feat: support graceful 404 pages for resources

src/pages/resources/404.tsx

@@ -0,0 +1,122 @@
+import { graphql, Link } from "gatsby"
+import React, { Component, Fragment } from "react"
+import { Location } from "@reach/router"
+
+import { SEO } from "../../components/SEO"
+
+// helper function to make matrix generation easier
+// credits to https://stackoverflow.com/a/13808461
+function makeMatrix(w, h, val) {
+  return Array(h)
+    .fill(null)
+    .map(() => Array(w).fill(val))
+}
+
+// calculate semantic difference
+// based on one character edits
+// efficient refactoring inspired by MIT licensed repo:
+// https://github.com/trekhleb/javascript-algorithms
+function levenshteinDistance(term1, term2) {
+  /* base case: empty strings */
+  if (term1.length == 0) return term2.length
+  if (term2.length == 0) return term1.length
+
+  // this will be our comparison matrix
+  const matrix = makeMatrix(term1.length + 1, term2.length + 1, null)
+
+  // make zeroeth row based off first term
+  for (let i = 0; i <= term1.length; i += 1) {
+    matrix[0][i] = i
+  }
+
+  // make zeroeth column based off second term
+  for (let j = 0; j <= term2.length; j += 1) {
+    matrix[j][0] = j
+  }
+
+  // iterative with full matrix implementation
+  // https://en.wikipedia.org/wiki/Levenshtein_distance
+  for (let j = 1; j <= term2.length; j += 1) {
+    for (let i = 1; i <= term1.length; i += 1) {
+      const substitutionCost = term1[i - 1] === term2[j - 1] ? 0 : 1
+
+      matrix[j][i] = Math.min(
+        matrix[j - 1][i] + 1, // deletion
+        matrix[j][i - 1] + 1, // insertion
+        matrix[j - 1][i - 1] + substitutionCost
+      ) // substitution
+    }
+  }
+
+  return matrix[term2.length][term1.length]
+}
+
+function getPossibleResources(location, data) {
+  // the data prop has the graphql result
+  // we're abstracting it to `link_array` to just have array of edges matched
+  // must use `.node.absolutePath` on each edge to get each node's absolute link
+  // we will compare this link
+  // however, the relative links are more user friendly
+  const link_array = data.allFile.edges
+
+  // location prop has several attributes
+  // location.origin is base url
+  // location.href is the window location
+  // location.pathname is link after protocol and hostname
+  // by replacing `"/resources/"`,
+  // we are left with only the relative path to `resources`
+  const search = location.pathname.replace("/resources/", "")
+
+  // filter based on distance
+  // levenshtein distance of x means how 'off' it was
+  const display_array = link_array.filter(
+    (value, index) =>
+      levenshteinDistance(
+        search.toLowerCase(),
+        value.node.relativePath.toLowerCase()
+      ) < 8
+  )
+
+  // helpful message if no matches found
+  const found = display_array.length == 0 ? "Oops, nothing similar found." : ""
+
+  return (
+    <Fragment>
+      <h3>Based off of "{search}" you may have meant:</h3>
+      <ul>
+        {display_array.map((value, index) => {
+          return (
+            <li key={index}>
+              <Link to={`${"resources/" + value.node.relativePath}`}>
+                {value.node.relativePath}
+              </Link>
+            </li>
+          )
+        })}
+      </ul>
+      {found}
+    </Fragment>
+  )
+}
+
+export default ({ location, data }) => (
+  <Fragment>
+    <SEO title="404: Resource Not found" />
+    <h1>RESOURCE NOT FOUND</h1>
+    <p>You just hit a route that doesn&#39;t exist... the sadness.</p>
+    <Location>
+      {({ navigate, location }) => getPossibleResources(location, data)}
+    </Location>
+  </Fragment>
+)
+export const query = graphql`
+  query {
+    allFile(filter: { sourceInstanceName: { eq: "resources" } }) {
+      edges {
+        node {
+          relativePath
+        }
+      }
+    }
+  }
+`

src/pages/resources/index.tsx

@@ -1,9 +1,9 @@
 import React, { Fragment } from "react"
 
-import packageJson from "../../package.json"
-import { Link } from "../components/Link"
-import { ResourcesList } from "../components/ResourcesList"
-import { SEO } from "../components/SEO"
+import packageJson from "../../../package.json"
+import { Link } from "../../components/Link"
+import { ResourcesList } from "../../components/ResourcesList"
+import { SEO } from "../../components/SEO"
 
 function ResourcesPage() {
   return (