initial commit

.gitignore

@@ -0,0 +1,33 @@
+.gradle
+build/
+!gradle/wrapper/gradle-wrapper.jar
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### IntelliJ IDEA ###
+.idea/
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+bin/
+!**/src/main/**/bin/
+!**/src/test/**/bin/
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store

build.gradle.kts

@@ -0,0 +1,9 @@
+plugins {
+    id("space.kscience.gradle.project")
+}
+
+group = "center.sciprog"
+version = "0.1.0"
+
+
+val attributesVersion: String by extra("0.1.0")

gradle.properties

@@ -0,0 +1,3 @@
+kotlin.code.style=official
+
+toolsVersion=0.15.2-kotlin-1.9.22

gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,6 @@
+#Wed Apr 03 19:58:49 MSK 2024
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.7-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

gradlew

@@ -0,0 +1,234 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/master/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+APP_HOME=$( cd "${APP_HOME:-./}" && pwd -P ) || exit
+
+APP_NAME="Gradle"
+APP_BASE_NAME=${0##*/}
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+# Collect all arguments for the java command;
+#   * $DEFAULT_JVM_OPTS, $JAVA_OPTS, and $GRADLE_OPTS can contain fragments of
+#     shell script including quotes and variable substitutions, so put them in
+#     double quotes to make sure that they get re-expanded; and
+#   * put everything else in single quotes, so that it's not re-expanded.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        org.gradle.wrapper.GradleWrapperMain \
+        "$@"
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"

gradlew.bat

@@ -0,0 +1,89 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

settings.gradle.kts

@@ -0,0 +1,42 @@
+rootProject.name = "WorkFlow"
+
+enableFeaturePreview("TYPESAFE_PROJECT_ACCESSORS")
+
+pluginManagement {
+    val toolsVersion: String by extra
+
+    repositories {
+        mavenLocal()
+        gradlePluginPortal()
+        mavenCentral()
+        maven("https://repo.kotlin.link")
+    }
+
+    plugins {
+        id("space.kscience.gradle.project") version toolsVersion
+        id("space.kscience.gradle.mpp") version toolsVersion
+    }
+}
+
+plugins {
+    id("org.gradle.toolchains.foojay-resolver-convention") version "0.8.0"
+}
+
+dependencyResolutionManagement {
+
+    val toolsVersion: String by extra
+
+    repositories {
+        mavenLocal()
+        mavenCentral()
+        maven("https://repo.kotlin.link")
+    }
+
+    versionCatalogs {
+        create("spclibs") {
+            from("space.kscience:version-catalog:$toolsVersion")
+        }
+    }
+}
+
+include(":workflow-core")

workflow-core/build.gradle.kts

@@ -0,0 +1,30 @@
+import space.kscience.gradle.Maturity
+
+plugins {
+    id("space.kscience.gradle.mpp")
+    `maven-publish`
+}
+
+val attributesVersion: String by rootProject.extra
+
+kscience {
+    jvm()
+    js()
+    native()
+    useCoroutines()
+    useSerialization()
+    commonMain {
+        api(spclibs.kotlinx.datetime)
+        api("space.kscience:attributes-kt:$attributesVersion")
+        api("com.benasher44:uuid:0.8.4")
+    }
+
+    jvmTest {
+        implementation(spclibs.logback.classic)
+    }
+}
+
+
+readme {
+    maturity = Maturity.EXPERIMENTAL
+}

workflow-core/src/commonMain/kotlin/center/sciprog/workflow/Resource.kt

@@ -0,0 +1,17 @@
+package center.sciprog.workflow
+
+import kotlinx.serialization.Serializable
+
+public interface Resource
+
+public interface Currency
+
+public data object Rubles : Currency
+
+@Serializable
+public data class Money(
+    @Serializable(MoneyNumberSerializer::class) val amount: Number,
+    val currency: Currency,
+) : Resource
+
+public val Number.rubles: Money get() = Money(this, Rubles)

workflow-core/src/commonMain/kotlin/center/sciprog/workflow/Subject.kt

@@ -0,0 +1,37 @@
+package center.sciprog.workflow
+
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.asFlow
+import kotlinx.coroutines.flow.map
+import space.kscience.attributes.AttributeContainer
+import space.kscience.attributes.Attributes
+
+public typealias SubjectId = String
+
+
+public sealed interface Subject : AttributeContainer {
+    public val id: SubjectId
+}
+
+public data class Person(
+    override val id: SubjectId,
+    public val name: String,
+    override val attributes: Attributes = Attributes.EMPTY,
+) : Subject
+
+public data class Organization(
+    override val id: SubjectId,
+    public val name: String,
+    override val attributes: Attributes = Attributes.EMPTY,
+) : Subject
+
+public interface SubjectProvider {
+    public suspend fun ids(): Flow<SubjectId>
+    public suspend fun provide(subjectId: SubjectId): Subject?
+}
+
+public class ListSubjectProvider(private val subjects: List<Subject>) : SubjectProvider {
+    override suspend fun ids(): Flow<SubjectId> = subjects.asFlow().map { it.id }
+
+    override suspend fun provide(subjectId: SubjectId): Subject? = subjects.find { it.id == subjectId }
+}

workflow-core/src/commonMain/kotlin/center/sciprog/workflow/Transaction.kt

@@ -0,0 +1,64 @@
+package center.sciprog.workflow
+
+import kotlinx.datetime.*
+import kotlinx.serialization.Serializable
+import space.kscience.attributes.Attributes
+import space.kscience.attributes.AttributesBuilder
+
+/**
+ * A money transaction
+ */
+public interface Transaction : WorkEvent {
+    public val fromSubject: Subject
+    public val toSubject: Subject
+    public val amount: Money
+}
+
+/**
+ * The transaction that has been executed. Some additional information could be encoded in [attributes]
+ */
+@Serializable
+public data class ExecutedTransaction(
+    override val id: EventId,
+    override val fromSubject: Subject,
+    override val toSubject: Subject,
+    override val amount: Money,
+    override val time: Instant,
+    override val attributes: Attributes,
+) : WorkEvent, Transaction
+
+public suspend fun WorkBuilder.transaction(
+    fromSubject: Subject,
+    toSubject: Subject,
+    amount: Money,
+    time: Instant = Clock.System.now(),
+    attributesBuilder: AttributesBuilder<ExecutedTransaction>.() -> Unit = {},
+) {
+    put(ExecutedTransaction(generateId(), fromSubject, toSubject, amount, time, Attributes(attributesBuilder)))
+}
+
+/**
+ * The transaction that is planned, but not yet executed
+ */
+@Serializable
+public data class PlannedTransaction(
+    override val id: EventId,
+    public val plannedOn: Instant,
+    override val fromSubject: Subject,
+    override val toSubject: Subject,
+    override val amount: Money,
+    override val time: Instant,
+    override val attributes: Attributes,
+) : WorkEvent, Transaction
+
+
+public suspend fun WorkBuilder.plannedTransaction(
+    fromSubject: Subject,
+    toSubject: Subject,
+    plannedOn: Instant,
+    amount: Money,
+    time: Instant = Clock.System.now(),
+    attributesBuilder: AttributesBuilder<PlannedTransaction>.() -> Unit = {},
+) {
+    put(PlannedTransaction(generateId(), plannedOn, fromSubject, toSubject, amount, time, Attributes(attributesBuilder)))
+}

workflow-core/src/commonMain/kotlin/center/sciprog/workflow/Work.kt

@@ -0,0 +1,50 @@
+package center.sciprog.workflow
+
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.merge
+import kotlinx.datetime.Instant
+import kotlinx.datetime.LocalDateTime
+import space.kscience.attributes.AttributeContainer
+
+public typealias WorkId = String
+
+public typealias EventId = String
+
+/**
+ * A generic operation in a workflow
+ */
+public interface WorkEvent : AttributeContainer {
+    /**
+     * A unique ID for the operation
+     */
+    public val id: EventId
+
+    /**
+     * A localized time operation is attributed to
+     */
+    public val time: Instant
+}
+
+/**
+ * A central API for all workflow computations
+ */
+public interface Work {
+
+    public fun flow(): Flow<WorkEvent>
+
+    public companion object {
+        /**
+         * Join several works into one
+         */
+        public fun join(vararg works: Work): Work = object : Work {
+            override fun flow(): Flow<WorkEvent> = works.map { it.flow() }.merge()
+        }
+    }
+}
+
+/**
+ * A work that can produce a modified work via [WorkBuilder]
+ */
+public interface WorkWithBuilder<W : Work> : Work {
+    public suspend fun modified(block: suspend WorkBuilder.() -> Unit): W
+}

workflow-core/src/commonMain/kotlin/center/sciprog/workflow/WorkBuilder.kt

@@ -0,0 +1,47 @@
+package center.sciprog.workflow
+
+import kotlinx.coroutines.flow.Flow
+
+
+public interface WorkBuilder {
+
+    /**
+     * Generate a unique event Id
+     */
+    public suspend fun generateId(): EventId
+
+    /**
+     * Add a single event to a builder
+     */
+    public suspend fun put(event: WorkEvent)
+
+    /**
+     *  Visit all events Remove or replace or don't change all events in the Work.
+     *  * If the result of the [visitor] is the same as input, no changes are done.
+     *  * If the result is a new event, the initial event is replaced
+     *  * if the result is null, the initial event is removed
+     */
+    public suspend fun visit(visitor: (WorkEvent) -> WorkEvent?)
+}
+
+/**
+ * Remove a single event with given ID from builder
+ */
+public suspend fun WorkBuilder.remove(id: EventId): Unit = visit { if (it.id == id) null else it }
+
+public suspend fun WorkBuilder.putAll(events: Collection<WorkEvent>) {
+    events.forEach {
+        put(it)
+    }
+}
+
+/**
+ * Suspends until all [events] are put into this builder
+ */
+public suspend fun WorkBuilder.putAll(events: Flow<WorkEvent>) {
+    events.collect {
+        put(it)
+    }
+}
+
+public suspend fun WorkBuilder.putAll(work: Work): Unit = putAll(work.flow())

workflow-core/src/commonMain/kotlin/center/sciprog/workflow/WorkFunction.kt

@@ -0,0 +1,37 @@
+package center.sciprog.workflow
+
+import kotlinx.coroutines.flow.filter
+import kotlinx.coroutines.flow.filterIsInstance
+import kotlinx.coroutines.flow.fold
+import kotlinx.datetime.Instant
+
+public interface WorkFunction<T> {
+    public val emptyBase: T
+    public suspend fun compute(work: Work, base: T = emptyBase): T
+}
+
+
+public class Payments(
+    public val subject: Subject,
+    public val timeFrame: ClosedRange<Instant>,
+    public val valueExtractor: (Money) -> Double,
+    override val emptyBase: Double = 0.0,
+) : WorkFunction<Double> {
+    override suspend fun compute(work: Work, base: Double): Double {
+        return work.flow().filterIsInstance<ExecutedTransaction>().filter {
+            it.toSubject == subject && it.time in timeFrame
+        }.fold(base) { acc, value -> acc + valueExtractor(value.amount) }
+    }
+
+    public companion object {
+        public fun inRubles(
+            subject: Subject,
+            timeFrame: ClosedRange<Instant> = Instant.DISTANT_PAST..Instant.DISTANT_FUTURE,
+        ): Payments = Payments(
+            subject,
+            timeFrame,
+            { if (it.currency == Rubles) it.amount.toDouble() else TODO("No currency converter") }
+        )
+
+    }
+}

workflow-core/src/commonMain/kotlin/center/sciprog/workflow/WorkList.kt

@@ -0,0 +1,47 @@
+package center.sciprog.workflow
+
+import com.benasher44.uuid.uuid4
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.asFlow
+
+private class WorkListBuilder(val idPrefix: String, val events: MutableList<WorkEvent>) : WorkBuilder {
+    override suspend fun generateId(): EventId = idPrefix + "-" + uuid4().toString()
+
+    override suspend fun put(event: WorkEvent) {
+        events.add(event)
+    }
+
+    override suspend fun visit(visitor: (WorkEvent) -> WorkEvent?) {
+        val iterator = events.listIterator()
+        while (iterator.hasNext()) {
+            val event = iterator.next()
+            val newEvent = visitor(event)
+            if (newEvent == null) {
+                iterator.remove()
+            } else if (newEvent != event) {
+                iterator.set(newEvent)
+            }
+        }
+    }
+}
+
+
+public class WorkList(private val events: List<WorkEvent>) : WorkWithBuilder<WorkList> {
+
+    override fun flow(): Flow<WorkEvent> = events.asFlow()
+
+    override suspend fun modified(block: suspend WorkBuilder.() -> Unit): WorkList {
+        val modifiedEvents = ArrayList(events)
+        val prefix = uuid4().leastSignificantBits.toString(16)
+        WorkListBuilder(prefix, modifiedEvents).block()
+        return WorkList((modifiedEvents))
+    }
+}
+
+public suspend fun WorkList(block: suspend WorkBuilder.() -> Unit): WorkList {
+    val events = mutableListOf<WorkEvent>()
+    val prefix = uuid4().leastSignificantBits.toString(16)
+    val builder = WorkListBuilder(prefix, events)
+    builder.block()
+    return WorkList(events)
+}

workflow-core/src/commonMain/kotlin/center/sciprog/workflow/serializers.kt

@@ -0,0 +1,22 @@
+package center.sciprog.workflow
+
+import kotlinx.serialization.KSerializer
+import kotlinx.serialization.builtins.serializer
+import kotlinx.serialization.descriptors.SerialDescriptor
+import kotlinx.serialization.encoding.Decoder
+import kotlinx.serialization.encoding.Encoder
+
+internal object MoneyNumberSerializer : KSerializer<Number> {
+    //TODO replace by proper BigDecimal serializer
+
+    private val proxySerializer = Double.serializer()
+
+    override val descriptor: SerialDescriptor get() = proxySerializer.descriptor
+
+    override fun deserialize(decoder: Decoder): Number =
+        decoder.decodeSerializableValue(proxySerializer)
+
+    override fun serialize(encoder: Encoder, value: Number) {
+        encoder.encodeSerializableValue(proxySerializer, value.toDouble())
+    }
+}

workflow-core/src/commonTest/kotlin/center/sciprog/workflow/WorkFunctionTest.kt

@@ -0,0 +1,25 @@
+package center.sciprog.workflow
+
+import kotlinx.coroutines.test.runTest
+import kotlinx.datetime.*
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.time.Duration.Companion.days
+
+internal class WorkFunctionTest {
+    @Test
+    fun testPayments() = runTest{
+        val person = Person("test","Test Subject")
+
+        val org = Organization("Master", "Master organization")
+
+        val work = WorkList {
+            val now = Clock.System.now()
+            repeat(10) {
+                transaction(org, person, 1000.rubles, time = now.minus((it*30).days))
+            }
+        }
+
+        assertEquals(10000.0, Payments.inRubles(person).compute(work), 1.0)
+    }
+}