package fileops

import (
	"os"
	"testing"
)

func writeTempFile(t *testing.T, content string) string {
	t.Helper()
	f, err := os.CreateTemp(t.TempDir(), "ts-test-*.txt")
	if err != nil {
		t.Fatal(err)
	}
	if _, err := f.WriteString(content); err != nil {
		t.Fatal(err)
	}
	f.Close()
	return f.Name()
}

func readTempFile(t *testing.T, path string) string {
	t.Helper()
	b, err := os.ReadFile(path)
	if err != nil {
		t.Fatal(err)
	}
	return string(b)
}

func equalIntSlice(a, b []int) bool {
	if len(a) != len(b) {
		return false
	}
	for i := range a {
		if a[i] != b[i] {
			return false
		}
	}
	return true
}

func TestReplaceInFile(t *testing.T) {
	tests := []struct {
		name        string
		content     string
		from, to    string
		dryRun      bool
		wantLines   []int
		wantContent string
	}{
		{
			name:        "single occurrence",
			content:     "foo bar\nbaz\n",
			from:        "foo",
			to:          "qux",
			wantLines:   []int{1},
			wantContent: "qux bar\nbaz\n",
		},
		{
			name:        "multiple occurrences on same line",
			content:     "foo foo foo\n",
			from:        "foo",
			to:          "x",
			wantLines:   []int{1},
			wantContent: "x x x\n",
		},
		{
			name:        "occurrences across multiple lines",
			content:     "keep\nfoo here\nalso foo\n",
			from:        "foo",
			to:          "bar",
			wantLines:   []int{2, 3},
			wantContent: "keep\nbar here\nalso bar\n",
		},
		{
			name:        "no match leaves file unchanged",
			content:     "hello world\n",
			from:        "xyz",
			to:          "abc",
			wantLines:   nil,
			wantContent: "hello world\n",
		},
		{
			name:        "dry run reports lines but does not write",
			content:     "foo bar\n",
			from:        "foo",
			to:          "baz",
			dryRun:      true,
			wantLines:   []int{1},
			wantContent: "foo bar\n",
		},
		{
			name:        "empty file",
			content:     "",
			from:        "foo",
			to:          "bar",
			wantLines:   nil,
			wantContent: "",
		},
		{
			name:        "replacement on last line without trailing newline",
			content:     "line1\nfoo",
			from:        "foo",
			to:          "bar",
			wantLines:   []int{2},
			wantContent: "line1\nbar\n",
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			path := writeTempFile(t, tt.content)
			res, err := ReplaceInFile(path, tt.from, tt.to, tt.dryRun)
			if err != nil {
				t.Fatalf("unexpected error: %v", err)
			}
			if !equalIntSlice(res.ChangedLines, tt.wantLines) {
				t.Errorf("ChangedLines = %v, want %v", res.ChangedLines, tt.wantLines)
			}
			got := readTempFile(t, path)
			if got != tt.wantContent {
				t.Errorf("file content = %q, want %q", got, tt.wantContent)
			}
		})
	}
}

func TestReplaceInFile_MissingFile(t *testing.T) {
	_, err := ReplaceInFile("/no/such/file.txt", "x", "y", false)
	if err == nil {
		t.Error("expected error for missing file, got nil")
	}
}

func TestReplaceInFileRegex(t *testing.T) {
	tests := []struct {
		name        string
		content     string
		pattern     string
		repl        string
		dryRun      bool
		wantLines   []int
		wantContent string
		wantErr     bool
	}{
		{
			name:        "basic regex replacement",
			content:     "foo123\nbar\nfoo456\n",
			pattern:     `foo\d+`,
			repl:        "replaced",
			wantLines:   []int{1, 3},
			wantContent: "replaced\nbar\nreplaced\n",
		},
		{
			name:        "capture group substitution",
			content:     "hello world\n",
			pattern:     `(hello) (world)`,
			repl:        "$2 $1",
			wantLines:   []int{1},
			wantContent: "world hello\n",
		},
		{
			name:        "no match",
			content:     "no match here\n",
			pattern:     `\d+`,
			repl:        "NUM",
			wantLines:   nil,
			wantContent: "no match here\n",
		},
		{
			name:    "invalid regex returns error",
			content: "foo\n",
			pattern: `[invalid`,
			repl:    "x",
			wantErr: true,
		},
		{
			name:        "dry run with regex",
			content:     "abc123\n",
			pattern:     `\d+`,
			repl:        "NUM",
			dryRun:      true,
			wantLines:   []int{1},
			wantContent: "abc123\n",
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			path := writeTempFile(t, tt.content)
			res, err := ReplaceInFileRegex(path, tt.pattern, tt.repl, tt.dryRun)
			if tt.wantErr {
				if err == nil {
					t.Error("expected error, got nil")
				}
				return
			}
			if err != nil {
				t.Fatalf("unexpected error: %v", err)
			}
			if !equalIntSlice(res.ChangedLines, tt.wantLines) {
				t.Errorf("ChangedLines = %v, want %v", res.ChangedLines, tt.wantLines)
			}
			got := readTempFile(t, path)
			if got != tt.wantContent {
				t.Errorf("file content = %q, want %q", got, tt.wantContent)
			}
		})
	}
}

func TestFormatLineNums(t *testing.T) {
	tests := []struct {
		nums []int
		want string
	}{
		{[]int{1}, "1"},
		{[]int{1, 2, 3}, "1, 2, 3"},
		{[]int{10, 47}, "10, 47"},
	}
	for _, tt := range tests {
		got := formatLineNums(tt.nums)
		if got != tt.want {
			t.Errorf("formatLineNums(%v) = %q, want %q", tt.nums, got, tt.want)
		}
	}
}