/**
 * Cell geometry resolution.
 *
 * Getting this right is the difference between a clean render and a flickering
 * one: the cell size decides how many rows an image occupies, and pi's TUI
 * falls back to a full clear-and-redraw whenever a reserved image block does
 * not fit where it expected.
 *
 * Measured on this setup:
 *   bare Ghostty  -> CSI 16 t replies "\x1b[6;21;10t"  (21px tall, 10px wide)
 *   Herdr pane    -> CSI 16 t replies NOTHING; herdr answers pane.graphics.info
 *
 * Herdr multiplexes the pty and does not forward the size report, so a pane
 * that trusted CSI 16 t silently kept pi-tui's 9x18 default and mis-sized every
 * image. Ask herdr directly when we are inside a pane.
 */

import { herdrRequest, isHerdrPane } from "./herdr-socket.ts";
import type { CellSize } from "./placeholder.ts";

/** pi-tui's built-in default. Only used when every probe fails. */
export const FALLBACK_CELL: CellSize = { widthPx: 9, heightPx: 18 };

/** Parse a CSI 16 t reply: ESC [ 6 ; <height> ; <width> t */
export function parseCellSizeReport(reply: string): CellSize | null {
	const match = /\x1b\[6;(\d+);(\d+)t/.exec(reply);
	if (!match) return null;
	const heightPx = Number(match[1]);
	const widthPx = Number(match[2]);
	if (!Number.isFinite(widthPx) || !Number.isFinite(heightPx)) return null;
	if (widthPx <= 0 || heightPx <= 0) return null;
	return { widthPx, heightPx };
}

async function fromHerdr(): Promise<CellSize | null> {
	const paneId = process.env.HERDR_PANE_ID;
	if (!paneId) return null;
	try {
		const result = await herdrRequest("pane.graphics.info", { pane_id: paneId });
		const widthPx = Number(result.cell_width_px ?? 0);
		const heightPx = Number(result.cell_height_px ?? 0);
		// Herdr reports 0 when the attached client has no graphics support. A
		// zero here means frames would be accepted and silently dropped, so it
		// must be treated as "unknown", not as a size.
		if (widthPx > 0 && heightPx > 0) return { widthPx, heightPx };
	} catch {
		// Fall through to the terminal probe.
	}
	return null;
}

/**
 * Resolve cell size once per session.
 *
 * `tuiCellSize` is pi-tui's own value (it queries the terminal at startup and
 * keeps the answer). We prefer it over re-probing because probing means writing
 * to the tty and reading stdin back, which races pi's input handling.
 */
export async function resolveCellSize(tuiCellSize?: CellSize): Promise<CellSize> {
	if (isHerdrPane()) {
		const fromPane = await fromHerdr();
		if (fromPane) return fromPane;
	}

	// Trust pi-tui only if it actually got a report. It exposes the 9x18 default
	// indistinguishably from a real answer, so treat exactly-default as unknown
	// when we have no other evidence. A real 9x18 terminal loses nothing: it
	// gets 9x18 back from the fallback anyway.
	if (
		tuiCellSize &&
		tuiCellSize.widthPx > 0 &&
		tuiCellSize.heightPx > 0 &&
		!(tuiCellSize.widthPx === FALLBACK_CELL.widthPx && tuiCellSize.heightPx === FALLBACK_CELL.heightPx)
	) {
		return tuiCellSize;
	}

	return FALLBACK_CELL;
}