package process

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"time"

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

	stdio "git.novox.be/novox/mesh-sdk/go"
)

// Emit publishes an event as this process's module (novox/hq ADR 0436 clause 4), under its module's own
// namespace (mesh.mod.<module>.event.<type>, the same subject the module's own principal would publish it
// on), with the SDK's own envelope and headers (stdio.go:498-509). A chosen message id
// (EmitOptions.MessageID) is sent as x-event-id, and as the bus's own dedup id (Nats-Msg-Id), so a second
// publish inside the stream's duplicate window is dropped; empty is a random one, as stdio.Emit on main.
func (c *Conn) Emit(eventType string, body any, opts ...stdio.EmitOptions) error {
	data, err := json.Marshal(body)
	if err != nil {
		return err
	}
	id := ""
	for _, o := range opts {
		if o.MessageID != "" {
			id = o.MessageID
		}
	}
	if id == "" {
		id = eventID()
	}
	msg := nats.NewMsg("mesh.mod." + c.account.Module + ".event." + eventType)
	msg.Header.Set("x-event-id", id)
	msg.Header.Set("x-source", c.account.Module)
	msg.Header.Set("x-node", c.account.Node)
	msg.Header.Set("x-time", time.Now().UTC().Format(time.RFC3339Nano))
	msg.Header.Set("content-type", "application/json")
	for _, o := range opts {
		if o.CausationID != "" {
			msg.Header.Set("x-causation-id", o.CausationID)
		}
		if o.Schema != "" {
			msg.Header.Set("x-schema", o.Schema)
		}
	}
	msg.Data = data
	js, err := jetstream.New(c.nc)
	if err != nil {
		return err
	}
	ctx, cancel := context.WithTimeout(context.Background(), StateTimeout)
	defer cancel()
	_, err = js.PublishMsg(ctx, msg, jetstream.WithMsgID(id))
	return err
}

// eventID is a random UUID, version 4, as stdio's own eventID (go/stdio.go:515-522) — duplicated rather
// than imported, since stdio's is unexported and this package touches none of stdio's bundle machinery.
func eventID() string {
	var b [16]byte
	_, _ = rand.Read(b[:])
	b[6] = (b[6] & 0x0f) | 0x40
	b[8] = (b[8] & 0x3f) | 0x80
	h := hex.EncodeToString(b[:])
	return h[0:8] + "-" + h[8:12] + "-" + h[12:16] + "-" + h[16:20] + "-" + h[20:32]
}