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BUGS.md

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+# Known Bugs and Issues
+
+This document lists identified bugs and potential issues in the Labelmaker codebase.
+
+## Critical Issues
+
+### 1. Race Condition in Image Generation
+
+**Location**: `lib/labelmaker_web/controllers/label_controller.ex:21-31`
+
+**Status**: ⚠️ **UNRESOLVED**
+
+**Issue**: When multiple requests arrive simultaneously for the same non-existent image, both will start generating it concurrently. Additionally, `send_file/3` is called immediately after starting generation without waiting for it to complete, which will cause a file-not-found error.
+
+```elixir
+unless File.exists?(filepath) do
+  basic_settings(options)
+  |> outline_settings(options)
+  |> size_settings(options)
+  |> final_settings(options)
+  |> generate_image()
+end
+
+conn
+|> put_resp_content_type("image/png")
+|> send_file(200, filepath)  # Called before generation completes!
+```
+
+**Impact**: High - Will cause 500 errors when requests race or when generation is slow
+
+**Suggested Fix**:
+- Use a mutex/lock mechanism (e.g., via `:global` or a GenServer) to ensure only one process generates a given image
+- Ensure `send_file` is only called after generation completes
+- Consider using a temporary file with atomic rename to prevent serving partially-written images
+
+```elixir
+# Example approach with synchronization
+case ensure_image_exists(filepath, options) do
+  :ok ->
+    conn
+    |> put_resp_content_type("image/png")
+    |> send_file(200, filepath)
+  {:error, reason} ->
+    conn
+    |> put_status(500)
+    |> json(%{error: "Failed to generate image"})
+end
+```
+
+### 2. Crash on Invalid Numeric Inputs
+
+**Location**: `lib/labelmaker_web/tools.ex:87-88, 136-137, 140-141`
+
+**Status**: ⚠️ **UNRESOLVED**
+
+**Issue**: When `height`, `width`, or `size` parameters contain non-numeric strings (e.g., "abc", "12.5px"), `String.to_integer/1` raises an `ArgumentError` that isn't caught, causing the entire request to crash.
+
+```elixir
+defp process_height(height, _parameters) do
+  height |> String.to_integer() |> max(0) |> min(Constants.max_height())
+end
+
+defp process_width(width, _parameters) do
+  width |> String.to_integer() |> max(0) |> min(Constants.max_width())
+end
+
+defp calculate_preview_height(parameters) do
+  size = parameters["size"] |> String.to_integer()
+  # ...
+end
+```
+
+**Impact**: High - User-supplied invalid input causes crashes
+
+**Suggested Fix**:
+```elixir
+defp process_height(height, _parameters) do
+  case Integer.parse(height) do
+    {int, _} -> int |> max(0) |> min(Constants.max_height())
+    :error -> String.to_integer(Constants.defaults().height)
+  end
+end
+
+defp process_width(width, _parameters) do
+  case Integer.parse(width) do
+    {int, _} -> int |> max(0) |> min(Constants.max_width())
+    :error -> String.to_integer(Constants.defaults().width)
+  end
+end
+
+defp calculate_preview_height(parameters) do
+  size = case Integer.parse(parameters["size"]) do
+    {int, _} -> int
+    :error -> 72  # default
+  end
+  rows = calculate_rows(parameters["label"])
+  size + size * rows
+end
+```
+
+## Moderate Issues
+
+### 3. Missing Error Handling on ImageMagick Command
+
+**Location**: `lib/labelmaker_web/controllers/label_controller.ex:112`
+
+**Status**: ⚠️ **UNRESOLVED**
+
+**Issue**: Pattern matching on `{_, 0}` will crash if ImageMagick returns a non-zero exit code (e.g., invalid arguments, ImageMagick not installed, permission errors, disk full).
+
+```elixir
+{_, 0} = System.cmd("magick", args)
+```
+
+**Impact**: Moderate - Crashes on ImageMagick errors instead of gracefully handling
+
+**Suggested Fix**:
+```elixir
+case System.cmd("magick", args, stderr_to_stdout: true) do
+  {_output, 0} ->
+    :ok
+  {error, code} ->
+    require Logger
+    Logger.error("ImageMagick failed with code #{code}: #{error}")
+    {:error, :image_generation_failed}
+end
+```
+
+Then handle the error tuple in the controller's `show/2` function and return appropriate HTTP error response.
+
+### 4. Potential nil Crash on Font Lookup
+
+**Location**: `lib/labelmaker_web/tools.ex:34-35`
+
+**Status**: ⚠️ **UNRESOLVED**
+
+**Issue**: If an invalid font is passed that isn't in the font_map, the map lookup returns `nil`. While later validation (line 64) filters it out, if defaults somehow don't include `font`, `nil` could be passed to ImageMagick causing cryptic errors.
+
+```elixir
+{:font, font} ->
+  {:font, Constants.font_map()[String.downcase(font)]}
+```
+
+**Impact**: Low-Moderate - Edge case but could cause ImageMagick errors
+
+**Suggested Fix**:
+```elixir
+{:font, font} ->
+  {:font, Map.get(Constants.font_map(), String.downcase(font), Constants.defaults().font)}
+```
+
+### 5. label_too_long Flag Logic Bug
+
+**Location**: `lib/labelmaker_web/tools.ex:40-41`
+
+**Status**: 🐛 **CONFIRMED BUG**
+
+**Issue**: The `label_too_long` flag is calculated AFTER the label has already been truncated in `process_label/1` (line 16-17). This means the flag will always be `false` because it's checking the length of the already-truncated label, not the original input.
+
+```elixir
+# Line 16-17: Label gets truncated here
+{"label", label} ->
+  {"label", process_label(label)}
+
+# Line 40-41: This checks the ALREADY TRUNCATED label
+{:label_too_long, _} ->
+  {:label_too_long, String.length(parameters["label"]) > Constants.max_label_length()}
+```
+
+**Impact**: Low - UI warning for long labels never appears
+
+**Suggested Fix**:
+Check the length before truncation, or pass the original length through:
+```elixir
+def process_parameters(parameters) do
+  # Calculate label_too_long before any processing
+  original_label_length = String.length(Map.get(parameters, "label", ""))
+
+  parameters =
+    Constants.defaults()
+    |> Map.new(fn {k, v} -> {Atom.to_string(k), v} end)
+    |> Map.merge(parameters)
+    |> Map.put("_original_label_length", original_label_length)
+    # ... rest of processing
+
+  # Later when setting the flag:
+  {:label_too_long, _} ->
+    {:label_too_long, parameters["_original_label_length"] > Constants.max_label_length()}
+```
+
+## Low Priority Issues
+
+### 6. Hash Collision Risk from inspect()
+
+**Location**: `lib/labelmaker_web/controllers/label_controller.ex:11-15`
+
+**Status**: ⚠️ **UNRESOLVED**
+
+**Issue**: Using `inspect/1` on a map for hashing is fragile. Map ordering isn't guaranteed to be consistent across Erlang/OTP versions or runtime conditions. Two identical maps could theoretically produce different inspect strings, leading to cache misses.
+
+```elixir
+filename =
+  options
+  |> inspect()
+  |> (fn str -> :crypto.hash(:sha256, str) end).()
+  |> Base.encode16(case: :lower)
+```
+
+**Impact**: Low - Mostly theoretical, but could cause unnecessary cache misses
+
+**Suggested Fix**: Hash a consistently-ordered representation:
+```elixir
+filename =
+  options
+  |> Map.take([:label, :color, :font, :outline, :size, :width, :height, :align])
+  |> Enum.sort()
+  |> :erlang.term_to_binary()
+  |> :crypto.hash(:sha256)
+  |> Base.encode16(case: :lower)
+```
+
+### 7. Missing Type Guards on String Operations
+
+**Location**: `lib/labelmaker_web/tools.ex:32, 35`
+
+**Status**: ⚠️ **UNRESOLVED**
+
+**Issue**: `String.downcase/1` is called on `align` and `font` parameters without verifying they're strings. Given the data flow this is unlikely to be a problem, but defensive programming would add guards.
+
+```elixir
+{:align, align} ->
+  {:align, align |> String.downcase()}
+
+{:font, font} ->
+  {:font, Constants.font_map()[String.downcase(font)]}
+```
+
+**Impact**: Very Low - Input validation earlier in the pipeline makes this unlikely
+
+**Suggested Fix**: Add type guards or convert to string first:
+```elixir
+{:align, align} when is_binary(align) ->
+  {:align, String.downcase(align)}
+
+# Or alternatively:
+{:align, align} ->
+  {:align, align |> to_string() |> String.downcase()}
+```
+
+## Fixed Issues
+
+### ✅ 8. ImageMagick Property Interpolation Warning
+
+**Location**: `lib/labelmaker_web/controllers/label_controller.ex:50, 65, 96`
+
+**Status**: ✅ **FIXED**
+
+**Issue**: Labels containing `%` characters (like "Test!@#$%" or URL-encoded text) caused ImageMagick to emit warnings about unknown properties like `%2`, `%20`, etc., because ImageMagick treats `%` as a special character for property interpolation.
+
+**Fix Applied**: All `%` characters are now escaped to `%%` in:
+1. Label text passed to `label:` and `caption:` commands
+2. Metadata stored in image comments
+
+```elixir
+# Lines 47-50, 62-65
+escaped_label =
+  options.label
+  |> String.slice(0, Constants.max_label_length())
+  |> String.replace("%", "%%")
+
+# Lines 91-96
+comment =
+  options
+  |> Map.drop([:filepath, :link])
+  |> Jason.encode!()
+  |> inspect()
+  |> String.replace("%", "%%")
+```
+
+## Notes
+
+- All critical and moderate issues should be addressed before deploying to production
+- The test suite (105 tests) currently passes but doesn't cover error conditions for many of these bugs
+- Consider adding integration tests that specifically test error handling paths

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+Labelmaker is a Phoenix LiveView web application that generates text-based images via URL. Users can visit `labelmaker.xyz/Your Text` to instantly get an image with their text, with various customization options (font, color, outline, size). The app is designed for creating decals in Tabletop Simulator.
+
+## Technology Stack
+
+- **Elixir + Phoenix Framework** (Phoenix 1.7+ with LiveView)
+- **ImageMagick** (`magick` command) for image generation
+- **Tailwind CSS** for styling
+- **esbuild** for JavaScript bundling
+
+## Common Commands
+
+### Development
+```sh
+# Install dependencies and set up assets
+mix setup
+
+# Start Phoenix server (runs on http://localhost:4000)
+mix phx.server
+
+# Start server with interactive Elixir shell
+iex -S mix phx.server
+```
+
+### Testing
+```sh
+# Run all tests
+mix test
+
+# Run a specific test file
+mix test test/labelmaker_web/controllers/label_controller_test.exs
+
+# Run a specific test
+mix test test/labelmaker_web/controllers/label_controller_test.exs:42
+```
+
+### Assets
+```sh
+# Install asset build tools (Tailwind, esbuild)
+mix assets.setup
+
+# Build assets for development
+mix assets.build
+
+# Build assets for production (minified + digest)
+mix assets.deploy
+```
+
+### Docker
+```sh
+docker build -t labelmaker .
+docker run -p 4000:4000 labelmaker
+```
+
+## Architecture
+
+### Request Flow
+
+1. **Homepage (`/`)**: `LabelmakerWeb.Home` LiveView provides an interactive form where users can preview text with different styling options
+2. **Image Generation (`/:label`)**: `LabelmakerWeb.LabelController.show/2` handles dynamic image generation
+
+### Core Components
+
+**`LabelmakerWeb.LabelController`** (lib/labelmaker_web/controllers/label_controller.ex)
+- Main entry point for image generation requests
+- Takes URL path (label text) and query parameters (color, font, outline, size, width, height, align)
+- Generates SHA256 hash from parameters to create unique filename for caching
+- Checks if cached image exists; if not, builds ImageMagick command and generates image
+- Stores generated images in `priv/static/labels/`
+- Returns image as PNG response
+
+**`LabelmakerWeb.Tools`** (lib/labelmaker_web/tools.ex)
+- Contains parameter processing and validation logic
+- `process_parameters/1`: Validates and normalizes user input against permitted values
+- Handles two sizing modes:
+  - **Font mode** (default): Uses `label:` with `-pointsize` for natural text sizing
+  - **Width x Height mode**: Uses `caption:` with `-size WxH` for fixed dimensions
+- `generate_link/1`: Creates URLs based on current parameters and sizing mode
+- `process_label/1`: Handles `\n` to actual newline conversion for multi-line labels
+- Input validation: filters colors, fonts, sizes, outlines against permitted lists
+
+**`LabelmakerWeb.Constants`** (lib/labelmaker_web/constants.ex)
+- Single source of truth for all permitted values and defaults
+- Defines available colors, fonts, sizes, alignments
+- Font map supports shortcuts (e.g., "h" → "Helvetica", "cs" → "Comic-Sans-MS")
+- Max dimensions: 1024x1024 pixels
+- Max label length: 1024 characters
+- Available fonts: Comic Sans, Courier, Georgia, Helvetica, Impact, Verdana
+
+**`LabelmakerWeb.Home`** (lib/labelmaker_web/live/home.ex)
+- LiveView for homepage with interactive preview
+- Handles real-time updates via `handle_event/3`:
+  - `update_label`: Updates label text and styling parameters
+  - `update_preview`: Changes preview background (gradient/solid)
+  - `update_sizing`: Toggles between font size mode and width×height mode
+  - `update_alignment`: Changes text alignment (left/center/right)
+- Redirects to `/:label` route when user submits the form
+
+**`LabelmakerWeb.RadioComponent`** (lib/labelmaker_web/live/components/radio_component.ex)
+- Reusable Phoenix Component for radio button groups
+- Used in the homepage form for alignment selection
+
+### ImageMagick Command Construction
+
+The controller builds ImageMagick commands programmatically:
+
+1. **Basic settings**: background, fill color, font
+2. **Outline settings**: stroke color and width (if not "none")
+3. **Size settings**: Either pointsize + `label:` OR width×height + `caption:`
+4. **Final settings**: Adds metadata comment and output filepath
+
+Example generated command:
+```sh
+magick -background none -fill black -font Helvetica -stroke white -strokewidth 1 -pointsize 72 label:Hello World output.png
+```
+
+### Sizing Modes
+
+The app supports two distinct sizing modes (controlled by `sizing` parameter):
+
+- **Font mode** (`sizing=font`): ImageMagick calculates image size based on font size; natural text rendering
+- **Width × Height mode** (`sizing=wxh`): Fixed canvas dimensions with text wrapped/aligned within bounds
+
+### Parameter Processing
+
+All parameters flow through `Tools.process_parameters/1`:
+1. Merge with defaults from `Constants.defaults()`
+2. Process label (convert `\n` escapes)
+3. Validate each parameter against permitted lists
+4. Filter out invalid values
+5. Calculate derived values (preview_height, rows, link)
+6. Return merged map with all parameters
+
+### Caching Strategy
+
+Images are cached using SHA256 hash of the processed options map:
+- Hash includes: label, color, font, outline, size, width, height, align
+- Cached files stored in `priv/static/labels/`
+- Before generating, checks if file exists
+- No expiration mechanism (cache persists until manually cleared)
+
+## Important Notes
+
+- **ImageMagick dependency**: The `magick` command must be available in PATH
+- **Alignment/Gravity mapping**: User-facing "left/center/right" maps to ImageMagick "west/center/east" gravity values (see `Tools.process_gravity/1`)
+- **URL escaping**: Special characters in labels must be URL-encoded; `\n` is processed as literal newline
+- **Main branch**: This repo uses `trunk` as the main branch (not `main` or `master`)