moth/theme/puzzle.js

// jshint asi:true

// devel_addin drops a bunch of development extensions into element e.
// It will only modify stuff inside e.
function devel_addin(obj, e) {
  let h = document.createElement("h2")
  e.appendChild(h)
  h.textContent = "Development Options"

  let g = document.createElement("p")
  e.appendChild(g)
  g.innerText = "This section will not appear for participants."
  
  let keys = Object.keys(obj)
  keys.sort()
  for (let key of keys) {
    switch (key) {
      case "body":
        continue
    }
    let val = obj[key]

    if ((! val) || (val.length === 0)) {
      // Empty, skip it
      continue
    }

    let d = document.createElement("div")
    e.appendChild(d)
    d.classList.add("kvpair")
    
    let ktxt = document.createElement("span")
    d.appendChild(ktxt)
    ktxt.textContent = key
    
    if (Array.isArray(val)) {
      let vi = document.createElement("select")
      d.appendChild(vi)
      vi.multiple = true
      for (let a of val) {
        let opt = document.createElement("option")
        vi.appendChild(opt)
        opt.innerText = a
      }
    } else {
      let vi = document.createElement("input")
      d.appendChild(vi)
      vi.value = val
      vi.disabled = true
    }
  }
}

// Hash routine used in v3.4 and earlier
function djb2hash(buf) {
  let h = 5381
  for (let c of (new TextEncoder()).encode(buf)) { // Encode as UTF-8 and read in each byte
    // JavaScript converts everything to a signed 32-bit integer when you do bitwise operations.
    // So we have to do "unsigned right shift" by zero to get it back to unsigned.
    h = (((h * 33) + c) & 0xffffffff) >>> 0
  }
  return h
}

// The routine used to hash answers in compiled puzzle packages
async function sha256Hash(message) {
  const msgUint8 = new TextEncoder().encode(message);                           // encode as (utf-8) Uint8Array
  const hashBuffer = await crypto.subtle.digest('SHA-256', msgUint8);           // hash the message
  const hashArray = Array.from(new Uint8Array(hashBuffer));                     // convert buffer to byte array
  const hashHex = hashArray.map(b => b.toString(16).padStart(2, '0')).join(''); // convert bytes to hex string
  return hashHex;
}

// Is the provided answer possibly correct?
async function possiblyCorrect(answer) {
  for (let correctHash of window.puzzle.hashes) {
    // CPU time is cheap. Especially if it's not our server's time.
    // So we'll just try absolutely everything and see what happens.
    // We're counting on hash collisions being extremely rare with the algorithm we use.
    // And honestly, this pales in comparison to the amount of CPU being eaten by
    // something like the github 404 page.
    
    if (djb2hash(answer) == correctHash) {
      return answer
    }
    for (let len = 0; len <= answer.length; len += 1) {
      if (window.puzzle.xAnchors.includes("end") && (len != answer.length)) {
        continue
      }
      for (let pos = 0; pos < answer.length - len + 1; pos += 1) {
        if (window.puzzle.xAnchors.includes("begin") && (pos > 0)) {
          continue
        }
        let sub = answer.substring(pos, pos+len)
        let digest = await sha256Hash(sub)
        
        if (digest == correctHash) {
          return sub
        }
      }
    }
  }
  return false
}


// Pop up a message
function toast(message, timeout=5000) {
  let p = document.createElement("p")
  
  p.innerText = message
  document.getElementById("messages").appendChild(p)
  setTimeout(
    e => { p.remove() },
    timeout
  )
}

// When the user submits an answer
function submit(e) {
  e.preventDefault()
  let data = new FormData(e.target)
  
  // Kludge for patterned answers
  let xAnswer = data.get("xAnswer")
  if (xAnswer) {
    data.set("answer", xAnswer)
  }
  window.data = data
  fetch("answer", {
    method: "POST",
    body: data,
  })
  .then(resp => {
    if (resp.ok) {
      resp.json()
      .then(obj => {
        toast(obj.data.description)
      })
    } else {
      toast("Error submitting your answer. Try again in a few seconds.")
      console.log(resp)
    }
  })
  .catch(err => {
    toast("Error submitting your answer. Try again in a few seconds.")
    console.log(err)
  })
}

function loadPuzzle(categoryName, points, puzzleId) {
  let puzzle = document.getElementById("puzzle")
  let base = "content/" + categoryName + "/" + puzzleId + "/"

  fetch(base + "puzzle.json")
  .then(resp => {
    return resp.json()
  })
  .then(obj => {
    // Populate authors
    document.getElementById("authors").textContent = obj.authors.join(", ")
    
    // Make the whole puzzle available
    window.puzzle = obj
    
    // If answers are provided, this is the devel server
    if (obj.answers) {
      devel_addin(obj, document.getElementById("devel"))
    }
    
    // Load scripts
    for (let script of obj.scripts) {
      let st = document.createElement("script")
      document.head.appendChild(st)
      st.src = base + script
    }
    
    // List associated files
    for (let fn of obj.files) {
      let li = document.createElement("li")
      let a = document.createElement("a")
      a.href = base + fn
      a.innerText = fn
      li.appendChild(a)
      document.getElementById("files").appendChild(li)
    }

    // Prefix `base` to relative URLs in the puzzle body
    let doc = new DOMParser().parseFromString(obj.body, "text/html")
    for (let se of doc.querySelectorAll("[src],[href]")) {
      se.outerHTML = se.outerHTML.replace(/(src|href)="([^/]+)"/i, "$1=\"" + base + "$2\"")
    }
    
    // If a validation pattern was provided, set that
    if (obj.pattern) {
      document.querySelector("#answer").pattern = obj.pattern
    }

    // Replace puzzle children with what's in `doc`
    Array.from(puzzle.childNodes).map(e => e.remove())
    Array.from(doc.body.childNodes).map(e => puzzle.appendChild(e))
  })
  .catch(err => {
    // Show error to the user
    Array.from(puzzle.childNodes).map(e => e.remove())
    let p = document.createElement("p")
    puzzle.appendChild(p)
    p.classList.add("Error")
    p.textContent = err
  })
  
  document.title = categoryName + " " + points
  document.querySelector("body > h1").innerText = document.title
  document.querySelector("input[name=cat]").value = categoryName
  document.querySelector("input[name=points]").value = points
}

// Check to see if the answer might be correct
// This might be better done with the "constraint validation API"
// https://developer.mozilla.org/en-US/docs/Learn/HTML/Forms/Form_validation#Validating_forms_using_JavaScript
function answerCheck(e) {
  let answer = e.target.value
  let ok = document.querySelector("#answer_ok")
  
  // You have to provide someplace to put the check
  if (! ok) {
    return
  }
  
  possiblyCorrect(answer)
  .then (correct => {
    document.querySelector("[name=xAnswer").value = correct || answer
    if (correct) {
      ok.textContent = "⭕"
      ok.title = "Possibly correct"
    } else {
      ok.textContent = "❌"
      ok.title = "Definitely not correct"
    }
  })
}

function init() {
  let params = new URLSearchParams(window.location.search)
  let categoryName = params.get("cat")
  let points = params.get("points")
  let puzzleId = params.get("pid")
  
  if (categoryName && points && puzzleId) {
    loadPuzzle(categoryName, points, puzzleId)
  }

  let teamId = sessionStorage.getItem("id")
  if (teamId) {
    document.querySelector("input[name=id]").value = teamId
  }
  
  if (document.querySelector("#answer")) {
    document.querySelector("#answer").addEventListener("input", answerCheck)
  }
  document.querySelector("form").addEventListener("submit", submit)
}

if (document.readyState === "loading") {
  document.addEventListener("DOMContentLoaded", init)
} else {
  init()
}