// Package cyutils provides utility functions for concurrent processing, HTTP requests with caching, and rate limiting.
package cyutils

import (
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"reflect"
	"sync"

	"github.com/bits-and-blooms/bloom/v3"
	"golang.org/x/time/rate"
)

// WithWorkers processes items concurrently using a specified number of worker goroutines.
// It accepts either a slice or map of items and applies the provided function to each item.
// The function receives the worker ID, key, and value for each item.
//
// Parameters:
//   - workers: Number of concurrent workers to spawn
//   - items: Collection of items to process (slice or map)
//   - fn: Function to apply to each item, receives (workerID, key, value)
//
// Example:
//
//	WithWorkers(3, []string{"a", "b", "c"}, func(worker, key, value string) {
//	    fmt.Printf("Worker %d processing %s\n", worker, value)
//	})
func WithWorkers[K comparable, V any, C []V | map[K]V](
	workers int,
	items C,
	fn func(worker int, key K, value V),
) {
	type KV struct {
		// A bit of type weaving...
		Key   any
		Value V
	}

	n := len(items)
	ingestChan := make(chan KV, n)

	go func() {
		switch v := any(items).(type) {
		case []V:
			for i, it := range v {
				ingestChan <- KV{Key: i, Value: it}
			}
		case map[K]V:
			for key, it := range v {
				ingestChan <- KV{Key: key, Value: it}
			}
		}
		close(ingestChan)
	}()

	var wg sync.WaitGroup
	wg.Add(workers)
	for i := 0; i < workers; i++ {
		go func(worker int) {
			defer wg.Done()
			for v := range ingestChan {
				fn(worker, v.Key.(K), v.Value)
			}
		}(i)
	}
	wg.Wait()
}

// Batched processes an array in batches of the specified size.
// The provided function is called for each batch with the batch slice.
//
// Parameters:
//   - arr: Array to process in batches
//   - batchSize: Maximum number of items per batch
//   - fn: Function to call for each batch
//
// Example:
//
//	Batched([]int{1, 2, 3, 4, 5}, 2, func(batch []int) {
//	    fmt.Printf("Processing batch: %v\n", batch)
//	})
func Batched[T any](arr []T, batchSize int, fn func(batch []T)) {
	for i := 0; i < len(arr); i += batchSize {
		start := i
		end := min(i+batchSize, len(arr))
		batch := arr[start:end]
		fn(batch)
	}
}

// RateLimitedTransport wraps an HTTP transport with rate limiting capabilities.
// It enforces request rate limits before executing HTTP requests.
type RateLimitedTransport struct {
	base    http.RoundTripper // Underlying transport
	limiter *rate.Limiter     // Rate limiter
}

// RoundTrip enforces rate limiting before executing the HTTP request.
// It waits for rate limiter permission before delegating to the underlying transport.
// Returns an error if the context is cancelled or times out while waiting.
func (t *RateLimitedTransport) RoundTrip(req *http.Request) (*http.Response, error) {
	ctx := req.Context()
	if err := t.limiter.Wait(ctx); err != nil {
		return nil, err // Handle context cancellation/timeout
	}
	return t.base.RoundTrip(req)
}

// LimitedHTTP creates an HTTP client with rate limiting capabilities.
// The client will respect the specified requests per second (rps) and burst limits.
//
// Parameters:
//   - rps: Maximum requests per second
//   - burst: Maximum burst capacity for rate limiting
//
// Returns an HTTP client configured with rate limiting and connection pooling.
func LimitedHTTP(rps float64, burst int) *http.Client {
	baseTransport := &http.Transport{
		MaxIdleConns:        100,
		MaxIdleConnsPerHost: 10,
	}

	// Initialize rate limiter
	limiter := rate.NewLimiter(rate.Limit(rps), burst)

	// Wrap transport with rate limiting
	transport := &RateLimitedTransport{
		base:    baseTransport,
		limiter: limiter,
	}

	// Return configured client
	return &http.Client{
		Transport: transport,
	}
}

var client = http.DefaultClient

// WithClient sets the default HTTP client used by caching functions.
// This allows customization of the HTTP client for all subsequent cached requests.
//
// Parameters:
//   - nclient: The HTTP client to use for future requests
func WithClient(nclient *http.Client) {
	client = nclient
}

// RequestCached performs an HTTP request with file-based caching.
// If the cache file exists, it returns the cached data. Otherwise, it makes the HTTP request,
// caches the response, and returns the result. For non-[]byte types, it attempts JSON unmarshaling.
//
// Parameters:
//   - req: HTTP request to execute
//   - filename: Path to cache file
//
// Returns the cached or fetched data of type T, or an error if the request fails.
//
// Example:
//
//	var result MyStruct
//	req, _ := http.NewRequest("GET", "https://api.example.com/data", nil)
//	err := RequestCached(req, "cache/data.json", &result)
func RequestCached[T any](req *http.Request, filename string) (T, error) {
	var zero T

	data, err := os.ReadFile(filename)
	if err != nil {
		if !os.IsNotExist(err) {
			return zero, fmt.Errorf("failed to read cache: %w", err)
		}

		resp, httpErr := client.Do(req)
		if httpErr != nil {
			return zero, fmt.Errorf("HTTP request failed: %w", httpErr)
		}
		defer resp.Body.Close()

		body, readErr := io.ReadAll(resp.Body)
		if readErr != nil {
			return zero, fmt.Errorf("failed to read response body: %w", readErr)
		}

		dir := filepath.Dir(filename)
		if dir != "." && dir != "" {
			if mkErr := os.MkdirAll(dir, 0o755); mkErr != nil {
				return zero, fmt.Errorf("failed to create cache dir %s: %w", dir, mkErr)
			}
		}
		if writeErr := os.WriteFile(filename, body, 0o644); writeErr != nil {
			return zero, fmt.Errorf("failed to write cache %s: %w", filename, writeErr)
		}
		data = body
	}

	if _, ok := any(zero).([]byte); ok {
		return any(data).(T), nil
	}

	var out T
	if err := json.Unmarshal(data, &out); err != nil {
		return zero, fmt.Errorf("failed to unmarshal cached response: %w", err)
	}
	return out, nil
}

// RequestCachedBytes is a convenience function for RequestCached that returns raw bytes.
// It's equivalent to calling RequestCached[[]byte] but provides a cleaner API for byte data.
//
// Parameters:
//   - req: HTTP request to execute
//   - filename: Path to cache file
//
// Returns the cached or fetched data as []byte, or an error if the request fails.
func RequestCachedBytes(req *http.Request, filename string) ([]byte, error) {
	return RequestCached[[]byte](req, filename)
}

// Memoized creates a memoized version of the provided function using reflection.
// The returned function caches results based on the string representation of arguments,
// returning cached results for repeated calls with the same arguments.
//
// Parameters:
//   - fn: The function to memoize (must be a function type)
//
// Returns a memoized version of the function with the same signature.
//
// Example:
//
//	func expensive(a string, b int) (string, error) {
//	    fmt.Println("Computing...")
//	    return fmt.Sprintf("Result: %s, %d", a, b), nil
//	}
//
//	memoized := Memoized(expensive).(func(string, int) (string, error))
//	result, _ := memoized("hello", 42) // Computes
//	result, _ = memoized("hello", 42)  // Returns cached result
//
// Note: The cache key is generated using fmt.Sprintf("%v", args), which may not
// uniquely identify all argument combinations. This function is not thread-safe.
func Memoized(fn interface{}) interface{} {
	fnVal := reflect.ValueOf(fn)
	fnType := fnVal.Type()

	cache := make(map[string][]reflect.Value)

	return reflect.MakeFunc(fnType, func(args []reflect.Value) []reflect.Value {
		key := fmt.Sprintf("%v", args)

		if cached, ok := cache[key]; ok {
			return cached
		}

		results := fnVal.Call(args)
		cache[key] = results
		return results
	}).Interface()
}

// MemoizedBloom creates a memoized version of the provided function using a Bloom filter
// to avoid caching "one hit wonders". Results are only cached on the second invocation
// with the same arguments, reducing memory usage for functions with many unique calls.
//
// The function uses a Bloom filter to track which arguments have been seen:
//   - First call: Executes function, adds to Bloom filter, returns result (not cached)
//   - Second call: Executes function, caches result, returns result
//   - Subsequent calls: Returns cached result
//
// Parameters:
//   - fn: The function to memoize (must be a function type)
//   - capacity: Expected number of unique argument combinations (default: 10000)
//   - falsePositiveRate: Desired false positive rate for Bloom filter (default: 0.01)
//
// Returns a memoized version of the function with the same signature.
//
// Example:
//
//	func expensive(a string, b int) (string, error) {
//	    fmt.Println("Computing...")
//	    return fmt.Sprintf("Result: %s, %d", a, b), nil
//	}
//
//	memoized := MemoizedBloom(expensive, 10000, 0.01).(func(string, int) (string, error))
//	result, _ := memoized("hello", 42) // Computes, adds to bloom filter
//	result, _ = memoized("hello", 42)  // Computes again, caches result
//	result, _ = memoized("hello", 42)  // Returns cached result
//
// Note: The cache key is generated using fmt.Sprintf("%v", args), which may not
// uniquely identify all argument combinations. This function is thread-safe.
func MemoizedBloom(fn interface{}, capacity uint, falsePositiveRate float64) interface{} {
	fnVal := reflect.ValueOf(fn)
	fnType := fnVal.Type()

	if capacity == 0 {
		capacity = 10000
	}
	if falsePositiveRate == 0 {
		falsePositiveRate = 0.01
	}

	bf := bloom.NewWithEstimates(capacity, falsePositiveRate)
	cache := make(map[string][]reflect.Value)
	var mu sync.Mutex

	return reflect.MakeFunc(fnType, func(args []reflect.Value) []reflect.Value {
		key := fmt.Sprintf("%v", args)
		keyBytes := []byte(key)

		mu.Lock()
		defer mu.Unlock()

		if cached, ok := cache[key]; ok {
			return cached
		}

		results := fnVal.Call(args)

		if bf.Test(keyBytes) {
			cache[key] = results
		} else {
			bf.Add(keyBytes)
		}

		return results
	}).Interface()
}