/**
 * useDocumentTotals
 *
 * Pure calculation hook for invoice-style documents (invoices, bills, estimates,
 * credit notes, vendor credits, etc.).
 *
 * Inputs
 * ────────────────────────────────────────────────────────────────────────────
 * lineItems      – flat array of all items (parts + services + expenses)
 * discountType   – 'no' | 'line_item_level' | 'transaction_level'
 * discountAmount – used when discountType === 'transaction_level'
 * taxRate        – percentage (e.g. 15 for 15 %). Undefined → no tax.
 *
 * Calculation order
 * ────────────────────────────────────────────────────────────────────────────
 * 1. subTotal          = Σ (qty × rate)
 * 2. lineItemDiscount  = Σ discount_amount  (only when discountType === 'line_item_level')
 * 3. transactionDiscount = discountAmount   (only when discountType === 'transaction_level')
 * 4. totalDiscount     = lineItemDiscount + transactionDiscount
 * 5. afterDiscount     = subTotal - totalDiscount
 * 6. taxAmount         = afterDiscount × (taxRate / 100)
 * 7. total             = afterDiscount + taxAmount
 */

export type DocumentLineItem = {
    quantity: number
    rate: number
    discount_amount?: number
}

export type UseDocumentTotalsInput = {
    lineItems: DocumentLineItem[]
    discountType?: string | null
    discountAmount?: number
    taxRate?: number
}

export type DocumentTotals = {
    subTotal: number
    lineItemDiscount: number
    transactionDiscount: number
    totalDiscount: number
    afterDiscount: number
    taxAmount: number
    total: number
    hasLineItems: boolean
}

export function useDocumentTotals({
    lineItems,
    discountType,
    discountAmount,
    taxRate,
}: UseDocumentTotalsInput): DocumentTotals {
    const subTotal = lineItems.reduce((sum, item) => {
        const qty = Number(item.quantity) || 0
        const rate = Number(item.rate) || 0
        return sum + qty * rate
    }, 0)

    const lineItemDiscount =
        discountType === "line_item_level"
            ? lineItems.reduce((sum, item) => sum + (Number(item.discount_amount) || 0), 0)
            : 0

    const transactionDiscount =
        discountType === "transaction_level" ? Number(discountAmount) || 0 : 0

    const totalDiscount = lineItemDiscount + transactionDiscount
    const afterDiscount = Math.max(0, subTotal - totalDiscount)
    const taxAmount = taxRate ? afterDiscount * (taxRate / 100) : 0
    const total = afterDiscount + taxAmount

    return {
        subTotal,
        lineItemDiscount,
        transactionDiscount,
        totalDiscount,
        afterDiscount,
        taxAmount,
        total,
        hasLineItems: lineItems.length > 0,
    }
}