// Package index provides index-level operations for OpenSearch.
package index

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"

	"es-demo/client"

	"github.com/opensearch-project/opensearch-go/v2/opensearchapi"
)

var (
	// ErrInvalidTemplate is returned when the template configuration is invalid.
	ErrInvalidTemplate = errors.New("invalid template configuration")

	// ErrTemplateNotFound is returned when the specified template does not exist.
	ErrTemplateNotFound = errors.New("template not found")
)

// Template represents an OpenSearch index template.
type Template struct {
	// IndexPatterns defines the index patterns this template applies to.
	IndexPatterns []string `json:"index_patterns"`

	// Settings contains index settings like number of shards and replicas.
	Settings map[string]any `json:"settings,omitempty"`

	// Mappings defines the field mappings for the index.
	Mappings map[string]any `json:"mappings,omitempty"`

	// Aliases defines index aliases.
	Aliases map[string]any `json:"aliases,omitempty"`

	// Priority determines template precedence when multiple templates match.
	Priority int `json:"priority,omitempty"`

	// Version is used for external version management.
	Version int `json:"version,omitempty"`
}

// TemplateResponse represents the response when getting a template.
type TemplateResponse struct {
	IndexTemplates []struct {
		Name          string   `json:"name"`
		IndexTemplate Template `json:"index_template"`
	} `json:"index_templates"`
}

// PutTemplate creates or updates an index template.
func PutTemplate(ctx context.Context, c *client.Client, name string, template *Template) error {
	if err := validateTemplate(template); err != nil {
		return err
	}

	if name == "" {
		return fmt.Errorf("%w: template name is required", ErrInvalidTemplate)
	}

	// Build template object with only non-empty fields
	templateObj := make(map[string]any)
	if len(template.Settings) > 0 {
		templateObj["settings"] = template.Settings
	}
	if len(template.Mappings) > 0 {
		templateObj["mappings"] = template.Mappings
	}
	if len(template.Aliases) > 0 {
		templateObj["aliases"] = template.Aliases
	}

	// Wrap template in template field for the API
	requestBody := map[string]any{
		"index_patterns": template.IndexPatterns,
	}

	// Only add template field if it has content
	if len(templateObj) > 0 {
		requestBody["template"] = templateObj
	}

	// Add optional fields
	if template.Priority > 0 {
		requestBody["priority"] = template.Priority
	}
	if template.Version > 0 {
		requestBody["version"] = template.Version
	}

	body, err := json.Marshal(requestBody)
	if err != nil {
		return fmt.Errorf("failed to marshal template: %w", err)
	}

	req := opensearchapi.IndicesPutIndexTemplateRequest{
		Name: name,
		Body: bytes.NewReader(body),
	}

	res, err := req.Do(ctx, c.GetClient())
	if err != nil {
		return fmt.Errorf("failed to execute put template request: %w", err)
	}
	defer func() {
		if closeErr := res.Body.Close(); closeErr != nil {
			fmt.Fprintf(os.Stderr, "warning: failed to close response body: %v\n", closeErr)
		}
	}()

	if res.IsError() {
		bodyBytes, _ := io.ReadAll(res.Body)
		return fmt.Errorf("put template failed with status %s: %s", res.Status(), string(bodyBytes))
	}

	return nil
}

// GetTemplate retrieves an index template by name.
func GetTemplate(ctx context.Context, c *client.Client, name string) (*Template, error) {
	if name == "" {
		return nil, fmt.Errorf("%w: template name is required", ErrInvalidTemplate)
	}

	req := opensearchapi.IndicesGetIndexTemplateRequest{
		Name: []string{name},
	}

	res, err := req.Do(ctx, c.GetClient())
	if err != nil {
		return nil, fmt.Errorf("failed to execute get template request: %w", err)
	}
	defer func() {
		if closeErr := res.Body.Close(); closeErr != nil {
			fmt.Fprintf(os.Stderr, "warning: failed to close response body: %v\n", closeErr)
		}
	}()

	if res.IsError() {
		if res.StatusCode == 404 {
			return nil, ErrTemplateNotFound
		}
		bodyBytes, _ := io.ReadAll(res.Body)
		return nil, fmt.Errorf("get template failed with status %s: %s", res.Status(), string(bodyBytes))
	}

	var response TemplateResponse
	if err := json.NewDecoder(res.Body).Decode(&response); err != nil {
		return nil, fmt.Errorf("failed to decode template response: %w", err)
	}

	if len(response.IndexTemplates) == 0 {
		return nil, ErrTemplateNotFound
	}

	return &response.IndexTemplates[0].IndexTemplate, nil
}

// DeleteTemplate deletes an index template.
func DeleteTemplate(ctx context.Context, c *client.Client, name string) error {
	if name == "" {
		return fmt.Errorf("%w: template name is required", ErrInvalidTemplate)
	}

	req := opensearchapi.IndicesDeleteIndexTemplateRequest{
		Name: name,
	}

	res, err := req.Do(ctx, c.GetClient())
	if err != nil {
		return fmt.Errorf("failed to execute delete template request: %w", err)
	}
	defer func() {
		if closeErr := res.Body.Close(); closeErr != nil {
			fmt.Fprintf(os.Stderr, "warning: failed to close response body: %v\n", closeErr)
		}
	}()

	if res.IsError() {
		if res.StatusCode == 404 {
			return ErrTemplateNotFound
		}
		bodyBytes, _ := io.ReadAll(res.Body)
		return fmt.Errorf("delete template failed with status %s: %s", res.Status(), string(bodyBytes))
	}

	return nil
}

// ListTemplates retrieves all index templates or templates matching a pattern.
func ListTemplates(ctx context.Context, c *client.Client, names ...string) (map[string]*Template, error) {
	var nameList []string
	if len(names) > 0 {
		nameList = names
	}

	req := opensearchapi.IndicesGetIndexTemplateRequest{
		Name: nameList,
	}

	res, err := req.Do(ctx, c.GetClient())
	if err != nil {
		return nil, fmt.Errorf("failed to execute list templates request: %w", err)
	}
	defer func() {
		if closeErr := res.Body.Close(); closeErr != nil {
			fmt.Fprintf(os.Stderr, "warning: failed to close response body: %v\n", closeErr)
		}
	}()

	if res.IsError() {
		if res.StatusCode == 404 {
			return make(map[string]*Template), nil
		}
		bodyBytes, _ := io.ReadAll(res.Body)
		return nil, fmt.Errorf("list templates failed with status %s: %s", res.Status(), string(bodyBytes))
	}

	var response TemplateResponse
	if err := json.NewDecoder(res.Body).Decode(&response); err != nil {
		return nil, fmt.Errorf("failed to decode templates response: %w", err)
	}

	templates := make(map[string]*Template)
	for _, item := range response.IndexTemplates {
		templates[item.Name] = &item.IndexTemplate
	}

	return templates, nil
}

// validateTemplate validates the template configuration.
func validateTemplate(template *Template) error {
	if template == nil {
		return fmt.Errorf("%w: template cannot be nil", ErrInvalidTemplate)
	}

	if len(template.IndexPatterns) == 0 {
		return fmt.Errorf("%w: index patterns are required", ErrInvalidTemplate)
	}

	return nil
}