Add prev/next button script

This isn't currently needed anywhere else, so the list of filenames
is just hard-coded into the script.  Instead of making substitutions
in the source data, this just generates the full data.

docs/sgtutorial/prevnext.py

@@ -0,0 +1,132 @@
+#!/usr/bin/python3
+#
+# Sets the contents of the "prevnext" sections, which have the prev/next
+# buttons.  Run this in the directory where the HTML files live.
+#
+# (This is currently just for the sgtutorial files; it's not written to
+# be a general-purpose utility.)
+#
+
+import filecmp
+import os.path
+import re
+import sys
+
+# List of files to process, in order.
+gFileList = [
+    "about-disasm.html",
+    "using-sourcegen.html",
+    "moving-around.html",
+    "simple-edits.html",
+    "labels-symbols.html",
+    "editing-data.html",
+    "generating-code.html",
+    "digging-deeper.html",
+    "string-formatting.html",
+    "local-variables.html",
+    "inline-data.html",
+    "odds-ends.html",
+    "advanced-topics.html",
+    "address-tables.html",
+    "extension-scripts.html",
+    "visualizations.html",
+]
+
+class LocalError(Exception):
+    """Errors generated internally"""
+    pass
+
+# Regex pattern for prevnext section.
+findChunk = re.compile(
+    '^\s*<div id="prevnext">\s*$.'
+    '(.*?)'
+    '^\s*<\/div>',
+    re.DOTALL | re.MULTILINE)
+GROUP_ALL = 0
+GROUP_CHUNK = 1
+
+
+def editFile(index, outFileName):
+    """ Edit a file, replacing blocks with the contents of other files. """
+
+    inFileName = gFileList[index]
+    try:
+        with open(inFileName, "r") as inFile:
+            fileData = inFile.read()
+        outFile = open(outFileName, "x")
+    except IOError as err:
+        raise LocalError(err)
+
+    # Find first (and presumably only) matching chunk.
+    match = findChunk.search(fileData)
+    if not match:
+        print("== No prevnext section found")
+        return
+
+    replSpan = match.span(GROUP_CHUNK)
+
+    chunk = fileData[replSpan[0] : replSpan[1]]
+    print("== Matched {0}:{1}".format(replSpan[0], replSpan[1]))
+
+
+    # copy everything up to the chunk
+    outFile.write(fileData[ : replSpan[0]])
+    # insert the file, tweaking active ID if appropriate
+    generatePrevNext(index, outFile)
+    # copy the rest of the file, including the </div>
+    outFile.write(fileData[match.end(GROUP_CHUNK) : ])
+
+    print("== done")
+    outFile.close()
+
+    return
+
+
+def generatePrevNext(index, outFile):
+    """ Generate prev/next button HTML """
+
+    # <a href="#" class="btn-previous">&laquo; Previous</a>
+    # <a href="#" class="btn-next">Next &raquo;</a>
+    if index > 0:
+        outFile.write('    <a href="')
+        outFile.write(gFileList[index - 1])
+        outFile.write('" class="btn-previous">&laquo; Previous</a>\n')
+
+    if index + 1 < len(gFileList):
+        outFile.write('    <a href="')
+        outFile.write(gFileList[index + 1])
+        outFile.write('" class="btn-next">Next &raquo;</a>\n')
+
+    return
+
+
+def main():
+    """ main """
+
+    outFileName = None
+
+    try:
+        for index in range(len(gFileList)):
+            name = gFileList[index]
+            print("Processing #{0}: {1}".format(index, name))
+            outFileName = name + "_NEW"
+            editFile(index, outFileName)
+
+            # See if the file has changed.  If it hasn't, keep the original
+            # so the file dates don't change.
+            if filecmp.cmp(name, outFileName, False):
+                print("== No changes, removing new")
+                os.remove(outFileName)
+            else:
+                print("== Changed, keeping new")
+                os.rename(outFileName, name)
+    except LocalError as err:
+        print("ERROR: {0}".format(err))
+        if outFileName:
+            print("  check " + outFileName)
+        sys.exit(1)
+
+    sys.exit(0)
+
+
+main()  # does not return