package main

import (
	"encoding/json"
	"io"
	"net/http"

	"git.k6n.net/mats/go-redis-inventory/pkg/inventory"
)

// batchItem is one stock set in a batch request. LocationID is optional; an
// empty value defaults to the service's country location (the same location the
// catalog-feed listener writes to).
type batchItem struct {
	SKU        string `json:"sku"`
	LocationID string `json:"locationId,omitempty"`
	Quantity   int64  `json:"quantity"`
}

// batchResult mirrors one input item with the location actually written and an
// optional per-item error (empty on success).
type batchResult struct {
	SKU        string `json:"sku"`
	LocationID string `json:"locationId"`
	Quantity   int64  `json:"quantity"`
	Error      string `json:"error,omitempty"`
}

// batchInventoryHandler SETS stock to absolute values for many SKUs in one
// pipelined call — for re-seeding/import and for testing the inventory + reserve
// paths directly. Same write as the catalog-feed listener (UpdateInventory +
// level crossing), so a value set here is authoritative until the next
// catalog.item_changed for that SKU overwrites it (catalog is the source of
// truth). Body is a JSON array of {sku, locationId?, quantity}.
func (srv *Server) batchInventoryHandler(w http.ResponseWriter, r *http.Request) {
	body, err := io.ReadAll(io.LimitReader(r.Body, 16<<20)) // 16 MiB
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	var items []batchItem
	if err := json.Unmarshal(body, &items); err != nil {
		http.Error(w, "body must be a JSON array of {sku, locationId?, quantity}: "+err.Error(), http.StatusBadRequest)
		return
	}
	if len(items) == 0 {
		http.Error(w, "empty batch", http.StatusBadRequest)
		return
	}

	ctx := r.Context()
	results := make([]batchResult, len(items))
	pipe := srv.rdb.Pipeline()
	for i, it := range items {
		loc := it.LocationID
		if loc == "" {
			loc = country
		}
		results[i] = batchResult{SKU: it.SKU, LocationID: loc, Quantity: it.Quantity}
		if it.SKU == "" {
			results[i].Error = "sku is required"
			continue
		}
		srv.inventoryService.UpdateInventory(ctx, pipe, inventory.SKU(it.SKU), inventory.LocationID(loc), it.Quantity)
	}

	hadError := false
	if _, err := pipe.Exec(ctx); err != nil {
		// Exec reports the first failing command; flag the whole batch rather than
		// guess which items committed.
		hadError = true
		for i := range results {
			if results[i].Error == "" {
				results[i].Error = err.Error()
			}
		}
	} else {
		// Emit level crossings for the items that were actually written, so the
		// finder/level listeners react the same way they do for catalog feeds.
		for i := range results {
			if results[i].Error == "" {
				emitLevelIfChanged(ctx, srv.rdb, srv.conn, country, lowWatermark, results[i].SKU, results[i].LocationID, results[i].Quantity)
			}
		}
	}
	for i := range results {
		if results[i].Error != "" {
			hadError = true
			break
		}
	}

	status := http.StatusOK
	if hadError {
		status = http.StatusMultiStatus // 207
	}
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	json.NewEncoder(w).Encode(map[string]any{"count": len(results), "results": results})
}