// ---------------------------------------------------------------------------
// Reasoning option parsing
//
// The MCP `reasoning` parameter is a hardcoded allow-list of `gpt-5.4` model
// variants paired with a Codex reasoning-effort level. Everything flowing
// through the tools is one of the exact strings in REASONING_OPTIONS — we
// split it into `{ model, effort }` at the boundary so the adapter chain can
// pass the two fields independently to Codex (`reasoningEffort` on
// thread/start, `effort` on turn/start).
// ---------------------------------------------------------------------------

export type ReasoningEffortLevel = 'low' | 'medium' | 'high' | 'xhigh';

/** The only model we expose. Hardcoded — do not add variants without intent. */
export const ALLOWED_MODEL = 'gpt-5.4';

/**
 * The full set of accepted `reasoning` values. Order matters for display:
 * medium/high first (the common cases), xhigh next (exceptional research),
 * low last (rare, kept for completeness).
 */
export const REASONING_OPTIONS = [
  'gpt-5.4(medium)',
  'gpt-5.4(high)',
  'gpt-5.4(xhigh)',
  'gpt-5.4(low)',
] as const;

export type ReasoningOption = (typeof REASONING_OPTIONS)[number];

const REASONING_PATTERN = /^(gpt-5\.4)\((low|medium|high|xhigh)\)$/;

export interface ParsedReasoning {
  model: string;
  effort: ReasoningEffortLevel;
}

export function isReasoningOption(value: unknown): value is ReasoningOption {
  return typeof value === 'string' && (REASONING_OPTIONS as readonly string[]).includes(value);
}

/**
 * Parse a `reasoning` value such as `gpt-5.4(high)` into its model id and
 * reasoning-effort level. Throws on any value not in {@link REASONING_OPTIONS}.
 */
export function parseReasoning(value: string): ParsedReasoning {
  const match = REASONING_PATTERN.exec(value);
  if (!match) {
    throw new Error(
      `Invalid reasoning option "${value}". Allowed: ${REASONING_OPTIONS.join(', ')}`,
    );
  }
  return {
    model: match[1]!,
    effort: match[2] as ReasoningEffortLevel,
  };
}