import type { SupabaseClient } from "@supabase/supabase-js";
import type { OrgEmployee } from "@/components/orgchart/types";
import { todayIso } from "./format";
import { deriveStatusAsOf } from "./reports";
import { fetchAllRows } from "./supabase/query";
import type { Database } from "./supabase/types";

// The Organigramm as it stood (or will stand) on a given date. Three sources
// have to be reconciled, because no single one covers the whole timeline:
//
//   past/today  employee_assignments — the interval covering `asOf`
//   future      pending_org_changes  — effective-dated moves not yet applied
//   membership  entry/exit/karenz    — who counted as staff on that date
//
// See supabase/migrations/*_employee_assignment_history.sql for why the
// placement timeline is captured by a trigger rather than per-RPC.

const ORG_COLUMNS =
  "id, personnel_number, first_name, last_name, job_title, manager_id, team_id, division_id, is_lead, org_level, entry_date, exit_date, karenz_start_date, karenz_return_date";

/** Change types that move someone in the org; the rest only affect status or contract. */
const PLACEMENT_CHANGES = ["transfer", "reorg", "promotion"] as const;

export type OrgAsOfResult = {
  employees: OrgEmployee[];
  /** How many placements were projected from not-yet-applied changes. */
  projectedCount: number;
  /** Earliest date the assignment history actually covers. */
  historyStartsAt: string | null;
};

type EmployeeRow = {
  id: string;
  personnel_number: number;
  first_name: string;
  last_name: string;
  job_title: string;
  manager_id: string | null;
  team_id: string | null;
  division_id: string;
  is_lead: boolean;
  org_level: number;
  entry_date: string;
  exit_date: string | null;
  karenz_start_date: string | null;
  karenz_return_date: string | null;
};

type AssignmentRow = {
  employee_id: string;
  manager_id: string | null;
  team_id: string | null;
  division_id: string;
  job_title: string;
  is_lead: boolean;
  org_level: number;
  valid_from: string;
};

type PendingRow = { employee_id: string; effective_date: string; payload: Record<string, unknown> };

type Placement = { team_id: string | null; division_id: string; job_title: string; is_lead: boolean; org_level: number };

// Mirrors resolve_manager_for() in supabase/migrations: an IC reports to
// their team's lead, a team lead to the division head, and anyone without a
// team to the CEO. Only used for employees a pending change actually moves —
// everyone else keeps the manager recorded on their assignment, so existing
// data that deviates from the rule is never silently "corrected".
function resolveManagerFor(placement: Placement, all: { id: string; placement: Placement }[]): string | null {
  if (placement.team_id && !placement.is_lead) {
    return all.find((e) => e.placement.team_id === placement.team_id && e.placement.is_lead)?.id ?? null;
  }
  if (placement.team_id && placement.is_lead) {
    return (
      all.find((e) => e.placement.division_id === placement.division_id && !e.placement.team_id && e.placement.org_level === 1)?.id ??
      null
    );
  }
  return all.find((e) => e.placement.org_level === 0)?.id ?? null;
}

export async function loadOrgAsOf(supabase: SupabaseClient<Database>, asOf: string): Promise<OrgAsOfResult> {
  const today = todayIso();

  const [allEmployees, assignments, teams, departments, pending] = await Promise.all([
    fetchAllRows(() => supabase.from("employees").select(ORG_COLUMNS).order("id")),
    fetchAllRows(() =>
      supabase
        .from("employee_assignments")
        .select("employee_id, manager_id, team_id, division_id, job_title, is_lead, org_level, valid_from")
        .lte("valid_from", asOf)
        .or(`valid_to.is.null,valid_to.gt.${asOf}`)
        .order("employee_id")
    ),
    fetchAllRows(() => supabase.from("teams").select("id, department_id").order("id")),
    fetchAllRows(() => supabase.from("departments").select("id, division_id").order("id")),
    asOf > today
      ? fetchAllRows(() =>
          supabase
            .from("pending_org_changes")
            .select("employee_id, change_type, effective_date, payload")
            .eq("status", "pending")
            .lte("effective_date", asOf)
            .in("change_type", [...PLACEMENT_CHANGES])
            .order("effective_date")
        )
      : Promise.resolve([]),
  ]);

  return resolveOrgSnapshot({ asOf, employees: allEmployees, assignments, teams, departments, pending });
}

// The pure half of the above: everything that turns the four row sets into a
// snapshot, with no Supabase client in sight, so the reconciliation rules can
// be tested directly.
export function resolveOrgSnapshot({
  asOf,
  employees: allEmployees,
  assignments,
  teams,
  departments,
  pending,
}: {
  asOf: string;
  employees: EmployeeRow[];
  assignments: AssignmentRow[];
  teams: { id: string; department_id: string }[];
  departments: { id: string; division_id: string }[];
  pending: PendingRow[];
}): OrgAsOfResult {
  const assignmentByEmployee = new Map(assignments.map((a) => [a.employee_id, a]));
  // A projected move names only the target team; its division follows from
  // the team's department, the same way the DB trigger derives it.
  const departmentDivision = new Map(departments.map((d) => [d.id, d.division_id]));
  const teamDivision = new Map(
    teams.flatMap((t) => {
      const divisionId = departmentDivision.get(t.department_id);
      return divisionId ? [[t.id, divisionId] as const] : [];
    })
  );

  // Employed (or on leave) on that date — the same derivation the Berichte
  // page uses, so the two can never disagree on who counted when.
  const staff = allEmployees.filter((e) => {
    const status = deriveStatusAsOf(e, asOf);
    return status === "Aktiv" || status === "Karenz";
  });

  const resolved = staff.map((e) => {
    const a = assignmentByEmployee.get(e.id);
    return {
      employee: e,
      managerId: a ? a.manager_id : e.manager_id,
      placement: {
        team_id: a ? a.team_id : e.team_id,
        division_id: a ? a.division_id : e.division_id,
        job_title: a ? a.job_title : e.job_title,
        is_lead: a ? a.is_lead : e.is_lead,
        org_level: a ? a.org_level : e.org_level,
      } satisfies Placement,
    };
  });

  // Project the future. Ordered by effective_date, so a later move wins.
  const byId = new Map(resolved.map((r) => [r.employee.id, r]));
  const moved = new Set<string>();
  for (const change of pending) {
    const target = byId.get(change.employee_id);
    if (!target) continue;
    const payload = change.payload as { new_team_id?: string; target_team_id?: string; new_title?: string };
    const newTeamId = payload.new_team_id ?? payload.target_team_id ?? null;
    if (newTeamId) {
      target.placement.team_id = newTeamId;
      const divisionId = teamDivision.get(newTeamId);
      if (divisionId) target.placement.division_id = divisionId;
      moved.add(target.employee.id);
    }
    if (payload.new_title) target.placement.job_title = payload.new_title;
  }

  // Second pass: a moved employee's manager follows from the *projected*
  // org, not the one they left — and the lead of their new team may itself
  // have moved in this same batch.
  for (const r of resolved) {
    if (moved.has(r.employee.id)) r.managerId = resolveManagerFor(r.placement, resolved.map((x) => ({ id: x.employee.id, placement: x.placement })));
  }

  // A manager who had not joined yet, or had already left, is not in this
  // set — without re-rooting, their whole reporting line would silently
  // vanish from the chart rather than showing up one level higher.
  const presentIds = new Set(resolved.map((r) => r.employee.id));

  const employees: OrgEmployee[] = resolved.map((r) => ({
    id: r.employee.id,
    personnel_number: r.employee.personnel_number,
    first_name: r.employee.first_name,
    last_name: r.employee.last_name,
    job_title: r.placement.job_title,
    manager_id: r.managerId && presentIds.has(r.managerId) ? r.managerId : null,
    team_id: r.placement.team_id,
    division_id: r.placement.division_id,
    is_lead: r.placement.is_lead,
    org_level: r.placement.org_level,
  }));

  const historyStartsAt = assignments.reduce<string | null>(
    (min, a) => (min === null || a.valid_from < min ? a.valid_from : min),
    null
  );

  return { employees, projectedCount: moved.size, historyStartsAt };
}