package broker

import (
	"context"
	"fmt"

	"git.novox.be/novox/mesh-sdk/go/delivery"
	"github.com/nats-io/nats.go/jetstream"
)

// The compositions' buckets (novox/hq ADR 0539 clauses 2 and 4): one per node, `composed-<node>`, holding that node's
// compositions, which only that node's node-engine reads, since a composition can carry a sealed value (ADR 0488 §2's
// reason); and `mesh-controller_composed`, holding each composition's digest and the judgement of its move, which the
// assigner reads. The controller writes both, by compare-and-set while it holds the lease; each keeps five revisions
// of a key. The names and layouts are mesh-sdk's (delivery.ComposedBucketFor, ControllerComposedBucket, ComposedKey).

// ComposedValueBytes is the most a composition may hold: a file over 64 KiB travels by digest, so a module's
// composition is far smaller; just under the server's largest message, which also carries the subject and headers.
const ComposedValueBytes = 1<<20 - 8<<10

// ComposedBucketBytes is a node's composition bucket's size: five revisions of every module's compositions of the node.
const ComposedBucketBytes = 256 << 20

// ComposedDigestsBytes is the size of the bucket of digests: a value of a few hundred bytes per node, module and
// fingerprint kept.
const ComposedDigestsBytes = 64 << 20

// ComposedConfig is a node's composition bucket as the controller asserts it.
func ComposedConfig(node string) (jetstream.KeyValueConfig, error) {
	bucket, err := delivery.ComposedBucketFor(node)
	if err != nil {
		return jetstream.KeyValueConfig{}, err
	}
	return jetstream.KeyValueConfig{
		Bucket: bucket,
		Description: "the compositions of " + node + " (novox/hq ADR 0539): each module's resources for this node at one " +
			"fingerprint, and the node's own, signed; written by the controller alone, read by this node's node-engine " +
			"alone; deleted when outside the module's five newest fingerprints and named by no want",
		History:      delivery.ComposedHistory,
		MaxValueSize: ComposedValueBytes,
		MaxBytes:     ComposedBucketBytes,
		Storage:      jetstream.FileStorage,
	}, nil
}

// ComposedDigestsConfig is the bucket of the compositions' digests as the controller asserts it.
func ComposedDigestsConfig() jetstream.KeyValueConfig {
	return jetstream.KeyValueConfig{
		Bucket: delivery.ControllerComposedBucket,
		Description: "each composition's digest and the judgement of its move from what the node runs (novox/hq ADR 0539 " +
			"clauses 2 and 14): written by the controller alone, read by the assigner",
		History:      delivery.ControllerComposedHistory,
		MaxValueSize: 4 << 10,
		MaxBytes:     ComposedDigestsBytes,
		Storage:      jetstream.FileStorage,
	}
}

// EnsureComposed creates the bucket of digests and each named node's composition bucket if absent and brings their
// options to match. An update, never a delete.
func EnsureComposed(ctx context.Context, js jetstream.JetStream, nodes ...string) error {
	if _, err := js.CreateOrUpdateKeyValue(ctx, ComposedDigestsConfig()); err != nil {
		return fmt.Errorf("asserting bucket %s: %w", delivery.ControllerComposedBucket, err)
	}
	for _, node := range nodes {
		cfg, err := ComposedConfig(node)
		if err != nil {
			return err
		}
		if _, err := js.CreateOrUpdateKeyValue(ctx, cfg); err != nil {
			return fmt.Errorf("asserting bucket %s: %w", cfg.Bucket, err)
		}
	}
	return nil
}

// ComposedWrites is what the controller publishes to write a node's compositions: the bucket's own subjects.
func ComposedWrites(node string) (string, error) {
	bucket, err := delivery.ComposedBucketFor(node)
	if err != nil {
		return "", err
	}
	return "$KV." + bucket + ".>", nil
}

// ComposedReads is what a node's node-engine publishes to follow its wants and compositions (ADR 0539 clauses 1, 2 and
// 9): every key of its own composition bucket, and its own wants (`want.<node>.<module>` and `want.<node>.node`) in the
// assigner's bucket; nothing of another node's, nor the bucket of digests.
func ComposedReads(node string) ([]string, error) {
	bucket, err := delivery.ComposedBucketFor(node)
	if err != nil {
		return nil, err
	}
	if !safeSubject.MatchString(node) {
		return nil, fmt.Errorf("%q cannot be part of a subject: a permission is a subject pattern, and this would widen it", node)
	}
	return append(readGrants(bucket, ""), readGrants(delivery.AssignerWantsBucket, "want."+node+".>")...), nil
}