import {
  BadRequestException,
  ConflictException,
  ForbiddenException,
  Inject,
  Injectable,
  NotFoundException,
} from '@nestjs/common';
import { PaginatedResponse } from '@edr/types';
import { CreateRateDto } from '../dto/create-rate.dto';
import { ListRatesQueryDto } from '../dto/list-rule-engine-query.dto';
import { UpdateRateDto } from '../dto/update-rate.dto';
import { Rate } from '../entities/rate.entity';
import { deriveRateType } from '../entities/rate-type.util';
import { allowedRateUnits, isRateUnitAllowed } from '../entities/rate-unit.util';
import { IRatesRepository, RATES_REPOSITORY } from '../interfaces/rates.repository.interface';

@Injectable()
export class RatesService {
  constructor(
    @Inject(RATES_REPOSITORY)
    private readonly repository: IRatesRepository,
  ) {}

  /** List rates — standard paginated envelope with server-side search. */
  async findAll(query: ListRatesQueryDto): Promise<PaginatedResponse<Rate>> {
    return this.repository.findPaged(query);
  }

  /** Return all currently LIVE rates. */
  async findLiveRates(): Promise<Rate[]> {
    return this.repository.findLiveRates();
  }

  /** Get a rate by ID. */
  async findById(id: string): Promise<Rate> {
    const entity = await this.repository.findById(id);
    if (!entity) throw new NotFoundException(`Rate ${id} not found`);
    return entity;
  }

  /**
   * Normalise + validate the weighting unit for a rate shape. Overweight is
   * always billed per excess ton, so its unit is forced to PER_TON regardless
   * of what the client sent. Every other shape must pick a unit the pricing
   * engine can actually apply (see `allowedRateUnits`).
   */
  private resolveRateUnit(
    appliesTo: Rate['appliesTo'],
    trigger: Rate['trigger'],
    requestedUnit: Rate['rateUnit'],
  ): Rate['rateUnit'] {
    // Overweight is per-ton, full stop.
    if (trigger === 'OVERWEIGHT') return 'PER_TON';

    if (!isRateUnitAllowed({ appliesTo, trigger, unit: requestedUnit })) {
      const allowed = allowedRateUnits({ appliesTo, trigger }).join(', ');
      throw new BadRequestException(
        `Rate unit "${requestedUnit}" is not valid for this rate. Allowed: ${allowed}.`,
      );
    }
    return requestedUnit;
  }

  /**
   * Reject a second rate with the same identity pattern (rateType + scope). With
   * effective-date windows gone, two LIVE/DRAFT rates for the same pattern would
   * make pricing ambiguous — so we allow exactly one per pattern.
   */
  private async assertNoDuplicatePattern(pattern: {
    rateType: string;
    rateUnit: string;
    containerTypeId: string | null;
    cargoTypeId: string | null;
    tradeDirection: string | null;
    ignoreId?: string;
  }): Promise<void> {
    const existing = await this.repository.findByPattern(pattern);
    if (existing && existing.id !== pattern.ignoreId) {
      throw new ConflictException(
        'A rate for this exact combination already exists. Edit or delete the existing rate instead of creating a duplicate.',
      );
    }
  }

  /** Create a rate in DRAFT status. */
  async create(dto: CreateRateDto, proposedByStaffId: string): Promise<Rate> {
    const appliesTo = dto.appliesTo as Rate['appliesTo'];
    const trigger = dto.trigger as Rate['trigger'];
    // Surcharges (trigger ≠ ALWAYS) carry no direction/scope — clear them so
    // the engine never accidentally narrows a surcharge by container/direction.
    const isSurcharge = trigger !== 'ALWAYS';
    const containerTypeId = isSurcharge ? null : (dto.containerTypeId ?? null);
    const cargoTypeId = isSurcharge ? null : (dto.cargoTypeId ?? null);
    const tradeDirection = isSurcharge ? null : (dto.tradeDirection ?? null);

    const rateType = deriveRateType({
      appliesTo,
      trigger,
      tradeDirection,
      isBulk: Boolean(cargoTypeId),
    });
    const rateUnit = this.resolveRateUnit(appliesTo, trigger, dto.rateUnit as Rate['rateUnit']);

    await this.assertNoDuplicatePattern({ rateType, rateUnit, containerTypeId, cargoTypeId, tradeDirection });

    return this.repository.create({
      appliesTo,
      trigger,
      rateType,
      containerTypeId,
      cargoTypeId,
      tradeDirection,
      currency: dto.currency ?? 'USD',
      rateValue: dto.rateValue,
      rateUnit,
      status: 'DRAFT',
      proposedByStaffId,
    });
  }

  /**
   * Update a DRAFT rate in place. Nothing prices off a draft, so a direct edit
   * is safe. A LIVE rate cannot take this path — see `applyApprovedUpdate`.
   */
  async update(id: string, dto: UpdateRateDto): Promise<Rate> {
    const existing = await this.findById(id);
    if (existing.status !== 'DRAFT') {
      throw new BadRequestException(
        existing.status === 'LIVE'
          ? 'A LIVE rate cannot be edited directly — file a rate change request so an approver can apply it.'
          : 'Only DRAFT rates can be updated',
      );
    }
    return this.applyUpdate(existing, dto);
  }

  /**
   * Apply an approved change request to a LIVE rate. Same validation as a
   * DRAFT edit — it just skips the DRAFT guard, because a LIVE rate reaching
   * here has already been through approval. Only ever called by
   * RateChangeRequestsService.approve.
   */
  async applyApprovedUpdate(id: string, dto: UpdateRateDto): Promise<Rate> {
    const existing = await this.findById(id);
    if (existing.status !== 'LIVE') {
      throw new BadRequestException(
        `Rate change requests apply to LIVE rates only — this rate is ${existing.status}.`,
      );
    }
    return this.applyUpdate(existing, dto);
  }

  /**
   * Validate a proposed patch against a rate without writing anything — lets a
   * change request be refused at submit time instead of surprising the
   * approver. Throws exactly what applying it would throw.
   */
  async assertUpdateValid(id: string, dto: UpdateRateDto): Promise<void> {
    await this.buildUpdate(await this.findById(id), dto);
  }

  private async applyUpdate(existing: Rate, dto: UpdateRateDto): Promise<Rate> {
    const updates = await this.buildUpdate(existing, dto);
    const updated = await this.repository.update(existing.id, updates);
    if (!updated) throw new NotFoundException(`Rate ${existing.id} not found`);
    return updated;
  }

  /**
   * The shared edit body: re-derives rateType, re-validates the unit against
   * the (possibly changed) shape, and guards pattern uniqueness. Status is
   * never touched — an approved edit to a LIVE rate stays LIVE. Pure apart
   * from the uniqueness read, so it doubles as the dry-run validator.
   */
  private async buildUpdate(existing: Rate, dto: UpdateRateDto): Promise<Partial<Rate>> {
    const id = existing.id;
    const updates: Partial<Rate> = {};

    const appliesTo = (dto.appliesTo as Rate['appliesTo']) ?? existing.appliesTo;
    const trigger = (dto.trigger as Rate['trigger']) ?? existing.trigger;
    const isSurcharge = trigger !== 'ALWAYS';

    if (dto.appliesTo) updates.appliesTo = appliesTo;
    if (dto.trigger) updates.trigger = trigger;

    const containerTypeId = isSurcharge
      ? null
      : dto.containerTypeId !== undefined
        ? dto.containerTypeId
        : existing.containerTypeId;
    const cargoTypeId = isSurcharge
      ? null
      : dto.cargoTypeId !== undefined
        ? dto.cargoTypeId
        : existing.cargoTypeId;
    const tradeDirection = isSurcharge
      ? null
      : dto.tradeDirection !== undefined
        ? dto.tradeDirection
        : existing.tradeDirection;

    updates.containerTypeId = containerTypeId ?? null;
    updates.cargoTypeId = cargoTypeId ?? null;
    updates.tradeDirection = tradeDirection ?? null;
    // Keep the derived rateType in sync with whatever changed.
    const rateType = deriveRateType({
      appliesTo,
      trigger,
      tradeDirection,
      isBulk: Boolean(cargoTypeId),
    });
    updates.rateType = rateType;

    // Re-validate the unit against the (possibly changed) shape; overweight is
    // forced to PER_TON.
    const requestedUnit = (dto.rateUnit as Rate['rateUnit']) ?? existing.rateUnit;
    updates.rateUnit = this.resolveRateUnit(appliesTo, trigger, requestedUnit);

    // Guard the pattern uniqueness for the new identity, ignoring this row.
    await this.assertNoDuplicatePattern({
      rateType,
      rateUnit: updates.rateUnit,
      containerTypeId: updates.containerTypeId,
      cargoTypeId: updates.cargoTypeId,
      tradeDirection: updates.tradeDirection,
      ignoreId: id,
    });

    updates.currency = dto.currency ?? existing.currency ?? 'USD';
    if (dto.rateValue !== undefined) updates.rateValue = dto.rateValue;
    return updates;
  }

  /** Submit a DRAFT rate for CEO approval. */
  async submitForApproval(id: string): Promise<Rate> {
    const rate = await this.findById(id);
    if (rate.status !== 'DRAFT') {
      throw new BadRequestException('Only DRAFT rates can be submitted for approval');
    }
    const updated = await this.repository.update(id, { status: 'PENDING_APPROVAL' });
    return updated!;
  }

  /** CEO approves a rate — moves to LIVE. */
  async approve(id: string, approverUserId: string, canSelfApprove = false): Promise<Rate> {
    const rate = await this.findById(id);
    if (rate.status !== 'PENDING_APPROVAL') {
      throw new BadRequestException('Only PENDING_APPROVAL rates can be approved');
    }
    // Separation of duties: the proposer cannot approve their own rate — except
    // super admins, who have full backoffice authority (propose + approve).
    // TODO: split approval into a distinct CEO/approver permission — a normal
    // proposer who also holds the approve permission is still the wrong signer.
    if (!canSelfApprove && approverUserId === rate.proposedByStaffId) {
      throw new ForbiddenException('You cannot approve a rate you proposed');
    }
    const updated = await this.repository.update(id, {
      status: 'LIVE',
      approvedByCeoId: approverUserId,
      approvedAt: new Date(),
    });
    return updated!;
  }

  /** Soft-delete a rate. */
  async remove(id: string): Promise<void> {
    await this.findById(id);
    await this.repository.softDelete(id);
  }
}