'use client';
import { createContext, type ReactNode, useCallback, useContext, useEffect, useMemo, useState } from 'react';
import type { ProvenanceEntry } from '@/lib/types';

/** What the drawer needs to explain one displayed value. `fallback` = the inline provenance the caller already has. */
export interface EvidenceTarget {
  slug: string;
  property: string;
  /** The displayed value (raw) — formatted in the drawer with `fmtValue(value, property)` unless `display` is given. */
  value?: unknown;
  display?: string;
  unit?: string | null;
  label?: string;
  fallback?: ProvenanceEntry | null;
  entity?: { name?: string; entity_type?: string } | null;
}

interface Ctx {
  target: EvidenceTarget | null;
  open: (t: EvidenceTarget) => void;
  close: () => void;
}
const EvidenceCtx = createContext<Ctx>({ target: null, open: () => undefined, close: () => undefined });

const HASH_RE = /^#evidence=([^:]+):(.+)$/;

/** Mounted once in the root layout. Mirrors the open target to `#evidence=<slug>:<property>` so a drawer can be linked. */
export function EvidenceProvider({ children }: { children: ReactNode }) {
  const [target, setTarget] = useState<EvidenceTarget | null>(null);
  const open = useCallback((t: EvidenceTarget) => {
    setTarget(t);
    try {
      history.replaceState(null, '', `#evidence=${encodeURIComponent(t.slug)}:${encodeURIComponent(t.property)}`);
    } catch {
      /* ignore */
    }
  }, []);
  const close = useCallback(() => {
    setTarget(null);
    try {
      if (HASH_RE.test(location.hash)) history.replaceState(null, '', location.pathname + location.search);
    } catch {
      /* ignore */
    }
  }, []);
  useEffect(() => {
    const m = HASH_RE.exec(location.hash);
    if (m) setTarget({ slug: decodeURIComponent(m[1] as string), property: decodeURIComponent(m[2] as string) });
  }, []);
  const value = useMemo(() => ({ target, open, close }), [target, open, close]);
  return <EvidenceCtx.Provider value={value}>{children}</EvidenceCtx.Provider>;
}

export function useEvidence(): Ctx {
  return useContext(EvidenceCtx);
}