import { asc, eq, inArray } from "drizzle-orm";
import { z } from "zod";
import { db } from "@/db";
import {
  comments,
  fontEnum,
  navItems,
  pages,
  postTags,
  posts,
  settings,
  tags,
  themeEnum,
  users,
} from "@/db/schema";
import { sanitizeHtml } from "@/lib/html";
import { isValidLinkUrl } from "@/lib/validation";
import { getSettings } from "./settings";

/**
 * Site backup format. Cross-references use slugs instead of database ids so
 * a file exported from one database imports cleanly into another (identity
 * columns are regenerated on import).
 */
export const SITE_EXPORT_FORMAT = "yap-blog-export";
// v1: posts/pages/tags/nav/settings. v2 adds comments. v3 adds
// posts.authorUsername so post ownership survives a restore. Older
// files still import (missing fields default to empty/unowned).
export const SITE_EXPORT_VERSION = 3;

const slugValue = z.string().trim().min(1).max(120);
const statusValue = z.enum(["draft", "published"]);
const bodyValue = z.string().max(500_000);
const timestampValue = z.coerce.date();

export const siteExportSchema = z
  .object({
    format: z.literal(SITE_EXPORT_FORMAT),
    version: z.union([z.literal(1), z.literal(2), z.literal(3)]),
    exportedAt: timestampValue,
    settings: z.object({
      siteTitle: z.string().trim().min(1).max(120),
      headerText: z.string().trim().max(300),
      footerText: z.string().trim().max(500),
      postsPerPage: z.number().int().min(1).max(50),
      excerptWords: z.number().int().min(5).max(200),
      homeMode: z.enum(["posts", "tag", "page"]),
      homeTagSlug: slugValue.nullable(),
      homePageSlug: slugValue.nullable(),
      theme: z.enum(themeEnum.enumValues),
      font: z.enum(fontEnum.enumValues),
    }),
    navItems: z
      .array(
        z.object({
          label: z.string().trim().min(1).max(80),
          url: z.string().trim().max(2000).nullable(),
          pageSlug: slugValue.nullable(),
        }),
      )
      .max(20),
    tags: z
      .array(z.object({ name: z.string().trim().min(1).max(80), slug: slugValue }))
      .max(5_000),
    pages: z
      .array(
        z.object({
          title: z.string().trim().min(1).max(200),
          slug: slugValue,
          body: bodyValue,
          status: statusValue,
          createdAt: timestampValue,
          updatedAt: timestampValue,
        }),
      )
      .max(10_000),
    posts: z
      .array(
        z.object({
          title: z.string().trim().min(1).max(200),
          slug: slugValue,
          body: bodyValue,
          authorName: z.string().trim().min(1).max(120),
          /**
           * Owning account's username. Accounts are not part of the export;
           * on import this is matched against existing usernames and posts
           * without a match become unowned (admin-managed).
           */
          authorUsername: z.string().trim().min(1).max(120).nullable().default(null),
          featuredImageUrl: z.string().trim().max(2000).nullable(),
          featuredImageAlt: z.string().trim().max(300).nullable(),
          status: statusValue,
          createdAt: timestampValue,
          updatedAt: timestampValue,
          publishedAt: timestampValue.nullable(),
          tagSlugs: z.array(slugValue).max(50),
        }),
      )
      .max(50_000),
    comments: z
      .array(
        z.object({
          /** Id local to this file (the exporter's DB id); remapped on import. */
          id: z.number().int().positive(),
          postSlug: slugValue,
          parentId: z.number().int().positive().nullable(),
          authorName: z.string().trim().min(1).max(120),
          authorEmail: z.string().trim().min(1).max(254),
          emailPublic: z.boolean(),
          body: z.string().min(1).max(5_000),
          status: z.enum(["pending", "approved"]),
          createdAt: timestampValue,
        }),
      )
      .max(100_000)
      .default([]),
  })
  .superRefine((data, ctx) => {
    const duplicate = (values: string[]): string | undefined => {
      const seen = new Set<string>();
      for (const value of values) {
        if (seen.has(value)) return value;
        seen.add(value);
      }
      return undefined;
    };

    const dupTag = duplicate(data.tags.map((t) => t.slug));
    if (dupTag) ctx.addIssue({ code: "custom", message: `Duplicate tag slug “${dupTag}”.` });
    const dupTagName = duplicate(data.tags.map((t) => t.name));
    if (dupTagName) {
      ctx.addIssue({ code: "custom", message: `Duplicate tag name “${dupTagName}”.` });
    }
    const dupPage = duplicate(data.pages.map((p) => p.slug));
    if (dupPage) ctx.addIssue({ code: "custom", message: `Duplicate page slug “${dupPage}”.` });
    const dupPost = duplicate(data.posts.map((p) => p.slug));
    if (dupPost) ctx.addIssue({ code: "custom", message: `Duplicate post slug “${dupPost}”.` });

    const tagSlugs = new Set(data.tags.map((t) => t.slug));
    const pageSlugs = new Set(data.pages.map((p) => p.slug));

    for (const post of data.posts) {
      for (const slug of post.tagSlugs) {
        if (!tagSlugs.has(slug)) {
          ctx.addIssue({
            code: "custom",
            message: `Post “${post.slug}” references unknown tag “${slug}”.`,
          });
        }
      }
    }

    for (const item of data.navItems) {
      const hasUrl = item.url !== null && item.url !== "";
      const hasPage = item.pageSlug !== null;
      if (hasUrl === hasPage) {
        ctx.addIssue({
          code: "custom",
          message: `Navigation item “${item.label}” must link to either a page or a URL.`,
        });
      } else if (hasUrl && !isValidLinkUrl(item.url as string)) {
        ctx.addIssue({
          code: "custom",
          message: `Navigation item “${item.label}” has an invalid URL.`,
        });
      } else if (hasPage && !pageSlugs.has(item.pageSlug as string)) {
        ctx.addIssue({
          code: "custom",
          message: `Navigation item “${item.label}” references unknown page “${item.pageSlug}”.`,
        });
      }
    }

    if (data.settings.homeMode === "tag") {
      if (!data.settings.homeTagSlug || !tagSlugs.has(data.settings.homeTagSlug)) {
        ctx.addIssue({
          code: "custom",
          message: "Settings use a home tag that is not in the export.",
        });
      }
    }
    if (data.settings.homeMode === "page") {
      if (!data.settings.homePageSlug || !pageSlugs.has(data.settings.homePageSlug)) {
        ctx.addIssue({
          code: "custom",
          message: "Settings use a home page that is not in the export.",
        });
      }
    }

    const postSlugs = new Set(data.posts.map((p) => p.slug));
    const commentById = new Map(data.comments.map((c) => [c.id, c]));
    if (commentById.size !== data.comments.length) {
      ctx.addIssue({ code: "custom", message: "Duplicate comment ids in the export." });
      return; // parent-chain checks below assume unique ids
    }
    for (const comment of data.comments) {
      if (!postSlugs.has(comment.postSlug)) {
        ctx.addIssue({
          code: "custom",
          message: `Comment ${comment.id} references unknown post “${comment.postSlug}”.`,
        });
        continue;
      }
      if (comment.parentId === null) continue;
      const parent = commentById.get(comment.parentId);
      if (!parent) {
        ctx.addIssue({
          code: "custom",
          message: `Comment ${comment.id} replies to unknown comment ${comment.parentId}.`,
        });
      } else if (parent.postSlug !== comment.postSlug) {
        ctx.addIssue({
          code: "custom",
          message: `Comment ${comment.id} replies to a comment on a different post.`,
        });
      }
    }
    // Reject parent cycles (impossible via the app, possible in a crafted
    // file) — the importer's parents-first insertion would never terminate.
    const commentDepthCache = new Map<number, boolean>();
    for (const comment of data.comments) {
      const seen = new Set<number>();
      let current: typeof comment | undefined = comment;
      while (current && current.parentId !== null) {
        if (commentDepthCache.get(current.id)) break; // known-good chain
        if (seen.has(current.id)) {
          ctx.addIssue({
            code: "custom",
            message: `Comment ${comment.id} is part of a reply cycle.`,
          });
          return;
        }
        seen.add(current.id);
        current = commentById.get(current.parentId);
      }
      for (const id of seen) commentDepthCache.set(id, true);
    }
  });

export type SiteExport = z.infer<typeof siteExportSchema>;

export function parseSiteExportJson(
  json: string,
): { data: SiteExport } | { error: string } {
  let raw: unknown;
  try {
    raw = JSON.parse(json);
  } catch {
    return { error: "That file is not valid JSON." };
  }
  const parsed = siteExportSchema.safeParse(raw);
  if (!parsed.success) {
    const issue = parsed.error.issues[0];
    const path = issue?.path.length ? ` (at ${issue.path.join(".")})` : "";
    return {
      error: `That file is not a valid site export: ${issue?.message ?? "unknown error"}${path}`,
    };
  }
  return { data: parsed.data };
}

/** Snapshot of everything the admin can edit: settings, nav, tags, pages, posts. */
export async function buildSiteExport(): Promise<SiteExport> {
  const [settingsRow, navRows, tagRows, pageRows, postRows, postTagRows, commentRows] =
    await Promise.all([
    getSettings(),
    db
      .select({ item: navItems, pageSlug: pages.slug })
      .from(navItems)
      .leftJoin(pages, eq(pages.id, navItems.pageId))
      .orderBy(asc(navItems.sortOrder), asc(navItems.id)),
    db.select().from(tags).orderBy(asc(tags.slug)),
    db.select().from(pages).orderBy(asc(pages.id)),
    db
      .select({ post: posts, authorUsername: users.username })
      .from(posts)
      .leftJoin(users, eq(users.id, posts.authorId))
      .orderBy(asc(posts.id)),
    db
      .select({ postId: postTags.postId, tagSlug: tags.slug })
      .from(postTags)
      .innerJoin(tags, eq(tags.id, postTags.tagId))
      .orderBy(asc(tags.slug)),
    db
      .select({ comment: comments, postSlug: posts.slug })
      .from(comments)
      .innerJoin(posts, eq(posts.id, comments.postId))
      .orderBy(asc(comments.id)),
  ]);

  const tagSlugsByPost = new Map<number, string[]>();
  for (const row of postTagRows) {
    const list = tagSlugsByPost.get(row.postId) ?? [];
    list.push(row.tagSlug);
    tagSlugsByPost.set(row.postId, list);
  }

  return {
    format: SITE_EXPORT_FORMAT,
    version: SITE_EXPORT_VERSION,
    exportedAt: new Date(),
    settings: {
      siteTitle: settingsRow.siteTitle,
      headerText: settingsRow.headerText,
      footerText: settingsRow.footerText,
      postsPerPage: settingsRow.postsPerPage,
      excerptWords: settingsRow.excerptWords,
      homeMode: settingsRow.homeMode,
      homeTagSlug: tagRows.find((t) => t.id === settingsRow.homeTagId)?.slug ?? null,
      homePageSlug:
        pageRows.find((p) => p.id === settingsRow.homePageId)?.slug ?? null,
      theme: settingsRow.theme,
      font: settingsRow.font,
    },
    navItems: navRows.map(({ item, pageSlug }) => ({
      label: item.label,
      url: item.url,
      pageSlug,
    })),
    tags: tagRows.map((t) => ({ name: t.name, slug: t.slug })),
    pages: pageRows.map((p) => ({
      title: p.title,
      slug: p.slug,
      body: p.body,
      status: p.status,
      createdAt: p.createdAt,
      updatedAt: p.updatedAt,
    })),
    posts: postRows.map(({ post: p, authorUsername }) => ({
      title: p.title,
      slug: p.slug,
      body: p.body,
      authorName: p.authorName,
      authorUsername,
      featuredImageUrl: p.featuredImageUrl,
      featuredImageAlt: p.featuredImageAlt,
      status: p.status,
      createdAt: p.createdAt,
      updatedAt: p.updatedAt,
      publishedAt: p.publishedAt,
      tagSlugs: tagSlugsByPost.get(p.id) ?? [],
    })),
    comments: commentRows.map(({ comment, postSlug }) => ({
      id: comment.id,
      postSlug,
      parentId: comment.parentId,
      authorName: comment.authorName,
      authorEmail: comment.authorEmail,
      emailPublic: comment.emailPublic,
      body: comment.body,
      status: comment.status,
      createdAt: comment.createdAt,
    })),
  };
}

/** Keeps multi-row inserts well under Postgres's 65535-parameter limit. */
function chunk<T>(items: T[], size: number): T[][] {
  const out: T[][] = [];
  for (let i = 0; i < items.length; i += size) out.push(items.slice(i, i + size));
  return out;
}

/**
 * Restores a backup by REPLACING all content: posts, tags, pages, navigation,
 * and settings. Users and sessions are untouched. Runs in one transaction, so
 * a failed import leaves the database exactly as it was.
 */
export async function importSiteExport(data: SiteExport): Promise<void> {
  await db.transaction(async (tx) => {
    // Deleting posts/pages/tags cascades post_tags, comments, and page nav
    // items away; the old settings row's home references become NULL via
    // ON DELETE SET NULL.
    await tx.delete(navItems);
    await tx.delete(posts);
    await tx.delete(pages);
    await tx.delete(tags);

    const tagIdBySlug = new Map<string, number>();
    for (const batch of chunk(data.tags, 1000)) {
      const inserted = await tx
        .insert(tags)
        .values(batch.map((t) => ({ name: t.name, slug: t.slug })))
        .returning({ id: tags.id, slug: tags.slug });
      for (const row of inserted) tagIdBySlug.set(row.slug, row.id);
    }

    const pageIdBySlug = new Map<string, number>();
    for (const batch of chunk(data.pages, 1000)) {
      const inserted = await tx
        .insert(pages)
        .values(
          batch.map((p) => ({
            title: p.title,
            slug: p.slug,
            // Bodies come from an uploaded file, so sanitize at this trust
            // boundary just like the editor actions do.
            body: sanitizeHtml(p.body),
            status: p.status,
            createdAt: p.createdAt,
            updatedAt: p.updatedAt,
          })),
        )
        .returning({ id: pages.id, slug: pages.slug });
      for (const row of inserted) pageIdBySlug.set(row.slug, row.id);
    }

    // Accounts survive an import untouched; posts re-attach to them by
    // username. Unknown usernames leave the post unowned (admin-managed).
    const exportUsernames = [
      ...new Set(
        data.posts.flatMap((p) => (p.authorUsername !== null ? [p.authorUsername] : [])),
      ),
    ];
    const userIdByUsername = new Map<string, number>();
    if (exportUsernames.length > 0) {
      const userRows = await tx
        .select({ id: users.id, username: users.username })
        .from(users)
        .where(inArray(users.username, exportUsernames));
      for (const row of userRows) userIdByUsername.set(row.username, row.id);
    }

    const postIdBySlug = new Map<string, number>();
    const links: Array<{ postId: number; tagId: number }> = [];
    for (const batch of chunk(data.posts, 1000)) {
      const inserted = await tx
        .insert(posts)
        .values(
          batch.map((p) => ({
            title: p.title,
            slug: p.slug,
            body: sanitizeHtml(p.body),
            authorName: p.authorName,
            authorId:
              p.authorUsername !== null
                ? (userIdByUsername.get(p.authorUsername) ?? null)
                : null,
            featuredImageUrl: p.featuredImageUrl,
            featuredImageAlt: p.featuredImageAlt,
            status: p.status,
            createdAt: p.createdAt,
            updatedAt: p.updatedAt,
            publishedAt: p.publishedAt,
          })),
        )
        .returning({ id: posts.id, slug: posts.slug });
      for (const row of inserted) postIdBySlug.set(row.slug, row.id);
      for (const post of batch) {
        const postId = postIdBySlug.get(post.slug);
        if (postId === undefined) continue;
        for (const tagSlug of post.tagSlugs) {
          const tagId = tagIdBySlug.get(tagSlug);
          if (tagId !== undefined) links.push({ postId, tagId });
        }
      }
    }
    for (const batch of chunk(links, 5000)) {
      await tx.insert(postTags).values(batch);
    }

    // Comments insert parents-first so replies can point at fresh ids;
    // the schema validation above guarantees the parent graph is acyclic,
    // so every pass makes progress. Comment bodies are plain text (rendered
    // escaped), so no HTML sanitizing is needed.
    const commentIdByLocal = new Map<number, number>();
    let pendingComments = data.comments;
    while (pendingComments.length > 0) {
      const ready = pendingComments.filter(
        (c) => c.parentId === null || commentIdByLocal.has(c.parentId),
      );
      if (ready.length === 0) {
        // Unreachable after schema validation; guards the loop all the same.
        throw new Error("Comment import stalled on an unresolvable parent reference.");
      }
      for (const batch of chunk(ready, 1000)) {
        const inserted = await tx
          .insert(comments)
          .values(
            batch.map((c) => ({
              postId: postIdBySlug.get(c.postSlug)!,
              parentId: c.parentId === null ? null : commentIdByLocal.get(c.parentId)!,
              authorName: c.authorName,
              authorEmail: c.authorEmail,
              emailPublic: c.emailPublic,
              body: c.body,
              status: c.status,
              createdAt: c.createdAt,
            })),
          )
          // Postgres returns multi-row INSERT ... RETURNING rows in values
          // order, which is what lets us zip local ids to new ids here.
          .returning({ id: comments.id });
        batch.forEach((c, i) => commentIdByLocal.set(c.id, inserted[i].id));
      }
      pendingComments = pendingComments.filter((c) => !commentIdByLocal.has(c.id));
    }

    if (data.navItems.length > 0) {
      await tx.insert(navItems).values(
        data.navItems.map((item, index) => ({
          label: item.label,
          url: item.pageSlug !== null ? null : item.url,
          pageId: item.pageSlug !== null ? (pageIdBySlug.get(item.pageSlug) ?? null) : null,
          sortOrder: index,
        })),
      );
    }

    const s = data.settings;
    const settingsValues = {
      siteTitle: s.siteTitle,
      headerText: s.headerText,
      footerText: s.footerText,
      postsPerPage: s.postsPerPage,
      excerptWords: s.excerptWords,
      homeMode: s.homeMode,
      homeTagId:
        s.homeMode === "tag" && s.homeTagSlug !== null
          ? (tagIdBySlug.get(s.homeTagSlug) ?? null)
          : null,
      homePageId:
        s.homeMode === "page" && s.homePageSlug !== null
          ? (pageIdBySlug.get(s.homePageSlug) ?? null)
          : null,
      theme: s.theme,
      font: s.font,
    };
    await tx
      .insert(settings)
      .values({ id: 1, ...settingsValues })
      .onConflictDoUpdate({ target: settings.id, set: settingsValues });
  });
}