import { $env, $flag } from "@oh-my-pi/pi-utils";

const SIXEL_START_REGEX = /\x1bP(?:[0-9;]*)q/u;
const SIXEL_END_SEQUENCE = "\x1b\\";
const SIXEL_END_BELL = "\x07";
const SIXEL_SEQUENCE_REGEX = /\x1bP(?:[0-9;]*)q[\s\S]*?(?:\x1b\\|\x07)/gu;
const SIXEL_PLACEHOLDER_PREFIX = "__OMP_SIXEL_SEQUENCE_";

/**
 * Returns whether SIXEL passthrough is explicitly enabled.
 *
 * Both gates must be enabled to preserve SIXEL control sequences:
 * - PI_FORCE_IMAGE_PROTOCOL=sixel
 * - PI_ALLOW_SIXEL_PASSTHROUGH=1
 */
export function isSixelPassthroughEnabled(): boolean {
	const forcedProtocol = $env.PI_FORCE_IMAGE_PROTOCOL?.trim().toLowerCase();
	return forcedProtocol === "sixel" && $flag("PI_ALLOW_SIXEL_PASSTHROUGH");
}
/** Returns true when the text contains a SIXEL start sequence. */
export function containsSixelSequence(text: string): boolean {
	return SIXEL_START_REGEX.test(text);
}

/**
 * Returns a boolean mask indicating which lines belong to a SIXEL sequence block.
 * Supports multi-line SIXEL payloads generated by libsixel.
 */
export function getSixelLineMask(lines: string[]): boolean[] {
	let inSequence = false;
	return lines.map(line => {
		const hasStart = containsSixelSequence(line);
		if (hasStart) {
			inSequence = true;
		}
		const isSixelLine = inSequence;
		if (inSequence && (line.includes(SIXEL_END_SEQUENCE) || line.includes(SIXEL_END_BELL))) {
			inSequence = false;
		}
		return isSixelLine;
	});
}

/** Returns true when the line contains a SIXEL start sequence. */
export function isSixelLine(line: string): boolean {
	return containsSixelSequence(line);
}

/**
 * Sanitizes text while preserving embedded SIXEL sequences when passthrough is enabled.
 */
export function sanitizeWithOptionalSixelPassthrough(text: string, sanitize: (text: string) => string): string {
	if (!isSixelPassthroughEnabled() || !containsSixelSequence(text)) {
		return sanitize(text);
	}

	const preservedSequences: string[] = [];
	const tokenized = text.replace(SIXEL_SEQUENCE_REGEX, match => {
		const token = `${SIXEL_PLACEHOLDER_PREFIX}${preservedSequences.length}__`;
		preservedSequences.push(match);
		return token;
	});

	const sanitized = sanitize(tokenized);
	return sanitized.replace(/__OMP_SIXEL_SEQUENCE_(\d+)__/gu, (_, indexText: string) => {
		const index = Number.parseInt(indexText, 10);
		return preservedSequences[index] ?? "";
	});
}