package schemav2validator

import (
	"context"
	"encoding/json"
	"fmt"
	"net/url"
	"strings"
	"sync"
	"time"

	"github.com/beckn-one/beckn-onix/pkg/log"
	"github.com/beckn-one/beckn-onix/pkg/model"

	"github.com/getkin/kin-openapi/openapi3"
)

// payload represents the structure of the data payload with context information.
type payload struct {
	Context struct {
		Action string `json:"action"`
	} `json:"context"`
}

// schemav2Validator implements the SchemaValidator interface.
type schemav2Validator struct {
	config    *Config
	spec      *cachedSpec
	specMutex sync.RWMutex
}

// cachedSpec holds a cached OpenAPI spec.
type cachedSpec struct {
	doc      *openapi3.T
	loadedAt time.Time
}

// Config struct for Schemav2Validator.
type Config struct {
	URL      string
	CacheTTL int
}

// New creates a new Schemav2Validator instance.
func New(ctx context.Context, config *Config) (*schemav2Validator, func() error, error) {
	if config == nil {
		return nil, nil, fmt.Errorf("config cannot be nil")
	}
	if config.URL == "" {
		return nil, nil, fmt.Errorf("config URL cannot be empty")
	}

	if config.CacheTTL == 0 {
		config.CacheTTL = 3600
	}

	v := &schemav2Validator{
		config: config,
	}

	if err := v.initialise(ctx); err != nil {
		return nil, nil, fmt.Errorf("failed to initialise schemav2Validator: %v", err)
	}

	go v.refreshLoop(ctx)

	return v, nil, nil
}

// Validate validates the given data against the OpenAPI schema.
func (v *schemav2Validator) Validate(ctx context.Context, reqURL *url.URL, data []byte) error {
	var payloadData payload
	err := json.Unmarshal(data, &payloadData)
	if err != nil {
		return model.NewBadReqErr(fmt.Errorf("failed to parse JSON payload: %v", err))
	}

	if payloadData.Context.Action == "" {
		return model.NewBadReqErr(fmt.Errorf("missing field Action in context"))
	}

	v.specMutex.RLock()
	spec := v.spec
	v.specMutex.RUnlock()

	if spec == nil || spec.doc == nil {
		return model.NewBadReqErr(fmt.Errorf("no OpenAPI spec loaded"))
	}

	action := payloadData.Context.Action
	var schema *openapi3.SchemaRef
	var matchedPath string

	// Search all spec paths for matching action in schema
	for path, item := range spec.doc.Paths.Map() {
		if item == nil {
			continue
		}
		// Check all HTTP methods for this path
		for _, op := range []*openapi3.Operation{item.Post, item.Get, item.Put, item.Patch, item.Delete} {
			if op == nil || op.RequestBody == nil || op.RequestBody.Value == nil {
				continue
			}
			content := op.RequestBody.Value.Content.Get("application/json")
			if content == nil || content.Schema == nil || content.Schema.Value == nil {
				continue
			}
			// Check if schema has action constraint matching our action
			if v.schemaMatchesAction(content.Schema.Value, action) {
				schema = content.Schema
				matchedPath = path
				break
			}
		}
		if schema != nil {
			break
		}
	}

	if schema == nil || schema.Value == nil {
		return model.NewBadReqErr(fmt.Errorf("unsupported action: %s", action))
	}

	log.Debugf(ctx, "Validating action: %s, matched path: %s", action, matchedPath)

	var jsonData any
	if err := json.Unmarshal(data, &jsonData); err != nil {
		return model.NewBadReqErr(fmt.Errorf("invalid JSON: %v", err))
	}

	opts := []openapi3.SchemaValidationOption{
		openapi3.VisitAsRequest(),
		openapi3.MultiErrors(),
		openapi3.EnableFormatValidation(),
	}
	if err := schema.Value.VisitJSON(jsonData, opts...); err != nil {
		log.Debugf(ctx, "Schema validation failed: %v", err)
		return v.formatValidationError(err)
	}

	return nil
}

// initialise loads the OpenAPI spec from the configuration.
func (v *schemav2Validator) initialise(ctx context.Context) error {
	return v.loadSpec(ctx)
}

// loadSpec loads the OpenAPI spec from URL or local path.
func (v *schemav2Validator) loadSpec(ctx context.Context) error {
	loader := openapi3.NewLoader()

	// Allow external references
	loader.IsExternalRefsAllowed = true

	var doc *openapi3.T
	var err error

	urlOrPath := v.config.URL

	if strings.HasPrefix(urlOrPath, "http://") || strings.HasPrefix(urlOrPath, "https://") {
		u, parseErr := url.Parse(urlOrPath)
		if parseErr != nil {
			return fmt.Errorf("failed to parse URL: %v", parseErr)
		}
		doc, err = loader.LoadFromURI(u)
	} else {
		doc, err = loader.LoadFromFile(urlOrPath)
	}

	if err != nil {
		log.Errorf(ctx, err, "Invalid URL or unreachable: %s", urlOrPath)
		return fmt.Errorf("failed to load OpenAPI document: %v", err)
	}

	// Validate spec (skip strict validation to allow JSON Schema keywords)
	if err := doc.Validate(ctx); err != nil {
		log.Debugf(ctx, "Spec validation warnings (non-fatal): %v", err)
	} else {
		log.Debugf(ctx, "Spec validation passed")
	}

	v.specMutex.Lock()
	v.spec = &cachedSpec{
		doc:      doc,
		loadedAt: time.Now(),
	}
	v.specMutex.Unlock()

	log.Debugf(ctx, "Loaded OpenAPI spec from %s", urlOrPath)
	return nil
}

// refreshLoop periodically reloads expired specs based on TTL.
func (v *schemav2Validator) refreshLoop(ctx context.Context) {
	ticker := time.NewTicker(time.Duration(v.config.CacheTTL) * time.Second)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			v.reloadExpiredSpec(ctx)
		}
	}
}

// reloadExpiredSpec reloads spec if it has exceeded its TTL.
func (v *schemav2Validator) reloadExpiredSpec(ctx context.Context) {
	v.specMutex.RLock()
	if v.spec == nil {
		v.specMutex.RUnlock()
		return
	}
	needsReload := time.Since(v.spec.loadedAt) >= time.Duration(v.config.CacheTTL)*time.Second
	v.specMutex.RUnlock()

	if needsReload {
		if err := v.loadSpec(ctx); err != nil {
			log.Errorf(ctx, err, "Failed to reload spec")
		} else {
			log.Debugf(ctx, "Reloaded spec from %s", v.config.URL)
		}
	}
}

// formatValidationError converts kin-openapi validation errors to ONIX error format.
func (v *schemav2Validator) formatValidationError(err error) error {
	var schemaErrors []model.Error

	// Check if it's a MultiError (collection of errors)
	if multiErr, ok := err.(openapi3.MultiError); ok {
		for _, e := range multiErr {
			v.extractSchemaErrors(e, &schemaErrors)
		}
	} else {
		v.extractSchemaErrors(err, &schemaErrors)
	}

	return &model.SchemaValidationErr{Errors: schemaErrors}
}

// extractSchemaErrors recursively extracts detailed error information from SchemaError.
func (v *schemav2Validator) extractSchemaErrors(err error, schemaErrors *[]model.Error) {
	if schemaErr, ok := err.(*openapi3.SchemaError); ok {
		// If there's an origin error, recursively extract from it
		if schemaErr.Origin != nil {
			v.extractSchemaErrors(schemaErr.Origin, schemaErrors)
		} else {
			// Leaf error - extract the actual validation failure
			pathParts := schemaErr.JSONPointer()
			path := strings.Join(pathParts, "/")
			if path == "" {
				path = schemaErr.SchemaField
			}
			*schemaErrors = append(*schemaErrors, model.Error{
				Paths:   path,
				Message: schemaErr.Reason,
			})
		}
	} else if multiErr, ok := err.(openapi3.MultiError); ok {
		// Nested MultiError
		for _, e := range multiErr {
			v.extractSchemaErrors(e, schemaErrors)
		}
	} else {
		// Generic error
		*schemaErrors = append(*schemaErrors, model.Error{
			Paths:   "",
			Message: err.Error(),
		})
	}
}

// schemaMatchesAction checks if a schema has an action constraint matching the given action.
func (v *schemav2Validator) schemaMatchesAction(schema *openapi3.Schema, action string) bool {
	// Check direct properties
	if ctxProp := schema.Properties["context"]; ctxProp != nil && ctxProp.Value != nil {
		if v.checkActionEnum(ctxProp.Value, action) {
			return true
		}
	}

	// Check allOf at schema level
	for _, allOfSchema := range schema.AllOf {
		if allOfSchema.Value != nil {
			if ctxProp := allOfSchema.Value.Properties["context"]; ctxProp != nil && ctxProp.Value != nil {
				if v.checkActionEnum(ctxProp.Value, action) {
					return true
				}
			}
		}
	}

	return false
}

// checkActionEnum checks if a context schema has action enum or const matching the given action.
func (v *schemav2Validator) checkActionEnum(contextSchema *openapi3.Schema, action string) bool {
	// Check direct action property
	if actionProp := contextSchema.Properties["action"]; actionProp != nil && actionProp.Value != nil {
		// Check const field (stored in Extensions by kin-openapi)
		if constVal, ok := actionProp.Value.Extensions["const"]; ok {
			if constVal == action {
				return true
			}
		}
		// Check enum field
		if len(actionProp.Value.Enum) > 0 {
			for _, e := range actionProp.Value.Enum {
				if e == action {
					return true
				}
			}
		}
	}

	// Check allOf in context
	for _, allOfSchema := range contextSchema.AllOf {
		if allOfSchema.Value != nil {
			if actionProp := allOfSchema.Value.Properties["action"]; actionProp != nil && actionProp.Value != nil {
				// Check const field (stored in Extensions by kin-openapi)
				if constVal, ok := actionProp.Value.Extensions["const"]; ok {
					if constVal == action {
						return true
					}
				}
				// Check enum field
				if len(actionProp.Value.Enum) > 0 {
					for _, e := range actionProp.Value.Enum {
						if e == action {
							return true
						}
					}
				}
			}
			// Recursively check nested allOf
			if v.checkActionEnum(allOfSchema.Value, action) {
				return true
			}
		}
	}

	return false
}