Improve timestamp formatting with local timezone support

- Change format from '2025-11-11T22:32:58Z' to '2025-11-29 14:32:58'
- Add local timezone support using time crate
- Implement WASM support via js-sys for browser timezone detection
- Create shared to_local_datetime() helper function
- Update LogView, TraceView, and GraphSelect widgets

Closes #132

Author: mutualideas

Cargo.lock

@@ -55,6 +55,7 @@ gantz_egui = { version = "0.1.0", path = "crates/gantz_egui" }
 gantz_std = { version = "0.1.0", path = "crates/gantz_std" }
 hex = "0.4"
 humantime = "2.3"
+js-sys = "0.3"
 log = { version = "0.4", features = ["serde"] }
 petgraph = { version = "0.8", features = ["serde-1"] }
 ron = "0.10"
@@ -64,6 +65,7 @@ steel-core = "0.7"
 steel-derive = "0.6"
 sublime_fuzzy = "0.7"
 thiserror = "2"
+time = { version = "0.3", features = ["local-offset", "formatting", "wasm-bindgen"] }
 tracing = "0.1"
 tracing-subscriber = "0.3"
 typetag = "0.2"

Cargo.toml

@@ -24,15 +24,18 @@ gantz_core.workspace = true
 gantz_std.workspace = true
 hex.workspace = true
 humantime.workspace = true
+js-sys.workspace = true
 log.workspace = true
 petgraph.workspace = true
 serde.workspace = true
 steel-core.workspace = true
 sublime_fuzzy.workspace = true
+time.workspace = true
 tracing = { workspace = true, optional = true }
 tracing-subscriber = { workspace = true, optional = true }
 web-time.workspace = true
 
+
 [dev-dependencies]
 dyn-clone.workspace = true
 eframe.workspace = true

crates/gantz_egui/Cargo.toml

@@ -1,4 +1,7 @@
 //! A collection of useful widgets for gantz.
+#[cfg(target_arch = "wasm32")]
+use js_sys::Date;
+use time::{OffsetDateTime, UtcOffset};
 
 pub use command_palette::CommandPalette;
 pub use gantz::{Gantz, GantzState, update_graph_pane_head};
@@ -30,6 +33,32 @@ pub mod perf_view;
 #[cfg(feature = "tracing")]
 pub mod trace_view;
 
+/// Convert a UTC datetime to local timezone, with fallback to UTC if unavailable.
+pub(crate) fn to_local_datetime(datetime: OffsetDateTime) -> OffsetDateTime {
+    #[cfg(not(target_arch = "wasm32"))]
+    {
+        // Native platforms: use time crate's built-in method
+        UtcOffset::current_local_offset()
+            .map(|offset| datetime.to_offset(offset))
+            .unwrap_or(datetime)
+    }
+
+    #[cfg(target_arch = "wasm32")]
+    {
+        // WASM: get timezone offset from JavaScript Date API
+        use js_sys::Date;
+
+        let js_date = Date::new_0();
+        let offset_minutes = js_date.get_timezone_offset();
+        let offset_seconds = -(offset_minutes as i32 * 60);
+
+        match UtcOffset::from_whole_seconds(offset_seconds) {
+            Ok(offset) => datetime.to_offset(offset),
+            Err(_) => datetime,
+        }
+    }
+}
+
 /// Simple shorthand for viewing steel code.
 pub fn steel_view(ui: &mut egui::Ui, code: &str) {
     let language = "scm";

crates/gantz_egui/src/widget.rs

@@ -1,7 +1,8 @@
 //! A simple widget for selecting between, naming and creating new graphs.
 
 use super::head_row::{HeadRowType, head_row};
-use std::collections::HashSet;
+use std::collections::{BTreeMap, HashSet};
+use time::{OffsetDateTime, UtcOffset, format_description};
 
 /// A widget for selecting between, naming, and creating new graphs.
 pub struct GraphSelect<'a> {
@@ -203,3 +204,18 @@ impl<'a> GraphSelect<'a> {
         response
     }
 }
+
+// Format the commit as a timestamp for listing unnamed commits.
+pub(super) fn fmt_commit_timestamp(timestamp: gantz_ca::Timestamp) -> String {
+    std::time::UNIX_EPOCH
+        .checked_add(timestamp)
+        .and_then(|system_time| {
+            let datetime = OffsetDateTime::from(system_time);
+            let local_datetime = crate::widget::to_local_datetime(datetime);
+
+            let format =
+                format_description::parse("[year]-[month]-[day] [hour]:[minute]:[second]").ok()?;
+            local_datetime.format(&format).ok()
+        })
+        .unwrap_or_else(|| "<invalid-timestamp>".to_string())
+}

crates/gantz_egui/src/widget/graph_select.rs

@@ -4,6 +4,7 @@ use std::{
     collections::VecDeque,
     sync::{Arc, Mutex},
 };
+use time::{OffsetDateTime, format_description};
 use web_time::SystemTime;
 
 /// A table presenting the
@@ -30,8 +31,16 @@ pub struct LogEntry {
 
 impl LogEntry {
     fn format_timestamp(&self) -> String {
-        let time = crate::system_time_from_web(self.timestamp).expect("failed to convert");
-        humantime::format_rfc3339_seconds(time).to_string()
+        let system_time = crate::system_time_from_web(self.timestamp).expect("failed to convert");
+        let datetime = OffsetDateTime::from(system_time);
+        let local_datetime = crate::widget::to_local_datetime(datetime);
+
+        let format = format_description::parse("[year]-[month]-[day] [hour]:[minute]:[second]")
+            .expect("invalid format");
+
+        local_datetime
+            .format(&format)
+            .unwrap_or_else(|_| "<invalid-timestamp>".to_string())
     }
 
     fn freshness(&self) -> f32 {

crates/gantz_egui/src/widget/log_view.rs

@@ -3,6 +3,7 @@ use std::{
     collections::VecDeque,
     sync::{Arc, Mutex},
 };
+use time::{OffsetDateTime, format_description};
 use tracing::{Level, level_filters::LevelFilter};
 use tracing_subscriber::Layer;
 use web_time::SystemTime;
@@ -47,8 +48,16 @@ struct MessageVisitor {
 
 impl TraceEntry {
     fn format_timestamp(&self) -> String {
-        let time = crate::system_time_from_web(self.timestamp).expect("failed to convert");
-        humantime::format_rfc3339_seconds(time).to_string()
+        let system_time = crate::system_time_from_web(self.timestamp).expect("failed to convert");
+        let datetime = OffsetDateTime::from(system_time);
+        let local_datetime = crate::widget::to_local_datetime(datetime);
+
+        let format = format_description::parse("[year]-[month]-[day] [hour]:[minute]:[second]")
+            .expect("invalid format");
+
+        local_datetime
+            .format(&format)
+            .unwrap_or_else(|_| "<invalid-timestamp>".to_string())
     }
 
     fn freshness(&self) -> f32 {