// SPDX-License-Identifier: GPL-3.0-or-later

package engine

import (
	"context"
	"fmt"
	"math/rand"
	"os"
	"path/filepath"
	"reflect"
	"strconv"
	"strings"
	"testing"
	"time"

	"krino/internal/journal"
	"krino/internal/plan"
)

// propertyNames are the file names generated trees draw from: ordinary,
// spaced, Polish, dash-led, newline-holding, double-extension and hidden.
var propertyNames = []string{"a.pdf", "b.pdf", "a copy.pdf", "zażółć.txt", "-dash.pdf", "new\nline.pdf", "notes.txt", "x.tar.gz", ".hidden.pdf"}

// propertyCase is one generated tree and rule set.
type propertyCase struct {
	files    map[string]string // path under ~/dl -> content
	existing map[string]string // path under ~ -> content, there before planning to force conflicts
	rules    string            // dirs/dl.conf
}

// genCase draws a case from r: one to six files (some nested, some sharing
// content), up to two files already sitting in destinations, and one to
// three rules mixing moves, copies, renames and trash under every conflict
// policy, with and without (stop). A (delete) is only ever a rule's last
// action - the config refuses any action after it. Permanent delete is left
// out: it cannot be undone by design.
func genCase(r *rand.Rand) propertyCase {
	c := propertyCase{files: map[string]string{}, existing: map[string]string{}}
	for i := 0; i < 1+r.Intn(6); i++ {
		name := propertyNames[r.Intn(len(propertyNames))]
		if r.Intn(3) == 0 {
			name = "sub/" + name
		}
		c.files[name] = []string{"one", "two", "one"}[r.Intn(3)] + " " + strconv.Itoa(r.Intn(3))
	}
	for i := 0; i < r.Intn(3); i++ {
		dir := []string{"dl/Out", "dl/Out/2026", "backup"}[r.Intn(3)]
		c.existing[dir+"/"+propertyNames[r.Intn(len(propertyNames))]] = "already here"
	}
	conds := []string{"", "(when (type pdf))", `(when (name "^a"))`, "(when (not (type txt)))"}
	actions := []string{`(move "Out")`, `(move "Out/{mtime:%Y}")`, `(copy "~/backup")`, `(rename "r-{name}")`}
	conflicts := []string{"", "(on-conflict suffix)", "(on-conflict skip)", "(on-conflict overwrite)"}
	var b strings.Builder
	b.WriteString("(path \"~/dl\")\n")
	if r.Intn(2) == 0 {
		b.WriteString("(recursive yes)\n")
	}
	for i := 0; i < 1+r.Intn(3); i++ {
		fmt.Fprintf(&b, "(rule \"r%d\" %s %s", i, conflicts[r.Intn(len(conflicts))], conds[r.Intn(len(conds))])
		for j := 0; j < 1+r.Intn(2); j++ {
			b.WriteString(" " + actions[r.Intn(len(actions))])
		}
		if r.Intn(4) == 0 {
			b.WriteString(" (delete)")
		}
		if r.Intn(2) == 0 {
			b.WriteString(" (stop)")
		}
		b.WriteString(")\n")
	}
	c.rules = b.String()
	return c
}

// propertySeeds is the seeds TestApplyUndoProperty runs: KRINO_PROPERTY_SEED
// alone when set (to rerun a failure), else 1..KRINO_PROPERTY_RUNS, 40 by
// default - raise it (say 2000) before a release.
func propertySeeds(t *testing.T) []int64 {
	if v := os.Getenv("KRINO_PROPERTY_SEED"); v != "" {
		s, err := strconv.ParseInt(v, 10, 64)
		if err != nil {
			t.Fatalf("KRINO_PROPERTY_SEED=%q", v)
		}
		return []int64{s}
	}
	n := 40
	if v := os.Getenv("KRINO_PROPERTY_RUNS"); v != "" {
		var err error
		if n, err = strconv.Atoi(v); err != nil || n < 1 {
			t.Fatalf("KRINO_PROPERTY_RUNS=%q", v)
		}
	}
	seeds := make([]int64, n)
	for i := range seeds {
		seeds[i] = int64(i + 1)
	}
	return seeds
}

// TestApplyUndoProperty: for generated trees and rules, applying every
// chain loses no content - every file's content is still somewhere under
// the home directory, the Trash included - and undoing the run then puts
// the home directory back exactly: every file's content, mode and
// modification time, and nothing extra. A failing subtest names its seed.
func TestApplyUndoProperty(t *testing.T) {
	for _, seed := range propertySeeds(t) {
		t.Run(fmt.Sprintf("seed=%d", seed), func(t *testing.T) {
			checkApplyUndo(t, genCase(rand.New(rand.NewSource(seed))))
		})
	}
}

// contentCounts counts the files of a snapshot by content hash.
func contentCounts(snap map[string]string) map[string]int {
	counts := map[string]int{}
	for _, v := range snap {
		counts[strings.Fields(v)[0]]++
	}
	return counts
}

// checkApplyUndo builds c in a sandbox, applies every chain, checks nothing
// was lost, undoes the run and checks the home directory is as it was.
func checkApplyUndo(t *testing.T, c propertyCase) {
	h := sandbox(t)
	old := time.Date(2026, 3, 1, 12, 0, 0, 0, time.UTC)
	put := func(p, body string) {
		t.Helper()
		if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
			t.Fatal(err)
		}
		if err := os.WriteFile(p, []byte(body), 0o644); err != nil {
			t.Fatal(err)
		}
		if err := os.Chtimes(p, old, old); err != nil {
			t.Fatal(err)
		}
	}
	if err := os.MkdirAll(filepath.Join(h, "dl"), 0o755); err != nil {
		t.Fatal(err)
	}
	for rel, body := range c.files {
		put(filepath.Join(h, "dl", rel), body)
	}
	for rel, body := range c.existing {
		put(filepath.Join(h, rel), body)
	}
	main := writeConfig(t, h, `(include "dl")`, map[string]string{"dl": c.rules})
	// userTree is the home directory without krino's own config and state.
	userTree := func() map[string]string {
		snap := snapshot(t, h)
		for rel := range snap {
			if strings.HasPrefix(rel, ".config/") || strings.HasPrefix(rel, ".local/") {
				delete(snap, rel)
			}
		}
		return snap
	}
	before := userTree()
	t.Logf("rules:\n%s", c.rules)

	e, errs := Load(main)
	if len(errs) > 0 {
		t.Fatalf("generated rules do not load: %v", errs)
	}
	ctx := context.Background()
	dp, err := e.Plan(ctx, e.Dirs[0], plan.NewClaims())
	if err != nil {
		t.Fatal(err)
	}
	approved := map[string]bool{}
	for _, ch := range dp.Chains {
		approved[ch.File.Rel] = true
	}
	logPath := filepath.Join(h, ".local", "state", "krino", "krino.log")
	j, err := journal.Open(logPath)
	if err != nil {
		t.Fatal(err)
	}
	run := journal.NewRunID(time.Now())
	res, err := e.Apply(ctx, dp, approved, j, run)
	j.Close()
	if err != nil {
		t.Fatal(err)
	}
	if res.Failed != 0 {
		t.Fatalf("%d files failed to apply: %+v", res.Failed, res.Files)
	}
	if len(res.Files) == 0 {
		// No file had a step, so nothing ran and nothing was logged: there
		// is no run to undo, and the tree must simply be untouched.
		if after := userTree(); !reflect.DeepEqual(after, before) {
			t.Fatalf("nothing was applied, yet the tree changed")
		}
		return
	}

	have := contentCounts(snapshot(t, h))
	for hash, n := range contentCounts(before) {
		if have[hash] < n {
			t.Errorf("after apply, content %s is in %d files, was in %d", hash[:12], have[hash], n)
		}
	}

	up, err := e.PlanUndo(run)
	if err != nil {
		t.Fatal(err)
	}
	for _, f := range up.Files {
		if f.Refused != "" {
			t.Fatalf("undo refused %q: %s", f.File, f.Refused)
		}
	}
	j2, err := journal.Open(logPath)
	if err != nil {
		t.Fatal(err)
	}
	ures, err := e.ApplyUndo(ctx, up, j2, journal.NewRunID(time.Now()))
	j2.Close()
	if err != nil {
		t.Fatal(err)
	}
	if ures.Failed != 0 {
		t.Fatalf("%d files failed to undo: %+v", ures.Failed, ures.Files)
	}
	if after := userTree(); !reflect.DeepEqual(after, before) {
		for rel, v := range before {
			if after[rel] != v {
				t.Errorf("%q after undo: %q, want %q", rel, after[rel], v)
			}
		}
		for rel := range after {
			if _, ok := before[rel]; !ok {
				t.Errorf("%q is left behind after undo", rel)
			}
		}
	}
}