package download

import (
	"bytes"
	"context"
	"crypto/sha256"
	"encoding/hex"
	"net/http"
	"net/http/httptest"
	"os"
	"path/filepath"
	"strings"
	"testing"
)

func sha256Hex(b []byte) string {
	sum := sha256.Sum256(b)
	return hex.EncodeToString(sum[:])
}

func serveBody(t *testing.T, body []byte) *httptest.Server {
	t.Helper()
	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "application/octet-stream")
		_, _ = w.Write(body)
	}))
	t.Cleanup(srv.Close)
	return srv
}

func TestFetchVerifiedHappyPath(t *testing.T) {
	body := bytes.Repeat([]byte("ok"), 1024)
	srv := serveBody(t, body)
	dst := filepath.Join(t.TempDir(), "out")

	n, err := FetchVerified(context.Background(), srv.Client(), srv.URL, sha256Hex(body), 1<<20, dst)
	if err != nil {
		t.Fatalf("FetchVerified: %v", err)
	}
	if n != int64(len(body)) {
		t.Fatalf("n = %d, want %d", n, len(body))
	}
	got, _ := os.ReadFile(dst)
	if !bytes.Equal(got, body) {
		t.Fatalf("file content differs from served body")
	}
}

func TestFetchVerifiedRejectsHashMismatch(t *testing.T) {
	body := []byte("payload")
	srv := serveBody(t, body)
	dst := filepath.Join(t.TempDir(), "out")
	wrongHash := sha256Hex([]byte("other"))

	_, err := FetchVerified(context.Background(), srv.Client(), srv.URL, wrongHash, 1<<10, dst)
	if err == nil || !strings.Contains(err.Error(), "sha256 mismatch") {
		t.Fatalf("err = %v, want sha256 mismatch", err)
	}
	if _, statErr := os.Stat(dst); !os.IsNotExist(statErr) {
		t.Fatalf("partial file should be removed; stat err = %v", statErr)
	}
}

func TestFetchVerifiedRejectsContentLengthOverCap(t *testing.T) {
	body := bytes.Repeat([]byte("x"), 2048)
	srv := serveBody(t, body)
	dst := filepath.Join(t.TempDir(), "out")

	_, err := FetchVerified(context.Background(), srv.Client(), srv.URL, sha256Hex(body), 64, dst)
	if err == nil || !strings.Contains(err.Error(), "cap") {
		t.Fatalf("err = %v, want cap rejection", err)
	}
	if _, statErr := os.Stat(dst); !os.IsNotExist(statErr) {
		t.Fatalf("dst created despite oversize Content-Length: %v", statErr)
	}
}

func TestFetchVerifiedRejectsLyingContentLength(t *testing.T) {
	// Server returns no Content-Length but a body bigger than cap.
	body := bytes.Repeat([]byte("y"), 2048)
	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Force chunked: don't set Content-Length.
		_, _ = w.Write(body)
	}))
	t.Cleanup(srv.Close)
	dst := filepath.Join(t.TempDir(), "out")

	_, err := FetchVerified(context.Background(), srv.Client(), srv.URL, sha256Hex(body), 64, dst)
	if err == nil || !strings.Contains(err.Error(), "cap") {
		t.Fatalf("err = %v, want cap rejection on lying server", err)
	}
	if _, statErr := os.Stat(dst); !os.IsNotExist(statErr) {
		t.Fatalf("partial file from lying server should be removed; stat err = %v", statErr)
	}
}

func TestFetchVerifiedRejectsHTTPError(t *testing.T) {
	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		http.Error(w, "missing", http.StatusNotFound)
	}))
	t.Cleanup(srv.Close)
	dst := filepath.Join(t.TempDir(), "out")

	_, err := FetchVerified(context.Background(), srv.Client(), srv.URL, sha256Hex([]byte{}), 1<<10, dst)
	if err == nil || !strings.Contains(err.Error(), "404") {
		t.Fatalf("err = %v, want 404 mention", err)
	}
}

func TestFetchVerifiedRejectsEmptyExpectedSHA(t *testing.T) {
	srv := serveBody(t, []byte("body"))
	dst := filepath.Join(t.TempDir(), "out")
	_, err := FetchVerified(context.Background(), srv.Client(), srv.URL, "", 1<<10, dst)
	if err == nil || !strings.Contains(err.Error(), "expectedSHA256") {
		t.Fatalf("err = %v, want empty-sha rejection", err)
	}
}

func TestFetchVerifiedRejectsZeroMaxBytes(t *testing.T) {
	srv := serveBody(t, []byte("body"))
	dst := filepath.Join(t.TempDir(), "out")
	_, err := FetchVerified(context.Background(), srv.Client(), srv.URL, sha256Hex([]byte("body")), 0, dst)
	if err == nil || !strings.Contains(err.Error(), "maxBytes") {
		t.Fatalf("err = %v, want maxBytes rejection", err)
	}
}