import { readFileSync } from 'node:fs';

const input = readFileSync('input', 'utf-8');

const [stackInput, movementInput] = input.split('\n\n', 2);

// Parse movements
const movements = movementInput
  .split('\n')
  .filter(movement => movement)
  .map(movement => {
    const match = movement.match(/move (\d+) from (\d+) to (\d+)/);
    if (!match) {
      throw new Error(`Invalid movement: ${movement}`);
    }
    return {
      count: parseInt(match[1]),
      from: parseInt(match[2]),
      to: parseInt(match[3])
    }
  });

// Parse stacks
const stackInputLines = stackInput.split('\n');
const columnDelimiter = ' ';
const columnPositions = stackInputLines
  // Locate delimiter positions
  .map(line => {
    const positions = [];
    let pos = -1;
    while (true) {
      pos = line.indexOf(columnDelimiter, pos + 1);
      if (pos === -1) {
        break;
      }
      positions.push(pos);
    }

    return positions;
  })
  .reduce((commonPositions, positions) =>
    commonPositions.filter(
      pos => positions.includes(pos)
    )
  );

const columns = new Array(columnPositions.length + 1)
  .fill(0)
  .map(column => []);

for (const line of [...stackInputLines].reverse()) {
  for (let i = 0; i <= columnPositions.length; i++) {
    const start = (columnPositions[i - 1] ?? -1) + 1;
    const end = columnPositions[i] ?? line.length;
    const value = line.slice(start, end);
    columns[i].push(value);
  }
}

class Stack {
  constructor(number, crates) {
    this.number = number;
    this.crates = crates;
  }

  get topCrate() {
    return this.crates[this.crates.length - 1];
  }

  move(count, toStack) {
    this._checkMoveCount(count);
    toStack.crates.push(...this.crates.splice(-count));
  }

  moveIndividually(count, toStack) {
    this._checkMoveCount(count);
    toStack.crates.push(...this.crates.splice(-count).reverse());
  }

  _checkMoveCount(count) {
    if (count > this.crates.length) {
      throw new Error(
        `Tried to move ${count} crates from a stack containing: ` +
        `${this.crates.length}`
      );
    }
  }
}

function buildStacks() {
  return new Map(columns
    .map(column => column
      .map(cell => cell.trim())
      .filter(cell => cell)
    )
    .map(column => {
      if (column.length < 1) {
        throw new Error('Invalid column');
      }

      const number = parseInt(column[0]);
      if (isNaN(number)) {
        throw new Error(`Invalid column number: ${number}`);
      }

      const crates = column
        .slice(1)
        .map(crate => crate.replaceAll(/\[?\]?/g, ''));

      return new Stack(number, crates);
    })
    .map(stack => [stack.number, stack])
  );
}

function getTopCrates(stacks) {
  return [...stacks.keys()]
    .sort()
    .map(number => stacks.get(number).topCrate)
    .reduce((crates, crate) => crates + crate);
}

function runSimulation(simulationCb) {
  for (const movement of movements) {
    const fromStack = stacks.get(movement.from);
    if (!fromStack) {
      throw new Error(`Tried to move from unknown stack: ${movement.from}`);
    }
    const toStack = stacks.get(movement.to);
    if (!toStack) {
      throw new Error(`Tried to move to unknown stack: ${movement.to}`);
    }
    simulationCb(movement.count, fromStack, toStack);
  }
}

let stacks;
let topCrates;

// CrateMover 9000 Simulation
stacks = buildStacks();
runSimulation((count, fromStack, toStack) =>
  fromStack.moveIndividually(count, toStack)
);
topCrates = getTopCrates(stacks);
console.log(`Top crates after CrateMover 9000 sort: ${topCrates}`);

// CrateMover 9001 Simulation
stacks = buildStacks();
runSimulation((count, fromStack, toStack) =>
  fromStack.move(count, toStack)
);
topCrates = getTopCrates(stacks);
console.log(`Top crates after CrateMover 9001 sort: ${topCrates}`);