package parser

import "fmt"

// Type represents built-in and user-defined types using compact enum representation.
// Uses single byte instead of string pointers to minimize memory usage.
type Type uint8

const (
	TypeUnknown Type = iota
	TypeNumber
	TypeString
	TypeBool
	TypeNil
	TypeTable
	TypeFunction
	TypeAny
	TypeStruct // struct types use StructID field for identification
)

// TypeInfo represents type information with zero-allocation design.
// Embeds directly in AST nodes instead of using pointers to reduce heap pressure.
// Common types are pre-allocated as globals to eliminate most allocations.
type TypeInfo struct {
	Type     Type   // Built-in type or TypeStruct for user types
	Inferred bool   // True if type was inferred, false if explicitly declared
	StructID uint16 // Index into global struct table for struct types (0 for non-structs)
}

// Pre-allocated common types - eliminates heap allocations for built-in types
var (
	UnknownType  = TypeInfo{Type: TypeUnknown, Inferred: true}
	NumberType   = TypeInfo{Type: TypeNumber, Inferred: true}
	StringType   = TypeInfo{Type: TypeString, Inferred: true}
	BoolType     = TypeInfo{Type: TypeBool, Inferred: true}
	NilType      = TypeInfo{Type: TypeNil, Inferred: true}
	TableType    = TypeInfo{Type: TypeTable, Inferred: true}
	FunctionType = TypeInfo{Type: TypeFunction, Inferred: true}
	AnyType      = TypeInfo{Type: TypeAny, Inferred: true}
)

// TypeError represents a type checking error with location information
type TypeError struct {
	Message string
	Line    int
	Column  int
	Node    Node
}

func (te TypeError) Error() string {
	return fmt.Sprintf("Type error at line %d, column %d: %s", te.Line, te.Column, te.Message)
}

// Symbol represents a variable in the symbol table with optimized type storage
type Symbol struct {
	Name     string
	Type     TypeInfo // Embed directly instead of pointer
	Declared bool
	Line     int
	Column   int
}

// Scope represents a scope in the symbol table
type Scope struct {
	symbols map[string]*Symbol
	parent  *Scope
}

func NewScope(parent *Scope) *Scope {
	return &Scope{
		symbols: make(map[string]*Symbol),
		parent:  parent,
	}
}

func (s *Scope) Define(symbol *Symbol) {
	s.symbols[symbol.Name] = symbol
}

func (s *Scope) Lookup(name string) *Symbol {
	if symbol, ok := s.symbols[name]; ok {
		return symbol
	}
	if s.parent != nil {
		return s.parent.Lookup(name)
	}
	return nil
}

// TypeInferrer performs type inference and checking with optimized allocations
type TypeInferrer struct {
	currentScope *Scope
	globalScope  *Scope
	errors       []TypeError

	// Struct definitions with ID mapping
	structs   map[string]*StructStatement
	structIDs map[uint16]*StructStatement
	nextID    uint16
}

// NewTypeInferrer creates a new type inference engine
func NewTypeInferrer() *TypeInferrer {
	globalScope := NewScope(nil)

	return &TypeInferrer{
		currentScope: globalScope,
		globalScope:  globalScope,
		errors:       []TypeError{},
		structs:      make(map[string]*StructStatement),
		structIDs:    make(map[uint16]*StructStatement),
		nextID:       1, // 0 reserved for non-struct types
	}
}

// RegisterStruct assigns ID to struct and tracks it
func (ti *TypeInferrer) RegisterStruct(stmt *StructStatement) {
	stmt.ID = ti.nextID
	ti.nextID++
	ti.structs[stmt.Name] = stmt
	ti.structIDs[stmt.ID] = stmt
}

// GetStructByID returns struct definition by ID
func (ti *TypeInferrer) GetStructByID(id uint16) *StructStatement {
	return ti.structIDs[id]
}

// CreateStructType creates TypeInfo for a struct
func (ti *TypeInferrer) CreateStructType(structID uint16) TypeInfo {
	return TypeInfo{Type: TypeStruct, StructID: structID, Inferred: true}
}

// InferTypes performs type inference on the entire program
func (ti *TypeInferrer) InferTypes(program *Program) []TypeError {
	// First pass: collect and register struct definitions
	for _, stmt := range program.Statements {
		if structStmt, ok := stmt.(*StructStatement); ok {
			ti.RegisterStruct(structStmt)
		}
	}

	// Second pass: infer types
	for _, stmt := range program.Statements {
		ti.inferStatement(stmt)
	}
	return ti.errors
}

// inferStatement infers types for statements
func (ti *TypeInferrer) inferStatement(stmt Statement) {
	switch s := stmt.(type) {
	case *StructStatement:
		ti.inferStructStatement(s)
	case *MethodDefinition:
		ti.inferMethodDefinition(s)
	case *Assignment:
		ti.inferAssignment(s)
	case *ExpressionStatement:
		ti.inferExpression(s.Expression)
	case *EchoStatement:
		ti.inferExpression(s.Value)
	case *IfStatement:
		ti.inferIfStatement(s)
	case *WhileStatement:
		ti.inferWhileStatement(s)
	case *ForStatement:
		ti.inferForStatement(s)
	case *ForInStatement:
		ti.inferForInStatement(s)
	case *ReturnStatement:
		if s.Value != nil {
			ti.inferExpression(s.Value)
		}
	case *ExitStatement:
		if s.Value != nil {
			ti.inferExpression(s.Value)
		}
	case *BreakStatement:
		// No-op
	}
}

func (ti *TypeInferrer) inferStructStatement(stmt *StructStatement) {
	for _, field := range stmt.Fields {
		if !ti.isValidType(field.TypeHint) {
			ti.addError(fmt.Sprintf("invalid field type in struct '%s'", stmt.Name), stmt)
		}
	}
}

func (ti *TypeInferrer) inferMethodDefinition(stmt *MethodDefinition) {
	structDef := ti.GetStructByID(stmt.StructID)
	if structDef == nil {
		ti.addError("method defined on undefined struct", stmt)
		return
	}

	ti.enterScope()
	// Add self parameter
	ti.currentScope.Define(&Symbol{
		Name:     "self",
		Type:     ti.CreateStructType(stmt.StructID),
		Declared: true,
	})

	// Add function parameters
	for _, param := range stmt.Function.Parameters {
		paramType := AnyType
		if param.TypeHint.Type != TypeUnknown {
			paramType = param.TypeHint
		}
		ti.currentScope.Define(&Symbol{
			Name:     param.Name,
			Type:     paramType,
			Declared: true,
		})
	}

	// Infer function body
	for _, bodyStmt := range stmt.Function.Body {
		ti.inferStatement(bodyStmt)
	}
	ti.exitScope()
}

func (ti *TypeInferrer) inferAssignment(stmt *Assignment) {
	valueType := ti.inferExpression(stmt.Value)

	if ident, ok := stmt.Target.(*Identifier); ok {
		if stmt.IsDeclaration {
			varType := valueType
			if stmt.TypeHint.Type != TypeUnknown {
				if !ti.isTypeCompatible(valueType, stmt.TypeHint) {
					ti.addError("type mismatch in assignment", stmt)
				}
				varType = stmt.TypeHint
			}

			ti.currentScope.Define(&Symbol{
				Name:     ident.Value,
				Type:     varType,
				Declared: true,
			})
			ident.typeInfo = varType
		} else {
			symbol := ti.currentScope.Lookup(ident.Value)
			if symbol == nil {
				ti.addError(fmt.Sprintf("undefined variable '%s'", ident.Value), stmt)
				return
			}
			if !ti.isTypeCompatible(valueType, symbol.Type) {
				ti.addError("type mismatch in assignment", stmt)
			}
			ident.typeInfo = symbol.Type
		}
	} else {
		// Member access assignment (table.key or table[index])
		ti.inferExpression(stmt.Target)
	}
}

func (ti *TypeInferrer) inferIfStatement(stmt *IfStatement) {
	ti.inferExpression(stmt.Condition)

	ti.enterScope()
	for _, s := range stmt.Body {
		ti.inferStatement(s)
	}
	ti.exitScope()

	for _, elseif := range stmt.ElseIfs {
		ti.inferExpression(elseif.Condition)
		ti.enterScope()
		for _, s := range elseif.Body {
			ti.inferStatement(s)
		}
		ti.exitScope()
	}

	if len(stmt.Else) > 0 {
		ti.enterScope()
		for _, s := range stmt.Else {
			ti.inferStatement(s)
		}
		ti.exitScope()
	}
}

func (ti *TypeInferrer) inferWhileStatement(stmt *WhileStatement) {
	ti.inferExpression(stmt.Condition)

	ti.enterScope()
	for _, s := range stmt.Body {
		ti.inferStatement(s)
	}
	ti.exitScope()
}

func (ti *TypeInferrer) inferForStatement(stmt *ForStatement) {
	ti.inferExpression(stmt.Start)
	ti.inferExpression(stmt.End)
	if stmt.Step != nil {
		ti.inferExpression(stmt.Step)
	}

	ti.enterScope()
	// Define loop variable as number
	ti.currentScope.Define(&Symbol{
		Name:     stmt.Variable.Value,
		Type:     NumberType,
		Declared: true,
	})
	stmt.Variable.typeInfo = NumberType

	for _, s := range stmt.Body {
		ti.inferStatement(s)
	}
	ti.exitScope()
}

func (ti *TypeInferrer) inferForInStatement(stmt *ForInStatement) {
	ti.inferExpression(stmt.Iterable)

	ti.enterScope()
	// Define loop variables
	if stmt.Key != nil {
		ti.currentScope.Define(&Symbol{
			Name:     stmt.Key.Value,
			Type:     AnyType,
			Declared: true,
		})
		stmt.Key.typeInfo = AnyType
	}

	ti.currentScope.Define(&Symbol{
		Name:     stmt.Value.Value,
		Type:     AnyType,
		Declared: true,
	})
	stmt.Value.typeInfo = AnyType

	for _, s := range stmt.Body {
		ti.inferStatement(s)
	}
	ti.exitScope()
}

// inferExpression infers the type of an expression
func (ti *TypeInferrer) inferExpression(expr Expression) TypeInfo {
	if expr == nil {
		return NilType
	}

	switch e := expr.(type) {
	case *Identifier:
		return ti.inferIdentifier(e)
	case *NumberLiteral:
		return NumberType
	case *StringLiteral:
		return StringType
	case *BooleanLiteral:
		return BoolType
	case *NilLiteral:
		return NilType
	case *TableLiteral:
		return ti.inferTableLiteral(e)
	case *StructConstructor:
		return ti.inferStructConstructor(e)
	case *FunctionLiteral:
		return ti.inferFunctionLiteral(e)
	case *CallExpression:
		return ti.inferCallExpression(e)
	case *PrefixExpression:
		return ti.inferPrefixExpression(e)
	case *InfixExpression:
		return ti.inferInfixExpression(e)
	case *IndexExpression:
		return ti.inferIndexExpression(e)
	case *DotExpression:
		return ti.inferDotExpression(e)
	case *Assignment:
		return ti.inferAssignmentExpression(e)
	default:
		ti.addError("unknown expression type", expr)
		return AnyType
	}
}

func (ti *TypeInferrer) inferIdentifier(ident *Identifier) TypeInfo {
	symbol := ti.currentScope.Lookup(ident.Value)
	if symbol == nil {
		ti.addError(fmt.Sprintf("undefined variable '%s'", ident.Value), ident)
		return AnyType
	}
	ident.typeInfo = symbol.Type
	return symbol.Type
}

func (ti *TypeInferrer) inferTableLiteral(table *TableLiteral) TypeInfo {
	// Infer types of all values
	for _, pair := range table.Pairs {
		if pair.Key != nil {
			ti.inferExpression(pair.Key)
		}
		ti.inferExpression(pair.Value)
	}
	return TableType
}

func (ti *TypeInferrer) inferStructConstructor(expr *StructConstructor) TypeInfo {
	structDef := ti.GetStructByID(expr.StructID)
	if structDef == nil {
		ti.addError("undefined struct in constructor", expr)
		return AnyType
	}

	// Validate field assignments
	for _, pair := range expr.Fields {
		if pair.Key != nil {
			fieldName := ""
			if ident, ok := pair.Key.(*Identifier); ok {
				fieldName = ident.Value
			} else if str, ok := pair.Key.(*StringLiteral); ok {
				fieldName = str.Value
			}

			// Find field in struct definition
			var fieldType TypeInfo
			found := false
			for _, field := range structDef.Fields {
				if field.Name == fieldName {
					fieldType = field.TypeHint
					found = true
					break
				}
			}

			if !found {
				ti.addError(fmt.Sprintf("struct has no field '%s'", fieldName), expr)
			} else {
				valueType := ti.inferExpression(pair.Value)
				if !ti.isTypeCompatible(valueType, fieldType) {
					ti.addError("field type mismatch in struct constructor", expr)
				}
			}
		} else {
			// Array-style assignment not valid for structs
			ti.addError("struct constructors require named field assignments", expr)
		}
	}

	structType := ti.CreateStructType(expr.StructID)
	expr.typeInfo = structType
	return structType
}

func (ti *TypeInferrer) inferFunctionLiteral(fn *FunctionLiteral) TypeInfo {
	ti.enterScope()

	// Define parameters in function scope
	for _, param := range fn.Parameters {
		paramType := AnyType
		if param.TypeHint.Type != TypeUnknown {
			paramType = param.TypeHint
		}

		ti.currentScope.Define(&Symbol{
			Name:     param.Name,
			Type:     paramType,
			Declared: true,
		})
	}

	// Infer body
	for _, stmt := range fn.Body {
		ti.inferStatement(stmt)
	}

	ti.exitScope()
	return FunctionType
}

func (ti *TypeInferrer) inferCallExpression(call *CallExpression) TypeInfo {
	ti.inferExpression(call.Function)

	// Infer argument types
	for _, arg := range call.Arguments {
		ti.inferExpression(arg)
	}

	call.typeInfo = AnyType
	return AnyType
}

func (ti *TypeInferrer) inferPrefixExpression(prefix *PrefixExpression) TypeInfo {
	rightType := ti.inferExpression(prefix.Right)

	var resultType TypeInfo
	switch prefix.Operator {
	case "-":
		if !ti.isNumericType(rightType) {
			ti.addError("unary minus requires numeric operand", prefix)
		}
		resultType = NumberType
	case "not":
		resultType = BoolType
	default:
		ti.addError(fmt.Sprintf("unknown prefix operator '%s'", prefix.Operator), prefix)
		resultType = AnyType
	}

	prefix.typeInfo = resultType
	return resultType
}

func (ti *TypeInferrer) inferInfixExpression(infix *InfixExpression) TypeInfo {
	leftType := ti.inferExpression(infix.Left)
	rightType := ti.inferExpression(infix.Right)

	var resultType TypeInfo

	switch infix.Operator {
	case "+", "-", "*", "/", "%":
		if !ti.isNumericType(leftType) || !ti.isNumericType(rightType) {
			ti.addError(fmt.Sprintf("arithmetic operator '%s' requires numeric operands", infix.Operator), infix)
		}
		resultType = NumberType

	case "==", "!=":
		// Equality works with any types
		resultType = BoolType

	case "<", ">", "<=", ">=":
		if !ti.isComparableTypes(leftType, rightType) {
			ti.addError(fmt.Sprintf("comparison operator '%s' requires compatible operands", infix.Operator), infix)
		}
		resultType = BoolType

	case "and", "or":
		resultType = BoolType

	default:
		ti.addError(fmt.Sprintf("unknown infix operator '%s'", infix.Operator), infix)
		resultType = AnyType
	}

	infix.typeInfo = resultType
	return resultType
}

func (ti *TypeInferrer) inferIndexExpression(index *IndexExpression) TypeInfo {
	leftType := ti.inferExpression(index.Left)
	ti.inferExpression(index.Index)

	// If indexing a struct, try to infer field type
	if ti.isStructType(leftType) {
		if strLit, ok := index.Index.(*StringLiteral); ok {
			if structDef := ti.GetStructByID(leftType.StructID); structDef != nil {
				for _, field := range structDef.Fields {
					if field.Name == strLit.Value {
						index.typeInfo = field.TypeHint
						return field.TypeHint
					}
				}
			}
		}
	}

	// For now, assume table/struct access returns any
	index.typeInfo = AnyType
	return AnyType
}

func (ti *TypeInferrer) inferDotExpression(dot *DotExpression) TypeInfo {
	leftType := ti.inferExpression(dot.Left)

	// If accessing a struct field, try to infer field type
	if ti.isStructType(leftType) {
		if structDef := ti.GetStructByID(leftType.StructID); structDef != nil {
			for _, field := range structDef.Fields {
				if field.Name == dot.Key {
					dot.typeInfo = field.TypeHint
					return field.TypeHint
				}
			}
		}
	}

	// For now, assume member access returns any
	dot.typeInfo = AnyType
	return AnyType
}

func (ti *TypeInferrer) inferAssignmentExpression(expr *Assignment) TypeInfo {
	valueType := ti.inferExpression(expr.Value)

	if ident, ok := expr.Target.(*Identifier); ok {
		if expr.IsDeclaration {
			varType := valueType
			if expr.TypeHint.Type != TypeUnknown {
				if !ti.isTypeCompatible(valueType, expr.TypeHint) {
					ti.addError("type mismatch in assignment", expr)
				}
				varType = expr.TypeHint
			}

			ti.currentScope.Define(&Symbol{
				Name:     ident.Value,
				Type:     varType,
				Declared: true,
			})
			ident.typeInfo = varType
		} else {
			symbol := ti.currentScope.Lookup(ident.Value)
			if symbol != nil {
				ident.typeInfo = symbol.Type
			}
		}
	} else {
		ti.inferExpression(expr.Target)
	}

	return valueType
}

// Helper methods
func (ti *TypeInferrer) enterScope() {
	ti.currentScope = NewScope(ti.currentScope)
}

func (ti *TypeInferrer) exitScope() {
	if ti.currentScope.parent != nil {
		ti.currentScope = ti.currentScope.parent
	}
}

func (ti *TypeInferrer) addError(message string, node Node) {
	pos := node.Pos()
	ti.errors = append(ti.errors, TypeError{
		Message: message,
		Line:    pos.Line,
		Column:  pos.Column,
		Node:    node,
	})
}

func (ti *TypeInferrer) isValidType(t TypeInfo) bool {
	if t.Type == TypeStruct {
		return ti.GetStructByID(t.StructID) != nil
	}
	return t.Type <= TypeStruct
}

func (ti *TypeInferrer) isTypeCompatible(valueType, targetType TypeInfo) bool {
	if targetType.Type == TypeAny || valueType.Type == TypeAny {
		return true
	}
	if valueType.Type == TypeStruct && targetType.Type == TypeStruct {
		return valueType.StructID == targetType.StructID
	}
	return valueType.Type == targetType.Type
}

func (ti *TypeInferrer) isNumericType(t TypeInfo) bool {
	return t.Type == TypeNumber
}

func (ti *TypeInferrer) isBooleanType(t TypeInfo) bool {
	return t.Type == TypeBool
}

func (ti *TypeInferrer) isTableType(t TypeInfo) bool {
	return t.Type == TypeTable
}

func (ti *TypeInferrer) isFunctionType(t TypeInfo) bool {
	return t.Type == TypeFunction
}

func (ti *TypeInferrer) isStructType(t TypeInfo) bool {
	return t.Type == TypeStruct
}

func (ti *TypeInferrer) isComparableTypes(left, right TypeInfo) bool {
	if left.Type == TypeAny || right.Type == TypeAny {
		return true
	}
	return left.Type == right.Type && (left.Type == TypeNumber || left.Type == TypeString)
}

// Error reporting
func (ti *TypeInferrer) Errors() []TypeError { return ti.errors }
func (ti *TypeInferrer) HasErrors() bool     { return len(ti.errors) > 0 }
func (ti *TypeInferrer) ErrorStrings() []string {
	result := make([]string, len(ti.errors))
	for i, err := range ti.errors {
		result[i] = err.Error()
	}
	return result
}

// Type string conversion
func TypeToString(t TypeInfo) string {
	switch t.Type {
	case TypeNumber:
		return "number"
	case TypeString:
		return "string"
	case TypeBool:
		return "bool"
	case TypeNil:
		return "nil"
	case TypeTable:
		return "table"
	case TypeFunction:
		return "function"
	case TypeAny:
		return "any"
	case TypeStruct:
		return fmt.Sprintf("struct<%d>", t.StructID)
	default:
		return "unknown"
	}
}