import { canArchiveAttachment, type MatrixAttachmentCandidate } from "@tactical-media-broadcast-hub/core";
import { toGroupFileMapping, type RoomMapping } from "./config.js";

/** Client-server API event shape (only the fields the bot reads). */
export interface MatrixEvent {
  type: string;
  event_id: string;
  sender: string;
  origin_server_ts?: number;
  state_key?: string;
  /** Room v1–v10 redactions carry the target here; v11+ moved it into content. */
  redacts?: string;
  content: Record<string, unknown>;
  unsigned?: { redacted_because?: unknown; [key: string]: unknown };
}

export type RoomEncryption = MatrixAttachmentCandidate["roomEncryption"];

export const ATTACHMENT_MSGTYPES = ["m.file", "m.image", "m.audio", "m.video"] as const;

export interface AttachmentWork {
  kind: "attachment";
  event: MatrixEvent;
  candidate: MatrixAttachmentCandidate;
  /** Sender-supplied display name; only ever used after normalisation. */
  displayName: string;
}

export type Classified =
  | AttachmentWork
  | { kind: "redaction"; event: MatrixEvent; redacts: string }
  | { kind: "skip"; event: MatrixEvent; reason: string };

function isRecord(value: unknown): value is Record<string, unknown> {
  return typeof value === "object" && value !== null && !Array.isArray(value);
}

/** Runtime guard for raw JSON from /sync or /messages. */
export function isMatrixEvent(value: unknown): value is MatrixEvent {
  return isRecord(value)
    && typeof value.type === "string"
    && typeof value.event_id === "string"
    && typeof value.sender === "string"
    && isRecord(value.content);
}

export function redactionTarget(event: MatrixEvent): string | null {
  const target = typeof event.content.redacts === "string" ? event.content.redacts : event.redacts;
  return typeof target === "string" && target.startsWith("$") ? target : null;
}

function isEdit(content: Record<string, unknown>): boolean {
  const relates = content["m.relates_to"];
  return (isRecord(relates) && relates.rel_type === "m.replace") || "m.new_content" in content;
}

/**
 * Decide what (if anything) to do with a timeline event in a mapped room.
 * Every exclusion from the processing contract lives here so it is unit-testable;
 * the final eligibility gate is the shared `canArchiveAttachment`.
 */
export function classifyEvent(
  event: MatrixEvent,
  mapping: RoomMapping,
  roomEncryption: RoomEncryption,
  botUserId: string,
): Classified {
  if (event.sender === botUserId) return { kind: "skip", event, reason: "own-event" };
  if (event.type === "m.room.redaction") {
    const redacts = redactionTarget(event);
    return redacts === null ? { kind: "skip", event, reason: "redaction-without-target" } : { kind: "redaction", event, redacts };
  }
  if (event.type === "m.room.encrypted") return { kind: "skip", event, reason: "encrypted-event" };
  if (event.type !== "m.room.message") return { kind: "skip", event, reason: "not-a-message" };
  if (event.unsigned?.redacted_because !== undefined) return { kind: "skip", event, reason: "redacted" };
  const { content } = event;
  const msgtype = typeof content.msgtype === "string" ? content.msgtype : "";
  if (!(ATTACHMENT_MSGTYPES as readonly string[]).includes(msgtype)) {
    return { kind: "skip", event, reason: "not-an-attachment" };
  }
  if (isEdit(content)) return { kind: "skip", event, reason: "edit" };
  if (content.file !== undefined) return { kind: "skip", event, reason: "encrypted-file" };
  if (roomEncryption !== "unencrypted") return { kind: "skip", event, reason: `room-${roomEncryption}` };

  const candidate: MatrixAttachmentCandidate = {
    roomId: mapping.roomId,
    eventId: event.event_id,
    senderId: event.sender,
    eventType: event.type,
    msgtype,
    roomEncryption,
    encryptedFile: content.file !== undefined,
    redacted: false,
    mxcUri: typeof content.url === "string" ? content.url : "",
  };
  if (!canArchiveAttachment(toGroupFileMapping(mapping), candidate)) {
    return { kind: "skip", event, reason: "ineligible" };
  }
  const filename = typeof content.filename === "string" && content.filename.trim() !== "" ? content.filename : null;
  const body = typeof content.body === "string" ? content.body : "";
  return { kind: "attachment", event, candidate, displayName: filename ?? body };
}

/** Split a validated `mxc://server/mediaId` into its parts. */
export function parseMxc(mxcUri: string): { serverName: string; mediaId: string } {
  const match = /^mxc:\/\/([^/\s]+)\/([^/\s?#]+)$/.exec(mxcUri);
  if (match === null || match[1] === undefined || match[2] === undefined) throw new Error("invalid mxc URI");
  return { serverName: match[1], mediaId: match[2] };
}