Function sequenceFromPath

packages/effect/test/Pathfinding.test.ts:156–199

(
  terrain: Terrain,
  path: Option.Option<Graph.PathResult<number>>
)

 * Derive a sequence of moves from a path.
 */
const sequenceFromPath = (
  terrain: Terrain,
  path: Option.Option<Graph.PathResult<number>>
): Sequence | undefined => {
  if (Option.isNone(path) || path.value.path.length === 0) {
    return undefined
  }

  const pathValue = path.value

  const sequence = []
  const start = terrain.coordinates.get(pathValue.path[0])!
  let previous = Graph.getNode(terrain.graph, terrain.nodes.get(start)!).pipe(
    Option.getOrThrowWith(() => new Error(`Start location ${start} not found in terrain`))
  )

  for (const index of pathValue.path.slice(1)) {
    const current = Graph.getNode(terrain.graph, index).pipe(
      Option.getOrThrowWith(() => new Error(`Location ${index} not found in terrain`))
    )

    if (current.x === previous.x) {
      if (current.y === previous.y - 1) {
        sequence.push("↑")
      } else if (current.y === previous.y + 1) {
        sequence.push("↓")
      } else {
        throw new Error(`Invalid move ${current.x}:${current.y} -> ${previous.x}:${previous.y}`)
      }
    } else if (current.y === previous.y) {
      if (current.x === previous.x - 1) {
        sequence.push("←")
      } else if (current.x === previous.x + 1) {
        sequence.push("→")
      } else {
        throw new Error(`Invalid move ${current.x}:${current.y} -> ${previous.x}:${previous.y}`)
      }
    }

    previous = current
  }

  return `${start};${sequence.join("")}`
}

// =============================================================================
// Terrain Parser