feat: event editing — change exchange rate and currency

- Added Edit button on open event cards in dashboard
- EditEvent handler returns dashboard.html with pre-filled form
- UpdateEvent handler (PUT /events/{id}) saves new currency + rate
- UpdateEvent in db.go updates base_currency and exchange_rate
- Form auto-switches between create (POST) and edit (PUT) mode
- Reuses the same conversion sample pattern as event creation

internal/database/db.go

@@ -287,6 +287,16 @@ func UpdateEventStatus(db *sql.DB, id, status string) error {
 	return err
 }
 
+// UpdateEvent updates the base currency and exchange rate of an existing event.
+func UpdateEvent(db *sql.DB, id, baseCurrency string, exchangeRate float64) error {
+	_, err := db.Exec("UPDATE events SET base_currency = ?, exchange_rate = ? WHERE id = ?", baseCurrency, exchangeRate, id)
+	if err != nil {
+		log.Printf("ERROR [%s] database: UpdateEvent(%s): %v",
+			time.Now().Format(time.RFC3339), id, err)
+	}
+	return err
+}
+
 // ---------------------------------------------------------------------------
 // Expense queries
 // ---------------------------------------------------------------------------

internal/handlers/events.go

@@ -259,3 +259,71 @@ func (h *EventHandler) ViewEventExpenses(w http.ResponseWriter, r *http.Request)
 			time.Now().Format(time.RFC3339), err)
 	}
 }
+
+// ---------------------------------------------------------------------------
+// GET /events/{id}/edit — EditEvent
+// ---------------------------------------------------------------------------
+
+// EditEvent returns the event edit form pre-filled with current event data.
+func (h *EventHandler) EditEvent(w http.ResponseWriter, r *http.Request) {
+	eventID := chi.URLParam(r, "id")
+	event, err := database.GetEventByID(h.DB, eventID)
+	if err != nil || event == nil || event.UserID != getUserID(r) {
+		http.Error(w, "Forbidden", http.StatusForbidden)
+		return
+	}
+
+	tmpl := getTemplate("dashboard.html")
+	data := map[string]interface{}{
+		"Event":          event,
+		"Editing":        true,
+		"Events":         []database.Event{},
+		"BaseCurrency":   event.BaseCurrency,
+		"ExchangeRate":   event.ExchangeRate,
+		"LastSampleRcpt": "",
+		"LastSampleClm":  "",
+	}
+	if err := tmpl.Execute(w, data); err != nil {
+		log.Printf("ERROR [%s] handlers: EditEvent: execute template: %v",
+			time.Now().Format(time.RFC3339), err)
+	}
+}
+
+// ---------------------------------------------------------------------------
+// PUT /events/{id} — UpdateEvent
+// ---------------------------------------------------------------------------
+
+// UpdateEvent updates the event's base currency and exchange rate.
+func (h *EventHandler) UpdateEvent(w http.ResponseWriter, r *http.Request) {
+	eventID := chi.URLParam(r, "id")
+	event, err := database.GetEventByID(h.DB, eventID)
+	if err != nil || event == nil || event.UserID != getUserID(r) {
+		http.Error(w, "Forbidden", http.StatusForbidden)
+		return
+	}
+
+	baseCurrency := r.FormValue("base_currency")
+	if baseCurrency == "" {
+		baseCurrency = "USD"
+	}
+
+	exchangeRate := 1.0
+	sampleReceipt := r.FormValue("sample_receipt_amount")
+	sampleClaim := r.FormValue("sample_claim_amount")
+	if sampleReceipt != "" && sampleClaim != "" {
+		sampleReceiptVal, err1 := strconv.ParseFloat(sampleReceipt, 64)
+		sampleClaimVal, err2 := strconv.ParseFloat(sampleClaim, 64)
+		if err1 == nil && err2 == nil && sampleReceiptVal > 0 && sampleClaimVal > 0 {
+			exchangeRate = sampleClaimVal / sampleReceiptVal
+		}
+	}
+
+	if err := database.UpdateEvent(h.DB, eventID, baseCurrency, exchangeRate); err != nil {
+		log.Printf("ERROR [%s] handlers: UpdateEvent: %v", time.Now().Format(time.RFC3339), err)
+		http.Error(w, "Failed to update event", http.StatusInternalServerError)
+		return
+	}
+
+	w.Header().Set("HX-Redirect", "/dashboard")
+	w.WriteHeader(http.StatusOK)
+}

main.go

@@ -205,6 +205,8 @@ func main() {
 		// Events.
 		r.Get("/dashboard", eventHandler.Dashboard)
 		r.Post("/events", eventHandler.CreateEvent)
+		r.Put("/events/{id}", eventHandler.UpdateEvent)
+		r.Get("/events/{id}/edit", eventHandler.EditEvent)
 		r.Put("/events/{id}/reopen", eventHandler.ReopenEvent)
 		r.Get("/events/{id}/expenses", eventHandler.ViewEventExpenses)
 

templates/dashboard.html

@@ -28,20 +28,26 @@
 
             <div id="create-event-form" class="hidden" style="margin-bottom: 1rem;">
                 <div class="card" style="padding: 1rem;">
+                    {{if .Editing}}
+                    <h3 style="margin-bottom: 1rem;">Edit Event</h3>
+                    <form hx-put="/events/{{.Event.ID}}" hx-target="body" hx-push-url="true">
+                    {{else}}
                     <form hx-post="/events" hx-target="body" hx-push-url="true">
+                    {{end}}
                         <div class="form-group">
-                            <input type="text" id="name" name="name" placeholder="Event name, e.g. WebSummit 2026" required>
+                            <label class="form-label">{{if .Editing}}Event{{else}}Event Name{{end}}</label>
+                            <input type="text" id="name" name="name" placeholder="Event name" value="{{.Event.Name}}" {{if not .Editing}}required{{end}}>
                         </div>
                         <div class="form-row">
                             <div class="form-group">
                                 <label class="form-label">Claim Currency</label>
-                                <input type="text" id="base_currency" name="base_currency" value="USD" placeholder="USD, EUR, KES…" required maxlength="3" style="text-transform: uppercase;">
+                                <input type="text" id="base_currency" name="base_currency" value="{{if .Editing}}{{.Event.BaseCurrency}}{{else}}USD{{end}}" placeholder="USD, EUR, KES…" required maxlength="3" style="text-transform: uppercase;">
                             </div>
                         </div>
                         <div style="background: #064e3b; border: 1px solid #065f46; border-radius: 0.5rem; padding: 0.75rem; margin-bottom: 0.5rem;">
                             <div style="font-size: 0.8rem; font-weight: 600; color: #6ee7b7; margin-bottom: 0.5rem;">Conversion Sample</div>
                             <p style="font-size: 0.75rem; color: var(--color-text-muted); margin-bottom: 0.5rem;">
-                                From a payment notification: receipt amount and what you were charged.
+                                {{if .Editing}}Update the sample to recalculate the rate.{{else}}From a payment notification: receipt amount and what you were charged.{{end}}
                             </p>
                             <div class="form-row">
                                 <div class="form-group">
@@ -50,15 +56,19 @@
                                 </div>
                                 <div class="form-group" style="flex: 0 0 110px;">
                                     <label class="form-label">Currency</label>
-                                    <input type="text" id="sample_receipt_currency" name="sample_receipt_currency" value="KES" placeholder="KES" required maxlength="3" style="text-transform: uppercase;">
+                                    <input type="text" id="sample_receipt_currency" name="sample_receipt_currency" value="{{if .Editing}}{{.Event.BaseCurrency}}{{else}}KES{{end}}" placeholder="KES" required maxlength="3" style="text-transform: uppercase;">
                                 </div>
                             </div>
                             <div class="form-group">
-                                <label class="form-label">What you were charged (claim currency)</label>
+                                <label class="form-label">{{if .Editing}}Converted amount{{else}}What you were charged (claim currency){{end}}</label>
                                 <input type="number" id="sample_claim_amount" name="sample_claim_amount" step="0.01" min="0.01" placeholder="e.g. 7.73" required>
                             </div>
                         </div>
-                        <button type="submit" class="btn btn-primary btn-block">Create Event</button>
+                        <button type="submit" class="btn btn-primary btn-block">{{if .Editing}}Save Changes{{else}}Create Event{{end}}</button>
+                        {{if .Editing}}
+                        <a href="/dashboard" class="btn btn-secondary btn-block" style="display: block; text-align: center; margin-top: 0.5rem;"
+                           hx-get="/dashboard" hx-target="body" hx-push-url="true">Cancel</a>
+                        {{end}}
                     </form>
                 </div>
             </div>
@@ -80,6 +90,15 @@
                                style="text-decoration: none;">
                                 Open
                             </a>
+                            {{if eq .Status "open"}}
+                            <button class="btn btn-secondary btn-sm"
+                                    hx-get="/events/{{.ID}}/edit"
+                                    hx-target="#create-event-form"
+                                    hx-swap="innerHTML"
+                                    style="font-size: 0.75rem;">
+                                Edit
+                            </button>
+                            {{end}}
                             {{if eq .Status "closed"}}
                             <button class="btn btn-secondary btn-sm"
                                     hx-put="/events/{{.ID}}/reopen"