the in-cluster service.
package vaultgpg

import (
	"context"
	"encoding/base64"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"

	vault "github.com/hashicorp/vault/api"
)

// Config configures the Vault client.
type Config struct {
	Address    string
	Mount      string // e.g. "gpg"
	AuthMethod string // "token" | "kubernetes"
	K8sRole    string
	K8sMount   string // e.g. "k8s/au/syd1"
	K8sJWTPath string
	CAFile     string
}

// Client wraps the Vault API client for GPG-engine operations.
type Client struct {
	api   *vault.Client
	mount string
}

// New builds a Client and authenticates per cfg.AuthMethod.
func New(ctx context.Context, cfg Config) (*Client, error) {
	vc := vault.DefaultConfig()
	if err := vc.ReadEnvironment(); err != nil {
		return nil, fmt.Errorf("read vault env: %w", err)
	}
	if cfg.Address != "" {
		vc.Address = cfg.Address
	}
	if cfg.CAFile != "" {
		if err := vc.ConfigureTLS(&vault.TLSConfig{CACert: cfg.CAFile}); err != nil {
			return nil, fmt.Errorf("configure vault tls: %w", err)
		}
	}
	api, err := vault.NewClient(vc)
	if err != nil {
		return nil, fmt.Errorf("new vault client: %w", err)
	}
	mount := cfg.Mount
	if mount == "" {
		mount = "gpg"
	}
	c := &Client{api: api, mount: strings.Trim(mount, "/")}

	switch cfg.AuthMethod {
	case "", "token":
		if api.Token() == "" {
			tok, err := resolveToken()
			if err != nil {
				return nil, err
			}
			api.SetToken(tok)
		}
	case "kubernetes":
		if err := c.k8sLogin(ctx, cfg); err != nil {
			return nil, err
		}
	default:
		return nil, fmt.Errorf("unknown vault auth_method %q", cfg.AuthMethod)
	}
	return c, nil
}

func (c *Client) k8sLogin(ctx context.Context, cfg Config) error {
	jwtPath := cfg.K8sJWTPath
	if jwtPath == "" {
		jwtPath = "/var/run/secrets/kubernetes.io/serviceaccount/token"
	}
	jwt, err := os.ReadFile(jwtPath)
	if err != nil {
		return fmt.Errorf("read service account token: %w", err)
	}
	mount := cfg.K8sMount
	if mount == "" {
		mount = "kubernetes"
	}
	path := fmt.Sprintf("auth/%s/login", strings.Trim(mount, "/"))
	secret, err := c.api.Logical().WriteWithContext(ctx, path, map[string]any{
		"role": cfg.K8sRole,
		"jwt":  strings.TrimSpace(string(jwt)),
	})
	if err != nil {
		return fmt.Errorf("kubernetes login: %w", err)
	}
	if secret == nil || secret.Auth == nil || secret.Auth.ClientToken == "" {
		return fmt.Errorf("kubernetes login returned no token")
	}
	c.api.SetToken(secret.Auth.ClientToken)
	return nil
}

// resolveToken mirrors passv: VAULT_TOKEN, else ~/.vault-token.
func resolveToken() (string, error) {
	if t := os.Getenv("VAULT_TOKEN"); t != "" {
		return t, nil
	}
	home, err := os.UserHomeDir()
	if err != nil {
		return "", fmt.Errorf("no VAULT_TOKEN and cannot find home dir: %w", err)
	}
	data, err := os.ReadFile(filepath.Join(home, ".vault-token"))
	if err != nil {
		return "", fmt.Errorf("no VAULT_TOKEN and no ~/.vault-token: %w", err)
	}
	tok := strings.TrimSpace(string(data))
	if tok == "" {
		return "", fmt.Errorf("~/.vault-token is empty")
	}
	return tok, nil
}

// PublicKey is the result of reading a GPG engine key.
type PublicKey struct {
	Armored     string
	Fingerprint string
}

// FetchPublicKey reads <mount>/keys/<name> and returns the latest armored public
// key and its fingerprint.
func (c *Client) FetchPublicKey(ctx context.Context, name string) (PublicKey, error) {
	path := fmt.Sprintf("%s/keys/%s", c.mount, name)
	secret, err := c.api.Logical().ReadWithContext(ctx, path)
	if err != nil {
		return PublicKey{}, fmt.Errorf("read %s: %w", path, err)
	}
	if secret == nil || secret.Data == nil {
		return PublicKey{}, fmt.Errorf("key %q not found at %s", name, path)
	}
	pub, _ := secret.Data["public_key"].(string)
	if pub == "" {
		return PublicKey{}, fmt.Errorf("key %q has no public_key field", name)
	}
	fpr, _ := secret.Data["fingerprint"].(string)
	return PublicKey{Armored: pub, Fingerprint: fpr}, nil
}

// Decrypt sends ciphertext (raw binary OpenPGP) to <mount>/decrypt/<name> and
// returns the plaintext. The engine auto-detects binary vs armored; we send
// base64 of the raw bytes, as passv does.
func (c *Client) Decrypt(ctx context.Context, name string, ciphertext []byte) ([]byte, error) {
	path := fmt.Sprintf("%s/decrypt/%s", c.mount, name)
	secret, err := c.api.Logical().WriteWithContext(ctx, path, map[string]any{
		"ciphertext": base64.StdEncoding.EncodeToString(ciphertext),
	})
	if err != nil {
		return nil, fmt.Errorf("decrypt via %s: %w", path, err)
	}
	if secret == nil || secret.Data == nil {
		return nil, fmt.Errorf("decrypt returned no data")
	}
	b64, _ := secret.Data["plaintext"].(string)
	if b64 == "" {
		return nil, fmt.Errorf("decrypt returned no plaintext")
	}
	plain, err := base64.StdEncoding.DecodeString(b64)
	if err != nil {
		return nil, fmt.Errorf("decode plaintext: %w", err)
	}
	return plain, nil
}

// TokenTTL returns the remaining lease TTL of the current token, for diagnostics.
func (c *Client) TokenTTL(ctx context.Context) (time.Duration, error) {
	secret, err := c.api.Auth().Token().LookupSelfWithContext(ctx)
	if err != nil {
		return 0, err
	}
	ttl, err := secret.TokenTTL()
	if err != nil {
		return 0, err
	}
	return ttl, nil
}