package broker

import (
	"context"
	"fmt"
	"time"

	"github.com/nats-io/nats.go/jetstream"
)

// The controller's own key-value buckets (novox/hq to-be 45 §1, §6, §7).
//
// **What the controller must remember across its own restart, it keeps on the bus.** A call's
// outcome lived in the memory of the process that served it (novox/hq issue 265), so a controller
// replaced while a push ran answered "no such call" for the one thing its caller had been told to
// ask about. The bus already outlives the controller and is the shape ADR 0201 gives a module's
// current state: one value per key, written by one owner, read by anybody granted it. These are the
// controller's, written by it alone — the writers table of to-be 45 §1 — and asserted on every start
// like the streams, so a bus raised from nothing has them before the first call is served.

// CallsBucket keeps every call of the mesh's own verbs and what came of it; HandActsBucket every act
// a person did by hand, with why.
var (
	CallsBucket    = BucketName(ControllerSeat, "calls")
	HandActsBucket = BucketName(ControllerSeat, "hand-acts")
)

// The bounds to-be 45 §6 sets for calls: the last thousand, or fourteen days, whichever is fewer.
// A call is two keys — its record, and its answer apart so a listing does not read every answer —
// so the stream holds twice as many messages as it keeps calls.
const (
	KeptCallsDurably = 1000
	CallsKeptFor     = 14 * 24 * time.Hour
	// CallAnswerBytes is the most of one answer kept: a whole declaration is far smaller, and an
	// answer larger is cut and says so.
	CallAnswerBytes = 64 << 10
	// HandActsKeptFor is as long as a condition's history (to-be 45 §2): an act by hand is read
	// back beside what it addressed.
	HandActsKeptFor = 90 * 24 * time.Hour
)

// IsControllerBucket says a bucket is the controller's own, not a module's state nothing declares.
func IsControllerBucket(bucket string) bool {
	return bucket == CallsBucket || bucket == HandActsBucket
}

// ControllerBucketsAsserter is what raising the controller's buckets needs of a connection.
type ControllerBucketsAsserter interface {
	EnsureControllerBuckets() error
}

// EnsureControllerBuckets creates the controller's buckets if absent and brings their options to
// match. An update, never a delete: what they hold is the record of what the mesh was asked.
func (j *JetStream) EnsureControllerBuckets() error {
	js, err := jetstream.New(j.conn)
	if err != nil {
		return err
	}
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	if _, err := js.CreateOrUpdateKeyValue(ctx, jetstream.KeyValueConfig{
		Bucket: CallsBucket,
		Description: "the calls of the mesh's own verbs and what came of each (novox/hq to-be 45 §6, issue " +
			"265): written by the controller alone, read through `calls`; the last thousand, or fourteen days",
		History:      1,
		TTL:          CallsKeptFor,
		MaxValueSize: CallAnswerBytes + 4<<10,
		MaxBytes:     2 * KeptCallsDurably * (CallAnswerBytes + 4<<10),
		Storage:      jetstream.FileStorage,
	}); err != nil {
		return fmt.Errorf("asserting bucket %s: %w", CallsBucket, err)
	}
	// **The count, on the stream under the bucket.** A bucket has an age and a size and no count;
	// the stream it is made of does, and with one value per key the oldest message is the oldest
	// call. Asserted after the bucket, every time, because asserting the bucket writes the stream's
	// configuration whole and puts the count back to none.
	stream, err := js.Stream(ctx, "KV_"+CallsBucket)
	if err != nil {
		return fmt.Errorf("reading the stream under %s: %w", CallsBucket, err)
	}
	cfg := stream.CachedInfo().Config
	if cfg.MaxMsgs != 2*KeptCallsDurably {
		cfg.MaxMsgs = 2 * KeptCallsDurably
		cfg.Discard = jetstream.DiscardOld
		if _, err := js.UpdateStream(ctx, cfg); err != nil {
			return fmt.Errorf("bounding %s to the last %d calls: %w", CallsBucket, KeptCallsDurably, err)
		}
	}
	if _, err := js.CreateOrUpdateKeyValue(ctx, jetstream.KeyValueConfig{
		Bucket: HandActsBucket,
		Description: "every act a person did by hand, with why (novox/hq to-be 45 §7): written by the " +
			"controller's repairing verbs and `hand-act record`, read through `hand-acts`",
		History:      1,
		TTL:          HandActsKeptFor,
		MaxValueSize: 16 << 10,
		MaxBytes:     64 << 20,
		Storage:      jetstream.FileStorage,
	}); err != nil {
		return fmt.Errorf("asserting bucket %s: %w", HandActsBucket, err)
	}
	return nil
}