package build

import (
	"os"
	"path/filepath"
	"strings"
	"testing"
)

func TestEnsureToolchain(t *testing.T) {
	cases := []struct {
		name string
		in   string
		want string
	}{
		{
			name: "missing line is added after go",
			in:   "go 1.27\n\nuse .\n",
			want: "go 1.27\n\n" + toolchainLine + "\n\nuse .\n",
		},
		{
			name: "our line is kept",
			in:   "go 1.27\n\n" + toolchainLine + "\n",
			want: "go 1.27\n\n" + toolchainLine + "\n",
		},
		{
			name: "newer toolchain is kept, not repeated",
			in:   "go 1.27\n\ntoolchain go1.99.2\n\nuse .\n",
			want: "go 1.27\n\ntoolchain go1.99.2\n\nuse .\n",
		},
		{
			name: "older toolchain is replaced",
			in:   "module x\n\ngo 1.25\n\ntoolchain go1.25.1\n",
			want: "module x\n\ngo 1.25\n\n" + toolchainLine + "\n",
		},
	}
	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			path := filepath.Join(t.TempDir(), "go.work")
			if err := os.WriteFile(path, []byte(tc.in), 0o644); err != nil {
				t.Fatal(err)
			}
			if err := ensureToolchain(path); err != nil {
				t.Fatalf("ensureToolchain: %v", err)
			}
			got, err := os.ReadFile(path)
			if err != nil {
				t.Fatal(err)
			}
			if string(got) != tc.want {
				t.Fatalf("got:\n%s\nwant:\n%s", got, tc.want)
			}
			if n := strings.Count(string(got), "\ntoolchain "); n != 1 {
				t.Fatalf("got %d toolchain lines, want 1", n)
			}
		})
	}
}