'''
The idea of this module is to avoid imports of external HPI modules and code evaluation via ast module etc.

This potentially allows it to be:

- robust: can discover modules that can't be imported, generally makes it foolproof
- faster: importing is slow and with tens of modules can be noteiceable
- secure: can be executed in a sandbox & used during setup

It should be free of external modules, importlib, exec, etc. etc.
'''

REQUIRES = 'REQUIRES'
NOT_HPI_MODULE_VAR = '__NOT_HPI_MODULE__'

###

import ast
from typing import Optional, Sequence, NamedTuple, Iterable, cast, Any
from pathlib import Path
import re
import logging

'''
None means that requirements weren't defined (different from empty requirements)
'''
Requires = Optional[Sequence[str]]


class HPIModule(NamedTuple):
    name: str
    skip_reason: Optional[str]
    doc: Optional[str] = None
    file: Optional[Path] = None
    requires: Requires = None


def ignored(m: str) -> bool:
    excluded = [
        # legacy stuff left for backwards compatibility
        'core.*',
        'config.*',
    ]
    exs = '|'.join(excluded)
    return re.match(f'^my.({exs})$', m) is not None


def has_stats(src: Path) -> bool:
    # todo make sure consistent with get_stats?
    return _has_stats(src.read_text())


def _has_stats(code: str) -> bool:
    a: ast.Module = ast.parse(code)
    for x in a.body:
        try: # maybe assign
            [tg] = cast(Any, x).targets
            if tg.id == 'stats':
                return True
        except:
            pass
        try: # maybe def?
            name = cast(Any, x).name
            if name == 'stats':
                return True
        except:
            pass
    return False


def _is_not_module_src(src: Path) -> bool:
    a: ast.Module = ast.parse(src.read_text())
    return _is_not_module_ast(a)


def _is_not_module_ast(a: ast.Module) -> bool:
    return any(
        getattr(node, 'name', None) == NOT_HPI_MODULE_VAR  # direct definition
        or any(getattr(n, 'name', None) == NOT_HPI_MODULE_VAR for n in getattr(node, 'names', []))  # import from
        for node in a.body
    )


# todo should be defensive? not sure
def _extract_requirements(a: ast.Module) -> Requires:
    # find the assignment..
    for x in a.body:
        if not isinstance(x, ast.Assign):
            continue
        tg = x.targets
        if len(tg) != 1:
            continue
        t = tg[0]
        # could be Subscript.. so best to keep dynamic
        id_ = getattr(t, 'id', None)
        if id_ != REQUIRES:
            continue
        vals = x.value
        # could be List/Tuple/Set?
        elts = getattr(vals, 'elts', None)
        if elts is None:
            continue
        deps = []
        for c in elts:
            if isinstance(c, ast.Constant):
                deps.append(c.value)
            elif isinstance(c, ast.Str):
                deps.append(c.s)
            else:
                raise RuntimeError(f"Expecting string contants only in {REQUIRES} declaration")
        return tuple(deps)
    return None


# todo should probably be more defensive..
def all_modules() -> Iterable[HPIModule]:
    """
    Experimental version, which isn't importing the modules, making it more robust and safe.
    """
    my_root = Path(__file__).absolute().parent.parent
    for f in sorted(my_root.rglob('*.py')):
        if f.is_symlink():
            continue  # meh
        mp = f.relative_to(my_root.parent)
        if mp.name == '__init__.py':
            mp = mp.parent
        m = str(mp.with_suffix('')).replace('/', '.')
        if ignored(m):
            continue
        a: ast.Module = ast.parse(f.read_text())
        if _is_not_module_ast(a):
            continue
        doc = ast.get_docstring(a, clean=False)

        requires: Requires = None
        try:
            requires = _extract_requirements(a)
        except Exception as e:
            logging.exception(e)

        yield HPIModule(
            name=m,
            skip_reason=None,
            doc=doc,
            file=f.relative_to(my_root.parent),
            requires=requires,
        )


def module_by_name(name: str) -> HPIModule:
    for m in all_modules():
        if m.name == name:
            return m
    raise RuntimeError(f'No such module: {name}')


### tests


def test() -> None:
    # TODO this should be a 'sanity check' or something
    assert len(list(all_modules())) > 10  # kinda arbitrary


def test_demo() -> None:
    demo = module_by_name('my.demo')
    assert demo.doc is not None
    assert str(demo.file) == 'my/demo.py'
    assert demo.requires is None


def test_excluded() -> None:
    for m in all_modules():
        assert 'my.core.' not in m.name


def test_requires() -> None:
    photos = module_by_name('my.photos.main')
    r = photos.requires
    assert r is not None
    assert len(r) == 2  # fragile, but ok for now


def test_pure() -> None:
    """
    We want to keep this module clean of other HPI imports
    """
    src = Path(__file__).read_text()
    assert 'import '  + 'my' not in src
    assert 'from ' + 'my' not in src


def test_has_stats() -> None:
    assert not _has_stats('')
    assert not _has_stats('x = lambda : whatever')

    assert _has_stats('''
def stats():
    pass
''')

    assert _has_stats('''
stats = lambda: "something"
''')

    assert _has_stats('''
stats = other_function
    ''')