type Position = { x: number; y: number }
export type Node = Position & { parent?: Node; g: number; h: number; f: number }

export class AStar {
  private static readonly DIRECTIONS = [
    { x: 0, y: -1 }, // Up
    { x: 0, y: 1 }, // Down
    { x: -1, y: 0 }, // Left
    { x: 1, y: 0 }, // Right
    { x: -1, y: -1 },
    { x: -1, y: 1 },
    { x: 1, y: -1 },
    { x: 1, y: 1 }
  ]

  static findPath(start: Position, end: Position, grid: number[][], allowDiagonal = false): Node[] {
    const openList: Node[] = [{ ...start, g: 0, h: 0, f: 0 }]
    const closedSet = new Set<string>()
    const getKey = (p: Position) => `${p.x},${p.y}`

    while (openList.length > 0) {
      const current = openList.reduce((min, node) => (node.f < min.f ? node : min))
      if (current.x === end.x && current.y === end.y) return this.reconstructPath(current)

      openList.splice(openList.indexOf(current), 1)
      closedSet.add(getKey(current))

      const neighbors = this.DIRECTIONS.slice(0, allowDiagonal ? 8 : 4)
        .map((dir) => ({ x: current.x + dir.x, y: current.y + dir.y }))
        .filter((pos) => this.isValidPosition(pos, grid, end))

      for (const neighbor of neighbors) {
        if (closedSet.has(getKey(neighbor))) continue

        const g = current.g + this.getDistance(current, neighbor)
        const existing = openList.find((node) => node.x === neighbor.x && node.y === neighbor.y)

        if (!existing || g < existing.g) {
          const h = this.getDistance(neighbor, end)
          const node: Node = { ...neighbor, g, h, f: g + h, parent: current }
          if (!existing) openList.push(node)
          else Object.assign(existing, node)
        }
      }
    }

    return [] // No path found
  }

  private static isValidPosition(pos: Position, grid: number[][], end: Position): boolean {
    return pos.x >= 0 && pos.y >= 0 && pos.x < grid[0].length && pos.y < grid.length && (grid[pos.y][pos.x] === 0 || (pos.x === end.x && pos.y === end.y))
  }

  private static getDistance(a: Position, b: Position): number {
    const dx = Math.abs(a.x - b.x),
      dy = Math.abs(a.y - b.y)
    // Manhattan distance for straight paths, then Euclidean for diagonals
    return dx + dy + (Math.sqrt(2) - 2) * Math.min(dx, dy)
  }

  private static reconstructPath(endNode: Node): Node[] {
    const path: Node[] = []
    for (let current: Node | undefined = endNode; current; current = current.parent) {
      path.unshift(current)
    }
    return path
  }
}