// package fetcher handles HTTP downloads and SHA-1 verification.
package fetcher

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

	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/pkg/utils"
)

// Download downloads a URL to dest, optionally verifying its SHA-1 hash.
// onProgress is called with (downloaded, total) bytes; total may be -1 if unknown.
func Download(url, dest, expectedSHA1 string, onProgress func(downloaded, total int64)) error {
	resp, err := http.Get(url)
	if err != nil {
		return fmt.Errorf("GET %s: %w", url, err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("GET %s → %d", url, resp.StatusCode)
	}

	if err := os.MkdirAll(filepath.Dir(dest), 0o755); err != nil {
		return fmt.Errorf("creating parent for %s: %w", dest, err)
	}

	tmp := dest + ".part"
	f, err := os.Create(tmp)
	if err != nil {
		return fmt.Errorf("creating %s: %w", tmp, err)
	}

	total := resp.ContentLength
	var written int64
	buf := make([]byte, 32*1024) // 32 KiB buffer

	for {
		n, readErr := resp.Body.Read(buf)
		if n > 0 {
			if _, writeErr := f.Write(buf[:n]); writeErr != nil {
				f.Close()
				os.Remove(tmp)
				return fmt.Errorf("writing %s: %w", tmp, writeErr)
			}
			written += int64(n)
			if onProgress != nil {
				onProgress(written, total)
			}
		}
		if readErr == io.EOF {
			break
		}
		if readErr != nil {
			f.Close()
			os.Remove(tmp)
			return fmt.Errorf("reading %s: %w", url, readErr)
		}
	}
	f.Close()

	// Verify SHA-1 if expected hash provided.
	if expectedSHA1 != "" {
		got, err := utils.SHA1File(tmp)
		if err != nil {
			os.Remove(tmp)
			return fmt.Errorf("hashing %s: %w", tmp, err)
		}
		if got != expectedSHA1 {
			os.Remove(tmp)
			return fmt.Errorf("SHA-1 mismatch: expected %s, got %s", expectedSHA1, got)
		}
	}

	return os.Rename(tmp, dest)
}

// WorkerPool runs download jobs concurrently with a bounded number of workers.
type WorkerPool struct {
	workers int
	jobs    chan func()
	wg      sync.WaitGroup
}

// NewWorkerPool creates a pool with the given number of workers.
func NewWorkerPool(workers int) *WorkerPool {
	p := &WorkerPool{
		workers: workers,
		jobs:    make(chan func(), 100),
	}
	for i := 0; i < workers; i++ {
		p.wg.Add(1)
		go func() {
			defer p.wg.Done()
			for job := range p.jobs {
				job()
			}
		}()
	}
	return p
}

// Submit adds a job to the pool.
func (p *WorkerPool) Submit(job func()) {
	p.jobs <- job
}

// Wait blocks until all submitted jobs are finished.
func (p *WorkerPool) Wait() {
	close(p.jobs)
	p.wg.Wait()
}