openrs2/deob/src/main/java/dev/openrs2/deob/transform/UnusedArgTransformer.kt

package dev.openrs2.deob.transform

import com.github.michaelbull.logging.InlineLogger
import dev.openrs2.asm.MemberRef
import dev.openrs2.asm.classpath.ClassPath
import dev.openrs2.asm.classpath.Library
import dev.openrs2.asm.hasCode
import dev.openrs2.asm.removeArgument
import dev.openrs2.asm.transform.Transformer
import dev.openrs2.common.collect.DisjointSet
import dev.openrs2.deob.ArgRef
import dev.openrs2.deob.analysis.ConstSourceInterpreter
import dev.openrs2.deob.analysis.ConstSourceValue
import dev.openrs2.deob.remap.TypedRemapper
import org.objectweb.asm.Opcodes
import org.objectweb.asm.Type
import org.objectweb.asm.tree.AbstractInsnNode
import org.objectweb.asm.tree.ClassNode
import org.objectweb.asm.tree.MethodInsnNode
import org.objectweb.asm.tree.MethodNode
import org.objectweb.asm.tree.VarInsnNode
import org.objectweb.asm.tree.analysis.Analyzer

class UnusedArgTransformer : Transformer() {
    private val retainedArgs = mutableSetOf<ArgRef>()
    private lateinit var inheritedMethodSets: DisjointSet<MemberRef>
    private var deletedArgs = 0

    override fun preTransform(classPath: ClassPath) {
        retainedArgs.clear()
        inheritedMethodSets = classPath.createInheritedMethodSets()
        deletedArgs = 0

        for (library in classPath.libraries) {
            for (clazz in library) {
                for (method in clazz.methods) {
                    if (method.hasCode()) {
                        populateRetainedArgs(classPath, clazz, method)
                    }
                }
            }
        }
    }

    private fun populateRetainedArgs(classPath: ClassPath, clazz: ClassNode, method: MethodNode) {
        val partition = inheritedMethodSets[MemberRef(clazz, method)]!!
        val localToArgMap = createLocalToArgMap(method)

        val analyzer = Analyzer(ConstSourceInterpreter())
        val frames = analyzer.analyze(clazz.name, method)

        frame@ for ((i, frame) in frames.withIndex()) {
            if (frame == null) {
                continue
            }

            val stackSize = frame.stackSize

            when (val insn = method.instructions[i]) {
                is VarInsnNode -> {
                    if (insn.opcode != Opcodes.ILOAD) {
                        continue@frame
                    }

                    val arg = localToArgMap[insn.`var`]
                    if (arg != null) {
                        retainedArgs.add(ArgRef(partition, arg))
                    }
                }
                is MethodInsnNode -> {
                    val invokePartition = inheritedMethodSets[MemberRef(insn)]
                    if (invokePartition == null || !TypedRemapper.isMethodRenamable(classPath, invokePartition)) {
                        continue@frame
                    }

                    val args = Type.getArgumentTypes(insn.desc).size
                    for (j in 0 until args) {
                        val source = frame.getStack(stackSize - args + j)
                        if (source !is ConstSourceValue.Single) {
                            retainedArgs.add(ArgRef(invokePartition, j))
                        }
                    }
                }
            }
        }
    }

    override fun preTransformMethod(
        classPath: ClassPath,
        library: Library,
        clazz: ClassNode,
        method: MethodNode
    ): Boolean {
        // delete unused int args from call sites
        if (!method.hasCode()) {
            return false
        }

        val analyzer = Analyzer(ConstSourceInterpreter())
        val frames = analyzer.analyze(clazz.name, method)
        val deadInsns = mutableListOf<AbstractInsnNode>()

        for ((i, frame) in frames.withIndex()) {
            if (frame == null) {
                continue
            }

            val stackSize = frame.stackSize

            val insn = method.instructions[i]
            if (insn !is MethodInsnNode) {
                continue
            }

            val partition = inheritedMethodSets[MemberRef(insn)]
            if (partition == null || !TypedRemapper.isMethodRenamable(classPath, partition)) {
                continue
            }

            val type = Type.getType(insn.desc)
            val argTypes = type.argumentTypes
            val newArgTypes = mutableListOf<Type>()

            for ((j, argType) in argTypes.withIndex()) {
                if (argType.sort in INT_SORTS && ArgRef(partition, j) !in retainedArgs) {
                    val value = frame.getStack(stackSize - argTypes.size + j) as ConstSourceValue.Single
                    deadInsns.add(value.source)
                } else {
                    newArgTypes.add(argType)
                }
            }

            insn.desc = Type.getMethodDescriptor(type.returnType, *newArgTypes.toTypedArray())
        }

        deadInsns.forEach(method.instructions::remove)

        return false
    }

    override fun postTransformMethod(
        classPath: ClassPath,
        library: Library,
        clazz: ClassNode,
        method: MethodNode
    ): Boolean {
        // delete unused int args from the method itself
        val partition = inheritedMethodSets[MemberRef(clazz, method)]!!
        if (!TypedRemapper.isMethodRenamable(classPath, partition)) {
            return false
        }

        val argTypes = Type.getType(method.desc).argumentTypes
        for ((i, argType) in argTypes.withIndex().reversed()) {
            if (argType.sort in INT_SORTS && ArgRef(partition, i) !in retainedArgs) {
                method.removeArgument(i)
                deletedArgs++
            }
        }

        return false
    }

    override fun postTransform(classPath: ClassPath) {
        logger.info { "Removed $deletedArgs dummy arguments" }
    }

    companion object {
        private val logger = InlineLogger()
        private val INT_SORTS = setOf(
            Type.BOOLEAN,
            Type.BYTE,
            Type.SHORT,
            Type.INT,
            Type.CHAR
        )

        private fun createLocalToArgMap(method: MethodNode): Map<Int, Int> {
            val argTypes = Type.getType(method.desc).argumentTypes

            val map = mutableMapOf<Int, Int>()
            var localIndex = 0

            if (method.access and Opcodes.ACC_STATIC == 0) {
                localIndex++
            }

            for ((argIndex, t) in argTypes.withIndex()) {
                map[localIndex] = argIndex
                localIndex += t.size
            }

            return map
        }
    }
}