// Cost of a run, and what the same work would have cost on Opus. Pure: no `$`.
//
// Prices: USD per million tokens, from platform.claude.com/docs/en/about-claude/pricing
// (read 2026-10-08). A setting can replace them.

export type Usage = {
  input_tokens: number
  output_tokens: number
  cache_creation_input_tokens?: number | null
  cache_read_input_tokens?: number | null
}

/** in, out, cache write (5 min), cache read: USD per MTok. */
export type Price = { in: number; out: number; write: number; read: number }

export type PriceRow = { match: string; price: Price; label: string }

// First match wins: more specific ids come first.
export const DEFAULT_PRICES: readonly PriceRow[] = [
  { match: 'fable-5-1', label: 'Fable 5.1', price: { in: 10, out: 50, write: 12.5, read: 0.25 } },
  { match: 'mythos-5-1', label: 'Mythos 5.1', price: { in: 10, out: 50, write: 12.5, read: 0.25 } },
  { match: 'opus-5-5', label: 'Opus 5.5', price: { in: 4, out: 20, write: 5, read: 0.2 } },
  { match: 'sonnet-5-5', label: 'Sonnet 5.5', price: { in: 2, out: 10, write: 2.5, read: 0.1 } },
  // Haiku 5.5 doubles past 100k-token prompts; a run's summed usage cannot tell, so the low tier is used.
  { match: 'haiku-5-5', label: 'Haiku 5.5', price: { in: 0.1, out: 0.5, write: 0.125, read: 0.01 } },
  { match: 'haiku-4-5', label: 'Haiku 4.5', price: { in: 1, out: 5, write: 1.25, read: 0.1 } },
  { match: 'fable-5', label: 'Fable 5', price: { in: 10, out: 50, write: 12.5, read: 1 } },
  { match: 'opus-5', label: 'Opus 5', price: { in: 5, out: 25, write: 6.25, read: 0.5 } },
  { match: 'sonnet-5', label: 'Sonnet 5', price: { in: 2, out: 10, write: 2.5, read: 0.2 } },
]

/** The model every saving is measured against. */
export const BASELINE = 'opus-5-5'

/**
 * Models before Claude 4.7 use a tokenizer that yields ~30% fewer tokens for
 * the same text, so their counts are scaled up before pricing them as Opus 5.5.
 */
const OLD_TOKENIZER = /(haiku-4-5|sonnet-4|opus-4-[0-6]|opus-4-1|opus-4(?!-)|haiku-3)/
export const tokenizerFactor = (modelId: string) => (OLD_TOKENIZER.test(modelId) ? 1.3 : 1)

export const priceRow = (modelId: string, table: readonly PriceRow[] = DEFAULT_PRICES) =>
  table.find(r => modelId.toLowerCase().includes(r.match))

/** USD for a usage at a price; tokens scaled by `factor`. */
export const cost = (u: Usage, p: Price, factor = 1) =>
  (factor *
    (u.input_tokens * p.in +
      u.output_tokens * p.out +
      (u.cache_creation_input_tokens ?? 0) * p.write +
      (u.cache_read_input_tokens ?? 0) * p.read)) /
  1_000_000

export type Priced = { actual: number; opus: number; known: boolean; label: string }

/** What a run cost on its own model, and the same tokens on the baseline. */
export const priceRun = (modelId: string, u: Usage, table: readonly PriceRow[] = DEFAULT_PRICES): Priced => {
  const row = priceRow(modelId, table)
  const base = priceRow(BASELINE, table)
  if (!row || !base) return { actual: 0, opus: 0, known: false, label: modelId }
  return {
    actual: cost(u, row.price),
    opus: cost(u, base.price, tokenizerFactor(modelId)),
    known: true,
    label: row.label,
  }
}

/** A task's running totals, across every agent and round it took. */
export type TaskCost = {
  task: string
  /** Writer runs on each model, USD. */
  writerActual: number
  /** Writer runs below Opus, priced at Opus: what Opus would have cost for the same tokens. */
  writerAsOpus: number
  /** Writer runs that were on Opus already, USD. */
  writerOnOpus: number
  /** Classifier and verifier calls the router added, USD. */
  overhead: number
  models: string[]
  unpriced: string[]
}

export const emptyTask = (task: string): TaskCost => ({
  task,
  writerActual: 0,
  writerAsOpus: 0,
  writerOnOpus: 0,
  overhead: 0,
  models: [],
  unpriced: [],
})

export const addWriterRun = (t: TaskCost, modelId: string, u: Usage, table?: readonly PriceRow[]): TaskCost => {
  const p = priceRun(modelId, u, table)
  const next = { ...t, models: [...t.models], unpriced: [...t.unpriced] }
  if (!p.known) {
    if (!next.unpriced.includes(modelId)) next.unpriced.push(modelId)
    return next
  }
  if (!next.models.includes(p.label)) next.models.push(p.label)
  next.writerActual += p.actual
  if (modelId.toLowerCase().includes(BASELINE)) next.writerOnOpus += p.actual
  else next.writerAsOpus += p.opus
  return next
}

export const addOverhead = (t: TaskCost, modelId: string, u: Usage, table?: readonly PriceRow[]): TaskCost => {
  const p = priceRun(modelId, u, table)
  return p.known ? { ...t, overhead: t.overhead + p.actual } : t
}

/**
 * What the task would have cost had it gone to Opus at once.
 *
 * When Opus wrote part of it (a rewrite after failed rounds, or an open
 * design), Opus's own runs are taken as what Opus alone would have needed:
 * the failed cheaper rounds then count as pure loss. Otherwise every writer
 * token is priced at Opus, an upper bound, since Opus may need fewer tokens.
 */
export const counterfactual = (t: TaskCost) => (t.writerOnOpus > 0 ? t.writerOnOpus : t.writerAsOpus)

export const actualTotal = (t: TaskCost) => t.writerActual + t.overhead

export const saved = (t: TaskCost) => counterfactual(t) - actualTotal(t)

export const savedPct = (t: TaskCost) => {
  const c = counterfactual(t)
  return c > 0 ? (saved(t) / c) * 100 : 0
}

/** Reads a prices setting: a JSON list of rows, or empty for the defaults. */
export const parsePrices = (json: string): readonly PriceRow[] => {
  if (!json.trim()) return DEFAULT_PRICES
  try {
    const rows = JSON.parse(json) as PriceRow[]
    const ok = Array.isArray(rows) && rows.every(r => typeof r.match === 'string' && typeof r.price?.in === 'number')
    return ok ? [...rows.map(r => ({ ...r, label: r.label ?? r.match })), ...DEFAULT_PRICES] : DEFAULT_PRICES
  } catch {
    return DEFAULT_PRICES
  }
}

export const usd = (n: number) => (Math.abs(n) < 0.01 && n !== 0 ? `$${n.toFixed(4)}` : `$${n.toFixed(2)}`)

/**
 * The savings table: per task, what it cost, what Opus would have cost, and
 * the difference, newest first; then the total over every task.
 */
export const savingsReport = (costs: Readonly<Record<string, TaskCost>>, limit: number, only?: string): string => {
  const ids = Object.keys(costs)
    .filter(id => !only || id === only)
    .sort((a, b) => Number(b.slice(1)) - Number(a.slice(1)))
  if (ids.length === 0) return only ? `model-router: no costs recorded for ${only}.` : 'savings: no agent runs recorded yet.'

  const row = (id: string, t: TaskCost) => {
    const pct = counterfactual(t) > 0 ? `${savedPct(t).toFixed(0)}%` : '-'
    const how = t.writerActual === 0 ? 'running' : t.writerOnOpus > 0 ? 'opus ran' : 'upper bound'
    return `${id.padEnd(5)} ${usd(actualTotal(t)).padStart(9)} ${usd(counterfactual(t)).padStart(9)} ${usd(saved(t)).padStart(9)} ${pct.padStart(5)}  ${how.padEnd(11)} ${t.models.join('+').padEnd(20)} ${t.task.slice(0, 32)}${t.unpriced.length ? `  [no price: ${t.unpriced.join(', ')}]` : ''}`
  }

  let actual = 0
  let opus = 0
  for (const id of Object.keys(costs)) {
    const t = costs[id]
    // a task whose writer has not finished has no comparison yet
    if (!t || t.writerActual === 0) continue
    actual += actualTotal(t)
    opus += counterfactual(t)
  }
  const shown = ids.slice(0, limit)
  const lines = [
    `savings vs Opus 5.5 (USD, API list prices)${only ? '' : ` - ${shown.length} of ${ids.length} tasks`}`,
    `task     actual  if opus     saved     %  basis       models               task`,
    ...shown.map(id => row(id, costs[id] as TaskCost)),
  ]
  if (!only)
    lines.push(
      `total ${usd(actual).padStart(9)} ${usd(opus).padStart(9)} ${usd(opus - actual).padStart(9)} ${(opus > 0 ? `${(((opus - actual) / opus) * 100).toFixed(0)}%` : '-').padStart(5)}`,
    )
  lines.push(
    'actual = writer runs + classifier + verifier. "upper bound": all tokens priced at Opus; Opus may need fewer. "opus ran": the Opus run stands for Opus alone, cheaper failed rounds count as loss.',
  )
  return lines.join('\n')
}