package main

import (
	"context"
	"log"
	"strconv"
	"time"

	"git.k6n.net/mats/platform/event"
	invlevel "git.k6n.net/mats/platform/inventory"
	"git.k6n.net/mats/platform/rabbit"
	"github.com/redis/go-redis/v9"
)

// emitLevelIfChanged classifies qty into a Level and emits an
// inventory.level_changed bus event only when it differs from the level last
// emitted for this SKU+location (the levelKey marker). Exact quantity never
// leaves the service; only the coarse crossing does. Shared by every write path
// (catalog feed, order.created commit). A nil conn (no bus) makes it a no-op.
func emitLevelIfChanged(ctx context.Context, rdb *redis.Client, conn *rabbit.Conn, country string, low int64, sku, loc string, qty int64) {
	if conn == nil {
		return
	}
	lvl := invlevel.LevelFor(qty, low)
	// Atomic read-old + write-new of the level marker; redis.Nil means the
	// marker didn't exist yet (first observation), which we treat as a crossing.
	prev, err := rdb.SetArgs(ctx, levelKey(sku, loc), string(lvl), redis.SetArgs{Get: true}).Result()
	if err != nil && err != redis.Nil {
		log.Printf("inventory: level marker sku=%s: %v", sku, err)
		return
	}
	if prev == string(lvl) {
		return // no threshold crossing — stay off the bus
	}
	payload, err := invlevel.LevelChanged{SKU: sku, Location: loc, Level: lvl}.Encode()
	if err != nil {
		log.Printf("inventory: encode level payload sku=%s: %v", sku, err)
		return
	}
	ev := event.Event{
		ID:      "invlvl-" + sku + "-" + loc + "-" + strconv.FormatInt(time.Now().UnixNano(), 36),
		Type:    event.InventoryLevelChanged,
		Source:  "inventory",
		Subject: sku,
		Payload: payload,
		Time:    time.Now(),
		Meta:    map[string]string{"country": country},
	}
	if err := rabbit.PublishEvent(conn.Connection(), "inventory", ev); err != nil {
		log.Printf("inventory: publish level event sku=%s: %v", sku, err)
	}
}