"""Pure logic for the egress-proxy mitmproxy addon (PRD 0017).

Split out of `egress_proxy_addon.py` so the host's unit tests can
exercise the parse + decision functions without depending on the
`mitmproxy` package. The companion module wraps these with the
`mitmproxy.http.HTTPFlow` API and is loaded inside the sidecar
container.

Stdlib only: this file ships into the egress-proxy image, where the
container's Python is whatever mitmproxy itself runs on.
"""

from __future__ import annotations

import json
import typing
from dataclasses import dataclass


@dataclass(frozen=True)
class Route:
    """One row of the egress-proxy route table.

    `host` is the request's `Host` header (or SNI hostname) to match
    against. `path_allowlist` is an optional tuple of absolute path
    prefixes the request path must start with; empty tuple means no
    path constraint. `auth_scheme` and `token_env` together form the
    credential-injection pair (both set or both empty); a non-empty
    pair tells the addon to overwrite the inbound Authorization with
    `<auth_scheme> <value-of-environ[token_env]>`.
    """

    host: str
    path_allowlist: tuple[str, ...] = ()
    auth_scheme: str = ""
    token_env: str = ""


@dataclass(frozen=True)
class Decision:
    """The result of `decide()`. Either forward (with optional
    `inject_authorization` header) or block (with a `reason` to surface
    to the agent)."""

    action: str  # "forward" or "block"
    reason: str = ""
    inject_authorization: str | None = None


def parse_routes(payload: object) -> tuple[Route, ...]:
    """Parse the routes-file payload (already JSON-decoded) into a
    tuple of `Route`s. Raises `ValueError` on any malformed entry —
    the caller decides whether to keep the old table or refuse to
    start.

    Schema:
      {
        "routes": [
          {
            "host": "api.github.com",
            "path_allowlist": ["/repos/x/", "/users/x"],   # optional
            "auth_scheme": "Bearer",                       # optional
            "token_env": "EGRESS_PROXY_TOKEN_0"            # optional
          },
          ...
        ]
      }
    """
    if not isinstance(payload, dict):
        raise ValueError("routes payload: top-level must be an object")
    raw = payload.get("routes")
    if not isinstance(raw, list):
        raise ValueError("routes payload: 'routes' must be a list")
    out: list[Route] = []
    for i, r in enumerate(raw):
        out.append(_parse_one(i, r))
    return tuple(out)


def _parse_one(idx: int, raw: object) -> Route:
    label = f"route[{idx}]"
    if not isinstance(raw, dict):
        raise ValueError(f"{label}: must be an object (got {type(raw).__name__})")
    host = raw.get("host")
    if not isinstance(host, str) or not host:
        raise ValueError(f"{label}: 'host' must be a non-empty string")

    path_allow_raw = raw.get("path_allowlist", [])
    if not isinstance(path_allow_raw, list):
        raise ValueError(f"{label} ({host}): 'path_allowlist' must be a list")
    prefixes: list[str] = []
    for j, p in enumerate(path_allow_raw):
        if not isinstance(p, str):
            raise ValueError(
                f"{label} ({host}): path_allowlist[{j}] must be a string"
            )
        if not p.startswith("/"):
            raise ValueError(
                f"{label} ({host}): path_allowlist[{j}] {p!r} must be an "
                f"absolute path prefix starting with '/'"
            )
        prefixes.append(p)

    auth_scheme = raw.get("auth_scheme", "")
    token_env = raw.get("token_env", "")
    if not isinstance(auth_scheme, str):
        raise ValueError(f"{label} ({host}): 'auth_scheme' must be a string")
    if not isinstance(token_env, str):
        raise ValueError(f"{label} ({host}): 'token_env' must be a string")
    # Both-or-neither: 'auth' on the manifest side renders to this
    # pair atomically. A partial pair here means the renderer or a
    # hand-edited file is broken.
    if bool(auth_scheme) != bool(token_env):
        raise ValueError(
            f"{label} ({host}): 'auth_scheme' and 'token_env' must be both "
            f"set or both empty (got auth_scheme={auth_scheme!r}, "
            f"token_env={token_env!r})"
        )

    return Route(
        host=host,
        path_allowlist=tuple(prefixes),
        auth_scheme=auth_scheme,
        token_env=token_env,
    )


def load_routes(text: str) -> tuple[Route, ...]:
    """Convenience: parse JSON text → routes. Raises `ValueError` for
    both decode and shape errors so callers handle them uniformly."""
    try:
        payload = json.loads(text)
    except json.JSONDecodeError as e:
        raise ValueError(f"routes payload: invalid JSON: {e}") from e
    return parse_routes(payload)


def is_git_push_request(path: str, query: str) -> bool:
    """Return True if the request is a git smart-HTTP push.

    git push over HTTPS hits two endpoints:
      GET <repo>/info/refs?service=git-receive-pack   (capabilities)
      POST <repo>/git-receive-pack                    (the push)

    Fetches use `service=git-upload-pack` / `/git-upload-pack` and
    are unaffected. Egress-proxy refuses HTTPS push because git-gate's
    pre-receive gitleaks scan is the gate for outbound git data;
    routing push through egress-proxy would bypass that. Use the
    bottle.git SSH path if you need to push.

    Universal across routes — the block fires even when no
    egress_proxy route matches the host. A bare-pass route (host with
    no auth, no path_allowlist) would otherwise let push through to
    pipelock + upstream untouched.
    """
    if path.endswith("/git-receive-pack"):
        return True
    if path.endswith("/info/refs"):
        # Query string is parsed leniently — `service=git-receive-pack`
        # may appear with other params in any order.
        for pair in query.split("&"):
            k, _, v = pair.partition("=")
            if k == "service" and v == "git-receive-pack":
                return True
    return False


def match_route(
    routes: typing.Sequence[Route],
    request_host: str,
) -> Route | None:
    """Return the first route whose `host` matches `request_host`
    exactly (case-insensitive). DNS names are case-insensitive.

    Wildcard hosts (`*.foo.com`) are NOT supported — they caused
    too many edge cases (apex match? cert validation? pipelock
    mirror mismatch?) for too little payoff. Operators that need
    multiple subdomains declare them individually (or one common
    parent host as a bare-pass route)."""
    target = request_host.lower()
    for r in routes:
        if r.host.lower() == target:
            return r
    return None


def decide(
    routes: typing.Sequence[Route],
    request_host: str,
    request_path: str,
    environ: typing.Mapping[str, str],
) -> Decision:
    """Pure decision: given a route table + request host + path + env,
    return what the addon should do with the request.

    - No matching route → BLOCK. The route table is the bottle's
      egress allowlist; defense-in-depth complements pipelock's
      hostname gate on the downstream leg. A bottle that wants a
      host reachable from the agent must declare a route for it
      (bare-pass route — no `auth`, no `path_allowlist` — is fine
      for hosts that just need passthrough).
    - Matching route with `path_allowlist` set, request path doesn't
      start with any of the allowed prefixes → block with a clear
      reason.
    - Matching route with an auth pair → forward + inject
      Authorization. Token comes from `environ[route.token_env]`;
      missing/empty values block (route declared auth but the secret
      isn't here — operator misconfig).
    """
    route = match_route(routes, request_host)
    if route is None:
        return Decision(
            action="block",
            reason=(
                f"egress-proxy: host {request_host!r} is not in the "
                f"bottle's egress_proxy.routes allowlist. Declare a "
                f"route for it or remove the request."
            ),
        )

    if route.path_allowlist:
        if not any(request_path.startswith(p) for p in route.path_allowlist):
            return Decision(
                action="block",
                reason=(
                    f"egress-proxy: path {request_path!r} not in "
                    f"path_allowlist for {route.host!r}"
                ),
            )

    if route.auth_scheme and route.token_env:
        token = environ.get(route.token_env, "")
        if not token:
            return Decision(
                action="block",
                reason=(
                    f"egress-proxy: route for {route.host!r} declared auth "
                    f"but env var {route.token_env!r} is unset"
                ),
            )
        return Decision(
            action="forward",
            inject_authorization=f"{route.auth_scheme} {token}",
        )

    return Decision(action="forward")


__all__ = [
    "Decision",
    "Route",
    "decide",
    "is_git_push_request",
    "load_routes",
    "match_route",
    "parse_routes",
]