package table

import error.CriticalLispException
import function.FunctionNames
import function.LispFunction
import io.github.classgraph.ClassGraph

object FunctionTable {

    private val table = mutableMapOf<String, LispFunction>()

    private val classGraph = ClassGraph()
        .disableJarScanning()
        .enableClassInfo()
        .enableAnnotationInfo()
        .whitelistPackages("function.builtin")

    private val allBuiltIns = with(classGraph.scan()) {
        getClassesWithAnnotation(FunctionNames::class.qualifiedName)
            .map { it.loadClass() }
            .filterIsInstance<Class<out LispFunction>>()
            .toSet()
    }

    init {
        initializeFunctionTable(allBuiltIns)
    }

    private fun initializeFunctionTable(builtIns: Set<Class<out LispFunction>>) {
        table.clear()

        for (function in builtIns)
            addBuiltInFunctionToTable(function)
    }

    private fun addBuiltInFunctionToTable(function: Class<out LispFunction>) {
        val functionNames = function.getAnnotation(FunctionNames::class.java)

        if (functionNames != null)
            addAllFunctionNamesToTable(function, functionNames.value)
    }

    private fun addAllFunctionNamesToTable(function: Class<out LispFunction>, names: Array<out String>) {
        for (name in names)
            table[name] = createInstance(function, name)
    }

    private fun createInstance(function: Class<out LispFunction>, name: String) = try {
        function.getConstructor(String::class.java).newInstance(name)
    } catch (e: Exception) {
        throw LispFunctionInstantiationException(function.name)
    }

    fun lookupFunction(functionName: String) = table[functionName]
    fun isAlreadyDefined(functionName: String) = table.containsKey(functionName)

    fun defineFunction(functionName: String, function: LispFunction) {
        table[functionName] = function
    }

    fun resetFunctionTable() {
        initializeFunctionTable(allBuiltIns)
    }

    internal fun resetFunctionTable(builtIns: Set<Class<out LispFunction>>) {
        initializeFunctionTable(builtIns)
    }

    class LispFunctionInstantiationException(private val functionName: String) : CriticalLispException() {

        override val message: String
            get() = "Could not create an instance of '$functionName'"
    }
}