using uCalcSoftware;

var uc = new uCalc();

static void EqSolveCb(uCalc.Callback cb) { // Callback based on the Bisection Method
   var expr = cb.ArgExpr(1);     // ByExpr: Unevaluated Expression object (lazy evaluation)
   var a = cb.Arg(2);            // Argument 2: Range Minimum
   var b = cb.Arg(3);            // Argument 3: Range Maximum
   var variable = cb.ArgItem(4); // ByHandle: The variable Item object

   // Helper to update the variable in the uCalc engine and evaluate the expression
   double EvaluateAt(double val) {
      variable.Value(val);   // Push the new test value to the variable
      return expr.Evaluate(); // Evaluate the pre-parsed expression
   }

   // Ensure f(a) < f(b) so we always know which direction to slide the bounds; swap a & b if necessary
   if (EvaluateAt(b) < EvaluateAt(a)) (a, b) = (b, a);

   var midpoint = 0.0;
   var fMidpoint = 0.0;

   // Bisection loop
   for (int i = 0; i <= 100; i++) {
      midpoint = (a + b) / 2;
      fMidpoint = EvaluateAt(midpoint);

      if (Math.Abs(fMidpoint) < 1e-7) break; // Stop if close enough to 0

      // Narrow the bounds (compact logic!)
      if (fMidpoint < 0) a = midpoint; else b = midpoint;
   }

   if (Math.Abs(fMidpoint) > 1e-5) cb.Error.Raise("No solution found in the given range.");
   cb.Return(Math.Round(midpoint, 7)); // Return the final solved value
}

// 1. Define variables that might be used by the end-user
uc.DefineVariable("x");
uc.DefineVariable("MyVar");

// 2. Transformer converts `EqSolve(L = R)` into `EqSolve(L - (R))` & sets defaults before it hits the parser
var t = uc.ExpressionTransformer;
t.FromTo("EqSolve({L} = {R} [[,]for {var}][, {min}, {max}])",
"EqSolve({L} - ({R}), {min}{!min:-10000}, {max}{!max: 10000}, {var}{!var: x})");

// 3. Define the custom function signature
uc.DefineFunction("EqSolve(ByExpr eq, min, max, ByHandle variable)", EqSolveCb);

// --- Demo Executions ---
System.Collections.Generic.List<string> eqList = new() {
   "EqSolve(x + 5 = 125)", // Using default range [-10000,10000]
   "EqSolve(x^2 + 5 = 105)", // Picks one result from the default range
   "EqSolve(x^2 + 5 = 105, 0, 100)", // Restricts to positive root
   "EqSolve(x^2 + 5 = 105, -100, 0)", // Restricts to negative root
   "EqSolve(x^2 + 1000 = 5)", // No existing solution
   "EqSolve(40 + MyVar * 6 = 88, for MyVar)" // Uses custom variable 'MyVar' instead of 'x'
};

foreach(var eq in eqList) {
   Console.WriteLine(uc.ExpressionTransformer.Transform(eq)); // Displays transformed expression
   Console.WriteLine($"Result: {uc.EvalStr(eq)}"); // Returns result
}