[HTML5] Add PWA support to the editor page.

This allows to install it as an app, and provide offline support (after
the first run).
Practically, this boils down to adding a JSON file as a manifest, an
offline page to be displayed when the cached files are not avaialble,
and a JS file to cache resources and return them.

The reason for the "first run requirements" is that some browsers, will
emit an "install" by just visiting the page (to see if the JS code is
compatibile), and we do not want to force casual visitors to just
download the 10 MiB+ compressed editor WebAssembly file without pressing
the start button.

Special thanks to Hugo Locurcio (Calinou) for the initial work.

3 files changed, 67 insertions, 42 deletions

diff --git a/platform/javascript/SCsub b/platform/javascript/SCsub
index 72e999b38d..a760e36982 100644
--- a/platform/javascript/SCsub
+++ b/platform/javascript/SCsub
@@ -86,40 +86,6 @@ wrap_list = [
 ]
 js_wrapped = env.Textfile("#bin/godot", [env.File(f) for f in wrap_list], TEXTFILESUFFIX="${PROGSUFFIX}.wrapped.js")
 
-zip_dir = env.Dir("#bin/.javascript_zip")
-binary_name = "godot.tools" if env["tools"] else "godot"
-out_files = [
-    zip_dir.File(binary_name + ".js"),
-    zip_dir.File(binary_name + ".wasm"),
-    zip_dir.File(binary_name + ".html"),
-    zip_dir.File(binary_name + ".audio.worklet.js"),
-]
-html_file = "#misc/dist/html/full-size.html"
-if env["tools"]:
-    subst_dict = {"@GODOT_VERSION@": env.GetBuildVersion()}
-    html_file = env.Substfile(
-        target="#bin/godot${PROGSUFFIX}.html", source="#misc/dist/html/editor.html", SUBST_DICT=subst_dict
-    )
-
-in_files = [js_wrapped, build[1], html_file, "#platform/javascript/js/libs/audio.worklet.js"]
-if env["gdnative_enabled"]:
-    in_files.append(build[2])  # Runtime
-    out_files.append(zip_dir.File(binary_name + ".side.wasm"))
-elif env["threads_enabled"]:
-    in_files.append(build[2])  # Worker
-    out_files.append(zip_dir.File(binary_name + ".worker.js"))
-
-if env["tools"]:
-    in_files.append("#misc/dist/html/logo.svg")
-    out_files.append(zip_dir.File("logo.svg"))
-    in_files.append("#icon.png")
-    out_files.append(zip_dir.File("favicon.png"))
-
-zip_files = env.InstallAs(out_files, in_files)
-env.Zip(
-    "#bin/godot",
-    zip_files,
-    ZIPROOT=zip_dir,
-    ZIPSUFFIX="${PROGSUFFIX}${ZIPSUFFIX}",
-    ZIPCOMSTR="Archiving $SOURCES as $TARGET",
-)
+# Extra will be the thread worker, or the GDNative side, or None
+extra = build[2] if len(build) > 2 else None
+env.CreateTemplateZip(js_wrapped, build[1], extra)
diff --git a/platform/javascript/detect.py b/platform/javascript/detect.py
index 4297088c09..e80ef374ec 100644
--- a/platform/javascript/detect.py
+++ b/platform/javascript/detect.py
@@ -7,7 +7,7 @@ from emscripten_helpers import (
     add_js_libraries,
     add_js_pre,
     add_js_externs,
-    get_build_version,
+    create_template_zip,
 )
 from methods import get_compiler_version
 from SCons.Util import WhereIs
@@ -147,12 +147,12 @@ def configure(env):
     env.AddMethod(add_js_pre, "AddJSPre")
     env.AddMethod(add_js_externs, "AddJSExterns")
 
-    # Add method for getting build version string.
-    env.AddMethod(get_build_version, "GetBuildVersion")
-
     # Add method that joins/compiles our Engine files.
     env.AddMethod(create_engine_file, "CreateEngineFile")
 
+    # Add method for creating the final zip file
+    env.AddMethod(create_template_zip, "CreateTemplateZip")
+
     # Closure compiler extern and support for ecmascript specs (const, let, etc).
     env["ENV"]["EMCC_CLOSURE_ARGS"] = "--language_in ECMASCRIPT6"
 
diff --git a/platform/javascript/emscripten_helpers.py b/platform/javascript/emscripten_helpers.py
index d08555916b..04fbba8a41 100644
--- a/platform/javascript/emscripten_helpers.py
+++ b/platform/javascript/emscripten_helpers.py
@@ -15,7 +15,7 @@ def run_closure_compiler(target, source, env, for_signature):
     return " ".join(cmd)
 
 
-def get_build_version(env):
+def get_build_version():
     import version
 
     name = "custom_build"
@@ -30,6 +30,65 @@ def create_engine_file(env, target, source, externs):
     return env.Textfile(target, [env.File(s) for s in source])
 
 
+def create_template_zip(env, js, wasm, extra):
+    binary_name = "godot.tools" if env["tools"] else "godot"
+    zip_dir = env.Dir("#bin/.javascript_zip")
+    in_files = [
+        js,
+        wasm,
+        "#platform/javascript/js/libs/audio.worklet.js",
+    ]
+    out_files = [
+        zip_dir.File(binary_name + ".js"),
+        zip_dir.File(binary_name + ".wasm"),
+        zip_dir.File(binary_name + ".audio.worklet.js"),
+    ]
+    # GDNative/Threads specific
+    if env["gdnative_enabled"]:
+        in_files.append(extra)  # Runtime
+        out_files.append(zip_dir.File(binary_name + ".side.wasm"))
+    elif env["threads_enabled"]:
+        in_files.append(extra)  # Worker
+        out_files.append(zip_dir.File(binary_name + ".worker.js"))
+
+    service_worker = "#misc/dist/html/service-worker.js"
+    if env["tools"]:
+        # HTML
+        html = "#misc/dist/html/editor.html"
+        subst_dict = {"@GODOT_VERSION@": get_build_version(), "@GODOT_NAME@": "GodotEngine"}
+        html = env.Substfile(target="#bin/godot${PROGSUFFIX}.html", source=html, SUBST_DICT=subst_dict)
+        in_files.append(html)
+        out_files.append(zip_dir.File(binary_name + ".html"))
+        # And logo/favicon
+        in_files.append("#misc/dist/html/logo.svg")
+        out_files.append(zip_dir.File("logo.svg"))
+        in_files.append("#icon.png")
+        out_files.append(zip_dir.File("favicon.png"))
+        # PWA
+        service_worker = env.Substfile(
+            target="#bin/godot${PROGSUFFIX}.service.worker.js", source=service_worker, SUBST_DICT=subst_dict
+        )
+        in_files.append(service_worker)
+        out_files.append(zip_dir.File("service.worker.js"))
+        in_files.append("#misc/dist/html/manifest.json")
+        out_files.append(zip_dir.File("manifest.json"))
+        in_files.append("#misc/dist/html/offline.html")
+        out_files.append(zip_dir.File("offline.html"))
+    else:
+        # HTML
+        in_files.append("#misc/dist/html/full-size.html")
+        out_files.append(zip_dir.File(binary_name + ".html"))
+
+    zip_files = env.InstallAs(out_files, in_files)
+    env.Zip(
+        "#bin/godot",
+        zip_files,
+        ZIPROOT=zip_dir,
+        ZIPSUFFIX="${PROGSUFFIX}${ZIPSUFFIX}",
+        ZIPCOMSTR="Archiving $SOURCES as $TARGET",
+    )
+
+
 def add_js_libraries(env, libraries):
     env.Append(JS_LIBS=env.File(libraries))