/**
 * Book + chapter derivation for transcriptions.
 *
 * Transcriptions carry a free-text scripture `reference` (e.g. "SB 1.2.3",
 * "BG Introduction", "CC Madhya-līlā 20.101") rather than structured
 * book/chapter columns. This module is the single source of truth for turning
 * those strings into a book identity and a chapter grouping, reused by the
 * books grid, the listing page, and the book browser.
 *
 * The book registry mirrors `TranscriptionBooks` in the Go BFF
 * (internal/repository/transcription_repo.go).
 */

export type BookCode = "SB" | "BG" | "CC" | "BS" | "NOD" | "ISO";

export const BOOKS: Record<BookCode, { title: string; order: number }> = {
  SB: { title: "Śrīmad-Bhāgavatam", order: 1 },
  BG: { title: "Bhagavad-gītā", order: 2 },
  CC: { title: "Caitanya-caritāmṛta", order: 3 },
  BS: { title: "Brahma-saṁhitā", order: 4 },
  NOD: { title: "The Nectar of Devotion", order: 5 },
  ISO: { title: "Śrī Īśopaniṣad", order: 6 },
};

/** Display title for a (possibly unknown) book code; "" if unknown. */
export function bookTitle(code: string): string {
  const b = BOOKS[code.toUpperCase() as BookCode];
  return b ? b.title : "";
}

/**
 * Extract the (starting) verse number from a reference, for ordering lectures
 * within a chapter. The verse is the last dotted numeric component, and for a
 * range we take the start: "BG 2.13" → 13, "SB 1.2.3" → 3, "SB 3.27.11–16" →
 * 11, "CC Madhya-līlā 20.101" → 101, "ISO Mantra 4" → 4. References with no
 * number (e.g. bare "NOD") sort last (stable → keep their incoming order).
 */
export function parseVerse(reference: string | null): number {
  const m = (reference ?? "").trim().match(/(\d+(?:\.\d+)*)/);
  if (!m) return Number.MAX_SAFE_INTEGER;
  const parts = m[1].split(".");
  return Number(parts[parts.length - 1]);
}

/** A section is a canto (SB) or līlā (CC); null for books without that level. */
export type ChapterSection = {
  key: string;
  label: string;
  order: number;
};

/** A chapter grouping for the accordion list. */
export type ChapterGroup = {
  key: string;
  label: string;
  sort: [number, number];
  /** Canto/līlā this chapter belongs to (SB, CC); null for flat books. */
  section: ChapterSection | null;
};

// Caitanya-caritāmṛta līlā ordering (Ādi → Madhya → Antya).
const LILA_ORDER: Record<string, { label: string; order: number }> = {
  ADI: { label: "Ādi-līlā", order: 1 },
  MADHYA: { label: "Madhya-līlā", order: 2 },
  ANTYA: { label: "Antya-līlā", order: 3 },
};

const OTHER: ChapterGroup = {
  key: "other",
  label: "Other",
  sort: [9999, 0],
  section: null,
};

/**
 * Parse a transcription reference into its chapter group, given the book code.
 * Tolerates the corpus's noise (en-dash vs hyphen, "Madhya" vs "Madhya-līlā",
 * a stray "SB 7", etc.). Unparseable / missing references fall into "Other".
 */
export function parseChapter(code: string, reference: string | null): ChapterGroup {
  const ref = (reference ?? "").trim();
  if (!ref) return OTHER;

  switch (code.toUpperCase() as BookCode) {
    case "BG": {
      if (/^BG\s+Introduction/i.test(ref)) {
        return {
          key: "bg-intro",
          label: "Introduction",
          sort: [0, 0],
          section: null,
        };
      }
      const m = ref.match(/^BG\s+(\d+)/);
      if (m) {
        const n = Number(m[1]);
        return {
          key: `bg-${n}`,
          label: `Chapter ${n}`,
          sort: [n, 0],
          section: null,
        };
      }
      return OTHER;
    }
    case "SB": {
      const m = ref.match(/^SB\s+(\d+)\.(\d+)/);
      if (m) {
        const c = Number(m[1]);
        const ch = Number(m[2]);
        return {
          key: `sb-${c}-${ch}`,
          label: `Chapter ${ch}`,
          sort: [c, ch],
          section: { key: `sb-${c}`, label: `Canto ${c}`, order: c },
        };
      }
      const cantoOnly = ref.match(/^SB\s+(\d+)\b/);
      if (cantoOnly) {
        const c = Number(cantoOnly[1]);
        return {
          key: `sb-${c}-0`,
          label: "Other",
          sort: [c, 0],
          section: { key: `sb-${c}`, label: `Canto ${c}`, order: c },
        };
      }
      return OTHER;
    }
    case "CC": {
      const m = ref.match(/^CC\s+(Ādi|Adi|Madhya|Antya)(?:-līlā)?\s+(\d+)/i);
      if (m) {
        const lila = LILA_ORDER[m[1].toUpperCase().replace("Ā", "A")];
        const ch = Number(m[2]);
        if (lila) {
          return {
            key: `cc-${lila.order}-${ch}`,
            label: `Chapter ${ch}`,
            sort: [lila.order, ch],
            section: {
              key: `cc-${lila.order}`,
              label: lila.label,
              order: lila.order,
            },
          };
        }
      }
      return OTHER;
    }
    case "BS": {
      const m = ref.match(/^BS\s+(\d+)/);
      if (m) {
        const n = Number(m[1]);
        return {
          key: `bs-${n}`,
          label: `Chapter ${n}`,
          sort: [n, 0],
          section: null,
        };
      }
      return OTHER;
    }
    case "ISO": {
      const m = ref.match(/^ISO\s+Mantra\s+(\d+)/i);
      if (m) {
        const n = Number(m[1]);
        return {
          key: `iso-${n}`,
          label: `Mantra ${n}`,
          sort: [n, 0],
          section: null,
        };
      }
      return { key: "iso", label: "Śrī Īśopaniṣad", sort: [0, 0], section: null };
    }
    case "NOD":
      return {
        key: "nod",
        label: "The Nectar of Devotion",
        sort: [0, 0],
        section: null,
      };
    default:
      return OTHER;
  }
}