/**
 * Thinking/reasoning parameter mapping.
 *
 * Different providers express the reasoning budget differently:
 *
 * - OpenAI-style (`openai-compatible`, `openrouter`): `reasoning_effort`
 *   (`"low" | "medium" | "high"`), optionally `max_tokens` for the reasoning
 *   budget.
 * - Anthropic: a `thinking` object `{ enabled: boolean, budget_tokens: number }`
 *   plus `thinking_budget` (must be <= 32768 and > 0).
 * - Google (Gemini): `reasoning_effort` + `thinking_budget`.
 *
 * This module normalizes the provider-agnostic `ThinkingConfig` into the
 * provider-specific wire format. See CHUNK#8.md §3.
 */

import type { ProviderKind, ThinkingConfig } from "./providers/types.js";

/** The maximum reasoning budget Anthropic accepts. */
const ANTHROPIC_MAX_THINKING_TOKENS = 32768;

/** Normalize a thinking config into the wire-format body fragment for a kind. */
export function normalizeThinking(
  kind: ProviderKind,
  thinking?: ThinkingConfig,
): Record<string, unknown> {
  if (!thinking?.enabled) {
    return {};
  }

  switch (kind) {
    case "anthropic":
      return normalizeAnthropicThinking(thinking);
    case "google":
      return normalizeGoogleThinking(thinking);
    case "openai-compatible":
    case "openrouter":
    default:
      return normalizeOpenAIThinking(thinking);
  }
}

/** OpenAI-style: `reasoning_effort` + optional `max_tokens`. */
function normalizeOpenAIThinking(thinking: ThinkingConfig): Record<string, unknown> {
  const effort = thinking.effort ?? "medium";
  const body: Record<string, unknown> = {
    reasoning_effort: effort,
  };
  if (typeof thinking.budget === "number") {
    body.max_tokens = thinking.budget;
  }
  return body;
}

/** Anthropic: `thinking` object + `thinking_budget`. */
function normalizeAnthropicThinking(thinking: ThinkingConfig): Record<string, unknown> {
  const budget =
    typeof thinking.budget === "number"
      ? Math.min(thinking.budget, ANTHROPIC_MAX_THINKING_TOKENS)
      : 2048;
  return {
    thinking: {
      enabled: true,
      budget_tokens: budget,
    },
    thinking_budget: budget,
  };
}

/** Google: `reasoning_effort` + `thinking_budget`. */
function normalizeGoogleThinking(thinking: ThinkingConfig): Record<string, unknown> {
  const effort = thinking.effort ?? "medium";
  const budget = typeof thinking.budget === "number" ? thinking.budget : 2048;
  return {
    reasoning_effort: effort,
    thinking_budget: budget,
  };
}

/**
 * Compute the reasoning budget (in tokens) to advertise to the budget engine,
 * so the output budget accounts for the reasoning spend. Returns 0 when
 * thinking is disabled.
 */
export function reasoningBudgetTokens(thinking?: ThinkingConfig): number {
  if (!thinking?.enabled) {
    return 0;
  }
  return typeof thinking.budget === "number" ? thinking.budget : 2048;
}