export interface DistributionBoardLoadBoardInput {
  id: string;
  name: string;
  boardNumber: string | null;
  simultaneityFactor: number;
  feedingDistributionBoardId: string | null;
  feedingCircuitId: string | null;
}

export interface DistributionBoardLoadCircuitInput {
  id: string;
  distributionBoardId: string;
  rows: Array<{
    activePowerKw: number;
    cosPhi: number | null;
  }>;
}

export interface DownstreamDistributionBoardLoad {
  distributionBoardId: string;
  name: string;
  boardNumber: string | null;
  activePowerKw: number;
  apparentPowerKva: number;
  cosPhi: number;
}

export interface CalculatedCircuitLoad {
  circuitId: string;
  deviceActivePowerKw: number;
  deviceApparentPowerKva: number;
  activePowerKw: number;
  apparentPowerKva: number;
  cosPhi: number;
  downstreamBoards: DownstreamDistributionBoardLoad[];
}

export interface CalculatedDistributionBoardLoad {
  distributionBoardId: string;
  activePowerBeforeSimultaneityKw: number;
  apparentPowerBeforeSimultaneityKva: number;
  demandActivePowerKw: number;
  demandApparentPowerKva: number;
  cosPhi: number;
}

export interface DistributionBoardLoadCalculation {
  boards: Map<string, CalculatedDistributionBoardLoad>;
  circuits: Map<string, CalculatedCircuitLoad>;
}

/**
 * Calculates one project graph. A child board enters exactly one feeder
 * circuit with its demand after the child's own board simultaneity factor.
 * Board-only relations form a hierarchy but intentionally add no load.
 */
export function calculateDistributionBoardLoads(input: {
  boards: DistributionBoardLoadBoardInput[];
  circuits: DistributionBoardLoadCircuitInput[];
}): DistributionBoardLoadCalculation {
  const boardById = new Map(input.boards.map((board) => [board.id, board]));
  const circuitById = new Map(input.circuits.map((circuit) => [circuit.id, circuit]));
  const circuitsByBoardId = groupBy(
    input.circuits,
    (circuit) => circuit.distributionBoardId
  );
  const childrenByCircuitId = new Map<string, DistributionBoardLoadBoardInput[]>();
  for (const board of input.boards) {
    assertBoardInput(board, boardById, circuitById);
    if (board.feedingCircuitId === null) continue;
    const children = childrenByCircuitId.get(board.feedingCircuitId) ?? [];
    children.push(board);
    childrenByCircuitId.set(board.feedingCircuitId, children);
  }

  const boards = new Map<string, CalculatedDistributionBoardLoad>();
  const circuits = new Map<string, CalculatedCircuitLoad>();
  const activePath = new Set<string>();

  const calculateBoard = (boardId: string): CalculatedDistributionBoardLoad => {
    const cached = boards.get(boardId);
    if (cached) return cached;
    if (activePath.has(boardId)) {
      throw new Error("Distribution-board feeding graph contains a cycle.");
    }
    const board = boardById.get(boardId);
    if (!board) throw new Error("Distribution board is missing from load graph.");
    activePath.add(boardId);

    let activePowerBeforeSimultaneityKw = 0;
    let apparentPowerBeforeSimultaneityKva = 0;
    for (const circuit of circuitsByBoardId.get(boardId) ?? []) {
      let deviceActivePowerKw = 0;
      let deviceApparentPowerKva = 0;
      for (const row of circuit.rows) {
        assertNonNegativeFinite(row.activePowerKw, "row active power");
        const cosPhi = row.cosPhi ?? 1;
        if (!Number.isFinite(cosPhi) || cosPhi <= 0 || cosPhi > 1) {
          throw new Error("Row cos phi must be greater than zero and at most one.");
        }
        deviceActivePowerKw += row.activePowerKw;
        deviceApparentPowerKva += row.activePowerKw / cosPhi;
      }
      const downstreamBoards = (childrenByCircuitId.get(circuit.id) ?? [])
        .map((child) => {
          const childLoad = calculateBoard(child.id);
          return {
            distributionBoardId: child.id,
            name: child.name,
            boardNumber: child.boardNumber,
            activePowerKw: childLoad.demandActivePowerKw,
            apparentPowerKva: childLoad.demandApparentPowerKva,
            cosPhi: effectiveCosPhi(
              childLoad.demandActivePowerKw,
              childLoad.demandApparentPowerKva
            ),
          };
        });
      const activePowerKw =
        deviceActivePowerKw +
        downstreamBoards.reduce((sum, child) => sum + child.activePowerKw, 0);
      const apparentPowerKva =
        deviceApparentPowerKva +
        downstreamBoards.reduce((sum, child) => sum + child.apparentPowerKva, 0);
      circuits.set(circuit.id, {
        circuitId: circuit.id,
        deviceActivePowerKw,
        deviceApparentPowerKva,
        activePowerKw,
        apparentPowerKva,
        cosPhi: effectiveCosPhi(activePowerKw, apparentPowerKva),
        downstreamBoards,
      });
      activePowerBeforeSimultaneityKw += activePowerKw;
      apparentPowerBeforeSimultaneityKva += apparentPowerKva;
    }

    activePath.delete(boardId);
    const result = {
      distributionBoardId: boardId,
      activePowerBeforeSimultaneityKw,
      apparentPowerBeforeSimultaneityKva,
      demandActivePowerKw:
        activePowerBeforeSimultaneityKw * board.simultaneityFactor,
      demandApparentPowerKva:
        apparentPowerBeforeSimultaneityKva * board.simultaneityFactor,
      cosPhi: effectiveCosPhi(
        activePowerBeforeSimultaneityKw,
        apparentPowerBeforeSimultaneityKva
      ),
    };
    boards.set(boardId, result);
    return result;
  };

  for (const board of input.boards) calculateBoard(board.id);
  return { boards, circuits };
}

function assertBoardInput(
  board: DistributionBoardLoadBoardInput,
  boardById: Map<string, DistributionBoardLoadBoardInput>,
  circuitById: Map<string, DistributionBoardLoadCircuitInput>
) {
  if (
    !Number.isFinite(board.simultaneityFactor) ||
    board.simultaneityFactor < 0 ||
    board.simultaneityFactor > 1
  ) {
    throw new Error("Board simultaneity factor must be between zero and one.");
  }
  if (board.feedingDistributionBoardId === board.id) {
    throw new Error("Distribution board cannot feed itself.");
  }
  if (
    board.feedingDistributionBoardId !== null &&
    !boardById.has(board.feedingDistributionBoardId)
  ) {
    throw new Error("Feeding distribution board is missing from load graph.");
  }
  if (
    board.feedingCircuitId !== null &&
    board.feedingDistributionBoardId === null
  ) {
    throw new Error("Feeding circuit requires a feeding distribution board.");
  }
  if (
    board.feedingCircuitId !== null &&
    circuitById.get(board.feedingCircuitId)?.distributionBoardId !==
      board.feedingDistributionBoardId
  ) {
    throw new Error("Feeding circuit belongs to another distribution board.");
  }
}

function effectiveCosPhi(activePowerKw: number, apparentPowerKva: number) {
  return activePowerKw > 0 && apparentPowerKva > 0
    ? activePowerKw / apparentPowerKva
    : 1;
}

function assertNonNegativeFinite(value: number, label: string) {
  if (!Number.isFinite(value) || value < 0) {
    throw new Error(`${label} must be a non-negative finite number.`);
  }
}

function groupBy<T>(values: T[], keyOf: (value: T) => string) {
  const groups = new Map<string, T[]>();
  for (const value of values) {
    const key = keyOf(value);
    const group = groups.get(key) ?? [];
    group.push(value);
    groups.set(key, group);
  }
  return groups;
}