/**
 * Client-side validation for {@link setFormFont} arguments. Mirrors the
 * Java FormFontValidator and .NET FormFontValidator added for PDF-2184.
 *
 * The engine validates again on receipt — this client check is the
 * fail-fast layer that surfaces obvious mistakes before any network I/O.
 */

const MAX_NAME_LENGTH = 63;
const MAX_FONT_BYTES = 50 * 1024 * 1024; // 50 MB
const ALLOWED_NAME = /^[A-Za-z0-9_\-.+]+$/;

/**
 * Validate a PDF font name. Allowed characters: letters, digits, '_', '-',
 * '.', '+'. The '+' is permitted to accept subset prefixes like
 * "AAAAAA+Poppins-Regular". Names must be 1-63 characters.
 *
 * @throws Error when the name fails validation.
 */
export function validateFormFontName(fontName: string): void {
	if (fontName == null || typeof fontName !== "string" || fontName.length === 0) {
		throw new Error("fontName must be a non-empty string");
	}
	if (fontName.length > MAX_NAME_LENGTH) {
		throw new Error(
			`fontName must be at most ${MAX_NAME_LENGTH} characters (got ${fontName.length})`
		);
	}
	if (!ALLOWED_NAME.test(fontName)) {
		throw new Error(
			"fontName may only contain letters, digits, and the characters '_', '-', '.', '+'"
		);
	}
}

/**
 * Validate raw font bytes look like a TrueType / OpenType / TTC sfnt
 * container. Catches the obvious cases: empty payload, oversize payload,
 * ASCII text passed instead of bytes, and all-zero payloads.
 *
 * @throws Error when the data fails validation.
 */
export function validateFormFontData(fontData: Buffer): void {
	if (!fontData || fontData.length === 0) {
		throw new Error("fontData must not be empty");
	}
	if (fontData.length > MAX_FONT_BYTES) {
		throw new Error(
			`fontData exceeds the ${MAX_FONT_BYTES} byte limit (got ${fontData.length})`
		);
	}
	if (fontData.length < 4) {
		throw new Error("fontData is too small to be a valid font file");
	}

	// Reject obviously-non-font payloads: all-zero buffer or a pure ASCII text
	// payload. We don't try to fully parse the sfnt header here — the engine
	// does that — but we do catch the common mistakes.
	let nonZero = false;
	let asciiOnly = true;
	for (let i = 0; i < Math.min(fontData.length, 4096); i++) {
		const b = fontData[i] ?? 0;
		if (b !== 0) nonZero = true;
		if (b > 0x7e || (b < 0x20 && b !== 0x09 && b !== 0x0a && b !== 0x0d)) {
			asciiOnly = false;
		}
	}
	if (!nonZero) {
		throw new Error("fontData is all zeros — not a valid font file");
	}
	if (asciiOnly) {
		throw new Error("fontData looks like ASCII text — not a valid font file");
	}

	// sfnt magic — TTF (0x00010000), OTF ('OTTO'), TTC ('ttcf'), or 'true'.
	const m0 = fontData[0], m1 = fontData[1], m2 = fontData[2], m3 = fontData[3];
	const isTtfV1 = m0 === 0x00 && m1 === 0x01 && m2 === 0x00 && m3 === 0x00;
	const isOtto = m0 === 0x4f && m1 === 0x54 && m2 === 0x54 && m3 === 0x4f;
	const isTtcf = m0 === 0x74 && m1 === 0x74 && m2 === 0x63 && m3 === 0x66;
	const isTrue = m0 === 0x74 && m1 === 0x72 && m2 === 0x75 && m3 === 0x65;
	if (!(isTtfV1 || isOtto || isTtcf || isTrue)) {
		throw new Error(
			"fontData does not have a recognised TTF/OTF/TTC sfnt magic"
		);
	}
}