package broker

import (
	"context"
	"fmt"
	"time"

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

// The object bucket a declaration's large files travel in (novox/hq ADR 0486, issues 1696 and 1697).
//
// **The controller alone writes it, and a node-engine reads an object by its name** (ADR 0486 §2): its account may
// neither list the bucket nor write it, and no other account has any access. A bucket of the bus's object store is a
// stream, OBJ_<bucket>, whose messages are the objects' metadata (`$O.<bucket>.M.<base64 of the name>`) and chunks
// (`$O.<bucket>.C.<nuid>`).

// DeclarationFilesBucket is the bucket's name, which mesh-sdk fixes for the node-engine and the controller alike.
const DeclarationFilesBucket = declaration.FileBucket

// DeclarationFilesStream is the stream under the bucket.
const DeclarationFilesStream = "OBJ_" + DeclarationFilesBucket

// DeclarationFilesMaxBytes is the bucket's size: the controller's objects are immutable and regenerable, and the
// largest declaration it composes holds well under a hundred megabytes of them.
const DeclarationFilesMaxBytes = 1 << 30

// DeclarationFilesKeptFor is how long an object stays after no node's latest declaration names it (ADR 0486 §3).
const DeclarationFilesKeptFor = 24 * time.Hour

// DeclarationFilesWrites is the one pattern the controller may publish to write the bucket: every object's metadata
// and chunks. The server's API for the stream is the controller's `$JS.API.>`.
const DeclarationFilesWrites = "$O." + DeclarationFilesBucket + ".>"

// DeclarationFilesReads is what a node-engine's account may publish to read an object by its name, and nothing more.
// The set is the one node-engine's own call (mesh-host internal/link FileObject) makes, for B the bucket and S its
// stream (issue 1697, notes 4 and 5):
//
//   - the object's metadata, by a direct get of the last message of the one subject that names it. **Only the suffixed
//     form**: the bare `$JS.API.DIRECT.GET.S` takes a sequence number and would read any message of the stream, every
//     object's name and chunks.
//   - the ordered consumer on that object's chunks: `$JS.API.CONSUMER.CREATE.S.<name>.$O.B.C.<nuid>`. **Not `S.>`**:
//     a consumer filtered on `$O.B.M.>` would read every object's name, the list that is refused. The chunks'
//     subject carries the nuid the metadata gives, which only a reader of the metadata knows.
//   - the flow-control replies of that consumer, without which a large object stalls at the flow-control window.
//   - the consumer's deletion, best effort: the consumer's inactivity threshold removes it if this is refused.
//
// **Never granted:** STREAM.INFO (a `subjects_filter` of `>` lists every name), STREAM.MSG.GET (any message by its
// sequence), a publish to `$O.B.>` (a write).
func DeclarationFilesReads() []string {
	return []string{
		"$JS.API.DIRECT.GET." + DeclarationFilesStream + ".$O." + DeclarationFilesBucket + ".M.*",
		"$JS.API.CONSUMER.CREATE." + DeclarationFilesStream + ".*.$O." + DeclarationFilesBucket + ".C.*",
		"$JS.API.CONSUMER.DELETE." + DeclarationFilesStream + ".*",
		"$JS.FC." + DeclarationFilesStream + ".>",
	}
}

// EnsureDeclarationFiles creates the bucket if it is absent and brings its options to match. The bucket exists
// whenever the bus does, so a node that is starting finds it (ADR 0486 §4). An update, never a delete.
func (j *JetStream) EnsureDeclarationFiles() error {
	js, err := jetstream.New(j.conn)
	if err != nil {
		return err
	}
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	return EnsureDeclarationFiles(ctx, js)
}

// EnsureDeclarationFiles is the same on a JetStream the caller holds.
func EnsureDeclarationFiles(ctx context.Context, js jetstream.JetStream) error {
	if _, err := js.CreateOrUpdateObjectStore(ctx, DeclarationFilesConfig()); err != nil {
		return fmt.Errorf("asserting the object bucket %s: %w", DeclarationFilesBucket, err)
	}
	return nil
}

// DeclarationFilesConfig is the bucket as the controller asserts it.
func DeclarationFilesConfig() jetstream.ObjectStoreConfig {
	return jetstream.ObjectStoreConfig{
		Bucket: DeclarationFilesBucket,
		Description: "the contents of a declaration's files over 64 KiB, each under the hex of its sha256 digest " +
			"(novox/hq ADR 0486): written by the controller alone, read by a node-engine by name, removed a day after " +
			"no node's latest declaration names it",
		MaxBytes: DeclarationFilesMaxBytes,
		Storage:  jetstream.FileStorage,
	}
}