import type { FastifyInstance, FastifyReply, FastifyRequest } from "fastify";
import { z } from "zod";
import { paginate, type PaginationInput } from "../fixtures/featureFixtures.js";
import { findProject } from "../fixtures/projectFixtures.js";
import {
  applyRelationshipFilters,
  createRelationship,
  deleteRelationship,
  findRelationship,
  listRelationshipsForProject,
} from "../fixtures/relationshipFixtures.js";
import { getRequestId } from "../plugins/requestId.js";
import type {
  RelationshipListFilters,
  RelationshipType,
  ReviewMutationResponseDto,
} from "../types/api.js";
import { errorEnvelope, successEnvelope } from "../utils/envelope.js";
import {
  getIdempotencyKey,
  getIdempotentResponse,
  setIdempotentResponse,
} from "../utils/idempotency.js";

const idSchema = z.string().min(1).regex(/^[A-Za-z0-9-]+$/);
const projectParamsSchema = z.object({ projectId: idSchema });
const relationshipParamsSchema = z.object({
  projectId: idSchema,
  relationshipId: idSchema,
});
const paginationQuerySchema = z.object({
  page: z.coerce.number().int().positive().default(1),
  pageSize: z.coerce.number().int().positive().max(100).default(25),
  cursor: z.string().optional(),
  sort: z.string().optional(),
});
const relationshipTypes = [
  "depends_on",
  "conflicts_with",
  "duplicates",
  "supersedes",
  "belongs_to",
  "implements",
  "references",
] as const;
const relationshipQuerySchema = paginationQuerySchema.extend({
  from: z.string().optional(),
  to: z.string().optional(),
  type: z.string().optional(),
  confidence: z.coerce.number().optional(),
  strength: z.coerce.number().int().min(1).max(5).optional(),
});
const createRelationshipBodySchema = z.object({
  from: z.string().optional(),
  to: z.string().optional(),
  type: z.enum(relationshipTypes).optional(),
  rationale: z.string().optional(),
  strength: z.number().int().min(1).max(5).optional(),
  confidence: z.number().min(0).max(5).optional(),
});

const sendValidationError = (
  request: FastifyRequest,
  reply: FastifyReply,
  validation: z.ZodIssue[],
) =>
  reply.status(400).send(
    errorEnvelope(
      "VALIDATION_ERROR",
      "Request validation failed",
      getRequestId(request),
      validation.map((issue) => ({
        field: issue.path.join("."),
        message: issue.message,
        code: issue.code,
      })),
    ),
  );

const parseParams = <TSchema extends z.ZodTypeAny>(
  schema: TSchema,
  request: FastifyRequest,
  reply: FastifyReply,
): z.output<TSchema> | undefined => {
  const parsed = schema.safeParse(request.params);
  if (!parsed.success) {
    sendValidationError(request, reply, parsed.error.issues);
    return undefined;
  }
  return parsed.data;
};

const parseQuery = <TSchema extends z.ZodTypeAny>(
  schema: TSchema,
  request: FastifyRequest,
  reply: FastifyReply,
): z.output<TSchema> | undefined => {
  const parsed = schema.safeParse(request.query);
  if (!parsed.success) {
    sendValidationError(request, reply, parsed.error.issues);
    return undefined;
  }
  return parsed.data;
};

const ensureProject = (
  request: FastifyRequest,
  reply: FastifyReply,
  projectId: string,
) => {
  const project = findProject(projectId);
  if (!project) {
    reply.status(404).send(
      errorEnvelope(
        "PROJECT_NOT_FOUND",
        `Project '${projectId}' was not found.`,
        getRequestId(request),
      ),
    );
    return undefined;
  }
  return project;
};

const splitCsv = (value: string | undefined): string[] =>
  value?.split(",").map((item) => item.trim()).filter(Boolean) ?? [];

const sortByField = <T extends Record<string, unknown>>(
  items: T[],
  sort: string | undefined,
): T[] => {
  if (!sort) return items;
  const [field, direction = "asc"] = sort.split(":");
  if (!field) return items;
  return [...items].sort((left, right) => {
    const comparison = String(left[field] ?? "").localeCompare(
      String(right[field] ?? ""),
      undefined,
      { numeric: true },
    );
    return direction === "desc" ? -comparison : comparison;
  });
};

const toPaginationInput = (
  query: z.output<typeof paginationQuerySchema>,
  filters: PaginationInput["filters"],
): PaginationInput => ({
  page: query.page,
  pageSize: query.pageSize,
  cursor: query.cursor,
  sort: query.sort,
  filters,
});

const toFilters = (
  query: z.output<typeof relationshipQuerySchema>,
): RelationshipListFilters => ({
  ...(query.from ? { from: query.from } : {}),
  ...(query.to ? { to: query.to } : {}),
  ...(query.type ? { type: splitCsv(query.type) as RelationshipType[] } : {}),
  ...(query.confidence !== undefined ? { confidence: query.confidence } : {}),
  ...(query.strength !== undefined ? { strength: query.strength } : {}),
  ...(query.cursor ? { cursor: query.cursor } : {}),
});

const getRequiredIdempotencyKey = (
  request: FastifyRequest,
  reply: FastifyReply,
): string | undefined => {
  const rawKey = request.headers["idempotency-key"];
  const idempotencyKey = Array.isArray(rawKey) ? rawKey[0] : rawKey;
  if (!idempotencyKey?.trim()) {
    reply.status(400).send(
      errorEnvelope(
        "IDEMPOTENCY_KEY_REQUIRED",
        "Idempotency-Key header is required.",
        getRequestId(request),
      ),
    );
    return undefined;
  }
  return idempotencyKey;
};

const sendRelationshipNotFound = (
  request: FastifyRequest,
  reply: FastifyReply,
  relationshipId: string,
) =>
  reply.status(404).send(
    errorEnvelope(
      "RELATIONSHIP_NOT_FOUND",
      `Relationship '${relationshipId}' was not found.`,
      getRequestId(request),
    ),
  );

export const registerRelationshipRoutes = async (app: FastifyInstance) => {
  app.get("/api/projects/:projectId/relationships", async (request, reply) => {
    const params = parseParams(projectParamsSchema, request, reply);
    if (!params) return reply;
    if (!ensureProject(request, reply, params.projectId)) return reply;
    const query = parseQuery(relationshipQuerySchema, request, reply);
    if (!query) return reply;

    const filters = toFilters(query);
    const relationships = sortByField(
      applyRelationshipFilters(
        listRelationshipsForProject(params.projectId),
        filters,
      ),
      query.sort,
    );

    return successEnvelope(
      paginate(relationships, toPaginationInput(query, filters)),
      getRequestId(request),
    );
  });

  app.get(
    "/api/projects/:projectId/relationships/:relationshipId",
    async (request, reply) => {
      const params = parseParams(relationshipParamsSchema, request, reply);
      if (!params) return reply;
      if (!ensureProject(request, reply, params.projectId)) return reply;
      const relationship = findRelationship(params.projectId, params.relationshipId);
      if (!relationship) {
        return sendRelationshipNotFound(request, reply, params.relationshipId);
      }
      return successEnvelope(relationship, getRequestId(request));
    },
  );

  app.post("/api/projects/:projectId/relationships", async (request, reply) => {
    const params = parseParams(projectParamsSchema, request, reply);
    if (!params) return reply;
    if (!ensureProject(request, reply, params.projectId)) return reply;
    const idempotencyKey = getRequiredIdempotencyKey(request, reply);
    if (!idempotencyKey) return reply;
    const cacheKey = getIdempotencyKey(request.method, request.url, idempotencyKey);
    const replay = getIdempotentResponse<unknown>(cacheKey);
    if (replay) return reply.status(replay.statusCode).send(replay.body);

    const parsedBody = createRelationshipBodySchema.safeParse(request.body);
    if (
      !parsedBody.success ||
      !parsedBody.data.from?.trim() ||
      !parsedBody.data.to?.trim() ||
      !parsedBody.data.type ||
      !parsedBody.data.rationale?.trim()
    ) {
      return reply.status(400).send(
        errorEnvelope(
          "RELATIONSHIP_VALIDATION_FAILED",
          "from, to, type and rationale are required to create a relationship.",
          getRequestId(request),
        ),
      );
    }

    const body = successEnvelope(
      createRelationship(params.projectId, {
        ...parsedBody.data,
        from: parsedBody.data.from,
        to: parsedBody.data.to,
        type: parsedBody.data.type,
        rationale: parsedBody.data.rationale,
      }),
      getRequestId(request),
    );
    setIdempotentResponse(cacheKey, { statusCode: 201, body });
    return reply.status(201).send(body);
  });

  app.delete(
    "/api/projects/:projectId/relationships/:relationshipId",
    async (request, reply) => {
      const params = parseParams(relationshipParamsSchema, request, reply);
      if (!params) return reply;
      if (!ensureProject(request, reply, params.projectId)) return reply;
      const idempotencyKey = getRequiredIdempotencyKey(request, reply);
      if (!idempotencyKey) return reply;
      const cacheKey = getIdempotencyKey(
        request.method,
        request.url,
        idempotencyKey,
      );
      const replay = getIdempotentResponse<unknown>(cacheKey);
      if (replay) return reply.status(replay.statusCode).send(replay.body);

      const relationship = deleteRelationship(
        params.projectId,
        params.relationshipId,
      );
      if (!relationship) {
        return sendRelationshipNotFound(request, reply, params.relationshipId);
      }

      const body = successEnvelope<ReviewMutationResponseDto>(
        {
          success: true,
          message: `Relationship '${params.relationshipId}' deleted.`,
          updatedEntityId: params.relationshipId,
          affectedEntities: [params.relationshipId],
        },
        getRequestId(request),
      );
      setIdempotentResponse(cacheKey, { statusCode: 200, body });
      return reply.status(200).send(body);
    },
  );
};