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import { redact } from '@/security/redact'
import { resolve } from '@/core/resolve'
import { Text } from '@/utils/Text'
import { Time } from '@/utils/Time'
import type { LogContext } from '@/types/logging/LogContext'
import type { LoggingSettings } from '@/types/LoggingSettings'
import type { LogLevel } from '@/types/logging/LogLevel'
/**
* Relative weight of each level, used to apply the threshold.
*
* @remarks
* `LogLevel` is declared in [`types/`](../types/index.ts) and imported as a type
* only. Keeping the runtime value here — rather than an enum shared with the
* configuration layer — is what stops `Logger → resolve → Defaults → Logger`
* from becoming a real import cycle.
*/
const WEIGHT: Record<LogLevel, number> = {
debug: 10,
info: 20,
warn: 30,
error: 40
}
/**
* What `service` reads when nothing names the deployment.
*
* @remarks
* A marker rather than an omitted field, and the distinction is the whole
* reason it exists. Every line is supposed to say which service wrote it, so
* that it still means something once it has left the console it was written to.
* A deployment that forgets to set `SERVICE_NAME` breaks that guarantee, and an
* absent key breaks it *invisibly* — the lines look ordinary, the Worker looks
* healthy, and nothing surfaces until someone needs to tell two services apart
* in one stream and cannot.
*
* This turns that into something a query finds: `service = unknown` returns
* every misconfigured deployment in the account.
*/
const UNNAMED = 'unknown'
/**
* Keys the line owns, which nothing else may occupy.
*
* @remarks
* Context and payload are both merged onto the line, and either could carry a
* key named `level` or `message` — a forwarded upstream record especially,
* where those names are exactly what a log line calls its own fields. Letting
* one through would leave a line whose severity disagrees with the stream it
* was written to, which is worse than losing the field: a collector indexes the
* value it sees, so an `error` payload could arrive filed as `info` and never
* surface in a severity filter.
*
* These three are written first and re-asserted against every merged key.
*/
const RESERVED = new Set(['level', 'event', 'message'])
/**
* @class
*
* Structured, level-classified logging — and nothing else.
*
* Each line is one JSON object emitted through the matching `console.*` method,
* so the runtime's log collector records the native level and keeps the fields
* searchable. Nothing here aggregates — that is {@link TelemetrySink}, a
* separate capability, because a sink samples at volume and is the wrong place
* for lines that have to be read back verbatim.
*
* @remarks
* ## An event name *and* a sentence
*
* The first argument is an **event name** — a stable, lowercase, dotted
* identifier such as `notification.sent` or `external_api.error` — emitted
* under the `event` key. A collector that indexes JSON fields turns that key
* into a column, so `event = notification.failed` becomes a filter rather than
* a substring search, and the count of one event over time becomes a series. A
* prose sentence can be neither: `'Failed to send notification for user 7'` is
* a different string on every line it is written.
*
* That is why the third argument exists rather than replacing the first. A
* `message` is written for whoever is *reading* the stream, and it is the only
* thing most log viewers show by default. Omit it and the event name stands in,
* so the column is never empty; supply it and the line says something in
* English without anyone opening it:
*
* ```ts
* log.warn('external_api.error', { provider, status }, `Telegram rejected the send (${status})`)
* ```
*
* Anything that varies belongs in the payload, where it stays structured and
* searchable on its own — never interpolated into the event name.
*
* ## One flat object
*
* Context and payload are flattened onto the line, not nested under a wrapper,
* so a field is indexed as `status` rather than `data.status`.
*
* Context passes through an allow-list first; see `LogFields`. Payload never
* does — it was named at the call site for this one call, and dropping it there
* would discard the answer somebody logged the line to get.
*
* ## Which deployment wrote it
*
* `service` names the deployment, from `SERVICE_NAME` in the environment or,
* failing that, `logging.service` on the configuration surface. It is context,
* so it reaches the line only while the allow-list admits it — which the kernel
* default does.
*
* Some runtimes already record it: Cloudflare stamps the script name on every
* log record before it is stored, so a Worker that never leaves that console
* gains nothing from a second copy and can drop the field. A deployment whose
* lines *travel* — exported to a file, shipped through Logpush, read on a
* runtime with no such column — should keep it, because a record that only
* makes sense inside one vendor's console is not a record.
*
* That is the trade the allow-list exists to let a deployment make, rather than
* this class making it for every consumer. The value comes from the environment
* rather than a constant compiled into the bundle, so whichever way it is
* decided the name cannot drift from the deployment it describes.
*
* `service` answers *which service*; a line that needs to say which part of it
* ran names a `component` in the context.
*
* The threshold comes from the surface registered by {@link configure}, and
* `LOG_LEVEL` in the environment overrides it per deployment, so staging can run
* at `debug` without a code change.
*
* Retention is the runtime's business, not this class's — it writes lines and
* stops there. Whether they are kept, and for how long, is a deployment setting
* wherever the process runs.
*
* @example
* ```ts
* const log = Logger.fromEnv(env, { component: 'ArticleService' })
*
* log.info('article.created', { id })
* log.info('article.created', { id }, `Article ${id} created`)
* ```
*
* @author Bayu Dwiyan Satria
* @version 1.2.1
* @since 1.0.0
*/
export class Logger {
/**
* Minimum weight a line must carry to be emitted.
*/
private readonly threshold: number
/**
* Fields repeated on every line.
*/
private readonly context: LogContext
/**
* Which of those fields the deployment actually wants ingested.
*/
private readonly fields: LogFields
/**
* Constructs a Logger.
*
* @param threshold Minimum weight to emit.
* @param context Fields repeated on every line.
* @param fields Which context fields reach the line.
*/
private constructor(threshold: number, context: LogContext, fields: LogFields) {
this.threshold = threshold
this.context = context
this.fields = fields
}
/**
* Builds a logger for the current environment.
*
* @remarks
* The parameter is structural rather than a named environment type. All this
* needs is a possible `LOG_LEVEL`, `SERVICE_NAME` and `LOG_FIELDS`, so asking
* for exactly that keeps the kernel free of any platform's environment shape
* — a runtime's `Env` object, a `process.env`, or a bare object literal all
* satisfy it.
*
* The service name is read from the environment first and the configuration
* surface second. The order is the point: a name in the environment sits
* beside the deployment's own name — in `wrangler.json`, two lines below
* `"name"` — where a rename that misses it shows up in the same diff. A name
* compiled into the bundle from `config/` sits in a different file that a
* rename does not touch, which is how a Worker came to spend production
* calling itself `cloudflare-boilerplate`. The configuration value remains
* the fallback for runtimes with no environment to read.
*
* With neither set the line still carries a `service`, reading `unknown`. A
* missing name is a deployment defect, and an omitted key would make it an
* invisible one — `service = unknown` is a query that finds every
* misconfigured deployment.
*
* @param env Anything carrying an optional `LOG_LEVEL`, `SERVICE_NAME` and
* `LOG_FIELDS`. Tolerates `null`.
* @param context Fields to repeat on every line.
* @returns A logger honouring the configured (or `LOG_LEVEL`) threshold, and
* emitting the context fields the deployment declared.
*/
public static fromEnv(
env: { LOG_LEVEL?: string; SERVICE_NAME?: string; LOG_FIELDS?: string } | null | undefined,
context: LogContext = {}
): Logger {
const settings = resolve<LoggingSettings>('logging')
const level = Logger.parse(env && env.LOG_LEVEL) || settings.level
const named = (env && env.SERVICE_NAME) || settings.service
const service = Text.isBlank(named) ? UNNAMED : (named as string)
return new Logger(WEIGHT[level], { service, ...context }, LogFields.fromEnv(env))
}
/**
* Derives a logger with extra context, sharing this one's threshold.
*
* @param context Fields to add to every line.
* @returns The derived logger.
*/
public child(context: LogContext): Logger {
return new Logger(this.threshold, { ...this.context, ...context }, this.fields)
}
/**
* Emits a `debug` line.
*
* @param event What happened, as a dotted event name.
* @param data Structured detail.
* @param message A sentence for someone reading the stream. Defaults to the
* event name.
*/
public debug(event: string, data?: Record<string, unknown>, message?: string): void {
this.emit('debug', event, data, message)
}
/**
* Emits an `info` line.
*
* @param event What happened, as a dotted event name.
* @param data Structured detail.
* @param message A sentence for someone reading the stream. Defaults to the
* event name.
*/
public info(event: string, data?: Record<string, unknown>, message?: string): void {
this.emit('info', event, data, message)
}
/**
* Emits a `warn` line.
*
* @param event What happened, as a dotted event name.
* @param data Structured detail.
* @param message A sentence for someone reading the stream. Defaults to the
* event name.
*/
public warn(event: string, data?: Record<string, unknown>, message?: string): void {
this.emit('warn', event, data, message)
}
/**
* Emits an `error` line.
*
* @param event What happened, as a dotted event name.
* @param data Structured detail.
* @param message A sentence for someone reading the stream. Defaults to the
* event name.
*/
public error(event: string, data?: Record<string, unknown>, message?: string): void {
this.emit('error', event, data, message)
}
/**
* Writes one line through the `console` method matching its level.
*
* @remarks
* Context and payload are both flattened onto the line rather than nested,
* so a collector indexes `status` rather than `data.status` and a dashboard
* column reads as a field name instead of a path.
*
* They are not treated alike. Context is ambient — stamped by middleware for
* the span of a request — and passes through the allow-list, because a
* deployment should be able to decide it does not want the point of presence
* on every line. Payload was typed out at the call site for this one call,
* so it is emitted whole: filtering it would silently discard the answer
* someone went to the trouble of logging.
*
* @param level Severity of the line.
* @param event What happened, as a dotted event name.
* @param data Structured detail.
* @param message A sentence for someone reading the stream.
*/
private emit(level: LogLevel, event: string, data?: Record<string, unknown>, message?: string): void {
if (WEIGHT[level] < this.threshold) {
return
}
const line = JSON.stringify(this.compose(level, event, data, message))
switch (level) {
case 'error':
console.error(line)
break
case 'warn':
console.warn(line)
break
case 'debug':
console.debug(line)
break
default:
console.info(line)
}
}
/**
* Assembles the object that becomes the line.
*
* @remarks
* The three reserved keys are written first so a raw line reads
* level-then-event-then-message, and re-asserted on every merge so nothing
* can displace them. `time` sits behind the allow-list like any other field:
* a runtime that stamps its own ingestion timestamp does not need a second
* one, and it is computed here rather than carried in the context so it
* records when the line was written and not when the logger was built.
*
* @param level Severity of the line.
* @param event What happened, as a dotted event name.
* @param data Structured detail.
* @param message A sentence for someone reading the stream.
* @returns The line, ready to serialise.
*/
private compose(
level: LogLevel,
event: string,
data?: Record<string, unknown>,
message?: string
): Record<string, unknown> {
const line: Record<string, unknown> = {
level,
event,
message: message === undefined ? event : message
}
if (this.fields.permits('time')) {
line.time = Time.nowIso()
}
for (const [key, value] of Object.entries(this.context)) {
if (!RESERVED.has(key) && this.fields.permits(key)) {
line[key] = value
}
}
if (data) {
for (const [key, value] of Object.entries(Logger.serialize(data))) {
if (!RESERVED.has(key)) {
line[key] = value
}
}
}
return line
}
/**
* Parses a level name, ignoring anything unrecognised.
*
* @param value The candidate level name.
* @returns The level, or `null` when the value is not one.
*/
private static parse(value?: string): LogLevel | null {
const level = (value || '').toLowerCase()
return (Object.keys(WEIGHT) as string[]).includes(level) ? (level as LogLevel) : null
}
/**
* Makes a data payload serialisable, and safe to ship.
*
* @remarks
* Two passes for two different problems. `redact` runs first, because a
* credential must not survive into the line whatever shape it arrived in;
* then `Error` expansion, which `JSON.stringify` would otherwise flatten to
* `{}`, losing the only useful part of an error line.
*
* The order is load-bearing in one direction only: redaction returns `Error`
* values untouched precisely so this pass can still recognise them.
*
* @param data The payload to convert.
* @returns The payload scrubbed of secrets, with errors expanded to message
* and stack.
*/
private static serialize(data: Record<string, unknown>): Record<string, unknown> {
const out: Record<string, unknown> = {}
for (const [key, value] of Object.entries(redact(data))) {
out[key] = value instanceof Error ? { message: value.message, stack: value.stack } : value
}
return out
}
}
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