// Package utils provides utility functions for the Yandex Music API client,
// including JSON handling, request signing, schema mismatch tracking, and error types.
package utils

import (
	"fmt"
	"log"
	"strings"
	"sync"
)

// SchemaMismatch represents a mismatch between expected and actual API response.
// It captures details about missing fields, unknown fields, and unknown values.
type SchemaMismatch struct {
	// ModelName is the name of the model that had the mismatch.
	ModelName string
	// MissingFields lists fields that were expected but not found in the response.
	MissingFields []string
	// UnknownFields lists fields that were not expected but found in the response.
	UnknownFields []string
	// UnknownValues maps unknown field names to their values.
	UnknownValues map[string]any
	// Endpoint is the API endpoint where the mismatch occurred.
	Endpoint string
	// LibraryVersion is the version of the library when the mismatch occurred.
	LibraryVersion string
}

// Describe returns a human-readable description of the schema mismatch.
func (sm *SchemaMismatch) Describe() string {
	var parts []string
	parts = append(parts, fmt.Sprintf("Model: %s", sm.ModelName))
	if len(sm.MissingFields) > 0 {
		parts = append(parts, fmt.Sprintf("Missing fields: %v", sm.MissingFields))
	}
	if len(sm.UnknownFields) > 0 {
		parts = append(parts, fmt.Sprintf("Unknown fields: %v", sm.UnknownFields))
	}
	if len(sm.UnknownValues) > 0 {
		parts = append(parts, fmt.Sprintf("Unknown field structures: %v", sm.UnknownValues))
	}
	parts = append(parts, fmt.Sprintf("Endpoint: %s", sm.Endpoint))
	parts = append(parts, fmt.Sprintf("Library version: %s", sm.LibraryVersion))
	return strings.Join(parts, "\n")
}

// SchemaMismatchHandler is a callback for handling schema mismatches.
// It is invoked when a schema mismatch is detected, if configured.
type SchemaMismatchHandler func(*SchemaMismatch)

// SchemaMismatchConfig holds configuration for schema mismatch handling.
type SchemaMismatchConfig struct {
	// ReportUnknownFields indicates whether unknown fields should be reported.
	ReportUnknownFields bool
	// Strict indicates whether schema mismatches should be treated as errors.
	Strict bool
	// OnSchemaMismatch is an optional callback for custom mismatch handling.
	OnSchemaMismatch SchemaMismatchHandler
}

// DefaultSchemaMismatchConfig returns the default configuration for schema mismatch handling.
// The default config does not report unknown fields, is not strict, and has no callback.
func DefaultSchemaMismatchConfig() SchemaMismatchConfig {
	return SchemaMismatchConfig{
		ReportUnknownFields: false,
		Strict:              false,
		OnSchemaMismatch:    nil,
	}
}

// ReportSchemaMismatch reports a schema mismatch according to the provided config.
// If a callback is configured, it is invoked with the mismatch details.
// If strict mode is enabled, an error is returned. Otherwise, a warning is logged.
func ReportSchemaMismatch(config SchemaMismatchConfig, modelName, endpoint string, missingFields, unknownFields []string, unknownValues map[string]any) error {
	mismatch := &SchemaMismatch{
		ModelName:      modelName,
		MissingFields:  missingFields,
		UnknownFields:  unknownFields,
		UnknownValues:  unknownValues,
		Endpoint:       endpoint,
		LibraryVersion: "go-port-0.1.0",
	}

	if config.OnSchemaMismatch != nil {
		config.OnSchemaMismatch(mismatch)
		return nil
	}

	msg := mismatch.Describe()
	if config.Strict {
		return fmt.Errorf("schema mismatch: %s", msg)
	}

	log.Printf("WARNING: Schema mismatch for %s:\n%s", modelName, msg)
	return nil
}

// SchemaMismatchTracker tracks reported mismatches to avoid duplicate reports.
// It is safe for concurrent use.
type SchemaMismatchTracker struct {
	mu       sync.Mutex
	reported map[string]bool
}

// NewSchemaMismatchTracker creates a new SchemaMismatchTracker.
func NewSchemaMismatchTracker() *SchemaMismatchTracker {
	return &SchemaMismatchTracker{
		reported: make(map[string]bool),
	}
}

// ShouldReport returns true if the given model and fields have not been reported before.
// It marks them as reported so subsequent calls return false for the same key.
func (t *SchemaMismatchTracker) ShouldReport(modelName string, fields []string) bool {
	t.mu.Lock()
	defer t.mu.Unlock()

	key := modelName + ":" + strings.Join(fields, ",")
	if t.reported[key] {
		return false
	}
	t.reported[key] = true
	return true
}