package compiler

import (
	"fmt"
	"jinx/pkg/lang/ast"
	"jinx/pkg/lang/compiler/scope"
	"jinx/pkg/lang/vm/code"
)

type Compiler struct {
	ast ast.Program

	funcs []*code.Builder

	scopes scope.ScopeChain
}

func New(ast ast.Program) *Compiler {
	return &Compiler{
		ast:    ast,
		funcs:  make([]*code.Builder, 0),
		scopes: scope.NewScopeChain(),
	}
}

func (comp *Compiler) Compile() (code.Code, error) {
	// Pre-declare all top-level functions
	for _, stmt := range comp.ast.Stmts {
		if stmt.Kind == ast.StmtKindFnDecl {
			if err := comp.preDeclareFunction(stmt.Value.(ast.StmtFnDecl)); err != nil {
				return code.Code{}, err
			}
		}
	}

	target := code.NewBuilder()

	for _, stmt := range comp.ast.Stmts {
		if err := comp.compileStmt(&target, stmt); err != nil {
			return code.Code{}, err
		}
	}

	target.AppendOp(code.OpHalt)

	for _, function := range comp.funcs {
		target.AppendBuilder(*function)
	}

	return target.Build()
}

func (comp *Compiler) preDeclareFunction(fnDeclStmt ast.StmtFnDecl) error {
	if _, ok := comp.scopes.DeclareFunction(fnDeclStmt.Name.Value, uint(len(fnDeclStmt.Args))); !ok {
		return fmt.Errorf("function %s already declared", fnDeclStmt.Name.Value)
	}

	return nil
}

func (comp *Compiler) compileStmt(t *code.Builder, stmt ast.Stmt) error {
	var err error
	switch stmt.Kind {
	case ast.StmtKindEmpty:
		// Do nothing.
	case ast.StmtKindUse:
		panic("use statements not implemented")
	case ast.StmtKindFnDecl:
		fnDeclStmt := stmt.Value.(ast.StmtFnDecl)
		err = comp.compileFnDeclStmt(t, fnDeclStmt)
	case ast.StmtKindObjectDecl:
		panic("object declaration statements not implemented")
	case ast.StmtKindVarDecl:
		decl := stmt.Value.(ast.StmtVarDecl)
		err = comp.compileVarDeclStmt(t, decl)
	case ast.StmtKindIf:
		ifStmt := stmt.Value.(ast.StmtIf)
		err = comp.compileIfStmt(t, ifStmt)
	case ast.StmtKindForCond:
		forCondStmt := stmt.Value.(ast.StmtForCond)
		err = comp.compileForCondStmt(t, forCondStmt)
	case ast.StmtKindForIn:
		forCondIn := stmt.Value.(ast.StmtForIn)
		err = comp.compileForInStmt(t, forCondIn)
	case ast.StmtKindTry:
		panic("try statements not implemented")
	case ast.StmtKindReturn:
		returnStmt := stmt.Value.(ast.StmtReturn)
		err = comp.compileReturnStmt(t, returnStmt)
	case ast.StmtKindContinue:
		panic("continue statements not implemented")
	case ast.StmtKindBreak:
		panic("break statements not implemented")
	case ast.StmtKindThrow:
		panic("throw statements not implemented")
	case ast.StmtKindExpr:
		expr := stmt.Value.(ast.StmtExpr).Value
		err = comp.compileExpr(t, expr)
	default:
		panic(fmt.Errorf("unknown statement kind: %d", stmt.Kind))
	}

	return err
}

func (comp *Compiler) compileFnDeclStmt(t *code.Builder, fnDeclStmt ast.StmtFnDecl) error {
	marker, ok := comp.scopes.DeclareFunction(fnDeclStmt.Name.Value, uint(len(fnDeclStmt.Args)))
	if !ok {
		// If we are in the root scope, the function was simply predeclared :)
		if comp.scopes.IsRootScope() {
			symbolID, ok := comp.scopes.Lookup(fnDeclStmt.Name.Value)
			if !ok {
				panic("function said it was declared but apparently it was lying")
			}

			symbol := comp.scopes.GetFunction(symbolID)

			marker = symbol.Data().Marker()
		} else {
			return fmt.Errorf("function %s already declared", fnDeclStmt.Name.Value)
		}
	}

	functionTarget := code.NewBuilder()

	functionTarget.PutMarker(marker)

	comp.scopes.EnterFunction(marker)

	for _, arg := range fnDeclStmt.Args {
		if _, ok := comp.scopes.Declare(arg.Value); !ok {
			return fmt.Errorf("variable %s already declared", arg.Value)
		}
	}

	if err := comp.compileBlockNode(&functionTarget, fnDeclStmt.Body); err != nil {
		return err
	}

	comp.scopes.Exit()

	comp.funcs = append(comp.funcs, &functionTarget)

	return nil
}

func (comp *Compiler) compileVarDeclStmt(t *code.Builder, decl ast.StmtVarDecl) error {
	if err := comp.compileExpr(t, decl.Value); err != nil {
		return err
	}

	if _, ok := comp.scopes.Declare(decl.Name.Value); !ok {
		return fmt.Errorf("variable %s already declared", decl.Name.Value)
	}

	return nil
}

func (comp *Compiler) compileIfStmt(t *code.Builder, ifStmt ast.StmtIf) error {
	// An if statement is composed out of CondNodes.
	// A cond node can be either the top `if` branch, and `elif` branch
	// inbetween, or `else` branch at the bottom.
	// `if` and `elif` are identical, but the Cond expr of an `else` node is an empty ast.Expr.
	//
	// Each compiled CondNode consists of 4 parts.
	// 1. Condition check => Compiled Cond expr, pushes a bool onto the stack
	//    Example: `push_false` for `if false {}`
	// 2. Condition jump => If the condition is false, jump to the **next** CondNode, if not last.
	//    Example: `jf @elif` or `jf @end`
	// 3. Then block => Anything the user wants to execute.
	//    Example: `push_int 1` or something
	// 4. Then jump => Since the condition was true, we have to jump to the end of the CondNode list,
	//				   preventing other CondNodes from running. This is missing from the last CondNode.
	//    Example: `jmp @end`

	// First we create all the markers we'll need for the if statement
	parentMarker := comp.scopes.CreateAnonymousFunctionSubUnit()

	endMarker := parentMarker.SubMarker("end")

	condMarkers := make([]code.Marker, 0, len(ifStmt.Conds)-1) // We don't need a marker for the first CondNode.
	for i := 0; i < len(ifStmt.Conds)-1; i++ {
		condMarker := parentMarker.SubMarker("cond_%d", i+1)
		condMarkers = append(condMarkers, condMarker)
	}

	for i, cond := range ifStmt.Conds {
		isFirst := i == 0
		isLast := i == len(ifStmt.Conds)-1

		// If we aren't in the first CondNode, the node before it needs a marker to here.
		if !isFirst {
			marker := condMarkers[i-1]
			t.PutMarker(marker)
		}

		if !cond.Cond.IsEmpty() {
			// Condition check
			if err := comp.compileExpr(t, cond.Cond); err != nil {
				return err
			}

			// Condition jump
			t.AppendOp(code.OpJf)
			if isLast {
				t.AppendMarkerReference(endMarker)
			} else {
				nextCondMarker := condMarkers[i]
				t.AppendMarkerReference(nextCondMarker)
			}
		}

		// Then block
		if err := comp.compileBlockNode(t, cond.Then); err != nil {
			return err
		}

		// Then jump
		if !isLast {
			t.AppendOp(code.OpJmp)
			t.AppendMarkerReference(endMarker)
		}
	}

	t.PutMarker(endMarker)

	return nil
}

func (comp *Compiler) compileForCondStmt(t *code.Builder, forCondStmt ast.StmtForCond) error {
	// Parts:
	// 1. Condition check: Decides whether the loop should run
	// 2. Condition jump: Jumps to the end of the for if condition was false
	// 3. Do block: Does something
	// 4. Repeat jump: Jumps back to start

	parentMarker := comp.scopes.CreateAnonymousFunctionSubUnit()

	startMarker := parentMarker.SubMarker("start")
	endMarker := parentMarker.SubMarker("end")

	t.PutMarker(startMarker)

	if !forCondStmt.Cond.IsEmpty() {
		// Condition check
		if err := comp.compileExpr(t, forCondStmt.Cond); err != nil {
			return err
		}

		// Condition check
		t.AppendOp(code.OpJf)
		t.AppendMarkerReference(endMarker)
	}

	// Do block
	if err := comp.compileBlockNode(t, forCondStmt.Do); err != nil {
		return err
	}

	// Repeat jump
	t.AppendOp(code.OpJmp)
	t.AppendMarkerReference(startMarker)

	t.PutMarker(endMarker)

	return nil
}

func (comp *Compiler) compileForInStmt(t *code.Builder, forInStmt ast.StmtForIn) error {
	// Mostly same as ForCond, but the condition is implicit.

	// Example for: `for x in [] {}`

	// 0. Preparation
	// push_array # collection stored in local 0
	// push_int 0 # i stored in local 1
	// push_null # x stored in local 2
	// 1. Condition check (i < x.length())
	// @check:
	// get_local 1
	// get_local 0
	// get_member "$length"
	// call 0
	// lt
	// 2. Condition jump
	// jf @end
	// 3.1 Do preparation (aka setting the x variable)
	// get_local 0
	// get_local 1
	// index
	// set_local 2

	// get_local 1
	// push_int 1
	// add
	// set_local 1
	// 3. Do block
	// ...
	// 4. Repeat jump:
	// jmp @check
	// @end:
	// halt

	parentMarker := comp.scopes.CreateAnonymousFunctionSubUnit()

	checkMarker := parentMarker.SubUnit("check")
	endMarker := parentMarker.SubUnit("end")

	// Preparation
	if err := comp.compileExpr(t, forInStmt.Collection); err != nil {
		return err
	}
	collectionLocal := comp.scopes.DeclareAnonymous()

	t.AppendOp(code.OpPushInt)
	t.AppendInt(0)
	iLocal := comp.scopes.DeclareAnonymous()

	t.AppendOp(code.OpPushNull)
	nameLocal, ok := comp.scopes.Declare(forInStmt.Name.Value)
	if !ok {
		return fmt.Errorf("variable %s already declared", forInStmt.Name.Value)
	}

	// Condition check
	t.PutMarker(checkMarker)

	t.AppendOp(code.OpGetLocal)
	t.AppendInt(int64(iLocal))

	t.AppendOp(code.OpGetLocal)
	t.AppendInt(int64(collectionLocal))

	t.AppendOp(code.OpGetMember)
	t.AppendString("length")

	t.AppendOp(code.OpCall)
	t.AppendInt(0)

	t.AppendOp(code.OpLt)

	// Condition jump
	t.AppendOp(code.OpJf)
	t.AppendMarkerReference(endMarker)

	// Do Preparation
	t.AppendOp(code.OpGetLocal)
	t.AppendInt(int64(collectionLocal))

	t.AppendOp(code.OpGetLocal)
	t.AppendInt(int64(iLocal))

	t.AppendOp(code.OpIndex)

	t.AppendOp(code.OpSetLocal)
	t.AppendInt(int64(nameLocal))

	t.AppendOp(code.OpGetLocal)
	t.AppendInt(int64(iLocal))

	t.AppendOp(code.OpPushInt)
	t.AppendInt(1)

	t.AppendOp(code.OpAdd)

	t.AppendOp(code.OpSetLocal)
	t.AppendInt(int64(iLocal))

	// Do block
	if err := comp.compileBlockNode(t, forInStmt.Do); err != nil {
		return err
	}

	// Repeat jump
	t.AppendOp(code.OpJmp)
	t.AppendMarkerReference(checkMarker)

	t.PutMarker(endMarker)

	return nil
}

func (comp *Compiler) compileReturnStmt(t *code.Builder, returnStmt ast.StmtReturn) error {
	// Check that we are in fact in a function
	functionScope := comp.scopes.CurrentFunction()
	if functionScope.IsRootScope() {
		return fmt.Errorf("can't return when not inside a function")
	}

	if returnStmt.Value.IsEmpty() {
		t.AppendOp(code.OpPushNull)
	} else {
		if err := comp.compileExpr(t, returnStmt.Value); err != nil {
			return err
		}
	}

	t.AppendOp(code.OpRet)

	return nil
}

func (comp *Compiler) compileExpr(t *code.Builder, expr ast.Expr) error {
	switch expr.Kind {
	case ast.ExprKindBinary:
		return comp.compileBinaryExpr(t, expr.Value.(ast.ExprBinary))
	case ast.ExprKindUnary:
		return comp.compileUnaryExpr(t, expr.Value.(ast.ExprUnary))
	case ast.ExprKindCall:
		return comp.compileCallExpr(t, expr.Value.(ast.ExprCall))
	case ast.ExprKindSubscription:
		return comp.compileSubscriptionExpr(t, expr.Value.(ast.ExprSubscription))

	case ast.ExprKindGroup:
		return comp.compileGroupExpr(t, expr.Value.(ast.ExprGroup))
	case ast.ExprKindFnLit:
		panic("not implemented")
	case ast.ExprKindArrayLit:
		return comp.compileArrayLitExpr(t, expr.Value.(ast.ExprArrayLit))
	case ast.ExprKindIdent:
		return comp.compileIdentExpr(t, expr.Value.(ast.ExprIdent))
	case ast.ExprKindIntLit:
		return comp.compileIntLitExpr(t, expr.Value.(ast.ExprIntLit))
	case ast.ExprKindFloatLit:
		return comp.compileFloatLitExpr(t, expr.Value.(ast.ExprFloatLit))
	case ast.ExprKindStringLit:
		return comp.compileStringLitExpr(t, expr.Value.(ast.ExprStringLit))
	case ast.ExprKindBoolLit:
		return comp.compileBoolLitExpr(t, expr.Value.(ast.ExprBoolLit))
	case ast.ExprKindNullLit:
		return comp.compileNullLitExpr(t, expr.Value.(ast.ExprNullLit))
	case ast.ExprKindThis:
		panic("not implemented")
	default:
		panic("unknown expression kind")
	}
}

func (comp *Compiler) compileBinaryExpr(t *code.Builder, expr ast.ExprBinary) error {
	if expr.Op == ast.BinOpAssign {
		return comp.compileAssignExpr(t, expr)
	}

	if err := comp.compileExpr(t, expr.Left); err != nil {
		return err
	}

	if err := comp.compileExpr(t, expr.Right); err != nil {
		return err
	}

	switch expr.Op {
	case ast.BinOpPlus:
		t.AppendOp(code.OpAdd)
	case ast.BinOpMinus:
		t.AppendOp(code.OpSub)
	case ast.BinOpStar:
		t.AppendOp(code.OpMul)
	case ast.BinOpSlash:
		t.AppendOp(code.OpDiv)
	case ast.BinOpPercent:
		t.AppendOp(code.OpMod)

	case ast.BinOpEq:
		t.AppendOp(code.OpEq)
	case ast.BinOpNeq:
		//t.AppendOp(code.OpNeq)
		panic("not implemented")
	case ast.BinOpLt:
		t.AppendOp(code.OpLt)
	case ast.BinOpLte:
		t.AppendOp(code.OpLte)
	case ast.BinOpGt:
		t.AppendOp(code.OpGt)
	case ast.BinOpGte:
		t.AppendOp(code.OpGte)
	default:
		panic("unknown binary operator")
	}

	return nil
}

func (comp *Compiler) compileAssignExpr(t *code.Builder, expr ast.ExprBinary) error {
	if expr.Left.Kind != ast.ExprKindIdent {
		return fmt.Errorf("lvalues other than identifiers not implemented")
	}

	name := expr.Left.Value.(ast.ExprIdent).Value.Value
	symbolId, ok := comp.scopes.Lookup(name)
	if !ok {
		return fmt.Errorf("variable %s not declared", name)
	}

	if symbolId.SymbolKind() != scope.SymbolKindVariable {
		return fmt.Errorf("can't assign to a %v", symbolId.SymbolKind())
	}

	symbol := comp.scopes.GetVariable(symbolId)

	if err := comp.compileExpr(t, expr.Right); err != nil {
		return err
	}

	t.AppendOp(code.OpSetLocal)
	t.AppendInt(int64(symbol.Data().LocalIndex()))

	return nil
}

func (comp *Compiler) compileUnaryExpr(t *code.Builder, expr ast.ExprUnary) error {
	if err := comp.compileExpr(t, expr.Value); err != nil {
		return err
	}

	switch expr.Op {
	case ast.UnOpBang:
		panic("not implemented")
	case ast.UnOpMinus:
		panic("not implemented")
	default:
		panic("unknown unary operator")
	}

	return nil
}

func (comp *Compiler) compileCallExpr(t *code.Builder, expr ast.ExprCall) error {
	if err := comp.compileExpr(t, expr.Callee); err != nil {
		return err
	}

	for i := 0; i < len(expr.Args); i++ {
		if err := comp.compileExpr(t, expr.Args[i]); err != nil {
			return err
		}
	}

	t.AppendOp(code.OpCall)
	t.AppendInt(int64(len(expr.Args)))

	return nil
}

func (comp *Compiler) compileSubscriptionExpr(t *code.Builder, expr ast.ExprSubscription) error {
	if err := comp.compileExpr(t, expr.Obj); err != nil {
		return err
	}

	if err := comp.compileExpr(t, expr.Key); err != nil {
		return err
	}

	t.AppendOp(code.OpIndex)
	return nil
}

func (comp *Compiler) compileGroupExpr(t *code.Builder, expr ast.ExprGroup) error {
	return comp.compileExpr(t, expr.Value)
}

func (comp *Compiler) compileArrayLitExpr(t *code.Builder, expr ast.ExprArrayLit) error {
	t.AppendOp(code.OpPushArray)
	arrayLocal := comp.scopes.DeclareTemporary()

	for _, value := range expr.Values {
		t.AppendOp(code.OpGetLocal)
		t.AppendInt(int64(arrayLocal))

		t.AppendOp(code.OpGetMember)
		t.AppendString("push")

		if err := comp.compileExpr(t, value); err != nil {
			return err
		}

		t.AppendOp(code.OpCall)
		t.AppendInt(1)
	}

	return nil
}

func (comp *Compiler) compileIdentExpr(t *code.Builder, expr ast.ExprIdent) error {
	symbolId, ok := comp.scopes.Lookup(expr.Value.Value)
	if !ok {
		return fmt.Errorf("undefined symbol %s", expr.Value.Value)
	}

	// TODO: Add other ways how the symbol should be fetched. (local, env, global, etc.)
	switch symbolId.SymbolKind() {
	case scope.SymbolKindVariable:
		symbol := comp.scopes.GetVariable(symbolId)

		t.AppendOp(code.OpGetLocal)
		t.AppendInt(int64(symbol.Data().LocalIndex()))
	case scope.SymbolKindFunction:
		symbol := comp.scopes.GetFunction(symbolId)

		t.AppendOp(code.OpPushFunction)
		t.AppendMarkerReference(symbol.Data().Marker())

		if symbol.Data().Args() != 0 {
			t.AppendOp(code.OpSetArgCount)
			t.AppendInt(int64(symbol.Data().Args()))
		}
	default:
		panic(fmt.Errorf("unknown symbol kind: %v", symbolId.SymbolKind()))
	}

	return nil
}

func (comp *Compiler) compileIntLitExpr(t *code.Builder, expr ast.ExprIntLit) error {
	t.AppendOp(code.OpPushInt)
	t.AppendInt(int64(expr.Value))
	return nil
}

func (comp *Compiler) compileFloatLitExpr(t *code.Builder, expr ast.ExprFloatLit) error {
	t.AppendOp(code.OpPushFloat)
	t.AppendFloat(expr.Value)
	return nil
}

func (comp *Compiler) compileStringLitExpr(t *code.Builder, expr ast.ExprStringLit) error {
	t.AppendOp(code.OpPushString)
	t.AppendString(expr.Value)
	return nil
}

func (comp *Compiler) compileBoolLitExpr(t *code.Builder, expr ast.ExprBoolLit) error {
	if expr.Value {
		t.AppendOp(code.OpPushTrue)
	} else {
		t.AppendOp(code.OpPushFalse)
	}
	return nil
}

func (comp *Compiler) compileNullLitExpr(t *code.Builder, expr ast.ExprNullLit) error {
	t.AppendOp(code.OpPushNull)
	return nil
}

func (comp *Compiler) compileBlockNode(t *code.Builder, block ast.BlockNode) error {
	for _, stmt := range block.Stmts {
		if err := comp.compileStmt(t, stmt); err != nil {
			return err
		}
	}

	return nil
}