feat: add support for intermediates/variables (closes #60)

app/src/main/java/net/youapps/calcyou/data/graphing/CompiledExpression.kt

@@ -12,8 +12,8 @@ class CompiledExpression internal constructor(
     fun execute(): Double? =
         Evaluator.execute(expression = this)
 
-    fun execute(constant: Pair<String, Double>): Double? =
-        Evaluator.execute(this, constant)
+    fun execute(constants: List<Pair<String, Double>>): Double? =
+        Evaluator.execute(this, constants)
 
     fun setConstant(name: String, value: Double) {
         configuration.setConstant(name = name, value = value)

app/src/main/java/net/youapps/calcyou/data/graphing/Constant.kt

@@ -0,0 +1,6 @@
+package net.youapps.calcyou.data.graphing
+
+data class Constant(
+    val identifier: Char,
+    val value: Double
+)

app/src/main/java/net/youapps/calcyou/data/graphing/Defaults.kt

@@ -46,6 +46,7 @@ object Defaults {
     val defaultVarNameChars: Set<Char> =
         "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_$".toCharArray().toSet()
     val defaultFuncNameChars: List<Char> = "fghijklmnopqrstuvw".toList()
+    val defaultConstantNameChars: List<Char> = "abcdeyz".toList()
 
     fun getDefaultGenericFunctions(): Map<String, EvalFunctionBlock> {
         return mapOf(

app/src/main/java/net/youapps/calcyou/data/graphing/Evaluator.kt

@@ -76,8 +76,11 @@ object Evaluator {
     fun execute(expression: CompiledExpression): Double? =
         evaluateToken(token = expression.root, configuration = expression.configuration)
 
-    fun execute(expression: CompiledExpression, constant: Pair<String, Double>): Double? {
-        configuration.setConstant(constant.first, constant.second)
+    fun execute(expression: CompiledExpression, constants: List<Pair<String, Double>>): Double? {
+        configuration.clearConstants()
+        for (constant in constants) {
+            configuration.setConstant(constant.first, constant.second)
+        }
         return evaluateToken(token = expression.root, configuration = configuration)
     }
 

app/src/main/java/net/youapps/calcyou/data/graphing/Function.kt

@@ -6,17 +6,22 @@ data class Function(
     val expression: String,
     val color: Color,
     val name: String,
-    val function: (Float) -> Float?
+    val compiled: CompiledExpression
 ) {
+    fun execute(variableX: Float, constants: List<Constant>): Float? {
+        val variables = listOf(
+            "x" to variableX.toDouble(),
+            *constants.map { it.identifier.toString() to it.value }.toTypedArray()
+        )
+        return compiled.execute(variables)?.toFloat()
+    }
 
     companion object {
         fun create(expression: String, color: Color, functionName: String): Function {
             val compiled: CompiledExpression = Evaluator.compile(expression)
             return Function(
-                expression, color, functionName
-            ) { value ->
-                compiled.execute("x" to value.toDouble())?.toFloat()
-            }
+                expression, color, functionName, compiled
+            )
         }
     }
 }

app/src/main/java/net/youapps/calcyou/ui/components/AddNewConstantDialog.kt

@@ -0,0 +1,97 @@
+package net.youapps.calcyou.ui.components
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.foundation.text.KeyboardOptions
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.OutlinedTextField
+import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
+import androidx.compose.material3.surfaceColorAtElevation
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.text.TextStyle
+import androidx.compose.ui.text.font.FontFamily
+import androidx.compose.ui.text.font.FontStyle
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.text.input.KeyboardType
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.window.Dialog
+import net.youapps.calcyou.R
+import net.youapps.calcyou.data.graphing.Constant
+
+@Composable
+fun AddNewConstantDialog(
+    modifier: Modifier = Modifier,
+    onConfirm: (constant: Constant) -> Unit,
+    onCancel: () -> Unit,
+    initialConstant: Constant,
+) {
+    Dialog(onCancel) {
+        Box(
+            modifier = modifier
+                .clip(RoundedCornerShape(16.dp))
+                .background(MaterialTheme.colorScheme.surfaceColorAtElevation(5.dp))
+        ) {
+            Column(Modifier.padding(16.dp), verticalArrangement = Arrangement.spacedBy(16.dp)) {
+                Text(
+                    text = stringResource(R.string.add_constant),
+                    style = MaterialTheme.typography.titleLarge
+                )
+                var text by remember { mutableStateOf(initialConstant.value.toString()) }
+                var isError by remember { mutableStateOf(false) }
+                OutlinedTextField(
+                    value = text,
+                    onValueChange = {
+                        text = it
+                        isError = strToDouble(it) == null
+                    },
+                    keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Number),
+                    prefix = {
+                        Text(
+                            text = "${initialConstant.identifier} = ", style = TextStyle(
+                                fontFamily = FontFamily.Serif,
+                                fontWeight = FontWeight.Medium,
+                                fontSize = MaterialTheme.typography.bodyLarge.fontSize,
+                                fontStyle = FontStyle.Italic
+                            )
+                        )
+                    },
+                    textStyle = TextStyle(
+                        fontFamily = FontFamily.Serif,
+                        fontWeight = FontWeight.Medium,
+                        fontSize = MaterialTheme.typography.bodyLarge.fontSize,
+                        fontStyle = FontStyle.Italic
+                    )
+                )
+                Row(Modifier.align(Alignment.End)) {
+                    TextButton(onClick = onCancel) {
+                        Text(text = stringResource(id = android.R.string.cancel))
+                    }
+                    TextButton(onClick = {
+                        val value = strToDouble(text) ?: return@TextButton
+                        onConfirm(initialConstant.copy(value = value))
+                    }, enabled = !isError) {
+                        Text(text = stringResource(id = android.R.string.ok))
+                    }
+                }
+            }
+        }
+    }
+}
+
+private fun strToDouble(string: String): Double? {
+    return string.replace(",", ".").toDoubleOrNull()
+}

app/src/main/java/net/youapps/calcyou/ui/screens/graphing/GraphingScreen.kt

@@ -1,12 +1,15 @@
 package net.youapps.calcyou.ui.screens.graphing
 
+import androidx.compose.animation.AnimatedVisibility
 import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.itemsIndexed
 import androidx.compose.foundation.shape.RoundedCornerShape
@@ -19,6 +22,7 @@ import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.Icon
 import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.OutlinedButton
 import androidx.compose.material3.Text
 import androidx.compose.material3.rememberBottomSheetScaffoldState
 import androidx.compose.material3.rememberStandardBottomSheetState
@@ -39,15 +43,18 @@ import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.viewmodel.compose.viewModel
 import net.youapps.calcyou.R
+import net.youapps.calcyou.data.graphing.Constant
 import net.youapps.calcyou.data.graphing.Defaults
 import net.youapps.calcyou.data.graphing.Function
+import net.youapps.calcyou.ui.components.AddNewConstantDialog
 import net.youapps.calcyou.ui.components.AddNewFunctionDialog
 import net.youapps.calcyou.viewmodels.GraphViewModel
 
 @OptIn(ExperimentalMaterial3Api::class)
 @Composable
 fun GraphingScreen(graphViewModel: GraphViewModel = viewModel()) {
     var showAddFunctionDialog by remember { mutableStateOf(false) }
+    var showAddConstantDialog by remember { mutableStateOf(false) }
     val bottomSheetState = rememberStandardBottomSheetState(
         skipHiddenState = true
     )
@@ -63,23 +70,41 @@ fun GraphingScreen(graphViewModel: GraphViewModel = viewModel()) {
                     .fillMaxWidth()
                     .padding(8.dp)
             ) {
-                FunctionList(
+                FunctionConstantsList(
                     modifier = Modifier.padding(top = 16.dp, start = 8.dp, end = 8.dp),
                     functions = graphViewModel.functions,
+                    constants = graphViewModel.constants,
                     onClickFunction = {
                         graphViewModel.updateSelectedFunction(it)
                         showAddFunctionDialog = true
                     },
-                    onClickRemove = {
+                    onClickRemoveFunction = {
                         graphViewModel.removeFunction(it)
-                    })
-                Button(
-                    modifier = Modifier.align(Alignment.CenterHorizontally),
-                    onClick = {
-                        graphViewModel.updateSelectedFunction(-1)
-                        showAddFunctionDialog = true
-                    }) {
-                    Text(text = stringResource(R.string.add_new_function))
+                    },
+                    onClickConstant = {
+                        graphViewModel.selectedConstantIndex = it
+                        showAddConstantDialog = true
+                    },
+                    onClickRemoveConstant = {
+                        graphViewModel.constants.removeAt(it)
+                    }
+                )
+                Row(horizontalArrangement = Arrangement.End, modifier = Modifier.fillMaxWidth()) {
+                    AnimatedVisibility(graphViewModel.constants.size < Defaults.defaultConstantNameChars.size) {
+                        OutlinedButton(onClick = {
+                            showAddConstantDialog = true
+                        }) {
+                            Text(text = stringResource(R.string.add_constant))
+                        }
+                    }
+                    Spacer(modifier = Modifier.width(10.dp))
+                    Button(
+                        onClick = {
+                            graphViewModel.updateSelectedFunction(-1)
+                            showAddFunctionDialog = true
+                        }) {
+                        Text(text = stringResource(R.string.add_new_function))
+                    }
                 }
             }
         }) {
@@ -99,38 +124,76 @@ fun GraphingScreen(graphViewModel: GraphViewModel = viewModel()) {
             remember(graphViewModel.selectedFunctionIndex) { graphViewModel.expression },
         )
     }
+    if (showAddConstantDialog) {
+        AddNewConstantDialog(
+            onConfirm = { constant ->
+                if (graphViewModel.selectedConstantIndex != -1) {
+                    graphViewModel.constants[graphViewModel.selectedConstantIndex] = constant
+                } else {
+                    graphViewModel.constants.add(constant)
+                }
+
+                graphViewModel.selectedConstantIndex = -1
+                showAddConstantDialog = false
+            },
+            onCancel = {
+                graphViewModel.selectedConstantIndex = -1
+                showAddConstantDialog = false
+            },
+            initialConstant = graphViewModel.constants.getOrNull(graphViewModel.selectedConstantIndex)
+                ?: Constant(
+                    Defaults.defaultConstantNameChars.first { identifier ->
+                        graphViewModel.constants.none { it.identifier == identifier }
+                    },
+                    0.0
+                )
+        )
+    }
 }
 
 @Composable
-fun FunctionList(
+fun FunctionConstantsList(
     modifier: Modifier = Modifier,
     functions: List<Function>,
+    constants: List<Constant>,
     onClickFunction: (Int) -> Unit,
-    onClickRemove: (Int) -> Unit
+    onClickRemoveFunction: (Int) -> Unit,
+    onClickConstant: (Int) -> Unit,
+    onClickRemoveConstant: (Int) -> Unit
 ) {
     LazyColumn(modifier = modifier) {
         itemsIndexed(
             functions,
             key = { index, function -> "$index-${function.hashCode()}" }) { index, function ->
             FunctionRow(
-                functionName = function.name,
+                lhsName = "${function.name}(x)",
                 text = function.expression,
                 color = function.color,
                 onClick = { onClickFunction(index) },
                 onClickRemove = {
-                    onClickRemove(index)
+                    onClickRemoveFunction(index)
                 }
             )
             Divider(Modifier.fillMaxWidth())
         }
+
+        itemsIndexed(constants, key = { _, constant -> constant.hashCode() }) { index, constant ->
+            FunctionRow(
+                lhsName = constant.identifier.toString(),
+                text = constant.value.toString(),
+                color = null,
+                onClick = { onClickConstant(index) },
+                onClickRemove = { onClickRemoveConstant(index) }
+            )
+        }
     }
 }
 
 @Composable
 fun FunctionRow(
-    functionName: String,
+    lhsName: String,
     text: String,
-    color: Color,
+    color: Color?,
     onClick: () -> Unit,
     onClickRemove: () -> Unit
 ) {
@@ -144,12 +207,12 @@ fun FunctionRow(
     ) {
 
         Text(
-            text = "${functionName}(x) = ", style = TextStyle(
+            text = "$lhsName = ", style = TextStyle(
                 fontFamily = FontFamily.Serif,
                 fontWeight = FontWeight.Bold,
                 fontSize = MaterialTheme.typography.titleMedium.fontSize,
                 fontStyle = FontStyle.Italic
-            ), color = color
+            ), color = color ?: MaterialTheme.colorScheme.primary
         )
         Text(
             text = text, style = TextStyle(