From 75a7d7a14b59566236f81e4734da034da4e50bd8 Mon Sep 17 00:00:00 2001
From: Spencer Brower <6729162+sbrow@users.noreply.github.com>
Date: Fri, 24 Jul 2026 11:32:47 -0400
Subject: [PATCH] refactor: Eliminated global TZ cache

The configured timezone (or local) is now set on Site directly.
---
 AGENTS.md                 | 15 ++++----
 TODOS.md                  |  4 ++-
 mustache/EXTENSIONS.md    | 20 +++++++++++
 mustache/format.odin      | 45 +++++++++++-------------
 mustache/format_test.odin | 40 ++++++---------------
 mustache/pipes.odin       | 28 ++++-----------
 mustache/pipes_test.odin  | 73 ++++++++++-----------------------------
 render.odin               | 14 ++++----
 site.odin                 | 19 +++++++++-
 9 files changed, 114 insertions(+), 144 deletions(-)

diff --git a/AGENTS.md b/AGENTS.md
index b852169..dcae28a 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -222,11 +222,14 @@ Data is passed as **typed structs** (not `map[string]any`). Mustache resolves st
 
 ```odin
 Base_Data :: struct {
-    now:    datetime.DateTime,
-    params: json.Value,
-    body:   string,
-    title:  string,
-    og:     Open_Graph,
+    now:          string,        // UTC ISO 8601 build timestamp
+    params:       json.Value,
+    body:         string,
+    title:        string,
+    description:  string,
+    og:           Open_Graph,
+    date_format:  string,        // from site.date.format (thor.json)
+    timezone:     ^datetime.TZ_Region,  // loaded from site.date.timezone or local, owned by Site
 }
 Page_Data :: struct {
     using base: Base_Data,  // fields promoted via reflection fallback
@@ -259,7 +262,7 @@ Section tags and interpolation tags may transform the resolved value before rend
 <time datetime="{{date}}">{{date | format}}</time>
 ```
 
-Currently implemented: `group_by <field>` (list → list-of-groups) and `format` (ISO date string → display string like "15 Mar 2026"). Filter results live in `context.temp_allocator` (render-scoped). See `mustache/EXTENSIONS.md` for syntax details, caps (`MAX_PIPES`, `MAX_PIPE_ARGS`), and the `Group` struct shape.
+Currently implemented: `group_by <field>` (list → list-of-groups) and `format` (ISO date string → display string like "15 Mar 2026"). The `format` pipe resolves `date_format` (string) and `timezone` (`^datetime.TZ_Region`) from the data context. When `timezone` is non-nil, dates are DST-aware converted before formatting. The `MST` token reflects the active timezone abbreviation (e.g. `"EST"`/`"EDT"`) or the source offset (e.g. `"UTC-04:00"`) when no target tz is configured. TZ data is loaded once by `init_site` via `timezone.region_load` using the site arena allocator, stored on `Site.tz`, and freed when the arena is destroyed. Filter results live in `context.temp_allocator` (render-scoped). See `mustache/EXTENSIONS.md` for syntax details, caps (`MAX_PIPES`, `MAX_PIPE_ARGS`), and the `Group` struct shape.
 
 ### Comments
 
diff --git a/TODOS.md b/TODOS.md
index ba5ed2a..889f30a 100644
--- a/TODOS.md
+++ b/TODOS.md
@@ -33,11 +33,13 @@
 - [x] Accept "strings"
 - [x] Accept keys
 - [x] handle timezones
-- [ ] Fix TZ cache leak in parallel tests: `tz_cache` uses `context.allocator` (tracking allocator in tests), but it's global state shared across parallel test threads. Race causes leak warnings. Fix: use heap allocator for TZ cache.
 - [ ] display an error when no part of the date appears in the output.
 - [x] use `date.format` as the default format.
 - [ ] Handle 0 and whitespace padding i.e. "_2" -> " 2"
 - [ ] Do we *need* mustache.Date_Components, or can we use core:time/datetime.DateTime?
+- [ ] show a proper diagnostic for timezones
+  - currently "unable to load timezone 'America/New_Yorkskie'"
+  - want rust style diagnostic and better message, maybe "unknown timezone 'America/New_Yorkskie'"
 
 ## General 
 - [ ] Integrity hash
diff --git a/mustache/EXTENSIONS.md b/mustache/EXTENSIONS.md
index 4b74851..1c911b8 100644
--- a/mustache/EXTENSIONS.md
+++ b/mustache/EXTENSIONS.md
@@ -67,6 +67,26 @@ Takes an optional arg for the Go reference-date layout to use:
 - A bare key, resolved from context like any other field: `{{date | format long}}` uses the value of `long` (e.g. a site-config field) as the layout.
 - No arg: falls back to the `date_format` context key (typically `date.format` from `thor.json`).
 
+#### Timezone conversion
+
+When the `timezone` context key is set (typically `date.timezone` from `thor.json`, an IANA name like `"America/New_York"`), the `format` pipe converts dates to that timezone before formatting:
+
+- **Date has offset + target tz**: adjusts to true UTC, then converts to the target timezone (DST-aware).
+- **Date has no offset + target tz**: assumes the date is already in the target timezone — no conversion, only resolves the abbreviation.
+- **Date has offset + no target tz**: displays in the source offset.
+- **Date has no offset + no target tz**: displays as-is, assumes UTC.
+
+The `MST` token reflects the active timezone:
+
+| Config tz | ISO has offset | `MST` output |
+|---|---|---|
+| `"America/New_York"` | yes | `"EST"` or `"EDT"` (DST-aware) |
+| `"America/New_York"` | no | `"EST"` or `"EDT"` |
+| not set | yes | `"UTC-04:00"` (from source offset) |
+| not set | no | `"UTC"` |
+
+Timezone data is loaded once by `init_site` via `core:time/timezone.region_load`, using the site arena allocator. The resolved `^datetime.TZ_Region` pointer is stored on `Site.tz` and passed to templates through `Base_Data.timezone`. The arena frees it automatically on `destroy_site`.
+
 ### Memory ownership
 
 - **Parsed pipe filters** (`Pipe_Filter` values) are stored inline on each `Node` via `[dynamic; MAX_PIPES]Pipe_Filter`, and `args` is inline on each `Pipe_Filter` via `[dynamic; MAX_PIPE_ARGS]string`. Both use Odin's fixed-capacity dynamic array type, so no per-tag heap allocations occur at parse time. The storage dies with the `Template` when `delete_template` is called.
diff --git a/mustache/format.odin b/mustache/format.odin
index d120da7..3c16cd2 100644
--- a/mustache/format.odin
+++ b/mustache/format.odin
@@ -240,33 +240,30 @@ format_offset :: proc(offset_seconds: int) -> string {
 	return fmt.tprintf("UTC%s%02d:%02d", sign, hours, minutes)
 }
 
-// tz_cache caches loaded TZ_Region pointers by timezone name.
-// Entries persist until destroy_tz_cache is called.
-tz_cache: map[string]^datetime.TZ_Region
-
-get_cached_tz :: proc(name: string) -> (^datetime.TZ_Region, bool) {
-	if name == "" || name == "UTC" {
-		return nil, true
+// resolve_tz looks up the `tz` field from the context stack and returns
+// the ^TZ_Region pointer, or nil if not set.
+resolve_tz :: proc(ctx: []any) -> ^datetime.TZ_Region {
+	raw := resolve_name("timezone", ctx)
+	if raw == nil do return nil
+	switch v in raw {
+	case ^datetime.TZ_Region:
+		return v
+	case:
+		return nil
 	}
-	if cached, ok := tz_cache[name]; ok {
-		return cached, true
-	}
-	tz, ok := timezone.region_load(name)
-	if !ok {
-		return nil, false
-	}
-	tz_cache[name] = tz
-	return tz, true
 }
 
-destroy_tz_cache :: proc() {
-	for _, tz in tz_cache {
-		if tz != nil {
-			timezone.region_destroy(tz)
-		}
-	}
-	delete(tz_cache)
-	tz_cache = nil
+// compute_utc_offset returns the UTC offset (in seconds) for the given
+// timezone at the current time. Returns (0, true) if tz is nil.
+compute_utc_offset :: proc(tz: ^datetime.TZ_Region) -> (offset: int, ok: bool) {
+	if tz == nil do return 0, true
+	tm := time.now()
+	dt_utc := time.time_to_datetime(tm) or_return
+	dt_local := timezone.datetime_to_tz(dt_utc, tz) or_return
+	tm_utc := time.datetime_to_time(dt_utc) or_return
+	tm_local := time.datetime_to_time(dt_local) or_return
+	offset = int(time.time_to_unix(tm_local) - time.time_to_unix(tm_utc))
+	return offset, true
 }
 
 // convert_to_tz converts date components from their source timezone to a
diff --git a/mustache/format_test.odin b/mustache/format_test.odin
index 3695ee5..7d10298 100644
--- a/mustache/format_test.odin
+++ b/mustache/format_test.odin
@@ -2,6 +2,7 @@
 package mustache
 
 import "core:testing"
+import "core:time/timezone"
 
 // ---------------------------------------------------------------------------
 // parse_iso_date
@@ -230,36 +231,15 @@ test_format_offset_positive :: proc(t: ^testing.T) {
 }
 
 // ---------------------------------------------------------------------------
-// get_cached_tz / convert_to_tz (require system zoneinfo)
+// convert_to_tz (require system zoneinfo)
 // ---------------------------------------------------------------------------
 
-@(test)
-test_get_cached_tz_utc_returns_nil :: proc(t: ^testing.T) {
-	tz, ok := get_cached_tz("UTC")
-	testing.expect_value(t, ok, true)
-	testing.expect_value(t, tz == nil, true)
-}
-
-@(test)
-test_get_cached_tz_empty_returns_nil :: proc(t: ^testing.T) {
-	tz, ok := get_cached_tz("")
-	testing.expect_value(t, ok, true)
-	testing.expect_value(t, tz == nil, true)
-}
-
-@(test)
-test_get_cached_tz_loads_named_region :: proc(t: ^testing.T) {
-	tz, ok := get_cached_tz("America/New_York")
-	defer destroy_tz_cache()
-	if !ok do return
-	testing.expect(t, tz != nil, "should load TZ_Region for America/New_York")
-}
-
 @(test)
 test_convert_to_tz_no_offset_assumes_target :: proc(t: ^testing.T) {
-	tz, tz_ok := get_cached_tz("America/New_York")
-	defer destroy_tz_cache()
+	tz, tz_ok := timezone.region_load("America/New_York", context.temp_allocator)
+	testing.expect(t, tz_ok, "should load timezone")
 	if !tz_ok do return
+	defer timezone.region_destroy(tz, context.temp_allocator)
 
 	c := Date_Components{
 		year = 2026, month = 3, day = 15,
@@ -274,9 +254,10 @@ test_convert_to_tz_no_offset_assumes_target :: proc(t: ^testing.T) {
 
 @(test)
 test_convert_to_tz_with_offset_converts :: proc(t: ^testing.T) {
-	tz, tz_ok := get_cached_tz("America/New_York")
-	defer destroy_tz_cache()
+	tz, tz_ok := timezone.region_load("America/New_York", context.temp_allocator)
+	testing.expect(t, tz_ok, "should load timezone")
 	if !tz_ok do return
+	defer timezone.region_destroy(tz, context.temp_allocator)
 
 	// 2026-03-15T12:49:54Z (UTC) → 08:49:54 EDT (UTC-4)
 	c := Date_Components{
@@ -294,9 +275,10 @@ test_convert_to_tz_with_offset_converts :: proc(t: ^testing.T) {
 
 @(test)
 test_convert_to_tz_with_negative_offset_converts :: proc(t: ^testing.T) {
-	tz, tz_ok := get_cached_tz("America/New_York")
-	defer destroy_tz_cache()
+	tz, tz_ok := timezone.region_load("America/New_York", context.temp_allocator)
+	testing.expect(t, tz_ok, "should load timezone")
 	if !tz_ok do return
+	defer timezone.region_destroy(tz, context.temp_allocator)
 
 	// 2026-03-15T08:49:54-04:00 → UTC 12:49:54 → EDT 08:49:54
 	c := Date_Components{
diff --git a/mustache/pipes.odin b/mustache/pipes.odin
index 9d63e28..d81d922 100644
--- a/mustache/pipes.odin
+++ b/mustache/pipes.odin
@@ -5,6 +5,7 @@ import "core:log"
 import "core:reflect"
 import "core:strings"
 import "core:time"
+import "core:time/datetime"
 
 // MAX_PIPES was chosen arbitrarily. It holds no performance or logical
 // significance.
@@ -228,15 +229,8 @@ apply_filter :: proc(value: any, filter: ^Pipe_Filter, pos: int, ctx: []any) ->
 			date_format = df
 		}
 
-		// Resolve timezone (optional — empty is fine, means display as-is)
-		tz_name := ""
-		if raw := resolve_name("timezone", ctx); raw != nil {
-			if s, s_ok := reflect.as_string(raw); s_ok {
-				tz_name = s
-			}
-		}
-
-		str2, err := apply_format(str, filter.args[:], pos, date_format, tz_name)
+		tz := resolve_tz(ctx)
+		str2, err := apply_format(str, filter.args[:], pos, date_format, tz)
 		if err != nil {
 			return value, err
 		} else {
@@ -257,7 +251,7 @@ apply_format :: proc(
 	args: []string,
 	pos: int,
 	date_format: string,
-	timezone_name: string,
+	tz: ^datetime.TZ_Region,
 ) -> (
 	result: string,
 	err: Error,
@@ -279,22 +273,12 @@ apply_format :: proc(
 		}
 	}
 
-	target_tz, tz_ok := get_cached_tz(timezone_name)
-	if !tz_ok {
-		return "", Error_Body {
-			msg = fmt.tprintf("unable to load timezone '%s'", timezone_name),
-			pos = pos,
-			kind = .Data,
-		}
-	}
-
-	if target_tz != nil {
-		components, _ = convert_to_tz(components, target_tz)
+	if tz != nil {
+		components, _ = convert_to_tz(components, tz)
 	} else if components.has_offset {
 		components.tz_abbr = format_offset(components.offset_seconds)
 	}
 
-	log.debugf("date: '%s' format: '%s' tz: '%s'", iso, date_format, timezone_name)
 	return format_date(components, fmt_str), nil
 }
 
diff --git a/mustache/pipes_test.odin b/mustache/pipes_test.odin
index 0a29d9b..54c193f 100644
--- a/mustache/pipes_test.odin
+++ b/mustache/pipes_test.odin
@@ -3,6 +3,8 @@ package mustache
 
 import "core:fmt"
 import "core:testing"
+import "core:time/datetime"
+import "core:time/timezone"
 
 Pipe_Post :: struct {
 	title: string,
@@ -209,7 +211,7 @@ test_interp_pipe_basic :: proc(t: ^testing.T) {
 	Scalar_Data :: struct {
 		name:        string,
 		date_format: string,
-		timezone:    string,
+		timezone:    ^datetime.TZ_Region,
 	}
 	data := Scalar_Data {
 		name = "2026-03-15T08:49:54-04:00",
@@ -223,9 +225,9 @@ test_interp_pipe_basic :: proc(t: ^testing.T) {
 @(test)
 test_interp_pipe_unescaped :: proc(t: ^testing.T) {
 	Scalar_Data :: struct {
-		name:         string,
-		date_format:  string,
-		date_timezone: string,
+		name:        string,
+		date_format: string,
+		timezone:    ^datetime.TZ_Region,
 	}
 	data := Scalar_Data {
 		name = "2025-12-25T00:00:00Z",
@@ -241,7 +243,7 @@ test_interp_pipe_dot_current :: proc(t: ^testing.T) {
 	List_Data :: struct {
 		items:       [3]string,
 		date_format: string,
-		timezone:    string,
+		timezone:    ^datetime.TZ_Region,
 	}
 	data := List_Data {
 		items = {"2026-01-06T00:00:00Z", "2026-06-15T00:00:00Z", "2026-10-15T00:00:00Z"},
@@ -257,9 +259,9 @@ test_interp_pipe_dot_current :: proc(t: ^testing.T) {
 // ---------------------------------------------------------------------------
 
 Format_Data :: struct {
-	date:       string,
+	date:        string,
 	date_format: string,
-	timezone:  string,
+	timezone:    ^datetime.TZ_Region,
 }
 
 @(test)
@@ -488,44 +490,21 @@ test_format_bare_numeric_arg_treated_as_key_not_literal :: proc(t: ^testing.T) {
 	testing.expect(t, err != nil, "bare numeric-looking arg should error as an unresolved key")
 }
 
-@(test)
-test_timezone_resolves_from_context :: proc(t: ^testing.T) {
-	TZ_Data :: struct {
-		timezone: string,
-	}
-	data := TZ_Data {
-		timezone = "America/New_York",
-	}
-	tpl, _ := parse("[{{timezone}}]", "<test>", allocator = context.temp_allocator)
-	result, _ := render(tpl, data, {}, context.temp_allocator)
-	testing.expect_value(t, result, "[America/New_York]")
-}
-
-@(test)
-test_timezone_empty_when_not_set :: proc(t: ^testing.T) {
-	TZ_Data :: struct {
-		timezone: string,
-	}
-	data := TZ_Data {}
-	tpl, _ := parse("[{{timezone}}]", "<test>", allocator = context.temp_allocator)
-	result, _ := render(tpl, data, {}, context.temp_allocator)
-	testing.expect_value(t, result, "[]")
-}
-
 // ---------------------------------------------------------------------------
 // format pipe with timezone conversion
 // ---------------------------------------------------------------------------
 
 @(test)
 test_format_with_timezone_summer :: proc(t: ^testing.T) {
-	tz, tz_ok := get_cached_tz("America/New_York")
-	defer destroy_tz_cache()
-	if !tz_ok || tz == nil do return
+	tz, ok := timezone.region_load("America/New_York", context.temp_allocator)
+	testing.expect(t, ok, "should load timezone")
+	if !ok do return
+	defer timezone.region_destroy(tz, context.temp_allocator)
 
 	data := Format_Data {
 		date        = "2026-03-15T12:49:54Z",
 		date_format = "15:04 MST",
-		timezone    = "America/New_York",
+		timezone    = tz,
 	}
 	tpl, _ := parse("{{date | format}}", "<test>", allocator = context.temp_allocator)
 	result, _ := render(tpl, data, {}, context.temp_allocator)
@@ -534,14 +513,15 @@ test_format_with_timezone_summer :: proc(t: ^testing.T) {
 
 @(test)
 test_format_with_timezone_winter :: proc(t: ^testing.T) {
-	tz, tz_ok := get_cached_tz("America/New_York")
-	defer destroy_tz_cache()
-	if !tz_ok || tz == nil do return
+	tz, ok := timezone.region_load("America/New_York", context.temp_allocator)
+	testing.expect(t, ok, "should load timezone")
+	if !ok do return
+	defer timezone.region_destroy(tz, context.temp_allocator)
 
 	data := Format_Data {
 		date        = "2026-01-15T12:49:54Z",
 		date_format = "15:04 MST",
-		timezone    = "America/New_York",
+		timezone    = tz,
 	}
 	tpl, _ := parse("{{date | format}}", "<test>", allocator = context.temp_allocator)
 	result, _ := render(tpl, data, {}, context.temp_allocator)
@@ -569,18 +549,3 @@ test_format_mst_no_offset_no_timezone :: proc(t: ^testing.T) {
 	result, _ := render(tpl, data, {}, context.temp_allocator)
 	testing.expect_value(t, result, "UTC")
 }
-
-@(test)
-test_format_invalid_timezone_errors :: proc(t: ^testing.T) {
-	defer destroy_tz_cache()
-
-	data := Format_Data {
-		date        = "2026-03-15",
-		date_format = "2 Jan 2006",
-		timezone    = "Invalid/Zone",
-	}
-	tpl, _ := parse("{{date | format}}", "<test>", allocator = context.temp_allocator)
-	defer delete_template(&tpl)
-	_, err := render(tpl, data, {}, context.temp_allocator)
-	testing.expect(t, err != nil, "invalid timezone should error")
-}
diff --git a/render.odin b/render.odin
index 0c012a5..a380793 100644
--- a/render.odin
+++ b/render.odin
@@ -25,8 +25,8 @@ Base_Data :: struct {
 	title:        string,
 	description:  string,
 	og:           Open_Graph,
-	date_format: string,
-	timezone:     string,
+	date_format:  string,
+	timezone:     ^datetime.TZ_Region,
 }
 
 Page_Data :: struct {
@@ -157,10 +157,10 @@ render_site :: proc(site: ^Site) {
 	template_cache: map[string]mustache.Template
 	defer delete(template_cache)
 
-	// TODO: CAlculate offset
-	offset := 0
-	now, ok := time.time_to_rfc3339(time.now(), offset, false, allocator)
+	offset, ok := mustache.compute_utc_offset(site.tz)
 	assert(ok)
+	now, ok2 := time.time_to_rfc3339(time.now(), offset, false, allocator)
+	assert(ok2)
 
 	// Build base data once
 	base := Base_Data {
@@ -168,8 +168,8 @@ render_site :: proc(site: ^Site) {
 		params       = site.params,
 		description  = site.description,
 		og           = site.og,
-		date_format = site.date.format,
-		timezone     = site.date.timezone,
+		date_format  = site.date.format,
+		timezone     = site.tz,
 	}
 
 	// Find home page
diff --git a/site.odin b/site.odin
index 0299d98..735ac70 100644
--- a/site.odin
+++ b/site.odin
@@ -7,6 +7,8 @@ import "core:log"
 import "core:mem"
 import "core:os"
 import "core:strings"
+import "core:time/datetime"
+import "core:time/timezone"
 
 import md "markdown"
 
@@ -30,6 +32,7 @@ Site :: struct {
 	markdown_extensions: bit_set[md.Extension],
 	og:                  Open_Graph,
 	date:                Date_Preferences,
+	tz:                  ^datetime.TZ_Region,
 }
 
 Date_Preferences :: struct {
@@ -115,8 +118,22 @@ init_site :: proc(site: ^Site, args: []string) {
 	site_apply_cli_flags(site, _flags)
 	site.config_path = path
 
-	// Build the resolved site-level OG now that every other field is set.
 	site.og = og_for_site(site)
+
+	tz_name := site.date.timezone
+	if tz_name == "" {
+		log.warnf("no timezone configured, falling back to local system timezone")
+		tz_name = "local"
+	}
+	tz, tz_ok := timezone.region_load(tz_name, alloc)
+	if tz_ok {
+		site.tz = tz
+		if site.date.timezone == "" {
+			log.debugf("detected local timezone: %s", tz.name)
+		}
+	} else if site.date.timezone != "" {
+		log.warnf("unable to load timezone '%s'", site.date.timezone)
+	}
 }
 
 load_config_file :: proc(