// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: PolyForm-Noncommercial-1.0.0

package qrcode

import (
	"os/exec"
	"strings"
	"testing"
)

// reference renders the same symbol with the system qrencode and
// returns its module matrix, or skips the test when the tool is absent.
func reference(t *testing.T, text string) [][]bool {
	t.Helper()
	binary, err := exec.LookPath("qrencode")
	if err != nil {
		t.Skip("qrencode is not installed; the differential test cannot run")
	}
	out, err := exec.Command(binary, "-l", "M", "-m", "0", "--type=ASCII", text).Output()
	if err != nil {
		t.Fatalf("qrencode: %v", err)
	}
	var rows [][]bool
	for line := range strings.SplitSeq(string(out), "\n") {
		line = strings.TrimSuffix(line, "\r")
		if line == "" {
			continue
		}
		// A row may be entirely light modules, which trims to spaces:
		// only a truly empty line separates rows, so nothing is dropped.
		if len(line)%2 != 0 {
			t.Fatalf("odd ASCII line %q", line)
		}
		row := make([]bool, len(line)/2)
		for i := range row {
			row[i] = line[i*2] == '#'
		}
		rows = append(rows, row)
	}
	return rows
}

// referenceMask decodes the mask the reference chose from its own
// format information, using the layout this package writes.
func referenceMask(t *testing.T, ref [][]bool) int {
	t.Helper()
	var word uint
	cells := func(y, x int) uint {
		if ref[y][x] {
			return 1
		}
		return 0
	}
	for i := range 6 {
		word = word<<1 | cells(8, i)
	}
	word = word<<1 | cells(8, 7)
	word = word<<1 | cells(8, 8)
	word = word<<1 | cells(7, 8)
	for i := range 6 {
		word = word<<1 | cells(5-i, 8)
	}
	// The stored word carries the XOR mask; the data sits on top once
	// it is undone.
	return int((word^0x5412)>>10) & 7
}

func diffMatrices(t *testing.T, text string) {
	t.Helper()
	// The reference's own mask, forced: every other bit of the symbol
	// must then match, which proves the encoding, the error correction,
	// the placement and the format information. The mask each encoder
	// picks for itself is a choice among equally valid symbols.
	theirs := reference(t, text)
	mask := referenceMask(t, theirs)
	ours, err := encodeMasked([]byte(text), mask)
	if err != nil {
		t.Fatalf("encode %q: %v", text, err)
	}
	if len(theirs) != len(ours) {
		t.Fatalf("%q: size %d, reference %d", text, len(ours), len(theirs))
	}
	for y := range ours {
		for x := range ours[y] {
			if ours[y][x] != theirs[y][x] {
				t.Fatalf("%q: module differs at (%d,%d)", text, x, y)
			}
		}
	}
}

// TestAgainstQrencode is the proof of the encoder: for the full range
// of payloads, every module must match the reference implementation
// once its own mask is forced. The payloads stay clear of the
// reference's segmentation optimiser: letters and underscores carry no
// alphanumeric runs worth switching for, so it speaks plain byte mode
// the way this package always does.
func TestAgainstQrencode(t *testing.T) {
	payloads := []string{
		"hello world",
		"otpauth_totp_volumen_petr_secret_and_issuer_example_uri",
		"https_petrbalvin_org_neco_delsi_cesta_query_hodnota_druha_ano",
		strings.Repeat("a", 14),  // v1 edge
		strings.Repeat("a", 15),  // v2
		strings.Repeat("b", 84),  // v5 edge
		strings.Repeat("b", 85),  // v6
		strings.Repeat("c", 180), // v9 edge
		strings.Repeat("c", 181), // v10 (16-bit count)
		strings.Repeat("d", 450), // v16 edge
	}
	for i := range 10 {
		payloads = append(payloads, strings.Repeat("x", 1+i*45))
	}
	for _, p := range payloads {
		diffMatrices(t, p)
	}
}

func TestSVGShape(t *testing.T) {
	svg, err := SVG("https://example.com/")
	if err != nil {
		t.Fatalf("SVG: %v", err)
	}
	for _, want := range []string{
		`viewBox="0 0 33 33"`, // v1 + quiet zone
		`<rect width="100%" height="100%" fill="#fff"/>`,
		`fill="#000"`,
		`</svg>`,
	} {
		if !strings.Contains(svg, want) {
			t.Fatalf("missing %q in %s", want, svg[:min(len(svg), 200)])
		}
	}
}

func TestTooLongIsRefused(t *testing.T) {
	if _, err := SVG(strings.Repeat("z", 450)); err != nil {
		t.Fatalf("version 16 capacity refused: %v", err)
	}
	if _, err := SVG(strings.Repeat("z", 451)); err == nil {
		t.Fatal("input beyond version 16 accepted")
	}
}