import { grid, cols, rows } from './state.js';
import { config } from './config.js';
import { createCell } from './physics.js';

const dxs = [-1, 1, 0, 0];
const dys = [0, 0, -1, 1];

export function updateGrass(x, y, cell) {
    // Spread along surface dirt/sand
    if (Math.random() < (config.grass?.growChance || 0.03)) {
        const dir = Math.floor(Math.random() * 4);
        const nx = x + dxs[dir];
        const ny = y + dys[dir];
        
        if (nx >= 0 && nx < cols && ny >= 0 && ny < rows && grid[nx][ny]) {
            const target = grid[nx][ny];
            if (target.type === 'dirt' || target.type === 'sand') {
                // Only colonize dirt if it has air/empty space nearby (surface grass)
                const aboveDirt = ny - 1;
                if (aboveDirt >= 0 && !grid[nx][aboveDirt]) {
                    grid[nx][ny] = createCell('grass');
                    return;
                }
            }
        }
    }

    // Sprout blade feelers upwards into open air
    if (Math.random() < (config.grass?.growChance || 0.03) * 0.4) {
        const r = Math.random();
        const dx = r < 0.3 ? -1 : (r > 0.7 ? 1 : 0);
        const nx = x + dx;
        const ny = y - 1;
        if (nx >= 0 && nx < cols && ny >= 0 && !grid[nx][ny]) {
            grid[nx][ny] = createCell('grass');
        }
    }
}