module Compiler
open Syntax
open ILInstructions

type PrimValue =
    | BoolVal of bool
    | IntVal of int

type MetaData =
    { locals : Map<string, int>
      nextLocal : int }

let initMetaData = { locals = Map.empty
                     nextLocal = 0 }

let rec evalExpr (meta : MetaData) expr =
    match expr with
    | ConstInt i                  -> [PushInt i]
    | Var name                    ->
        match Map.tryFind name meta.locals with
        | None    -> failwith "Variable '%s' does not exist." name
        | Some(i) -> [LoadLocal i]
    | PrimOp ("+", lOper, rOper)        -> evalNumericExpr meta Add lOper rOper
    | PrimOp ("-", lOper, rOper)        -> evalNumericExpr meta Sub lOper rOper
    | PrimOp ("*", lOper, rOper)        -> evalNumericExpr meta Mul lOper rOper
    | PrimOp ("/", lOper, rOper)        -> evalNumericExpr meta Div lOper rOper
    | PrimOp (">", lOper, rOper)        -> evalNumericExpr meta Gt lOper rOper
    | PrimOp ("<", lOper, rOper)        -> evalNumericExpr meta Lt lOper rOper
    | Let(name, valExpr)                -> evalLet meta name valExpr
    | FunCall (funName, arg)            -> evalFunCall meta funName arg
    | If (ifExpr, thenExpr, elseExpr )  -> evalIf meta ifExpr thenExpr elseExpr
    | _                                 -> failwith "Syntax error"

and evalNumericExpr meta op lOper rOper =
    let left = evalExpr meta lOper
    let right = evalExpr meta rOper
    op :: (right @ left)

and evalLet meta name valExpr =
    let valInstr = evalExpr meta valExpr
    let storeInstr = StoreLocal meta.nextLocal
    let updatedMeta = { meta with locals = Map.add name meta.nextLocal meta.locals
                                  nextLocal = meta.nextLocal + 1}
    storeInstr :: valInstr

and evalIf meta ifExpr thenExpr elseExpr =
    let ifInstr = evalExpr meta ifExpr
    let thenInstr = evalExpr meta thenExpr |> List.rev
    let elseInstr = evalExpr meta elseExpr |> List.rev
    Branch (thenInstr, elseInstr) :: ifInstr

and evalFunCall meta name expr =
    let argument = evalExpr meta expr
    match name with
    | (Var "print") -> Print :: argument
    | (Var funName) -> [MethodCall (funName, argument)]
    | _             -> failwith "Syntax error: expected (Var name)"

let evalFuncDef meta funcDefs =
    match funcDefs with
    | FuncDef (name, argName, expr) ->
        let storeInstr = StoreLocal meta.nextLocal
        let updatedMeta = { meta with locals = Map.add argName meta.nextLocal meta.locals
                                      nextLocal = meta.nextLocal + 1}
        let funcInstr = evalExpr updatedMeta expr |> List.rev
        Method(name, [argName], funcInstr)

let evalProgram (meta : MetaData) program =
    match program with
    | Program (funcDefs, expr) ->
        let evaluatedFuncDefs = List.map (evalFuncDef meta) funcDefs |> List.rev
        let mainInstr = evalExpr meta expr |> List.rev
        Class ("Program", evaluatedFuncDefs @ [EntryMethod("Main", [],  mainInstr)])

let compile program =
    evalProgram initMetaData program