// Package schema handles YAML schema parsing and validation for part numbering.
package schema

import (
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strings"

	"gopkg.in/yaml.v3"
)

// Schema represents a part numbering schema.
type Schema struct {
	Name            string           `yaml:"name"`
	Version         int              `yaml:"version"`
	Description     string           `yaml:"description"`
	Separator       string           `yaml:"separator"`
	Uniqueness      Uniqueness       `yaml:"uniqueness"`
	Segments        []Segment        `yaml:"segments"`
	Format          string           `yaml:"format"`
	Examples        []string         `yaml:"examples"`
	PropertySchemas *PropertySchemas `yaml:"property_schemas,omitempty"`
	UI              *UIConfig        `yaml:"ui,omitempty" json:"ui,omitempty"`
}

// UIConfig defines form layout for all clients.
type UIConfig struct {
	CategoryPicker      *CategoryPickerConfig            `yaml:"category_picker,omitempty" json:"category_picker,omitempty"`
	ItemFields          map[string]ItemFieldDef           `yaml:"item_fields,omitempty" json:"item_fields,omitempty"`
	FieldGroups         map[string]FieldGroup             `yaml:"field_groups,omitempty" json:"field_groups"`
	CategoryFieldGroups map[string]map[string]FieldGroup  `yaml:"category_field_groups,omitempty" json:"category_field_groups,omitempty"`
	FieldOverrides      map[string]FieldOverride          `yaml:"field_overrides,omitempty" json:"field_overrides,omitempty"`
}

// CategoryPickerConfig defines how the category picker is rendered.
type CategoryPickerConfig struct {
	Style  string                `yaml:"style" json:"style"`
	Stages []CategoryPickerStage `yaml:"stages" json:"stages"`
}

// CategoryPickerStage defines one stage of a multi-stage category picker.
type CategoryPickerStage struct {
	Name   string            `yaml:"name" json:"name"`
	Label  string            `yaml:"label" json:"label"`
	Values map[string]string `yaml:"values,omitempty" json:"values,omitempty"`
}

// ItemFieldDef defines a field stored on the items table (not in revision properties).
type ItemFieldDef struct {
	Type                string            `yaml:"type" json:"type"`
	Widget              string            `yaml:"widget" json:"widget"`
	Label               string            `yaml:"label" json:"label"`
	Required            bool              `yaml:"required,omitempty" json:"required,omitempty"`
	Default             any               `yaml:"default,omitempty" json:"default,omitempty"`
	Options             []string          `yaml:"options,omitempty" json:"options,omitempty"`
	DerivedFromCategory map[string]string `yaml:"derived_from_category,omitempty" json:"derived_from_category,omitempty"`
	SearchEndpoint      string            `yaml:"search_endpoint,omitempty" json:"search_endpoint,omitempty"`
}

// FieldGroup defines an ordered group of fields for form layout.
type FieldGroup struct {
	Label  string   `yaml:"label" json:"label"`
	Order  int      `yaml:"order" json:"order"`
	Fields []string `yaml:"fields" json:"fields"`
}

// FieldOverride overrides display hints for a field.
type FieldOverride struct {
	Widget   string   `yaml:"widget,omitempty" json:"widget,omitempty"`
	Currency string   `yaml:"currency,omitempty" json:"currency,omitempty"`
	Options  []string `yaml:"options,omitempty" json:"options,omitempty"`
}

// PropertySchemas defines property schemas per category.
type PropertySchemas struct {
	Version    int                                      `yaml:"version" json:"version"`
	Defaults   map[string]PropertyDefinition            `yaml:"defaults" json:"defaults"`
	Categories map[string]map[string]PropertyDefinition `yaml:"categories" json:"categories"`
}

// PropertyDefinition defines a single property's schema.
type PropertyDefinition struct {
	Type        string `yaml:"type" json:"type"` // string, number, boolean, date
	Default     any    `yaml:"default" json:"default"`
	Required    bool   `yaml:"required,omitempty" json:"required,omitempty"`
	Unit        string `yaml:"unit,omitempty" json:"unit,omitempty"`
	Description string `yaml:"description,omitempty" json:"description,omitempty"`
}

// GetPropertiesForCategory returns merged properties for a category.
func (ps *PropertySchemas) GetPropertiesForCategory(category string) map[string]PropertyDefinition {
	result := make(map[string]PropertyDefinition)

	// Start with defaults
	for k, v := range ps.Defaults {
		result[k] = v
	}

	// Add category-specific (first character of category code)
	if len(category) > 0 {
		categoryPrefix := string(category[0])
		if catProps, ok := ps.Categories[categoryPrefix]; ok {
			for k, v := range catProps {
				result[k] = v
			}
		}
	}

	return result
}

// ApplyDefaults fills in missing properties with defaults.
func (ps *PropertySchemas) ApplyDefaults(properties map[string]any, category string) map[string]any {
	if properties == nil {
		properties = make(map[string]any)
	}

	defs := ps.GetPropertiesForCategory(category)

	for key, def := range defs {
		if _, exists := properties[key]; !exists && def.Default != nil {
			properties[key] = def.Default
		}
	}

	return properties
}

// Uniqueness defines how part number uniqueness is enforced.
type Uniqueness struct {
	Scope         string `yaml:"scope"`          // global, per-project, per-type, per-schema
	CaseSensitive bool   `yaml:"case_sensitive"` // default false
}

// Segment represents a part number segment.
type Segment struct {
	Name        string            `yaml:"name"`
	Type        string            `yaml:"type"` // string, enum, serial, date, constant
	Length      int               `yaml:"length"`
	MinLength   int               `yaml:"min_length"`
	MaxLength   int               `yaml:"max_length"`
	Case        string            `yaml:"case"` // upper, lower, preserve
	Padding     string            `yaml:"padding"`
	Start       int               `yaml:"start"`
	Scope       string            `yaml:"scope"` // template for serial scope
	Value       string            `yaml:"value"` // for constant type
	Values      map[string]string `yaml:"values"`
	Validation  Validation        `yaml:"validation"`
	Required    bool              `yaml:"required"`
	Description string            `yaml:"description"`
}

// Validation defines validation rules for a segment.
type Validation struct {
	Pattern string `yaml:"pattern"`
	Message string `yaml:"message"`
}

// SchemaFile wraps the schema in a file structure.
type SchemaFile struct {
	Schema Schema `yaml:"schema"`
}

// Load reads a schema from a YAML file.
func Load(path string) (*Schema, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("reading schema file: %w", err)
	}

	var sf SchemaFile
	if err := yaml.Unmarshal(data, &sf); err != nil {
		return nil, fmt.Errorf("parsing schema YAML: %w", err)
	}

	// Set defaults
	if sf.Schema.Separator == "" {
		sf.Schema.Separator = "-"
	}
	if sf.Schema.Uniqueness.Scope == "" {
		sf.Schema.Uniqueness.Scope = "global"
	}

	return &sf.Schema, nil
}

// LoadAll reads all schemas from a directory.
func LoadAll(dir string) (map[string]*Schema, error) {
	schemas := make(map[string]*Schema)

	entries, err := os.ReadDir(dir)
	if err != nil {
		return nil, fmt.Errorf("reading schema directory: %w", err)
	}

	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}
		if !strings.HasSuffix(entry.Name(), ".yaml") && !strings.HasSuffix(entry.Name(), ".yml") {
			continue
		}

		path := filepath.Join(dir, entry.Name())
		schema, err := Load(path)
		if err != nil {
			return nil, fmt.Errorf("loading %s: %w", entry.Name(), err)
		}
		schemas[schema.Name] = schema
	}

	return schemas, nil
}

// Validate checks that the schema definition is valid.
func (s *Schema) Validate() error {
	if s.Name == "" {
		return fmt.Errorf("schema name is required")
	}
	if len(s.Segments) == 0 {
		return fmt.Errorf("schema must have at least one segment")
	}

	for i, seg := range s.Segments {
		if err := seg.Validate(); err != nil {
			return fmt.Errorf("segment %d (%s): %w", i, seg.Name, err)
		}
	}

	if err := s.ValidateUI(); err != nil {
		return err
	}

	return nil
}

// Validate checks that a segment definition is valid.
func (seg *Segment) Validate() error {
	if seg.Name == "" {
		return fmt.Errorf("segment name is required")
	}

	validTypes := map[string]bool{
		"string":   true,
		"enum":     true,
		"serial":   true,
		"date":     true,
		"constant": true,
	}
	if !validTypes[seg.Type] {
		return fmt.Errorf("invalid segment type: %s", seg.Type)
	}

	switch seg.Type {
	case "enum":
		if len(seg.Values) == 0 {
			return fmt.Errorf("enum segment requires values")
		}
	case "constant":
		if seg.Value == "" {
			return fmt.Errorf("constant segment requires value")
		}
	case "serial":
		if seg.Length <= 0 {
			return fmt.Errorf("serial segment requires positive length")
		}
	}

	if seg.Validation.Pattern != "" {
		if _, err := regexp.Compile(seg.Validation.Pattern); err != nil {
			return fmt.Errorf("invalid validation pattern: %w", err)
		}
	}

	return nil
}

// ValuesByDomain groups category enum values by their first character (domain prefix).
func (s *Schema) ValuesByDomain() map[string]map[string]string {
	catSeg := s.GetSegment("category")
	if catSeg == nil {
		return nil
	}
	result := make(map[string]map[string]string)
	for code, desc := range catSeg.Values {
		if len(code) == 0 {
			continue
		}
		domain := string(code[0])
		if result[domain] == nil {
			result[domain] = make(map[string]string)
		}
		result[domain][code] = desc
	}
	return result
}

// ValidateUI validates the UI configuration against property schemas and segments.
func (s *Schema) ValidateUI() error {
	if s.UI == nil {
		return nil
	}

	// Build a set of all known fields (item_fields + property defaults)
	knownGlobal := make(map[string]bool)
	if s.UI.ItemFields != nil {
		for k := range s.UI.ItemFields {
			knownGlobal[k] = true
		}
	}
	if s.PropertySchemas != nil {
		for k := range s.PropertySchemas.Defaults {
			knownGlobal[k] = true
		}
	}

	// Validate field_groups: every field must be a known global field
	for groupKey, group := range s.UI.FieldGroups {
		for _, field := range group.Fields {
			if !knownGlobal[field] {
				return fmt.Errorf("ui.field_groups.%s: field %q not found in item_fields or property_schemas.defaults", groupKey, field)
			}
		}
	}

	// Validate category_field_groups: every field must exist in the category's property schema
	if s.PropertySchemas != nil {
		for prefix, groups := range s.UI.CategoryFieldGroups {
			catProps := s.PropertySchemas.Categories[prefix]
			for groupKey, group := range groups {
				for _, field := range group.Fields {
					if catProps == nil {
						return fmt.Errorf("ui.category_field_groups.%s.%s: category prefix %q has no property schema", prefix, groupKey, prefix)
					}
					if _, ok := catProps[field]; !ok {
						return fmt.Errorf("ui.category_field_groups.%s.%s: field %q not found in property_schemas.categories.%s", prefix, groupKey, field, prefix)
					}
				}
			}
		}
	}

	// Validate field_overrides: keys must be known fields
	for key := range s.UI.FieldOverrides {
		if !knownGlobal[key] {
			// Also check category-level properties
			found := false
			if s.PropertySchemas != nil {
				for _, catProps := range s.PropertySchemas.Categories {
					if _, ok := catProps[key]; ok {
						found = true
						break
					}
				}
			}
			if !found {
				return fmt.Errorf("ui.field_overrides: field %q not found in any property schema", key)
			}
		}
	}

	// Validate category_picker stages: first stage values must be valid domain prefixes
	if s.UI.CategoryPicker != nil && len(s.UI.CategoryPicker.Stages) > 0 {
		catSeg := s.GetSegment("category")
		if catSeg != nil {
			validPrefixes := make(map[string]bool)
			for code := range catSeg.Values {
				if len(code) > 0 {
					validPrefixes[string(code[0])] = true
				}
			}
			firstStage := s.UI.CategoryPicker.Stages[0]
			for key := range firstStage.Values {
				if !validPrefixes[key] {
					return fmt.Errorf("ui.category_picker.stages[0]: value %q is not a valid category prefix", key)
				}
			}
		}
	}

	return nil
}

// GetSegment returns a segment by name.
func (s *Schema) GetSegment(name string) *Segment {
	for i := range s.Segments {
		if s.Segments[i].Name == name {
			return &s.Segments[i]
		}
	}
	return nil
}