// Package parser provides ER diagram parsing based on erDiagram.jison
package parser

import (
	"fmt"
	"strings"

	"mermaid-go/pkg/ast"
	"mermaid-go/pkg/lexer"
)

// ERParser implements ER diagram parsing following erDiagram.jison
type ERParser struct {
	tokens    []lexer.Token
	current   int
	diagram   *ast.ERDiagram
	entityMap map[string]*ast.EREntity // Keep track of entities by name for quick lookup
}

// NewERParser creates a new ER parser
func NewERParser() *ERParser {
	return &ERParser{
		diagram:   ast.NewERDiagram(),
		entityMap: make(map[string]*ast.EREntity),
	}
}

// Parse parses ER diagram syntax
func (p *ERParser) Parse(input string) (*ast.ERDiagram, error) {
	// Tokenize
	l := lexer.NewLexer(input)
	tokens, err := l.Tokenize()
	if err != nil {
		return nil, fmt.Errorf("lexical analysis failed: %w", err)
	}

	// Filter tokens
	p.tokens = lexer.FilterTokens(tokens)
	p.current = 0
	p.diagram = ast.NewERDiagram()

	// Parse document
	err = p.parseDocument()
	if err != nil {
		return nil, fmt.Errorf("syntax analysis failed: %w", err)
	}

	return p.diagram, nil
}

// parseDocument parses the ER diagram document
func (p *ERParser) parseDocument() error {
	// Expect erDiagram
	if !p.check(lexer.TokenID) || p.peek().Value != "erDiagram" {
		return p.error("expected 'erDiagram'")
	}
	p.advance()

	// Parse statements
	for !p.isAtEnd() {
		if err := p.parseStatement(); err != nil {
			return err
		}
	}

	return nil
}

// parseStatement parses individual ER diagram statements
func (p *ERParser) parseStatement() error {
	if p.isAtEnd() {
		return nil
	}

	switch {
	case p.check(lexer.TokenNewline):
		p.advance() // Skip newlines
		return nil
	case p.checkKeyword("direction"):
		return p.parseDirectionStatement()
	case p.check(lexer.TokenID):
		// Try to parse as entity or relationship
		return p.parseEntityOrRelationship()
	default:
		token := p.peek()
		return p.error(fmt.Sprintf("unexpected token: %s", token.Value))
	}
}

// parseEntityOrRelationship attempts to parse either an entity definition or a relationship
func (p *ERParser) parseEntityOrRelationship() error {
	entityName := p.advance().Value

	// Check if this is a relationship (has cardinality symbols)
	if p.checkCardinality() {
		return p.parseRelationship(entityName)
	}

	// Check if this is an entity with attributes (has {)
	if p.check(lexer.TokenOpenBrace) {
		return p.parseEntityWithAttributes(entityName)
	}

	// Simple entity without attributes
	p.addEntity(entityName)
	return nil
}

// parseRelationship parses a relationship between two entities
func (p *ERParser) parseRelationship(fromEntity string) error {
	// Parse relationship type (already tokenized as compound token)
	relType, err := p.parseRelType()
	if err != nil {
		return err
	}

	// Parse second entity
	if !p.check(lexer.TokenID) {
		return p.error("expected second entity name")
	}
	toEntity := p.advance().Value

	// Ensure both entities exist
	p.addEntity(fromEntity)
	p.addEntity(toEntity)

	// Parse optional label
	var label *string
	if p.check(lexer.TokenColon) {
		p.advance() // consume ':'
		var labelParts []string
		for !p.check(lexer.TokenNewline) && !p.isAtEnd() {
			labelParts = append(labelParts, p.advance().Value)
		}
		labelStr := strings.TrimSpace(strings.Join(labelParts, " "))
		label = &labelStr
	}

	// Create relationship
	relation := &ast.ERRelation{
		From:  fromEntity,
		To:    toEntity,
		Type:  relType,
		Label: label,
	}

	p.diagram.Relations = append(p.diagram.Relations, relation)
	return nil
}

// parseEntityWithAttributes parses an entity with attribute definitions
func (p *ERParser) parseEntityWithAttributes(entityName string) error {
	p.advance() // consume '{'

	entity := p.addEntity(entityName)

	// Parse attributes
	for !p.check(lexer.TokenCloseBrace) && !p.isAtEnd() {
		if p.check(lexer.TokenNewline) {
			p.advance()
			continue
		}

		attribute, err := p.parseAttribute()
		if err != nil {
			return err
		}
		entity.Attributes = append(entity.Attributes, attribute)
	}

	if !p.check(lexer.TokenCloseBrace) {
		return p.error("expected '}' to close entity attributes")
	}
	p.advance() // consume '}'

	return nil
}

// parseAttribute parses an attribute definition
func (p *ERParser) parseAttribute() (*ast.ERAttribute, error) {
	// Parse attribute type
	if !p.check(lexer.TokenID) {
		return nil, p.error("expected attribute type")
	}
	attrType := p.advance().Value

	// Parse attribute name
	if !p.check(lexer.TokenID) {
		return nil, p.error("expected attribute name")
	}
	attrName := p.advance().Value

	attribute := &ast.ERAttribute{
		Type: attrType,
		Name: attrName,
	}

	// Parse optional key (PK, FK, UK)
	if p.check(lexer.TokenID) && p.isKeyWord() {
		keyStr := p.advance().Value
		key := ast.ERKeyType(keyStr)
		attribute.Key = &key
	}

	// Parse optional comment (quoted string)
	if p.check(lexer.TokenString) {
		comment := p.advance().Value
		// Remove quotes
		if strings.HasPrefix(comment, "\"") && strings.HasSuffix(comment, "\"") {
			comment = comment[1 : len(comment)-1]
		}
		attribute.Comment = &comment
	}

	return attribute, nil
}

// parseRelType parses relationship type symbols
func (p *ERParser) parseRelType() (ast.ERRelationType, error) {
	if p.isAtEnd() {
		return "", p.error("expected relationship type")
	}

	token := p.peek()

	// Check for compound ER relationship tokens first
	switch token.Type {
	case lexer.TokenEROneToMany:
		p.advance()
		return ast.ERRelationOneToMany, nil
	case lexer.TokenEROneToManyAlt:
		p.advance()
		return ast.ERRelationOneToManyAlt, nil
	case lexer.TokenERManyToOne:
		p.advance()
		return ast.ERRelationManyToOne, nil
	case lexer.TokenEROneToOne:
		p.advance()
		return ast.ERRelationOneToOne, nil
	case lexer.TokenERManyToMany:
		p.advance()
		return ast.ERRelationManyToMany, nil
	case lexer.TokenERManyToManyAlt:
		p.advance()
		return ast.ERRelationManyToManyAlt, nil
	case lexer.TokenERZeroToOne:
		p.advance()
		return ast.ERRelationZeroToOne, nil
	}

	// Fall back to individual token parsing for patterns not covered by compound tokens
	// Look ahead to match relationship patterns
	if p.matchString("||--||") {
		p.advance() // consume '|'
		p.advance() // consume '|'
		p.advance() // consume '-'
		p.advance() // consume '-'
		p.advance() // consume '|'
		p.advance() // consume '|'
		return ast.ERRelationOneToOne, nil
	}
	if p.matchString("||--o{") {
		p.advance() // consume '|'
		p.advance() // consume '|'
		p.advance() // consume '-'
		p.advance() // consume '-'
		p.advance() // consume 'o'
		p.advance() // consume '{'
		return ast.ERRelationOneToMany, nil
	}
	if p.matchString("}o--||") {
		p.advance() // consume '}'
		p.advance() // consume 'o'
		p.advance() // consume '-'
		p.advance() // consume '-'
		p.advance() // consume '|'
		p.advance() // consume '|'
		return ast.ERRelationManyToOne, nil
	}
	if p.matchString("}o--o{") {
		p.advance() // consume '}'
		p.advance() // consume 'o'
		p.advance() // consume '-'
		p.advance() // consume '-'
		p.advance() // consume 'o'
		p.advance() // consume '{'
		return ast.ERRelationManyToMany, nil
	}
	if p.matchString("||--o|") {
		p.advance() // consume '|'
		p.advance() // consume '|'
		p.advance() // consume '-'
		p.advance() // consume '-'
		p.advance() // consume 'o'
		p.advance() // consume '|'
		return ast.ERRelationZeroToOne, nil
	}
	if p.matchString("}o..o{") {
		p.advance() // consume '}'
		p.advance() // consume 'o'
		p.advance() // consume '.'
		p.advance() // consume '.'
		p.advance() // consume 'o'
		p.advance() // consume '{'
		return ast.ERRelationManyToMany, nil
	}
	if p.matchString("||..||") {
		p.advance() // consume '|'
		p.advance() // consume '|'
		p.advance() // consume '.'
		p.advance() // consume '.'
		p.advance() // consume '|'
		p.advance() // consume '|'
		return ast.ERRelationOneToOne, nil
	}

	return "", p.error("unrecognized relationship pattern")
}

// Helper methods
func (p *ERParser) addEntity(name string) *ast.EREntity {
	if entity, exists := p.entityMap[name]; exists {
		return entity
	}

	entity := &ast.EREntity{
		ID:         fmt.Sprintf("entity-%s-%d", name, len(p.diagram.Entities)),
		Name:       name,
		Attributes: make([]*ast.ERAttribute, 0),
		CssClasses: []string{"default"},
	}

	p.entityMap[name] = entity
	p.diagram.Entities = append(p.diagram.Entities, entity)
	return entity
}

func (p *ERParser) checkCardinality() bool {
	if p.isAtEnd() {
		return false
	}

	token := p.peek()

	// Check for compound ER relationship tokens
	switch token.Type {
	case lexer.TokenEROneToMany, lexer.TokenEROneToManyAlt, lexer.TokenERManyToOne,
		lexer.TokenEROneToOne, lexer.TokenERManyToMany, lexer.TokenERManyToManyAlt, lexer.TokenERZeroToOne:
		return true
	}

	// Fall back to string matching for patterns not covered by compound tokens
	return p.matchString("||--||") || p.matchString("||--o{") || p.matchString("}o--||") ||
		p.matchString("}o--o{") || p.matchString("||--o|") || p.matchString("}o..o{") ||
		p.matchString("||..||")
}

func (p *ERParser) isKeyWord() bool {
	if p.isAtEnd() {
		return false
	}
	token := p.peek()
	return token.Type == lexer.TokenID && (token.Value == "PK" || token.Value == "FK" || token.Value == "UK")
}

func (p *ERParser) matchString(s string) bool {
	if p.current+len(s)-1 >= len(p.tokens) {
		return false
	}

	var actual strings.Builder
	for i := 0; i < len(s); i++ {
		if p.current+i >= len(p.tokens) {
			return false
		}
		actual.WriteString(p.tokens[p.current+i].Value)
	}

	return actual.String() == s
}

func (p *ERParser) check(tokenType lexer.TokenType) bool {
	if p.isAtEnd() {
		return false
	}
	return p.peek().Type == tokenType
}

func (p *ERParser) checkKeyword(keyword string) bool {
	if p.isAtEnd() {
		return false
	}
	token := p.peek()
	return token.Type == lexer.TokenID && strings.EqualFold(token.Value, keyword)
}

func (p *ERParser) advance() lexer.Token {
	if !p.isAtEnd() {
		p.current++
	}
	return p.previous()
}

func (p *ERParser) isAtEnd() bool {
	return p.current >= len(p.tokens) || p.peek().Type == lexer.TokenEOF
}

func (p *ERParser) peek() lexer.Token {
	if p.current >= len(p.tokens) {
		return lexer.Token{Type: lexer.TokenEOF}
	}
	return p.tokens[p.current]
}

func (p *ERParser) previous() lexer.Token {
	if p.current <= 0 {
		return lexer.Token{Type: lexer.TokenEOF}
	}
	return p.tokens[p.current-1]
}

func (p *ERParser) parseDirectionStatement() error {
	p.advance() // consume 'direction'

	if !p.check(lexer.TokenID) {
		return p.error("expected direction (TB, BT, RL, LR)")
	}

	// For now, we'll just consume the direction token
	// The existing ERDiagram struct doesn't have a Direction field
	p.advance()

	return nil
}

func (p *ERParser) error(message string) error {
	token := p.peek()
	return fmt.Errorf("parse error at line %d, column %d: %s (got %s)",
		token.Line, token.Column, message, token.Type.String())
}