ahbeng/NUSMods

import { flatMap, get, sortBy, values } from 'lodash';
import { ModuleCode, Semester, Semesters } from 'types/modules';
import {
  PlannerState,
  ModulesMap,
  ModuleCodeMap,
  CustomModuleData,
  PlannerTime,
} from 'types/reducers';
import config from 'config';
import { getYearsBetween, subtractAcadYear } from 'utils/modules';
import {
  checkPrerequisite,
  EXEMPTION_SEMESTER,
  EXEMPTION_YEAR,
  IBLOCS_SEMESTER,
  PLAN_TO_TAKE_SEMESTER,
  PLAN_TO_TAKE_YEAR,
} from 'utils/planner';
import { findExamClashes } from 'utils/timetables';
import { Conflict, PlannerModuleInfo, PlannerModulesWithInfo } from 'types/planner';
import placeholders from 'utils/placeholders';
import { notNull } from 'types/utils';
import { State } from 'types/state';
import { ExamClashes } from 'types/views';

/**
 * Get a list of modules planned for a specific semester in an acad year
 * in the order specified by the index
 */
export function filterModuleForSemester(
  modules: PlannerState['modules'],
  year: string,
  semester: Semester,
) {
  const moduleTimes = values(modules).filter(
    (module) => module.year === year && module.semester === semester,
  );
  return sortBy(moduleTimes, (module) => module.index);
}

/**
 * Conflict checkers - checks if a module has some issue that requires displaying
 * the yellow triangle in the UI.
 *
 * All conflict checks below are higher order functions returning
 * a (ModuleCode) => Conflict | null which can be passed into the last parameter
 * of mapModuleInfo
 */

/**
 * Checks if a module has unfulfilled prereqs
 */
const prereqConflict =
  (modulesMap: ModulesMap, modulesTaken: Set<ModuleCode>) =>
  (moduleCode: ModuleCode): Conflict | null => {
    const prereqs = get(modulesMap, [moduleCode, 'prereqTree']);
    if (!prereqs) return null;

    const unfulfilledPrereqs = checkPrerequisite(modulesTaken, prereqs);
    if (!unfulfilledPrereqs || !unfulfilledPrereqs.length) return null;

    return { type: 'prereq', unfulfilledPrereqs };
  };

/**
 * Checks if a module exists in our data
 */
const noInfoConflict =
  (moduleCodeMap: ModuleCodeMap, customData: CustomModuleData) =>
  (moduleCode: ModuleCode): Conflict | null =>
    moduleCodeMap[moduleCode] || customData[moduleCode] ? null : { type: 'noInfo' };

/**
 * Checks if modules are added to semesters in which they are not available
 */
const semesterConflict =
  (moduleCodeMap: ModuleCodeMap, semester: Semester) =>
  (moduleCode: ModuleCode): Conflict | null => {
    const moduleCondensed = moduleCodeMap[moduleCode];
    if (!moduleCondensed) return null;
    if (!moduleCondensed.semesters.includes(semester)) {
      return { type: 'semester', semestersOffered: moduleCondensed.semesters };
    }

    return null;
  };

/**
 * Checks if there are exam clashes. The clashes come from the caller since the exam clash function
 * calculates clashes for all modules in one semester, so it would be wasteful to rerun the exam
 * clash function for every call to this function.
 */
const examConflict =
  (clashes: ExamClashes) =>
  (moduleCode: ModuleCode): Conflict | null => {
    const clash = values(clashes).find((modules) =>
      Boolean(modules.find((module) => module.moduleCode === moduleCode)),
    );

    if (clash) {
      return { type: 'exam', conflictModules: clash.map((module) => module.moduleCode) };
    }

    return null;
  };

function mapModuleToInfo(
  module: PlannerTime,
  modulesMap: ModulesMap,
  customModules: CustomModuleData,
  conflictChecks: ((moduleCode: ModuleCode) => Conflict | null)[],
): PlannerModuleInfo {
  const { id, moduleCode, placeholderId } = module;
  const moduleInfo: PlannerModuleInfo = {
    id,
    moduleCode,
    conflict: null,
  };

  if (placeholderId) {
    moduleInfo.placeholder = placeholders[placeholderId];
    moduleInfo.customInfo = {
      moduleCredit: 4,
    };
  }

  if (moduleCode) {
    // Only continue checking until the first conflict is found
    let index = 0;
    while (!moduleInfo.conflict && index < conflictChecks.length) {
      moduleInfo.conflict = conflictChecks[index](moduleCode);
      index += 1;
    }

    // Insert customInfo and moduleInfo
    moduleInfo.moduleInfo = modulesMap[moduleCode];
    moduleInfo.customInfo = customModules[moduleCode];
  }

  return moduleInfo;
}

export function getPrereqModuleCode(moduleCode: ModuleCode): ModuleCode[] {
  const moduleCodes = [moduleCode];

  // Also try to match the non-variant version (without the suffix alphabets)
  // of the module code
  const match = /([A-Z]+\d+)[A-Z]+$/gi.exec(moduleCode);
  if (match) moduleCodes.push(match[1]);

  return moduleCodes;
}

/**
 * Maps modules from sources outside the normal timetable,
 * such as exemptions, "plan to take" and iBLOCs modules
 */
export function mapNonTimetableModules(
  state: State,
  year: string,
  semester: Semester,
): PlannerModuleInfo[] {
  const { planner, moduleBank } = state;
  const conflictChecks = [noInfoConflict(moduleBank.moduleCodes, planner.custom)];

  return filterModuleForSemester(planner.modules, year, semester).map((moduleCode) =>
    mapModuleToInfo(moduleCode, moduleBank.modules, planner.custom, conflictChecks),
  );
}

export const getIBLOCs = (state: State): PlannerModuleInfo[] => {
  if (!state.planner.iblocs) return [];
  const iblocsYear = subtractAcadYear(state.planner.minYear);
  return mapNonTimetableModules(state, iblocsYear, IBLOCS_SEMESTER);
};

export const getExemptions = (state: State): PlannerModuleInfo[] =>
  mapNonTimetableModules(state, EXEMPTION_YEAR, EXEMPTION_SEMESTER);

export const getPlanToTake = (state: State): PlannerModuleInfo[] =>
  mapNonTimetableModules(state, PLAN_TO_TAKE_YEAR, PLAN_TO_TAKE_SEMESTER);

/**
 * Convert PlannerState into PlannerModulesWithInfo form which is more easily
 * consumed by the UI
 */
export function getAcadYearModules(state: State): PlannerModulesWithInfo {
  const { planner, moduleBank } = state;
  const years = getYearsBetween(planner.minYear, planner.maxYear);
  const exemptions = [
    // Normal exemptions
    ...getExemptions(state),
    // iBLOCs modules, if there are any, since they are also not included in acad year modules
    ...getIBLOCs(state),
  ];
  const modulesTaken = new Set<ModuleCode>(
    flatMap(exemptions, (module) =>
      module.moduleCode ? getPrereqModuleCode(module.moduleCode) : [],
    ),
  );

  // Same type as PlannerModulesWithInfo, but writable so we can build it here
  const modules: { [year: string]: { [semester: string]: PlannerModuleInfo[] } } = {};
  years.forEach((year) => {
    modules[year] = {};

    Semesters.forEach((semester) => {
      const moduleTimes = filterModuleForSemester(planner.modules, year, semester);

      // Only check for exam clashes for modules in the current year
      let clashes = {};
      if (year === config.academicYear) {
        const semesterModules = moduleTimes
          .map((moduleTime) => moduleTime.moduleCode)
          .filter(notNull)
          .map((moduleCode) => moduleBank.modules[moduleCode])
          .filter(notNull);

        clashes = findExamClashes(semesterModules, semester);
      }

      const conflictChecks = [
        noInfoConflict(moduleBank.moduleCodes, planner.custom),
        semesterConflict(moduleBank.moduleCodes, semester),
        examConflict(clashes),
      ];

      if (!planner.ignorePrereqCheck) {
        conflictChecks.push(prereqConflict(moduleBank.modules, modulesTaken));
      }

      modules[year][semester] = moduleTimes.map((moduleCode) =>
        mapModuleToInfo(moduleCode, moduleBank.modules, planner.custom, conflictChecks),
      );

      // Add taken modules to set of modules taken for prerequisite calculation
      moduleTimes.forEach((moduleTime) => {
        if (!moduleTime.moduleCode) return;
        getPrereqModuleCode(moduleTime.moduleCode).forEach((prereq) => modulesTaken.add(prereq));
      });
    });
  });

  return modules;
}