#!/usr/bin/env python3
"""Insert implementation into an official CODESYS-generated external stub.
Fails closed on unexpected syntax; never invents ABI, signature or checksum.
"""
import argparse
from pathlib import Path
import re

def prepare(source, interface, sdk, destination):
    if source.stem != 'CmpAtomModbus' or interface.name != 'CmpAtomModbusItf.m4':
        raise ValueError('Generate component CmpAtomModbus, with its matching Itf.m4')
    c=source.read_text(); m4=interface.read_text()
    match=re.search(r'\batmbcall_cext\s*\(\s*(\w+)\s*\*\s*(\w+)\s*\)\s*\{',c,re.I)
    if not match: raise ValueError('Cannot find one-struct-pointer atMbCall_cext stub')
    typ,param=match.groups()
    structs=re.findall(r'typedef\s+struct(?:\s+\w+)?\s*\{([^{}]*)\}\s*(\w+)\s*;',m4,re.S)
    fields=next((body for body,name in structs if name==typ),None)
    if fields is None: raise ValueError('Cannot find the generated parameter struct in M4')
    names=re.findall(r'\b(\w+)\s*(?:\[[^\]]*\])?\s*;',fields)
    lookup={n.lower():n for n in names}
    args=['command','handle','ipaddress','port','unitid','functioncode','startaddress',
          'quantity','pdata','datacapacity','pstatus','statuscapacity','nowms',
          'connecttimeoutms','responsetimeoutms','retrydelayms']
    for n in args+['atmbcall_cext']:
        if n not in lookup: raise ValueError('Missing generated field '+n)
    # Match the stub body, preserving all surrounding generated source.
    start=match.end()-1; depth=1; end=start+1
    # Stub bodies must be empty or comments, not application code.
    while end<len(c) and depth:
        if c[end]=='{': depth+=1
        elif c[end]=='}': depth-=1
        end+=1
    if depth: raise ValueError('Unbalanced generated stub')
    old=c[start+1:end-1]
    old=re.sub(r'/\*.*?\*/|//[^\n]*','',old,flags=re.S).strip()
    if old: raise ValueError('Stub contains code; inspect manually instead of replacing it')
    body='{\n    '+param+'->'+lookup['atmbcall_cext']+' = ab_call(\n        '
    body+=',\n        '.join(param+'->'+lookup[n] for n in args)+');\n}'
    c=c[:start]+body+c[end:]
    # Use one component C translation unit because the supplied SDK derives
    # component identity from the top-level C filename list.
    c='#include "../src/atom_bridge.h"\n'+c
    c+='\n#include "../src/atom_mb.c"\n#include "../src/atom_bridge.c"\n'
    frame=(sdk/'src/CmpFrame.c').read_text()
    hook=re.search(r'(static\s+RTS_RESULT\s+CDECL\s+HookFunction\([^)]*\)\s*\{)',frame)
    if not hook: raise ValueError('Unexpected SDK HookFunction; inspect manually')
    frame=frame[:hook.end()]+'\n    if (ulHook == CH_EXIT) ab_shutdown();\n'+frame[hook.end():]
    frame='#include "../src/atom_bridge.h"\n'+frame
    destination.mkdir(parents=True,exist_ok=True)
    if any(destination.iterdir()): raise ValueError('Destination must be empty; preserve existing build work')
    (destination/'CmpAtomModbus.c').write_text(c)
    (destination/interface.name).write_text(m4)
    (destination/'CmpFrame.c').write_text(frame)
    (destination/'makefile').write_text('''# Generated from supplied ExtensionSDK; native build on ARM64 Pi.
SDKDIR ?= ../../ExtensionSDK
MAJORVER=0
MINORVER=2
CMPVERSION=0x00020000
# Local development ID; check no other component uses this ID.
CMPID=0x2001
DOS2UNIX=dos2unix
M4=m4
CC ?= gcc
# The SDK otherwise includes CmpFrame in its component identity wildcard.
override CSRC := CmpAtomModbus.c
include $(SDKDIR)/makefile
''')

if __name__=='__main__':
    p=argparse.ArgumentParser(description=__doc__)
    p.add_argument('source',type=Path); p.add_argument('interface',type=Path)
    p.add_argument('--sdk',required=True,type=Path)
    p.add_argument('--out',type=Path,default=Path('component'))
    a=p.parse_args()
    prepare(a.source,a.interface,a.sdk,a.out)
    print('Prepared component; compile and validate the generated interface on target.')