package postfix

import (
	"bufio"
	"context"
	"fmt"
	"os"
	"os/exec"
	"strings"
	"testing"
)

// TestFakePostqueue is not a test: it is the fake `postqueue -p` the tests
// below run in place of the real one, writing SP_FAKE_POSTQUEUE_BYTES bytes of
// queue entries composed by hand after the layout of Postfix 3.7.11's
// src/postqueue/showq_compat.c.
func TestFakePostqueue(t *testing.T) {
	if os.Getenv("SP_FAKE_POSTQUEUE") != "1" {
		t.Skip("helper process")
	}
	var size int
	fmt.Sscan(os.Getenv("SP_FAKE_POSTQUEUE_BYTES"), &size)
	out := bufio.NewWriter(os.Stdout)
	fmt.Fprintln(out, "-Queue ID-  --Size-- ----Arrival Time---- -Sender/Recipient-------")
	for n, i := 0, 0; n < size; i++ {
		entry := fmt.Sprintf("%010X      446 Fri Aug  8 10:13:31  app@example.com\n%41s rcpt@example.net\n\n", i, "")
		out.WriteString(entry)
		n += len(entry)
	}
	out.Flush()
	os.Exit(0)
}

// fakePostqueue puts a postqueue that lists about size bytes of entries in
// place of the real one for the rest of the test.
func fakePostqueue(t *testing.T, size int) {
	t.Helper()
	old := postqueueP
	postqueueP = func(ctx context.Context) *exec.Cmd {
		cmd := exec.CommandContext(ctx, os.Args[0], "-test.run=^TestFakePostqueue$")
		cmd.Env = append(os.Environ(), "SP_FAKE_POSTQUEUE=1", fmt.Sprintf("SP_FAKE_POSTQUEUE_BYTES=%d", size))
		return cmd
	}
	t.Cleanup(func() { postqueueP = old })
}

// A listing over the cap is no listing for the reconcile sweep: the messages
// past the cut are still queued, and taking the first 4 MiB of ids for the
// whole queue closed every row past it as bounced (audit 2026-10-12, H3).
// The queue page still shows the cut listing, with the note.
func TestQueueIDsRefusesATruncatedListing(t *testing.T) {
	fakePostqueue(t, 5<<20)
	if ids, err := QueueIDs(); err == nil || !strings.Contains(err.Error(), "listing is larger than") {
		t.Fatalf("QueueIDs on a 5 MiB listing = %d ids, %v; want the listing refused for its size", len(ids), err)
	}
	text, err := Queue()
	if err != nil {
		t.Fatalf("Queue on a 5 MiB listing: %v", err)
	}
	if !strings.HasSuffix(text, fmt.Sprintf("[listing truncated at %d bytes]\n", maxQueueOutput)) {
		t.Fatalf("Queue on a 5 MiB listing does not end with the truncation note: ...%q", text[len(text)-80:])
	}
}

func TestQueueIDsReadsAListingUnderTheCap(t *testing.T) {
	fakePostqueue(t, 1000)
	ids, err := QueueIDs()
	if err != nil {
		t.Fatal(err)
	}
	if _, ok := ids["0000000000"]; !ok || len(ids) < 5 {
		t.Fatalf("QueueIDs on a small listing = %v", ids)
	}
}

// The reconcile sweep decides whether a message is still Postfix's problem, so
// the parser must pick queue ids out of a listing and nothing else out of it:
// not the header, not the byte-count trailer, and above all not a deferred
// entry's reason line. The listing is composed by hand. Postfix 3.7.11
// (src/postqueue/showq_compat.c, showq_message()) right-aligns a reason to
// column 76, so it reaches the left margin only when it is 76 characters or
// longer; the one here is put at the margin as the hard case.
func TestParseQueueIDs(t *testing.T) {
	listing := `-Queue ID-  --Size-- ----Arrival Time---- -Sender/Recipient-------
3C5B04E6C1*     446 Fri Aug  8 10:12:31  app@example.com
                                         rcpt@example.net

5B4A2C1D3E      446 Fri Aug  8 10:13:31  app@example.com
(connect to mx.example.net[203.0.113.9]:25: Connection timed out)
                                         deferred@example.net

A1B2C3D4E5F!    891 Fri Aug  8 10:14:31  app@example.com
                                         held@example.net

-- 1 Kbytes in 3 Requests.
`
	ids := parseQueueIDs(listing)
	want := []string{"3C5B04E6C1", "5B4A2C1D3E", "A1B2C3D4E5F"}
	for _, id := range want {
		if _, ok := ids[id]; !ok {
			t.Errorf("queue id %s not found in %v", id, ids)
		}
	}
	if len(ids) != len(want) {
		t.Errorf("got %d ids %v, want exactly %v", len(ids), ids, want)
	}
}

// An empty queue must come back as an empty set, not as a phantom id parsed out
// of Postfix's prose — every stale row would otherwise be compared against a
// listing that claims to hold a message called "Mail".
func TestParseQueueIDsOnAnEmptyQueue(t *testing.T) {
	if ids := parseQueueIDs("Mail queue is empty\n"); len(ids) != 0 {
		t.Errorf("got %v, want no ids", ids)
	}
}

// The queue listing is held in memory and rendered into a page, so a very large
// queue must not size the panel's allocation: the writer keeps the cap and
// reports the rest as dropped, while still accepting every write so postqueue
// itself is never cut short.
func TestLimitWriterCapsOutput(t *testing.T) {
	w := &limitWriter{remaining: 8}
	n, err := w.Write([]byte("12345"))
	if n != 5 || err != nil {
		t.Fatalf("first write = %d, %v", n, err)
	}
	if w.truncated {
		t.Fatal("truncated before the cap was reached")
	}
	n, err = w.Write([]byte("67890"))
	if n != 5 || err != nil {
		t.Fatalf("second write = %d, %v", n, err)
	}
	if !w.truncated {
		t.Fatal("write past the cap was not recorded as truncated")
	}
	if got := w.buf.String(); got != "12345678" {
		t.Fatalf("kept %q, want the first 8 bytes", got)
	}
	if n, err := w.Write([]byte("more")); n != 4 || err != nil {
		t.Fatalf("write after the cap = %d, %v (must still accept)", n, err)
	}
	if got := w.buf.String(); got != "12345678" {
		t.Fatalf("buffer grew past the cap: %q", got)
	}
}