import {
  NEW_WORKSPACE_PICKER_ATTACHMENT_OWNER,
  type UserComposerAttachment,
} from "@/attachments/types";
import type { PickerItem } from "./new-workspace-picker-item";

export interface PickerSelectionState {
  selectedItem: PickerItem | null;
  allowAutoPrSelection: boolean;
}

export type PickerSelectionEvent =
  | { type: "pr-detected" }
  | { type: "pr-added"; item: Extract<PickerItem, { kind: "github-pr" }> }
  | { type: "picker-selected"; item: PickerItem }
  | { type: "target-changed" };

export const initialPickerSelectionState: PickerSelectionState = {
  selectedItem: null,
  allowAutoPrSelection: false,
};

export function reducePickerSelection(
  state: PickerSelectionState,
  event: PickerSelectionEvent,
): PickerSelectionState {
  switch (event.type) {
    case "pr-detected":
      return { ...state, allowAutoPrSelection: true };
    case "pr-added":
      return state.allowAutoPrSelection
        ? { selectedItem: event.item, allowAutoPrSelection: false }
        : state;
    case "picker-selected":
      return { selectedItem: event.item, allowAutoPrSelection: false };
    case "target-changed":
      return initialPickerSelectionState;
  }
}

function isPrAttachment(
  attachment: UserComposerAttachment,
): attachment is Extract<UserComposerAttachment, { kind: "forge_change_request" | "github_pr" }> {
  return attachment.kind === "forge_change_request" || attachment.kind === "github_pr";
}

function isPickerOwnedPrAttachment(attachment: UserComposerAttachment): attachment is Extract<
  UserComposerAttachment,
  { kind: "github_pr" }
> & {
  owner: typeof NEW_WORKSPACE_PICKER_ATTACHMENT_OWNER;
} {
  return (
    attachment.kind === "github_pr" && attachment.owner === NEW_WORKSPACE_PICKER_ATTACHMENT_OWNER
  );
}

// Ownership lives on the attachment because drafts outlive this component.
// The picker owns at most one PR; user-added PRs and issues remain untouched.
export function syncPickerPrAttachment(input: {
  attachments: UserComposerAttachment[];
  item: PickerItem | null;
}): UserComposerAttachment[] {
  const nextAttachments = input.attachments.filter(
    (attachment) => !isPickerOwnedPrAttachment(attachment),
  );

  if (input.item?.kind === "github-pr") {
    const selectedPr = input.item.item;
    const hasExistingPrAttachment = nextAttachments.some(
      (attachment) => isPrAttachment(attachment) && attachment.item.number === selectedPr.number,
    );
    if (!hasExistingPrAttachment) {
      return [
        ...nextAttachments,
        {
          kind: "github_pr",
          item: selectedPr,
          owner: NEW_WORKSPACE_PICKER_ATTACHMENT_OWNER,
        },
      ];
    }
  }

  return nextAttachments;
}

export function clearPickerPrAttachmentForTargetChange(input: {
  attachments: UserComposerAttachment[];
  currentTargetId: string;
  nextTargetId: string;
}): UserComposerAttachment[] {
  if (input.currentTargetId === input.nextTargetId) {
    return input.attachments;
  }
  return input.attachments.filter((attachment) => !isPrAttachment(attachment));
}