"""`pyproject.toml` and `requirements*.txt` -> PyPI dependencies.

PEP 508 markers, extras and environment conditions all appear in the wild here,
so the name is taken as the leading identifier and everything after the first
comparator is the constraint. Anything that is not a single `==` pin is
reported unpinned rather than guessed at.
"""

from __future__ import annotations

import re
from pathlib import Path

import tomllib

from dep_freshness._tables import GITTAG, PYPI, TOOLCHAIN
from dep_freshness.models import Dep
from dep_freshness.parsers._lines import index
from dep_freshness.registries import gittag
from dep_freshness.versions import exact_pin

_REQ = re.compile(
    r"^\s*(?P<name>[A-Za-z0-9][A-Za-z0-9._-]*)"
    r"(?:\[(?P<extras>[^\]]*)\])?"
    r"\s*(?P<constraint>.*)$"
)
_SKIP_PREFIXES = ("-", "#", "git+", "http://", "https://", ".", "/")

# PEP 508 direct reference: `crdt-sync @ git+https://.../utils@crdt-sync-v0.9.0`
# The shared Python libraries are consumed this way, so "latest" for them is a
# git tag, exactly as for the Dart libraries. Without this the requirement
# parses as an unpinned PyPI package that does not exist on PyPI, the answer
# comes back undeterminable, and four minor versions of drift stay invisible --
# which is how wake-alarm sat on gatelock-v0.4.1 against v0.7.1 and
# crdt-sync-v0.5.1 against v0.9.0 with a green gate.
_DIRECT = re.compile(
    r"^\s*(?P<name>[A-Za-z0-9][A-Za-z0-9._-]*)"
    r"(?:\[[^\]]*\])?"
    r"\s*@\s*git\+(?P<url>\S+?)@(?P<ref>[A-Za-z0-9_.-]+-v[0-9][^\s#]*)"
)


def _direct_reference(requirement: str, path: Path, line: int) -> Dep | None:
    """A `<name> @ git+<url>@<pkg>-vX.Y.Z` requirement as a git-tag dep."""
    match = _DIRECT.match(requirement.split(";", 1)[0].strip())
    if not match:
        return None
    ref = match.group("ref")
    package, _, version = ref.rpartition("-v")
    name = gittag.qualified_name(match.group("url"), package or match.group("name"))
    return Dep(
        ecosystem=GITTAG, name=name, constraint=ref,
        path=path, line=line or _ref_line(path, ref), pinned=version or None,
    )


def _ref_line(path: Path, ref: str) -> int:
    """Locate `ref` textually. A TOML dependency list has no `key =` to index.

    `"gatelock @ git+...@gatelock-v0.7.1"` is a bare string inside an array,
    so the shared key indexer finds nothing and the finding would report
    line 0 -- a fix the reader has to go looking for.
    """
    try:
        text = path.read_text(encoding="utf-8", errors="replace")
    except OSError:
        return 0
    for number, line in enumerate(text.splitlines(), start=1):
        if ref in line:
            return number
    return 0


def _split(requirement: str) -> tuple[str, str] | None:
    """`('ruff', '==0.16.5')` from a PEP 508 requirement string."""
    text = requirement.split("#", 1)[0].split(";", 1)[0].strip()
    if not text or text.startswith(_SKIP_PREFIXES):
        return None
    match = _REQ.match(text)
    if not match:
        return None
    return (match.group("name"), match.group("constraint").strip())


def _dep(name: str, constraint: str, path: Path, line: int) -> Dep:
    pinned = exact_pin(constraint) if constraint.startswith("==") else None
    return Dep(
        ecosystem=PYPI, name=name, constraint=constraint or "(unconstrained)",
        path=path, line=line, pinned=pinned,
    )


def parse_requirements(path: Path) -> list[Dep]:
    try:
        text = path.read_text(encoding="utf-8")
    except OSError:
        return []
    deps: list[Dep] = []
    for number, raw in enumerate(text.splitlines(), start=1):
        direct = _direct_reference(raw, path, number)
        if direct is not None:
            deps.append(direct)
            continue
        split = _split(raw)
        if split:
            deps.append(_dep(split[0], split[1], path, number))
    return deps


def parse_pyproject(path: Path) -> list[Dep]:
    try:
        data = tomllib.loads(path.read_text(encoding="utf-8"))
    except (OSError, tomllib.TOMLDecodeError):
        return []
    lines = index(path)
    project = data.get("project") or {}
    deps: list[Dep] = []

    requires = project.get("requires-python")
    if isinstance(requires, str):
        deps.append(Dep(
            ecosystem=TOOLCHAIN, name="python", constraint=requires, path=path,
            line=lines.get("requires-python", 0), caret_ok=True,
        ))

    groups: list[list] = [list(project.get("dependencies") or [])]
    for extra in (project.get("optional-dependencies") or {}).values():
        groups.append(list(extra))
    for group in (data.get("dependency-groups") or {}).values():
        groups.append([g for g in group if isinstance(g, str)])

    for group in groups:
        for requirement in group:
            text = str(requirement)
            name = _REQ.match(text.strip())
            line = lines.get(name.group("name"), 0) if name else 0
            direct = _direct_reference(text, path, line)
            if direct is not None:
                deps.append(direct)
                continue
            split = _split(text)
            if split:
                deps.append(_dep(split[0], split[1], path, lines.get(split[0], 0)))
    return deps


def parse_python_version(path: Path) -> list[Dep]:
    """`.python-version` — compared against the installed interpreter."""
    try:
        value = path.read_text(encoding="utf-8").strip().splitlines()[0].strip()
    except (OSError, IndexError):
        return []
    return [Dep(
        ecosystem=TOOLCHAIN, name="python", constraint=value, path=path,
        line=1, pinned=exact_pin(value),
    )]