/**
 * What counts as a valid discount amount, for the UI and the API alike.
 *
 * `Disc` is always the computed monetary discount and `RecDisc` is the
 * record-level discount already pro-rated onto a line, so a negative value in
 * either increases what a sale customer is charged. A return reverses its original discounts with nonpositive amounts. This
 * module decides that question once, so the Angular client and the Node API
 * cannot disagree about whether a given value is acceptable.
 *
 * Deliberately not in scope: whether a discount is *authorized*, whether `Disc`
 * agrees with `Perc`, whether a line's reference price was inflated, and
 * reconciling document totals. Those need a trusted basis and stored policy,
 * neither of which belongs in a pure function.
 *
 * Sharing the implementation removes drift between the two callers. It does not
 * make the client trustworthy: an installed client can be an old version or be
 * bypassed entirely, so the API remains the authority and must run these checks
 * at its own write boundary regardless of what the client did.
 *
 * Returns findings rather than throwing. The caller decides what a finding
 * means -- an HTTP 400 on the server, a red field on the client -- and the
 * stable `Code` lets the UI phrase its own message without depending on server
 * wording.
 */
export declare const DiscountIssueCodes: Readonly<{
    /** The exact decimal value is below zero. */
    readonly NEGATIVE_AMOUNT: "NEGATIVE_AMOUNT";
    /** Not a number at all, or not a finite one: NaN, Infinity, text, an object. */
    readonly INVALID_NUMBER: "INVALID_NUMBER";
}>;
export type DiscountIssueCode = typeof DiscountIssueCodes[keyof typeof DiscountIssueCodes];
export interface DiscountIssue {
    /** Where the offending value sits, e.g. `Items[3].RecDisc`. */
    readonly Field: string;
    readonly Code: DiscountIssueCode;
    /** Diagnostic text for logs and server messages. The UI should use `Code`. */
    readonly Detail: string;
}
/**
 * The shared shape these checks read.
 *
 * Declared here as plain data on purpose. The package must not know about
 * Mongoose documents or about any one endpoint's request envelope: a caller
 * passes something structurally like this, and gets findings back.
 */
export interface DiscountLineInput {
    readonly Disc?: unknown;
    readonly RecDisc?: unknown;
}
export interface InvoiceDiscountInput {
    readonly Disc?: unknown;
    readonly PDisc?: unknown;
    readonly LDisc?: unknown;
    readonly Items?: unknown;
    readonly Ops?: unknown;
}
export interface SalesReceiptDiscountInput {
    readonly Disc?: unknown;
    readonly Items?: unknown;
}
/**
 * Checks one discount amount, returning a finding or `null`.
 *
 * An absent value is not a finding: on a patch an omitted amount keeps whatever
 * is stored, and on a create it means no discount.
 *
 * A numeric string is accepted because clients do send them and Mongoose casts
 * one to a number on the way in. The parse is strict rather than `Number()`,
 * which reads `""` and `"   "` as zero -- a forgiving fallback would turn
 * invalid input into "no discount" instead of reporting it.
 *
 * The sign is taken from the exact decimal value through `Big`, never from the
 * converted double. `Number("-0.000…001")` with enough zeros underflows to `-0`,
 * and `-0 < 0` is false, so a float comparison would pass a value whose written
 * form is negative. `"-0"` and `"-0.0"` are accepted, because their exact value
 * is zero.
 */
export declare function CheckDiscountAmount(value: unknown, field: string): DiscountIssue | null;
/** Convenience for a UI field check, where only valid/invalid matters. */
export declare function IsValidDiscountAmount(value: unknown): boolean;
/**
 * Checks the discount amounts on one line.
 *
 * A returned line is not exempt. A sales-receipt return is a negative quantity
 * alongside a return marker; that negative quantity is legitimate and is not
 * read here. The discount on such a line still describes a reduction and is
 * nonpositive when allowReturns is set; invoice lines retain the sale rule.
 */
export declare function CheckLineDiscounts(line: DiscountLineInput | unknown, fieldPath: string, allowReturns?: boolean): DiscountIssue[];
/**
 * Every discount finding on an invoice: its header amounts and both line arrays.
 *
 * `fieldPath` prefixes the reported fields, for a caller that nests the document
 * inside an envelope.
 */
export declare function FindInvoiceDiscountIssues(document: InvoiceDiscountInput | unknown, fieldPath?: string): DiscountIssue[];
/** The sales-receipt equivalent. Receipts carry `Items` only, and no `Ops`. */
export declare function FindSalesReceiptDiscountIssues(document: SalesReceiptDiscountInput | unknown, fieldPath?: string): DiscountIssue[];
/** One line of text summarising findings, for a server error message or a log. */
export declare function DescribeDiscountIssues(issues: readonly DiscountIssue[]): string;