From 713f9c1629488807ebb3b250dbf9f0c3933c18e5 Mon Sep 17 00:00:00 2001
From: Khinshan Khan <khanshan501@gmail.com>
Date: Sat, 25 Jan 2020 15:34:34 -0500
Subject: [PATCH] refact(404): abstract 404 link correction logic for
 collections to a component

---
 src/components/404LinkCorrection/index.tsx | 108 +++++++++++++++++++++
 src/pages/resources/404.tsx                | 108 +--------------------
 2 files changed, 111 insertions(+), 105 deletions(-)
 create mode 100644 src/components/404LinkCorrection/index.tsx

diff --git a/src/components/404LinkCorrection/index.tsx b/src/components/404LinkCorrection/index.tsx
new file mode 100644
index 0000000..7d3339e
--- /dev/null
+++ b/src/components/404LinkCorrection/index.tsx
@@ -0,0 +1,108 @@
+import { WindowLocation } from "@reach/router"
+import { Link } from "gatsby"
+import React, { Fragment } from "react"
+
+import { FileConnection } from "../../../generated/graphql"
+
+// helper function to make matrix generation easier
+// credits to https://stackoverflow.com/a/13808461
+function makeMatrix(w: number, h: number, val: any = null) {
+  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: string, term2: string) {
+  /* 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]
+}
+
+export const getPossibleCorrections = (
+  basepath: string,
+  location: WindowLocation,
+  data: { allFile: FileConnection }
+) => {
+  // the data prop has the graphql result
+  // we're abstracting it to `linkArray` 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 linkArray = 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(`/${basepath}/`, "")
+
+  // filter based on distance
+  // levenshtein distance of x means how 'off' it was
+  const displayArray = linkArray.filter(
+    value =>
+      levenshteinDistance(
+        search.toLowerCase(),
+        value.node!.relativePath!.toLowerCase()
+      ) < 8
+  )
+
+  // helpful message if no matches found
+  const found = displayArray.length === 0 ? "Oops, nothing similar found." : ""
+
+  return (
+    <Fragment>
+      <h3>Based off of "{search}" you may have meant:</h3>
+      <ul>
+        {displayArray.map((value, index) => {
+          return (
+            <li key={index}>
+              <Link to={`${basepath}/${value.node.relativePath}`}>
+                {value.node.relativePath}
+              </Link>
+            </li>
+          )
+        })}
+      </ul>
+      {found}
+    </Fragment>
+  )
+}
diff --git a/src/pages/resources/404.tsx b/src/pages/resources/404.tsx
index aaa6267..bd3990f 100644
--- a/src/pages/resources/404.tsx
+++ b/src/pages/resources/404.tsx
@@ -1,114 +1,12 @@
-import { Location, WindowLocation } from "@reach/router"
-import { graphql, Link } from "gatsby"
+import { Location } from "@reach/router"
+import { graphql } from "gatsby"
 import React, { Fragment } from "react"
 
 import { FileConnection } from "../../../generated/graphql"
 import { ComponentQuery } from "../../../typings"
+import { getPossibleCorrections } from "../../components/404LinkCorrection"
 import { SEO } from "../../components/SEO"
 
-// helper function to make matrix generation easier
-// credits to https://stackoverflow.com/a/13808461
-function makeMatrix(w: number, h: number, val: any = null) {
-  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: string, term2: string) {
-  /* 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 getPossibleCorrections(
-  basepath: string,
-  location: WindowLocation,
-  data: { allFile: FileConnection }
-) {
-  // the data prop has the graphql result
-  // we're abstracting it to `linkArray` 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 linkArray = 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(`/${basepath}/`, "")
-
-  // filter based on distance
-  // levenshtein distance of x means how 'off' it was
-  const displayArray = linkArray.filter(
-    value =>
-      levenshteinDistance(
-        search.toLowerCase(),
-        value.node!.relativePath!.toLowerCase()
-      ) < 8
-  )
-
-  // helpful message if no matches found
-  const found = displayArray.length === 0 ? "Oops, nothing similar found." : ""
-
-  return (
-    <Fragment>
-      <h3>Based off of "{search}" you may have meant:</h3>
-      <ul>
-        {displayArray.map((value, index) => {
-          return (
-            <li key={index}>
-              <Link to={`${basepath}/${value.node.relativePath}`}>
-                {value.node.relativePath}
-              </Link>
-            </li>
-          )
-        })}
-      </ul>
-      {found}
-    </Fragment>
-  )
-}
-
 export default ({ data }: ComponentQuery<{ allFile: FileConnection }>) => (
   <Fragment>
     <SEO title="404: Resource Not found" />