Enhance ticker search and validation in "Convert to Trade" form (#688)

- Updated resolution logic to support combobox-based ticker selection and validation.
- Added market price display with validation against entered prices to detect significant mismatches.
- Improved messaging and UI for custom ticker input and market price warnings.

Co-authored-by: luckyPipewrench <luckypipewrench@proton.me>

app/javascript/controllers/convert_to_trade_controller.js

@@ -1,7 +1,11 @@
 import { Controller } from "@hotwired/stimulus"
 
 export default class extends Controller {
-  static targets = ["customWrapper", "customField", "tickerSelect"]
+  static targets = ["customWrapper", "customField", "tickerSelect", "qtyField", "priceField", "priceWarning", "priceWarningMessage"]
+  static values = {
+    amountCents: Number,
+    currency: String
+  }
 
   toggleCustomTicker(event) {
     const value = event.target.value
@@ -18,4 +22,76 @@ export default class extends Controller {
       this.customFieldTarget.value = ""
     }
   }
+
+  validatePrice() {
+    // Get the selected security's market price (in cents)
+    const selectedOption = this.tickerSelectTarget.selectedOptions[0]
+    if (!selectedOption || selectedOption.value === "" || selectedOption.value === "__custom__") {
+      this.hidePriceWarning()
+      return
+    }
+
+    const marketPriceCents = selectedOption.dataset.priceCents
+    const ticker = selectedOption.dataset.ticker
+
+    // If no market price data, can't validate
+    if (!marketPriceCents || marketPriceCents === "null") {
+      this.hidePriceWarning()
+      return
+    }
+
+    // Calculate the implied/entered price
+    let enteredPriceCents = null
+    const qty = Number.parseFloat(this.qtyFieldTarget?.value)
+    const enteredPrice = Number.parseFloat(this.priceFieldTarget?.value)
+
+    if (enteredPrice && enteredPrice > 0) {
+      // User entered a price directly
+      enteredPriceCents = enteredPrice * 100
+    } else if (qty && qty > 0 && this.amountCentsValue > 0) {
+      // Calculate price from amount / qty
+      enteredPriceCents = this.amountCentsValue / qty
+    }
+
+    if (!enteredPriceCents || enteredPriceCents <= 0) {
+      this.hidePriceWarning()
+      return
+    }
+
+    // Compare prices - warn if they differ by more than 50%
+    const marketPrice = Number.parseFloat(marketPriceCents)
+    const ratio = enteredPriceCents / marketPrice
+
+    if (ratio < 0.5 || ratio > 2.0) {
+      this.showPriceWarning(ticker, enteredPriceCents, marketPrice)
+    } else {
+      this.hidePriceWarning()
+    }
+  }
+
+  showPriceWarning(ticker, enteredPriceCents, marketPriceCents) {
+    if (!this.hasPriceWarningTarget) return
+
+    const enteredPrice = this.formatMoney(enteredPriceCents)
+    const marketPrice = this.formatMoney(marketPriceCents)
+
+    // Build warning message
+    const message = `Your price (${enteredPrice}/share) differs significantly from ${ticker}'s current market price (${marketPrice}). If this seems wrong, you may have selected the wrong security — try using "Enter custom ticker" to specify the correct one.`
+
+    this.priceWarningMessageTarget.textContent = message
+    this.priceWarningTarget.classList.remove("hidden")
+  }
+
+  hidePriceWarning() {
+    if (!this.hasPriceWarningTarget) return
+    this.priceWarningTarget.classList.add("hidden")
+  }
+
+  formatMoney(cents) {
+    const dollars = cents / 100
+    return new Intl.NumberFormat('en-US', {
+      style: 'currency',
+      currency: this.currencyValue || 'USD'
+    }).format(dollars)
+  }
 }