package compiler

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

type Compiler struct {
	ast     ast.Program
	builder code.Builder

	scopes ScopeChain
}

func New(ast ast.Program) *Compiler {
	return &Compiler{
		ast:     ast,
		builder: code.NewBuilder(),

		scopes: NewScopeChain(),
	}
}

func (comp *Compiler) Compile() (code.Code, error) {
	for _, stmt := range comp.ast.Stmts {
		if err := comp.compileStmt(stmt); err != nil {
			return code.Code{}, err
		}
	}

	return comp.builder.Build(), nil
}

func (comp *Compiler) compileStmt(stmt ast.Stmt) error {
	var err error
	switch stmt.Kind {
	case ast.StmtKindEmpty:
		// Do nothing.
	case ast.StmtKindVarDecl:
		decl := stmt.Value.(ast.StmtVarDecl)
		err = comp.compileVarDeclStmt(decl)
	case ast.StmtKindExpr:
		expr := stmt.Value.(ast.StmtExpr).Value
		err = comp.compileExpr(expr)
	default:
		panic("statements other than expressions, variable declarations, var and empties not implemented")
	}

	return err
}

func (comp *Compiler) compileVarDeclStmt(decl ast.StmtVarDecl) error {
	if !comp.scopes.Declare(decl.Name.Value) {
		return fmt.Errorf("variable %s already declared", decl.Name.Value)
	}

	if err := comp.compileExpr(decl.Value); err != nil {
		return err
	}

	return nil
}

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

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

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

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

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

	switch expr.Op {
	case ast.BinOpPlus:
		comp.builder.AppendOp(code.OpAdd)
	case ast.BinOpMinus:
		comp.builder.AppendOp(code.OpSub)
	case ast.BinOpStar:
		// comp.builder.AppendOp(code.OpMul)
		panic("not implemented")
	case ast.BinOpSlash:
		// comp.builder.AppendOp(code.OpDiv)
		panic("not implemented")
	case ast.BinOpPercent:
		// comp.builder.AppendOp(code.OpMod)
		panic("not implemented")

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

	return nil
}

func (comp *Compiler) compileAssignExpr(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
	symbol, ok := comp.scopes.Lookup(name)
	if !ok {
		return fmt.Errorf("variable %s not declared", name)
	}

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

	comp.builder.AppendOp(code.OpSetLocal)
	comp.builder.AppendInt(int64(symbol.localIndex))

	return nil
}

func (comp *Compiler) compileUnaryExpr(expr ast.ExprUnary) error {
	if err := comp.compileExpr(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(expr ast.ExprCall) error {
	for i := len(expr.Args) - 1; i >= 0; i-- {
		if err := comp.compileExpr(expr.Args[i]); err != nil {
			return err
		}
	}

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

	comp.builder.AppendOp(code.OpCall)
	comp.builder.AppendInt(int64(len(expr.Args)))

	return nil
}

func (comp *Compiler) compileSubscriptionExpr(expr ast.ExprSubscription) error {
	if err := comp.compileExpr(expr.Key); err != nil {
		return err
	}

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

	comp.builder.AppendOp(code.OpIndex)
	return nil
}

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

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

	// TODO: Add boundries to check how the symbol should be fetched. (local, env, global, etc.)
	comp.builder.AppendOp(code.OpGetLocal)
	comp.builder.AppendInt(int64(symbol.localIndex))

	return nil
}

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

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

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

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

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