// Package partnum handles part number generation from schemas.
package partnum

import (
	"context"
	"fmt"
	"regexp"
	"strings"
	"time"

	"github.com/kindredsystems/silo/internal/schema"
)

// SequenceStore provides atomic sequence number generation.
type SequenceStore interface {
	NextValue(ctx context.Context, schemaID string, scope string) (int, error)
}

// Generator creates part numbers from schemas.
type Generator struct {
	schemas  map[string]*schema.Schema
	seqStore SequenceStore
}

// NewGenerator creates a new part number generator.
func NewGenerator(schemas map[string]*schema.Schema, seqStore SequenceStore) *Generator {
	return &Generator{
		schemas:  schemas,
		seqStore: seqStore,
	}
}

// Input provides values for part number generation.
type Input struct {
	SchemaName string
	Values     map[string]string // segment name -> value
}

// Generate creates a new part number.
func (g *Generator) Generate(ctx context.Context, input Input) (string, error) {
	s, ok := g.schemas[input.SchemaName]
	if !ok {
		return "", fmt.Errorf("unknown schema: %s", input.SchemaName)
	}

	segments := make([]string, len(s.Segments))
	resolvedValues := make(map[string]string)

	for i, seg := range s.Segments {
		val, err := g.resolveSegment(ctx, s, &seg, input.Values, resolvedValues)
		if err != nil {
			return "", fmt.Errorf("segment %s: %w", seg.Name, err)
		}
		segments[i] = val
		resolvedValues[seg.Name] = val
	}

	// Use format template if provided, otherwise join with separator
	if s.Format != "" {
		return g.applyFormat(s.Format, resolvedValues), nil
	}

	return strings.Join(segments, s.Separator), nil
}

func (g *Generator) resolveSegment(
	ctx context.Context,
	s *schema.Schema,
	seg *schema.Segment,
	input map[string]string,
	resolved map[string]string,
) (string, error) {
	switch seg.Type {
	case "constant":
		return seg.Value, nil

	case "string":
		val, ok := input[seg.Name]
		if !ok && seg.Required {
			return "", fmt.Errorf("required value not provided")
		}
		return g.formatString(seg, val)

	case "enum":
		val, ok := input[seg.Name]
		if !ok && seg.Required {
			return "", fmt.Errorf("required value not provided")
		}
		if _, valid := seg.Values[val]; !valid {
			return "", fmt.Errorf("invalid enum value: %s", val)
		}
		return val, nil

	case "serial":
		scope := g.resolveScope(seg.Scope, resolved)
		next, err := g.seqStore.NextValue(ctx, s.Name, scope)
		if err != nil {
			return "", fmt.Errorf("getting sequence: %w", err)
		}
		return g.formatSerial(seg, next), nil

	case "date":
		layout := seg.Value
		if layout == "" {
			layout = "20060102"
		}
		return time.Now().UTC().Format(layout), nil

	default:
		return "", fmt.Errorf("unknown segment type: %s", seg.Type)
	}
}

func (g *Generator) formatString(seg *schema.Segment, val string) (string, error) {
	// Apply case transformation
	switch seg.Case {
	case "upper":
		val = strings.ToUpper(val)
	case "lower":
		val = strings.ToLower(val)
	}

	// Validate length
	if seg.Length > 0 && len(val) != seg.Length {
		return "", fmt.Errorf("value must be exactly %d characters", seg.Length)
	}
	if seg.MinLength > 0 && len(val) < seg.MinLength {
		return "", fmt.Errorf("value must be at least %d characters", seg.MinLength)
	}
	if seg.MaxLength > 0 && len(val) > seg.MaxLength {
		return "", fmt.Errorf("value must be at most %d characters", seg.MaxLength)
	}

	// Validate pattern
	if seg.Validation.Pattern != "" {
		re := regexp.MustCompile(seg.Validation.Pattern)
		if !re.MatchString(val) {
			msg := seg.Validation.Message
			if msg == "" {
				msg = fmt.Sprintf("value does not match pattern %s", seg.Validation.Pattern)
			}
			return "", fmt.Errorf("%s", msg)
		}
	}

	return val, nil
}

func (g *Generator) formatSerial(seg *schema.Segment, val int) string {
	format := fmt.Sprintf("%%0%dd", seg.Length)
	return fmt.Sprintf(format, val)
}

func (g *Generator) resolveScope(scopeTemplate string, resolved map[string]string) string {
	if scopeTemplate == "" {
		return "_global_"
	}

	result := scopeTemplate
	for name, val := range resolved {
		result = strings.ReplaceAll(result, "{"+name+"}", val)
	}
	return result
}

func (g *Generator) applyFormat(format string, resolved map[string]string) string {
	result := format
	for name, val := range resolved {
		result = strings.ReplaceAll(result, "{"+name+"}", val)
	}
	return result
}

// Validate checks if a part number matches a schema.
func (g *Generator) Validate(partNumber string, schemaName string) error {
	s, ok := g.schemas[schemaName]
	if !ok {
		return fmt.Errorf("unknown schema: %s", schemaName)
	}

	parts := strings.Split(partNumber, s.Separator)
	if len(parts) != len(s.Segments) {
		return fmt.Errorf("expected %d segments, got %d", len(s.Segments), len(parts))
	}

	for i, seg := range s.Segments {
		val := parts[i]
		if err := g.validateSegment(&seg, val); err != nil {
			return fmt.Errorf("segment %s: %w", seg.Name, err)
		}
	}

	return nil
}

// validateSegment checks that a single segment value is valid.
func (g *Generator) validateSegment(seg *schema.Segment, val string) error {
	switch seg.Type {
	case "constant":
		if val != seg.Value {
			return fmt.Errorf("expected %q, got %q", seg.Value, val)
		}

	case "enum":
		if _, ok := seg.Values[val]; !ok {
			return fmt.Errorf("invalid enum value: %s", val)
		}

	case "string":
		if seg.Length > 0 && len(val) != seg.Length {
			return fmt.Errorf("value must be exactly %d characters", seg.Length)
		}
		if seg.MinLength > 0 && len(val) < seg.MinLength {
			return fmt.Errorf("value must be at least %d characters", seg.MinLength)
		}
		if seg.MaxLength > 0 && len(val) > seg.MaxLength {
			return fmt.Errorf("value must be at most %d characters", seg.MaxLength)
		}
		if seg.Case == "upper" && val != strings.ToUpper(val) {
			return fmt.Errorf("value must be uppercase")
		}
		if seg.Case == "lower" && val != strings.ToLower(val) {
			return fmt.Errorf("value must be lowercase")
		}
		if seg.Validation.Pattern != "" {
			re := regexp.MustCompile(seg.Validation.Pattern)
			if !re.MatchString(val) {
				msg := seg.Validation.Message
				if msg == "" {
					msg = fmt.Sprintf("value does not match pattern %s", seg.Validation.Pattern)
				}
				return fmt.Errorf("%s", msg)
			}
		}

	case "serial":
		if seg.Length > 0 && len(val) != seg.Length {
			return fmt.Errorf("value must be exactly %d characters", seg.Length)
		}
		for _, ch := range val {
			if ch < '0' || ch > '9' {
				return fmt.Errorf("serial must be numeric")
			}
		}

	case "date":
		layout := seg.Value
		if layout == "" {
			layout = "20060102"
		}
		expected := time.Now().UTC().Format(layout)
		if len(val) != len(expected) {
			return fmt.Errorf("date segment length mismatch: expected %d, got %d", len(expected), len(val))
		}

	default:
		return fmt.Errorf("unknown segment type: %s", seg.Type)
	}

	return nil
}