from __future__ import annotations

import json
import time
import urllib.error
import urllib.parse
import urllib.request
from collections.abc import Callable, Iterator
from datetime import UTC, datetime

from slop_farmer.data.http import urlopen_with_retry


class PullRequestDiffTooLargeError(RuntimeError):
    """Raised when GitHub refuses to render a PR diff because it is too large."""


class GitHubApiRequestError(RuntimeError):
    """Raised when GitHub returns a non-recoverable HTTP response."""

    def __init__(self, status_code: int, path: str, detail: str):
        self.status_code = status_code
        self.path = path
        self.detail = detail
        super().__init__(f"GitHub API request failed: {status_code} {path} {detail}")


class GitHubClient:
    def __init__(
        self,
        token: str | None,
        per_page: int = 100,
        timeout: int = 180,
        max_retries: int = 5,
        log: Callable[[str], None] | None = None,
    ):
        self.token = token
        self.per_page = per_page
        self.timeout = timeout
        self.max_retries = max_retries
        self.log = log
        self.base_url = "https://api.github.com"
        self.request_count = 0
        self.rate_limit_log_every = 25
        self._rate_limit_thresholds_logged: dict[str, set[int]] = {}

    @staticmethod
    def _header_int(headers: dict[str, str], name: str) -> int | None:
        value = headers.get(name)
        if value is None:
            return None
        try:
            return int(value)
        except ValueError:
            return None

    def _maybe_log_rate_limit(self, path: str, headers: dict[str, str]) -> None:
        self.request_count += 1
        if not self.log:
            return
        limit = self._header_int(headers, "x-ratelimit-limit")
        remaining = self._header_int(headers, "x-ratelimit-remaining")
        used = self._header_int(headers, "x-ratelimit-used")
        reset_at = self._header_int(headers, "x-ratelimit-reset")
        resource = headers.get("x-ratelimit-resource", "?")
        if limit is None or remaining is None:
            return
        should_log = self.request_count == 1 or self.request_count % self.rate_limit_log_every == 0
        thresholds = (1000, 500, 250, 100, 50, 25, 10, 5, 1, 0)
        logged = self._rate_limit_thresholds_logged.setdefault(resource, set())
        for threshold in thresholds:
            if remaining <= threshold and threshold not in logged:
                should_log = True
                logged.add(threshold)
        if not should_log:
            return
        reset_text = "?"
        if reset_at is not None:
            reset_text = datetime.fromtimestamp(reset_at, tz=UTC).strftime("%Y-%m-%dT%H:%M:%SZ")
        used_text = "?" if used is None else str(used)
        self.log(
            f"GitHub rate limit: resource={resource} used={used_text} remaining={remaining}/{limit} "
            f"reset={reset_text} after {path} (request {self.request_count})"
        )

    def _request(
        self,
        path: str,
        params: dict[str, object] | None = None,
        accept: str = "application/vnd.github+json",
    ) -> tuple[object, dict[str, str]]:
        query = f"?{urllib.parse.urlencode(params)}" if params else ""
        url = f"{self.base_url}{path}{query}"
        request = urllib.request.Request(url)
        request.add_header("Accept", accept)
        request.add_header("X-GitHub-Api-Version", "2022-11-28")
        if self.token:
            request.add_header("Authorization", f"Bearer {self.token}")
        while True:
            try:
                with urlopen_with_retry(
                    request,
                    timeout=self.timeout,
                    max_retries=self.max_retries,
                    log=self.log,
                    label=path,
                ) as response:
                    payload = response.read().decode("utf-8")
                    headers = {k.lower(): v for k, v in response.headers.items()}
                    self._maybe_log_rate_limit(path, headers)
                    return json.loads(payload), headers
            except urllib.error.HTTPError as exc:
                if exc.code == 403 and exc.headers.get("X-RateLimit-Remaining") == "0":
                    reset_at = int(exc.headers.get("X-RateLimit-Reset", "0") or "0")
                    sleep_for = max(reset_at - int(time.time()), 1)
                    if self.log:
                        self.log(
                            f"GitHub rate limit reached for {path}; sleeping {sleep_for}s until reset"
                        )
                    time.sleep(sleep_for)
                    continue
                detail = exc.read().decode("utf-8", errors="replace")
                if (
                    exc.code == 406
                    and '"field":"diff"' in detail
                    and '"code":"too_large"' in detail
                ):
                    raise PullRequestDiffTooLargeError(
                        f"GitHub diff too large: {path} {detail}"
                    ) from exc
                raise GitHubApiRequestError(exc.code, path, detail) from exc

    def _request_text(
        self,
        path: str,
        params: dict[str, object] | None = None,
        accept: str = "application/vnd.github.diff",
    ) -> tuple[str, dict[str, str]]:
        query = f"?{urllib.parse.urlencode(params)}" if params else ""
        url = f"{self.base_url}{path}{query}"
        request = urllib.request.Request(url)
        request.add_header("Accept", accept)
        request.add_header("X-GitHub-Api-Version", "2022-11-28")
        if self.token:
            request.add_header("Authorization", f"Bearer {self.token}")
        while True:
            try:
                with urlopen_with_retry(
                    request,
                    timeout=self.timeout,
                    max_retries=self.max_retries,
                    log=self.log,
                    label=path,
                ) as response:
                    payload = response.read().decode("utf-8", errors="replace")
                    headers = {k.lower(): v for k, v in response.headers.items()}
                    self._maybe_log_rate_limit(path, headers)
                    return payload, headers
            except urllib.error.HTTPError as exc:
                if exc.code == 403 and exc.headers.get("X-RateLimit-Remaining") == "0":
                    reset_at = int(exc.headers.get("X-RateLimit-Reset", "0") or "0")
                    sleep_for = max(reset_at - int(time.time()), 1)
                    if self.log:
                        self.log(
                            f"GitHub rate limit reached for {path}; sleeping {sleep_for}s until reset"
                        )
                    time.sleep(sleep_for)
                    continue
                detail = exc.read().decode("utf-8", errors="replace")
                if (
                    exc.code == 406
                    and '"field":"diff"' in detail
                    and '"code":"too_large"' in detail
                ):
                    raise PullRequestDiffTooLargeError(
                        f"GitHub diff too large: {path} {detail}"
                    ) from exc
                raise GitHubApiRequestError(exc.code, path, detail) from exc

    def paginate(
        self,
        path: str,
        params: dict[str, object] | None = None,
        accept: str = "application/vnd.github+json",
        limit: int | None = None,
    ) -> Iterator[dict]:
        page = 1
        yielded = 0
        params = dict(params or {})
        params["per_page"] = self.per_page
        while True:
            params["page"] = page
            payload, _headers = self._request(path, params=params, accept=accept)
            if not isinstance(payload, list):
                raise RuntimeError(f"Expected list payload from {path}, got {type(payload)!r}")
            if not payload:
                break
            for item in payload:
                if not isinstance(item, dict):
                    continue
                yield item
                yielded += 1
                if limit is not None and yielded >= limit:
                    return
            if len(payload) < self.per_page:
                break
            page += 1

    def get_json(self, path: str, accept: str = "application/vnd.github+json") -> dict:
        payload, _headers = self._request(path, accept=accept)
        if not isinstance(payload, dict):
            raise RuntimeError(f"Expected dict payload from {path}, got {type(payload)!r}")
        return payload

    def iter_repo_issues(
        self, owner: str, repo: str, since: str | None, limit: int | None
    ) -> Iterator[dict]:
        direction = "asc"
        if since is None and limit is not None:
            # When the caller asks for a bounded first pass without a watermark,
            # prefer the most recently updated items. Using ascending order here
            # causes small smoke tests to read the stalest issue/PR stubs first,
            # which can make recent-age filters appear to return an empty repo.
            direction = "desc"
        params: dict[str, object] = {"state": "all", "sort": "updated", "direction": direction}
        if since:
            params["since"] = since
        yield from self.paginate(f"/repos/{owner}/{repo}/issues", params=params, limit=limit)

    def iter_issue_comments(
        self, owner: str, repo: str, since: str | None, limit: int | None
    ) -> Iterator[dict]:
        params: dict[str, object] = {"sort": "updated", "direction": "asc"}
        if since:
            params["since"] = since
        yield from self.paginate(
            f"/repos/{owner}/{repo}/issues/comments", params=params, limit=limit
        )

    def iter_issue_comments_for_number(
        self,
        owner: str,
        repo: str,
        number: int,
        since: str | None,
        limit: int | None = None,
    ) -> Iterator[dict]:
        params: dict[str, object] = {"sort": "updated", "direction": "asc"}
        if since:
            params["since"] = since
        yield from self.paginate(
            f"/repos/{owner}/{repo}/issues/{number}/comments", params=params, limit=limit
        )

    def get_pull_request(self, owner: str, repo: str, number: int) -> dict:
        return self.get_json(f"/repos/{owner}/{repo}/pulls/{number}")

    def iter_pull_reviews(
        self, owner: str, repo: str, number: int, limit: int | None = None
    ) -> Iterator[dict]:
        yield from self.paginate(f"/repos/{owner}/{repo}/pulls/{number}/reviews", limit=limit)

    def iter_pull_review_comments(
        self, owner: str, repo: str, number: int, limit: int | None = None
    ) -> Iterator[dict]:
        yield from self.paginate(
            f"/repos/{owner}/{repo}/pulls/{number}/comments",
            params={"sort": "updated", "direction": "asc"},
            limit=limit,
        )

    def iter_pull_files(
        self, owner: str, repo: str, number: int, limit: int | None = None
    ) -> Iterator[dict]:
        yield from self.paginate(f"/repos/{owner}/{repo}/pulls/{number}/files", limit=limit)

    def get_pull_request_diff(self, owner: str, repo: str, number: int) -> str:
        path = f"/repos/{owner}/{repo}/pulls/{number}"
        try:
            payload, _headers = self._request_text(
                path,
                accept="application/vnd.github.diff",
            )
            return payload
        except PullRequestDiffTooLargeError:
            if self.log:
                self.log(
                    f"Skipping unified diff for pull request #{number}; GitHub reports diff too large"
                )
            return ""

    def iter_issue_timeline(
        self, owner: str, repo: str, number: int, limit: int | None = None
    ) -> Iterator[dict]:
        path = f"/repos/{owner}/{repo}/issues/{number}/timeline"
        try:
            yield from self.paginate(
                path,
                accept="application/vnd.github+json, application/vnd.github.mockingbird-preview+json",
                limit=limit,
            )
        except GitHubApiRequestError as exc:
            if exc.status_code < 500:
                raise
            if self.log:
                self.log(
                    f"Skipping timeline fetch for issue #{number} after GitHub {exc.status_code}: {path}"
                )
            return