package vault

import (
	"encoding/json"
	"fmt"
	"path"
	"sync"
	"time"

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

const (
	// expirationSubPath is the sub-path used for the expiration manager
	// view. This is nested under the system view.
	expirationSubPath = "expire/"
)

// ExpirationManager is used by the Core to manage leases. Secrets
// can provide a lease, meaning that they can be renewed or revoked.
// If a secret is not renewed in timely manner, it may be expired, and
// the ExpirationManager will handle doing automatic revocation.
type ExpirationManager struct {
	router   *Router
	view     *BarrierView
	doneCh   chan struct{}
	stopCh   chan struct{}
	stopLock sync.Mutex
}

// NewExpirationManager creates a new ExpirationManager that is backed
// using a given view, and uses the provided router for revocation.
func NewExpirationManager(router *Router, view *BarrierView) *ExpirationManager {
	exp := &ExpirationManager{
		router: router,
		view:   view,
	}
	return exp
}

// setupExpiration is invoked after we've loaded the mount table to
// initialize the expiration manager
func (c *Core) setupExpiration() error {
	// Create a sub-view
	view := c.systemView.SubView(expirationSubPath)

	// Create the manager
	mgr := NewExpirationManager(c.router, view)
	c.expiration = mgr

	// Restore the existing state
	if err := c.expiration.Restore(); err != nil {
		return fmt.Errorf("expiration state restore failed: %v", err)
	}

	// Start the expiration manager
	if err := c.expiration.Start(); err != nil {
		return fmt.Errorf("expiration start failed: %v", err)
	}
	return nil
}

// stopExpiration is used to stop the expiration manager before
// sealing the Vault.
func (c *Core) stopExpiration() error {
	if err := c.expiration.Stop(); err != nil {
		return err
	}
	c.expiration = nil
	return nil
}

// Restore is used to recover the lease states when starting.
// This is used after starting the vault.
func (m *ExpirationManager) Restore() error {
	m.stopLock.Lock()
	defer m.stopLock.Unlock()
	if m.stopCh != nil {
		return fmt.Errorf("cannot restore while running")
	}

	// TODO: Restore...
	return nil
}

// Start is used to continue automatic revocation. This
// should only be called when the Vault is unsealed.
func (m *ExpirationManager) Start() error {
	m.stopLock.Lock()
	defer m.stopLock.Unlock()
	if m.stopCh == nil {
		m.doneCh = make(chan struct{})
		m.stopCh = make(chan struct{})
		go m.run(m.doneCh, m.stopCh)
	}
	return nil
}

// Stop is used to prevent further automatic revocations.
// This must be called before sealing the view.
func (m *ExpirationManager) Stop() error {
	m.stopLock.Lock()
	defer m.stopLock.Unlock()
	if m.stopCh != nil {
		doneCh := m.doneCh
		close(m.stopCh)
		m.stopCh = nil
		m.doneCh = nil
		<-doneCh // Wait for completion
	}
	return nil
}

// run is a long running goroutine that manages background expiration
func (m *ExpirationManager) run(doneCh, stopCh chan struct{}) {
	defer close(doneCh)
	for {
		select {
		case <-stopCh:
			return
		}
	}
}

// Revoke is used to revoke a secret named by the given vaultID
func (m *ExpirationManager) Revoke(vaultID string) error {
	return nil
}

// RevokePrefix is used to revoke all secrets with a given prefix.
// The prefix maps to that of the mount table to make this simpler
// to reason about.
func (m *ExpirationManager) RevokePrefix(prefix string) error {
	return nil
}

// Renew is used to renew a secret using the given vaultID
// and a renew interval. The increment may be ignored.
func (m *ExpirationManager) Renew(vaultID string, increment time.Duration) (*logical.Lease, error) {
	return nil, nil
}

// Register is used to take a request and response with an associated
// lease. The secret gets assigned a vaultId and the management of
// of lease is assumed by the expiration manager.
func (m *ExpirationManager) Register(req *logical.Request, resp *logical.Response) (string, error) {
	// Ignore if there is no lease
	if resp == nil || resp.Lease == nil {
		return "", nil
	}

	// Validate the lease
	if err := resp.Lease.Validate(); err != nil {
		return "", err
	}

	// Cannot register a non-secret (e.g. a policy or configuration key)
	if !resp.IsSecret {
		return "", fmt.Errorf("cannot attach lease to non-secret")
	}

	// Create a lease entry
	now := time.Now().UTC()
	le := leaseEntry{
		VaultID:   path.Join(req.Path, generateUUID()),
		Path:      req.Path,
		Data:      resp.Data,
		Lease:     resp.Lease,
		IssueTime: now,
		RenewTime: now,
	}

	// Encode the entry
	buf, err := le.encode()
	if err != nil {
		return "", fmt.Errorf("failed to encode lease entry: %v", err)
	}

	// Write out to the view
	ent := logical.StorageEntry{
		Key:   le.VaultID,
		Value: buf,
	}
	if err := m.view.Put(&ent); err != nil {
		return "", fmt.Errorf("failed to persist lease entry: %v", err)
	}

	// TODO: Automatic revoke timer...

	// Done
	return le.VaultID, nil
}

// leaseEntry is used to structure the values the expiration
// manager stores. This is used to handle renew and revocation.
type leaseEntry struct {
	VaultID   string
	Path      string
	Data      map[string]interface{}
	Lease     *logical.Lease
	IssueTime time.Time
	RenewTime time.Time
}

// encode is used to JSON encode the lease entry
func (l *leaseEntry) encode() ([]byte, error) {
	return json.Marshal(l)
}

// decodeLeaseEntry is used to reverse encode and return a new entry
func decodeLeaseEntry(buf []byte) (*leaseEntry, error) {
	out := new(leaseEntry)
	return out, json.Unmarshal(buf, out)
}