// The one JSON-LD @graph of a page: the CMS's nodes (the resolve answer's
// jsonld) plus the nodes layers and pages add through useSchemaNode, merged
// by @id. Pure, so `node --test` drives it directly.

import type { SeoJsonLd, SeoSchemaNode } from './types.ts'

const SCHEMA_CONTEXT = 'https://schema.org'

function isNode(value: unknown): value is SeoSchemaNode {
  return value !== null && typeof value === 'object' && !Array.isArray(value)
}

/** The nodes of a jsonld value: its @graph, or the value itself when it is a single node. */
function nodesOf(jsonld: unknown): SeoSchemaNode[] {
  if (!isNode(jsonld)) return []
  const graph = (jsonld as SeoJsonLd)['@graph']
  if (Array.isArray(graph)) return graph.filter(isNode)
  const { '@context': _context, ...node } = jsonld as Record<string, unknown>
  return Object.keys(node).length > 0 ? [node as SeoSchemaNode] : []
}

/**
 * Merges the CMS graph and the layer nodes into one {"@context", "@graph"}
 * object, or null when there is no node at all (then the page gets no
 * JSON-LD script). A layer node whose @id matches a node already in the
 * graph is merged into it, the values already there first (the CMS is the
 * editor's source of truth; the layer fills in what it lacks); a node
 * without @id or with a new @id is appended. The order of first appearance
 * is kept, so the output is stable between renders.
 */
export function mergeGraph(cmsJsonld: unknown, nodes: readonly unknown[] = []): { '@context': string; '@graph': SeoSchemaNode[] } | null {
  const graph: SeoSchemaNode[] = []
  const byId = new Map<string, number>()
  const add = (node: SeoSchemaNode) => {
    const id = typeof node['@id'] === 'string' && node['@id'] !== '' ? node['@id'] : null
    const { '@context': _context, ...clean } = node as Record<string, unknown>
    if (id !== null && byId.has(id)) {
      const at = byId.get(id) as number
      graph[at] = { ...clean, ...graph[at] } as SeoSchemaNode
      return
    }
    if (id !== null) byId.set(id, graph.length)
    graph.push({ ...clean } as SeoSchemaNode)
  }
  for (const node of nodesOf(cmsJsonld)) add(node)
  for (const node of nodes) if (isNode(node)) add(node)
  if (graph.length === 0) return null
  const context = isNode(cmsJsonld) && typeof (cmsJsonld as SeoJsonLd)['@context'] === 'string' ? ((cmsJsonld as SeoJsonLd)['@context'] as string) : SCHEMA_CONTEXT
  return { '@context': context, '@graph': graph }
}