/**
 * Graph respects explicit dependencies
 * and implicit by resources (via positions)
 */
export const makeGraphFromTasks = (tasks: Array<Task>): Graph => {
  // task and blockedBy
  const graph: Graph = new Map();
  const resourcesTasks = new Map<ID, Array<Task>>();

  // Create graphs
  for (const t of tasks) {
    // resource and its tasks
    const tasksOfResource = resourcesTasks.get(t.resourceId) ?? [];
    tasksOfResource.push(t);

    resourcesTasks.set(t.resourceId, tasksOfResource);

    graph.set(t.id, new Set(t.blockedBy ?? []));
  }

  // Now add deps
  for (const tasksOfResource of resourcesTasks.values()) {
    // first sort by position so links of tasks starts with higher position
    // then topological sort to reduce cyclic deps
    tasksOfResource.sort((a, b) => a.position - b.position);
    // is toposort needed?
    const sortedTasks = toposort(graph, tasksOfResource);

    // add to graph such edges so current node has prev as dependency (blocked by prev)
    let prevTask: Task | void;
    for (const task of sortedTasks) {
      if (
        prevTask &&
        prevTask.id !== task.id &&
        // has no incoming edge as well (otherwise it will be cyclic dep)
        !graph.get(prevTask.id)?.has(task.id)
      ) {
        graph.get(task.id)?.add(prevTask.id);
      }
      prevTask = task;
    }
  }

  return graph;
};