1 files changed, 198 insertions, 0 deletions
diff --git a/_static/describe_version.js b/_static/describe_version.js
new file mode 100644
index 000000000..19cd8d41e
--- /dev/null
+++ b/_static/describe_version.js
@@ -0,0 +1,198 @@
+/**
+ * Match a PEP 440 version string. The full regex given in PEP 440 is not used.
+ * This subset covers what we expect to encounter in our projects.
+ */
+const versionRe = new RegExp([
+  "^",
+  "(?:(?<epoch>[1-9][0-9]*)!)?",
+  "(?<version>(?:0|[1-9][0-9]*)(?:\\.(?:0|[1-9][0-9]*))*)",
+  "(?:(?<preL>a|b|rc)(?<preN>0|[1-9][0-9]*))?",
+  "(?:\\.post(?<postN>0|[1-9][0-9]*))?",
+  "(?:\\.dev(?<devN>0|[1-9][0-9]*))?",
+  "$",
+].join(""))
+
+/**
+ * Parse a PEP 440 version string into an object.
+ *
+ * @param {string} value
+ * @returns {Object} parsed version information
+ */
+function parseVersion(value) {
+  let {groups: {epoch, version, preL, preN, postN, devN}} = versionRe.exec(value)
+  return {
+    value: value,
+    parts:  [
+      parseInt(epoch) || 0, ...version.split(".").map(p => parseInt(p))
+    ],
+    isPre: Boolean(preL),
+    preL: preL || "",
+    preN: parseInt(preN) || 0,
+    isPost: Boolean(postN),
+    postN: parseInt(postN) || 0,
+    isDev: Boolean(devN),
+    devN: parseInt(devN) || 0,
+  }
+}
+
+/**
+ * Compare two version objects.
+ *
+ * @param {Object} a left side of comparison
+ * @param {Object} b right side of comparison
+ * @returns {number} -1 less than, 0 equal to, 1 greater than
+ */
+function compareVersions(a, b) {
+  for (let [i, an] of a.parts.entries()) {
+    let bn = i < b.parts.length ? b.parts[i] : 0
+
+    if (an < bn) {
+      return -1
+    } else if (an > bn) {
+      return 1
+    }
+  }
+
+  if (a.parts.length < b.parts.length) {
+    return -1
+  }
+
+  return 0
+}
+
+/**
+ * Get the list of released versions for the project from PyPI. Prerelease and
+ * development versions are discarded. The list is sorted in descending order,
+ * highest version first.
+ *
+ * This will be called on every page load. To avoid making excessive requests to
+ * PyPI, the result is cached for 1 day. PyPI also sends cache headers, so a
+ * subsequent request may still be more efficient, but it only specifies caching
+ * the full response for 5 minutes.
+ *
+ * @param {string} name The normalized PyPI project name to query.
+ * @returns {Promise<Object[]>} A sorted list of version objects.
+ */
+async function getReleasedVersions(name) {
+  // The response from PyPI is only cached for 5 minutes. Extend that to 1 day.
+  let cacheTime = localStorage.getItem("describeVersion-time")
+  let cacheResult = localStorage.getItem("describeVersion-result")
+
+  // if there is a cached value
+  if (cacheTime && cacheResult) {
+    // if the cache is younger than 1 day
+    if (Number(cacheTime) >= Date.now() - 86400000) {
+      // Use the cached value instead of making another request.
+      return JSON.parse(cacheResult)
+    }
+  }
+
+  let response = await fetch(
+    `https://pypi.org/simple/${name}/`,
+    {"headers": {"Accept": "application/vnd.pypi.simple.v1+json"}}
+  )
+  let data = await response.json()
+  let result = data["versions"]
+    .map(parseVersion)
+    .filter(v => !(v.isPre || v.isDev))
+    .sort(compareVersions)
+    .reverse()
+  localStorage.setItem("describeVersion-time", Date.now().toString())
+  localStorage.setItem("describeVersion-result", JSON.stringify(result))
+  return result
+}
+
+/**
+ * Get the highest released version of the project from PyPI, and compare the
+ * version being documented. Returns a list of two values, the comparison
+ * result and the highest version.
+ *
+ * @param name The normalized PyPI project name.
+ * @param value The version being documented.
+ * @returns {Promise<[number, Object|null]>}
+ */
+async function describeVersion(name, value) {
+  if (value.endsWith(".x")) {
+    value = value.slice(0, -2)
+  }
+
+  let currentVersion = parseVersion(value)
+  let releasedVersions = await getReleasedVersions(name)
+
+  if (releasedVersions.length === 0) {
+    return [1, null]
+  }
+
+  let highestVersion = releasedVersions[0]
+  let compared = compareVersions(currentVersion, highestVersion)
+
+  if (compared === 1) {
+    return [1, highestVersion]
+  }
+
+  // If the current version including trailing zeros is a prefix of the highest
+  // version, then these are the stable docs. For example, 2.0.x becomes 2.0,
+  // which is a prefix of 2.0.3. If we were just looking at the compare result,
+  // it would incorrectly be marked as an old version.
+  if (currentVersion.parts.every((n, i) => n === highestVersion.parts[i])) {
+    return [0, highestVersion]
+  }
+
+  return [-1, highestVersion]
+}
+
+/**
+ * Compare the version being documented to the highest released version, and
+ * display a warning banner if it is not the highest version.
+ *
+ * @param project The normalized PyPI project name.
+ * @param version The version being documented.
+ * @returns {Promise<void>}
+ */
+async function createBanner(project, version) {
+  let [compared, stable] = await describeVersion(project, version)
+
+  // No banner if this is the highest version or there are no other versions.
+  if (compared === 0 || stable === null) {
+    return
+  }
+
+  let banner = document.createElement("p")
+  banner.className = "version-warning"
+
+  if (compared === 1) {
+    banner.textContent = "This is the development version. The stable version is "
+  } else if (compared === -1) {
+    banner.textContent = "This is an old version. The current version is "
+  }
+
+  let canonical = document.querySelector('link[rel="canonical"]')
+
+  if (canonical !== null) {
+    // If a canonical URL is available, the version is a link to it.
+    let link = document.createElement("a")
+    link.href = canonical.href
+    link.textContent = stable.value
+    banner.append(link, ".")
+  } else {
+    // Otherwise, the version is text only.
+    banner.append(stable.value, ".")
+  }
+
+  document.getElementsByClassName("document")[0].prepend(banner)
+  // Set scroll-padding-top to prevent the banner from overlapping anchors.
+  // It's also set in CSS assuming the banner text is only 1 line.
+  let bannerStyle = window.getComputedStyle(banner)
+  let bannerMarginTop = parseFloat(bannerStyle["margin-top"])
+  let bannerMarginBottom = parseFloat(bannerStyle["margin-bottom"])
+  let height = banner.offsetHeight + bannerMarginTop + bannerMarginBottom
+  document.documentElement.style["scroll-padding-top"] = `${height}px`
+}
+
+(() => {
+  // currentScript is only available during init, not during callbacks.
+  let {project, version} = document.currentScript.dataset
+  document.addEventListener("DOMContentLoaded", async () => {
+    await createBanner(project, version)
+  })
+})()