Create merger

15 files changed, 766 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..b63da45
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,42 @@
+.gradle
+build/
+!gradle/wrapper/gradle-wrapper.jar
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+*.iws
+*.iml
+*.ipr
+out/
+!**/src/main/**/out/
+!**/src/test/**/out/
+
+### 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
\ No newline at end of file
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..bdabff0
--- /dev/null
+++ b/README.md
@@ -0,0 +1,21 @@
+# Zwirn
+
+> Merging, diffing and converting of tiny/yarn and other mapping formats
+
+```
+    mappings {
+        searge()
+        mapping(rootProject.files("yarn.zip"), "yarn") {
+            outputs("yarn", true) { listOf("searge") }
+            mapNamespace("named", "yarn")
+            mapNamespace("intermediary", "searge")
+            sourceNamespace("searge")
+            renest()
+        }
+    }
+```
+
+
+
+
+
diff --git a/build.gradle.kts b/build.gradle.kts
new file mode 100644
index 0000000..c273390
--- /dev/null
+++ b/build.gradle.kts
@@ -0,0 +1,29 @@
+plugins {
+    java
+}
+
+group = "moe.nea"
+version = "1.0-SNAPSHOT"
+
+repositories {
+    mavenCentral()
+    maven("https://maven.architectury.dev")
+    maven("https://maven.fabricmc.net")
+    maven("https://maven.minecraftforge.net")
+}
+
+dependencies {
+    implementation("net.fabricmc:stitch:0.6.2")
+    compileOnly("org.jetbrains:annotations:24.0.0")
+    implementation("net.minecraftforge:srgutils:0.4.13")
+    implementation("net.fabricmc:tiny-remapper:0.8.6")
+    testImplementation("org.junit.jupiter:junit-jupiter:5.9.2")
+}
+
+java {
+    this.toolchain.languageVersion.set(JavaLanguageVersion.of(17))
+}
+
+tasks.test {
+    useJUnitPlatform()
+}
\ No newline at end of file
diff --git a/gradle.properties b/gradle.properties
new file mode 100644
index 0000000..7fc6f1f
--- /dev/null
+++ b/gradle.properties
@@ -0,0 +1 @@
+kotlin.code.style=official
diff --git a/gradle/wrapper/gradle-wrapper.jar b/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 0000000..249e583
--- /dev/null
+++ b/gradle/wrapper/gradle-wrapper.jar
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
new file mode 100644
index 0000000..74150a7
--- /dev/null
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,6 @@
+#Thu Feb 29 22:57:36 CET 2024
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.4-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
diff --git a/gradlew b/gradlew
new file mode 100755
index 0000000..1b6c787
--- /dev/null
+++ b/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 "$JAVACMD" "$@"
diff --git a/gradlew.bat b/gradlew.bat
new file mode 100644
index 0000000..107acd3
--- /dev/null
+++ b/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
diff --git a/out.tiny b/out.tiny
new file mode 100644
index 0000000..718ff9b
--- /dev/null
+++ b/out.tiny
@@ -0,0 +1,7 @@
+tiny	2	0	official	intermediary	named
+c	A	ClassA	SomeClassButNamedBetter
+	c	some comment
+	f	a	a	field_a	myFieldButNamedCool
+		c	Field comment
+		c	Better comment
+c	B	B	OtherClass
diff --git a/settings.gradle.kts b/settings.gradle.kts
new file mode 100644
index 0000000..ee5ae04
--- /dev/null
+++ b/settings.gradle.kts
@@ -0,0 +1,5 @@
+plugins {
+    id("org.gradle.toolchains.foojay-resolver-convention") version "0.5.0"
+}
+rootProject.name = "zwirn"
+
diff --git a/src/main/java/moe/nea/zwirn/Index.java b/src/main/java/moe/nea/zwirn/Index.java
new file mode 100644
index 0000000..a27344e
--- /dev/null
+++ b/src/main/java/moe/nea/zwirn/Index.java
@@ -0,0 +1,30 @@
+package moe.nea.zwirn;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Function;
+
+public class Index<K, V> {
+    Map<K, Set<V>> map = new HashMap<>();
+
+    public void addToIndex(K k, V v) {
+        find(k).add(v);
+    }
+
+    public Set<K> keys() {
+        return map.keySet();
+    }
+
+    public <T> void loadFrom(Iterable<T> it, Function<T, K> keyExtractor, Function<T, V> valueExtractor) {
+        for (T t : it) {
+            addToIndex(keyExtractor.apply(t), valueExtractor.apply(t));
+        }
+    }
+
+    public Set<V> find(K k) {
+        return map.computeIfAbsent(k, ignored -> new HashSet<>());
+    }
+
+}
\ No newline at end of file
diff --git a/src/main/java/moe/nea/zwirn/TinyMerger.java b/src/main/java/moe/nea/zwirn/TinyMerger.java
new file mode 100644
index 0000000..97b245b
--- /dev/null
+++ b/src/main/java/moe/nea/zwirn/TinyMerger.java
@@ -0,0 +1,227 @@
+package moe.nea.zwirn;
+
+import net.fabricmc.stitch.commands.tinyv2.*;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.*;
+import java.util.function.BiFunction;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+class TinyMerger {
+    private final @NotNull TinyFile base;
+    private final @NotNull TinyFile overlay;
+    private final @NotNull String sharedNamespace;
+    private final int baseSharedIndex;
+    private final int overlaySharedIndex;
+    private final @NotNull Map<@NotNull String, @NotNull TinyClass> overlayLUT;
+    private final @NotNull Map<@NotNull String, @NotNull TinyClass> baseLUT;
+    private final Integer[] baseToOverlayIndexMap;
+    private final @NotNull List<@NotNull TinyClass> entries = new ArrayList<>();
+
+    public TinyMerger(TinyFile base, TinyFile overlay, String sharedNamespace) {
+        this.base = base;
+        this.overlay = overlay;
+        this.sharedNamespace = sharedNamespace;
+        this.baseSharedIndex = base.getHeader().getNamespaces().indexOf(sharedNamespace);
+        this.overlaySharedIndex = overlay.getHeader().getNamespaces().indexOf(sharedNamespace);
+        this.overlayLUT = overlay.getClassEntries().stream()
+                .collect(Collectors.toMap(it -> it.getClassNames().get(this.overlaySharedIndex), Function.identity()));
+        this.baseLUT = base.getClassEntries().stream()
+                .collect(Collectors.toMap(it -> it.getClassNames().get(this.baseSharedIndex), Function.identity()));
+        this.baseToOverlayIndexMap = base.getHeader().getNamespaces()
+                .stream().map(it -> overlay.getHeader().getNamespaces().indexOf(it))
+                .map(it -> it < 0 ? null : it)
+                .toArray(Integer[]::new);
+    }
+
+    public @NotNull TinyFile merge() {
+        mergeClasses();
+        var baseHeader = base.getHeader();
+        return new TinyFile(
+                new TinyHeader(baseHeader.getNamespaces(), baseHeader.getMajorVersion(), baseHeader.getMinorVersion(), baseHeader.getProperties()),
+                entries
+        );
+    }
+
+
+    private @NotNull List<@NotNull String> mergeNames(
+            @NotNull List<@NotNull String> baseNames,
+            @NotNull List<@NotNull String> overlayNames) {
+        List<String> mergedNames = new ArrayList<>(baseNames);
+        String sharedName = baseNames.get(baseSharedIndex);
+        for (int i = 0; i < mergedNames.size(); i++) {
+            Integer overlayIndex = this.baseToOverlayIndexMap[i];
+            if (overlayIndex == null) continue;
+            String overlayName = overlayNames.get(overlayIndex);
+            if (overlayName.isEmpty() || sharedName.equals(overlayName))
+                continue;
+            mergedNames.set(i, overlayName);
+        }
+        return mergedNames;
+    }
+
+    private <T> List<String> mergeNames(@Nullable T baseObject, @Nullable T overlayObject, @NotNull Function<@NotNull T, @NotNull List<@NotNull String>> nameExtractor) {
+        if (baseObject == null && overlayObject == null)
+            throw new IllegalArgumentException("Either baseObject or overlayObject must not be null");
+        if (overlayObject == null)
+            return nameExtractor.apply(baseObject);
+        if (baseObject == null) {
+            if (base.getHeader().getNamespaces().size() != overlay.getHeader().getNamespaces().size())
+                throw new IllegalStateException("Can only merge unnamed base objects if both files have the same namespaces");
+            List<String> names = new ArrayList<>();
+            for (int i = 0; i < base.getHeader().getNamespaces().size(); i++) {
+                names.add("");
+            }
+            List<@NotNull String> mergedNames = mergeNames(names, nameExtractor.apply(overlayObject));
+            for (var name : mergedNames) {
+                if (name.isEmpty())
+                    throw new RuntimeException("Invariant violated: unnamed overlay name");
+            }
+            return mergedNames;
+        }
+        return mergeNames(nameExtractor.apply(baseObject), nameExtractor.apply(overlayObject));
+    }
+
+    private <T> @NotNull List<@NotNull String> mergeComments(@Nullable T baseObject, @Nullable T overlayObject, @NotNull Function<@NotNull T, ? extends @NotNull Collection<@NotNull String>> commentExtractor) {
+        List<String> comments = new ArrayList<>();
+        if (baseObject != null)
+            comments.addAll(commentExtractor.apply(baseObject));
+        if (overlayObject != null)
+            comments.addAll(commentExtractor.apply(overlayObject));
+        return comments;
+    }
+
+    private TinyClass mergeClass(@Nullable TinyClass baseClass, @Nullable TinyClass overlayClass) {
+        return new TinyClass(
+                mergeNames(baseClass, overlayClass, TinyClass::getClassNames),
+                mergeMethods(baseClass, overlayClass),
+                mergeFields(baseClass, overlayClass),
+                mergeComments(baseClass, overlayClass, TinyClass::getComments)
+        );
+    }
+
+    private Collection<TinyField> mergeFields(@Nullable TinyClass baseClass, @Nullable TinyClass overlayClass) {
+        return mergeChildren(baseClass, overlayClass,
+                it -> it.getFieldNames().get(baseSharedIndex),
+                it -> it.getFieldNames().get(overlaySharedIndex),
+                TinyClass::getFields,
+                this::mergeField);
+    }
+
+    private TinyField mergeField(@Nullable TinyField baseField, @Nullable TinyField overlayField) {
+        var mergedNames = mergeNames(baseField, overlayField, TinyField::getFieldNames);
+        return new TinyField(
+                mergedNames.get(0),
+                mergedNames,
+                mergeComments(baseField, overlayField, TinyField::getComments)
+        );
+    }
+
+    private Collection<TinyMethod> mergeMethods(@Nullable TinyClass baseClass, @Nullable TinyClass overlayClass) {
+        return mergeChildren(baseClass, overlayClass,
+                it -> it.getMethodNames().get(baseSharedIndex),
+                it -> it.getMethodNames().get(overlaySharedIndex),
+                TinyClass::getMethods,
+                this::mergeMethod);
+    }
+
+    private @NotNull TinyMethod mergeMethod(@Nullable TinyMethod baseMethod, @Nullable TinyMethod overlayMethod) {
+        var mergedNames = mergeNames(baseMethod, overlayMethod, TinyMethod::getMethodNames);
+        return new TinyMethod(
+                mergedNames.get(0),
+                mergedNames,
+                mergeChildren(baseMethod, overlayMethod,
+                        TinyMethodParameter::getLvIndex,
+                        TinyMethodParameter::getLvIndex,
+                        TinyMethod::getParameters,
+                        this::mergeMethodParameter),
+                mergeChildren(baseMethod, overlayMethod,
+                        TinyLocalVariable::getLvIndex,
+                        TinyLocalVariable::getLvIndex,
+                        TinyMethod::getLocalVariables,
+                        this::mergeLocalVariable),
+                mergeComments(baseMethod, overlayMethod, TinyMethod::getComments)
+        );
+    }
+
+    private TinyLocalVariable mergeLocalVariable(
+            @Nullable TinyLocalVariable baseVariable,
+            @Nullable TinyLocalVariable overlayVariable) {
+        if (baseVariable == null && overlayVariable == null)
+            throw new NullPointerException();
+        if (overlayVariable != null && baseVariable != null) {
+            if (overlayVariable.getLvIndex() != baseVariable.getLvIndex())
+                throw new IllegalArgumentException("lvIndex must match on local variables with the same shared name");
+            if (overlayVariable.getLvStartOffset() != baseVariable.getLvStartOffset())
+                throw new IllegalArgumentException("lvStartOffset must match on local variables with the same shared name");
+            if (overlayVariable.getLvTableIndex() != baseVariable.getLvTableIndex())
+                throw new IllegalArgumentException("lvTableIndex must match on local variables with the same shared name");
+        }
+        return new TinyLocalVariable(
+                baseVariable == null ? overlayVariable.getLvIndex() : baseVariable.getLvIndex(),
+                baseVariable == null ? overlayVariable.getLvStartOffset() : baseVariable.getLvStartOffset(),
+                baseVariable == null ? overlayVariable.getLvTableIndex() : baseVariable.getLvTableIndex(),
+                mergeNames(baseVariable, overlayVariable, TinyLocalVariable::getLocalVariableNames),
+                mergeComments(baseVariable, overlayVariable, TinyLocalVariable::getComments)
+        );
+    }
+
+    private TinyMethodParameter mergeMethodParameter(
+            @Nullable TinyMethodParameter baseParam,
+            @Nullable TinyMethodParameter overlayParam) {
+        if (baseParam == null && overlayParam == null)
+            throw new NullPointerException();
+        if (overlayParam != null && baseParam != null && overlayParam.getLvIndex() != baseParam.getLvIndex())
+            throw new IllegalArgumentException("lvIndex must match on method parameters with the same shared name");
+        return new TinyMethodParameter(
+                baseParam != null ? baseParam.getLvIndex() : overlayParam.getLvIndex(),
+                mergeNames(baseParam, overlayParam, TinyMethodParameter::getParameterNames),
+                mergeComments(baseParam, overlayParam, TinyMethodParameter::getComments)
+        );
+    }
+
+    private <B, C, K> List<C> mergeChildren(
+            @Nullable B base,
+            @Nullable B overlay,
+            @NotNull Function<@NotNull C, @NotNull K> sharedBaseName,
+            @NotNull Function<@NotNull C, @NotNull K> sharedOverlayName,
+            @NotNull Function<@NotNull B, ? extends @NotNull Collection<@NotNull C>> childExtractor,
+            @NotNull BiFunction<@Nullable C, @Nullable C, @NotNull C> childMerger
+    ) {
+        Map<K, C> baseIndex =
+                base == null ? Collections.emptyMap() : childExtractor.apply(base).stream()
+                        .collect(Collectors.toMap(sharedBaseName, Function.identity()));
+        Map<K, C> overlayIndex =
+                overlay == null ? Collections.emptyMap() : childExtractor.apply(overlay).stream()
+                        .collect(Collectors.toMap(sharedOverlayName, Function.identity()));
+        var results = new ArrayList<C>();
+        if (base != null)
+            for (var baseObject : childExtractor.apply(base)) {
+                var sharedName = sharedBaseName.apply(baseObject);
+                var overlayObject = overlayIndex.get(sharedName);
+                var mergedClass = childMerger.apply(baseObject, overlayObject);
+                results.add(mergedClass);
+            }
+        if (overlay != null)
+            for (var overlayObject : childExtractor.apply(overlay)) {
+                var sharedName = sharedOverlayName.apply(overlayObject);
+                if (baseIndex.containsKey(sharedName))
+                    continue;
+                results.add(overlayObject);
+            }
+        return results;
+    }
+
+    private void mergeClasses() {
+        entries.addAll(mergeChildren(
+                base,
+                overlay,
+                it -> it.getClassNames().get(baseSharedIndex),
+                it -> it.getClassNames().get(overlaySharedIndex),
+                TinyFile::getClassEntries,
+                this::mergeClass
+        ));
+    }
+}
diff --git a/src/main/java/moe/nea/zwirn/Zwirn.java b/src/main/java/moe/nea/zwirn/Zwirn.java
new file mode 100644
index 0000000..db616d7
--- /dev/null
+++ b/src/main/java/moe/nea/zwirn/Zwirn.java
@@ -0,0 +1,17 @@
+package moe.nea.zwirn;
+
+import net.fabricmc.stitch.commands.tinyv2.TinyFile;
+import org.jetbrains.annotations.NotNull;
+
+public class Zwirn {
+    public static @NotNull TinyFile mergeTinyFile(
+            @NotNull TinyFile base, @NotNull TinyFile overlay,
+            @NotNull String sharedNamespace) {
+        var namespaces = base.getHeader().getNamespaces();
+        if (!namespaces.containsAll(overlay.getHeader().getNamespaces()))
+            throw new IllegalArgumentException("When merging a tiny file, overlay may not introduce a new namespace.");
+        if (!overlay.getHeader().getNamespaces().contains(sharedNamespace))
+            throw new IllegalArgumentException("When merging a tiny file, overlay must contain the shared namespace");
+        return new TinyMerger(base, overlay, sharedNamespace).merge();
+    }
+}
diff --git a/src/main/java/moe/nea/zwirn/ZwirnUtil.java b/src/main/java/moe/nea/zwirn/ZwirnUtil.java
new file mode 100644
index 0000000..f17eae6
--- /dev/null
+++ b/src/main/java/moe/nea/zwirn/ZwirnUtil.java
@@ -0,0 +1,7 @@
+package moe.nea.zwirn;
+
+public class ZwirnUtil {
+    private static <T> T TODO(String message) {
+        throw new RuntimeException("Not yet implemented: " + message);
+    }
+}
diff --git a/src/test/java/moe/nea/zwirn/ZwirnTest.java b/src/test/java/moe/nea/zwirn/ZwirnTest.java
new file mode 100644
index 0000000..2f80964
--- /dev/null
+++ b/src/test/java/moe/nea/zwirn/ZwirnTest.java
@@ -0,0 +1,51 @@
+package moe.nea.zwirn;
+
+import net.fabricmc.stitch.commands.tinyv2.*;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.HashMap;
+
+class ZwirnTest {
+
+    @Test
+    void mergeTinyFile() throws IOException {
+        var base = new TinyFile(
+                new TinyHeader(
+                        Arrays.asList("official", "intermediary", "named"),
+                        2, 0, new HashMap<>()
+                ),
+                Arrays.asList(
+                        new TinyClass(
+                                Arrays.asList("A", "ClassA", "SomeClass"),
+                                Arrays.asList(),
+                                Arrays.asList(new TinyField("a",
+                                        Arrays.asList("a", "field_a", "myField"), Arrays.asList("Field comment"))),
+                                Arrays.asList("some comment")
+                        )
+                )
+        );
+        var overlay = new TinyFile(
+                new TinyHeader(
+                        Arrays.asList("official", "intermediary", "named"),
+                        2, 0, new HashMap<>()
+                ),
+                Arrays.asList(
+                        new TinyClass(
+                                Arrays.asList("A", "A", "SomeClassButNamedBetter"),
+                                Arrays.asList(),
+                                Arrays.asList(new TinyField("a",
+                                        Arrays.asList("a", "a", "myFieldButNamedCool"), Arrays.asList("Better comment"))),
+                                Arrays.asList()
+                        ),
+                        new TinyClass(
+                                Arrays.asList("B", "B", "OtherClass")
+                        )
+                )
+        );
+        var merged = Zwirn.mergeTinyFile(base, overlay, "official");
+        TinyV2Writer.write(merged, Path.of("out.tiny"));
+    }
+}
\ No newline at end of file