import {
  getStudyProfileRemote,
  saveStudyProfileRemote,
  type StudyProfileRemote,
} from "@/lib/api/study-profile";
import {
  getLearningState,
  type LearningStateSummary,
} from "@/lib/api/learning-state";
import { hasLiveSession } from "@/lib/api/mode";
import { getAuthToken, getStoredUser } from "@/lib/auth/auth-client";
import { readLocalTuitionSetup } from "@/components/tuition/tuitionSetupPersistence";

// =============================================================================
// Single source of truth for "who is this student and what are they studying".
//
// The app previously had three competing truths — the backend study profile,
// the localStorage onboarding payload, and the tuition setup — and pages
// disagreed about whether onboarding was complete (Home keyed on
// `study_focus.subject`, which onboarding never collects). Every consumer
// (Home focus card, StudyChat session context, Progress, Tuition entry) should
// read THIS module instead of the raw stores.
//
// Field-mapping note (legacy, do not "fix" silently): the onboarding flow
// stores dailyTime in the profile's `primary_need` column and preferredTime in
// `language_preference`. That mapping is quarantined here so consumers only
// ever see `dailyTime` / `preferredTime`.
// =============================================================================

export const ONBOARDING_COMPLETED_KEY = "docdoe-onboarding-completed";
export const ONBOARDING_PROFILE_KEY = "docdoe-onboarding-profile";
/**
 * Which account the device-local onboarding cache belongs to. Without this
 * tag, a shared computer leaks one student's identity into the next: the old
 * local profile renders in the header AND `repairRemoteProfile` pushes it up
 * into the newly signed-in account's backend profile.
 */
export const ONBOARDING_OWNER_KEY = "docdoe-onboarding-owner";

function currentUserId(): string | null {
  const stored = getStoredUser();
  if (stored?.id) return stored.id;
  const token = getAuthToken();
  if (!token) return null;
  try {
    const payload = JSON.parse(
      atob((token.split(".")[1] ?? "").replace(/-/g, "+").replace(/_/g, "/")),
    ) as { sub?: unknown };
    return typeof payload.sub === "string" ? payload.sub : null;
  } catch {
    return null;
  }
}

/**
 * Tag the device-local onboarding cache as belonging to the signed-in
 * account. Call after writing ONBOARDING_PROFILE_KEY on behalf of a user.
 */
export function claimLocalOnboardingOwnership(): void {
  if (typeof window === "undefined") return;
  const uid = currentUserId();
  if (uid) window.localStorage.setItem(ONBOARDING_OWNER_KEY, uid);
}

/**
 * True when the device-local onboarding cache is safe to use for the current
 * viewer. Logged out: any local data is the device user's own. Signed in: the
 * cache must be tagged with this exact account — an untagged or foreign cache
 * is another student's data and must be ignored (and never pushed remote).
 */
function localOnboardingUsable(): boolean {
  if (typeof window === "undefined") return false;
  const uid = currentUserId();
  if (!uid) return true;
  return window.localStorage.getItem(ONBOARDING_OWNER_KEY) === uid;
}

export type StudentContext = {
  /** Where the strongest signal came from. */
  source: "remote" | "local" | "none";
  /** True when the backend has a saved profile (survives device changes). */
  synced: boolean;
  onboardingComplete: boolean;
  classLevel: string | null;
  board: string | null;
  goal: string | null;
  examDate: string | null;
  dailyTime: string | null;
  preferredTime: string | null;
  subjects: string[];
  languagePreference: string | null;
  learningStyle: string | null;
  /** Active subject — from the tuition setup or the saved profile. */
  subject: string | null;
  /** Onboarding "what should DocDoe focus on" picks. Not evidence-based weak topics. */
  focusAreas: string[];
};

export const EMPTY_STUDENT_CONTEXT: StudentContext = {
  source: "none",
  synced: false,
  onboardingComplete: false,
  classLevel: null,
  board: null,
  goal: null,
  examDate: null,
  dailyTime: null,
  preferredTime: null,
  subjects: [],
  languagePreference: null,
  learningStyle: null,
  subject: null,
  focusAreas: [],
};

type LocalOnboarding = {
  goal?: string;
  class?: string;
  board?: string;
  examDate?: string;
  dailyTime?: string;
  preferredTime?: string;
  subjects?: string[];
  languagePreference?: string;
  learningStyle?: string;
  focus?: string[];
};

function readLocalOnboarding(): {
  completed: boolean;
  data: LocalOnboarding | null;
} {
  if (typeof window === "undefined") return { completed: false, data: null };
  const completed =
    window.localStorage.getItem(ONBOARDING_COMPLETED_KEY) === "true";
  try {
    const raw = window.localStorage.getItem(ONBOARDING_PROFILE_KEY);
    return {
      completed,
      data: raw ? (JSON.parse(raw) as LocalOnboarding) : null,
    };
  } catch {
    return { completed, data: null };
  }
}

function localSubject(): string | null {
  const setup = readLocalTuitionSetup();
  return setup.activeSubject || setup.subjects[0] || null;
}

/**
 * Synchronous context from local stores only — safe for first paint.
 * `synced` is always false here; call loadStudentContext() for the real merge.
 */
export function getLocalStudentContext(): StudentContext {
  if (!localOnboardingUsable()) return EMPTY_STUDENT_CONTEXT;
  const { completed, data } = readLocalOnboarding();
  if (!completed && !data) return EMPTY_STUDENT_CONTEXT;
  return {
    source: "local",
    synced: false,
    onboardingComplete: completed,
    classLevel: data?.class || null,
    board: data?.board || null,
    goal: data?.goal || null,
    examDate: data?.examDate || null,
    dailyTime: data?.dailyTime || null,
    preferredTime: data?.preferredTime || null,
    subject: data?.subjects?.[0] || localSubject(),
    subjects: data?.subjects?.filter(Boolean) ?? [],
    languagePreference: data?.languagePreference || null,
    learningStyle: data?.learningStyle || null,
    focusAreas: data?.focus ?? [],
  };
}

function extraString(
  extra: Record<string, unknown>,
  key: string,
): string | null {
  return typeof extra[key] === "string" && extra[key]
    ? String(extra[key])
    : null;
}

function extraStrings(extra: Record<string, unknown>, key: string): string[] {
  return Array.isArray(extra[key])
    ? (extra[key] as unknown[]).filter(
        (value): value is string => typeof value === "string" && Boolean(value),
      )
    : [];
}

function contextFromRemote(
  profile: StudyProfileRemote,
  local: StudentContext,
): StudentContext {
  const extra = profile.extra ?? {};
  const subjects = extraStrings(extra, "subjects");
  const focusAreas = extraStrings(extra, "focus_areas");
  return {
    source: "remote",
    synced: true,
    // Backend truth wins; a locally-completed onboarding still counts.
    onboardingComplete:
      profile.onboarding_completed || local.onboardingComplete,
    classLevel: profile.grade ?? local.classLevel,
    board: profile.board ?? local.board,
    goal: profile.goal ?? local.goal,
    examDate: profile.time_left ?? local.examDate,
    dailyTime:
      extraString(extra, "daily_time") ??
      profile.primary_need ??
      local.dailyTime,
    preferredTime:
      extraString(extra, "preferred_time") ??
      local.preferredTime ??
      profile.language_preference,
    subject: profile.subject ?? subjects[0] ?? local.subject,
    subjects: subjects.length
      ? subjects
      : profile.subject
        ? [profile.subject]
        : local.subjects,
    languagePreference:
      profile.language_preference ??
      extraString(extra, "language_preference") ??
      local.languagePreference,
    learningStyle: extraString(extra, "learning_style") ?? local.learningStyle,
    focusAreas: focusAreas.length
      ? focusAreas
      : profile.weak_areas?.length
        ? profile.weak_areas
        : local.focusAreas,
  };
}

function dailyTimeFromMinutes(minutes: number): string | null {
  if (!Number.isFinite(minutes) || minutes <= 0) return null;
  return minutes === 120 ? "2 hours" : `${minutes} min`;
}

/**
 * Phase 4 learning state owns the active planning profile. The older study
 * profile still carries a few optional preferences, so it remains a fallback
 * rather than a competing completion signal.
 */
function contextFromLearningState(
  state: LearningStateSummary,
  fallback: StudentContext,
): StudentContext {
  const profile = state.profile;
  if (!profile) return fallback;
  const subjects = state.subjects.map((item) => item.name).filter(Boolean);
  const currentSubject =
    state.subjects.find((item) => item.id === profile.current_subject_id)?.name ??
    subjects[0] ??
    fallback.subject;
  return {
    ...fallback,
    source: "remote",
    synced: true,
    onboardingComplete:
      profile.onboarding_completed || fallback.onboardingComplete,
    classLevel: profile.class_level || fallback.classLevel,
    board: profile.board || fallback.board,
    goal: profile.goal || fallback.goal,
    examDate: profile.exam_date ?? fallback.examDate,
    dailyTime:
      dailyTimeFromMinutes(profile.daily_minutes) ?? fallback.dailyTime,
    preferredTime: profile.preferred_time ?? fallback.preferredTime,
    subjects: subjects.length ? subjects : fallback.subjects,
    subject: currentSubject,
  };
}

function cacheCompletedContext(context: StudentContext): void {
  if (typeof window === "undefined" || !context.onboardingComplete) return;
  window.localStorage.setItem(ONBOARDING_COMPLETED_KEY, "true");
  claimLocalOnboardingOwnership();
  window.localStorage.setItem(
    ONBOARDING_PROFILE_KEY,
    JSON.stringify({
      goal: context.goal ?? "",
      class: context.classLevel ?? "",
      board: context.board ?? "",
      examDate: context.examDate ?? "",
      dailyTime: context.dailyTime ?? "",
      preferredTime: context.preferredTime ?? "",
      subjects: context.subjects,
      languagePreference: context.languagePreference ?? "",
      learningStyle: context.learningStyle ?? "",
      focus: context.focusAreas,
    } satisfies LocalOnboarding),
  );
}

/**
 * The full merge: backend profile (when signed in) over local onboarding.
 *
 * Self-heals the split-truth bug: if onboarding was completed on this device
 * but the backend has no (or an incomplete) profile — e.g. the account
 * predates the write-through, or the original save failed — the local profile
 * is pushed up once, fire-and-forget, so every other device converges.
 */
// Short-lived cache so navigating between pages doesn't refetch the profile
// on every mount — the context changes rarely (onboarding, settings), and a
// snappy page-to-page feel matters more than 30s-stale sync metadata.
const CONTEXT_CACHE_MS = 30_000;
let contextCache: { at: number; userId: string | null; value: StudentContext } | null = null;

export async function loadStudentContext(): Promise<StudentContext> {
  const local = getLocalStudentContext();
  if (!hasLiveSession()) return local;

  const viewerId = currentUserId();
  if (
    contextCache &&
    contextCache.userId === viewerId &&
    Date.now() - contextCache.at < CONTEXT_CACHE_MS
  ) {
    return contextCache.value;
  }

  const merged = await loadStudentContextUncached(local);
  contextCache = { at: Date.now(), userId: viewerId, value: merged };
  return merged;
}

/** Drop the cache after anything that changes the profile (e.g. onboarding). */
export function invalidateStudentContext(): void {
  contextCache = null;
  remoteOnboardingCheck = null;
}

async function loadStudentContextUncached(
  local: StudentContext,
): Promise<StudentContext> {
  const [remote, learningState] = await Promise.all([
    getStudyProfileRemote().catch(() => null),
    getLearningState().catch(() => null),
  ]);
  const legacyContext = remote ? contextFromRemote(remote, local) : local;
  const merged = learningState
    ? contextFromLearningState(learningState, legacyContext)
    : legacyContext;

  if (remote || learningState?.profile) {
    cacheCompletedContext(merged);
    if (merged.onboardingComplete && !remote?.onboarding_completed) {
      void repairRemoteProfile(merged);
    }
    return merged;
  }

  // Signed in but no backend profile: repair from local when we can.
  if (local.onboardingComplete) {
    const saved = await repairRemoteProfile(local);
    return { ...local, synced: saved };
  }
  return local;
}

async function repairRemoteProfile(local: StudentContext): Promise<boolean> {
  return saveStudyProfileRemote({
    goal: local.goal,
    grade: local.classLevel,
    board: local.board,
    time_left: local.examDate,
    primary_need: local.dailyTime,
    language_preference: local.languagePreference,
    subject: local.subject,
    weak_areas: [],
    onboarding_completed: true,
    extra: {
      schema_version: 2,
      subjects: local.subjects,
      daily_time: local.dailyTime,
      preferred_time: local.preferredTime,
      language_preference: local.languagePreference,
      learning_style: local.learningStyle,
      focus_areas: local.focusAreas,
    },
  });
}

/** One-line summary for focus cards, e.g. "SSLC / 10th · Kerala State Board". */
export function studentContextHeadline(ctx: StudentContext): string | null {
  const parts = [ctx.classLevel, ctx.board].filter(Boolean);
  return parts.length ? parts.join(" · ") : null;
}

// ── Onboarding gate ──────────────────────────────────────────────────────────
// The route guard used to trust localStorage alone, so a signed-in student on
// a fresh device (backend profile complete, local flag absent) was forced back
// through onboarding. This checks the backend once per page load and backfills
// the local cache so the fast path works next time.

let remoteOnboardingCheck: {
  userId: string | null;
  promise: Promise<boolean>;
} | null = null;

export function isOnboardingCompleteEffective(): Promise<boolean> {
  if (
    typeof window !== "undefined" &&
    window.localStorage.getItem(ONBOARDING_COMPLETED_KEY) === "true" &&
    localOnboardingUsable()
  ) {
    return Promise.resolve(true);
  }
  if (!hasLiveSession()) return Promise.resolve(false);
  const viewerId = currentUserId();
  if (!remoteOnboardingCheck || remoteOnboardingCheck.userId !== viewerId) {
    const promise = Promise.all([
      getStudyProfileRemote().catch(() => null),
      getLearningState().catch(() => null),
    ]).then(([legacyProfile, learningState]) => {
      const local = getLocalStudentContext();
      const legacyContext = legacyProfile
        ? contextFromRemote(legacyProfile, local)
        : local;
      const merged = learningState
        ? contextFromLearningState(learningState, legacyContext)
        : legacyContext;
      cacheCompletedContext(merged);
      return merged.onboardingComplete;
    });
    remoteOnboardingCheck = { userId: viewerId, promise };
  }
  return remoteOnboardingCheck.promise;
}