# Capability Spec: i18n-formatter-collator (i18n-formatter-collator) **Package**: `@suaveplan/i18n-formatter-collator` **Status**: ACTIVE > Every requirement below carries a `**Verified by:**` line at authoring time. (See `openspec/AGENTS.md` Section 13.) > > NEW formatter — no source in current monolith. Closes the gap from the original `i18n-formatters` change scope. ## Requirements ### Requirement: CollatorFormatter class wrapping `Intl.Collator` The package SHALL export a `CollatorFormatter` class that wraps `Intl.Collator` with construction-time Zod validation of options and `compare(a: string, b: string, locale: string): -1 | 0 | 1` and `sort(values: readonly string[], locale: string): string[]` methods. Construction with malformed options SHALL throw `I18nError(I18N.INVALID_FORMATTER_OPTIONS)`. #### Scenario: compare with default options - **GIVEN** `const f = new CollatorFormatter()` - **WHEN** `f.compare("a", "b", "en-GB")` is called - **THEN** the result equals `-1` #### Scenario: invalid options throw INVALID_FORMATTER_OPTIONS - **WHEN** `new CollatorFormatter({ usage: "invalid" as never })` is called - **THEN** the call throws `I18nError` with code `"I18N.INVALID_FORMATTER_OPTIONS"` **Verified by:** `packages/i18n/i18n-formatter-collator/src/formatter.test.ts::"CollatorFormatter compares with default options"` AND `packages/i18n/i18n-formatter-collator/src/formatter.test.ts::"CollatorFormatter rejects invalid options with INVALID_FORMATTER_OPTIONS"` ### Requirement: `compareStrings` standalone helper The package SHALL export a `compareStrings(a, b, locale, options?)` standalone helper that returns `-1`, `0`, or `1` per `Intl.Collator.compare` semantics. #### Scenario: standalone compares with default options - **WHEN** `compareStrings("apple", "banana", "en-GB")` is called - **THEN** the result equals `-1` #### Scenario: standalone twins class output - **WHEN** both `compareStrings(a, b, l, opts)` and `new CollatorFormatter(opts).compare(a, b, l)` are called for the same `(a, b, l, opts)` - **THEN** the results are identical **Verified by:** `packages/i18n/i18n-formatter-collator/src/formatter.test.ts::"compareStrings compares apple and banana"` AND `packages/i18n/i18n-formatter-collator/src/formatter.test.ts::"compareStrings output twins CollatorFormatter.compare output"` ### Requirement: `formatCollation` standalone helper returns sorted array The package SHALL export a `formatCollation(values, locale, options?)` standalone helper that returns a sorted (immutable copy) array per the configured collator. The input array SHALL NOT be mutated. #### Scenario: formatCollation sorts ascending - **WHEN** `formatCollation(["c", "a", "b"], "en-GB")` is called - **THEN** the result equals `["a", "b", "c"]` #### Scenario: formatCollation does not mutate the input - **GIVEN** `const input = ["c", "a", "b"]` - **WHEN** `formatCollation(input, "en-GB")` is called - **THEN** `input` still equals `["c", "a", "b"]` **Verified by:** `packages/i18n/i18n-formatter-collator/src/formatter.test.ts::"formatCollation sorts ascending"` AND `packages/i18n/i18n-formatter-collator/src/formatter.test.ts::"formatCollation does not mutate input array"` ### Requirement: `Intl.Collator` `RangeError` maps to `UNSUPPORTED_LOCALE` The package SHALL catch every `RangeError` thrown by the `Intl.Collator` constructor and re-throw it as `I18nError(I18N.UNSUPPORTED_LOCALE)` with the original error attached as `cause` and the locale string in `context`. #### Scenario: bogus locale throws UNSUPPORTED_LOCALE - **WHEN** `compareStrings("a", "b", "xx-bogus-tag-!!!")` is called - **THEN** the call throws `I18nError` with code `"I18N.UNSUPPORTED_LOCALE"` AND the error's `cause` is the original `RangeError` **Verified by:** `packages/i18n/i18n-formatter-collator/src/formatter.test.ts::"unsupported locale throws UNSUPPORTED_LOCALE with cause"` ### Requirement: Per-(locale, options-hash) cache The package SHALL maintain an internal `Map` keyed by `${locale}|${JSON.stringify(options)}`. Repeated calls with identical `(locale, options)` SHALL reuse the same `Intl.Collator` instance. The package SHALL export a `clearCollatorCache()` test-only helper. #### Scenario: identical options reuse the same Intl.Collator - **GIVEN** the cache is empty - **WHEN** `compareStrings("a", "b", "en-GB")` is called twice in sequence - **THEN** only one `Intl.Collator` constructor invocation occurs #### Scenario: distinct options create distinct cache entries - **WHEN** `compareStrings("a", "b", "en-GB", { sensitivity: "base" })` and `compareStrings("a", "b", "en-GB", { sensitivity: "accent" })` are called - **THEN** two distinct `Intl.Collator` instances are created and cached **Verified by:** `packages/i18n/i18n-formatter-collator/src/formatter.test.ts::"identical options reuse cached Intl.Collator"` AND `packages/i18n/i18n-formatter-collator/src/formatter.test.ts::"distinct options create distinct cache entries"` ### Requirement: OTel histogram `i18n.format.collator.duration_ms` The package SHALL emit an OTel histogram named exactly `i18n.format.collator.duration_ms` (unit `ms`) on every successful `compareStrings` or `formatCollation` call, tagged with `locale`, `usage`, and `sensitivity`. #### Scenario: histogram emitted on every call - **GIVEN** an OTel test exporter capturing histogram observations - **WHEN** `compareStrings("a", "b", "en-GB", { sensitivity: "base", usage: "sort" })` is called - **THEN** exactly one observation appears under `i18n.format.collator.duration_ms` with `locale`, `usage`, and `sensitivity` attributes **Verified by:** `packages/i18n/i18n-formatter-collator/src/observability.test.ts::"emits i18n.format.collator.duration_ms histogram on every call"` ### Requirement: OTel cache-hit counter `i18n.format.cache_hit` The package SHALL emit an OTel counter `i18n.format.cache_hit` tagged with `formatter: "collator"` on every cache hit. The counter SHALL NOT increment on the first (cache-miss) call. #### Scenario: cache-hit counter increments only on second call - **GIVEN** an OTel test exporter capturing counter observations and an empty cache - **WHEN** `compareStrings("a", "b", "en-GB")` is called twice in sequence - **THEN** the counter `i18n.format.cache_hit{formatter="collator"}` shows exactly one increment **Verified by:** `packages/i18n/i18n-formatter-collator/src/observability.test.ts::"cache-hit counter increments only on second call with same options"` ### Requirement: Ergonomic helpers — case-insensitive, numeric-aware, sort The package SHALL export three ergonomic helpers: - `compareCaseInsensitive(a, b, locale)` — pre-binds `sensitivity: "accent"` - `compareNumericAware(a, b, locale)` — pre-binds `numeric: true` for natural sort (`"file2" < "file10"`) - `sortStrings(values, locale, options?)` — returns sorted immutable copy #### Scenario: compareCaseInsensitive treats a and A as equal - **WHEN** `compareCaseInsensitive("a", "A", "en-GB")` is called - **THEN** the result equals `0` #### Scenario: compareNumericAware orders file2 before file10 - **WHEN** `compareNumericAware("file2", "file10", "en-GB")` is called - **THEN** the result equals `-1` #### Scenario: sortStrings sorts and returns immutable copy - **GIVEN** `const input = ["c", "a", "b"]` - **WHEN** `const out = sortStrings(input, "en-GB")` is called - **THEN** `out` equals `["a", "b", "c"]` AND `input` still equals `["c", "a", "b"]` **Verified by:** `packages/i18n/i18n-formatter-collator/src/helpers.test.ts::"compareCaseInsensitive treats a and A as equal"` AND `packages/i18n/i18n-formatter-collator/src/helpers.test.ts::"compareNumericAware orders file2 before file10"` AND `packages/i18n/i18n-formatter-collator/src/helpers.test.ts::"sortStrings sorts and returns immutable copy"` ### Requirement: Subpath exports The package SHALL declare subpath exports in `package.json`: - `@suaveplan/i18n-formatter-collator` — root barrel - `@suaveplan/i18n-formatter-collator/formatter` — `CollatorFormatter` class + `compareStrings` + `formatCollation` + types + schema only - `@suaveplan/i18n-formatter-collator/helpers` — three ergonomic helpers only #### Scenario: every documented subpath resolves - **WHEN** every documented subpath is imported in a consumer test fixture - **THEN** every import resolves with no `Module not found` errors **Verified by:** `packages/i18n/i18n-formatter-collator/src/index.test.ts::"every documented subpath export resolves"` ### Requirement: Side-effect-free package The package SHALL declare `"sideEffects": false` in `package.json`. #### Scenario: package.json declares sideEffects false - **WHEN** `package.json` is parsed - **THEN** the `sideEffects` field equals `false` **Verified by:** `packages/i18n/i18n-formatter-collator/src/index.test.ts::"package.json declares sideEffects false"`