/**
 * Data access layer for The Science of Self-Realization (SSR).
 *
 * Reads from MongoDB via Prisma.
 * SSR is a large prose book with 6 intro segments (front-pages, dedication,
 * foreword, introduction, appreciations, about-the-author) and 8 parent
 * chapters, each containing multiple sub-chapters (e.g., "1-1", "1-2", "2-1").
 *
 * Collections used:
 *   - book_meta (via Prisma BookMeta model)
 *   - prose_chapters (via Prisma ProseChapter model)
 */

import { prisma } from "@/lib/db";
import type { JsonValue } from "@prisma/client/runtime/library";

// ---------------------------------------------------------------------------
// Constants
// ---------------------------------------------------------------------------

const BOOK = "ssr";

/** Volume sentinel for books without volumes. */
const NO_VOLUME = 0;

// ---------------------------------------------------------------------------
// Types
// ---------------------------------------------------------------------------

export type SsrMeta = {
  book: string;
  title: string;
  author: string;
  year: number;
  description: string;
  totalChapters: number;
  chapters: SsrParentChapter[];
};

export type SsrParentChapter = {
  number: number;
  title: string;
  subChapters: SsrSubChapterEntry[];
};

export type SsrSubChapterEntry = {
  slug: string; // "1-1", "1-2", etc.
  title: string;
};

export type SsrIntroSegment = {
  slug: string;
  title: string;
  type: string;
  book: string;
  order: number;
  paragraphs: string[];
};

export type SsrChapter = {
  book: string;
  chapter: string; // "1-1", "2-1", etc.
  parentChapter: number;
  subChapter: number;
  title: string;
  parentTitle: string;
  type: string;
  paragraphs: string[];
};

/** Union type used in sidebar / table-of-contents navigation. */
export type SsrSidebarItem = {
  /** URL-safe slug: "intro-front-pages", "1-1", "parent-1", "intro-about-the-author" */
  slug: string;
  /** Human-readable label for the sidebar */
  label: string;
  /** "intro-segment" | "parent" | "sub-chapter" */
  type: string;
  /** Parent chapter number, or null for intro segments */
  parentChapter: number | null;
};

// ---------------------------------------------------------------------------
// HTML sanitisation
// ---------------------------------------------------------------------------

function sanitizeHtml(html: string): string {
  let clean = html.replace(/<script[\s>][\s\S]*?<\/script>/gi, "");
  clean = clean.replace(/<style[\s>][\s\S]*?<\/style>/gi, "");
  clean = clean.replace(/<iframe[\s>][\s\S]*?<\/iframe>/gi, "");
  clean = clean.replace(
    /<\/?(?:script|style|iframe|object|embed|form|input|textarea|select|button)[^>]*>/gi,
    "",
  );
  clean = clean.replace(/\s+on\w+\s*=\s*(?:"[^"]*"|'[^']*'|[^\s>]+)/gi, "");
  clean = clean.replace(/href\s*=\s*"javascript:[^"]*"/gi, 'href=""');
  clean = clean.replace(/href\s*=\s*'javascript:[^']*'/gi, "href=''");
  return clean;
}

/** Normalize paragraphs — handles both native arrays and stringified JSON. */
function normalizeParagraphs(paragraphs: string[] | JsonValue): string[] {
  let result: string[];

  if (typeof paragraphs === "string") {
    try {
      const parsed = JSON.parse(paragraphs);
      result = Array.isArray(parsed) ? parsed : [paragraphs];
    } catch {
      result = [paragraphs];
    }
  } else if (Array.isArray(paragraphs)) {
    result = paragraphs as string[];
  } else {
    result = [];
  }

  return result.map(sanitizeHtml);
}

// ---------------------------------------------------------------------------
// Book meta
// ---------------------------------------------------------------------------

/**
 * Book-level metadata (title, author, chapter list with sub-chapters, etc.)
 */
export async function getSsrMeta(): Promise<SsrMeta | null> {
  const meta = await prisma.bookMeta.findUnique({ where: { book: BOOK } });
  if (!meta) return null;
  return meta.data as unknown as SsrMeta;
}

// ---------------------------------------------------------------------------
// Intro segments
// ---------------------------------------------------------------------------

/**
 * All intro segments, ordered by their `order` field.
 */
export async function getSsrIntroSegments(): Promise<SsrIntroSegment[]> {
  const results = await prisma.proseChapter.findMany({
    where: { book: BOOK, volume: NO_VOLUME, type: "intro-segment" },
    orderBy: { order: "asc" },
  });

  return results.map((doc) => ({
    slug: doc.slug,
    title: doc.title,
    type: doc.type,
    book: doc.book,
    order: doc.order,
    paragraphs: normalizeParagraphs(doc.paragraphs),
  }));
}

/**
 * A single intro segment by slug.
 * Accepts both "intro-front-pages" (URL slug) and "front-pages" (raw slug).
 */
export async function getSsrIntroSegment(
  slug: string,
): Promise<SsrIntroSegment | null> {
  // DB stores with "intro-" prefix; accept either form
  const dbSlug = slug.startsWith("intro-") ? slug : `intro-${slug}`;

  const doc = await prisma.proseChapter.findUnique({
    where: {
      book_volume_slug: { book: BOOK, volume: NO_VOLUME, slug: dbSlug },
    },
  });
  if (!doc) return null;

  return {
    slug: doc.slug,
    title: doc.title,
    type: doc.type,
    book: doc.book,
    order: doc.order,
    paragraphs: normalizeParagraphs(doc.paragraphs),
  };
}

// ---------------------------------------------------------------------------
// Chapters (sub-chapters like "1-1", "2-3", etc.)
// ---------------------------------------------------------------------------

/**
 * A sub-chapter by its slug (e.g. "1-1", "2-3").
 */
export async function getSsrChapter(slug: string): Promise<SsrChapter | null> {
  const doc = await prisma.proseChapter.findUnique({
    where: {
      book_volume_slug: {
        book: BOOK,
        volume: NO_VOLUME,
        slug,
      },
    },
  });
  if (!doc) return null;

  // Parse parentChapter and subChapter from slug "X-Y"
  const parts = slug.split("-");
  const parentChapter = parseInt(parts[0], 10);
  const subChapter = parseInt(parts[1], 10);

  // Derive parentTitle from meta if available
  const meta = await getSsrMeta();
  const parentEntry = meta?.chapters.find((ch) => ch.number === parentChapter);
  const parentTitle = parentEntry?.title ?? "";

  return {
    book: doc.book,
    chapter: slug,
    parentChapter,
    subChapter,
    title: doc.title,
    parentTitle,
    type: doc.type,
    paragraphs: normalizeParagraphs(doc.paragraphs),
  };
}

// ---------------------------------------------------------------------------
// Unified content accessor
// ---------------------------------------------------------------------------

/**
 * Get content by URL slug.
 *
 *   "intro-front-pages"      → intro segment
 *   "intro-dedication"       → intro segment
 *   "intro-about-the-author" → intro segment
 *   "1-1", "2-3", etc.       → sub-chapter
 */
export async function getSsrContent(
  slug: string,
): Promise<SsrChapter | SsrIntroSegment | null> {
  if (slug.startsWith("intro-")) {
    return getSsrIntroSegment(slug);
  }

  // Sub-chapter slug like "1-1", "2-3"
  return getSsrChapter(slug);
}

// ---------------------------------------------------------------------------
// Sidebar navigation
// ---------------------------------------------------------------------------

/**
 * Build the full sidebar navigation list with hierarchical structure.
 *
 * Order: front-pages → dedication → foreword → introduction → appreciations
 *        → parent-1 (label) → 1-1, 1-2, ... → parent-2 (label) → 2-1, 2-2, ...
 *        → about-the-author
 *
 * "parent" type items are non-clickable headings. Only "intro-segment" and
 * "sub-chapter" items are navigable pages.
 */
export async function getSsrSidebarItems(): Promise<SsrSidebarItem[]> {
  const [meta, allDocs] = await Promise.all([
    getSsrMeta(),
    prisma.proseChapter.findMany({
      where: { book: BOOK, volume: NO_VOLUME },
      orderBy: { order: "asc" },
      select: {
        slug: true,
        title: true,
        type: true,
        chapter: true,
        order: true,
      },
    }),
  ]);

  if (!meta) return [];

  const items: SsrSidebarItem[] = [];

  // Intro segments that come BEFORE chapters (order < 99)
  for (const doc of allDocs) {
    if (doc.type === "intro-segment" && doc.order < 99) {
      items.push({
        slug: doc.slug,
        label: doc.title,
        type: "intro-segment",
        parentChapter: null,
      });
    }
  }

  // Chapters — grouped by parent chapter with sub-chapters
  for (const ch of meta.chapters) {
    // Parent heading (non-clickable label)
    items.push({
      slug: `parent-${ch.number}`,
      label: `${ch.number}. ${ch.title}`,
      type: "parent",
      parentChapter: ch.number,
    });

    // Sub-chapters under this parent
    for (const sub of ch.subChapters) {
      items.push({
        slug: sub.slug,
        label: sub.title,
        type: "sub-chapter",
        parentChapter: ch.number,
      });
    }
  }

  // Intro segments that come AFTER chapters (order >= 99, e.g., about-the-author)
  for (const doc of allDocs) {
    if (doc.type === "intro-segment" && doc.order >= 99) {
      items.push({
        slug: doc.slug,
        label: doc.title,
        type: "intro-segment",
        parentChapter: null,
      });
    }
  }

  return items;
}

/**
 * Get the flat list of navigable sidebar items (excludes "parent" headings).
 * Used for prev/next navigation.
 */
export function getNavigableItems(items: SsrSidebarItem[]): SsrSidebarItem[] {
  return items.filter((item) => item.type !== "parent");
}