/**
 * Read tool output limits. Two caps apply to text reads:
 *
 * | limit | default | checks | cost | on overflow |
 * |---------------|---------|---------------------------|---------------|-----------------|
 * | maxSizeBytes | 256 KB | TOTAL FILE SIZE (not out) | 1 stat | throws pre-read |
 * | maxTokens | 25000 | actual output tokens | API roundtrip | throws post-read|
 *
 * Known mismatch: maxSizeBytes gates on total file size, not the slice.
 * Tested truncating instead of throwing for explicit-limit reads that
 * exceed the byte cap (#21841, Mar 2026). Reverted: tool error rate
 * dropped but mean tokens rose — the throw path yields a ~100-byte error
 * tool-result while truncation yields ~25K tokens of content at the cap.
 */
import memoize from 'lodash-es/memoize.js'
import { getFeatureValue_CACHED_MAY_BE_STALE } from 'src/services/analytics/growthbook.js'
import { MAX_OUTPUT_SIZE } from 'src/utils/file.js'
export const DEFAULT_MAX_OUTPUT_TOKENS = 25000

/**
 * Env var override for max output tokens. Returns undefined when unset/invalid
 * so the caller can fall through to the next precedence tier.
 */
function getEnvMaxTokens(): number | undefined {
 const override = process.env.CLAUDE_CODE_FILE_READ_MAX_OUTPUT_TOKENS
 if (override) {
 const parsed = parseInt(override, 10)
 if (!isNaN(parsed) && parsed > 0) {
 return parsed
 }
 }
 return undefined
}

export type FileReadingLimits = {
 maxTokens: number
 maxSizeBytes: number
 includeMaxSizeInPrompt?: boolean
 targetedRangeNudge?: boolean
}

/**
 * Default limits for Read tool when the ToolUseContext doesn't supply an
 * override. Memoized so the GrowthBook value is fixed at first call — avoids
 * the cap changing mid-session as the flag refreshes in the background.
 *
 * Precedence for maxTokens: env var > GrowthBook > DEFAULT_MAX_OUTPUT_TOKENS.
 * (Env var is a user-set override, should beat experiment infrastructure.)
 *
 * Defensive: each field is individually validated; invalid values fall
 * through to the hardcoded defaults (no route to cap=0).
 */
export const getDefaultFileReadingLimits = memoize((): FileReadingLimits => {
 const override =
 getFeatureValue_CACHED_MAY_BE_STALE<Partial<FileReadingLimits> | null>(
 'tengu_amber_wren',
 {},
 )

 const maxSizeBytes =
 typeof override?.maxSizeBytes === 'number' &&
 Number.isFinite(override.maxSizeBytes) &&
 override.maxSizeBytes > 0
 ? override.maxSizeBytes
 : MAX_OUTPUT_SIZE

 const envMaxTokens = getEnvMaxTokens()
 const maxTokens =
 envMaxTokens ??
 (typeof override?.maxTokens === 'number' &&
 Number.isFinite(override.maxTokens) &&
 override.maxTokens > 0
 ? override.maxTokens
 : DEFAULT_MAX_OUTPUT_TOKENS)

 const includeMaxSizeInPrompt =
 typeof override?.includeMaxSizeInPrompt === 'boolean'
 ? override.includeMaxSizeInPrompt
 : undefined

 const targetedRangeNudge =
 typeof override?.targetedRangeNudge === 'boolean'
 ? override.targetedRangeNudge
 : undefined

 return {
 maxSizeBytes,
 maxTokens,
 includeMaxSizeInPrompt,
 targetedRangeNudge,
 }
})