function init() {
  const map = document.querySelector('.map')
  const spriteContainer = document.querySelector('.sprite_container')
  const instruction = document.querySelector('.instruction')
  const sprite = document.querySelector('.sprite')
  const motionSpeed = 150
  const height = 10
  const width = 20
  const delay = 20
  let cellSize = 40
  let spritePos = -cellSize
  let x = 0
  let y = 0
  let instructionTimer
  let motionTimer
  let displayTimer
  let boneTimer
  let start = 42
  let goal = 0
  let carryOn = true
  let triedAnotherWay = false
  let route = []
  let happy
  let happyFrame = 10

  const cellsWithWalls = [
    31,45,69,68,71,73,82,83,85,88,91,94,95,96,98,105,110,111,112,123,125,128,137,141,142,143,145,146,154,156,157,171
  ]

  const bone = `
    <svg class ="bone" x="0px" y="0px" width="100%" height="100%" viewBox="0 0 151.9 151.9" >
    <style type="text/css">
    .st0{fill:#FFFFFF;}
    </style>
    <polygon class="st0" points="39.2,53.7 44.6,56.9 50.4,62.3 102.8,62.3 106.4,59.3 111.2,53.7 120.8,53.7 125.3,58 130.4,63.8 
    130.4,67.2 125.1,73.2 120.6,77.3 124.8,81.5 130.4,86.5 130.4,91.6 125.9,95.7 120.8,100.4 111.4,100.4 106.9,96.3 101.9,91.6 
    50,91.4 45.9,95.7 40.8,100.4 30.9,100.4 26.4,96.3 21.7,91.2 21.7,86.7 26.4,82.2 30.9,77.1 26.4,72.5 21.7,67.2 21.7,63.2 
    27,58.1 30.7,53.7 "/>
    <g>
    <g>
      <g>
        <path d="M24.1,70.2c-1.6,0-3.1,0-4.7,0c0-3.2,0-6.3,0-9.5c1.6,0,3.1,0,4.7,0c0-1.6,0-3.2,0-4.7c1.5,0,3,0,4.5,0c0-1.5,0-3,0-4.5
          c4.8,0,9.5,0,14.3,0c0,1.5,0,2.9,0,4.5c1.6,0,3.2,0,4.8,0c0,1.6,0,3.2,0,4.7c18.9,0,37.7,0,56.5,0c0-1.6,0-3.1,0-4.7
          c1.6,0,3.2,0,4.8,0c0-1.5,0-3,0-4.5c4.7,0,9.4,0,14.1,0c0,1.5,0,3,0,4.5c1.6,0,3.1,0,4.7,0c0,1.6,0,3.2,0,4.7c1.6,0,3.2,0,4.8,0
          c0,3.2,0,6.4,0,9.6c-1.6,0-3.1,0-4.7,0c0,0,0,0,0,0c0-3.1,0-6.2,0-9.3c-1.6,0-3.1,0-4.7,0c0-1.6,0-3.1,0-4.7c-4.7,0-9.4,0-14.1,0
          c0,1.6,0,3.1,0,4.7c-1.6,0-3.2,0-4.8,0c0,1.6,0,3,0,4.5c-18.9,0-37.7,0-56.5,0c0-1.5,0-3,0-4.5c-1.6,0-3.2,0-4.8,0
          c0-1.6,0-3.2,0-4.7c-4.7,0-9.4,0-14,0c0,1.5,0,3,0,4.6c-1.6,0-3.2,0-4.7,0C24.2,64,24.2,67.1,24.1,70.2
          C24.1,70.2,24.1,70.2,24.1,70.2z"/>
        <path d="M127.9,93.8c0,1.6,0,3.1,0,4.7c-1.6,0-3.1,0-4.8,0c0,1.6,0,3.1,0,4.7c-4.7,0-9.3,0-14,0c0-1.6,0-3.1,0-4.7
          c-1.6,0-3.2,0-4.8,0c0-1.6,0-3.2,0-4.8c-18.9,0-37.7,0-56.5,0c0,1.6,0,3.1,0,4.7c-1.6,0-3.2,0-4.9,0c0,1.6,0,3.2,0,4.7
          c-4.7,0-9.3,0-14,0c-0.1-0.1-0.2-0.2-0.3-0.3c0-1.4,0-2.9,0-4.4c-1.5,0-3,0-4.6,0c0-1.6,0-3.2,0-4.7c0,0,0,0,0,0
          c1.6,0,3.1,0,4.7,0c0,1.6,0,3,0,4.6c4.7,0,9.3,0,14,0c0-1.5,0-3,0-4.7c1.6,0,3.2,0,4.8,0c0-1.6,0-3.1,0-4.6c18.9,0,37.7,0,56.5,0
          c0,1.5,0,3,0,4.6c1.6,0,3.2,0,4.8,0c0,1.7,0,3.2,0,4.7c4.7,0,9.3,0,14,0c0-1.5,0-3,0-4.5C124.8,93.8,126.3,93.8,127.9,93.8
          C127.9,93.8,127.9,93.8,127.9,93.8z"/>
        <path d="M24.1,93.8c-1.6,0-3.1,0-4.7,0c0-3.2,0-6.3,0-9.5c1.6,0,3.1,0,4.7,0c0-1.6,0-3.2,0-4.8c1.5,0,3,0,4.5,0c0-1.5,0-3,0-4.6
          c-1.5,0-3,0-4.5,0c0-1.6,0-3.2,0-4.7c0,0,0,0,0,0c1.6,0,3.1,0,4.7,0c0,1.6,0,3,0,4.6c1.5,0,3,0,4.2,0c0.3,0.2,0.4,0.2,0.4,0.2
          c0,1.7,0,3.2,0,4.8c-1.6,0-3.1,0-4.6,0c0,1.5,0,3,0,4.6c-1.6,0-3.2,0-4.7,0C24.2,87.6,24.2,90.7,24.1,93.8
          C24.1,93.8,24.1,93.8,24.1,93.8z"/>
        <path d="M127.9,70.2c0,1.6,0,3.1,0,4.7c-1.6,0-3.2,0-4.7,0c0,1.5,0,3,0,4.5c1.5,0,3.1,0,4.7,0c0,1.6,0,3.2,0,4.8
          c1.6,0,3.2,0,4.8,0c0,3.2,0,6.3,0,9.6c-1.6,0-3.1,0-4.7,0c0,0,0,0,0,0c0-3.1,0-6.2,0-9.3c-1.6,0-3.1,0-4.7,0c0-1.6,0-3.1,0-4.7
          c-1.6,0-3.2,0-4.7,0c0-1.6,0-3.2,0-4.9c1.5,0,3.1,0,4.7,0c0-1.7,0-3.1,0-4.7C124.8,70.1,126.3,70.1,127.9,70.2
          C127.9,70.2,127.9,70.2,127.9,70.2z"/>
      </g>
    </g>
    </g>
  </svg>
  `

  const searchMemory = new Array(height * width).fill('').map(()=>{
    return {
      path: null,
      searched: false,
      prev: null
    }
  })

  const mapMap = ()=>{
    const mapArr = []   
    for (let i = 0; i < (width * height); i++){
      mapArr.push(i)
    }

    return mapArr.map((ele,i)=>{
      const dataX = i % width
      const dataY = Math.floor(i / width)

      return `
        <div 
          class="map_tile"
          data-index=${i}
          data-x=${dataX}
          data-y=${dataY}
        >
        </div>  
      `
    }).join('')
  }

  map.innerHTML = mapMap()
  const mapTiles = document.querySelectorAll('.map_tile')

  const setX = num =>{
    x = num
    spriteContainer.style.left = `${x}px`
  }

  const setY = num =>{
    y = num
    spriteContainer.style.top = `${y}px`
  }

  const setSpritePos = num =>{
    spritePos = num
    sprite.style.marginLeft = `${spritePos}px`
  }

  const positionSprite = pos =>{
    const paraX = pos % width * cellSize
    const paraY = Math.floor(pos / width) * cellSize
    setX(paraX)
    setY(paraY)
  }

  const NoWall = pos =>{
    return !mapTiles[pos].classList.contains('wall')
  }

  const setUpWalls = ()=>{
    cellsWithWalls.forEach(cell=>{
      mapTiles[cell].classList.add('wall')
    })
    mapTiles.forEach(tile=>{
      if (tile.dataset.y === '0' || 
          tile.dataset.y === '9' || 
          tile.dataset.x === '0' || 
          tile.dataset.x === '19') tile.classList.add('wall')
    })
  }

  const clearTiles = ()=>{
    mapTiles[goal].innerHTML = ''
    mapTiles.forEach(tile=>{
      tile.className = 'map_tile'
    })
    setUpWalls()
  }

  const spriteWalk = e=>{
    if (!e) return

    const direction = e.key ? e.key.toLowerCase().replace('arrow','') : e
    const current = (x / cellSize) + ((y / cellSize) * width)
    let m = -cellSize
    switch (direction) {
      case 'right': 
        if (x < ((width - 1) * cellSize) && NoWall(current + 1)) setX(x + cellSize)
        m = spritePos === m * 8 ? m * 9 : m * 8
        break
      case 'left': 
        if (x > 0 && NoWall(current - 1)) setX(x - cellSize)
        m = spritePos === m * 6 ? m * 7 : m * 6
        break
      case 'up': 
        if (y > 0 && NoWall(current - width)) setY(y - cellSize)
        m = spritePos === m * 3 ? m * 5 : m * 3
        break
      case 'down': 
        if (y < ((height - 1) * cellSize) && NoWall(current + width)) setY(y + cellSize)
        m = spritePos === m * 0 ? m * 2 : m * 0
        break
      default:
        console.log('invalid command')
    }
    setSpritePos(m)
    start = (x / cellSize) + ((y / cellSize) * width)
    if (goal === (x / cellSize) + ((y / cellSize) * width)) {
      boneTimer = setTimeout(()=>{
        mapTiles[goal].innerHTML = ''
        animateHappyDog()
      },100)  
    }
  }

  const chainMotion = (instruction,index) => {
    if (index >= instruction.length) return
    
    spriteWalk(instruction[index])
    motionTimer = setTimeout(()=>{
      chainMotion(instruction, index + 1)
    },motionSpeed)
  }

  const displayPath = current =>{
    searchMemory[current].path = 'path'
    mapTiles[current].classList.add('path')
    let prev = searchMemory[current].prev
    
    //! when sprite is one square away from start and prev is undefined, prev is corrected.
    if (current - width === start ||
      current + width === start ||
      current - 1 === start ||
      current + 1 === start) prev = start

    let direction
    if (current - width === prev) direction = 'down'
    if (current + width === prev) direction = 'up'
    if (current - 1 === prev) direction = 'right'
    if (current + 1 === prev) direction = 'left'
    
    if (prev) route.push(direction)

    if (!prev) {
      route.push('reset')
      return
    }

    if (prev === start || !prev) {
      const reversedRoute = route.reverse()
      chainMotion(reversedRoute,0)
      return
    }

    displayTimer = setTimeout(()=>{
      displayPath(prev)
    },delay)
  }

  const distanceBetween = (a,b) =>{
    return Math.abs(a % width - b % width) + Math.abs(Math.floor(a / width) - Math.floor(b / width))
  }

  const decideNextMove = (current, count) =>{
    if (!carryOn) return
    const possibleDestination = [
      current + 1,
      current - 1,
      current - width,
      current + width  
    ]
    const mapInfo = []
    if (possibleDestination.filter(cell=> cell === goal).length === 1) {
      carryOn = false
      searchMemory[goal].prev = current
      displayPath(goal)
      return
    }
    possibleDestination.forEach(option=>{  
      if (mapTiles[option] && 
          !mapTiles[option].classList.contains('wall') && 
          !searchMemory[option].searched && 
          option !== start) {
        mapInfo.push(
          { 
            cell: option,
            prev: current,
            distanceFromStart: distanceBetween(start,option),
            distanceToGoal: distanceBetween(goal,option)
          }
        )
      }
    })
    const minValue = Math.min(...mapInfo.map(cell=> cell.distanceFromStart + cell.distanceToGoal))
    const optionsWithMinValue = mapInfo.filter(cell=> (cell.distanceFromStart + cell.distanceToGoal) === minValue)

    mapInfo.filter(cell=> (cell.distanceFromStart + cell.distanceToGoal) !== minValue).forEach(option=>{
      mapTiles[option.cell].classList.add('sub_node')
    })

    if (optionsWithMinValue.length === 0 && !triedAnotherWay) {
      triedAnotherWay = true
      tryAnotherWay(count)
    }

    optionsWithMinValue.forEach(option=>{
      searchMemory[option.cell].searched = true 
      searchMemory[option.cell].prev = current
      mapTiles[option.cell].classList.add('node')   
      setTimeout(()=>{
        decideNextMove(option.cell, count + 1)
      },delay)
    })
  }

  const tryAnotherWay = count =>{
    if (!carryOn) return
    const possibleDestination = [
      start + 1,
      start - 1,
      start - width,
      start + width  
    ]
    possibleDestination.forEach(path=>{
      if (mapTiles[path] && 
          !searchMemory[path].searched && 
          !mapTiles[path].classList.contains('wall')) {
        decideNextMove(path, count + 1)
      }
    })
  }

  const resetMotion = () =>{
    clearTimeout(motionTimer)
    clearTimeout(displayTimer)
    clearTimeout(boneTimer)
    clearInterval(happy)
    clearTiles()
    searchMemory.forEach(memory=>{
      memory.path = null,
      memory.searched = false,
      memory.prev = null
    })
    route = []
    carryOn = true
    triedAnotherWay = false
  }

  const triggerMotion = e =>{
    if (Number(e.target.dataset.index) === goal || !e.target.dataset.index) return 
    instruction.classList.add('hide')
    clearTimeout(instructionTimer)
    instructionTimer = setTimeout(()=>{
      instruction.classList.remove('hide')
    },5 * 1000)
    mapTiles[goal].innerHTML = ''
    goal = Number(e.target.dataset.index)
    if (mapTiles[goal].classList.contains('wall')) return
    resetMotion()
    mapTiles[start].classList.add('start')
    positionSprite(start)
    mapTiles[goal].classList.add('goal')
    mapTiles[goal].innerHTML = bone
    searchMemory[start].path = 'start'
    searchMemory[goal].path = 'goal'
    decideNextMove(start, 0)
  }

  const animateHappyDog = () =>{
    happy = setInterval(()=>{
      happyFrame = happyFrame === 10 ? 11 : 10
      setSpritePos(happyFrame * -cellSize)
    },150)
  }

  //! comment this bit out to enable keyboard control
  // window.addEventListener('keydown', spriteWalk)

   const resize = () =>{
    const wrapper = document.querySelector('.wrapper')
    let pWidth = 800
    if (wrapper.offsetWidth < 800) {
      pWidth = wrapper.offsetWidth
    } 
    cellSize = Math.floor(pWidth / width)
    const calcWidth = Math.floor(pWidth / width) * width
    const mapCover = document.querySelector('.map_cover')

    //*resize sprite
    positionSprite(start)
    setSpritePos(-cellSize)
    sprite.style.height = `${cellSize}px`
    sprite.style.width = `${cellSize * 12}px`
    spriteContainer.style.height = `${cellSize}px`
    spriteContainer.style.width = `${cellSize}px`

    //* resize map
    map.style.width = `${calcWidth}px`
    map.style.height = `${calcWidth / 2}px`
    mapCover.style.width = `${calcWidth}px`
    mapCover.style.height = `${calcWidth / 2}px`
    mapCover.style.marginTop = `-${calcWidth / 2}px`
    mapTiles.forEach(tile=>{
      tile.style.width = `${cellSize}px`
      tile.style.height = `${cellSize}px`
    })
  }
  
  //*setup
  setUpWalls()
  positionSprite(start)
  mapTiles.forEach(mapTile=>{
    mapTile.addEventListener('click', triggerMotion)
  })
  resize()
  window.addEventListener('resize', resize)
}

window.addEventListener('DOMContentLoaded', init)