import type {
  EnvironmentId,
  PullRequestActor,
  PullRequestComment,
  PullRequestDetailView,
  PullRequestRef,
  ScopedThreadRef,
} from "@t3tools/contracts";
import {
  ArrowDownUpIcon,
  ChevronDownIcon,
  ChevronRightIcon,
  GitPullRequestClosedIcon,
  HammerIcon,
  PencilIcon,
  RotateCcwIcon,
  SendIcon,
  TagIcon,
  UsersIcon,
} from "lucide-react";
import { useId, useRef, useState, type ReactNode } from "react";

import { useAtomCommand } from "~/state/use-atom-command";
import { pullRequestEnvironment } from "~/state/pullRequests";
import { cn } from "~/lib/utils";
import { useOpenLink } from "~/browser/useOpenLink";
import { formatRelativeTimeLabel } from "~/timestampFormat";

import { Button } from "../ui/button";
import { Collapsible, CollapsiblePanel, CollapsibleTrigger } from "../ui/collapsible";
import { Textarea } from "../ui/textarea";
import { toastManager } from "../ui/toast";
import { Tooltip, TooltipPopup, TooltipTrigger } from "../ui/tooltip";
import {
  PullRequestActorAvatar,
  PullRequestActorLabel,
  PullRequestCheckStatusIcon,
  PullRequestReviewOutcomeBadge,
  pullRequestCheckStatusLabel,
  pullRequestReviewOutcomeLabel,
  pullRequestReviewOutcomeRingClassName,
  pullRequestReviewOutcomeStaleLabel,
} from "./pullRequestPresentation";
import { PullRequestLabelPicker } from "./PullRequestLabelPicker";
import { PullRequestReviewerPicker } from "./PullRequestReviewerPicker";
import { PullRequestActivityUnavailableState } from "./PullRequestActivityUnavailableState";
import {
  latestPullRequestReviewOutcomes,
  orderPullRequestComments,
  pullRequestFindingKey,
  pullRequestReviewOutcome,
  visibleBody,
  type PullRequestFinding,
} from "./pullRequestDetail.logic";
import {
  canEditPullRequestChangeRequest,
  canEditPullRequestComment,
} from "./pullRequestEditing.logic";
import { PullRequestMarkdown } from "./PullRequestMarkdown";
import { PullRequestMarkdownEditor } from "./PullRequestMarkdownEditor";
import { PullRequestReactionBar } from "./PullRequestReactions";
import { PullRequestConversationGhost } from "./PullRequestGhosts";
import { pullRequestLabelColor } from "./pullRequestList.logic";
import { sectionCollapseAnchorScrollTop } from "./pullRequestSummaryScroll.logic";

/** One reviewer, however a host happens to have cased their login this time. */
function reviewerKey(login: string): string {
  return login.toLowerCase();
}

/** The avatar carries the attribution alone; who it is arrives on hover, like the reviewer row. */
function CommentAuthor({ actor }: { actor: PullRequestActor | null }) {
  const login = actor?.login ?? "ghost";
  return (
    <Tooltip>
      <TooltipTrigger render={<span className="shrink-0 rounded-full" aria-label={login} />}>
        <PullRequestActorAvatar actor={actor} />
      </TooltipTrigger>
      <TooltipPopup side="bottom">
        {actor?.name && actor.name !== login ? `${actor.name} (@${login})` : login}
      </TooltipPopup>
    </Tooltip>
  );
}

/** "CHANGES_REQUESTED" reads as "Changes requested": one capital, the host's underscores gone. */
function reviewStateLabel(state: string): string {
  const words = state.toLowerCase().replace(/_/g, " ");
  return words.charAt(0).toUpperCase() + words.slice(1);
}

/** What every remark in the conversation needs to be rewritten where it sits. */
interface CommentEditing {
  readonly cwd: string;
  readonly environmentId: EnvironmentId;
  readonly threadRef: ScopedThreadRef | null;
  readonly canEdit: (comment: PullRequestComment) => boolean;
  readonly editingId: string | null;
  readonly saving: boolean;
  readonly onEdit: (comment: PullRequestComment | null) => void;
  readonly onSave: (comment: PullRequestComment, body: string) => void;
}

/**
 * A remark's words, and the pencil that swaps them for the editor. The pencil is revealed by
 * hovering the remark, like the reaction bar's own, so the parent must carry `group`.
 */
function CommentBody({
  comment,
  editing,
  className,
}: {
  comment: PullRequestComment;
  editing: CommentEditing;
  className?: string | undefined;
}) {
  if (editing.editingId === comment.id) {
    return (
      <PullRequestMarkdownEditor
        className={className}
        value={comment.body}
        cwd={editing.cwd}
        environmentId={editing.environmentId}
        threadRef={editing.threadRef}
        label="Edit comment"
        saving={editing.saving}
        onSave={(body) => editing.onSave(comment, body)}
        onCancel={() => editing.onEdit(null)}
      />
    );
  }
  return (
    <div className={cn("flex items-start gap-1", className)}>
      <PullRequestMarkdown
        className="min-w-0 flex-1"
        text={comment.body}
        cwd={editing.cwd}
        environmentId={editing.environmentId}
        threadRef={editing.threadRef}
      />
      {editing.canEdit(comment) ? (
        <Button
          size="icon-xs"
          variant="ghost"
          className="shrink-0 text-muted-foreground opacity-0 transition-opacity group-focus-within:opacity-100 group-hover:opacity-100 focus-visible:opacity-100"
          aria-label="Edit comment"
          onClick={() => editing.onEdit(comment)}
        >
          <PencilIcon className="size-3" />
        </Button>
      ) : null}
    </div>
  );
}

/** Finished work — a resolved conversation or a dismissed approval — opens collapsed. */
function CollapsedComment({
  comment,
  editing,
  label,
  body,
  reactionBar,
}: {
  comment: PullRequestComment;
  editing: CommentEditing;
  label: string;
  /** Null where the remark is nothing but its verdict, which a dismissal usually is. */
  body: string | null;
  reactionBar: ReactNode;
}) {
  const [open, setOpen] = useState(false);
  return (
    <Collapsible open={open} onOpenChange={setOpen}>
      <article className="group rounded-lg border border-border/60 [contain-intrinsic-block-size:44px] [content-visibility:auto]">
        <CollapsibleTrigger
          className={cn(
            "flex w-full items-center gap-2 p-3 text-left transition-opacity hover:opacity-100",
            open ? "opacity-100" : "opacity-65",
          )}
        >
          <span className="flex min-w-0 flex-1 items-center gap-2 text-xs text-muted-foreground">
            <CommentAuthor actor={comment.author} />
            <span>{formatRelativeTimeLabel(comment.createdAt)}</span>
            <span>{label}</span>
          </span>
          <ChevronDownIcon
            aria-hidden
            className={cn(
              "size-3.5 shrink-0 text-muted-foreground/60 transition-transform",
              open && "rotate-180",
            )}
          />
        </CollapsibleTrigger>
        <CollapsiblePanel>
          {open ? (
            <div className="px-3 pb-3">
              {comment.path ? (
                <Tooltip>
                  <TooltipTrigger
                    render={
                      <p className="truncate text-xs text-muted-foreground">{comment.path}</p>
                    }
                  />
                  <TooltipPopup side="top">{comment.path}</TooltipPopup>
                </Tooltip>
              ) : null}
              {/* A dismissal carries no more words than an approval does, and an empty markdown
                  block reads as a card somebody forgot to fill in. */}
              {body === null && !editing.canEdit(comment) ? null : (
                <CommentBody className="mt-2" comment={comment} editing={editing} />
              )}
              {reactionBar}
            </div>
          ) : null}
        </CollapsiblePanel>
      </article>
    </Collapsible>
  );
}

function MetaRow({
  icon,
  label,
  children,
}: {
  icon: ReactNode;
  label: string;
  children: ReactNode;
}) {
  return (
    <div className="grid min-w-0 grid-cols-[6rem_minmax(0,1fr)] items-center gap-2 text-xs">
      <span className="flex items-center gap-1.5 text-muted-foreground">
        {icon}
        {label}
      </span>
      <span className="min-w-0 text-foreground">{children}</span>
    </div>
  );
}

function Section({
  title,
  defaultOpen = true,
  actions,
  children,
}: {
  title: string;
  defaultOpen?: boolean;
  /** Heading controls stay separate from the collapse trigger so they remain independently usable. */
  actions?: ReactNode;
  children: ReactNode;
}) {
  const [open, setOpen] = useState(defaultOpen);
  const headingRef = useRef<HTMLDivElement>(null);
  const setOpenWithScrollAnchor = (nextOpen: boolean) => {
    if (!nextOpen) {
      const heading = headingRef.current;
      const section = heading?.closest<HTMLElement>("[data-pull-request-summary-section]");
      const scroller = heading?.closest<HTMLElement>("[data-pull-request-summary-scroll]");
      if (heading && section && scroller) {
        const target = sectionCollapseAnchorScrollTop({
          scrollTop: scroller.scrollTop,
          viewportTop: scroller.getBoundingClientRect().top,
          sectionTop: section.getBoundingClientRect().top,
          headingTop: heading.getBoundingClientRect().top,
        });
        // Synchronous with the press: React commits the collapsed height before the browser
        // paints, so the reader sees the heading they pressed stay put rather than a jump first.
        if (target !== null) scroller.scrollTop = target;
      }
    }
    setOpen(nextOpen);
  };
  return (
    <Collapsible
      open={open}
      onOpenChange={setOpenWithScrollAnchor}
      data-pull-request-summary-section
    >
      {/* The heading rides the top of the scroll box the way a diff's file header does, so a
          section can be collapsed from wherever its body has been read to rather than only from
          where it started. Opaque, because the rows it covers scroll beneath it. */}
      <div
        ref={headingRef}
        className="sticky top-0 z-10 flex w-full items-center bg-background pr-4"
      >
        <CollapsibleTrigger className="flex min-w-0 flex-1 items-center gap-1.5 px-4 py-3 text-left text-xs font-medium text-muted-foreground hover:text-foreground">
          <span>{title}</span>
          <ChevronRightIcon
            aria-hidden
            className={cn(
              "size-3.5 text-muted-foreground/60 transition-transform",
              open && "rotate-90",
            )}
          />
        </CollapsibleTrigger>
        {actions}
      </div>
      <CollapsiblePanel>
        <div className="px-4 pb-4">{children}</div>
      </CollapsiblePanel>
    </Collapsible>
  );
}

function CommentComposer({
  environmentId,
  reference,
  detail,
  actionPending,
  onCommentAction,
  onCommented,
}: {
  environmentId: EnvironmentId;
  reference: PullRequestRef;
  detail: PullRequestDetailView;
  actionPending: boolean;
  onCommentAction: (
    body: string,
    action: "close" | "reopen",
  ) => Promise<{ readonly commentPosted: boolean }>;
  onCommented: () => void;
}) {
  const [body, setBody] = useState("");
  const [submitting, setSubmitting] = useState<"comment" | "close" | "reopen" | null>(null);
  const postComment = useAtomCommand(pullRequestEnvironment.comment, { reportFailure: false });
  const followUpAction =
    detail.state === "open" &&
    detail.capabilities.actions.includes("close") &&
    detail.viewerPermissions.actions.includes("close")
      ? ("close" as const)
      : detail.state === "closed" &&
          detail.capabilities.actions.includes("reopen") &&
          detail.viewerPermissions.actions.includes("reopen")
        ? ("reopen" as const)
        : null;

  const submit = async (action: "comment" | "close" | "reopen") => {
    const trimmed = body.trim();
    if (trimmed.length === 0 || submitting !== null || actionPending) return;
    setSubmitting(action);
    if (action !== "comment") {
      const result = await onCommentAction(trimmed, action);
      if (result.commentPosted) setBody("");
      setSubmitting(null);
      return;
    }
    const result = await postComment({
      environmentId,
      input: {
        ...reference,
        body: trimmed,
      },
    });
    if (result._tag === "Failure") {
      setSubmitting(null);
      toastManager.add({ type: "error", title: "Could not post the comment" });
      return;
    }
    setBody("");
    setSubmitting(null);
    onCommented();
  };

  return (
    <div className="mt-3 space-y-2">
      <Textarea
        // Locked while posting: the body is cleared on success, which would otherwise throw
        // away a new draft typed while the request was still in flight.
        disabled={submitting !== null || actionPending}
        value={body}
        rows={3}
        placeholder="Leave a comment"
        aria-label="Comment on this pull request"
        onChange={(event) => setBody(event.target.value)}
      />
      <div className="flex justify-end gap-2">
        {followUpAction === null ? null : (
          <Button
            size="xs"
            variant={followUpAction === "close" ? "destructive-outline" : "outline"}
            disabled={body.trim().length === 0 || submitting !== null || actionPending}
            onClick={() => void submit(followUpAction)}
          >
            {followUpAction === "close" ? (
              <GitPullRequestClosedIcon className="size-3.5" />
            ) : (
              <RotateCcwIcon className="size-3.5" />
            )}
            {submitting === followUpAction
              ? followUpAction === "close"
                ? "Closing..."
                : "Reopening..."
              : followUpAction === "close"
                ? "Close with comment"
                : "Reopen with comment"}
          </Button>
        )}
        <Button
          size="xs"
          variant="outline"
          disabled={body.trim().length === 0 || submitting !== null || actionPending}
          onClick={() => void submit("comment")}
        >
          <SendIcon className="size-3.5" />
          {submitting === "comment" ? "Posting..." : "Comment"}
        </Button>
      </div>
    </div>
  );
}

/**
 * What a first render of the conversation carries. A pull request with two hundred comments is
 * two hundred markdown documents, and the ones worth arriving for are the recent ones.
 */
const COMMENT_PAGE = 30;

export function PullRequestSummaryTab({
  environmentId,
  threadRef,
  reference,
  detail,
  activityPending,
  activityError,
  pendingFinding,
  fixFindingLabel = "Fix in a thread",
  fixCheckLabel = "Fix",
  onFixFinding,
  actionPending,
  onCommentAction,
  onRefresh,
}: {
  environmentId: EnvironmentId;
  threadRef: ScopedThreadRef | null;
  reference: PullRequestRef;
  detail: PullRequestDetailView;
  activityPending: boolean;
  activityError: string | null;
  /** The hand-off currently preparing, if any, so only the finding it belongs to says so. */
  pendingFinding?: string | null;
  fixFindingLabel?: string;
  fixCheckLabel?: string;
  onFixFinding?: (finding: PullRequestFinding) => void;
  actionPending: boolean;
  onCommentAction: (
    body: string,
    action: "close" | "reopen",
  ) => Promise<{ readonly commentPosted: boolean }>;
  onRefresh: () => void;
}) {
  // Keyed by the pull request, so opening another one starts at the end of its conversation
  // rather than wherever the last one had been read back to.
  const [shown, setShown] = useState({ url: detail.url, count: COMMENT_PAGE });
  const checksId = useId();
  const [expandedChecksUrl, setExpandedChecksUrl] = useState<string | null>(null);
  const showChecks = expandedChecksUrl === detail.url;
  const shownComments = shown.url === detail.url ? shown.count : COMMENT_PAGE;
  // Windowed by recency regardless of display order: expanding always reaches further back in
  // time, whether the newest comment currently reads first or last.
  const recentComments = detail.comments.slice(Math.max(0, detail.comments.length - shownComments));
  const hiddenCommentCount = detail.comments.length - recentComments.length;
  const [commentOrder, setCommentOrder] = useState<"newest" | "oldest">("newest");
  const visibleComments = orderPullRequestComments(recentComments, commentOrder);
  const showOldestCommentsButton =
    hiddenCommentCount > 0 ? (
      <Button
        size="sm"
        variant="outline"
        className="w-full"
        onClick={() => setShown({ url: detail.url, count: shownComments + COMMENT_PAGE })}
      >
        Show {Math.min(hiddenCommentCount, COMMENT_PAGE)} oldest{" "}
        {hiddenCommentCount === 1 ? "comment" : "comments"}
      </Button>
    ) : null;
  // Read from the whole conversation, not the window shown below it: a verdict older than the
  // last thirty comments still stands.
  const reviewOutcomes = latestPullRequestReviewOutcomes(detail.comments, detail.commits);
  // Hosts do not promise one casing for a login across two fields of the same response, and
  // none of them lets `Octocat` and `octocat` be two people — so matching on the literal string
  // would show one reviewer twice and drop the verdict off both.
  const outcomeByLogin = new Map(
    reviewOutcomes.flatMap((entry) =>
      entry.actor ? [[reviewerKey(entry.actor.login), entry] as const] : [],
    ),
  );
  // Everyone whose face belongs on this row: the people a review was asked of, then anyone who
  // ruled without being on that list. A host drops a reviewer from the requested set once they
  // have reviewed, and their verdict is the thing this row now exists to show.
  const reviewerEntries = [
    ...detail.reviewers.map((actor) => ({
      key: actor.login,
      actor,
      outcome: outcomeByLogin.get(reviewerKey(actor.login))?.outcome ?? null,
      stale: outcomeByLogin.get(reviewerKey(actor.login))?.stale ?? false,
    })),
    ...reviewOutcomes
      .filter(
        (entry) =>
          !detail.reviewers.some(
            (actor) =>
              entry.actor !== null && reviewerKey(actor.login) === reviewerKey(entry.actor.login),
          ),
      )
      .map((entry) => ({
        key: entry.key,
        actor: entry.actor,
        outcome: entry.outcome,
        stale: entry.stale,
      })),
  ];

  // A comment that already lives on a review thread is that thread: the thread carries the line
  // and side the bare comment has lost, and a resolved one is finished work nobody should be
  // invited to fix again — the same call the whole-review hand-off makes.
  const threadByCommentId = new Map(
    detail.reviewThreads.flatMap((thread) =>
      thread.comments.map((comment) => [comment.id, thread] as const),
    ),
  );

  const openLink = useOpenLink(threadRef);
  const openCheck = (url: string) => {
    void openLink(url).catch((error: unknown) => {
      console.error(error);
      toastManager.add({ type: "error", title: "Unable to open check details" });
    });
  };

  const update = useAtomCommand(pullRequestEnvironment.update, { reportFailure: false });
  const updateComment = useAtomCommand(pullRequestEnvironment.updateComment, {
    reportFailure: false,
  });
  // Keyed by the pull request, like the comment window above it, so an editor left open never
  // reappears over the next pull request's description.
  const [bodyScope, setBodyScope] = useState<string | null>(null);
  const [bodySaving, setBodySaving] = useState(false);
  // The remark being rewritten, named with the pull request it belongs to: a comment id is the
  // host's own, and two hosts — or two pull requests on Azure DevOps, which numbers a remark
  // inside its thread — hand out the same one. Without the pull request beside it, opening a
  // different one would leave its like-numbered remark sitting open in an editor.
  const [commentScope, setCommentScope] = useState<{
    readonly pullRequest: string;
    readonly commentId: string;
  } | null>(null);
  const [commentSaving, setCommentSaving] = useState(false);
  const editingCommentId = commentScope?.pullRequest === detail.url ? commentScope.commentId : null;

  const saveBody = async (body: string) => {
    if (bodySaving) return;
    setBodySaving(true);
    const result = await update({ environmentId, input: { ...reference, body } });
    setBodySaving(false);
    if (result._tag === "Failure") {
      toastManager.add({ type: "error", title: "Could not save the description" });
      return;
    }
    setBodyScope(null);
    onRefresh();
  };

  const commentEditing: CommentEditing = {
    cwd: detail.workspaceRoot,
    environmentId,
    threadRef,
    canEdit: (comment) => canEditPullRequestComment(detail, comment),
    editingId: editingCommentId,
    saving: commentSaving,
    onEdit: (comment) =>
      setCommentScope(comment === null ? null : { pullRequest: detail.url, commentId: comment.id }),
    onSave: async (comment, body) => {
      // A review's own summary is not a kind any host rewrites, which is why no pencil is ever
      // offered on one; the check is here because the comment's own type still allows it.
      if (commentSaving || comment.kind === "review") return;
      setCommentSaving(true);
      const result = await updateComment({
        environmentId,
        input: { ...reference, commentId: comment.id, kind: comment.kind, body },
      });
      setCommentSaving(false);
      if (result._tag === "Failure") {
        toastManager.add({ type: "error", title: "Could not save the comment" });
        return;
      }
      setCommentScope(null);
      onRefresh();
    },
  };

  return (
    <div className="h-full overflow-y-auto" data-pull-request-summary-scroll>
      <section className="px-4 py-2.5">
        <div className="space-y-2">
          <MetaRow icon={<UsersIcon className="size-3.5" />} label="Reviewers">
            <span className="flex min-w-0 flex-wrap items-center gap-1.5">
              {reviewerEntries.length === 0 ? (
                <span className="text-muted-foreground">None</span>
              ) : (
                <span className="flex items-center -space-x-1">
                  {reviewerEntries.map((entry) => {
                    const login = entry.actor?.login ?? "ghost";
                    const named =
                      entry.actor?.name && entry.actor.name !== login
                        ? `${entry.actor.name} (@${login})`
                        : login;
                    return (
                      <Tooltip key={entry.key}>
                        {/* A verdict rides the face that earned it rather than a row of its own:
                            the ring sits outside the one that separates overlapping avatars, so
                            it reads at a glance without adding anything to scroll past. */}
                        <TooltipTrigger
                          render={
                            <span
                              className={cn(
                                "relative rounded-full hover:z-10",
                                // The verdict replaces the separator rather than ringing it. Both
                                // occupy the same 2px immediately outside a 16px avatar, so the
                                // colour costs no size: anything drawn further out would be a
                                // halo wide enough to eclipse the neighbour this stack overlaps
                                // by 4px. Painted by this wrapper because a child's box-shadow
                                // covers its parent's, never the other way round.
                                entry.outcome
                                  ? pullRequestReviewOutcomeRingClassName(
                                      entry.outcome,
                                      entry.stale,
                                    )
                                  : undefined,
                              )}
                            />
                          }
                        >
                          <PullRequestActorLabel
                            actor={entry.actor}
                            tooltip={false}
                            className={cn(
                              "gap-0 [&>span:last-child]:sr-only",
                              // Only where the wrapper is not already drawing one, or the opaque
                              // separator would cover the verdict in the band they share.
                              entry.outcome
                                ? undefined
                                : "[&>img]:ring-2 [&>img]:ring-background [&>span:first-child]:ring-2 [&>span:first-child]:ring-background",
                            )}
                          />
                          {/* Colour alone says nothing to a reader who cannot see it, and the
                              login beside this is already in the accessible name. */}
                          {entry.outcome ? (
                            <span className="sr-only">
                              {entry.stale
                                ? pullRequestReviewOutcomeStaleLabel(entry.outcome)
                                : pullRequestReviewOutcomeLabel(entry.outcome)}
                            </span>
                          ) : null}
                        </TooltipTrigger>
                        <TooltipPopup side="bottom">
                          {entry.outcome
                            ? `${named} — ${
                                entry.stale
                                  ? pullRequestReviewOutcomeStaleLabel(entry.outcome)
                                  : pullRequestReviewOutcomeLabel(entry.outcome)
                              }`
                            : named}
                        </TooltipPopup>
                      </Tooltip>
                    );
                  })}
                </span>
              )}
              {/* Shown wherever the host can take a review request at all, and disabled with the
                  reason where this account may not make one: a control that vanishes teaches
                  nobody why, and "you need write access" is the answer to the question a reader
                  actually has. Azure DevOps is the exception — it takes a reviewer but will not
                  say who could be one, so there is nothing to open. */}
              {detail.capabilities.reviewers.request &&
              detail.capabilities.reviewers.listCandidates ? (
                <PullRequestReviewerPicker
                  environmentId={environmentId}
                  reference={reference}
                  allowed={detail.viewerPermissions.requestReviewers}
                />
              ) : null}
            </span>
          </MetaRow>
          {/* The row is shown empty only where a label could be put on it from here; on a host
              with none to offer, an empty row is a row about nothing. */}
          {detail.labels.length > 0 || detail.capabilities.labels === true ? (
            <MetaRow icon={<TagIcon className="size-3.5" />} label="Labels">
              <span className="flex min-w-0 flex-wrap items-center gap-1">
                {detail.labels.length === 0 ? (
                  <span className="text-muted-foreground">None</span>
                ) : (
                  detail.labels.map((label) => {
                    const dot = pullRequestLabelColor(label.color);
                    return (
                      <span
                        key={label.name}
                        className="inline-flex max-w-48 items-center gap-1.5 rounded-full bg-muted/40 py-0.5 pl-1.5 pr-2 text-xs"
                      >
                        <span
                          aria-hidden
                          className="size-2 shrink-0 rounded-full bg-muted-foreground"
                          {...(dot ? { style: { backgroundColor: dot } } : {})}
                        />
                        <span className="truncate">{label.name}</span>
                      </span>
                    );
                  })
                )}
                {detail.capabilities.labels === true ? (
                  <PullRequestLabelPicker
                    environmentId={environmentId}
                    reference={reference}
                    allowed={detail.viewerPermissions.labels !== false}
                  />
                ) : null}
              </span>
            </MetaRow>
          ) : null}
        </div>
      </section>

      <section aria-label="Description" className="px-4 pt-2 pb-4">
        <div className="group">
          {bodyScope === detail.url ? (
            <PullRequestMarkdownEditor
              // Empty is a real answer here: saving nothing is how a description is cleared.
              allowEmpty
              value={detail.body}
              cwd={detail.workspaceRoot}
              environmentId={environmentId}
              threadRef={threadRef}
              label="Pull request description"
              placeholder="Describe this pull request"
              saving={bodySaving}
              onSave={(body) => void saveBody(body)}
              onCancel={() => setBodyScope(null)}
            />
          ) : (
            <div className="flex items-start gap-1">
              <PullRequestMarkdown
                className="min-w-0 flex-1"
                text={detail.body.trim().length > 0 ? detail.body : "_No description provided._"}
                cwd={detail.workspaceRoot}
                environmentId={environmentId}
                threadRef={threadRef}
              />
              {canEditPullRequestChangeRequest(detail) ? (
                <Button
                  size="icon-xs"
                  variant="ghost"
                  className="shrink-0 text-muted-foreground opacity-0 transition-opacity group-focus-within:opacity-100 group-hover:opacity-100 focus-visible:opacity-100"
                  aria-label="Edit description"
                  onClick={() => setBodyScope(detail.url)}
                >
                  <PencilIcon className="size-3" />
                </Button>
              ) : null}
            </div>
          )}
          <PullRequestReactionBar
            className="mt-2"
            reactions={detail.reactions ?? []}
            canReact={detail.capabilities.reactions === true}
            environmentId={environmentId}
            reference={reference}
            onRefresh={onRefresh}
          />
        </div>
      </section>

      <section aria-label="Checks" className="px-4 py-3">
        {detail.checks.length === 0 ? (
          <p className="text-xs text-muted-foreground">No checks reported.</p>
        ) : (
          <div>
            <div className="flex items-center gap-1 text-xs">
              <span className="font-medium text-muted-foreground">Checks</span>
              <Button
                size="icon-xs"
                variant="ghost-muted"
                aria-label={showChecks ? "Hide checks" : "Show checks"}
                aria-expanded={showChecks}
                aria-controls={checksId}
                onClick={() => setExpandedChecksUrl(showChecks ? null : detail.url)}
              >
                <ChevronRightIcon
                  aria-hidden
                  className={cn("size-3.5 text-muted-foreground/60", showChecks && "rotate-90")}
                />
              </Button>
            </div>
            <div id={checksId} className={showChecks ? "mt-2" : "hidden"}>
              {(showChecks ? detail.checks : []).map((check, index) => {
                const finding = { kind: "check", check } as const;
                const failing = check.status === "failure" || check.status === "cancelled";
                return (
                  <div
                    // Position too: the host decides how many runs share a name, and a repeated
                    // key would be a rendering fault on top of whatever the list already says.
                    key={`${index}:${check.name}:${check.url ?? ""}`}
                    className="group flex items-center gap-2 rounded-md pr-1 hover:bg-accent/60"
                  >
                    <button
                      type="button"
                      disabled={!check.url}
                      onClick={() => check.url && openCheck(check.url)}
                      className={cn(
                        "flex min-w-0 flex-1 items-start gap-2 rounded-md px-2 py-2 text-left text-xs leading-5 [&>svg]:mt-0.5",
                        check.url ? undefined : "cursor-default",
                      )}
                    >
                      <PullRequestCheckStatusIcon status={check.status} />
                      <span className="min-w-0 flex-1 wrap-anywhere">{check.name}</span>
                      <span className="shrink-0 text-muted-foreground">
                        {pullRequestCheckStatusLabel(check)}
                      </span>
                    </button>
                    {/* Only where there is something to fix. A passing check has no failure to
                      reproduce, and the button would be an invitation to waste a thread. */}
                    {onFixFinding && failing ? (
                      <Button
                        size="xs"
                        variant="ghost"
                        className="shrink-0"
                        disabled={pendingFinding !== null && pendingFinding !== undefined}
                        onClick={() => onFixFinding(finding)}
                      >
                        <HammerIcon className="size-3" />
                        {pendingFinding === pullRequestFindingKey(finding)
                          ? "Preparing..."
                          : fixCheckLabel}
                      </Button>
                    ) : null}
                  </div>
                );
              })}
            </div>
          </div>
        )}
      </section>

      <Section
        title="Comments"
        actions={
          <Button
            size="xs"
            variant="ghost"
            className="h-7 shrink-0 px-2 text-[10px] text-muted-foreground"
            aria-label={
              commentOrder === "newest"
                ? "Show oldest comments first"
                : "Show newest comments first"
            }
            onClick={() => setCommentOrder((value) => (value === "newest" ? "oldest" : "newest"))}
          >
            <ArrowDownUpIcon aria-hidden className="size-3" />
            {commentOrder === "newest" ? "Newest first" : "Oldest first"}
          </Button>
        }
      >
        {activityPending ? (
          <PullRequestConversationGhost />
        ) : activityError ? (
          <PullRequestActivityUnavailableState compact error={activityError} onRetry={onRefresh} />
        ) : (
          <>
            {detail.commentsTruncated ? (
              <p className="mb-2 rounded-md border border-amber-500/30 bg-amber-500/5 px-2 py-1.5 text-xs">
                This conversation is longer than this page reads in one go. The most recent{" "}
                {detail.comments.length} are here; open it on the host to read the rest.
              </p>
            ) : null}
            {detail.comments.length === 0 ? (
              <p className="py-2 text-xs text-muted-foreground">No comments yet.</p>
            ) : (
              <div className="space-y-3">
                {commentOrder === "oldest" ? showOldestCommentsButton : null}
                {visibleComments.map((comment) => {
                  const thread = threadByCommentId.get(comment.id);
                  const body = visibleBody(comment.body);
                  const outcome = pullRequestReviewOutcome(comment.reviewState);
                  if (thread?.isResolved || outcome === "dismissed") {
                    return (
                      <CollapsedComment
                        key={comment.id}
                        comment={comment}
                        editing={commentEditing}
                        label={thread?.isResolved ? "Resolved" : "Approval dismissed"}
                        body={body}
                        reactionBar={
                          <PullRequestReactionBar
                            className="mt-2"
                            reactions={comment.reactions ?? []}
                            canReact={detail.capabilities.reactions === true}
                            subjectId={comment.id}
                            environmentId={environmentId}
                            reference={reference}
                            onRefresh={onRefresh}
                          />
                        }
                      />
                    );
                  }
                  // An approval is a verdict, not a finding: there is nothing in it to fix.
                  const finding: PullRequestFinding | null =
                    (comment.kind !== "review" && comment.kind !== "review-comment") ||
                    outcome === "approved"
                      ? null
                      : thread === undefined
                        ? // Nor is a remark with nothing in it: offering to hand an empty review
                          // to a thread promises work it does not describe.
                          body === null
                          ? null
                          : { kind: "comment", comment }
                        : { kind: "thread", thread };
                  // One bar, two homes. Under a card with words in it, it is the row beneath
                  // them. A bodiless verdict has nothing above it, so a row reserved for an add
                  // button nobody can see until they hover is a hole — there it rides the header
                  // line instead, which keeps the affordance every sibling card offers.
                  const reactionBar = (
                    <PullRequestReactionBar
                      reactions={comment.reactions ?? []}
                      canReact={detail.capabilities.reactions === true}
                      subjectId={comment.id}
                      environmentId={environmentId}
                      reference={reference}
                      onRefresh={onRefresh}
                      {...(body === null ? {} : { className: "mt-2" })}
                    />
                  );
                  return (
                    <article
                      key={comment.id}
                      // Offscreen comments skip style, layout and paint. Bot comments carry pages of
                      // highlighted code, and the conversation is below the description either way.
                      className="group rounded-lg border border-border/60 p-3 [contain-intrinsic-block-size:120px] [content-visibility:auto]"
                    >
                      <div className="flex items-start gap-2">
                        <span className="flex min-w-0 flex-1 items-center gap-2 text-xs text-muted-foreground">
                          <CommentAuthor actor={comment.author} />
                          <span>{formatRelativeTimeLabel(comment.createdAt)}</span>
                          {outcome ? (
                            <PullRequestReviewOutcomeBadge outcome={outcome} />
                          ) : comment.reviewState ? (
                            <span>{reviewStateLabel(comment.reviewState)}</span>
                          ) : null}
                          {body === null ? reactionBar : null}
                        </span>
                        {/* Review remarks only. A plain conversation comment is talk, not a finding,
                      and offering to fix one would promise more than it says. */}
                        {onFixFinding && finding ? (
                          <Button
                            size="xs"
                            variant="ghost"
                            className="-mt-1 shrink-0"
                            disabled={pendingFinding !== null && pendingFinding !== undefined}
                            onClick={() => onFixFinding(finding)}
                          >
                            <HammerIcon className="size-3" />
                            {pendingFinding === pullRequestFindingKey(finding)
                              ? "Preparing..."
                              : fixFindingLabel}
                          </Button>
                        ) : null}
                      </div>
                      {comment.path ? (
                        <Tooltip>
                          <TooltipTrigger
                            render={
                              <p className="mt-1 truncate text-xs text-muted-foreground">
                                {comment.path}
                              </p>
                            }
                          />
                          <TooltipPopup side="top">{comment.path}</TooltipPopup>
                        </Tooltip>
                      ) : null}
                      {/* A verdict usually carries no words, and an empty markdown block reads as
                          a card somebody forgot to fill in — the badge above already said it.
                          Kept where this reader may rewrite the remark: the pencil lives in here,
                          and hiding the block would take away the only way back to it. */}
                      {body === null && !commentEditing.canEdit(comment) ? null : (
                        <CommentBody className="mt-2" comment={comment} editing={commentEditing} />
                      )}
                      {body === null ? null : reactionBar}
                    </article>
                  );
                })}
                {commentOrder === "newest" ? showOldestCommentsButton : null}
              </div>
            )}
          </>
        )}
        {/* Posting is a core capability and remains usable even if the activity read failed. */}
        {detail.capabilities.comment && detail.viewerPermissions.comment ? (
          <CommentComposer
            reference={reference}
            key={JSON.stringify([
              environmentId,
              reference.projectId,
              reference.host,
              reference.repository,
              reference.number,
            ])}
            environmentId={environmentId}
            detail={detail}
            actionPending={actionPending}
            onCommentAction={onCommentAction}
            onCommented={onRefresh}
          />
        ) : null}
      </Section>
    </div>
  );
}