feat: add support for kotlin bindings

.github/workflows/kotlin.yaml

@@ -0,0 +1,139 @@
+name: Kotlin
+env:
+  WORKING_DIRECTORY: bindings/kotlin
+
+on:
+  push:
+    branches:
+      - master
+    tags-ignore:
+      - '**'
+    paths:
+      - 'bindings/kotlin/**'
+      - 'core/**'
+      - 'test-data/**'
+      - '.github/workflows/kotlin.yaml'
+  pull_request:
+    paths:
+      - 'bindings/kotlin/**'
+      - 'core/**'
+      - 'test-data/**'
+      - '.github/workflows/kotlin.yaml'
+
+jobs:
+  build:
+    if: "!contains(github.event.head_commit.message, 'skip ci')"
+
+    strategy:
+      fail-fast: true
+      matrix:
+        settings:
+          - host: windows-latest
+            target: 'x86_64-pc-windows-msvc'
+            extension: "dll"
+            lib_dir: TODO
+          - host: macos-13
+            target: 'x86_64-apple-darwin'
+            extension: "dylib"
+            lib_dir: TODO
+          - host: macos-14
+            target: 'aarch64-apple-darwin'
+            extension: "dylib"
+            lib_dir: 'darwin-aarch64'
+          - host: ubuntu-latest
+            target: 'x86_64-unknown-linux-gnu'
+            extension: "so"
+            lib_dir: TODO
+          - host: ubuntu-latest
+            target: 'aarch64-unknown-linux-gnu'
+            extension: ".so"
+            lib_dir: TODO
+
+    name: stable - ${{ matrix.settings.target }} - kotlin@17
+    runs-on: ${{ matrix.settings.host }}
+    defaults:
+      run:
+        working-directory: ${{ env.WORKING_DIRECTORY }}
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          override: true
+          target: ${{ matrix.settings.target }}
+
+      - name: Cache cargo registry
+        uses: actions/cache@v3
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+            .cargo-cache
+          key: ${{ matrix.settings.target }}-cargo-registry
+
+      - name: Build
+        shell: bash
+        run: cargo build --lib --release --target ${{ matrix.settings.target }}
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v3
+        with:
+          name: ${{ matrix.settings.lib_dir }}
+          path: ./../target/release/libzen_kotlin.${{ matrix.settings.extension }}
+
+  release:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: ${{ env.WORKING_DIRECTORY }}
+    needs: [build]
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          override: true
+          target: ${{ matrix.settings.target }}
+
+      - name: Cache cargo registry
+        uses: actions/cache@v3
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+            .cargo-cache
+          key: ${{ matrix.settings.target }}-cargo-registry
+
+      - name: Validate Gradle wrapper jar
+        uses: gradle/wrapper-validation-action@v1
+
+      - name: Setup Gradle
+        uses: gradle/gradle-build-action@v2
+
+      - name: Download all artifacts
+        uses: actions/download-artifact@v3
+        with:
+          path: build/generated/main/resources
+
+      - name: Generate Kotlin sources
+        run: |
+          cargo run \
+            --bin uniffi-bindgen \
+            --features "uniffi/cli" \
+            -- generate \ 
+            --library build/generated/resources/libs/libzen_kotlin.dylib \
+            --language kotlin \
+            --out-dir build/generated/main/kotlin
+
+#    TODO
+#      - name: Setup Maven Repository credentials
+#        run:
+
+      - name: Publish Maven Artifact
+        run: ./gradlew publish

bindings/kotlin/.gitignore

@@ -0,0 +1,3 @@
+.idea
+.gradle
+build/

bindings/kotlin/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "zen-kotlin"
+version = "0.34.1"
+edition = "2021"
+license = "MIT"
+publish = false
+
+[lib]
+crate-type = ["cdylib"]
+
+[[bin]]
+name = "uniffi-bindgen"
+path = "uniffi-bindgen.rs"
+
+[dependencies]
+uniffi = { version = "0.28.3", features = ["tokio"] }
+serde_json = { workspace = true }
+zen-engine = { path = "../../core/engine" }
+zen-expression = { path = "../../core/expression" }
+zen-tmpl = { path = "../../core/template" }
+serde = { workspace = true, features = ["derive"] }
+async-trait = "0.1.83"
+tokio = "1.42.0"
+
+[build-dependencies]
+uniffi = { version = "0.28.3", features = ["build"] }

bindings/kotlin/build.gradle.kts

@@ -0,0 +1,39 @@
+plugins {
+    kotlin("jvm") version "2.1.0"
+    id("maven-publish")
+}
+
+group = "io.gorules"
+version = "0.36.1"
+
+dependencies {
+    implementation("net.java.dev.jna:jna:5.15.0")
+    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.9.0")
+}
+
+repositories {
+    mavenCentral()
+}
+
+sourceSets {
+    main {
+        kotlin {
+            srcDirs("build/generated/main/kotlin")
+        }
+        resources {
+            srcDirs("build/generated/main/resources")
+        }
+    }
+}
+
+publishing {
+    publications {
+        create<MavenPublication>("mavenJava") {
+            from(components["java"])
+            artifact(tasks["kotlinSourcesJar"])
+        }
+    }
+    repositories {
+        mavenLocal()
+    }
+}

bindings/kotlin/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.10-bin.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

bindings/kotlin/gradlew

@@ -0,0 +1,252 @@
+#!/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.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+##############################################################################
+#
+#   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/HEAD/platforms/jvm/plugins-application/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
+
+# This is normally unused
+# shellcheck disable=SC2034
+APP_BASE_NAME=${0##*/}
+# Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
+APP_HOME=$( cd -P "${APP_HOME:-./}" > /dev/null && printf '%s
+' "$PWD" ) || exit
+
+# 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: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    if ! command -v java >/dev/null 2>&1
+    then
+        die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        # In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        # In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        ulimit -n "$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
+
+
+# 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"'
+
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        org.gradle.wrapper.GradleWrapperMain \
+        "$@"
+
+# Stop when "xargs" is not available.
+if ! command -v xargs >/dev/null 2>&1
+then
+    die "xargs is not available"
+fi
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$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 "$JAVACMD" "$@"

bindings/kotlin/gradlew.bat

@@ -0,0 +1,94 @@
+@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
+@rem SPDX-License-Identifier: Apache-2.0
+@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=.
+@rem This is normally unused
+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% equ 0 goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME% 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+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% equ 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!
+set EXIT_CODE=%ERRORLEVEL%
+if %EXIT_CODE% equ 0 set EXIT_CODE=1
+if not ""=="%GRADLE_EXIT_CONSOLE%" exit %EXIT_CODE%
+exit /b %EXIT_CODE%
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

bindings/kotlin/settings.gradle.kts

@@ -0,0 +1 @@
+rootProject.name = "zen_kotlin"

bindings/kotlin/src/config.rs

@@ -0,0 +1,14 @@
+use std::sync::atomic::Ordering;
+use zen_engine::ZEN_CONFIG;
+
+#[derive(uniffi::Record)]
+pub struct ZenConfig {
+    pub nodes_in_context: Option<bool>
+}
+
+#[uniffi::export]
+pub fn override_config(config: ZenConfig) {
+    if let Some(val) = config.nodes_in_context {
+        ZEN_CONFIG.nodes_in_context.store(val, Ordering::Relaxed)
+    }
+}

bindings/kotlin/src/custom_node.rs

@@ -0,0 +1,58 @@
+use crate::error::ZenError;
+use crate::types::{DecisionNode, JsonBuffer, ZenEngineHandlerRequest, ZenEngineHandlerResponse};
+use serde_json::Value;
+use uniffi::deps::anyhow::anyhow;
+use zen_engine::handler::custom_node_adapter::{CustomNodeAdapter, CustomNodeRequest};
+use zen_engine::handler::node::{NodeResponse, NodeResult};
+use zen_expression::Variable;
+use crate::loader::ZenDecisionLoaderCallback;
+
+#[uniffi::export(callback_interface)]
+#[async_trait::async_trait]
+pub trait ZenCustomNodeCallback: Send + Sync {
+    async fn handle(
+        &self,
+        key: ZenEngineHandlerRequest,
+    ) -> Result<ZenEngineHandlerResponse, ZenError>;
+}
+
+pub struct NoopCustomNodeCallback;
+
+#[async_trait::async_trait]
+impl ZenCustomNodeCallback for NoopCustomNodeCallback {
+    async fn handle(&self, key: ZenEngineHandlerRequest) -> Result<ZenEngineHandlerResponse, ZenError> {
+        Err(ZenError::Zero)
+    }
+}
+
+pub struct ZenCustomNodeCallbackWrapper(pub Box<dyn ZenCustomNodeCallback>);
+
+impl CustomNodeAdapter for ZenCustomNodeCallbackWrapper {
+    async fn handle(&self, request: CustomNodeRequest) -> NodeResult {
+        let input = request
+            .input
+            .to_value()
+            .try_into()
+            .map_err(|err: ZenError| anyhow!(err))?;
+
+        let node = DecisionNode::from(request.node);
+
+        let result = self
+            .0
+            .handle(ZenEngineHandlerRequest { input, node })
+            .await
+            .map_err(|err| anyhow!(err.details()))?;
+
+        let output: Value = result
+            .output
+            .try_into()
+            .map_err(|err: ZenError| anyhow!(err))?;
+
+        let trace_data: Option<Value> = result.trace_data.and_then(|trace| trace.try_into().ok());
+
+        Ok(NodeResponse {
+            output: Variable::from(output),
+            trace_data,
+        })
+    }
+}

bindings/kotlin/src/decision.rs

@@ -0,0 +1,72 @@
+use crate::custom_node::ZenCustomNodeCallbackWrapper;
+use crate::engine::ZenEvaluateOptions;
+use crate::error::ZenError;
+use crate::loader::ZenDecisionLoaderCallbackWrapper;
+use crate::types::{JsonBuffer, ZenEngineResponse};
+use serde_json::Value;
+use std::sync::Arc;
+use tokio::runtime::Handle;
+use tokio::task;
+use zen_engine::{Decision, DecisionGraphValidationError, EvaluationOptions};
+
+#[derive(uniffi::Object)]
+pub struct ZenDecision {
+    decision: Arc<Decision<ZenDecisionLoaderCallbackWrapper, ZenCustomNodeCallbackWrapper>>,
+}
+
+impl From<Decision<ZenDecisionLoaderCallbackWrapper, ZenCustomNodeCallbackWrapper>>
+    for ZenDecision
+{
+    fn from(
+        value: Decision<ZenDecisionLoaderCallbackWrapper, ZenCustomNodeCallbackWrapper>,
+    ) -> Self {
+        Self {
+            decision: Arc::new(value),
+        }
+    }
+}
+
+#[uniffi::export(async_runtime = "tokio")]
+impl ZenDecision {
+    pub async fn evaluate(
+        &self,
+        context: JsonBuffer,
+        options: Option<ZenEvaluateOptions>,
+    ) -> Result<ZenEngineResponse, ZenError> {
+        let options = options.unwrap_or_default();
+        let context: Value = context.try_into()?;
+
+        let decision = self.decision.clone();
+        let evaluation_options = EvaluationOptions {
+            max_depth: options.max_depth,
+            trace: options.trace,
+        };
+
+        // Use spawn_blocking to run the non-Send code synchronously
+        let response = task::spawn_blocking(move || {
+            // The blocking code that uses non-Send types
+            Handle::current().block_on(async move {
+                decision
+                    .evaluate_with_opts(context.into(), evaluation_options)
+                    .await
+                    .map(|response| ZenEngineResponse::from(response))
+                    .map_err(|err| {
+                        ZenError::EvaluationError(
+                            serde_json::to_string(&err.as_ref())
+                                .unwrap_or_else(|_| err.to_string()),
+                        )
+                    })
+            })
+        })
+        .await
+        .map_err(|e| ZenError::EvaluationError(format!("Task failed: {:?}", e)))??;
+
+        Ok(response)
+    }
+
+    pub fn validate(&self) -> Result<(), ZenError> {
+        self.decision.validate().map_err(|e| {
+            ZenError::ValidationError(serde_json::to_string(&e).unwrap_or_else(|_| e.to_string()))
+        })
+    }
+}

bindings/kotlin/src/engine.rs

@@ -0,0 +1,132 @@
+use crate::custom_node::{NoopCustomNodeCallback, ZenCustomNodeCallback, ZenCustomNodeCallbackWrapper};
+use crate::decision::ZenDecision;
+use crate::error::ZenError;
+use crate::loader::{
+    NoopDecisionLoader, ZenDecisionLoaderCallback, ZenDecisionLoaderCallbackWrapper,
+};
+use crate::types::{
+    JsonBuffer, ZenEngineHandlerRequest, ZenEngineHandlerResponse, ZenEngineResponse,
+};
+use async_trait::async_trait;
+use serde_json::Value;
+use std::future::Future;
+use std::sync::Arc;
+use tokio::runtime::Handle;
+use tokio::task;
+use uniffi::deps::anyhow::anyhow;
+use zen_engine::handler::custom_node_adapter::{
+    CustomNodeAdapter, CustomNodeRequest, NoopCustomNode,
+};
+use zen_engine::handler::node::NodeResult;
+use zen_engine::loader::{DecisionLoader, NoopLoader};
+use zen_engine::model::DecisionContent;
+use zen_engine::{DecisionEngine, EvaluationOptions};
+use zen_expression::parser::Node;
+
+#[derive(uniffi::Object)]
+pub(crate) struct ZenEngine {
+    engine: Arc<DecisionEngine<ZenDecisionLoaderCallbackWrapper, ZenCustomNodeCallbackWrapper>>,
+}
+
+#[derive(uniffi::Record)]
+pub struct ZenEvaluateOptions {
+    pub max_depth: Option<u8>,
+    pub trace: Option<bool>,
+}
+
+impl Default for ZenEvaluateOptions {
+    fn default() -> Self {
+        Self {
+            max_depth: Some(5),
+            trace: Some(false),
+        }
+    }
+}
+
+#[uniffi::export(async_runtime = "tokio")]
+impl ZenEngine {
+    #[uniffi::constructor]
+    pub fn new(
+        loader: Option<Box<dyn ZenDecisionLoaderCallback>>,
+        custom_node: Option<Box<dyn ZenCustomNodeCallback>>,
+    ) -> Self {
+        Self {
+            engine: Arc::new(DecisionEngine::new(
+                Arc::new(ZenDecisionLoaderCallbackWrapper(
+                    loader.unwrap_or_else(|| Box::new(NoopDecisionLoader)),
+                )),
+                Arc::new(ZenCustomNodeCallbackWrapper(
+                    custom_node.unwrap_or_else(|| Box::new(NoopCustomNodeCallback))
+                )),
+            )),
+        }
+    }
+
+    pub async fn evaluate(
+        &self,
+        key: String,
+        context: JsonBuffer,
+        options: Option<ZenEvaluateOptions>,
+    ) -> Result<ZenEngineResponse, ZenError> {
+        let options = options.unwrap_or_default();
+        let context: Value = context.try_into()?;
+
+        let engine = self.engine.clone();
+        let evaluation_options = EvaluationOptions {
+            max_depth: options.max_depth,
+            trace: options.trace,
+        };
+
+        // Use spawn_blocking to run the non-Send code synchronously
+        let response = task::spawn_blocking(move || {
+            // The blocking code that uses non-Send types
+            Handle::current().block_on(async move {
+                engine
+                    .evaluate_with_opts(key, context.into(), evaluation_options)
+                    .await
+                    .map(|response| ZenEngineResponse::from(response))
+                    .map_err(|err| {
+                        ZenError::EvaluationError(
+                            serde_json::to_string(&err.as_ref())
+                                .unwrap_or_else(|_| err.to_string()),
+                        )
+                    })
+            })
+        })
+        .await
+        .map_err(|e| ZenError::EvaluationError(format!("Task failed: {:?}", e)))??;
+
+        Ok(response)
+    }
+
+    pub fn create_decision(&self, content: JsonBuffer) -> Result<ZenDecision, ZenError> {
+        let decision = self.engine.create_decision(Arc::new(
+            serde_json::from_slice(&content.0).map_err(|_| ZenError::JsonDeserializationFailed)?,
+        ));
+
+        Ok(ZenDecision::from(decision))
+    }
+
+    pub async fn get_decision(&self, key: String) -> Result<ZenDecision, ZenError> {
+        let engine = self.engine.clone();
+
+        // Use spawn_blocking to run the non-Send code synchronously
+        let decision = task::spawn_blocking(move || {
+            // The blocking code that uses non-Send types
+            Handle::current().block_on(async move {
+                engine
+                    .get_decision(&key)
+                    .await
+                    .map_err(|e| ZenError::LoaderInternalError {
+                        key,
+                        details: e.to_string(),
+                    })
+                    .map(ZenDecision::from)
+            })
+        })
+        .await
+        .map_err(|e| ZenError::EvaluationError(format!("Task failed: {:?}", e)))??;
+
+        Ok(decision)
+    }
+}

bindings/kotlin/src/error.rs

@@ -0,0 +1,54 @@
+use serde_json::json;
+use std::fmt::Formatter;
+
+#[allow(dead_code)]
+#[derive(Debug, uniffi::Error)]
+pub enum ZenError {
+    Zero,
+
+    InvalidArgument,
+    StringNullError,
+    StringUtf8Error,
+    JsonSerializationFailed,
+    JsonDeserializationFailed,
+    ExecutionTaskSpawnError,
+
+    IsolateError(String),
+    EvaluationError(String),
+    ValidationError(String),
+
+    LoaderKeyNotFound { key: String },
+    LoaderInternalError { key: String, details: String },
+
+    TemplateEngineError { template: String, details: String },
+}
+
+impl ZenError {
+    pub fn details(&self) -> String {
+        match &self {
+            ZenError::IsolateError(error) => error.to_string(),
+            ZenError::EvaluationError(error) => error.to_string(),
+            ZenError::ValidationError(error) => error.to_string(),
+            ZenError::LoaderKeyNotFound { key } => json!({ "key": key }).to_string(),
+            ZenError::LoaderInternalError { key, details } => {
+                json!({ "key": key, "details": details }).to_string()
+            }
+            ZenError::TemplateEngineError { template, details } => {
+                json!({ "template": template, "details": details }).to_string()
+            }
+            ZenError::Zero => String::from("Zero"),
+            ZenError::InvalidArgument => String::from("InvalidArgument"),
+            ZenError::StringNullError => String::from("StringNullError"),
+            ZenError::StringUtf8Error => String::from("StringUtf8Error"),
+            ZenError::JsonSerializationFailed => String::from("JsonSerializationFailed"),
+            ZenError::JsonDeserializationFailed => String::from("JsonDeserializationFailed"),
+            ZenError::ExecutionTaskSpawnError => String::from("ExecutionTaskSpawnError"),
+        }
+    }
+}
+
+impl std::fmt::Display for ZenError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        self.details().fmt(f)
+    }
+}

bindings/kotlin/src/expression.rs

@@ -0,0 +1,92 @@
+use crate::error::ZenError;
+use crate::types::JsonBuffer;
+use serde_json::Value;
+use tokio::task;
+use uniffi::deps::anyhow::anyhow;
+
+#[uniffi::export()]
+pub fn evaluate_expression_sync(
+    expression: String,
+    context: Option<JsonBuffer>,
+) -> Result<JsonBuffer, ZenError> {
+    let ctx: Value = context
+        .and_then(|v| v.try_into().ok())
+        .unwrap_or(Value::Null);
+
+    Ok(
+        zen_expression::evaluate_expression(expression.as_str(), ctx.into())
+            .map_err(|e| {
+                ZenError::EvaluationError(
+                    serde_json::to_string(&e).unwrap_or_else(|_| e.to_string()),
+                )
+            })?
+            .to_value()
+            .try_into()?,
+    )
+}
+
+#[allow(dead_code)]
+#[uniffi::export()]
+pub fn evaluate_unary_expression_sync(
+    expression: String,
+    context: JsonBuffer,
+) -> Result<bool, ZenError> {
+    let ctx: Value = context.try_into()?;
+
+    Ok(
+        zen_expression::evaluate_unary_expression(expression.as_str(), ctx.into()).map_err(
+            |e| {
+                ZenError::EvaluationError(
+                    serde_json::to_string(&e).unwrap_or_else(|_| e.to_string()),
+                )
+            },
+        )?,
+    )
+}
+
+#[allow(dead_code)]
+#[uniffi::export()]
+pub fn render_template_sync(template: String, context: JsonBuffer) -> Result<JsonBuffer, ZenError> {
+    let ctx: Value = context.try_into()?;
+
+    Ok(zen_tmpl::render(template.as_str(), ctx.into())
+        .map_err(|e| ZenError::TemplateEngineError {
+            template,
+            details: serde_json::to_string(&e).unwrap_or_else(|_| e.to_string()),
+        })?
+        .to_value()
+        .try_into()?)
+}
+
+#[allow(dead_code)]
+#[uniffi::export(async_runtime = "tokio")]
+pub async fn evaluate_expression(
+    expression: String,
+    context: Option<JsonBuffer>,
+) -> Result<JsonBuffer, ZenError> {
+    task::spawn_blocking(move || evaluate_expression_sync(expression, context))
+        .await
+        .map_err(|e| ZenError::ExecutionTaskSpawnError)?
+}
+
+#[allow(dead_code)]
+#[uniffi::export(async_runtime = "tokio")]
+pub async fn evaluate_unary_expression(
+    expression: String,
+    context: JsonBuffer,
+) -> Result<bool, ZenError> {
+    task::spawn_blocking(move || evaluate_unary_expression_sync(expression, context))
+        .await
+        .map_err(|e| ZenError::ExecutionTaskSpawnError)?
+}
+
+#[allow(dead_code)]
+#[uniffi::export(async_runtime = "tokio")]
+pub async fn render_template(
+    template: String,
+    context: JsonBuffer,
+) -> Result<JsonBuffer, ZenError> {
+    task::spawn_blocking(move || render_template_sync(template, context))
+        .await
+        .map_err(|e| ZenError::ExecutionTaskSpawnError)?
+}

bindings/kotlin/src/lib.rs

@@ -0,0 +1,9 @@
+uniffi::setup_scaffolding!();
+mod config;
+mod custom_node;
+mod decision;
+mod engine;
+mod error;
+mod expression;
+mod loader;
+mod types;

bindings/kotlin/src/loader.rs

@@ -0,0 +1,43 @@
+use crate::error::ZenError;
+use std::future::Future;
+use std::sync::Arc;
+use uniffi::deps::anyhow::anyhow;
+use zen_engine::loader::{DecisionLoader, LoaderError, LoaderResponse};
+use zen_engine::model::DecisionContent;
+use crate::types::JsonBuffer;
+
+#[uniffi::export(callback_interface)]
+#[async_trait::async_trait]
+pub trait ZenDecisionLoaderCallback: Send + Sync {
+    async fn load(&self, key: String) -> Result<JsonBuffer, ZenError>;
+}
+
+pub struct NoopDecisionLoader;
+
+#[async_trait::async_trait]
+impl ZenDecisionLoaderCallback for NoopDecisionLoader {
+    async fn load(&self, key: String) -> Result<JsonBuffer, ZenError> {
+        Err(ZenError::Zero)
+    }
+}
+
+pub struct ZenDecisionLoaderCallbackWrapper(pub Box<dyn ZenDecisionLoaderCallback>);
+
+impl DecisionLoader for ZenDecisionLoaderCallbackWrapper {
+    fn load<'a>(&'a self, key: &'a str) -> impl Future<Output = LoaderResponse> + 'a {
+        async move {
+            let maybe_raw = self.0.load(key.into()).await;
+            if maybe_raw.is_err() {
+                return Err(LoaderError::NotFound(key.to_string()).into());
+            }
+
+            let decision_content: DecisionContent = serde_json::from_slice(&maybe_raw.unwrap().0)
+                .map_err(|e| LoaderError::Internal {
+                    key: key.to_string(),
+                    source: anyhow!(e),
+                })?;
+
+            Ok(Arc::new(decision_content))
+        }
+    }
+}

bindings/kotlin/src/types.rs

@@ -0,0 +1,103 @@
+use crate::error::ZenError;
+use serde_json::Value;
+use std::collections::HashMap;
+use zen_engine::handler::custom_node_adapter::CustomDecisionNode;
+use zen_engine::{DecisionGraphResponse, DecisionGraphTrace};
+
+pub struct JsonBuffer(pub Vec<u8>);
+uniffi::custom_newtype!(JsonBuffer, Vec<u8>);
+
+impl TryFrom<JsonBuffer> for Value {
+    type Error = ZenError;
+
+    fn try_from(value: JsonBuffer) -> Result<Self, Self::Error> {
+        serde_json::from_slice(&value.0).map_err(|_| ZenError::JsonDeserializationFailed)
+    }
+}
+
+impl TryFrom<Value> for JsonBuffer {
+    type Error = ZenError;
+
+    fn try_from(value: Value) -> Result<Self, Self::Error> {
+        serde_json::to_vec(&value)
+            .map(|v| JsonBuffer(v))
+            .map_err(|_| ZenError::JsonSerializationFailed)
+    }
+}
+
+#[derive(uniffi::Record)]
+pub struct ZenEngineTrace {
+    pub id: String,
+    pub name: String,
+    pub input: JsonBuffer,
+    pub output: JsonBuffer,
+    pub performance: Option<String>,
+    pub trace_data: Option<JsonBuffer>,
+    pub order: u32,
+}
+
+impl From<DecisionGraphTrace> for ZenEngineTrace {
+    fn from(value: DecisionGraphTrace) -> Self {
+        Self {
+            id: value.id,
+            name: value.name,
+            input: value.input.to_value().try_into().unwrap(),
+            output: value.output.to_value().try_into().unwrap(),
+            performance: value.performance,
+            trace_data: value.trace_data.map(|data| data.try_into().unwrap()),
+            order: value.order,
+        }
+    }
+}
+
+#[derive(uniffi::Record)]
+pub struct ZenEngineResponse {
+    pub performance: String,
+    pub result: JsonBuffer,
+    pub trace: Option<HashMap<String, ZenEngineTrace>>,
+}
+
+impl From<DecisionGraphResponse> for ZenEngineResponse {
+    fn from(value: DecisionGraphResponse) -> Self {
+        Self {
+            performance: value.performance,
+            result: value.result.to_value().try_into().unwrap(),
+            trace: value.trace.map(|opt| {
+                opt.into_iter()
+                    .map(|(key, value)| (key, ZenEngineTrace::from(value)))
+                    .collect()
+            }),
+        }
+    }
+}
+
+#[derive(uniffi::Record)]
+pub struct ZenEngineHandlerResponse {
+    pub output: JsonBuffer,
+    pub trace_data: Option<JsonBuffer>,
+}
+
+#[derive(uniffi::Record)]
+pub struct DecisionNode {
+    pub id: String,
+    pub name: String,
+    pub kind: String,
+    pub config: JsonBuffer,
+}
+
+impl From<CustomDecisionNode> for DecisionNode {
+    fn from(value: CustomDecisionNode) -> Self {
+        Self {
+            id: value.id,
+            name: value.name,
+            kind: value.kind,
+            config: JsonBuffer(serde_json::to_vec(&value.config).unwrap()),
+        }
+    }
+}
+
+#[derive(uniffi::Record)]
+pub struct ZenEngineHandlerRequest {
+    pub input: JsonBuffer,
+    pub node: DecisionNode,
+}

bindings/kotlin/uniffi-bindgen.rs

@@ -0,0 +1,3 @@
+fn main() {
+    uniffi::uniffi_bindgen_main()
+}

bindings/kotlin/uniffi.toml

@@ -0,0 +1,2 @@
+[bindings.kotlin]
+package_name = "io.gorules.zen_engine"