drinktracker/src/lib/mcp/render.ts

import type { CallToolResult } from "@modelcontextprotocol/server"

/**
 * Shaping tool output.
 *
 * Every result carries both `content` text and `structuredContent`. The text is
 * what Claude actually reads; structuredContent is there for clients that parse
 * it. No `outputSchema` is declared anywhere - declaring one makes
 * structuredContent mandatory per spec and adds schema bloat to every tools/list,
 * whereas returning it undeclared is allowed.
 *
 * Text is compact lines, never a JSON dump. The id comes first on every line so
 * the model can quote it straight into the next call - every write tool takes one.
 */

/**
 * claude.ai accepts about 150,000 characters per tool result. This budget is far
 * lower on purpose: the model pays for every character on every subsequent turn,
 * so a result worth truncating is a result worth paginating.
 */
export const MAX_TOOL_TEXT = 40_000

/** Hard ceiling on any list tool's page size. The REST API allows 100. */
export const MAX_PAGE_SIZE = 50
export const DEFAULT_PAGE_SIZE = 20

export function truncateToolText(text: string, limit = MAX_TOOL_TEXT): string {
  if (text.length <= limit) return text
  const cut = text.slice(0, limit)
  // Don't strand a half-written line - the model may try to parse it as an id.
  const lastBreak = cut.lastIndexOf("\n")
  const body = lastBreak > limit * 0.8 ? cut.slice(0, lastBreak) : cut
  return `${body}\n… output truncated. Narrow the search or request the next page.`
}

export function ok(
  text: string,
  structuredContent?: Record<string, unknown>
): CallToolResult {
  return {
    content: [{ type: "text", text: truncateToolText(text) }],
    ...(structuredContent ? { structuredContent } : {}),
  }
}

export function fail(message: string): CallToolResult {
  return { content: [{ type: "text", text: message }], isError: true }
}

/**
 * The trailer models follow reliably. Always emitted by list tools, even on a
 * single page, so "is there more" never needs a second call to answer.
 */
export function paginationTrailer(
  page: number,
  pageSize: number,
  total: number
): string {
  const totalPages = Math.max(1, Math.ceil(total / pageSize))
  if (total === 0) return "no matches"
  const more =
    page < totalPages ? ` · pass page=${page + 1} for more` : " · end of results"
  return `page ${page} of ${totalPages} · ${total} total${more}`
}

/** Joins non-empty parts with a separator, dropping blanks. */
function join(parts: (string | null | undefined)[], sep = " · "): string {
  return parts.filter((p): p is string => !!p && p.length > 0).join(sep)
}

export function formatAbv(abv: number | null | undefined): string | null {
  return typeof abv === "number" ? `${abv.toFixed(1)}%` : null
}

export function formatDrinkLine(d: {
  id: string
  name: string
  type: string
  subType?: string | null
  brewery?: string | null
  region?: string | null
  abv?: number | null
  avgRating?: number | null
  ratingCount?: number
}): string {
  const kind = d.subType ? `${d.type} / ${d.subType}` : d.type
  const rating =
    d.avgRating != null && d.ratingCount
      ? `★${d.avgRating.toFixed(1)} (${d.ratingCount})`
      : "unrated"
  return `[${d.id}] ${d.name} — ${join([
    kind,
    d.brewery,
    d.region,
    formatAbv(d.abv),
    rating,
  ])}`
}

export function formatBarItemLine(b: {
  id: string
  name: string
  category: string
  quantity: string
  notes?: string | null
}): string {
  return `[${b.id}] ${b.name} — ${join([b.category, b.quantity, b.notes])}`
}

export function formatRatingLine(r: {
  id: string
  score: number
  wouldReorder: boolean
  location?: string | null
  notes?: string | null
  createdAt: Date
  drink?: { name: string } | null
}): string {
  const when = r.createdAt.toISOString().slice(0, 10)
  return `[${r.id}] ${r.drink?.name ?? "?"} — ${join([
    `★${r.score}`,
    when,
    r.location,
    r.wouldReorder ? "would reorder" : null,
    r.notes,
  ])}`
}

export function formatRecipeLine(r: {
  id: string
  title: string
  missingCount: number
  ingredients: { name: string; available: boolean }[]
  glassware?: string | null
}): string {
  const status =
    r.missingCount === 0
      ? "can make now"
      : `missing ${r.missingCount}: ${r.ingredients
          .filter((i) => !i.available)
          .map((i) => i.name)
          .join(", ")}`
  return `[${r.id}] ${r.title} — ${join([
    `${r.ingredients.length} ingredients`,
    status,
    r.glassware,
  ])}`
}

export function formatWishlistLine(w: {
  id: string
  name: string
  type: string
  subType?: string | null
  brewery?: string | null
  notes?: string | null
}): string {
  const kind = w.subType ? `${w.type} / ${w.subType}` : w.type
  return `[${w.id}] ${w.name} — ${join([kind, w.brewery, w.notes])}`
}