import type { Usage } from './types.js';

/**
 * List prices in USD per 1M tokens (first-party API rates, cached 2026-06). Used only for the
 * cost ledger (§169); billing truth lives with the provider. Update when prices change.
 */
export interface ModelPrice {
  input: number;
  output: number;
  /** cache read multiplier vs input (Anthropic: 0.1) */
  cacheRead: number;
  /** cache write multiplier vs input (Anthropic: 1.25) */
  cacheWrite: number;
}

export const PRICE_TABLE: Record<string, ModelPrice> = {
  'claude-opus-5': { input: 5, output: 25, cacheRead: 0.1, cacheWrite: 1.25 },
  'claude-opus-4-8': { input: 5, output: 25, cacheRead: 0.1, cacheWrite: 1.25 },
  'claude-sonnet-5': { input: 2, output: 10, cacheRead: 0.1, cacheWrite: 1.25 },
  'claude-sonnet-4-6': { input: 3, output: 15, cacheRead: 0.1, cacheWrite: 1.25 },
  'claude-haiku-4-5': { input: 1, output: 5, cacheRead: 0.1, cacheWrite: 1.25 },
  'claude-fable-5-1': { input: 10, output: 50, cacheRead: 0.1, cacheWrite: 1.25 },
  // OpenAI (approximate list prices; verify before relying on them)
  'gpt-5': { input: 1.25, output: 10, cacheRead: 0.1, cacheWrite: 1 },
  'gpt-5-mini': { input: 0.25, output: 2, cacheRead: 0.1, cacheWrite: 1 },
  'gpt-4o-mini': { input: 0.15, output: 0.6, cacheRead: 0.5, cacheWrite: 1 },
  'text-embedding-3-small': { input: 0.02, output: 0, cacheRead: 1, cacheWrite: 1 },
  'text-embedding-3-large': { input: 0.13, output: 0, cacheRead: 1, cacheWrite: 1 },
};

/** Local/self-hosted models cost nothing at the API layer. */
export function priceFor(model: string): ModelPrice | null {
  if (PRICE_TABLE[model]) return PRICE_TABLE[model]!;
  const base = Object.keys(PRICE_TABLE).find((k) => model.startsWith(k));
  return base ? PRICE_TABLE[base]! : null;
}

export function estimateUsd(model: string, usage: Usage): number {
  const p = priceFor(model);
  if (!p) return 0;
  const usd =
    (usage.inputTokens * p.input + usage.outputTokens * p.output + usage.cacheReadTokens * p.input * p.cacheRead + usage.cacheWriteTokens * p.input * p.cacheWrite) / 1_000_000;
  return Math.round(usd * 1e6) / 1e6;
}

export const ZERO_USAGE: Usage = { inputTokens: 0, outputTokens: 0, cacheReadTokens: 0, cacheWriteTokens: 0 };

export function addUsage(a: Usage, b: Usage): Usage {
  return {
    inputTokens: a.inputTokens + b.inputTokens,
    outputTokens: a.outputTokens + b.outputTokens,
    cacheReadTokens: a.cacheReadTokens + b.cacheReadTokens,
    cacheWriteTokens: a.cacheWriteTokens + b.cacheWriteTokens,
  };
}