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

package main

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"sort"
	"strconv"
	"strings"

	"golang.org/x/term"

	"krino/internal/config"
	"krino/internal/engine"
	"krino/internal/journal"
	"krino/internal/lock"
	"krino/internal/tui"
	"krino/internal/xdg"
)

func init() { commands["undo"] = cmdUndo }

// cmdUndo reverses a run: the one named on the command line, or (spec §10)
// the most recent one otherwise. Since the newest run in the log can never
// itself be marked Undone - that would require a still-later run to have
// reversed it - "the most recent run" and "the most recent run that has not
// been undone" are the same run in every case, including the one this
// task's own test exercises: undoing an undo run a second time with no RUN
// argument targets that very undo run, which PlanUndo then refuses by name.
//
// Undo builds a plan like any other, shown and approved the same way (spec
// §10) - reviewUndoDir/-Files/-PerFile below are undo's own counterpart to
// review.go's reviewChains/reviewPerFile, not a call into them: an undo plan
// is []engine.UndoFile, which can span several directories in one flat
// list, so two files from different directories can share the same Rel and
// approval here is keyed by index rather than by name.
func cmdUndo(g *globals, args []string, stdout, stderr io.Writer) int {
	fs := flagSet("undo", g)
	// The defaults are the values run() already parsed, so -y or -n written
	// before "undo" survives registering them again here.
	fs.BoolVar(&g.yes, "y", g.yes, "")
	fs.BoolVar(&g.dry, "n", g.dry, "")
	if code, ok := parse(fs, args, stdout, stderr); !ok {
		return code
	}
	if g.yes && g.dry {
		return usageError(stderr, "-y and -n cannot be used together")
	}
	rest := fs.Args()
	if len(rest) > 1 {
		return usageError(stderr, "usage: krino undo [RUN]")
	}

	e, errs := engine.Load(mainFile(g))
	if len(errs) > 0 {
		printDiags(stderr, errs)
		return 2
	}
	p := palette{on: colourOn(g, stdout)}

	// Spec §8.4/§10: with neither -y nor -n, krino asks; a non-terminal
	// stdin would just hang, so it refuses instead - the same check
	// cmdSort makes before it ever shows a plan.
	if !g.yes && !g.dry && !term.IsTerminal(int(stdin.Fd())) {
		return usageError(stderr, "refusing to prompt: stdin is not a terminal (use -y or -n)")
	}

	// Installed here, before any paging or review, not just around
	// ApplyUndo: Ruling 5 (Task 7) is that SIGTERM landing between
	// keystrokes or during the pager needs the terminal restored, and that
	// window starts as soon as this command might show something on a
	// terminal.
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	stopSignals := installSignalHandler(cancel)
	defer stopSignals()

	runID := ""
	if len(rest) == 1 {
		runID = rest[0]
	} else {
		runs, err := e.Runs(1)
		if err != nil {
			if errors.Is(err, os.ErrNotExist) {
				fmt.Fprintln(stdout, "nothing logged yet; nothing to undo")
				return 0
			}
			fmt.Fprintf(stderr, "krino: %v\n", err)
			return 1
		}
		if len(runs) == 0 {
			fmt.Fprintln(stdout, "nothing logged yet; nothing to undo")
			return 0
		}
		runID = runs[0].ID
	}

	// PlanUndo only reads the log; nothing is touched yet (spec §10), which
	// is what makes it safe to call before any lock is taken.
	up, err := e.PlanUndo(runID)
	if err != nil {
		fmt.Fprintf(stderr, "krino: %v\n", err)
		return 1
	}

	// Fix round 2026-09-12 (widened per the coordinator's follow-up
	// ruling): an undo moves files just as an apply does, so it needs
	// cmdSort's same per-directory guard (spec §11: a second krino on the
	// same directory waits for the lock, or fails immediately with -y),
	// held across the SAME window cmdSort holds its own lock across - the
	// plan display and the review, not just the apply. Failing before the
	// plan is even shown is strictly kinder than making the user review
	// (potentially hundreds of files) only to be refused afterward, and it
	// means a plan actually reviewed cannot go stale under the reader's
	// eyes from another krino moving those same files mid-review. -n never
	// reaches this: it changes nothing, so it takes no lock either. One
	// undo run can span several directories (UndoFile.Dir is per file), so
	// every distinct one up.Files touches is locked, in a fixed (sorted)
	// order, and released on every path below - including [s]/[q], every
	// early return, and a later ApplyUndo failure - by the single defer
	// right after acquisition.
	var locks []*lock.Lock
	if !g.dry {
		locks, err = acquireUndoLocks(ctx, e.Config, undoDirNames(up.Files), !g.yes)
		if err != nil {
			if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
				return 130
			}
			fmt.Fprintf(stderr, "krino: %v\n", err)
			return 1
		}
		defer func() {
			for _, rerr := range releaseUndoLocks(locks) {
				fmt.Fprintf(stderr, "krino: %v\n", rerr)
			}
		}()
	}

	fmt.Fprintln(stdout, p.bold("krino: undo "+up.Run))
	var buf bytes.Buffer
	printUndoPlan(&buf, up)
	text := colourRefused(buf.String(), p)
	// Ruling 6 (Task 7), carried over: the plan goes through tui.Page for
	// -n as much as for -y and the interactive path.
	if err := tui.Page(stdout, text); err != nil {
		fmt.Fprintf(stderr, "krino: %v\n", err)
		return 1
	}

	if g.dry {
		return 0
	}

	if undoActionableCount(up.Files) == 0 {
		// Every file was refused, or the run touched none at all: neither
		// -y nor the interactive menu has anything useful to do (mirrors
		// cmdSort's identical check before it ever asks).
		fmt.Fprintln(stdout, zeroOutcome)
		return 0
	}

	var approved map[int]bool
	var action rune
	if g.yes {
		approved, action = approveAllUndo(up.Files), 'a'
	} else {
		var rerr error
		approved, action, rerr = reviewUndoDir(stdout, up.Files, p)
		if rerr != nil {
			fmt.Fprintf(stderr, "krino: %v\n", rerr)
			return 1
		}
	}

	if action == 's' || action == 'q' {
		fmt.Fprintln(stdout, zeroOutcome)
		return 0
	}

	toApply := finalizeUndoPlan(up, approved)

	// Ruling 2 (Task 7), carried over: journal.Open creates the state
	// directory and the log file as a side effect of merely being called,
	// so it is opened only once we know something will actually be
	// applied - never for -n (returned above), and not merely because -y
	// or a review session ran, unlike cmdSort's own eager-open (which opens
	// before it knows whether anything is actionable, a difference forced
	// by cmdSort not yet having a plan to inspect at that point in its
	// flow; undo already does, so it opens later, and never opens if
	// undoActionableCount was 0 or the user chose [s]/[q] above).
	j, err := journal.Open(e.Config.LogFile())
	if err != nil {
		fmt.Fprintf(stderr, "krino: %v\n", err)
		return 1
	}
	defer func() {
		if cerr := j.Close(); cerr != nil {
			fmt.Fprintf(stderr, "krino: %v\n", cerr)
		}
	}()
	run := journal.NewRunID(e.Now())

	res, aerr := e.ApplyUndo(ctx, toApply, j, run)
	if aerr != nil {
		if errors.Is(aerr, context.Canceled) || errors.Is(aerr, context.DeadlineExceeded) {
			// Interrupted mid-apply: the ctx.Err() check below turns this
			// into exit 130, same as cmdSort.
			return 130
		}
		fmt.Fprintf(stderr, "krino: %v\n", aerr)
		return 1
	}
	fmt.Fprintln(stdout, outcome(p, res.Applied, res.Failed, res.Declined))

	if ctx.Err() != nil {
		return 130
	}
	if res.Failed > 0 {
		return 1
	}
	return 0
}

// undoActionableCount counts the files in files that PlanUndo has not
// already refused - the same "is there anything to even ask about" gate
// cmdSort's actionableChains serves for a sort plan.
func undoActionableCount(files []engine.UndoFile) int {
	n := 0
	for _, f := range files {
		if f.Refused == "" {
			n++
		}
	}
	return n
}

// undoDirNames returns the distinct directory names an undo plan's files
// touch, sorted: a fixed order so two processes each locking a plan that
// shares more than one directory always acquire them in the same sequence,
// the standard way to avoid a lock-order deadlock. UndoFile.Dir is the
// journal's own `dir` column - the directory's config NAME (e.g. "dl"), not
// a filesystem path - which is exactly what config.Config.LockFile takes.
func undoDirNames(files []engine.UndoFile) []string {
	seen := map[string]bool{}
	var out []string
	for _, f := range files {
		if f.Dir != "" && !seen[f.Dir] {
			seen[f.Dir] = true
			out = append(out, f.Dir)
		}
	}
	sort.Strings(out)
	return out
}

// acquireUndoLocks takes the lock for every name in dirs, in order,
// mirroring cmdSort's per-directory lock.Acquire call. If any acquisition
// fails - held with wait false, or ctx cancelled while waiting - every lock
// already taken is released before returning, so a partial lock set is
// never left held while the caller reports the error and stops.
func acquireUndoLocks(ctx context.Context, cfg *config.Config, dirs []string, wait bool) ([]*lock.Lock, error) {
	locks := make([]*lock.Lock, 0, len(dirs))
	for _, name := range dirs {
		l, err := lock.Acquire(ctx, cfg.LockFile(name), wait)
		if err != nil {
			releaseUndoLocks(locks)
			return nil, fmt.Errorf("%s: %w", name, err)
		}
		locks = append(locks, l)
	}
	return locks, nil
}

// releaseUndoLocks releases every lock in locks and returns any release
// errors, one lock's failure never stopping the rest from being released -
// the same "release on every path" guarantee cmdSort gives its own single
// lock, extended to however many an undo plan needed.
func releaseUndoLocks(locks []*lock.Lock) []error {
	var errs []error
	for _, l := range locks {
		if err := l.Release(); err != nil {
			errs = append(errs, err)
		}
	}
	return errs
}

// finalizeUndoPlan builds the *engine.UndoPlan ApplyUndo actually runs,
// preserving up.Files' own order: every refused file rides along unchanged
// (ApplyUndo declines these itself, silently, exactly as it already does
// when handed the unfiltered plan - spec §10's refusal is not this task's
// to make noisier); every actionable file approved marks true rides along
// unchanged too. A file the user said no to, or left unmarked when [d] or
// [q] cut a per-file review short, is not dropped - fix round 2026-09-12,
// item 2 of Task 8's review: spec §9 says a declined file is logged even
// though nothing happens to it, the same as the forward path already does,
// so it is kept with Declined set, which tells ApplyUndo to log its steps
// as declined rather than reverse them.
func finalizeUndoPlan(up *engine.UndoPlan, approved map[int]bool) *engine.UndoPlan {
	out := &engine.UndoPlan{Run: up.Run}
	for i, f := range up.Files {
		if f.Refused == "" && !approved[i] {
			f.Declined = true
		}
		out.Files = append(out.Files, f)
	}
	return out
}

// reviewUndoDir drives the interactive review over the real terminal,
// mirroring review.go's reviewDir for the forward path; p styles the
// prompts.
func reviewUndoDir(out io.Writer, files []engine.UndoFile, p palette) (map[int]bool, rune, error) {
	return reviewUndoFiles(keyReader{stdin}, out, files, p)
}

// reviewUndoFiles is spec §10's approval flow for an undo plan: the
// top-level
//
//	[a] apply all  [c] choose per file  [s] skip  [q] quit
//
// menu, and, for [c], the per-file
//
//	[y] yes  [n] no  [a] yes to this and all remaining  [d] done, apply chosen so far  [q] quit, apply nothing
//
// prompt - the same shape as review.go's reviewChains/reviewPerFile, over a
// different plan shape (approved is keyed by index into files, not by
// name). action is always one of 'a', 'c', 's' or 'q', with the same [q]
// folding rule reviewChains uses: a [c] session's own [q] becomes the same
// top-level 'q', and approved is emptied to match.
func reviewUndoFiles(in io.Reader, out io.Writer, files []engine.UndoFile, p palette) (map[int]bool, rune, error) {
	fmt.Fprint(out, "\n"+p.keys("[a] apply all  [c] choose per file  [s] skip  [q] quit")+"\n")
	for {
		key, err := readKey(in)
		if err != nil {
			return nil, 0, err
		}
		switch key {
		case 'a':
			return approveAllUndo(files), 'a', nil
		case 's':
			return map[int]bool{}, 's', nil
		case 'q':
			return map[int]bool{}, 'q', nil
		case 'c':
			approved, quit, err := reviewUndoPerFile(in, out, files, p)
			if err != nil {
				return nil, 0, err
			}
			if quit {
				return map[int]bool{}, 'q', nil
			}
			return approved, 'c', nil
		default:
			fmt.Fprintf(out, "%q is not a, c, s or q\n", key)
		}
	}
}

// reviewUndoPerFile is the per-file half of reviewUndoFiles. A file already
// refused at planning time is never asked about - spec §10 shows it with
// its reason and reverses nothing of it regardless of anything chosen here
// - but it still gets its own [i/N] line, so the numbering accounts for
// every file in the plan, not just the reversible ones.
func reviewUndoPerFile(in io.Reader, out io.Writer, files []engine.UndoFile, p palette) (approved map[int]bool, quit bool, err error) {
	approved = map[int]bool{}
	yesRest := false
	for i, f := range files {
		fmt.Fprintf(out, "\n[%d/%d] %s/%s\n", i+1, len(files), f.Dir, f.File)
		for _, s := range f.Steps {
			fmt.Fprintf(out, "       %s\n", undoActionCell(s))
		}
		if f.Refused != "" {
			fmt.Fprintf(out, "  refused: %s\n", f.Refused)
			continue
		}
		if yesRest {
			approved[i] = true
			continue
		}

		fmt.Fprint(out, "  "+p.keys("[y] yes  [n] no  [a] yes to this and all remaining  [d] done, apply chosen so far  [q] quit, apply nothing")+"\n")
		for {
			key, kerr := readKey(in)
			if kerr != nil {
				return nil, false, kerr
			}
			switch key {
			case 'y':
				approved[i] = true
			case 'n':
				// leave unapproved
			case 'a':
				approved[i] = true
				yesRest = true
			case 'd':
				return approved, false, nil
			case 'q':
				return nil, true, nil
			default:
				fmt.Fprintf(out, "%q is not y, n, a, d or q\n", key)
				continue
			}
			break
		}
	}
	return approved, false, nil
}

// approveAllUndo approves every reversible file in files by index - [a]
// apply all, at either the top level or mid per-file review. A refused file
// is never marked true: nothing would happen to it anyway (ApplyUndo skips
// it unconditionally), and leaving it unmarked here keeps this function's
// contract simple - "true means ask ApplyUndo to reverse it" - rather than
// also being the thing that decides refused files ride along regardless
// (finalizeUndoPlan does that, independently of this map).
func approveAllUndo(files []engine.UndoFile) map[int]bool {
	approved := make(map[int]bool, len(files))
	for i, f := range files {
		if f.Refused == "" {
			approved[i] = true
		}
	}
	return approved
}

// undoStepWidth is the widest undo action word (padCell aligns every
// arrow), matching render.go's actionKindWidth for the forward table.
const undoStepWidth = len("undo-displace")

// undoActionCell renders one undo step: its own refusal reason when it has
// one (a sibling directory not yet empty for undo-mkdir - spec §10's one
// case where a step's own failure does not refuse its whole file), the
// directory removed for undo-mkdir (no destination to show), the file being
// trashed for undo-copy (fix wave item 3: its Dst is deliberately empty -
// trash.Put only chooses the entry name at execution time - so this is the
// one action with no path to point an arrow at; before this fix the cell
// rendered as a bare "undo-copy      → ", the plan's one row that said
// nothing about what it would do to the user's file), or an arrow to where
// the step puts the file back, ~-abbreviated - undo has no single root the
// way a sort plan does (one run can span several directories), so there is
// no root-relative form to render here the way actionCell has.
func undoActionCell(s engine.UndoStep) string {
	if s.Refused != "" {
		return padCell(s.Action, undoStepWidth) + "  refused: " + s.Refused
	}
	switch s.Action {
	case "undo-mkdir":
		return padCell(s.Action, undoStepWidth) + "  " + xdg.Abbrev(s.Src)
	case "undo-copy":
		return padCell(s.Action, undoStepWidth) + "  " + xdg.Abbrev(s.Src) + " → trash"
	}
	return padCell(s.Action, undoStepWidth) + "  → " + xdg.Abbrev(s.Dst)
}

// printUndoPlan renders an undo plan the way krino undo shows it, below the
// "krino: undo RUN" header line cmdUndo has already written: a counts line,
// then the numbered table, mirroring printPlan's shape for a sort plan
// (spec §10: "shown ... the same way").
func printUndoPlan(w io.Writer, up *engine.UndoPlan) {
	actionable := undoActionableCount(up.Files)
	fmt.Fprintf(w, "%d files · %d to reverse · %d refused\n", len(up.Files), actionable, len(up.Files)-actionable)
	if len(up.Files) == 0 {
		return
	}
	fmt.Fprintln(w)
	printUndoTable(w, up.Files)
}

// undoRow is one line of the undo table: a file's first step (num and file
// set) or a continuation line (both blank), the same layout planRow uses
// for a sort plan.
type undoRow struct {
	num, file, action string
}

// undoRows turns files into table rows. A refused file gets exactly one
// row - there is nothing to reverse, so no per-step continuation lines -
// showing its reason in place of any step.
func undoRows(files []engine.UndoFile) []undoRow {
	var rows []undoRow
	for i, f := range files {
		label := f.Dir + "/" + f.File
		if f.Refused != "" {
			rows = append(rows, undoRow{num: strconv.Itoa(i + 1), file: label, action: "refused: " + f.Refused})
			continue
		}
		for j, s := range f.Steps {
			row := undoRow{action: undoActionCell(s)}
			if j == 0 {
				row.num = strconv.Itoa(i + 1)
				row.file = label
			}
			rows = append(rows, row)
		}
	}
	return rows
}

// printUndoTable prints rows in the same #, file, action layout
// printPlanTable uses for a sort plan, reusing its column-width helpers
// (relWidth/padCell/padLeft/colWidth, render.go) rather than re-deriving
// them.
func printUndoTable(w io.Writer, files []engine.UndoFile) {
	rows := undoRows(files)
	nums := make([]string, len(rows))
	fls := make([]string, len(rows))
	for i, r := range rows {
		nums[i], fls[i] = r.num, r.file
	}
	numW := colWidth(nums, 0)
	fileW := relWidth(fls)

	fmt.Fprintf(w, "  %s  %s  steps\n", padLeft("#", numW), padCell("file", fileW))
	for _, r := range rows {
		fmt.Fprintf(w, "  %s  %s  %s\n", padLeft(r.num, numW), padCell(r.file, fileW), r.action)
	}
}

// colourRefused styles every "refused:" in an undo plan bold red (spec
// §8.2): the one thing an undo plan singles out is the file or step nothing
// will be reversed for. With the plain palette the text is untouched, which
// keeps every escape byte out of a plan piped to a file or read by another
// tool.
func colourRefused(text string, p palette) string {
	if !p.on {
		return text
	}
	return strings.ReplaceAll(text, "refused:", p.alarm("refused:"))
}