package secrets

import (
	"container/heap"
	"context"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"path"
	"sync"
	"time"

	glos "code.crute.us/mcrute/golib/os"

	"github.com/hashicorp/vault/api"
	"github.com/hashicorp/vault/api/auth/approle"
	"github.com/mitchellh/mapstructure"
)

const (
	renewalStartPercent = 0.8
	notificationChanLen = 100
	defaultIncrement    = 30 * 60 // 30 minutes (as seconds)
	defaultTimeout      = 10 * time.Second
	renewalWindow       = 30 * time.Second
)

type vaultRenewalMinHeap []*VaultHandle

func (h vaultRenewalMinHeap) Len() int           { return len(h) }
func (h vaultRenewalMinHeap) Less(i, j int) bool { return h[i].renewAfter() < h[j].renewAfter() }
func (h vaultRenewalMinHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
func (h *vaultRenewalMinHeap) Push(x any)        { *h = append(*h, x.(*VaultHandle)) }
func (h vaultRenewalMinHeap) Root() *VaultHandle { return h[0] }

// Convenience methods to hide the collections/heap stuff from users
func (h *vaultRenewalMinHeap) PopHeap() *VaultHandle   { return heap.Pop(h).(*VaultHandle) }
func (h *vaultRenewalMinHeap) PushHeap(i *VaultHandle) { heap.Push(h, i) }
func (h *vaultRenewalMinHeap) Init()                   { heap.Init(h) }

func (h *vaultRenewalMinHeap) Pop() any {
	old := *h
	n := len(old)
	item := old[n-1]
	old[n-1] = nil // avoid memory leak
	*h = old[0 : n-1]
	return item
}

func (h *vaultRenewalMinHeap) FindRemove(handle *VaultHandle) bool {
	for i, hnd := range *h {
		if hnd.name == handle.name {
			heap.Remove(h, i)
			return true
		}
	}
	return false
}

type VaultHandle struct {
	name     string
	critical bool
	acquired time.Time
	secret   *api.Secret
}

var _ Handle = (*VaultHandle)(nil)

func (h *VaultHandle) isAuthToken() bool {
	return h.secret.Auth != nil
}

func (h *VaultHandle) renewAfter() time.Duration {
	after := float64(h.leaseDuration().Nanoseconds()) * renewalStartPercent
	afterTime := h.acquired.Add(time.Duration(after))
	return afterTime.Sub(time.Now()).Round(time.Second)
}

func (h *VaultHandle) leaseDuration() time.Duration {
	duration := time.Duration(h.secret.LeaseDuration) * time.Second
	if h.isAuthToken() {
		return time.Duration(h.secret.Auth.LeaseDuration) * time.Second
	}
	return duration
}

func (h *VaultHandle) renew(ctx context.Context, c VaultServiceClient, inc int) (err error) {
	var s *api.Secret

	vctx, cancel := context.WithTimeout(ctx, defaultTimeout)
	defer cancel()

	if h.isAuthToken() {
		s, err = c.Auth().Token().RenewTokenAsSelfWithContext(vctx, h.secret.Auth.ClientToken, inc)
		if err != nil {
			return err
		}
	} else {
		s, err = c.Sys().RenewWithContext(vctx, h.secret.LeaseID, inc)
		if err != nil {
			return err
		}
	}

	h.secret = s
	h.acquired = time.Now()

	return nil
}

func (h *VaultHandle) Reference() string {
	return h.name
}

type VaultServiceClient interface {
	Auth() *api.Auth
	Sys() *api.Sys
	Token() string
}

type VaultClient struct {
	sync.Mutex

	client         VaultServiceClient
	logical        *api.Logical
	auth           *approle.AppRoleAuth
	secrets        vaultRenewalMinHeap
	renewIncrement int
	notifications  chan Renewal
}

var _ Client = (*VaultClient)(nil)
var _ ClientManager = (*VaultClient)(nil)

type VaultClientConfig struct {
	Host        string `env:"VAULT_ADDR"`
	Token       string `env:"VAULT_TOKEN"`
	RoleId      string `env:"VAULT_ROLE_ID"`
	RoleSecret  string `env:"VAULT_SECRET_ID"`
	Increment   int    `env:"VAULT_INCREMENT"`
	AppRoleAuth *approle.AppRoleAuth
}

func (c *VaultClientConfig) Validate() error {
	if c.Host == "" {
		return fmt.Errorf("VaultClientConfig: Vault host is not specified")
	}

	// The presence of a token is always assumed to be valid, client errors
	// will occur otherwise.
	if c.Token != "" {
		return nil
	}

	// This constructor does a bunch of validation internally so just let
	// it do its thing and return any errors from that directly to the
	// user.
	ar, err := approle.NewAppRoleAuth(c.RoleId, &approle.SecretID{FromString: c.RoleSecret})
	if err != nil {
		return fmt.Errorf("VaultClientConfig: AppRole credentials invalid: %w", err)
	}
	c.AppRoleAuth = ar

	return nil
}

// NewVaultClient will attempt to create a secrets.Client from the
// passed config. Config can be nil, in which case an attempt will
// be made to load the configuration from environment variables. See
// VaultClientConfig for the expected names of those variables.
func NewVaultClient(cfg *VaultClientConfig) (ClientManager, error) {
	if cfg == nil {
		cfg = &VaultClientConfig{}
	}

	if err := glos.UnmarshalEnvironment(cfg); err != nil {
		return nil, err
	}

	if err := cfg.Validate(); err != nil {
		return nil, err
	}

	vc, err := api.NewClient(api.DefaultConfig())
	if err != nil {
		return nil, fmt.Errorf("NewVaultClient: error building client config: %w", err)
	}
	vc.SetAddress(cfg.Host)

	if cfg.Token != "" {
		vc.SetToken(cfg.Token)
	}

	c := &VaultClient{
		client:         vc,
		logical:        vc.Logical(),
		secrets:        vaultRenewalMinHeap{},
		notifications:  make(chan Renewal, notificationChanLen),
		auth:           cfg.AppRoleAuth,
		renewIncrement: cfg.Increment,
	}

	c.secrets.Init()

	if c.renewIncrement == 0 {
		c.renewIncrement = defaultIncrement
	}

	return c, nil
}

func (c *VaultClient) Notifications() <-chan Renewal {
	return c.notifications
}

func (c *VaultClient) Authenticate(ctx context.Context) error {
	if c.auth == nil {
		return c.authToken(ctx)
	} else {
		return c.authAppRole(ctx)
	}
}

// VaultToken is not part of the official API but is exposed for
// clients that need to gain access to this for some reason. There are
// no compatibility guarantees with this method and it's use limits
// portability.
func (c *VaultClient) VaultToken() string {
	return c.client.Token()
}

func (c *VaultClient) authToken(ctx context.Context) error {
	if c.client.Token() == "" {
		return fmt.Errorf("Authenticate: unable to authenticate, neither token nor approle provided")
	}

	vctx, cancel := context.WithTimeout(ctx, defaultTimeout)
	defer cancel()

	secret, err := c.client.Auth().Token().LookupSelfWithContext(vctx)
	if err != nil {
		return err
	}

	// Looking up self does not return an auth token just a map of data
	// about the current token. Convert this into a SecretAuth so that
	// downstream renewal code does the right thing.
	secret.Auth = &api.SecretAuth{}
	if err := mapstructure.Decode(secret.Data, secret.Auth); err != nil {
		return err
	}
	secret.Auth.ClientToken = c.client.Token()

	c.makeHandle("login", secret)

	return nil
}

func (c *VaultClient) authAppRole(ctx context.Context) error {
	vctx, cancel := context.WithTimeout(ctx, defaultTimeout)
	defer cancel()

	s, err := c.client.Auth().Login(vctx, c.auth)
	if err != nil {
		return fmt.Errorf("Authenticate: error logging in to vault: %w", err)
	}
	c.makeHandle("login", s)
	return err
}

// makeHandle creates a secret handle and schedules it for renewal if it
// is renewable.
func (c *VaultClient) makeHandle(name string, s *api.Secret) Handle {
	h := &VaultHandle{
		name:     name,
		critical: true, // Everything is critical unless marked otherwise
		acquired: time.Now(),
		secret:   s,
	}

	// If this is renewable then schedule it for renewal
	if (s.Auth != nil && s.Auth.Renewable) || s.Renewable {
		c.Lock()
		c.secrets.PushHeap(h)
		c.Unlock()
	}

	return h
}

func (c *VaultClient) writeHandle(ctx context.Context, prefix, suffix string, data map[string]any) (Handle, error) {
	key := suffix
	if prefix != "" {
		key = path.Join(prefix, suffix)
	}

	s, err := c.logical.WriteWithContext(ctx, key, data)
	if err != nil {
		return nil, fmt.Errorf("writeHandle: error writing to Vault: %w", err)
	}

	return c.makeHandle(key, s), nil
}

func (c *VaultClient) read(ctx context.Context, prefix, suffix string) (Handle, error) {
	key := suffix
	if prefix != "" {
		key = path.Join(prefix, suffix)
	}

	s, err := c.logical.ReadWithContext(ctx, key)
	if err != nil {
		return nil, fmt.Errorf("read: error reading from Vault: %w", err)
	}

	return c.makeHandle(key, s), nil
}

func (c *VaultClient) isRecoverableDbError(err error) bool {
	var apiErr *api.ResponseError
	return errors.Is(api.ErrSecretNotFound, err) ||
		(errors.As(err, &apiErr) && apiErr.StatusCode == http.StatusForbidden)
}

func (c *VaultClient) DatabaseCredential(ctx context.Context, suffix string) (*Credential, Handle, error) {
	cred, hnd, err := c.databaseCredentialDynamic(ctx, suffix)
	if err != nil {
		if c.isRecoverableDbError(err) {
			cred, hnd, err = c.databaseCredentialStatic(ctx, suffix)
		}
	}
	return cred, hnd, err
}

func (c *VaultClient) databaseCredentialDynamic(ctx context.Context, suffix string) (*Credential, Handle, error) {
	h, err := c.read(ctx, "database/creds", suffix)
	if err != nil {
		return nil, nil, err
	}
	vh := h.(*VaultHandle)

	var d Credential
	if err = mapstructure.Decode(vh.secret.Data, &d); err != nil {
		return nil, nil, fmt.Errorf("databaseCredentialStatic: error decoding secret: %w", err)
	}

	return &d, h, nil
}

func (c *VaultClient) databaseCredentialStatic(ctx context.Context, suffix string) (*Credential, Handle, error) {
	h, err := c.read(ctx, "database/static-creds", suffix)
	if err != nil {
		return nil, nil, err
	}

	var d Credential
	if err = mapstructure.Decode(h.(*VaultHandle).secret.Data, &d); err != nil {
		return nil, nil, fmt.Errorf("databaseCredentialStatic: error decoding secret: %w", err)
	}

	return &d, h, nil
}

func (c *VaultClient) Secret(ctx context.Context, suffix string, out any) (Handle, error) {
	h, err := c.read(ctx, "kv/data", suffix)
	if err != nil {
		return nil, err
	}

	if err = mapstructure.Decode(h.(*VaultHandle).secret.Data["data"], out); err != nil {
		return nil, err
	}

	return h, nil
}

func (c *VaultClient) RawSecret(ctx context.Context, path string, out any) (Handle, error) {
	h, err := c.read(ctx, "", path)
	if err != nil {
		return nil, err
	}

	if err = mapstructure.Decode(h.(*VaultHandle).secret.Data["data"], out); err != nil {
		return nil, err
	}

	return h, nil
}

func (c *VaultClient) AWSAssumeRoleSimple(ctx context.Context, name string) (*AWSCredential, Handle, error) {
	return c.AWSAssumeRole(ctx, name, fmt.Sprintf("%s-%d", name, time.Now().UnixNano()), time.Hour)
}

func (c *VaultClient) AWSAssumeRole(ctx context.Context, name string, sessionName string, ttl time.Duration) (*AWSCredential, Handle, error) {
	h, err := c.writeHandle(ctx, "aws/sts", name, map[string]any{
		"role_session_name": sessionName,
		"ttl":               ttl.String(),
	})
	if err != nil {
		return nil, nil, err
	}

	var d AWSCredential
	if err = mapstructure.Decode(h.(*VaultHandle).secret.Data, &d); err != nil {
		return nil, nil, fmt.Errorf("AWSIAMUser: error decoding secret: %w", err)
	}

	return nil, nil, nil
}

func (c *VaultClient) AWSIAMUser(ctx context.Context, name string) (*AWSCredential, Handle, error) {
	h, err := c.read(ctx, "aws/creds", name)
	if err != nil {
		return nil, nil, err
	}

	var d AWSCredential
	if err = mapstructure.Decode(h.(*VaultHandle).secret.Data, &d); err != nil {
		return nil, nil, fmt.Errorf("AWSIAMUser: error decoding secret: %w", err)
	}

	return &d, h, nil
}

func (c *VaultClient) WriteSecret(ctx context.Context, suffix string, in any) error {
	inb, err := json.Marshal(in)
	if err != nil {
		return fmt.Errorf("WriteSecret: error encoding json: %w", err)
	}

	if _, err = c.logical.WriteBytesWithContext(ctx, path.Join("kv/data", suffix), inb); err != nil {
		return fmt.Errorf("WriteSecret: error writing to vault: %w", err)
	}

	return nil
}

func (c *VaultClient) Encrypt(ctx context.Context, suffix string, data []byte) (string, error) {
	s, err := c.logical.WriteWithContext(
		ctx,
		path.Join("transit/encrypt", suffix),
		map[string]any{"plaintext": base64.StdEncoding.EncodeToString(data)},
	)
	if err != nil {
		return "", fmt.Errorf("Encrypt: unable to write to vault: %w", err)
	}

	return s.Data["ciphertext"].(string), nil
}

func (c *VaultClient) Decrypt(ctx context.Context, suffix, data string) ([]byte, error) {
	s, err := c.logical.WriteWithContext(
		ctx,
		path.Join("transit/decrypt", suffix),
		map[string]any{"ciphertext": data},
	)
	if err != nil {
		return nil, fmt.Errorf("Decrypt: unable to write to vault: %w", err)
	}

	d, err := base64.StdEncoding.DecodeString(s.Data["plaintext"].(string))
	if err != nil {
		return nil, fmt.Errorf("Decrypt: unable to base64 decode plaintext: %w", err)
	}

	return d, nil
}

func (c *VaultClient) Destroy(h Handle) error {
	c.Lock()
	defer c.Unlock()

	c.secrets.FindRemove(h.(*VaultHandle))

	return nil
}

func (c *VaultClient) MakeNonCritical(h Handle) error {
	h.(*VaultHandle).critical = false
	return nil
}

func (c *VaultClient) renewAttempt(ctx context.Context) (next time.Duration) {
	c.Lock()
	defer c.Unlock()

	// In the absence of any other time, run once a second
	next = 5 * time.Second

	if c.secrets.Len() < 1 {
		return
	}

	for {
		s := c.secrets.PopHeap()
		if s.renewAfter() < renewalWindow {
			// Underlying client does backoff and retry
			c.notifications <- Renewal{
				Name:     s.name,
				Critical: s.critical,
				Time:     time.Now(),
				Error:    s.renew(ctx, c.client, c.renewIncrement),
			}
			c.secrets.PushHeap(s)
		} else {
			c.secrets.PushHeap(s)
			next = c.secrets.Root().renewAfter()
			break
		}
	}

	return next
}

func (c *VaultClient) Run(ctx context.Context, wg *sync.WaitGroup) error {
	wg.Add(1)
	defer wg.Done()

	for {
		sleepTime := c.renewAttempt(ctx)

		select {
		case <-time.After(sleepTime):
			continue
		case <-ctx.Done():
			return nil
		}
	}
}