1 files changed, 153 insertions, 0 deletions
diff --git a/src/pallets_sphinx_themes/versions.py b/src/pallets_sphinx_themes/versions.py
new file mode 100644
index 0000000..62c77e4
--- /dev/null
+++ b/src/pallets_sphinx_themes/versions.py
@@ -0,0 +1,153 @@
+import json
+import os
+from collections import namedtuple
+
+from jinja2 import pass_context
+from packaging import version as pv
+
+from .theme_check import only_pallets_theme
+
+
+@only_pallets_theme()
+def load_versions(app):
+    if os.environ.get("READTHEDOCS"):
+        versions = readthedocs_versions(app)
+    else:
+        versions = local_versions(app)
+
+    context = app.config.html_context
+    context["versions"] = versions
+    context["current_version"] = next((v for v in versions if v.current), None)
+    context["latest_version"] = next((v for v in versions if v.latest), None)
+
+
+def local_versions(app):
+    config_versions = app.config.html_context.get("versions")
+
+    if isinstance(config_versions, str):
+        if os.path.isfile(config_versions):
+            with open(config_versions, encoding="utf8") as f:
+                config_versions = json.load(f)
+        else:
+            config_versions = json.loads(config_versions)
+
+    if not config_versions:
+        return []
+
+    versions = []
+
+    for version in config_versions:
+        if isinstance(version, dict):
+            version = DocVersion(**version)
+
+        versions.append(version)
+
+    slug = app.config.version
+    dev = "dev" in app.config.release
+    seen_latest = False
+
+    for i, version in enumerate(versions):
+        if version.slug == "dev":
+            versions[i] = version._replace(dev=True, current=dev)
+
+        if version.slug == slug:
+            versions[i] = version._replace(current=True)
+
+        if not seen_latest and version.version is not None:
+            seen_latest = True
+            versions[i] = version._replace(latest=True)
+
+    return versions
+
+
+def readthedocs_versions(app):
+    config_versions = app.config.html_context["versions"]
+    current_slug = app.config.html_context["current_version"]
+    number_versions = []
+    name_versions = []
+
+    for slug, _ in config_versions:
+        dev = slug in {"main", "master", "default", "latest"}
+        version = _parse_version(slug)
+
+        if version is not None:
+            name = slug
+            append_to = number_versions
+        else:
+            name = "Development" if dev else slug.title()
+            append_to = name_versions
+
+        append_to.append(
+            DocVersion(name=name, slug=slug, dev=dev, current=slug == current_slug)
+        )
+
+    # put the newest numbered version first
+    number_versions.sort(key=lambda x: x.version, reverse=True)
+    # put non-dev named versions first
+    name_versions.sort(key=lambda x: x.dev, reverse=True)
+    versions = number_versions + name_versions
+
+    # if there are non-dev versions, mark the newest one as the latest
+    if versions and not versions[0].dev:
+        versions[0] = versions[0]._replace(latest=True)
+
+    return versions
+
+
+def _parse_version(value: str, placeholder: str = "x"):
+    if value.endswith(f".{placeholder}"):
+        value = value[: -(len(placeholder) + 1)]
+
+    try:
+        return pv.Version(value)
+    except pv.InvalidVersion:
+        return None
+
+
+class DocVersion(
+    namedtuple("DocVersion", ("name", "slug", "version", "latest", "dev", "current"))
+):
+    __slots__ = ()
+
+    def __new__(cls, name, slug=None, latest=False, dev=False, current=False):
+        slug = slug or name
+        version = _parse_version(slug)
+
+        if version is not None:
+            name = "Version " + name
+
+        return super().__new__(cls, name, slug, version, latest, dev, current)
+
+    @pass_context
+    def href(self, context):
+        pathto = context["pathto"]
+        master_doc = context["master_doc"]
+        pagename = context["pagename"]
+
+        builder = pathto.__closure__[0].cell_contents
+        master = pathto(master_doc).rstrip("#/") or "."
+        path = builder.get_target_uri(pagename)
+        return "/".join((master, "..", self.slug, path))
+
+    @pass_context
+    def banner(self, context):
+        if self.latest:
+            return
+
+        latest = context["latest_version"]
+
+        # Don't show a banner if the latest version couldn't be determined, or if this
+        # is the "stable" version.
+        if latest is None or self.name == "stable":
+            return
+
+        if self.dev:
+            return (
+                "This is the development version. The latest stable"
+                ' version is <a href="{href}">{latest}</a>.'
+            ).format(latest=latest.name, href=latest.href(context))
+
+        return (
+            "This is an old version. The latest stable version is"
+            ' <a href="{href}">{latest}</a>.'
+        ).format(latest=latest.name, href=latest.href(context))