export const DEFAULT_ROW_LIMIT = 100
export const MAX_ROW_LIMIT = 1000

export const clampLimit = (
    requested: number | undefined,
    fallback = DEFAULT_ROW_LIMIT,
    max = MAX_ROW_LIMIT
): number => {
    if (requested === undefined) {
        return fallback
    }
    return Math.max(1, Math.min(Math.trunc(requested), max))
}

export const truncateRows = <T>(rows: T[], limit: number): { rows: T[]; truncated: boolean } =>
    rows.length > limit
        ? { rows: rows.slice(0, limit), truncated: true }
        : { rows, truncated: false }

// Slice a string to at most `maxBytes` UTF-8 bytes without splitting a
// multi-byte sequence (back off to a code-point boundary).
export const sliceUtf8 = (s: string, maxBytes: number): string => {
    const buf = Buffer.from(s, 'utf8')
    if (buf.length <= maxBytes) {
        return s
    }
    let end = maxBytes
    while (end > 0 && (buf[end] & 0xc0) === 0x80) {
        end -= 1
    }
    return buf.subarray(0, end).toString('utf8')
}

// Serialize `value` to JSON and, if it exceeds `maxBytes` (UTF-8), return a
// truncated marker object whose own serialization stays within `maxBytes`.
export const truncateJsonBudget = (
    value: unknown,
    maxBytes: number
): { body: unknown; truncated: boolean } => {
    const text = JSON.stringify(value)
    if (text === undefined) {
        return { body: value, truncated: false }
    }
    const bytes = Buffer.byteLength(text, 'utf8')
    if (bytes <= maxBytes) {
        return { body: value, truncated: false }
    }
    const RESERVE = 256
    const preview = sliceUtf8(text, Math.max(0, maxBytes - RESERVE))
    return {
        body: { _truncated: true, _originalBytes: bytes, _maxBytes: maxBytes, preview },
        truncated: true
    }
}