/** Child LLM route selection for the subagent tool. */

import { ReasoningEffortId } from '@deepseek-ai/dsh-llm'
import type { LlmRuntime } from '@deepseek-ai/dsh-llm'
import type { AgentOptions } from '@deepseek-ai/dsh-agent'

/** Model-facing child LLM route fields. */
export interface DelegationModelRequest {
  readonly provider?: string
  readonly model?: string
  readonly reasoning_effort?: string
}

/**
 * Whether a call explicitly selects any child LLM value.
 * @param request - Model-facing route fields from the tool call.
 * @returns Whether at least one route or effort field is present.
 */
export function hasDelegationModelRequest(request: DelegationModelRequest): boolean {
  return request.provider !== undefined
    || request.model !== undefined
    || request.reasoning_effort !== undefined
}

/** Reject an empty model-facing route value at the tool JSON boundary. */
function assertNonEmpty(value: string | undefined, field: keyof DelegationModelRequest): void {
  if (value !== undefined && value.length === 0) {
    throw new Error(`child LLM \`${field}\` must be non-empty`)
  }
}

/**
 * Merge model-supplied selection fields over configured child defaults.
 * Provider and model form one route and must be supplied together. Changing
 * that route without an effort clears the configured route-owned effort.
 * @param parentOptions - Current parent values that supply missing child values.
 * @param configured - Tool-instance child defaults.
 * @param request - Model-facing route override.
 * @param enabled - Whether this tool instance permits model-facing selection.
 * @returns Child Agent options, preserving omission when no layer contributes one.
 */
export function requestedAgentOptions(
  parentOptions: AgentOptions,
  configured: AgentOptions | undefined,
  request: DelegationModelRequest,
  enabled: boolean,
): AgentOptions | undefined {
  if (!hasDelegationModelRequest(request)) return configured
  if (!enabled) {
    throw new Error('child model selection is disabled for this tool instance')
  }
  assertNonEmpty(request.provider, 'provider')
  assertNonEmpty(request.model, 'model')
  assertNonEmpty(request.reasoning_effort, 'reasoning_effort')
  if ((request.provider === undefined) !== (request.model === undefined)) {
    throw new Error('child LLM `provider` and `model` must be supplied together')
  }

  const baselineProvider = configured?.provider ?? parentOptions.provider
  const baselineModel = configured?.model ?? parentOptions.model
  const routeChanged = request.provider !== undefined
    && (request.provider !== baselineProvider || request.model !== baselineModel)
  const { reasoningEffort: _configuredReasoningEffort, ...configuredWithoutReasoning } = configured ?? {}
  return {
    ...routeChanged && request.reasoning_effort === undefined ? configuredWithoutReasoning : configured,
    ...request.provider === undefined ? {} : { provider: request.provider, model: request.model },
    ...request.reasoning_effort === undefined
      ? {}
      : { reasoningEffort: ReasoningEffortId(request.reasoning_effort) },
  }
}

/**
 * Whether configured Agent options require route validation before delegation.
 * @param options - Tool-instance child defaults.
 * @returns Whether configured provider, model, or effort values must be resolved.
 */
export function hasConfiguredLlmSelection(options: AgentOptions | undefined): boolean {
  return options?.provider !== undefined
    || options?.model !== undefined
    || options?.reasoningEffort !== undefined
}

/**
 * Resolve an effective child route through its live adapter before the child is
 * created. The LLM runtime owns provider lookup, exact-model metadata, effort
 * validation, and adapter defaults.
 * @param llm - Live LLM runtime.
 * @param parentOptions - Current parent values whose compatible fields the child inherits.
 * @param requested - Per-child options after request/config merging.
 * @param signal - Tool-call cancellation signal.
 * @param inheritParentReasoningEffort - Whether an omitted effort may inherit from the parent route.
 */
export async function preflightChildLlmRoute(
  llm: LlmRuntime,
  parentOptions: AgentOptions,
  requested: AgentOptions | undefined,
  signal: AbortSignal,
  inheritParentReasoningEffort = true,
): Promise<void> {
  const provider = requested?.provider ?? parentOptions.provider
  const model = requested?.model ?? parentOptions.model
  if (provider === undefined || model === undefined) {
    throw new Error('cannot select child LLM values without an effective provider and model')
  }
  const routeChanged = provider !== parentOptions.provider || model !== parentOptions.model
  const reasoningEffort = requested?.reasoningEffort
    ?? (inheritParentReasoningEffort && !routeChanged ? parentOptions.reasoningEffort : undefined)
  await llm.resolveCallConfig({
    provider,
    model,
    ...reasoningEffort === undefined ? {} : { reasoningEffort },
  }, signal)
}