# Flex / Bison comparison benchmark
#
# Runnable harness that builds the same arithmetic grammar with three
# tools and compares parse speed, RSS, and CPU on a fixed input
# corpus:
#
#   1. Lime  -- bench_arith_grammar.y (already generated by lime)
#   2. Bison -- bench_arith.y   (Bison-style version of the same grammar)
#   3. Flex  -- bench_arith.l   (lexer paired with the Bison parser)
#
# When `flex` or `bison` is not on $PATH, the build prints a friendly
# diagnostic and skips the comparison cleanly.  When both are present
# the bench_compare driver runs each parser on the same input,
# collects timing + getrusage data, and prints a CSV summary.

# Detect tool availability at configure time, including a runtime probe
# because some sandboxed environments accept `find_program` for a path
# but block invocation.  flex_prog / bison_prog are now defined in the
# parent bench/meson.build; re-probe their actual invocability here.
flex_bison_ok = false
if flex_prog.found() and bison_prog.found()
  fres = run_command(flex_prog, '--version', check : false)
  bres = run_command(bison_prog, '--version', check : false)
  if fres.returncode() == 0 and bres.returncode() == 0
    # macOS /usr/bin/bison ships GNU Bison 2.3 (GPLv2-licenced; Apple
    # never updated past it).  Our .y files use '%define api.prefix
    # {bison_}' which requires Bison >= 3.0.  Probe the version and
    # disable the bench cleanly on older bisons rather than failing
    # the build with a syntax error mid-bison.
    bison_ver_match = bres.stdout().split('\n')[0]
    if bison_ver_match.contains('3.') or bison_ver_match.contains('4.')
      flex_bison_ok = true
    else
      message('Flex / Bison bench: DISABLED (bison too old: ' + bison_ver_match + ')')
    endif
  endif
endif

if flex_bison_ok
  message('Flex / Bison comparison benchmark: ENABLED')

  # Bison parser
  bison_gen = custom_target('bench_arith_bison',
    input   : ['bench_arith.y'],
    output  : ['bench_arith.tab.c', 'bench_arith.tab.h'],
    command : [
      bison_prog,
      '-d',
      '-o', '@OUTPUT0@',
      '@INPUT@',
    ],
  )

  # Flex lexer
  flex_gen = custom_target('bench_arith_flex',
    input   : ['bench_arith.l'],
    output  : ['bench_arith.lex.c'],
    command : [
      flex_prog,
      '-o', '@OUTPUT@',
      '@INPUT@',
    ],
  )

  # Bison parser for JSON
  bison_json_gen = custom_target('bench_json_bison',
    input   : ['bench_json.y'],
    output  : ['bench_json.tab.c', 'bench_json.tab.h'],
    command : [
      bison_prog,
      '-d',
      '-o', '@OUTPUT0@',
      '@INPUT@',
    ],
  )

  # Flex lexer for JSON
  flex_json_gen = custom_target('bench_json_flex',
    input   : ['bench_json.l'],
    output  : ['bench_json.lex.c'],
    command : [
      flex_prog,
      '-o', '@OUTPUT@',
      '@INPUT@',
    ],
  )

  # Lime parser tables for the same grammar (generated by the
  # existing bench_arith_gen custom_target above; we just reuse its
  # outputs).

  bench_compare = executable('bench_flex_bison_compare',
    'bench_flex_bison_compare.c',
    bison_gen,
    flex_gen,
    bison_json_gen,
    flex_json_gen,
    bench_arith_gen,
    bench_json_gen,
    # Both *_snapshot.c files emit lime_snapshot_entry by default;
    # suppress one of them via the documented macro guard so the
    # static link succeeds.  ArithBuildSnapshot / JsonParserBuildSnapshot
    # remain available unconditionally.
    c_args : ['-DLIME_NO_SNAPSHOT_ENTRY_ALIAS=1'],
    dependencies : lime_parser_dep,
    include_directories : include_directories('../../src'),
    link_args : ['-lm'],
  )
else
  message('Flex / Bison comparison benchmark: SKIPPED ' +
          '(install flex and bison to enable)')
endif