const mongoose = require('mongoose')
const ObjectID = mongoose.Schema.Types.ObjectId

// Running balance snapshot per (item × warehouse)
// Updated atomically on each transaction using $inc
// Acts as a fast-read cache — transactions are the source of truth
const warehouseItemStockSchema = new mongoose.Schema(
    {
        item: {
            type: ObjectID,
            ref: 'WarehouseItem',
            required: true,
        },
        warehouse: {
            type: ObjectID,
            ref: 'Warehouse',
            required: true,
        },
        quantity: {
            type: Number,
            default: 0, // current balance
        },
        unit: {
            type: String,
        },
        unitEn: {
            type: String,
        },
    },
    {
        timestamps: true,
    }
)

// Guarantee one document per (item, warehouse) combination
warehouseItemStockSchema.index({ item: 1, warehouse: 1 }, { unique: true })

const WarehouseItemStock = mongoose.model('WarehouseItemStock', warehouseItemStockSchema)
module.exports = WarehouseItemStock