package physical

import (
	"context"
	"strings"

	log "github.com/hashicorp/go-hclog"
)

const DefaultParallelOperations = 128

// The operation type
type Operation string

const (
	DeleteOperation Operation = "delete"
	GetOperation              = "get"
	ListOperation             = "list"
	PutOperation              = "put"
)

const (
	ErrValueTooLarge = "put failed due to value being too large"
)

// Backend is the interface required for a physical
// backend. A physical backend is used to durably store
// data outside of Vault. As such, it is completely untrusted,
// and is only accessed via a security barrier. The backends
// must represent keys in a hierarchical manner. All methods
// are expected to be thread safe.
type Backend interface {
	// Put is used to insert or update an entry
	Put(ctx context.Context, entry *Entry) error

	// Get is used to fetch an entry
	Get(ctx context.Context, key string) (*Entry, error)

	// Delete is used to permanently delete an entry
	Delete(ctx context.Context, key string) error

	// List is used to list all the keys under a given
	// prefix, up to the next prefix.
	List(ctx context.Context, prefix string) ([]string, error)
}

// HABackend is an extensions to the standard physical
// backend to support high-availability. Vault only expects to
// use mutual exclusion to allow multiple instances to act as a
// hot standby for a leader that services all requests.
type HABackend interface {
	// LockWith is used for mutual exclusion based on the given key.
	LockWith(key, value string) (Lock, error)

	// Whether or not HA functionality is enabled
	HAEnabled() bool
}

// ToggleablePurgemonster is an interface for backends that can toggle on or
// off special functionality and/or support purging. This is only used for the
// cache, don't use it for other things.
type ToggleablePurgemonster interface {
	Purge(ctx context.Context)
	SetEnabled(bool)
}

// RedirectDetect is an optional interface that an HABackend
// can implement. If they do, a redirect address can be automatically
// detected.
type RedirectDetect interface {
	// DetectHostAddr is used to detect the host address
	DetectHostAddr() (string, error)
}

type Lock interface {
	// Lock is used to acquire the given lock
	// The stopCh is optional and if closed should interrupt the lock
	// acquisition attempt. The return struct should be closed when
	// leadership is lost.
	Lock(stopCh <-chan struct{}) (<-chan struct{}, error)

	// Unlock is used to release the lock
	Unlock() error

	// Returns the value of the lock and if it is held
	Value() (bool, string, error)
}

// Factory is the factory function to create a physical backend.
type Factory func(config map[string]string, logger log.Logger) (Backend, error)

// PermitPool is used to limit maximum outstanding requests
type PermitPool struct {
	sem chan int
}

// NewPermitPool returns a new permit pool with the provided
// number of permits
func NewPermitPool(permits int) *PermitPool {
	if permits < 1 {
		permits = DefaultParallelOperations
	}
	return &PermitPool{
		sem: make(chan int, permits),
	}
}

// Acquire returns when a permit has been acquired
func (c *PermitPool) Acquire() {
	c.sem <- 1
}

// Release returns a permit to the pool
func (c *PermitPool) Release() {
	<-c.sem
}

// Get number of requests in the permit pool
func (c *PermitPool) CurrentPermits() int {
	return len(c.sem)
}

// Prefixes is a shared helper function returns all parent 'folders' for a
// given vault key.
// e.g. for 'foo/bar/baz', it returns ['foo', 'foo/bar']
func Prefixes(s string) []string {
	components := strings.Split(s, "/")
	result := []string{}
	for i := 1; i < len(components); i++ {
		result = append(result, strings.Join(components[:i], "/"))
	}
	return result
}