import { NextRequest, NextResponse } from "next/server";
import path from "node:path";
import { findVideosForCode } from "@/lib/video";
import { assertLocalRequest } from "@/lib/api/localOnly";
import { getStoredVideoMetadata, serializeVideoMetadata } from "@/lib/video/metadata";
import { variantLabel } from "@/lib/video/partClassify";

export const runtime = "nodejs";
export const dynamic = "force-dynamic";

interface VariantOut {
  /** Absolute 0-based index into the original findVideosForCode result.
   *  Used as the `?part=` query value for stream/HLS endpoints. */
  partIdx: number;
  abs: string;
  rel: string;
  filename: string;
  size: number;
  label: string;
  metadata: ReturnType<typeof serializeVideoMetadata>;
}

interface PartOut {
  /** 1-based display index for the parts strip. */
  partIndex: number;
  /** Index into `variants[]` to use when no user pick has been made. */
  defaultIdx: number;
  variants: VariantOut[];
}

function stemOf(filename: string): string {
  const ext = path.extname(filename);
  return ext ? filename.slice(0, -ext.length) : filename;
}

/**
 * Group raw video files into parts (sequential CDs/discs) with
 * variants (alt encodes of the same part). Uses classification from
 * the metadata table; falls back to "every file is its own part" when
 * classification hasn't run yet.
 */
export async function GET(req: NextRequest, ctx: { params: Promise<{ code: string }> }) {
  const blocked = assertLocalRequest(req);
  if (blocked) return blocked;
  const { code } = await ctx.params;
  const decoded = decodeURIComponent(code);
  const files = findVideosForCode(decoded);

  // Build per-part groups.
  const partMap = new Map<string, VariantOut[]>();
  const orderedKeys: string[] = [];

  files.forEach((f, i) => {
    const meta = getStoredVideoMetadata(f.abs);
    const stem = stemOf(f.filename);
    const kind = meta?.partKind;
    const idx = meta?.partIndex ?? null;
    const group = meta?.variantGroup ?? null;

    // Group key strategy:
    //  - "part"    → group by the part's variantGroup (variants attach via dot-prefix)
    //  - "variant" → group by their attached variantGroup
    //  - "single" / unclassified → a singleton group keyed by abs path
    let key: string;
    if ((kind === "part" || kind === "variant") && group != null) {
      key = `g:${group}`;
    } else {
      key = `s:${f.abs}`;
    }

    const variant: VariantOut = {
      partIdx: i,
      abs: f.abs,
      rel: f.rel,
      filename: f.filename,
      size: f.size,
      label: group ? variantLabel(stem, group) : "original",
      metadata: serializeVideoMetadata(meta),
    };
    // Stash the underlying part index for sorting; non-parts get +Infinity.
    (variant as VariantOut & { __sort: number }).__sort = idx ?? (kind === "variant" ? -1 : Number.MAX_SAFE_INTEGER);

    let arr = partMap.get(key);
    if (!arr) {
      arr = [];
      partMap.set(key, arr);
      orderedKeys.push(key);
    }
    arr.push(variant);
  });

  // Build the ordered parts list. Sort parts by their lowest known
  // partIndex (singles fall to the end), preserving insertion order
  // as a tiebreak.
  const partEntries = orderedKeys.map((k) => {
    const variants = partMap.get(k)!;
    const minSort = Math.min(...variants.map((v) => (v as VariantOut & { __sort: number }).__sort));
    return { key: k, variants, sort: minSort };
  });
  partEntries.sort((a, b) => {
    if (a.sort !== b.sort) return a.sort - b.sort;
    return a.variants[0]!.partIdx - b.variants[0]!.partIdx;
  });

  const parts: PartOut[] = partEntries.map((entry, i) => {
    const variants = entry.variants;
    // Strip the sort helper field.
    for (const v of variants) delete (v as Partial<VariantOut & { __sort: number }>).__sort;
    // Default = the variant whose stem == group (the "base" file). If
    // none, alphabetically first by filename.
    const groupKey = entry.key.startsWith("g:") ? entry.key.slice(2) : null;
    let defaultIdx = 0;
    if (groupKey != null) {
      const exact = variants.findIndex((v) => stemOf(v.filename) === groupKey);
      if (exact >= 0) defaultIdx = exact;
      else {
        const sortedAlpha = [...variants].sort((a, b) => a.filename.localeCompare(b.filename));
        defaultIdx = variants.indexOf(sortedAlpha[0]!);
      }
    }
    return {
      partIndex: i + 1,
      defaultIdx,
      variants,
    };
  });

  // Backwards-compatible flat list — the default variant of each part
  // in display order. Existing consumers that only need one entry per
  // part keep working without changes.
  const flat = parts.map((p) => p.variants[p.defaultIdx]!);

  return NextResponse.json({
    parts,
    files: flat.map((v) => ({
      abs: v.abs,
      rel: v.rel,
      filename: v.filename,
      size: v.size,
      metadata: v.metadata,
    })),
  });
}