import {State} from "./state";
import Coordinates from "../model/coordinates.ts";
import {MazeCell} from "../model/maze.ts";

export default function handleUserClicked(state: State, x: number, y: number): State {
    if (isClickAllowed(x, y, state)) {
        const maze = state.maze!;
        // Okay, we clicked a cell that's adjacent to the end of the userpath (or which IS the end of the userpath)
        // and that's not blocked by a wall. Now let's see.
        if (-1 === state.userPath.findIndex(step => step.x === x && step.y === y)) {
            // The clicked cell is not yet part of the userpath --> add it.
            // If it's the end tile, also show a congratulation message
            const showMessage = x === maze.end.x && y === maze.end.y;
            return {
                ...state,
                userPath: [...state.userPath, {x, y}],
                errorMessage: showMessage ? "Congratulations! You won!" : state.errorMessage
            };
        } else {
            // The clicked cell IS part of the userpath. Is it the last cell of it?
            const lastCoordsFromUserPath = getLastCoordsFromUserPath(state)!;
            if (lastCoordsFromUserPath.x === x && lastCoordsFromUserPath.y === y) {
                // Yes, it's the last cell of the userpath --> remove it.
                return {
                    ...state,
                    userPath: state.userPath.filter(step => step.x !== x || step.y !== y),
                    errorMessage: null
                }
            }
        }
    }
    // Not allowed to toggle that cell. Don't apply any change to the state.
    return state;
}

function isClickAllowed(x: number, y: number, state: State): boolean {
    const lastCoordsFromUserPath = getLastCoordsFromUserPath(state);
    if (!lastCoordsFromUserPath) {
        // when nothing has been marked yet, we can only toggle the starting position
        return x === state.maze!.start.x && y === state.maze!.start.y;
    }
    if (lastCoordsFromUserPath.x === x && lastCoordsFromUserPath.y === y) {
        // toggling the last position in the path is always allowed
        return true;
    }

    if (Math.abs(x - lastCoordsFromUserPath.x) + Math.abs(y - lastCoordsFromUserPath.y) !== 1) {
        // It's not a neighbor. So it's not allowed.
        return false;
    }

    const lastCell = getCellAt(lastCoordsFromUserPath, state);
    if (x === lastCoordsFromUserPath.x + 1) {
        // There must be no wall to the right of the last cell.
        return !lastCell.right;
    }
    if (x === lastCoordsFromUserPath.x - 1) {
        // There must be no wall to the left of the last cell.
        return !lastCell.left;
    }
    if (y === lastCoordsFromUserPath.y + 1) {
        // There must be no wall below the last cell.
        return !lastCell.bottom;
    }
    if (y === lastCoordsFromUserPath.y - 1) {
        // There must be no wall above the last cell.
        return !lastCell.top;
    }

    return false;
}

function getCellAt(coords: Coordinates, state: State): MazeCell {
    return state.maze!.grid[coords.y][coords.x];
}

function getLastCoordsFromUserPath(state: State): Coordinates | null {
    if (state.userPath.length > 0) {
        return state.userPath[state.userPath.length - 1];
    }
    return null;
}