import {
  BadRequestException,
  ConflictException,
  Injectable,
  Logger,
  NotFoundException,
} from "@nestjs/common";
import { ConfigService } from "@nestjs/config";
import { InjectDataSource } from "@nestjs/typeorm";
import { DataSource, EntityManager } from "typeorm";
import type { QueryDeepPartialEntity } from "typeorm/query-builder/QueryPartialEntity.js";

import { EimsConfig } from "../../config/eims.config";
import { Invoice } from "../billing/entities/invoice.entity";
import {
  EimsInvoiceRequest,
  EimsMapperLine,
  toEimsInvoice,
} from "../billing/eims-invoice.mapper";
import { EimsAuthService } from "./eims-auth.service";
import { EimsClientService } from "./eims-client.service";
import { EimsApiException } from "./eims.errors";
import { EimsSystemState } from "./entities/eims-system-state.entity";
import {
  assertEimsInvoiceConfig,
  buildEimsContext,
  buildEimsSeller,
} from "./eims-invoice-context";
import {
  EimsInvoiceError,
  EimsInvoiceStatus,
  EimsInvoiceStatusView,
  EimsRegisterResponse,
  EimsVerifyRequest,
  EimsVerifyResponse,
} from "./eims-registration.types";

/**
 * Failure kinds where the gateway gave a complete answer: the document was rejected and is
 * definitively not registered. These clear the system-wide block; anything else does not.
 */
const DETERMINISTIC_KINDS = new Set(["SCHEMA_VALIDATION", "RULE_VALIDATION", "AUTH", "FORBIDDEN"]);

interface Reservation {
  stateId: string;
  invoiceCounter: number;
  previousIrn: string;
}

/**
 * Registers a single invoice with MoR EIMS.
 *
 * Sequencing is a **durable reservation**: the counter is consumed and the holder recorded in a
 * committed transaction *before* the request leaves the process, and the network call happens
 * outside any transaction. That gives three properties the naive design could not:
 *
 *  - a counter is never reused once an attempt has begun, even across a crash;
 *  - a crash mid-flight leaves the reservation standing, so nothing blindly resubmits a document
 *    that may already have reached MoR;
 *  - an ambiguous result blocks every invoice for the system number, not just its own, because
 *    `PreviousIrn` is unknown and any later document would chain to a stale IRN.
 *
 * Signing, authentication and error normalisation belong to `EimsClientService`. Manual only —
 * nothing in invoice creation calls this.
 */
@Injectable()
export class EimsInvoiceRegistrationService {
  private readonly logger = new Logger(EimsInvoiceRegistrationService.name);

  constructor(
    @InjectDataSource() private readonly dataSource: DataSource,
    private readonly config: ConfigService,
    private readonly client: EimsClientService,
    private readonly auth: EimsAuthService,
  ) {}

  private get cfg(): EimsConfig {
    return this.config.get<EimsConfig>("eims")!;
  }

  async registerInvoiceWithEims(invoiceId: string): Promise<EimsInvoiceStatusView> {
    const cfg = this.cfg;
    // Static seller/tax configuration is validated before anything is locked, allocated or sent.
    assertEimsInvoiceConfig(cfg);

    const invoice = await this.loadInvoiceForMapping(invoiceId);
    if (invoice.eimsIrn) return this.toView(invoice);

    // Authenticate before reserving: the source system comes from the token, and the state row is
    // keyed by it. A login failure here costs nothing — no counter has been consumed yet.
    const session = await this.auth.getSessionContext();

    const reservation = await this.reserve(invoiceId, session.systemNumber);
    if (!reservation) return this.getEimsStatus(invoiceId);

    // The request can only be built now: InvoiceCounter and PreviousIrn come from the reservation.
    const request = toEimsInvoice(
      invoice,
      buildEimsSeller(cfg),
      buildEimsContext(cfg, {
        // Our own invoice number is the document number; EIMS only requires it to be unique.
        documentNumber: invoice.invoiceNumber,
        invoiceCounter: reservation.invoiceCounter,
        previousIrn: reservation.previousIrn,
        session,
      }),
    );

    let irn: string;
    let ackDate: string | undefined;
    try {
      // Deliberately outside every transaction — no DB lock is held across the wire.
      const result = await this.submit(request);
      irn = result.irn;
      ackDate = result.ackDate;
    } catch (err) {
      await this.settleFailure(invoiceId, reservation, err);
      throw err;
    }

    await this.settleSuccess(invoiceId, reservation, irn, ackDate);
    this.logger.log(
      `Invoice ${invoice.invoiceNumber} registered with EIMS (counter ${reservation.invoiceCounter})`,
    );
    return this.getEimsStatus(invoiceId);
  }

  /**
   * Verify a registered invoice at `POST /v1/verify`.
   *
   * Requires a stored IRN. An invoice whose submission was never acknowledged cannot be reconciled
   * here — the gateway offers no lookup by document number — so it must be resolved with MoR and
   * recorded through `resolveEimsRegistration`.
   */
  async verifyInvoiceWithEims(invoiceId: string): Promise<EimsVerifyResponse> {
    const invoice = await this.loadInvoiceRow(this.dataSource.manager, invoiceId);
    if (!invoice.eimsIrn) {
      throw new BadRequestException({
        code: "EIMS_NO_IRN",
        message:
          `Invoice ${invoice.invoiceNumber} has no EIMS IRN to verify (status ${invoice.eimsStatus}). ` +
          "EIMS can only be queried by IRN, so an unacknowledged submission must be resolved with MoR first.",
      });
    }
    return this.queryVerify(invoice.eimsIrn);
  }

  /**
   * `POST /v1/verify` for one IRN, with the one check that always applies: the gateway must echo
   * an `Irn` back. A 200 without it is not a confirmation of anything.
   *
   * The request property is lowercase `irn`; the response spells it `Irn`. The two are never
   * compared — the supplied collection's own fixture uses different example values on each side,
   * so equality there would assert a property of the mock rather than of the gateway.
   *
   * Bearer-authenticated but unsigned, via `postBearer` — see that method for why.
   */
  private async queryVerify(irn: string): Promise<EimsVerifyResponse> {
    const response = await this.client.postBearer<EimsVerifyRequest, EimsVerifyResponse>(
      "/v1/verify",
      { irn },
    );
    if (!response?.body?.Irn?.trim()) {
      throw new EimsApiException(
        "SCHEMA_VALIDATION",
        "EIMS verify returned no Irn in its response body",
        response?.statusCode,
      );
    }
    return response;
  }

  /**
   * Refuse a manual resolution unless the gateway confirms *both* halves of the claim: that this
   * IRN is the one it holds, and that it belongs to this invoice.
   *
   * The document-number check is against `DocumentDetails.DocumentNumber`, which registration set
   * from our own `invoiceNumber` — the only field tying an IRN back to a row in this database.
   *
   * Recording a wrong IRN is not a local mistake: it marks an unregistered invoice as filed and
   * chains every later document to a stranger's reference, so both checks are refusals rather
   * than warnings.
   */
  private async assertIrnBelongsToInvoice(
    irn: string,
    expectedDocumentNumber: string,
  ): Promise<void> {
    const response = await this.queryVerify(irn);
    const returnedIrn = response.body?.Irn?.trim();
    const documentNumber = response.body?.DocumentDetails?.DocumentNumber?.trim();

    if (returnedIrn !== irn) {
      throw new ConflictException({
        code: "EIMS_RESOLVE_IRN_MISMATCH",
        message:
          `EIMS answered the lookup for IRN ${irn} with ${returnedIrn ?? "(none)"}. ` +
          "Refusing to record it — recheck the IRN in the MoR portal.",
      });
    }

    if (documentNumber !== expectedDocumentNumber) {
      throw new ConflictException({
        code: "EIMS_RESOLVE_DOCUMENT_MISMATCH",
        message:
          `EIMS reports IRN ${irn} against document ${documentNumber ?? "(none)"}, not ` +
          `${expectedDocumentNumber}. Refusing to record it — recheck the IRN in the MoR portal.`,
      });
    }
  }

  /**
   * Manual reconciliation of a blocked system number.
   *
   * With an `irn` (found in the MoR portal) the invoice is recorded as registered and the chain
   * resumes from it. With `discard` the invoice is marked failed and the chain resumes from the
   * previous IRN. Either way the block is cleared — this is the only exit from an ambiguous result.
   *
   * An IRN is never taken on trust: it is verified at the gateway first, and the document it
   * belongs to must be *this* invoice. A transposed digit would otherwise chain every later
   * document to a stranger's IRN and mark this invoice registered when it is not.
   */
  async resolveEimsRegistration(
    invoiceId: string,
    input: { irn?: string; discard?: boolean },
  ): Promise<EimsInvoiceStatusView> {
    const irn = input.irn?.trim();
    if (!irn && !input.discard) {
      throw new BadRequestException({
        code: "EIMS_RESOLVE_INPUT_REQUIRED",
        message: "Provide the IRN confirmed with MoR, or discard: true to abandon the submission",
      });
    }

    // Outside the transaction: no lock is held across the wire, and a refused verification must
    // leave the block exactly as it was.
    if (irn) {
      const invoice = await this.loadInvoiceRow(this.dataSource.manager, invoiceId);
      await this.assertIrnBelongsToInvoice(irn, invoice.invoiceNumber);
    }

    // Same source of truth as registration: the state row is keyed by the token's system number.
    const session = await this.auth.getSessionContext();

    await this.dataSource.transaction(async (manager) => {
      const state = await this.lockSystemState(manager, session.systemNumber);
      if (state.inFlightInvoiceId && state.inFlightInvoiceId !== invoiceId) {
        throw new ConflictException({
          code: "EIMS_RESOLVE_WRONG_INVOICE",
          message: `The in-flight EIMS submission is invoice ${state.inFlightInvoiceId}, not ${invoiceId}`,
        });
      }
      const invoice = await this.lockInvoice(manager, invoiceId);
      if (invoice.eimsIrn) {
        throw new ConflictException({
          code: "EIMS_ALREADY_REGISTERED",
          message: `Invoice ${invoice.invoiceNumber} already has IRN ${invoice.eimsIrn}`,
        });
      }

      await manager.update(Invoice, invoiceId, {
        eimsStatus: irn ? EimsInvoiceStatus.Registered : EimsInvoiceStatus.Failed,
        eimsIrn: irn ?? null,
      });
      await manager.update(EimsSystemState, state.id, {
        // Only a confirmed IRN may advance the chain; a discard leaves it where it was.
        ...(irn ? { previousIrn: irn } : {}),
        inFlightInvoiceId: null,
        inFlightCounter: null,
        blockedReason: null,
      });
    });

    this.logger.warn(
      `EIMS block on invoice ${invoiceId} resolved manually (${irn ? "IRN recorded" : "discarded"})`,
    );
    return this.getEimsStatus(invoiceId);
  }

  async getEimsStatus(invoiceId: string): Promise<EimsInvoiceStatusView> {
    return this.toView(await this.loadInvoiceRow(this.dataSource.manager, invoiceId));
  }

  // ── transactions ─────────────────────────────────────────────────────────────────────────────

  /**
   * TX1. Consume a counter and record the holder, committed before any HTTP call. Returns `null`
   * when the invoice turned out to be registered already (checked under the lock).
   */
  private async reserve(invoiceId: string, systemNumber: string): Promise<Reservation | null> {
    return this.dataSource.transaction(async (manager) => {
      const state = await this.lockSystemState(manager, systemNumber);

      if (state.blockedReason) {
        throw new ConflictException({
          code: "EIMS_SYSTEM_BLOCKED",
          message:
            `EIMS registration is blocked for system ${systemNumber}: ${state.blockedReason}. ` +
            "Resolve the affected invoice before registering anything else.",
        });
      }
      if (state.inFlightInvoiceId) {
        throw new ConflictException({
          code: "EIMS_SUBMISSION_IN_FLIGHT",
          message:
            `A submission for invoice ${state.inFlightInvoiceId} is already in flight on system ` +
            `${systemNumber}. Wait for it to settle, or resolve it if the process was interrupted.`,
        });
      }

      const invoice = await this.lockInvoice(manager, invoiceId);
      if (invoice.eimsIrn) return null;

      const invoiceCounter = Number(state.nextInvoiceCounter);
      const previousIrn = state.previousIrn ?? "";

      // Counter consumed here, not on success: once an attempt begins it can never be reused,
      // whatever happens next. A gap is harmless at MoR; a collision is not.
      await manager.update(EimsSystemState, state.id, {
        nextInvoiceCounter: invoiceCounter + 1,
        inFlightInvoiceId: invoiceId,
        inFlightCounter: invoiceCounter,
      });
      await manager.update(Invoice, invoiceId, {
        eimsStatus: EimsInvoiceStatus.Submitting,
        eimsInvoiceCounter: invoiceCounter,
        eimsSubmittedAt: new Date(),
        eimsLastError: null,
      });

      return { stateId: state.id, invoiceCounter, previousIrn };
    });
  }

  /** TX2a. Record the IRN, advance the chain, release the reservation. */
  private async settleSuccess(
    invoiceId: string,
    reservation: Reservation,
    irn: string,
    ackDate?: string,
  ): Promise<void> {
    await this.dataSource.transaction(async (manager) => {
      await this.lockInvoice(manager, invoiceId);
      await manager.update(Invoice, invoiceId, {
        eimsStatus: EimsInvoiceStatus.Registered,
        eimsIrn: irn,
        eimsAckDate: ackDate ?? null,
        eimsLastError: null,
      });
      await manager.update(EimsSystemState, reservation.stateId, {
        previousIrn: irn,
        inFlightInvoiceId: null,
        inFlightCounter: null,
        blockedReason: null,
      });
    });
  }

  /**
   * TX2b. A deterministic rejection releases the reservation; an ambiguous result keeps it and
   * blocks the system number, because `PreviousIrn` is now unknown for every later document.
   * The counter stays consumed either way.
   */
  private async settleFailure(
    invoiceId: string,
    reservation: Reservation,
    err: unknown,
  ): Promise<void> {
    const api = err instanceof EimsApiException ? err : null;
    const deterministic = api ? DETERMINISTIC_KINDS.has(api.kind) : false;
    const status = deterministic ? EimsInvoiceStatus.Failed : EimsInvoiceStatus.Unknown;
    const lastError: EimsInvoiceError = {
      kind: api?.kind ?? "UNKNOWN",
      message: (err as Error)?.message ?? "unknown error",
      httpStatus: api?.httpStatus,
      details: api?.details,
      at: new Date().toISOString(),
    };

    await this.dataSource.transaction(async (manager) => {
      await manager.update(Invoice, invoiceId, {
        eimsStatus: status,
        eimsLastError: lastError,
      } as QueryDeepPartialEntity<Invoice>);

      await manager.update(
        EimsSystemState,
        reservation.stateId,
        deterministic
          ? { inFlightInvoiceId: null, inFlightCounter: null, blockedReason: null }
          : {
              blockedReason:
                `Invoice ${invoiceId} was submitted with counter ${reservation.invoiceCounter} but ` +
                `never acknowledged (${lastError.kind}). Its IRN is unknown, so no further document ` +
                "can be chained until it is resolved with MoR.",
            },
      );
    });

    this.logger.error(`Invoice ${invoiceId} EIMS registration ${status}: ${lastError.message}`);
  }

  // ── internals ────────────────────────────────────────────────────────────────────────────────

  /** A non-empty IRN is the only success signal; anything else is a failed registration. */
  private async submit(request: EimsInvoiceRequest): Promise<{ irn: string; ackDate?: string }> {
    const response = await this.client.postSigned<EimsInvoiceRequest, EimsRegisterResponse>(
      "/v1/register",
      request,
    );
    const irn = response?.body?.irn;
    if (!irn) {
      // The gateway answered, so this is deterministic: the document is not registered.
      throw new EimsApiException(
        "SCHEMA_VALIDATION",
        `EIMS register returned no IRN${response?.body?.errorMessage ? `: ${response.body.errorMessage}` : ""}`,
        response?.statusCode,
      );
    }
    return { irn, ackDate: response.body?.ackDate };
  }

  private async lockInvoice(manager: EntityManager, invoiceId: string): Promise<Invoice> {
    const invoice = await manager
      .createQueryBuilder(Invoice, "invoice")
      .setLock("pessimistic_write")
      .where("invoice.id = :invoiceId", { invoiceId })
      .getOne();
    if (!invoice) throw new NotFoundException(`Invoice ${invoiceId} not found`);
    return invoice;
  }

  /** Locks the system-state row, creating it on first use. */
  private async lockSystemState(
    manager: EntityManager,
    systemNumber: string,
  ): Promise<EimsSystemState> {
    const select = () =>
      manager
        .createQueryBuilder(EimsSystemState, "state")
        .setLock("pessimistic_write")
        .where("state.system_number = :systemNumber", { systemNumber })
        .getOne();

    const existing = await select();
    if (existing) return existing;

    await manager.query(
      `INSERT INTO freight.eims_system_state (system_number) VALUES ($1)
       ON CONFLICT (system_number) DO NOTHING`,
      [systemNumber],
    );
    const created = await select();
    if (!created) throw new Error(`Could not initialise EIMS system state for ${systemNumber}`);
    return created;
  }

  /** Header + buyer + lines — everything the mapper needs. */
  private async loadInvoiceForMapping(
    invoiceId: string,
  ): Promise<Invoice & { lines: EimsMapperLine[] }> {
    const invoice = await this.dataSource.getRepository(Invoice).findOne({
      where: { id: invoiceId },
      relations: { company: true, companyProfile: true },
    });
    if (!invoice) throw new NotFoundException(`Invoice ${invoiceId} not found`);

    const lines: EimsMapperLine[] = await this.dataSource.query(
      `SELECT charge_type AS "chargeType", description, quantity, unit_rate AS "unitRate",
              amount, currency, metadata
         FROM freight.invoice_lines
        WHERE invoice_id = $1 AND deleted_at IS NULL
        ORDER BY created_at ASC`,
      [invoiceId],
    );
    return Object.assign(invoice, { lines });
  }

  private async loadInvoiceRow(manager: EntityManager, invoiceId: string): Promise<Invoice> {
    const invoice = await manager.findOne(Invoice, { where: { id: invoiceId } });
    if (!invoice) throw new NotFoundException(`Invoice ${invoiceId} not found`);
    return invoice;
  }

  private toView(invoice: Invoice): EimsInvoiceStatusView {
    const counter = invoice.eimsInvoiceCounter;
    return {
      invoiceId: invoice.id,
      invoiceNumber: invoice.invoiceNumber,
      eimsStatus: invoice.eimsStatus ?? EimsInvoiceStatus.NotSubmitted,
      eimsIrn: invoice.eimsIrn ?? null,
      eimsInvoiceCounter: counter === null || counter === undefined ? null : Number(counter),
      eimsSubmittedAt: invoice.eimsSubmittedAt ?? null,
      eimsAckDate: invoice.eimsAckDate ?? null,
      eimsLastError: invoice.eimsLastError ?? null,
    };
  }
}