package workerruntime

import (
	"context"
	"crypto/sha256"
	"errors"
	"time"
)

var (
	ErrInvalidStore                 = errors.New("invalid worker runtime store")
	ErrInvalidSession               = errors.New("invalid worker runtime session")
	ErrInvalidReport                = errors.New("invalid worker runtime report")
	ErrInvalidQuery                 = errors.New("invalid worker runtime query")
	ErrStaleSession                 = errors.New("stale worker runtime session")
	ErrStaleReport                  = errors.New("stale worker runtime report")
	ErrConflictingReport            = errors.New("conflicting worker runtime report")
	ErrInvalidSnapshotReference     = errors.New("invalid worker snapshot reference")
	ErrInvalidAcknowledgement       = errors.New("invalid worker snapshot acknowledgement")
	ErrSnapshotMismatch             = errors.New("worker snapshot does not match acknowledged state")
	ErrStaleSnapshotReference       = errors.New("stale worker snapshot reference")
	ErrConflictingSnapshotReference = errors.New("conflicting worker snapshot reference")
	ErrStaleAcknowledgement         = errors.New("stale worker snapshot acknowledgement")
)

type Session struct {
	WorkerID             string
	InstanceID           string
	SessionID            string
	Zone                 string
	ProtocolVersion      uint32
	Labels               map[string]string
	AckedSnapshotVersion uint64
	AckedOwnershipEpoch  uint64
	AckedChecksum        [sha256.Size]byte
	RuntimeEnabled       bool
}

type SnapshotReference struct {
	WorkerID       string
	Version        uint64
	OwnershipEpoch uint64
	Checksum       [sha256.Size]byte
}

type SnapshotAcknowledgement struct {
	WorkerID  string
	SessionID string
	Reference SnapshotReference
	Applied   bool
	ErrorCode string
}

type Counter struct {
	ProxyID  string
	Active   int64
	Reserved int64
	Draining bool
}

// Report is a complete sparse replacement. Missing counters are zero for the
// reported Worker snapshot; callers must increase Sequence for every update.
type Report struct {
	WorkerID        string
	SessionID       string
	Sequence        uint64
	SnapshotVersion uint64
	OwnershipEpoch  uint64
	ObservedAt      time.Time
	Counters        []Counter
}

type OwnedProxy struct {
	ProxyID        string
	WorkerID       string
	OwnershipEpoch uint64
}

type Snapshot struct {
	ProxyID  string
	Active   int64
	Reserved int64
	Draining bool
	Fresh    bool
}

type SessionWriter interface {
	ReplaceSession(context.Context, Session, time.Duration) error
}

type ControlStore interface {
	CurrentOwnershipEpoch(context.Context) (uint64, error)
	OpenSession(context.Context, Session, time.Duration) error
	RecordIssuedSnapshot(context.Context, SnapshotReference, time.Duration) error
	AcknowledgeSnapshot(context.Context, SnapshotAcknowledgement, time.Duration) error
	ReplaceRuntime(context.Context, Report, time.Duration) error
}

type ReportWriter interface {
	ReplaceRuntime(context.Context, Report, time.Duration) error
}

type RuntimeReader interface {
	ReadRuntime(context.Context, []OwnedProxy) ([]Snapshot, error)
}