Add printer-config integration and Rust transformation flow docs

PrintService/Services/ConfigurationService.cs

@@ -0,0 +1,87 @@
+using System.Text.Json;
+using PrintService.Models;
+
+namespace PrintService.Services;
+
+/// <summary>
+/// Loads printer-config.json (global and local), merging local over global.
+/// Mirrors the same logic used in PrintServiceTray.
+/// </summary>
+public class ConfigurationService
+{
+    private readonly string _globalConfigPath;
+    private readonly string _localConfigPath;
+    private readonly ILogger<ConfigurationService> _logger;
+
+    public ConfigurationService(ILogger<ConfigurationService> logger)
+    {
+        _logger = logger;
+
+        _globalConfigPath = Path.Combine(
+            Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData),
+            "LAAPC", "printer-config.json");
+
+        _localConfigPath = Path.Combine(
+            Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
+            "LAAPC", "printer-config.json");
+    }
+
+    /// <summary>
+    /// Load merged configuration. Returns an empty config (not null) if no files exist.
+    /// </summary>
+    public PrinterConfiguration Load()
+    {
+        var config = new PrinterConfiguration();
+
+        if (File.Exists(_globalConfigPath))
+        {
+            try
+            {
+                var json = File.ReadAllText(_globalConfigPath);
+                var global = JsonSerializer.Deserialize<PrinterConfiguration>(json);
+                if (global != null)
+                    config = global;
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to read global printer config from {Path}", _globalConfigPath);
+            }
+        }
+
+        if (File.Exists(_localConfigPath))
+        {
+            try
+            {
+                var json = File.ReadAllText(_localConfigPath);
+                var local = JsonSerializer.Deserialize<PrinterConfiguration>(json);
+                if (local != null)
+                {
+                    // Local overrides global per document type
+                    foreach (var kvp in local.DocumentTypes)
+                        config.DocumentTypes[kvp.Key] = kvp.Value;
+                }
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to read local printer config from {Path}", _localConfigPath);
+            }
+        }
+
+        if (config.DocumentTypes.Count == 0)
+            _logger.LogWarning("No document types found in printer-config.json. Checked: {Global} and {Local}",
+                _globalConfigPath, _localConfigPath);
+
+        return config;
+    }
+
+    /// <summary>
+    /// Get a single document type config by name (case-insensitive).
+    /// </summary>
+    public DocumentTypeConfig? GetDocumentType(string documentType)
+    {
+        var config = Load();
+        return config.DocumentTypes
+            .FirstOrDefault(kvp => kvp.Key.Equals(documentType, StringComparison.OrdinalIgnoreCase))
+            .Value;
+    }
+}