package nigiri

import (
	"reflect"
	"strings"
)

// ============================================================================
// Type Definitions
// ============================================================================

type ConstraintType string

const (
	ConstraintUnique     ConstraintType = "unique"
	ConstraintForeign    ConstraintType = "fkey"
	ConstraintRequired   ConstraintType = "required"
	ConstraintIndex      ConstraintType = "index"
	ConstraintOneToOne   ConstraintType = "one_to_one"
	ConstraintOneToMany  ConstraintType = "one_to_many"
	ConstraintManyToOne  ConstraintType = "many_to_one"
	ConstraintManyToMany ConstraintType = "many_to_many"
)

type RelationshipType string

const (
	RelationshipOneToOne   RelationshipType = "one_to_one"
	RelationshipOneToMany  RelationshipType = "one_to_many"
	RelationshipManyToOne  RelationshipType = "many_to_one"
	RelationshipManyToMany RelationshipType = "many_to_many"
)

type FieldConstraint struct {
	Type         ConstraintType
	Field        string
	Target       string
	IndexName    string
	Relationship RelationshipType
	TargetType   reflect.Type
}

type SchemaInfo struct {
	Fields        map[string]reflect.Type
	Constraints   map[string][]FieldConstraint
	Indices       map[string]string
	Relationships map[string]FieldConstraint
}

// ============================================================================
// Schema Parsing
// ============================================================================

func ParseSchema[T any]() *SchemaInfo {
	var zero T
	t := reflect.TypeOf(zero)
	if t.Kind() == reflect.Pointer {
		t = t.Elem()
	}

	schema := &SchemaInfo{
		Fields:        make(map[string]reflect.Type),
		Constraints:   make(map[string][]FieldConstraint),
		Indices:       make(map[string]string),
		Relationships: make(map[string]FieldConstraint),
	}

	for i := 0; i < t.NumField(); i++ {
		field := t.Field(i)
		fieldName := field.Name
		fieldType := field.Type
		schema.Fields[fieldName] = fieldType

		if relationship := detectRelationship(fieldName, fieldType); relationship != nil {
			schema.Relationships[fieldName] = *relationship
			schema.Constraints[fieldName] = append(schema.Constraints[fieldName], *relationship)
		}

		if dbTag := field.Tag.Get("db"); dbTag != "" {
			if constraints := parseDBTag(fieldName, dbTag); len(constraints) > 0 {
				schema.Constraints[fieldName] = append(schema.Constraints[fieldName], constraints...)
			}
		}

		for _, constraint := range schema.Constraints[fieldName] {
			if constraint.Type == ConstraintUnique || constraint.Type == ConstraintIndex {
				indexName := constraint.IndexName
				if indexName == "" {
					indexName = fieldName + "_idx"
				}
				schema.Indices[fieldName] = indexName
			}
		}
	}

	return schema
}

// ============================================================================
// Relationship Detection
// ============================================================================

func detectRelationship(fieldName string, fieldType reflect.Type) *FieldConstraint {
	switch fieldType.Kind() {
	case reflect.Pointer:
		elemType := fieldType.Elem()
		if isEntityType(elemType) {
			return &FieldConstraint{
				Type:         ConstraintManyToOne,
				Field:        fieldName,
				Relationship: RelationshipManyToOne,
				TargetType:   elemType,
				Target:       getEntityName(elemType),
			}
		}

	case reflect.Slice:
		elemType := fieldType.Elem()
		if elemType.Kind() == reflect.Pointer {
			ptrTargetType := elemType.Elem()
			if isEntityType(ptrTargetType) {
				return &FieldConstraint{
					Type:         ConstraintOneToMany,
					Field:        fieldName,
					Relationship: RelationshipOneToMany,
					TargetType:   ptrTargetType,
					Target:       getEntityName(ptrTargetType),
				}
			}
		}
	}

	return nil
}

// ============================================================================
// Tag Parsing
// ============================================================================

func parseDBTag(fieldName, tag string) []FieldConstraint {
	var constraints []FieldConstraint
	parts := strings.SplitSeq(tag, ",")

	for part := range parts {
		part = strings.TrimSpace(part)
		if part == "" {
			continue
		}

		switch {
		case part == "unique":
			constraints = append(constraints, FieldConstraint{
				Type:  ConstraintUnique,
				Field: fieldName,
			})
		case part == "required":
			constraints = append(constraints, FieldConstraint{
				Type:  ConstraintRequired,
				Field: fieldName,
			})
		case part == "index":
			constraints = append(constraints, FieldConstraint{
				Type:  ConstraintIndex,
				Field: fieldName,
			})
		case strings.HasPrefix(part, "index:"):
			indexName := strings.TrimPrefix(part, "index:")
			constraints = append(constraints, FieldConstraint{
				Type:      ConstraintIndex,
				Field:     fieldName,
				IndexName: indexName,
			})
		case strings.HasPrefix(part, "fkey:"):
			target := strings.TrimPrefix(part, "fkey:")
			constraints = append(constraints, FieldConstraint{
				Type:   ConstraintForeign,
				Field:  fieldName,
				Target: target,
			})
		}
	}

	return constraints
}

// ============================================================================
// Utility Functions
// ============================================================================

func isEntityType(t reflect.Type) bool {
	if t.Kind() != reflect.Struct {
		return false
	}

	for i := 0; i < t.NumField(); i++ {
		field := t.Field(i)
		if field.Name == "ID" && field.Type.Kind() == reflect.Int {
			return true
		}
	}

	return false
}

func getEntityName(t reflect.Type) string {
	name := t.Name()
	if name == "" {
		name = t.String()
	}
	return strings.ToLower(name)
}