import { FreshContext, Handlers } from "$fresh/server.ts";
import { db } from "$root/databases/db.ts";
import {
  ajustements,
  enseignements,
  modules,
  notes,
  promotions,
  students,
  ueModules,
  ues,
} from "$root/databases/schema.ts";
import { AuthenticatedState } from "$root/defaults/interfaces.ts";
import { eq } from "npm:drizzle-orm@0.45.2";

const NOT_FOUND = () =>
  new Response(
    JSON.stringify({ error: "Ressource introuvable" }),
    { status: 404, headers: { "content-type": "application/json" } },
  );

const FORBIDDEN = () => new Response(null, { status: 403 });

export const handler: Handlers<null, AuthenticatedState> = {
  // #15 GET /promotions/{idPromo}
  async GET(
    _request: Request,
    context: FreshContext<AuthenticatedState>,
  ): Promise<Response> {
    if (context.state.session.eduPersonPrimaryAffiliation !== "employee") {
      return FORBIDDEN();
    }

    const promo = await db
      .select()
      .from(promotions)
      .where(eq(promotions.id, context.params.idPromo))
      .then((rows) => rows[0] ?? null);

    if (!promo) return NOT_FOUND();

    return new Response(JSON.stringify(promo), {
      headers: { "content-type": "application/json" },
    });
  },

  // #16 PUT /promotions/{idPromo}
  async PUT(
    request: Request,
    context: FreshContext<AuthenticatedState>,
  ): Promise<Response> {
    if (context.state.session.eduPersonPrimaryAffiliation !== "employee") {
      return FORBIDDEN();
    }

    const body: { annee: string } = await request.json();

    const [updated] = await db
      .update(promotions)
      .set({ annee: body.annee })
      .where(eq(promotions.id, context.params.idPromo))
      .returning();

    if (!updated) return NOT_FOUND();

    return new Response(JSON.stringify(updated), {
      headers: { "content-type": "application/json" },
    });
  },

  // #17 DELETE /promotions/{idPromo}
  // Blocked if students are still assigned (409).
  // Cascade: deletes linked ue_modules, enseignements, and orphaned
  // modules (+ their notes) & UEs (+ their ajustements).
  async DELETE(
    _request: Request,
    context: FreshContext<AuthenticatedState>,
  ): Promise<Response> {
    if (context.state.session.eduPersonPrimaryAffiliation !== "employee") {
      return FORBIDDEN();
    }

    const idPromo = context.params.idPromo;

    const promo = await db
      .select()
      .from(promotions)
      .where(eq(promotions.id, idPromo))
      .then((r) => r[0] ?? null);

    if (!promo) return NOT_FOUND();

    // Block deletion if students are still assigned
    const assignedStudents = await db
      .select()
      .from(students)
      .where(eq(students.idPromo, idPromo))
      .then((r) => r.length);

    if (assignedStudents > 0) {
      return new Response(
        JSON.stringify({
          error:
            `Impossible de supprimer : ${assignedStudents} étudiant(s) encore assigné(s) à cette promotion`,
        }),
        { status: 409, headers: { "content-type": "application/json" } },
      );
    }

    await db.transaction(async (tx) => {
      // Collect linked module IDs and UE IDs before deleting junction rows
      const linkedUeModules = await tx
        .select({ idModule: ueModules.idModule, idUE: ueModules.idUE })
        .from(ueModules)
        .where(eq(ueModules.idPromo, idPromo));

      const linkedEns = await tx
        .select({ idModule: enseignements.idModule })
        .from(enseignements)
        .where(eq(enseignements.idPromo, idPromo));

      const moduleIds = [
        ...new Set([
          ...linkedUeModules.map((um) => um.idModule),
          ...linkedEns.map((e) => e.idModule),
        ]),
      ];
      const ueIds = [...new Set(linkedUeModules.map((um) => um.idUE))];

      // Delete junction rows that directly reference this promo
      await tx.delete(ueModules).where(eq(ueModules.idPromo, idPromo));
      await tx.delete(enseignements).where(eq(enseignements.idPromo, idPromo));

      // Delete orphaned modules (not used by another promo) and their notes
      for (const modId of moduleIds) {
        const stillInUeModules = await tx
          .select()
          .from(ueModules)
          .where(eq(ueModules.idModule, modId))
          .then((r) => r.length > 0);
        const stillInEns = await tx
          .select()
          .from(enseignements)
          .where(eq(enseignements.idModule, modId))
          .then((r) => r.length > 0);

        if (!stillInUeModules && !stillInEns) {
          await tx.delete(notes).where(eq(notes.idModule, modId));
          await tx.delete(modules).where(eq(modules.id, modId));
        }
      }

      // Delete orphaned UEs (not used by another promo) and their ajustements
      for (const ueId of ueIds) {
        const stillUsed = await tx
          .select()
          .from(ueModules)
          .where(eq(ueModules.idUE, ueId))
          .then((r) => r.length > 0);

        if (!stillUsed) {
          await tx.delete(ajustements).where(eq(ajustements.idUE, ueId));
          await tx.delete(ues).where(eq(ues.id, ueId));
        }
      }

      // Delete the promotion
      await tx.delete(promotions).where(eq(promotions.id, idPromo));
    });

    return new Response(null, { status: 204 });
  },
};