wyrm/src/lib/game/chronicle.ts

// The chronicle: every move told as the table saw it, with what followed
// from it. A Griffon leaps and a Dwarf trudges, a capture names who lost
// what, a Basilisk's gaze falls on whatever stops above it, and a King that
// steps off the land is told what it has done. The lines are read off a
// replay of the moves, so the chronicle is a function of the game and
// never part of the ledger: rewording it changes no rules.

import { type Cell, type Kind, type Side, PER_LEVEL, NAMES, frozen, kindOf, levelOf, opening, other, playOn, rankOf, sideOf, squareName } from './board';
import { playerName, type Move, type State } from './index';

export type LineKind = 'move' | 'capture' | 'check' | 'freeze' | 'promotion' | 'end' | 'note';

export interface Line {
	kind: LineKind;
	text: string;
}

export interface Telling {
	/** The move's number, from one. */
	ply: number;
	move: Move;
	lines: Line[];
	/** The boards as they stood once the move was made. */
	after: Cell[];
}

const WORLD: Record<number, string> = { 3: 'the air', 2: 'the land', 1: 'the underworld' };

/** How each piece goes when it simply moves on its own board. */
const GOES: Record<Kind, string> = {
	S: 'drifts', G: 'leaps', R: 'glides', W: 'steps', O: 'lumbers', U: 'springs', T: 'slips', H: 'bounds',
	C: 'walks', M: 'sweeps', K: 'steps', P: 'rides', D: 'trudges', B: 'slithers', E: 'grinds'
};

/** The word for a piece that changes boards, going up or down. */
function crossing(kind: Kind, from: number, to: number): string {
	const up = levelOf(to) > levelOf(from);
	if (kind === 'G') return up ? 'takes wing' : 'swoops down';
	if (kind === 'P') return up ? 'vaults up' : 'vaults down';
	if (kind === 'H') return up ? 'springs up' : 'springs down';
	if (kind === 'M') return up ? 'ascends' : 'descends';
	if (kind === 'D') return up ? 'bursts up' : 'drops back';
	if (kind === 'E') return up ? 'heaves itself up' : 'sinks';
	if (kind === 'S') return up ? 'rises' : 'dives';
	return up ? 'climbs' : 'drops';
}

/** How a victim is told. */
function falls(victim: Kind, owner: string, where: string): string {
	switch (victim) {
		case 'R': return `${owner} Dragon falls from the sky at ${where}`;
		case 'B': return `${owner} Basilisk is crushed at ${where}, and its gaze is broken`;
		case 'S': return `${owner} Sylph is scattered at ${where}`;
		case 'E': return `${owner} Elemental is shattered at ${where}`;
		default: return `${owner} ${NAMES[victim]} falls at ${where}`;
	}
}

/** The pieces on the land held frozen, by square. */
function frozenSquares(cells: Cell[]): Set<number> {
	const held = new Set<number>();
	for (let i = PER_LEVEL; i < PER_LEVEL * 2; i++) if (cells[i] !== '' && frozen(cells, i)) held.add(i);
	return held;
}

/** Whose a piece is, as a possessive: "Aud’s", "Scarlet’s", or "Your" at a lesson. */
export type Owner = (side: Side) => string;

/** Tell one move from the position it was made in. */
function tellOne(before: Cell[], move: Move, owner: Owner): { lines: Line[]; after: Cell[] } {
	const who = owner(move.by);
	const foe = owner(other(move.by));
	const piece = NAMES[move.kind];
	const from = squareName(move.from);
	const to = squareName(move.to);
	const played = playOn(before, move.from, move.to);
	const after = played.cells;
	const lines: Line[] = [];

	if (move.afar) {
		lines.push({ kind: 'capture', text: `${who} Dragon strikes down from ${from} without leaving the air, and ${falls(move.captured!, foe, to)}.` });
	} else if (levelOf(move.from) !== levelOf(move.to)) {
		const verb = crossing(move.kind, move.from, move.to);
		if (move.captured) lines.push({ kind: 'capture', text: `${who} ${piece} ${verb} from ${from} onto ${to}, and ${falls(move.captured, foe, to)}.` });
		else lines.push({ kind: 'move', text: `${who} ${piece} ${verb} from ${from} to ${to}, into ${WORLD[levelOf(move.to)]}.` });
	} else if (move.captured) {
		lines.push({ kind: 'capture', text: `${who} ${piece} ${GOES[move.kind]} from ${from} to ${to}, and ${falls(move.captured, foe, to)}.` });
	} else {
		lines.push({ kind: 'move', text: `${who} ${piece} ${GOES[move.kind]} from ${from} to ${to}.` });
	}

	if (move.promoted) lines.push({ kind: 'promotion', text: `On the far rank the Warrior stands up a Hero.` });

	// What the move did to the land beneath and above: a gaze that falls, a gaze that lifts.
	const heldBefore = frozenSquares(before);
	const heldAfter = frozenSquares(after);
	for (const i of heldAfter) {
		if (heldBefore.has(i) && (move.afar || i !== move.to)) continue;
		const owner = sideOf(after[i]) === move.by ? who : foe;
		lines.push({ kind: 'freeze', text: `The Basilisk’s gaze falls on ${owner} ${NAMES[kindOf(after[i])]} at ${squareName(i)}, which cannot stir.` });
	}
	for (const i of heldBefore) {
		// The same piece, still there and no longer held; a piece that has just arrived is another story.
		if (heldAfter.has(i) || after[i] === '' || after[i] !== before[i] || i === move.from || i === move.to) continue;
		const owner = sideOf(after[i]) === move.by ? who : foe;
		lines.push({ kind: 'note', text: `${owner} ${NAMES[kindOf(after[i])]} at ${squareName(i)} is free to move again.` });
	}

	// A piece that has put itself somewhere it can do little.
	const landed = after[move.to];
	if (landed !== '' && !move.afar) {
		const k = kindOf(landed);
		const lv = levelOf(move.to);
		if (k === 'K' && lv !== 2) lines.push({ kind: 'note', text: `Off the land the King can do nothing but come back.` });
		if (k === 'S' && lv === 2) lines.push({ kind: 'note', text: `Grounded, the Sylph can only rise again.` });
		if (k === 'E' && lv === 2) lines.push({ kind: 'note', text: `On the land the Elemental is a rock until it sinks again.` });
		if (k === 'W' && !move.promoted && rankOf(move.to) === (move.by === 'gold' ? 6 : 1)) lines.push({ kind: 'note', text: `One more step and it is a Hero.` });
	}

	if (move.check) lines.push({ kind: 'check', text: `${foe} King is in check.` });
	return { lines, after };
}

/** The whole game told, one entry a move, from a replay of the moves. A game begun from the opening needs no `start`. */
export function narrate(state: State, start?: Cell[]): Telling[] {
	const owner: Owner = (side) => `${playerName(state, side)}’s`;
	let cells = start ?? opening(state.setup);
	const out: Telling[] = [];
	state.moves.forEach((move, n) => {
		const { lines, after } = tellOne(cells, move, owner);
		cells = after;
		out.push({ ply: n + 1, move, lines, after });
	});
	if (state.over && out.length) out[out.length - 1].lines.push({ kind: 'end', text: state.over.reason });
	return out;
}

/** One move told on its own, from the position it was made in. */
export function tell(before: Cell[], move: Move, owner: Owner): string {
	return tellOne(before, move, owner).lines.map((l) => l.text).join(' ');
}