bookhoard/TIMEZONE_PLAN.md

Timezone Implementation Plan

Overview

Add per-user timezone support with system-wide fallback (set via docker-compose), defaulting to UTC. The database already stores all timestamps as UTC via TIMESTAMPTZ columns, so this is primarily a display-layer feature.

Display format: MM-DD-YYYY HH:MM (US convention, no timezone abbreviation shown)

Timezone selection: Manual dropdown only (no browser auto-detect)

---

Phase 1: Database Schema

File: database/schema/schema.sql

1. Add timezone column to users table:

ALTER TABLE users ADD COLUMN IF NOT EXISTS timezone VARCHAR(50) DEFAULT 'UTC';

2. Add system-wide default timezone to system_settings:

INSERT INTO system_settings (setting_key, setting_value, description) VALUES
('default_timezone', 'UTC', 'System default timezone')
ON CONFLICT (setting_key) DO NOTHING;

3. Add index:

CREATE INDEX IF NOT EXISTS idx_users_timezone ON users(timezone);

4. Regenerate sqlc code:

cd internal/database && sqlc generate

---

Phase 2: Database Queries

File: internal/database/queries/queries.sql

Add new queries:

-- name: UpdateUserTimezone :exec
UPDATE users SET timezone = $2, updated_at = NOW() WHERE id = $1;

-- name: GetSystemTimezone :one
SELECT setting_value FROM system_settings WHERE setting_key = 'default_timezone';

-- name: UpdateSystemTimezone :exec
UPDATE system_settings SET setting_value = $2, updated_at = NOW() WHERE setting_key = 'default_timezone';

Regenerate after adding queries:

cd internal/database && sqlc generate

---

Phase 3: Template Utilities

File: templates/utils.go

Add timezone-aware time formatting helpers:

package templates

import (
    "time"

    "github.com/jackc/pgx/v5/pgtype"
)

// FormatInTimezone formats a time.Time in the specified timezone as MM-DD-YYYY HH:MM
func FormatInTimezone(t time.Time, timezone string) string {
    if t.IsZero() {
        return ""
    }

    loc, err := time.LoadLocation(timezone)
    if err != nil {
        loc = time.UTC
    }

    return t.In(loc).Format("01-02-2006 15:04")
}

// FormatTimestamptzInTimezone formats a pgtype.Timestamptz in the specified timezone
func FormatTimestamptzInTimezone(t pgtype.Timestamptz, timezone string) string {
    if !t.Valid {
        return ""
    }
    return FormatInTimezone(t.Time, timezone)
}

---

Phase 4: User Context Update

File: templates/types.go

Add Timezone field to the User struct:

type User struct {
    ID        string
    Email     string
    Username  string
    Role      string
    Theme     string
    FirstName string
    LastName  string
    CreatedAt time.Time
    Token     string
    Timezone  string
}

File: internal/router/helpers.go

Update getTemplateUserWithTheme() to include timezone:

userTimezone := "UTC"
if userDB.Timezone.Valid {
    userTimezone = userDB.Timezone.String
}

return templates.User{
    // ... existing fields ...
    Timezone: userTimezone,
}

---

Phase 5: Handlers

File: internal/handlers/auth.go

Update UpdateProfileRequest struct:

type UpdateProfileRequest struct {
    Username  string `json:"username,omitempty" validate:"omitempty,min=3,max=50"`
    Email     string `json:"email,omitempty" validate:"omitempty,email"`
    FirstName string `json:"first_name,omitempty" validate:"omitempty,max=100"`
    LastName  string `json:"last_name,omitempty" validate:"omitempty,max=100"`
    Theme     string `json:"theme,omitempty" validate:"omitempty"`
    Timezone  string `json:"timezone,omitempty" validate:"omitempty"`
}

Add timezone update logic in UpdateProfile():

if req.Timezone != "" {
    if _, err := time.LoadLocation(req.Timezone); err != nil {
        return c.JSON(http.StatusBadRequest, map[string]string{
            "error": "Invalid timezone",
        })
    }
    err := h.db.UpdateUserTimezone(ctx, database.UpdateUserTimezoneParams{
        ID:       pgtype.UUID{Bytes: userUUID, Valid: true},
        Timezone: pgtype.Text{String: req.Timezone, Valid: true},
    })
    if err != nil {
        return err
    }
}

File: internal/handlers/system_settings.go

Add timezone settings handler:

type UpdateTimezoneSettingsRequest struct {
    DefaultTimezone string `json:"default_timezone" validate:"required"`
}

func (h *SystemSettingsHandler) UpdateTimezoneSettings(c *echo.Context) error {
    var req UpdateTimezoneSettingsRequest
    if err := c.Bind(&req); err != nil {
        return c.JSON(http.StatusBadRequest, map[string]string{"error": "Invalid request"})
    }
    if _, err := time.LoadLocation(req.DefaultTimezone); err != nil {
        return c.JSON(http.StatusBadRequest, map[string]string{"error": "Invalid timezone"})
    }
    err := h.db.UpdateSystemTimezone(c.Request().Context(), database.UpdateSystemTimezoneParams{
        SettingKey:   "default_timezone",
        SettingValue: req.DefaultTimezone,
    })
    if err != nil {
        return err
    }
    return c.JSON(http.StatusOK, map[string]string{"message": "Timezone updated"})
}

---

Phase 6: User Profile UI

File: templates/profile_form.templ

Add timezone dropdown after the theme field:

<div class="form-group">
    <label for="timezone">Timezone</label>
    <select name="timezone" id="timezone" class="form-select">
        <option value="UTC" selected?={ user.Timezone == "UTC" }>UTC (Coordinated Universal Time)</option>
        <option value="America/New_York" selected?={ user.Timezone == "America/New_York" }>Eastern Time</option>
        <option value="America/Chicago" selected?={ user.Timezone == "America/Chicago" }>Central Time</option>
        <option value="America/Denver" selected?={ user.Timezone == "America/Denver" }>Mountain Time</option>
        <option value="America/Los_Angeles" selected?={ user.Timezone == "America/Los_Angeles" }>Pacific Time</option>
        <option value="America/Phoenix" selected?={ user.Timezone == "America/Phoenix" }>Mountain Time (no DST)</option>
        <option value="America/Anchorage" selected?={ user.Timezone == "America/Anchorage" }>Alaska Time</option>
        <option value="Pacific/Honolulu" selected?={ user.Timezone == "Pacific/Honolulu" }>Hawaii Time</option>
    </select>
</div>

Include timezone in the HTMX form submission payload.

---

Phase 7: Admin Settings UI

File: templates/admin_settings.templ

Add system default timezone setting:

<div class="setting-group">
    <h3>System Defaults</h3>
    <label for="default_timezone">Default Timezone</label>
    <select name="default_timezone" id="default_timezone">
        <option value="UTC">UTC (Coordinated Universal Time)</option>
        <option value="America/New_York">Eastern Time</option>
        <option value="America/Chicago">Central Time</option>
        <option value="America/Denver">Mountain Time</option>
        <option value="America/Los_Angeles">Pacific Time</option>
        <option value="America/Phoenix">Mountain Time (no DST)</option>
        <option value="America/Anchorage">Alaska Time</option>
        <option value="Pacific/Honolulu">Hawaii Time</option>
    </select>
</div>

---

Phase 8: Template Time Display Updates

Files to update

Template	Line(s)	Field(s)
templates/book_detail.templ	~253, ~282	LastReadAt, DatePublished
templates/book_detail_modals.templ	~68, ~113	Timestamp, LastReadAt
templates/devices.templ	~83, ~91, ~174	LastSync, LastSeen, ExpiresAt
templates/conflicts.templ	~114	CreatedAt
templates/admin_users.templ	~89	CreatedAt
templates/queue.templ	~138	CreatedAt

Change pattern

<!-- Before -->
{ book.ReadingProgress.LastReadAt.Time.Format("2006-01-02 15:04") }

<!-- After -->
{ templates.FormatTimestamptzInTimezone(book.ReadingProgress.LastReadAt, user.Timezone) }

For time.Time fields:

<!-- Before -->
{ device.LastSync.Format("2006-01-02 15:04") }

<!-- After -->
{ templates.FormatInTimezone(device.LastSync, user.Timezone) }

---

Phase 9: Docker Configuration

File: docker-compose.yml

services:
  server:
    environment:
      - TZ=UTC

File: .env.example

# System default timezone (fallback if not set in DB)
TZ=UTC

---

Files Modified Summary

File	Change
database/schema/schema.sql	Add timezone column to users, system_setting row
internal/database/queries/queries.sql	Add UpdateUserTimezone, GetSystemTimezone, UpdateSystemTimezone
templates/utils.go	Add FormatInTimezone, FormatTimestamptzInTimezone
templates/types.go	Add Timezone field to User struct
internal/router/helpers.go	Pass timezone to template User
internal/handlers/auth.go	Handle timezone updates in UpdateProfile
internal/handlers/system_settings.go	Add timezone settings handler
templates/profile_form.templ	Add timezone dropdown
templates/admin_settings.templ	Add default timezone setting
templates/book_detail.templ	Update time displays
templates/book_detail_modals.templ	Update time displays
templates/devices.templ	Update time displays
templates/conflicts.templ	Update time displays
templates/admin_users.templ	Update time displays
templates/queue.templ	Update time displays
docker-compose.yml	Add TZ env var
.env.example	Add TZ example

---

Testing Checklist

• Create user, set timezone to Eastern, verify times display in MM-DD-YYYY HH:MM format
• Create user, set timezone to Pacific, verify different offset
• Test system default timezone fallback for users with no timezone set
• Verify invalid timezone values are rejected by the API
• Verify existing users (no timezone set) fall back to system default
• Verify all templates show consistent MM-DD-YYYY HH:MM format
• Run make test-integration to verify no regressions

---

Deployment Steps

1. Update database/schema/schema.sql with new column and settings
2. Regenerate sqlc: cd internal/database && sqlc generate
3. Apply schema changes (restart database container with make rebuild-force-db)
4. Deploy backend code changes
5. Verify with existing data