package main

import (
	"context"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"testing"
	"time"
)

// fake is a machine for a test: a tree standing in for /proc and /sys, a statfs answering from a table,
// a runner answering from a table, and a wait that turns the tree into its second reading.
type fake struct {
	t       *testing.T
	root    string
	later   map[string]string
	gone    []string
	space   map[string]FSStat
	answers map[string]string
	calls   []string
	waited  time.Duration
}

func newFake(t *testing.T) *fake {
	t.Helper()
	return &fake{t: t, root: t.TempDir(), later: map[string]string{}, space: map[string]FSStat{}, answers: map[string]string{}}
}

func (f *fake) machine() *Machine {
	return &Machine{
		Root: f.root,
		Run: func(_ context.Context, name string, args ...string) (string, error) {
			line := strings.TrimSpace(name + " " + strings.Join(args, " "))
			f.calls = append(f.calls, line)
			if out, ok := f.answers[line]; ok {
				return out, nil
			}
			return "", fmt.Errorf("%s: not found", name)
		},
		Wait: func(d time.Duration) {
			f.waited += d
			for p, c := range f.later {
				f.file(p, c)
			}
			for _, p := range f.gone {
				os.RemoveAll(filepath.Join(f.root, p))
			}
		},
		Statfs: func(path string) (FSStat, error) {
			rel, _ := filepath.Rel(f.root, path)
			s, ok := f.space[filepath.Clean("/"+filepath.ToSlash(rel))]
			if !ok {
				return FSStat{}, fmt.Errorf("no such filesystem")
			}
			return s, nil
		},
	}
}

// file writes a file under the fake root.
func (f *fake) file(path, content string) {
	f.t.Helper()
	full := filepath.Join(f.root, path)
	if err := os.MkdirAll(filepath.Dir(full), 0o755); err != nil {
		f.t.Fatal(err)
	}
	if err := os.WriteFile(full, []byte(content), 0o644); err != nil {
		f.t.Fatal(err)
	}
}

// dir makes a directory under the fake root: sysfs's entries that are links on a real machine are
// directories here, because the module only lists their names.
func (f *fake) dir(path string) {
	f.t.Helper()
	if err := os.MkdirAll(filepath.Join(f.root, path), 0o755); err != nil {
		f.t.Fatal(err)
	}
}

// then is a file's content at the second reading.
func (f *fake) then(path, content string) { f.later[path] = content }