import {
  BadRequestException,
  Injectable,
  NotFoundException,
} from '@nestjs/common';
import { PrismaService } from '../prisma/prisma.service';
import { AuditLogService } from '../audit/audit-log.service';
import { WebhooksService } from '../webhooks/webhooks.service';
import { AutomationService } from '../automation/automation.service';
import { BottlingBatch, Prisma } from '../../generated/prisma';
import { CreateBottlingBatchDto } from './dto/create-bottling-batch.dto';
import { UpdateBottlingBatchDto } from './dto/update-bottling-batch.dto';

const bottlingBatchInclude = {
  honeyBatch: true,
  product: true,
} as const;

export interface BottlingBatchFilter {
  honeyBatchId?: string;
}

/**
 * Amounts are kept in kilograms with gram precision. Rounding on every write
 * keeps a honey batch's remaining amount from drifting when a bottling batch
 * is corrected or removed and its amount is given back.
 */
function roundKg(amount: number): number {
  return Math.round(amount * 1000) / 1000;
}

const INSUFFICIENT_AMOUNT_MESSAGE =
  'Abfüllmenge übersteigt die verfügbare Menge der Honigcharge';

type Tx = Prisma.TransactionClient;

/**
 * Deducts `amount` kg from a honey batch in one conditional UPDATE, so the
 * database - not a value read earlier - decides whether enough is left.
 * A batch without a recorded amount (null) is not tracked and stays null.
 */
async function takeFromHoneyBatch(
  tx: Tx,
  honeyBatchId: string,
  amount: number,
): Promise<void> {
  const current = await tx.honeyBatch.findUnique({
    where: { id: honeyBatchId },
    select: { amount: true },
  });
  if (!current) {
    throw new NotFoundException('Honey batch not found');
  }
  if (current.amount === null) {
    await tx.honeyBatch.update({
      where: { id: honeyBatchId },
      data: { status: 'BOTTLED' },
    });
    return;
  }
  // Tolerance of half a gram absorbs float noise from earlier writes.
  const booked = await tx.honeyBatch.updateMany({
    where: { id: honeyBatchId, amount: { gte: amount - 0.0005 } },
    data: { amount: { decrement: amount }, status: 'BOTTLED' },
  });
  if (booked.count === 0) {
    throw new BadRequestException(INSUFFICIENT_AMOUNT_MESSAGE);
  }
  await normalizeAmount(tx, honeyBatchId);
}

async function giveBackToHoneyBatch(
  tx: Tx,
  honeyBatchId: string,
  amount: number,
): Promise<void> {
  await tx.honeyBatch.updateMany({
    where: { id: honeyBatchId, amount: { not: null } },
    data: { amount: { increment: amount } },
  });
  await normalizeAmount(tx, honeyBatchId);
}

/** Keeps gram precision and clamps float noise below zero to exactly 0. */
async function normalizeAmount(tx: Tx, honeyBatchId: string): Promise<void> {
  const row = await tx.honeyBatch.findUnique({
    where: { id: honeyBatchId },
    select: { amount: true },
  });
  if (row?.amount == null) return;
  const normalized = Math.max(0, roundKg(row.amount));
  if (normalized !== row.amount) {
    await tx.honeyBatch.update({
      where: { id: honeyBatchId },
      data: { amount: normalized },
    });
  }
}

@Injectable()
export class BottlingService {
  constructor(
    private readonly prisma: PrismaService,
    private readonly auditLog: AuditLogService,
    private readonly webhooks: WebhooksService,
    private readonly automation: AutomationService,
  ) {}

  async findAll(filter: BottlingBatchFilter = {}) {
    return this.prisma.bottlingBatch.findMany({
      where: { honeyBatchId: filter.honeyBatchId },
      include: bottlingBatchInclude,
      orderBy: { date: 'desc' },
    });
  }

  async findById(id: string) {
    const bottlingBatch = await this.prisma.bottlingBatch.findUnique({
      where: { id },
      include: bottlingBatchInclude,
    });
    if (!bottlingBatch) {
      throw new NotFoundException('Bottling batch not found');
    }
    return bottlingBatch;
  }

  async create(dto: CreateBottlingBatchDto, actingUserId: string) {
    const honeyBatch = await this.prisma.honeyBatch.findUnique({
      where: { id: dto.honeyBatchId },
    });
    if (!honeyBatch) {
      throw new NotFoundException('Honey batch not found');
    }
    if (dto.productId) {
      const product = await this.prisma.product.findUnique({
        where: { id: dto.productId },
      });
      if (!product) {
        throw new NotFoundException('Product not found');
      }
    }

    const totalAmount = roundKg((dto.jarSize * dto.jarCount) / 1000);
    if (honeyBatch.amount !== null && totalAmount > honeyBatch.amount) {
      throw new BadRequestException(INSUFFICIENT_AMOUNT_MESSAGE);
    }

    const lotNumber =
      dto.lotNumber ??
      (await this.automation.generateNumber('BOTTLING_LOT_NUMBER_FORMAT'));
    if (!lotNumber) {
      throw new BadRequestException(
        'Los-/Chargennummer erforderlich (oder Automatisierung "Los-/Chargennummer-Format" aktivieren)',
      );
    }

    const bottlingBatch: BottlingBatch = await this.prisma.$transaction(
      async (tx) => {
        // Booked against the stored amount inside the transaction, never
        // against the value read above: two bottlings submitted at the same
        // time (double tap, two devices) must not both pass the check and
        // overwrite each other's deduction.
        await takeFromHoneyBatch(tx, dto.honeyBatchId, totalAmount);
        return tx.bottlingBatch.create({
          data: {
            honeyBatchId: dto.honeyBatchId,
            productId: dto.productId,
            date: new Date(dto.date),
            jarSize: dto.jarSize,
            jarCount: dto.jarCount,
            totalAmount,
            bestBeforeDate: new Date(dto.bestBeforeDate),
            lotNumber,
            userId: actingUserId,
          },
        });
      },
    );

    await this.auditLog.record({
      entityType: 'BottlingBatch',
      entityId: bottlingBatch.id,
      action: 'CREATE',
      userId: actingUserId,
      afterData: bottlingBatch,
    });

    const created = await this.findById(bottlingBatch.id);
    await this.webhooks.dispatch('batch.updated', created.honeyBatch);
    return created;
  }

  /**
   * Corrects any field of an existing bottling batch. Changing the honey
   * batch, the jar size or the jar count also rebalances the remaining amount
   * of the affected honey batch(es): the previously bottled amount is given
   * back before the corrected amount is taken again, so a correction never
   * double-charges the source batch.
   */
  async update(id: string, dto: UpdateBottlingBatchDto, actingUserId: string) {
    const before = await this.findById(id);

    if (dto.productId) {
      const product = await this.prisma.product.findUnique({
        where: { id: dto.productId },
      });
      if (!product) {
        throw new NotFoundException('Product not found');
      }
    }

    const honeyBatchId = dto.honeyBatchId ?? before.honeyBatchId;
    const movedToOtherHoneyBatch = honeyBatchId !== before.honeyBatchId;
    const jarSize = dto.jarSize ?? before.jarSize;
    const jarCount = dto.jarCount ?? before.jarCount;
    const totalAmount = roundKg((jarSize * jarCount) / 1000);

    const targetHoneyBatch = movedToOtherHoneyBatch
      ? await this.prisma.honeyBatch.findUnique({ where: { id: honeyBatchId } })
      : before.honeyBatch;
    if (!targetHoneyBatch) {
      throw new NotFoundException('Honey batch not found');
    }

    // Early, friendly check against the amounts read above. The booking
    // itself happens atomically inside the transaction below.
    const availableOnTarget =
      targetHoneyBatch.amount === null
        ? null
        : roundKg(
            targetHoneyBatch.amount +
              (movedToOtherHoneyBatch ? 0 : before.totalAmount),
          );
    if (availableOnTarget !== null && totalAmount > availableOnTarget) {
      throw new BadRequestException(INSUFFICIENT_AMOUNT_MESSAGE);
    }

    // A duplicate lotNumber surfaces as Prisma P2002 and is turned into a
    // 409 with a field-specific message by AllExceptionsFilter.
    await this.prisma.$transaction(async (tx) => {
      const amountChanged =
        movedToOtherHoneyBatch || totalAmount !== before.totalAmount;
      if (amountChanged) {
        // Give the previous amount back first, then take the corrected one -
        // a correction never double-charges the source batch.
        await giveBackToHoneyBatch(tx, before.honeyBatchId, before.totalAmount);
        await takeFromHoneyBatch(tx, honeyBatchId, totalAmount);
      }
      if (movedToOtherHoneyBatch) {
        await tx.honeyBatch.update({
          where: { id: honeyBatchId },
          data: { status: 'BOTTLED' },
        });
      }
      await tx.bottlingBatch.update({
        where: { id },
        data: {
          honeyBatchId,
          productId: dto.productId === undefined ? undefined : dto.productId,
          date: dto.date ? new Date(dto.date) : undefined,
          jarSize,
          jarCount,
          totalAmount,
          bestBeforeDate: dto.bestBeforeDate
            ? new Date(dto.bestBeforeDate)
            : undefined,
          lotNumber: dto.lotNumber,
        },
      });
    });

    const bottlingBatch = await this.findById(id);
    await this.auditLog.record({
      entityType: 'BottlingBatch',
      entityId: id,
      action: 'UPDATE',
      userId: actingUserId,
      beforeData: before,
      afterData: bottlingBatch,
    });
    await this.webhooks.dispatch('batch.updated', bottlingBatch.honeyBatch);
    return bottlingBatch;
  }

  /**
   * Removes a bottling batch that was entered by mistake and gives its amount
   * back to the honey batch. The full record is kept in the audit log
   * (action DELETE, beforeData), so the history survives the row.
   *
   * The honey batch's status is deliberately left untouched: the status it
   * held before being bottled is not recoverable here, and guessing it would
   * write a fact that never happened.
   */
  async remove(id: string, actingUserId: string) {
    const before = await this.findById(id);

    await this.prisma.$transaction(async (tx) => {
      await tx.bottlingBatch.delete({ where: { id } });
      await giveBackToHoneyBatch(tx, before.honeyBatchId, before.totalAmount);
    });

    await this.auditLog.record({
      entityType: 'BottlingBatch',
      entityId: id,
      action: 'DELETE',
      userId: actingUserId,
      beforeData: before,
    });
    await this.webhooks.dispatch('batch.updated', before.honeyBatch);
    return { id };
  }
}