package shared

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"

	"git.unkin.net/unkin/golib/keyring"
)

// KeyringDesc names the kernel keyring key that seals cached tokens; vcm and
// vctx share it. Tests override it.
var KeyringDesc = "vcm"

// ErrLocked means a cached token exists but cannot be decrypted: the per-boot
// keyring key is gone (reboot) or the file predates encryption.
var ErrLocked = errors.New("token locked")

// Token is the cached result of a successful login. It stores enough detail to
// later inspect or revoke the token (accessor, policies) and to reason about
// its lifetime (issued/expiry, renewable) — not just the secret itself.
type Token struct {
	// Context is the name of the context this token belongs to.
	Context string `json:"context"`
	// Address is the Vault address the token is valid against.
	Address string `json:"address"`
	// Namespace is the Vault namespace the token was issued in (may be empty).
	Namespace string `json:"namespace,omitempty"`

	// Token is the client token secret.
	Token string `json:"token"`
	// Accessor identifies the token without exposing it — enough to revoke it
	// via /auth/token/revoke-accessor.
	Accessor string `json:"accessor,omitempty"`
	// Policies are the policies attached to the token.
	Policies []string `json:"policies,omitempty"`

	// Renewable reports whether the token can be renewed.
	Renewable bool `json:"renewable"`
	// LeaseDurationSeconds is the TTL granted at issue/renew time.
	LeaseDurationSeconds int `json:"lease_duration_seconds,omitempty"`

	// IssuedAt is when this token was obtained (login) or last renewed.
	IssuedAt time.Time `json:"issued_at"`
	// ExpiresAt is IssuedAt + LeaseDuration; zero for non-expiring tokens.
	ExpiresAt time.Time `json:"expires_at,omitempty"`
}

// CacheDir returns the XDG_CACHE_HOME/vcm directory that holds token files.
func CacheDir() string {
	base := os.Getenv("XDG_CACHE_HOME")
	if base == "" {
		home, _ := os.UserHomeDir()
		base = filepath.Join(home, ".cache")
	}
	return filepath.Join(base, appDir)
}

// TokenPath returns the on-disk path for a context's cached token. A context
// name with slashes (e.g. "staging/sydney") maps to a nested path under
// CacheDir. The name is validated to prevent escaping the cache directory.
func TokenPath(context string) (string, error) {
	if err := validateContextName(context); err != nil {
		return "", err
	}
	// Use forward slashes as path separators regardless of platform, matching
	// how contexts are written in the config file.
	rel := filepath.FromSlash(context)
	return filepath.Join(CacheDir(), rel), nil
}

// validateContextName rejects names that could escape the cache directory or
// are otherwise unusable as a relative path.
func validateContextName(context string) error {
	if context == "" {
		return fmt.Errorf("empty context name")
	}
	if strings.HasPrefix(context, "/") || filepath.IsAbs(context) {
		return fmt.Errorf("context name %q must not be absolute", context)
	}
	for _, seg := range strings.Split(context, "/") {
		if seg == "" {
			return fmt.Errorf("context name %q has an empty path segment", context)
		}
		if seg == "." || seg == ".." {
			return fmt.Errorf("context name %q must not contain %q segments", context, seg)
		}
	}
	return nil
}

// SaveToken writes a token to its cache path as keyring-sealed JSON, creating
// parent directories (0700) as needed and writing the file with 0600
// permissions.
func SaveToken(t *Token) error {
	path, err := TokenPath(t.Context)
	if err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
		return fmt.Errorf("creating cache dir: %w", err)
	}
	data, err := json.MarshalIndent(t, "", "  ")
	if err != nil {
		return fmt.Errorf("encoding token: %w", err)
	}
	k, err := keyring.Open(KeyringDesc)
	if err != nil {
		return err
	}
	sealed, err := k.Seal(data)
	if err != nil {
		return fmt.Errorf("encrypting token: %w", err)
	}

	// Write via a unique temp file + rename so a token file is never left
	// partially written and concurrent writers never share a temp file.
	f, err := os.CreateTemp(filepath.Dir(path), ".tmp-*")
	if err != nil {
		return fmt.Errorf("writing token: %w", err)
	}
	defer func() { _ = os.Remove(f.Name()) }()
	_, err = f.Write(sealed)
	if cerr := f.Close(); err == nil {
		err = cerr
	}
	if err != nil {
		return fmt.Errorf("writing token: %w", err)
	}
	if err := os.Rename(f.Name(), path); err != nil {
		return fmt.Errorf("saving token: %w", err)
	}
	return nil
}

// LoadToken reads and decrypts a cached token for a context. A missing token
// wraps os.ErrNotExist; one that cannot be decrypted (key lost on reboot, or a
// legacy plaintext file) wraps ErrLocked. Both mean "run vcm login".
func LoadToken(context string) (*Token, error) {
	path, err := TokenPath(context)
	if err != nil {
		return nil, err
	}
	data, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, fmt.Errorf("no cached token for context %q (run 'vcm login %s'): %w", context, context, os.ErrNotExist)
		}
		return nil, fmt.Errorf("reading token %s: %w", path, err)
	}
	if json.Valid(data) {
		return nil, lockedErr(context)
	}
	k, err := keyring.Open(KeyringDesc)
	if err != nil {
		return nil, err
	}
	plain, err := k.Unseal(data)
	if errors.Is(err, keyring.ErrKeyUnavailable) {
		return nil, lockedErr(context)
	}
	if err != nil {
		return nil, fmt.Errorf("decrypting token %s: %w", path, err)
	}
	var t Token
	if err := json.Unmarshal(plain, &t); err != nil {
		return nil, fmt.Errorf("parsing token %s: %w", path, err)
	}
	return &t, nil
}

func lockedErr(context string) error {
	return fmt.Errorf("cached token for context %q is locked (run 'vcm login %s'): %w", context, context, ErrLocked)
}

// DeleteToken removes a context's cached token file, if present.
func DeleteToken(context string) error {
	path, err := TokenPath(context)
	if err != nil {
		return err
	}
	if err := os.Remove(path); err != nil && !os.IsNotExist(err) {
		return fmt.Errorf("removing token %s: %w", path, err)
	}
	return nil
}