First step to derivedformula

TODO.md

@@ -60,8 +60,11 @@
 - [R] When _FormulaScreenState._evaluateFormula() detect an error, instead of show an SnackBar, show a ExpansionTile with "⚠️ There were an error. Show details..." with the details of the exception. The ExpansionTile will be invisible if there is no error.
 - [R] When FormulaEditor._save formula, ensure formula is updated in the initial FormulaList
 - [R] In FormulaEditor, add a button to "Save as copy", additional to the existing button "Save". It doesnt matter if the copy has the same name as the original formula, since they are identified by a internal UUID.
-- [ ] Add a button for each input variable in FormulaScreen. 
+- [R] Add a button for each input variable in FormulaScreen.
   - This button will create a DerivedFormula, with the input variable as output, and the rest of the input variables as inputs.
   - The DerivedFormula will then be displayed in the FormulaScreen
-- [ ] If the Formula displayed in FormulaScreen is a DerivedFormula, the edit button will be disabled
+- [R] If the Formula displayed in FormulaScreen is a DerivedFormula, the edit button will be disabled
+- [ ] When a formula is derived in FormulaScreen, the new FormulaScreen is not pushed in navigator, it replacles the current FormulaScreen
+- [ ] In FormulaScreen, a Formula cant be derived if DerivedFormula.isDerivable() returns false
+- [ ] The algorithm of formulaSolver should be https://en.wikipedia.org/wiki/Newton%27s_method
 - [ ] Add a uuid column to the table or FormulaElements, so it is not necessary to load all the formulas to find a formula by uuid. This will improve performance when updating and deleting.

lib/ai/formula_screen.dart

@@ -12,7 +12,7 @@ import 'unit_dropdown.dart';
 import 'formula_editor.dart';
 
 class FormulaScreen extends StatefulWidget {
-  final Formula initialFormula;
+  final FormulaInterface initialFormula;
   final Corpus corpus;
   final Function(Formula)? onSave; // Callback when formula is saved
 
@@ -31,13 +31,13 @@ class _FormulaScreenState extends State<FormulaScreen> {
   String? _result;
   String? _selectedOutputUnit;
   bool _isDescriptionExpanded = false; // Track description expansion state
-  late Formula _formula;
+  late FormulaInterface _formula;
 
-  Formula get formula => _formula;
+  FormulaInterface get formula => _formula;
   String? _errorMessage; // Track error message for expansion tile
   bool _isErrorExpanded = false; // Track error expansion state
 
-  set formula(Formula newFormula) {
+  set formula(FormulaInterface newFormula) {
     _formula = newFormula;
 
     // Initialize controllers and units with listeners
@@ -121,8 +121,9 @@ class _FormulaScreenState extends State<FormulaScreen> {
         result = formulaSolver(formula, formula.output.name, inputValues,);
       }
       else {
+        print( "TODO: MAYBE ONLY FORMULASOLVER IS NECCESSARY");
         final evaluator = FormulaEvaluator();
-        result = evaluator.evaluate(formula, inputValues);
+        result = evaluator.evaluate(formula as Formula, inputValues);
       }
 
       // Convert output to selected unit if needed
@@ -154,13 +155,15 @@ class _FormulaScreenState extends State<FormulaScreen> {
         actions: [
           IconButton(
             icon: const Icon(Icons.edit),
-            onPressed: () {
+            onPressed: formula is DerivedFormula
+                ? null
+                : () {
                     Navigator.push(
                       context,
                       MaterialPageRoute(
                         builder: (context) =>
                             FormulaEditor(
-                        formula: formula,
+                              formula: formula as Formula,
                               corpus: widget.corpus,
                               onSave: (updatedFormula) {
                                 widget.onSave?.call(updatedFormula);
@@ -172,7 +175,9 @@ class _FormulaScreenState extends State<FormulaScreen> {
                       ),
                     );
                   },
-            tooltip: 'Edit Formula',
+            tooltip: formula is DerivedFormula
+                ? 'Cannot edit derived formula'
+                : 'Edit Formula',
           ),
         ],
       ),
@@ -426,7 +431,15 @@ class _FormulaScreenState extends State<FormulaScreen> {
             ),
           ),
           const SizedBox(width: 8),
-          if (variable.unit != null)
+          if (variable.unit != null && !isCategorical)
+            IconButton(
+              icon: const Icon(Icons.swap_horiz),
+              tooltip: 'Solve for ${variable.name}',
+              onPressed: () {
+                _solveForVariable(variable);
+              },
+            ),
+          if (variable.unit != null && !isCategorical)
             UnitDropdown(
               corpus: widget.corpus,
               variable: variable,
@@ -442,4 +455,39 @@ class _FormulaScreenState extends State<FormulaScreen> {
       ),
     );
   }
+
+  void _solveForVariable(VariableSpec variable) {
+    // Check if the formula is already a DerivedFormula
+    if (formula is DerivedFormula) {
+      ScaffoldMessenger.of(context).showSnackBar(
+        const SnackBar(
+          content: Text('Cannot create derived formula from another derived formula'),
+          duration: Duration(seconds: 2),
+        ),
+      );
+      return;
+    }
+
+    try {
+      // Create a DerivedFormula with this input variable as output
+      final derivedFormula = DerivedFormula(
+        outputName: variable.name,
+        originalFormula: formula,
+      );
+
+      // Navigate to the new DerivedFormula screen
+      Navigator.push(
+        context,
+        MaterialPageRoute(
+          builder: (context) => FormulaScreen(
+            formula: derivedFormula,
+            corpus: widget.corpus,
+            onSave: widget.onSave,
+          ),
+        ),
+      );
+    } catch (e, st) {
+      errorHandler.notify(e,st);
+    }
+  }
 }

lib/error_handler.dart

@@ -9,6 +9,17 @@ class ErrorHandler {
   /// Callback function to handle errors - can be overridden for custom behavior
   void Function(Object error, [StackTrace? stackTrace])? onError;
 
+
+  // TODO: SET A DEFAULT ONERROR LIKE
+  //     ScaffoldMessenger.of(context).showSnackBar(
+  //      SnackBar(
+  //        content: Text('Error creating derived formula: $e'),
+  //        duration: const Duration(seconds: 3),
+  //      ),
+  //    );
+  //  }
+
+
   /// Notifies the error handler of an exception
   void notify(Object error, [StackTrace? stackTrace]) {
     // Print the exception to stdout as requested

lib/formula_evaluator.dart

@@ -272,7 +272,7 @@ class FormulaEvaluator {
 }
 
 Number formulaSolver(
-  Formula formula,
+  FormulaInterface formulaInterface,
   String variableToSolve,
   Map<String, dynamic> fixedInputValues, {
   Number hint = 0,
@@ -280,6 +280,9 @@ Number formulaSolver(
   Number maxDelta = 0.01,
   int maxTries = 1000,
 }) {
+
+  var formula = FormulaInterface.getRootFormula(formulaInterface);
+
   if (variableToSolve == formula.output.name) {
     return FormulaEvaluator().evaluate(formula, fixedInputValues);
   }

lib/formula_models.dart

@@ -148,6 +148,16 @@ abstract class FormulaInterface {
   Map<String, dynamic> toMap();
 
   Formula get originalFormula;
+
+  static Formula getRootFormula( FormulaInterface fi ){
+    if( fi is DerivedFormula ){
+       return getRootFormula(fi.originalFormula);
+    }
+    if( fi is Formula ){
+       return fi as Formula;
+    }
+    throw ArgumentError("Is not a known Formula subclass: ${fi} ${fi.runtimeType}");
+  }
 }
 
 class DerivedFormula implements FormulaInterface {
@@ -155,7 +165,7 @@ class DerivedFormula implements FormulaInterface {
   String get uuid => originalFormula.uuid;
 
   @override
-  String get name => originalFormula.name;
+  String get name => "${originalFormula.name} (Solving for ${_output.name})";
 
   @override
   String? get description => originalFormula.description;
@@ -173,7 +183,7 @@ class DerivedFormula implements FormulaInterface {
   List<String> get tags => originalFormula.tags;
 
   @override
-  final Formula originalFormula;
+  late final Formula originalFormula;
 
   @override
   Map<String, dynamic> toMap() => originalFormula.toMap();
@@ -182,14 +192,22 @@ class DerivedFormula implements FormulaInterface {
   late List<VariableSpec> _input;
   late VariableSpec _output;
 
-  DerivedFormula({required this.outputName, required this.originalFormula}) {
+  static bool isDerivable(Formula f){
-
+    return f.input.every( (vs) => vs.unit != "string") && f.output.unit != "string";
-    if( originalFormula.input.any( (vs) => vs.unit == "string") || originalFormula.output.unit == "string") {
-      throw ArgumentError(
-          "Derived formulas are not supported for formulas with string inputs, because we can't solve for them. Original formula: ${originalFormula
-              .toString()}");
   }
 
+  DerivedFormula({required this.outputName, required FormulaInterface originalFormula}) {
+
+    this.originalFormula = FormulaInterface.getRootFormula(originalFormula);
+
+    if( !isDerivable(this.originalFormula) ){
+      throw ArgumentError(
+          "Derived formulas are not supported for formulas with string inputs, because we can't solve for them. Original formula: ${originalFormula.toString()}");
+    }
+    _init();
+  }
+
+  void _init(){
     var newInput = List<VariableSpec>.from(originalFormula.input).where((v) => v.name != outputName).toList();
     newInput.add(originalFormula.output);
     _input = newInput.toList(growable: false);