"""Version checking and self-update commands for specify_cli.

Pure helpers for comparing PEP 440 versions and fetching the latest GitHub
release tag.  The ``self_app`` Typer sub-command group is co-located here so
all version-related logic lives in one place.

Dependencies: stdlib + packaging + ._console only (no other internal imports
at module level, keeping this layer thin and circular-import-safe).
"""
from __future__ import annotations

import json
import urllib.error

import typer
from packaging.version import InvalidVersion, Version

from ._console import console

GITHUB_API_LATEST = "https://api.github.com/repos/github/spec-kit/releases/latest"


def _get_installed_version() -> str:
    """Return the installed specify-cli distribution version or 'unknown'.

    Uses importlib.metadata so the value reflects what was actually installed
    by pip/uv/pipx — not a value read from pyproject.toml. This is
    intentional for `specify self check`, which should reason about the
    installed distribution rather than a source-tree fallback. Callers must
    treat the sentinel string 'unknown' as an indeterminate value (see FR-020).
    """
    import importlib.metadata

    metadata_errors = [importlib.metadata.PackageNotFoundError]
    invalid_metadata_error = getattr(importlib.metadata, "InvalidMetadataError", None)
    if invalid_metadata_error is not None:
        metadata_errors.append(invalid_metadata_error)

    try:
        return importlib.metadata.version("specify-cli")
    except tuple(metadata_errors):
        return "unknown"


def _normalize_tag(tag: str) -> str:
    """Strip exactly one leading 'v' from a release tag.

    Returns the rest of the string unchanged. This handles the common
    'vX.Y.Z' tag convention in this repo; it MUST NOT strip more
    aggressively (e.g., two leading 'v's keeps one).
    """
    return tag[1:] if tag.startswith("v") else tag


def _is_newer(latest: str, current: str) -> bool:
    """Return True iff `latest` is strictly greater than `current` under PEP 440.

    Returns False whenever either side is 'unknown' or fails to parse; this
    keeps the comparison indeterminate (rather than crashing or falsely
    recommending a downgrade) on edge inputs.
    """
    if latest == "unknown" or current == "unknown":
        return False
    try:
        return Version(latest) > Version(current)
    except InvalidVersion:
        return False


def _fetch_latest_release_tag() -> tuple[str | None, str | None]:
    """Return (tag, failure_category). Exactly one outbound call, 5 s timeout.

    On success: (tag_name, None).
    On a documented network/HTTP failure (added in T029/T030): (None, category).
    On anything else — including a malformed response body — the exception
    propagates; there is no catch-all (research D-006).
    """
    from .authentication.http import open_url

    try:
        with open_url(
            GITHUB_API_LATEST,
            timeout=5,
            extra_headers={"Accept": "application/vnd.github+json"},
        ) as resp:
            payload = json.loads(resp.read().decode("utf-8"))
            tag = payload.get("tag_name")
            if not isinstance(tag, str) or not tag:
                raise ValueError("GitHub API response missing valid tag_name")
            return tag, None
    except urllib.error.HTTPError as e:
        # Order matters: HTTPError is a subclass of URLError.
        if e.code == 403:
            return None, (
                "rate limited (configure ~/.specify/auth.json with a GitHub token)"
            )
        return None, f"HTTP {e.code}"
    except (urllib.error.URLError, OSError):
        return None, "offline or timeout"


# ===== Self Commands =====

self_app = typer.Typer(
    name="self",
    help="Manage the specify CLI itself (read-only check and reserved upgrade command).",
    add_completion=False,
)


@self_app.command("check")
def self_check() -> None:
    """Check whether a newer specify-cli release is available. Read-only.

    This command only checks for updates; it does not modify your installation.
    The reserved (and currently non-destructive) `specify self upgrade` command
    is the name that a future release will use for actual self-upgrade — its
    behavior is not implemented in this release and is intentionally out of
    scope here. See `specify self upgrade --help` for its current status.
    """
    installed = _get_installed_version()
    tag, failure_reason = _fetch_latest_release_tag()

    if tag is None:
        # Graceful-failure path (FR-008). `failure_reason` is one of the
        # enumerated strings produced by _fetch_latest_release_tag() — it
        # never contains a URL, headers, response body, or traceback.
        assert failure_reason is not None
        console.print(f"Installed: {installed}")
        console.print(f"[yellow]Could not check latest release:[/yellow] {failure_reason}")
        return

    latest_normalized = _normalize_tag(tag)

    if installed == "unknown":
        # FR-020: surface the latest release and the recovery action even
        # when the local distribution metadata is unavailable.
        console.print("Current version could not be determined.")
        console.print(f"Latest release: {latest_normalized}")
        console.print("\nTo reinstall:")
        console.print("  uv tool install specify-cli --force \\")
        console.print(f"    --from git+https://github.com/github/spec-kit.git@{tag}")
        return

    if _is_newer(latest_normalized, installed):
        console.print(f"[green]Update available:[/green] {installed} → {latest_normalized}")
        console.print("\nTo upgrade:")
        console.print("  uv tool install specify-cli --force \\")
        console.print(f"    --from git+https://github.com/github/spec-kit.git@{tag}")
        return

    # Installed is parseable AND is >= latest → "up to date" (FR-006).
    # Also reached when the tag is unparseable (InvalidVersion) → _is_newer
    # returns False, and the up-to-date branch is the safer default per
    # FR-004 / test T016.
    console.print(f"[green]Up to date:[/green] {installed}")


@self_app.command("upgrade")
def self_upgrade() -> None:
    """Reserved command surface for self-upgrade; not implemented in this release.

    This command is a documented non-destructive stub in this release: it
    performs no outbound network request, no install-method detection, and
    invokes no installer. It prints a three-line guidance message and exits 0.
    Actual self-upgrade is planned as follow-up work.

    Use `specify self check` today to see whether a newer release is available
    and to get a copy-pasteable reinstall command.
    """
    console.print("specify self upgrade is not implemented yet.")
    console.print("Run 'specify self check' to see whether a newer release is available.")
    console.print("Actual self-upgrade is planned as follow-up work.")