" Debugger plugin using gdb.
"
" WORK IN PROGRESS - much doesn't work yet
"
" Open two visible terminal windows:
" 1. run a pty, as with ":term NONE"
" 2. run gdb, passing the pty
" The current window is used to view source code and follows gdb.
"
" A third terminal window is hidden, it is used for communication with gdb.
"
" The communication with gdb uses GDB/MI.  See:
" https://sourceware.org/gdb/current/onlinedocs/gdb/GDB_002fMI.html
"
" Author: Bram Moolenaar
" Copyright: Vim license applies, see ":help license"

" The command that starts debugging, e.g. ":Termdebug vim".
" To end type "quit" in the gdb window.
command -nargs=* -complete=file Termdebug call s:StartDebug(<q-args>)

" Name of the gdb command, defaults to "gdb".
if !exists('termdebugger')
  let termdebugger = 'gdb'
endif

" Sign used to highlight the line where the program has stopped.
" There can be only one.
sign define debugPC linehl=debugPC
let s:pc_id = 12
let s:break_id = 13

" Sign used to indicate a breakpoint.
" Can be used multiple times.
sign define debugBreakpoint text=>> texthl=debugBreakpoint

if &background == 'light'
  hi default debugPC term=reverse ctermbg=lightblue guibg=lightblue
else
  hi default debugPC term=reverse ctermbg=darkblue guibg=darkblue
endif
hi default debugBreakpoint term=reverse ctermbg=red guibg=red

func s:StartDebug(cmd)
  let s:startwin = win_getid(winnr())
  let s:startsigncolumn = &signcolumn

  " Open a terminal window without a job, to run the debugged program
  let s:ptybuf = term_start('NONE', {
	\ 'term_name': 'gdb program',
	\ })
  if s:ptybuf == 0
    echoerr 'Failed to open the program terminal window'
    return
  endif
  let pty = job_info(term_getjob(s:ptybuf))['tty_out']

  " Create a hidden terminal window to communicate with gdb
  let s:commbuf = term_start('NONE', {
	\ 'term_name': 'gdb communication',
	\ 'out_cb': function('s:CommOutput'),
	\ 'hidden': 1,
	\ })
  if s:commbuf == 0
    echoerr 'Failed to open the communication terminal window'
    exe 'bwipe! ' . s:ptybuf
    return
  endif
  let commpty = job_info(term_getjob(s:commbuf))['tty_out']

  " Open a terminal window to run the debugger.
  let cmd = [g:termdebugger, '-tty', pty, a:cmd]
  echomsg 'executing "' . join(cmd) . '"'
  let gdbbuf = term_start(cmd, {
	\ 'exit_cb': function('s:EndDebug'),
	\ 'term_finish': 'close',
	\ })
  if gdbbuf == 0
    echoerr 'Failed to open the gdb terminal window'
    exe 'bwipe! ' . s:ptybuf
    exe 'bwipe! ' . s:commbuf
    return
  endif

  " Connect gdb to the communication pty, using the GDB/MI interface
  call term_sendkeys(gdbbuf, 'new-ui mi ' . commpty . "\r")

  " Install debugger commands.
  call s:InstallCommands()

  let s:breakpoints = {}
endfunc

func s:EndDebug(job, status)
  exe 'bwipe! ' . s:ptybuf
  exe 'bwipe! ' . s:commbuf

  let curwinid = win_getid(winnr())

  call win_gotoid(s:startwin)
  let &signcolumn = s:startsigncolumn
  call s:DeleteCommands()

  call win_gotoid(curwinid)
endfunc

" Handle a message received from gdb on the GDB/MI interface.
func s:CommOutput(chan, msg)
  let msgs = split(a:msg, "\r")

  for msg in msgs
    " remove prefixed NL
    if msg[0] == "\n"
      let msg = msg[1:]
    endif
    if msg != ''
      if msg =~ '^\*\(stopped\|running\)'
	call s:HandleCursor(msg)
      elseif msg =~ '^\^done,bkpt='
	call s:HandleNewBreakpoint(msg)
      elseif msg =~ '^=breakpoint-deleted,'
	call s:HandleBreakpointDelete(msg)
      endif
    endif
  endfor
endfunc

" Install commands in the current window to control the debugger.
func s:InstallCommands()
  command Break call s:SetBreakpoint()
  command Delete call s:DeleteBreakpoint()
  command Step call s:SendCommand('-exec-step')
  command NNext call s:SendCommand('-exec-next')
  command Finish call s:SendCommand('-exec-finish')
  command Continue call s:SendCommand('-exec-continue')
endfunc

" Delete installed debugger commands in the current window.
func s:DeleteCommands()
  delcommand Break
  delcommand Delete
  delcommand Step
  delcommand NNext
  delcommand Finish
  delcommand Continue
endfunc

" :Break - Set a breakpoint at the cursor position.
func s:SetBreakpoint()
  call term_sendkeys(s:commbuf, '-break-insert --source '
	\ . fnameescape(expand('%:p')) . ' --line ' . line('.') . "\r")
endfunc

" :Delete - Delete a breakpoint at the cursor position.
func s:DeleteBreakpoint()
  let fname = fnameescape(expand('%:p'))
  let lnum = line('.')
  for [key, val] in items(s:breakpoints)
    if val['fname'] == fname && val['lnum'] == lnum
      call term_sendkeys(s:commbuf, '-break-delete ' . key . "\r")
      " Assume this always wors, the reply is simply "^done".
      exe 'sign unplace ' . (s:break_id + key)
      unlet s:breakpoints[key]
      break
    endif
  endfor
endfunc

" :Next, :Continue, etc - send a command to gdb
func s:SendCommand(cmd)
  call term_sendkeys(s:commbuf, a:cmd . "\r")
endfunc

" Handle stopping and running message from gdb.
" Will update the sign that shows the current position.
func s:HandleCursor(msg)
  let wid = win_getid(winnr())

  if win_gotoid(s:startwin)
    if a:msg =~ '^\*stopped'
      let fname = substitute(a:msg, '.*fullname="\([^"]*\)".*', '\1', '')
      let lnum = substitute(a:msg, '.*line="\([^"]*\)".*', '\1', '')
      if lnum =~ '^[0-9]*$'
	if expand('%:h') != fname
	  if &modified
	    " TODO: find existing window
	    exe 'split ' . fnameescape(fname)
	    let s:startwin = win_getid(winnr())
	  else
	    exe 'edit ' . fnameescape(fname)
	  endif
	endif
	exe lnum
	exe 'sign place ' . s:pc_id . ' line=' . lnum . ' name=debugPC file=' . fnameescape(fname)
	setlocal signcolumn=yes
      endif
    else
      exe 'sign unplace ' . s:pc_id
    endif

    call win_gotoid(wid)
  endif
endfunc

" Handle setting a breakpoint
" Will update the sign that shows the breakpoint
func s:HandleNewBreakpoint(msg)
  let nr = substitute(a:msg, '.*number="\([0-9]\)*\".*', '\1', '') + 0
  if nr == 0
    return
  endif

  if has_key(s:breakpoints, nr)
    let entry = s:breakpoints[nr]
  else
    let entry = {}
    let s:breakpoints[nr] = entry
  endif

  let fname = substitute(a:msg, '.*fullname="\([^"]*\)".*', '\1', '')
  let lnum = substitute(a:msg, '.*line="\([^"]*\)".*', '\1', '')

  exe 'sign place ' . (s:break_id + nr) . ' line=' . lnum . ' name=debugBreakpoint file=' . fnameescape(fname)

  let entry['fname'] = fname
  let entry['lnum'] = lnum
endfunc

" Handle deleting a breakpoint
" Will remove the sign that shows the breakpoint
func s:HandleBreakpointDelete(msg)
  let nr = substitute(a:msg, '.*id="\([0-9]*\)\".*', '\1', '') + 0
  if nr == 0
    return
  endif
  exe 'sign unplace ' . (s:break_id + nr)
  unlet s:breakpoints[nr]
endfunc