import type { TuitionLessonStepId } from "./classSessionData";
import { tuitionLessonSteps } from "./classSessionData";
import type { TuitionSessionData } from "./sessionData";

/**
 * Tuition class session progress.
 *
 * The 11-step guided class (TuitionClassSessionView) held all progress in
 * ephemeral React state, so a refresh lost everything. This persists the
 * resumable parts keyed by the class session, so /tuition restores where the
 * student left off. localStorage is the offline source of truth; the backend
 * (classSessionProgressApi) syncs it across devices.
 */

const VALID_STEP_IDS = new Set(tuitionLessonSteps.map((step) => step.id));

/** Map legacy step ids (e.g. "recap") onto the current continuous flow. */
export function normalizeLessonStepId(stepId: string | undefined | null): TuitionLessonStepId {
  if (stepId === "recap") return "save-revision";
  if (stepId && VALID_STEP_IDS.has(stepId as TuitionLessonStepId)) {
    return stepId as TuitionLessonStepId;
  }
  return tuitionLessonSteps[0].id;
}

export type ClassSessionProgressState = {
  started: boolean;
  activeStepId: TuitionLessonStepId;
  maxUnlockedIndex: number;
  recallAnswer: string;
  recallSubmitted: boolean;
  practiceAnswer: string;
  practiceSubmitted: boolean;
  quizAnswers: Record<string, string>;
  quizSubmitted: boolean;
  revisionSaved: boolean;
  trickSaved: boolean;
  assessmentAttemptId?: string | null;
  lessonProgressId?: string | null;
  /** Steps the student explicitly completed in the class flow (not mastery). */
  completedStepIds?: TuitionLessonStepId[];
  /** Authoritative session id/revision when this is an authenticated class. */
  tuitionSessionId?: string | null;
  tuitionSessionRevision?: number | null;
  writtenAttemptId?: string | null;
  /** Number of authoritative written submissions for this class. */
  writtenAttemptCount?: number;
  /** Adaptive checkpoint loop state (runId keeps replays idempotent). */
  checkpointState?: {
    runId: string;
    questions: Record<
      string,
      {
        phase: "answering" | "hint_retry" | "explained" | "transfer" | "done";
        attempt: number;
        correct: boolean | null;
        transferCorrect: boolean | null;
        errorCategory: string | null;
      }
    >;
  } | null;
};

export type ClassSessionProgress = ClassSessionProgressState & {
  classSessionId: string;
  updatedAt: string;
};

export const CLASS_SESSION_PROGRESS_PREFIX = "docdoe:tuition-class-progress:";

type SessionIdParts = Pick<TuitionSessionData, "board" | "subject" | "chapterId" | "missionId">;

/** Stable id for a class session, used as the persistence key. */
export function classSessionId(session: SessionIdParts): string {
  return [session.board ?? "", session.subject ?? "", session.chapterId ?? "chapter", session.missionId ?? "mission"]
    .map((part) => part.trim())
    .join("|");
}

export function readClassSessionProgress(id: string): ClassSessionProgress | null {
  if (typeof window === "undefined") return null;
  try {
    const raw = window.localStorage.getItem(CLASS_SESSION_PROGRESS_PREFIX + id);
    return raw ? (JSON.parse(raw) as ClassSessionProgress) : null;
  } catch {
    return null;
  }
}

export function writeClassSessionProgress(id: string, state: ClassSessionProgressState): ClassSessionProgress {
  const payload: ClassSessionProgress = { ...state, classSessionId: id, updatedAt: new Date().toISOString() };
  if (typeof window !== "undefined") {
    try {
      window.localStorage.setItem(CLASS_SESSION_PROGRESS_PREFIX + id, JSON.stringify(payload));
    } catch {
      // Storage is a convenience layer; the backend copy remains authoritative.
    }
  }
  return payload;
}

/** Merge a stored snapshot into the default state (used to seed React state). */
export function applyClassSessionProgress(
  defaults: ClassSessionProgressState,
  saved: ClassSessionProgress | null,
): ClassSessionProgressState {
  if (!saved) return defaults;
  const activeStepId = normalizeLessonStepId(saved.activeStepId ?? defaults.activeStepId);
  const maxStepIndex = Math.max(0, tuitionLessonSteps.length - 1);
  const maxUnlockedIndex = Math.max(
    0,
    Math.min(maxStepIndex, saved.maxUnlockedIndex ?? defaults.maxUnlockedIndex),
  );
  // Empty practice answers are never treated as submitted after refresh.
  const practiceAnswer = saved.practiceAnswer ?? defaults.practiceAnswer;
  const practiceSubmitted =
    Boolean(saved.practiceSubmitted ?? defaults.practiceSubmitted) && practiceAnswer.trim().length > 0;

  return {
    started: saved.started ?? defaults.started,
    activeStepId,
    maxUnlockedIndex,
    recallAnswer: saved.recallAnswer ?? defaults.recallAnswer,
    recallSubmitted: saved.recallSubmitted ?? defaults.recallSubmitted,
    practiceAnswer,
    practiceSubmitted,
    quizAnswers: saved.quizAnswers ?? defaults.quizAnswers,
    quizSubmitted: saved.quizSubmitted ?? defaults.quizSubmitted,
    revisionSaved: saved.revisionSaved ?? defaults.revisionSaved,
    trickSaved: saved.trickSaved ?? defaults.trickSaved,
    assessmentAttemptId:
      saved.assessmentAttemptId ?? defaults.assessmentAttemptId ?? null,
    lessonProgressId:
      saved.lessonProgressId ?? defaults.lessonProgressId ?? null,
    completedStepIds:
      saved.completedStepIds ?? defaults.completedStepIds ?? [],
    tuitionSessionId:
      saved.tuitionSessionId ?? defaults.tuitionSessionId ?? null,
    tuitionSessionRevision:
      saved.tuitionSessionRevision ?? defaults.tuitionSessionRevision ?? null,
    writtenAttemptId:
      saved.writtenAttemptId ?? defaults.writtenAttemptId ?? null,
    writtenAttemptCount:
      saved.writtenAttemptCount ?? defaults.writtenAttemptCount ?? 0,
    checkpointState: saved.checkpointState ?? defaults.checkpointState ?? null,
  };
}