/**
 * 排课冲突检测（纯函数）
 *
 * 冲突维度（P3）：
 *   - teacher: 同一教师在同一时间段有排课冲突
 *   - class: 同一班级在同一时间段有排课冲突
 *
 * room_id 仅预留字段（ISSUE-006 决策 #2），P3 不校验教室冲突。
 */

export interface ScheduleSlot {
  id: string;
  teacherId: string;
  classId: string;
  startTime: Date;
  endTime: Date;
  roomId?: string | null;
}

export interface ConflictResult {
  hasConflict: boolean;
  conflictingSlot?: ScheduleSlot;
  conflictType: "teacher" | "class" | null;
}

/**
 * 检查时间区间重叠。
 * [startA, endA) 与 [startB, endB) 重叠的条件：startA < endB && startB < endA
 */
export function isTimeOverlap(
  startA: Date,
  endA: Date,
  startB: Date,
  endB: Date,
): boolean {
  return startA < endB && startB < endA;
}

/**
 * 检查新排课与现有排课列表的冲突。
 * 排除自身（如果是更新场景，传入 excludeId）。
 */
export function detectConflict(
  newSlot: Omit<ScheduleSlot, "id"> & { id?: string },
  existingSlots: ScheduleSlot[],
  excludeId?: string,
): ConflictResult {
  for (const slot of existingSlots) {
    if (excludeId && slot.id === excludeId) continue;

    if (
      !isTimeOverlap(
        newSlot.startTime,
        newSlot.endTime,
        slot.startTime,
        slot.endTime,
      )
    ) {
      continue;
    }

    // 教师冲突
    if (newSlot.teacherId === slot.teacherId) {
      return {
        hasConflict: true,
        conflictingSlot: slot,
        conflictType: "teacher",
      };
    }

    // 班级冲突
    if (newSlot.classId === slot.classId) {
      return {
        hasConflict: true,
        conflictingSlot: slot,
        conflictType: "class",
      };
    }
  }

  return { hasConflict: false, conflictType: null };
}