package parser

import (
	"fmt"
)

// Type constants for built-in types
const (
	TypeNumber   = "number"
	TypeString   = "string"
	TypeBool     = "bool"
	TypeNil      = "nil"
	TypeTable    = "table"
	TypeFunction = "function"
	TypeAny      = "any"
)

// TypeError represents a type checking error
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
type Symbol struct {
	Name     string
	Type     *TypeInfo
	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
type TypeInferrer struct {
	currentScope *Scope
	globalScope  *Scope
	errors       []TypeError

	// Pre-allocated type objects for performance
	numberType *TypeInfo
	stringType *TypeInfo
	boolType   *TypeInfo
	nilType    *TypeInfo
	tableType  *TypeInfo
	anyType    *TypeInfo
}

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

	ti := &TypeInferrer{
		currentScope: globalScope,
		globalScope:  globalScope,
		errors:       []TypeError{},

		// Pre-allocate common types to reduce allocations
		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},
		anyType:    &TypeInfo{Type: TypeAny, Inferred: true},
	}

	return ti
}

// InferTypes performs type inference on the entire program
func (ti *TypeInferrer) InferTypes(program *Program) []TypeError {
	for _, stmt := range program.Statements {
		ti.inferStatement(stmt)
	}
	return ti.errors
}

// enterScope creates a new scope
func (ti *TypeInferrer) enterScope() {
	ti.currentScope = NewScope(ti.currentScope)
}

// exitScope returns to the parent scope
func (ti *TypeInferrer) exitScope() {
	if ti.currentScope.parent != nil {
		ti.currentScope = ti.currentScope.parent
	}
}

// addError adds a type error
func (ti *TypeInferrer) addError(message string, node Node) {
	ti.errors = append(ti.errors, TypeError{
		Message: message,
		Line:    0, // Would need to track position in AST nodes
		Column:  0,
		Node:    node,
	})
}

// inferStatement infers types for statements
func (ti *TypeInferrer) inferStatement(stmt Statement) {
	switch s := stmt.(type) {
	case *AssignStatement:
		ti.inferAssignStatement(s)
	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)
		}
	}
}

// inferAssignStatement handles variable assignments with type checking
func (ti *TypeInferrer) inferAssignStatement(stmt *AssignStatement) {
	// Infer the type of the value expression
	valueType := ti.inferExpression(stmt.Value)

	if ident, ok := stmt.Name.(*Identifier); ok {
		// Simple variable assignment
		symbol := ti.currentScope.Lookup(ident.Value)

		if stmt.IsDeclaration {
			// New variable declaration
			varType := valueType

			// If there's a type hint, validate it
			if stmt.TypeHint != nil {
				if !ti.isTypeCompatible(valueType, stmt.TypeHint) {
					ti.addError(fmt.Sprintf("cannot assign %s to variable of type %s",
						valueType.Type, stmt.TypeHint.Type), stmt)
				}
				varType = stmt.TypeHint
				varType.Inferred = false
			}

			// Define the new symbol
			ti.currentScope.Define(&Symbol{
				Name:     ident.Value,
				Type:     varType,
				Declared: true,
			})

			ident.SetType(varType)
		} else {
			// Assignment to existing variable
			if symbol == nil {
				ti.addError(fmt.Sprintf("undefined variable '%s'", ident.Value), stmt)
				return
			}

			// Check type compatibility
			if !ti.isTypeCompatible(valueType, symbol.Type) {
				ti.addError(fmt.Sprintf("cannot assign %s to variable of type %s",
					valueType.Type, symbol.Type.Type), stmt)
			}

			ident.SetType(symbol.Type)
		}
	} else {
		// Member access assignment (table.key or table[index])
		ti.inferExpression(stmt.Name)
	}
}

// inferIfStatement handles if statements
func (ti *TypeInferrer) inferIfStatement(stmt *IfStatement) {
	condType := ti.inferExpression(stmt.Condition)
	ti.validateBooleanContext(condType, stmt.Condition)

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

	for _, elseif := range stmt.ElseIfs {
		condType := ti.inferExpression(elseif.Condition)
		ti.validateBooleanContext(condType, 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()
	}
}

// inferWhileStatement handles while loops
func (ti *TypeInferrer) inferWhileStatement(stmt *WhileStatement) {
	condType := ti.inferExpression(stmt.Condition)
	ti.validateBooleanContext(condType, stmt.Condition)

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

// inferForStatement handles numeric for loops
func (ti *TypeInferrer) inferForStatement(stmt *ForStatement) {
	startType := ti.inferExpression(stmt.Start)
	endType := ti.inferExpression(stmt.End)

	if !ti.isNumericType(startType) {
		ti.addError("for loop start value must be numeric", stmt.Start)
	}
	if !ti.isNumericType(endType) {
		ti.addError("for loop end value must be numeric", stmt.End)
	}

	if stmt.Step != nil {
		stepType := ti.inferExpression(stmt.Step)
		if !ti.isNumericType(stepType) {
			ti.addError("for loop step value must be numeric", stmt.Step)
		}
	}

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

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

// inferForInStatement handles for-in loops
func (ti *TypeInferrer) inferForInStatement(stmt *ForInStatement) {
	iterableType := ti.inferExpression(stmt.Iterable)

	// For now, assume iterable is a table
	if !ti.isTableType(iterableType) {
		ti.addError("for-in requires an iterable (table)", stmt.Iterable)
	}

	ti.enterScope()

	// Define loop variables (key and value are any for now)
	if stmt.Key != nil {
		ti.currentScope.Define(&Symbol{
			Name:     stmt.Key.Value,
			Type:     ti.anyType,
			Declared: true,
		})
		stmt.Key.SetType(ti.anyType)
	}

	ti.currentScope.Define(&Symbol{
		Name:     stmt.Value.Value,
		Type:     ti.anyType,
		Declared: true,
	})
	stmt.Value.SetType(ti.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 ti.nilType
	}

	switch e := expr.(type) {
	case *Identifier:
		return ti.inferIdentifier(e)
	case *NumberLiteral:
		e.SetType(ti.numberType)
		return ti.numberType
	case *StringLiteral:
		e.SetType(ti.stringType)
		return ti.stringType
	case *BooleanLiteral:
		e.SetType(ti.boolType)
		return ti.boolType
	case *NilLiteral:
		e.SetType(ti.nilType)
		return ti.nilType
	case *TableLiteral:
		return ti.inferTableLiteral(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)
	default:
		ti.addError("unknown expression type", expr)
		return ti.anyType
	}
}

// inferIdentifier looks up identifier type in symbol table
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 ti.anyType
	}

	ident.SetType(symbol.Type)
	return symbol.Type
}

// inferTableLiteral infers table 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)
	}

	table.SetType(ti.tableType)
	return ti.tableType
}

// inferFunctionLiteral infers function type
func (ti *TypeInferrer) inferFunctionLiteral(fn *FunctionLiteral) *TypeInfo {
	ti.enterScope()

	// Define parameters in function scope
	for _, param := range fn.Parameters {
		paramType := ti.anyType
		if param.TypeHint != nil {
			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()

	// For now, all functions have type "function"
	funcType := &TypeInfo{Type: TypeFunction, Inferred: true}
	fn.SetType(funcType)
	return funcType
}

// inferCallExpression infers function call return type
func (ti *TypeInferrer) inferCallExpression(call *CallExpression) *TypeInfo {
	funcType := ti.inferExpression(call.Function)

	if !ti.isFunctionType(funcType) {
		ti.addError("cannot call non-function", call.Function)
		return ti.anyType
	}

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

	// For now, assume function calls return any
	call.SetType(ti.anyType)
	return ti.anyType
}

// inferPrefixExpression infers prefix operation type
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 = ti.numberType
	case "not":
		resultType = ti.boolType
	default:
		ti.addError(fmt.Sprintf("unknown prefix operator '%s'", prefix.Operator), prefix)
		resultType = ti.anyType
	}

	prefix.SetType(resultType)
	return resultType
}

// inferInfixExpression infers binary operation type
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 = ti.numberType

	case "==", "!=":
		// Equality works with any types
		resultType = ti.boolType

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

	case "and", "or":
		ti.validateBooleanContext(leftType, infix.Left)
		ti.validateBooleanContext(rightType, infix.Right)
		resultType = ti.boolType

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

	infix.SetType(resultType)
	return resultType
}

// inferIndexExpression infers table[index] type
func (ti *TypeInferrer) inferIndexExpression(index *IndexExpression) *TypeInfo {
	ti.inferExpression(index.Left)
	ti.inferExpression(index.Index)

	// For now, assume table access returns any
	index.SetType(ti.anyType)
	return ti.anyType
}

// inferDotExpression infers table.key type
func (ti *TypeInferrer) inferDotExpression(dot *DotExpression) *TypeInfo {
	ti.inferExpression(dot.Left)

	// For now, assume member access returns any
	dot.SetType(ti.anyType)
	return ti.anyType
}

// Type checking helper methods

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

func (ti *TypeInferrer) validateBooleanContext(t *TypeInfo, expr Expression) {
	// In many languages, non-boolean values can be used in boolean context
	// For strictness, we could require boolean type here
	// For now, allow any type (truthy/falsy semantics)
}

// Errors returns all type checking errors
func (ti *TypeInferrer) Errors() []TypeError {
	return ti.errors
}

// HasErrors returns true if there are any type errors
func (ti *TypeInferrer) HasErrors() bool {
	return len(ti.errors) > 0
}

// ErrorStrings returns error messages as strings
func (ti *TypeInferrer) ErrorStrings() []string {
	result := make([]string, len(ti.errors))
	for i, err := range ti.errors {
		result[i] = err.Error()
	}
	return result
}

// ValidTypeName checks if a string is a valid type name
func ValidTypeName(name string) bool {
	validTypes := []string{TypeNumber, TypeString, TypeBool, TypeNil, TypeTable, TypeFunction, TypeAny}
	for _, validType := range validTypes {
		if name == validType {
			return true
		}
	}
	return false
}

// ParseTypeName converts a string to a TypeInfo (for parsing type hints)
func ParseTypeName(name string) *TypeInfo {
	if ValidTypeName(name) {
		return &TypeInfo{Type: name, Inferred: false}
	}
	return nil
}