// (c) 2024-2024 Fair Isaac Corporation

/**
 * Project planning: MIP example. A company has several projects that it must
 * undertake in the next few months. Each project lasts for a given time (its
 * duration) and uses up one resource as soon as it starts. The resource profile
 * is the amount of the resource that is used in the months following the start
 * of the project. For instance, project 1 uses up 3 units of resource in the
 * month it starts, 4 units in its second month, and 2 units in its last month.
 * The problem is to decide when to start each project, subject to not using
 * more of any resource in a given month than is available. The benefit from the
 * project only starts to accrue when the project has been completed, and then
 * it accrues at BEN[p] per month for project p, up to the end of the time
 * horizon.
 */
#include <iostream>
#include <xpress.hpp>

using namespace xpress;
using namespace xpress::objects;
using xpress::objects::utils::sum;

std::vector<std::string> const PROJ{"A", "B", "C"}; /* Set of projects */
int const NM = 6;                                   /* Time horizon (months) */
std::vector<int> const MONTHS{
    1, 2, 3, 4, 5, 6}; /* Set of time periods (months) to plan for */
std::vector<int> const DUR{3, 3, 4}; /* Duration of project p */
std::vector<int> const RESMAX{5, 6, 7,
                              7, 6, 6}; /* Resource available in month m */
std::vector<double> const BEN{
    10.2, 12.3, 11.2}; /* Benefit per month once project finished */
std::vector<std::vector<int>> const RESUSE{
    /* Res. usage of proj. p in its t'th month */
    std::vector<int>{3, 4, 2, 0, 0, 0}, std::vector<int>{4, 1, 5, 0, 0, 0},
    std::vector<int>{3, 2, 1, 2, 0, 0}};

int main(void) {
  XpressProblem prob;

  // Create the decision variables
  // 1 if proj p starts in month m, else 0
  auto start =
      prob.addVariables(PROJ.size(), NM)
          .withType(ColumnType::Binary)
          .withName([](auto p, auto m) {
            return "start(" + PROJ[p] + "," + std::to_string(MONTHS[m]) + ")";
          })
          .toArray();

  // Each project starts once and only once
  prob.addConstraints(PROJ.size(), [&](auto p) { return sum(start[p]) == 1; });

  // Resource availability. A project starting in month m is in its k-m month in
  // month k:
  // sum(p in PROJ, m in 0..k) RESUSE[p,k-m]*start[p,m] <= RESMAX[k]
  prob.addConstraints(NM, [&](auto k) {
                            return sum(PROJ.size(), k + 1, [&](auto p, auto m) {
                                     return start[p][m] * RESUSE[p][k - m];
                                   })
                                   <= RESMAX[k];
  });

  /*
   * Objective: Maximize Benefit If project p starts in month m, it finishes in
   * month m+DUR[p]-1 and contributes a benefit of BEN[p] for the remaining
   * NM-[m+DUR[p]-1] months:
   */
  LinExpression obj = LinExpression::create();
  for (unsigned p = 0; p < PROJ.size(); p++) {
    for (int m = 0; m < NM - DUR[p]; m++) {
      obj.addTerm(start[p][m], BEN[p] * (NM - m - DUR[p]));
    }
  }
  prob.setObjective(obj, ObjSense::Maximize);

  // Solve the problem
  prob.optimize("");

  std::cout << "Problem status: " << prob.attributes.getMipStatus()
            << std::endl;
  if (prob.attributes.getMipStatus() != MIPStatus::Solution &&
      prob.attributes.getMipStatus() != MIPStatus::Optimal)
    throw std::runtime_error("optimization failed with status " +
                             to_string(prob.attributes.getMipStatus()));

  // Solution printing
  std::cout << "Solution value is: " << prob.attributes.getObjVal()
            << std::endl;
  auto sol = prob.getSolution();
  for (unsigned p = 0; p < PROJ.size(); p++)
    for (int m = 0; m < NM; m++) {
      if (start[p][m].getValue(sol) > 0.5)
        std::cout << "Project " << PROJ[p] << " starts in month " << MONTHS[m]
                  << std::endl;
    }
  return 0;
}