Function buildGeminiUsage

packages/ai-gemini/src/usage.ts:121–207

(
  usageMetadata: GenerateContentResponseUsageMetadata | undefined | null,
)

 * fabricating zeroed totals.
 */
export function buildGeminiUsage(
  usageMetadata: GenerateContentResponseUsageMetadata | undefined | null,
): TokenUsage<GeminiProviderUsageDetails> | undefined {
  if (!usageMetadata) return undefined

  const promptTokens = usageMetadata.promptTokenCount ?? 0
  const completionTokens = usageMetadata.candidatesTokenCount ?? 0

  const result = buildBaseUsage<GeminiProviderUsageDetails>({
    promptTokens: promptTokens,
    completionTokens: completionTokens,
    totalTokens:
      usageMetadata.totalTokenCount ?? promptTokens + completionTokens,
  })

  // Add prompt token details
  // Flatten modality breakdown for prompt
  const promptModalities = flattenModalityTokenCounts(
    usageMetadata.promptTokensDetails,
  )
  const cachedTokens = usageMetadata.cachedContentTokenCount

  const promptTokensDetails = {
    ...(hasModalityTokens(promptModalities) ? promptModalities : {}),
    ...(cachedTokens !== undefined && cachedTokens > 0 ? { cachedTokens } : {}),
  }

  // Add completion token details
  // Flatten modality breakdown for candidates (output)
  const completionModalities = flattenModalityTokenCounts(
    usageMetadata.candidatesTokensDetails,
  )
  const thoughtsTokens = usageMetadata.thoughtsTokenCount

  const completionTokensDetails = {
    ...(hasModalityTokens(completionModalities) ? completionModalities : {}),
    // Map thoughtsTokenCount to reasoningTokens for consistency with OpenAI
    ...(thoughtsTokens !== undefined && thoughtsTokens > 0
      ? { reasoningTokens: thoughtsTokens }
      : {}),
  }

  // Add provider-specific details
  const providerDetails: GeminiProviderUsageDetails = {
    ...(usageMetadata.trafficType
      ? { trafficType: usageMetadata.trafficType }
      : {}),
    ...(usageMetadata.toolUsePromptTokenCount !== undefined &&
    usageMetadata.toolUsePromptTokenCount > 0
      ? { toolUsePromptTokenCount: usageMetadata.toolUsePromptTokenCount }
      : {}),
    ...(usageMetadata.toolUsePromptTokensDetails &&
    usageMetadata.toolUsePromptTokensDetails.length > 0
      ? {
          toolUsePromptTokensDetails:
            usageMetadata.toolUsePromptTokensDetails.map((item) => ({
              modality: item.modality || 'UNKNOWN',
              tokenCount: item.tokenCount ?? 0,