kotlinlox/src/main/fr/celticinfo/lox/Interpreter.kt

package fr.celticinfo.lox

import fr.celticinfo.lox.TokenType.*

class Interpreter: ExprVisitor<Any?>, StmtVisitor<Unit>{
    var globals = Environment()
    private var environment = globals

    constructor() {
        globals.define("clock", object : LoxCallable {
            override fun arity(): Int {
                return 0
            }

            override fun call(interpreter: Interpreter, arguments: List<Any?>): Any? {
                return System.currentTimeMillis().toDouble() / 1000.0
            }

            override fun toString(): String {
                return "<native fn>"
            }
        })
    }

    fun interpret(statements: List<Stmt?>) {
        try {
            for (statement in statements) {
                execute(statement)
            }
        } catch (error: RuntimeError) {
            Lox.runtimeError(error)
            throw error
        }
    }

    private fun execute(stmt: Stmt?) {
        stmt?.accept(this)
    }

    override fun visitBlock(stmt: Block) {
        executeBlock(stmt.statements, Environment(environment))
    }

    fun executeBlock(statements: List<Stmt?>, environment: Environment) {
        val previous = this.environment
        try {
            this.environment = environment
            for (statement in statements) {
                execute(statement)
            }
        } finally {
            this.environment = previous
        }
    }

    private fun evaluate(expr: Expr?): Any? {
        return expr?.accept(this)
    }

    override fun visitExpression(stmt: Expression) {
        evaluate(stmt.expression)
    }

    override fun visitFunction(stmt: Function) {
        val function = LoxFunction(stmt, environment)
        environment.define(stmt.name.lexeme, function)
    }

    override fun visitIf(stmt: If) {
        if (isTruthy(evaluate(stmt.condition))) {
            execute(stmt.thenBranch)
        } else {
            stmt.elseBranch?.let { execute(it) }
        }
    }

    override fun visitWhile(stmt: While) {
        while (isTruthy(evaluate(stmt.condition))) {
            execute(stmt.body)
        }
    }

    override fun visitPrint(stmt: Print) {
        val value = evaluate(stmt.expression)
        println(stringify(value))
    }

    override fun visitReturn(stmt: Return) {
        val value = stmt.value?.let { evaluate(it) }
        throw LoxReturn(value)
    }

    override fun visitVar(stmt: Var) {
        val value = evaluate(stmt.initializer)
        environment.define(stmt.name.lexeme, value)
    }

    override fun visitAssign(expr: Assign): Any? {
        val value = evaluate(expr.value)
        environment.assign(expr.name, value)
        return value
    }

    override fun visitBinary(expr: Binary): Any? {
        val left = evaluate(expr.left)
        val right = evaluate(expr.right)

        return when (expr.operator.type) {
            MINUS -> {
                checkNumberOperands(expr.operator, left, right)
                left as Double - right as Double
            }
            SLASH -> {
                checkNumberOperands(expr.operator, left, right)
                if (right == 0.0) {
                    throw RuntimeError(expr.operator, "Division by zero")
                }
                left as Double / right as Double
            }
            STAR -> {
                checkNumberOperands(expr.operator, left, right)
                left as Double * right as Double
            }
            PLUS -> {
                if (left is Double && right is Double) {
                    left + right
                } else if (left is String && right is String) {
                    left + right
                } else {
                    throw RuntimeError(expr.operator, "Operands must be two numbers or two strings")
                }
            }
            GREATER -> {
                checkNumberOperands(expr.operator, left, right)
                left as Double > right as Double
            }
            GREATER_EQUAL -> {
                checkNumberOperands(expr.operator, left, right)
                left as Double >= right as Double
            }
            LESS -> {
                checkNumberOperands(expr.operator, left, right)
                (left as Double) < right as Double
            }
            LESS_EQUAL -> {
                checkNumberOperands(expr.operator, left, right)
                left as Double <= right as Double
            }
            BANG_EQUAL -> return !isEqual(left, right)
            EQUAL_EQUAL -> return isEqual(left, right)
            else -> null
        }
    }

    override fun visitCall(expr: Call): Any? {
        val callee = evaluate(expr.callee)

        val arguments = expr.arguments.map { evaluate(it) }

        if (callee !is LoxCallable) {
            throw RuntimeError(expr.paren, "Can only call functions and classes")
        }

        if (arguments.size != callee.arity()) {
            throw RuntimeError(expr.paren, "Expected ${callee.arity()} arguments but got ${arguments.size}")
        }

        return callee.call(this, arguments)
    }

    override fun visitGrouping(expr: Grouping): Any? {
        return evaluate(expr.expression)
    }

    override fun visitLiteral(expr: Literal): Any? {
        return expr.value
    }

    override fun visitLogical(expr: Logical): Any? {
        val left = evaluate(expr.left)

        if (expr.operator.type == OR) {
            if (isTruthy(left)) return left
        } else {
            if (!isTruthy(left)) return left
        }

        return evaluate(expr.right)
    }

    override fun visitUnary(expr: Unary): Any? {
        val right = evaluate(expr.right)

        return when (expr.operator.type) {
            MINUS -> {
                checkNumberOperand(expr.operator, right)
                -(right as Double)
            }
            BANG -> !isTruthy(right)
            else -> null
        }
    }

    override fun visitVariable(expr: Variable): Any? {
        return environment.get(expr.name)
    }

    private fun isTruthy(obj: Any?): Boolean {
        return when (obj) {
            null -> false
            is Boolean -> obj
            else -> true
        }
    }

    private fun isEqual(left: Any?, right: Any?): Boolean {
        return if (left == null && right == null) {
            true
        } else if (left == null) {
            false
        } else {
            left == right
        }
    }

    private fun checkNumberOperand(operator: Token, right: Any?) {
        if (right !is Double) {
            throw RuntimeError(operator, "Operand must be a number")
        }
    }

    private fun checkNumberOperands(operator: Token, left: Any?, right: Any?) {
        if (left !is Double || right !is Double) {
            throw RuntimeError(operator, "Operands must be numbers")
        }
    }

    private fun stringify(obj: Any?): String {
        return when (obj) {
            null -> "nil"
            is Double -> {
                var text = obj.toString()
                if (text.endsWith(".0")) {
                    text = text.substring(0, text.length - 2)
                }
                text
            }
            else -> obj.toString()
        }
    }
}