package editor

import (
	"log"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"time"

	"pad/internal/browser"
	"pad/internal/io/pool"
	"pad/internal/io/pool/mock"
	"pad/internal/io/pool/types"
	"pad/internal/ui"
)

// ConfigEvent represents a window configuration change (resize, orientation).
// PixelWidth and PixelHeight are the raw pixel dimensions from Gio.
type ConfigEvent struct {
	PixelWidth  int
	PixelHeight int
}

// ScaleEvent represents a metric change (HiDPI scale factor).
type ScaleEvent struct {
	Scale float32
	// FontScale is the user font-size setting (Metric.PxPerSp / PxPerDp).
	// The shaper draws baselines in sp, so the rendered line pitch in
	// density-dp is EditorLineHeight()*FontScale; all geometry bookkeeping
	// follows it (see EffectiveLineHeight). 0 = unknown, treated as 1.0.
	FontScale float32
}

// ConfigUpdate is a common interface for all configuration updates.
// Both ConfigEvent and ScaleEvent implement this interface.
type ConfigUpdate interface {
	apply(*State)
}

func (e ConfigEvent) apply(s *State) {
	s.PixelWidth = e.PixelWidth
	s.PixelHeight = e.PixelHeight
}

func (e ScaleEvent) apply(s *State) {
	s.SetScale(e.Scale)
	s.SetFontScale(e.FontScale)
}

// ResultEvent represents a completed async task result.
type ResultEvent struct {
	// Future: add result fields here
}

// Logic runs the logic goroutine and provides channels for communication.
//
// Single-owner invariant (architecture.md §1): the logic goroutine is the
// sole reader/writer of l.state. Every other goroutine talks to it through
// the channels below. The only exception is Inspect, a test-only request
// channel whose fn still executes on the owner.
type Logic struct {
	state           *State
	browserManager  *browser.BrowserManager
	configChan      chan ConfigUpdate
	frameChan       chan Frame // frames carry the view-state snapshot
	inputChan       chan []ui.InputEvent
	layoutChan      chan ui.LayoutFeedback
	resultChan      chan ResultEvent
	searchQueryChan chan string
	findQueryChan   chan string // in-file search text (main-owned "find_bar")
	openFileChan    chan string
	retryChan       chan string   // auto-save retries
	autosaveChan    chan struct{} // auto-save debounce ticks (timer -> owner)
	// flushSession: one-shot request to persist the session snapshot now
	// (the OS activity onStop hook, see FlushSession). Buffered 1 so the
	// requester never blocks, even if an earlier flush is still queued.
	flushSession chan struct{}
	inspectChan  chan *inspectReq

	// Per-file write protocol (see requestSave). Workers are a shared pool and
	// the on-disk staging file is per-file, so two concurrent writes for the
	// same file would interleave on the temp file; the protocol keeps at most
	// one write in flight per file and re-issues deferred saves from the write
	// result, so the rename that lands last always carries the newest content.
	// All three maps are touched only on the owner goroutine.
	writeInFlight  map[string]int       // filename -> fileVersion carried by the in-flight write
	savePending    map[string]bool      // filename -> save requested while a write was in flight
	retryScheduled map[string]time.Time // filename -> armed-but-unfired backoff retry
	workerPool     *pool.WorkerPool
	mockFS         pool.FileSystem
	done           chan struct{}
	exitWg         sync.WaitGroup
	saveTimer      *time.Timer // auto-save debounce timer; non-nil while pending
	lastEmit       time.Time   // time of the last frame emission (profiler cadence)
	debugCmdC      chan string // one-shot debug commands from the cmd-file poller; nil = disabled

	// Relaunch state restoration (spec §7, see session.go): session is the
	// snapshot handed in by the cmd layer via BeginRestore (zero = none),
	// restoreFile names the open whose stat/read results are the restore's
	// ("" = none; any other open cancels it). sessionSaver is the cmd layer's
	// file writer; lastSession/lastSessionSave drive the rate-limited
	// change-detected save from emitFrame. All touched only on the owner.
	session     SessionState
	restoreFile string
	// restoreScroll/restoreScrollArmed hold the snapshot's scroll offset
	// until it is safe to apply it: only on an emitFrame whose layout pass
	// saw a trustworthy viewport (scale known, size known, restored content
	// present — the layout computes MaxScroll and one-way-clamps the offset,
	// and on device the first ScaleEvent can precede the size ConfigEvent).
	// scaleSeen tracks the first ScaleEvent; restoreContentLanded marks the
	// read result that filled the buffer (FileLen alone is set earlier, by
	// the stat result, and is not a content-arrival signal).
	restoreScroll      ui.Dp
	restoreScrollArmed bool
	// restoreScrollLine/restoreScrollSub/restorePinDeadline implement the
	// restore line-pin (see refreshRestorePin in session.go): the
	// line-derived scroll offset is only consistent with the all-estimate
	// WrapIndex, so while relaunch restore is settling, every wrap-count
	// correction landing below the pinned line shifts the offset-to-line
	// mapping and would drag the viewport off the restored line. Until the
	// restored window itself has shaped (or a timeout, or the user or a
	// search takes over), the offset is re-derived from the pinned line
	// after each correction.
	restoreScrollLine    int
	restoreScrollSub     float64
	restorePinDeadline   time.Time
	scaleSeen            bool
	restoreContentLanded bool
	sessionSaver         func(SessionState)
	lastSession          SessionState
	lastSessionSave      time.Time
}

// NewLogic creates a new Logic instance, accepting an optional mockFS.
func NewLogic(mfs pool.FileSystem, path string, openfunc func(string)) *Logic {
	state := NewState()
	TheState = state
	// The openfunc (e.g. the Android Termux bridge) is kept on TheState.open
	// as an optional external hook, but it is NOT the tap path: tapping a file
	// must open it in the in-app editor (doc/spec.md). The previous wiring set
	// ui.OpenFile = openfunc, which routed every tap through the external
	// bridge and bypassed the editor entirely.
	TheState.open = openfunc
	ui.OpenFile = func(path string) { OpenFile(path) }

	// Initialize mock filesystem if nil
	mockFS := mfs
	if mockFS == nil {
		mockFS = mock.NewFileSystem()
		populateMockFileSystem(mockFS)
	}

	// Initialize worker pool
	wp := pool.NewWorkerPool(8) // Increased worker pool size to 8
	wp.Start()

	state.Browser.CurrentPath = path
	bm, _ := browser.NewBrowserManager(&state.Browser, wp, mockFS)

	TheLogic = &Logic{
		state:           state,
		browserManager:  bm,
		configChan:      make(chan ConfigUpdate),
		frameChan:       make(chan Frame, 1),
		inputChan:       make(chan []ui.InputEvent),
		layoutChan:      make(chan ui.LayoutFeedback),
		resultChan:      make(chan ResultEvent),
		searchQueryChan: make(chan string),
		findQueryChan:   make(chan string),
		openFileChan:    make(chan string),
		retryChan:       make(chan string, 1), // Buffered channel
		autosaveChan:    make(chan struct{}),
		flushSession:    make(chan struct{}, 1),
		inspectChan:     make(chan *inspectReq),
		writeInFlight:   make(map[string]int),
		savePending:     make(map[string]bool),
		retryScheduled:  make(map[string]time.Time),
		workerPool:      wp,
		mockFS:          mockFS,
		done:            make(chan struct{}),
	}
	return TheLogic
}

// ConfigChan returns the unified config channel for the logic goroutine.
// Accepts ConfigEvent (size) and ScaleEvent (scale factor).
func (l *Logic) ConfigChan() chan<- ConfigUpdate {
	return l.configChan
}

// FrameChan returns the frame channel for the logic goroutine.
func (l *Logic) FrameChan() <-chan Frame {
	return l.frameChan
}

// InputChan returns the input channel for the logic goroutine.
func (l *Logic) InputChan() chan<- []ui.InputEvent {
	return l.inputChan
}

// LayoutChan returns the glyph layout feedback channel.
func (l *Logic) LayoutChan() chan<- ui.LayoutFeedback {
	return l.layoutChan
}

// ResultChan returns the result channel for the logic goroutine.
func (l *Logic) ResultChan() chan<- ResultEvent {
	return l.resultChan
}

// SearchQueryChan returns the search query channel for the logic goroutine.
// The main goroutine sends updated search text here when it detects a change.
func (l *Logic) SearchQueryChan() chan<- string {
	return l.searchQueryChan
}

// FindQueryChan returns the in-file search query channel. The main goroutine
// forwards the "find_bar" widget's text here when it changes (see
// search.go).
func (l *Logic) FindQueryChan() chan<- string {
	return l.findQueryChan
}

// ClipboardSetChan returns the channel the logic goroutine uses to request a
// system clipboard write; the main goroutine executes the Gio clipboard op.
func (l *Logic) ClipboardSetChan() <-chan string {
	return l.state.clipboardSetChan
}

// PasteReqChan returns the channel the logic goroutine uses to request the
// system clipboard content for paste.
func (l *Logic) PasteReqChan() <-chan struct{} {
	return l.state.pasteReqChan
}

// PasteChan delivers system clipboard content to the logic goroutine for
// paste (tests use it to inject clipboard text without a main loop).
func (l *Logic) PasteChan() chan<- string {
	return l.state.pasteChan
}

var TheState *State
var TheLogic *Logic

// Run runs the logic goroutine loop.
func (l *Logic) Run() {
	l.exitWg.Add(1)
	defer l.exitWg.Done()

	// Dispatch initial directory index build on startup
	l.workerPool.Dispatch(pool.NewBuildIndexTask(l.state.Browser.CurrentPath, l.mockFS))

	// Relaunch restoration (spec §7): re-open the last file if a session
	// was handed in before Run (BeginRestore). The browser index is still
	// built: the back button must land on a populated browser.
	if l.session.File != "" {
		l.restoreFile = l.session.File
		l.openFile(l.session.File)
	}

	for {
		select {
		case <-l.done:
			// Settle in-flight file writes before exiting: the post-exit
			// synchronous FlushAll and workerPool.Stop must not race a
			// straggling worker write, whose rename could otherwise land after
			// the final flush and promote a stale snapshot.
			l.drainWrites()
			return
		case <-l.flushSession:
			// Persist now, bypassing the rate limit: the activity is going
			// away (recents-wipe or app switch) and the process may die
			// shortly after this returns.
			l.flushSessionSave()
		case update := <-l.configChan:
			update.apply(l.state)
			if _, ok := update.(ScaleEvent); ok {
				l.scaleSeen = true
			}
			l.emitFrame()
		case fb := <-l.layoutChan:
			// Store the full GlyphLayout on editor state.
			// Derive LastLineY from it for scroll clamping.
			layout := fb.GlyphLayout
			l.state.Editor.GlyphLayout = layout
			var derivedLastLineY ui.Dp
			if len(layout.Y) > 0 {
				derivedLastLineY = layout.Y[len(layout.Y)-1]
			}
			// Wrap-count correction (see WrapIndex): the layout describes the
			// window it was shaped for (fb.WindowStartLine); apply its visual
			// line counts to those lines, but only if no edit has shifted the
			// lines since shaping (fb.EditSeq correlates with the content).
			if fb.EditSeq == l.state.Editor.EditSeq {
				l.state.applyWrapCounts(fb)
				// Restore line-pin (see refreshRestorePin): a correction
				// landing below the pinned line shifted the offset-to-line
				// mapping, so re-derive the offset from the pinned line under
				// the corrected index. The restored window's own shaping means
				// its neighborhood is real and the pin can stand down.
				if l.restoreScrollLine >= 0 {
					if fb.WindowStartLine == l.restoreScrollLine {
						l.restoreScrollLine = -1
					} else {
						l.refreshRestorePin()
					}
				}
				// Search settle (see EditorState.findSettle): the shaping above
				// may have corrected the wrap counts around a find-jumped
				// viewport; re-scroll while the correction still matters.
				if l.state.Editor.findSettle() {
					l.emitFrame()
				}
			}
			if derivedLastLineY != l.state.LastLineY {
				l.state.LastLineY = derivedLastLineY
				l.emitFrame()
			}
		case events := <-l.inputChan:
			for _, evt := range events {
				evt.Handler(evt.Data)
			}
			l.emitFrame()
		case query := <-l.searchQueryChan:
			if query != l.state.Browser.Query {
				l.state.Browser.Query = query
				if l.state.page == BrowserPage {
					browser.HandleSearch(&l.state.Browser, query)
				}
			}
			l.emitFrame()
		case q := <-l.findQueryChan:
			l.state.Editor.findSetQuery(q)
			l.emitFrame()
		case path := <-l.openFileChan:
			l.openFile(path)
		case filename := <-l.retryChan:
			log.Printf("Logic: Retrying save for %s", filename)
			delete(l.retryScheduled, filename)
			l.requestSave(filename)
		case <-l.autosaveChan:
			// Auto-save debounce tick. The timer goroutine only sent a token;
			// the owner snapshots content and dispatches the write.
			l.saveTimer = nil
			l.requestSave(l.state.Editor.Filename)
		case p := <-l.state.pasteChan:
			// Clipboard content arrived from the main goroutine: insert it
			// (replacing any live selection, per the selection-aware edit rule).
			HandlePaste(p)
			l.emitFrame()
		case req := <-l.inspectChan:
			// Test-only: fn runs on the owner, preserving single ownership.
			req.resp <- req.fn(l.state)
		case res := <-l.workerPool.ResultChan():
			l.handleWorkerResult(res)
		case <-l.resultChan:
			l.emitFrame()
		case cmd := <-l.debugCmdC:
			l.applyDebugCmd(cmd)
		}
	}
}

// openFile starts loading path in the editor (a browser row tap or the
// relaunch restore). Any open of a file that is not the in-flight restore
// cancels the restore: its late stat/read results must not re-apply the
// snapshot's positions to a different file. Must be called on the logic
// goroutine.
func (l *Logic) openFile(path string) {
	if l.restoreFile != "" && l.restoreFile != path {
		l.abortRestore() // a different open cancels the in-flight one
	}
	// Discard find results for the previous file; the query is kept
	// (see EditorState.findReset) and re-scanned against the new file.
	TheState.Editor.findReset()
	// Create chunked buffer for virtual scrolling
	chunkSize := DefaultChunkSize
	cb := NewChunkedBuffer(path, chunkSize, l.mockFS, "")
	cb.SetWorkerPool(l.workerPool)
	TheState.Editor.ChunkedBuffer = cb

	// Dispatch stat task to get file size
	l.workerPool.Dispatch(pool.NewStatFileTask(path, l.mockFS))
}

// emitFrame computes the current frame, records a profiler probe (if enabled),
// and hands it to the main goroutine. Centralizing emission here ensures the
// in-app profiler (PerfRecord) sees every frame exactly once, on the owner
// goroutine. Must be called on the logic goroutine.
func (l *Logic) emitFrame() {
	// Relaunch snapshot (spec §7): persist when the state has changed and
	// the rate limit elapsed (tiny JSON file, see session.go).
	l.saveSessionIfChanged()
	elems := l.state.layout(l.browserManager)
	// Relaunch restore (spec §7): land the armed restore scroll AFTER the
	// layout pass above (it refreshed MaxScroll for the current viewport and
	// one-way-clamps any offset set against an earlier, smaller one). The
	// guard defers the application until the viewport is trustworthy — on
	// device the first ScaleEvent can precede the size ConfigEvent. The
	// re-layout makes this frame carry the restored viewport. The restore is
	// complete once the scroll lands; drop restoreFile so a later open of
	// this same file is treated as a fresh one.
	if l.restoreScrollArmed && l.maybeApplyRestoreScroll() {
		l.restoreFile = ""
		elems = l.state.layout(l.browserManager)
	}
	now := time.Now()
	if PerfRecord != nil {
		var delta time.Duration
		if !l.lastEmit.IsZero() {
			delta = now.Sub(l.lastEmit)
		}
		l.lastEmit = now
		s := l.state
		rec := ProbeRecord{T: now, DeltaMs: float64(delta.Nanoseconds()) / 1e6, Page: pageName(s.page)}
		if s.page == EditorPage {
			rec.ScrollDP = float32(s.ScrollOffset)
			rec.MaxScrollDP = float32(s.MaxScroll)
			rec.VisStart = s.VisibleStart
			rec.VisEnd = s.VisibleEnd
			if cb := s.Editor.ChunkedBuffer; cb != nil {
				if li := cb.LineIndex; li != nil {
					rec.TotalLines = li.LineCount()
				}
			}
		} else {
			rec.ScrollDP = float32(s.Browser.ScrollOffset)
		}
		PerfRecord(rec)
	}
	f := l.frameOf(elems)
	select {
	case l.frameChan <- f:
	default:
		// Main has not consumed the previous frame yet. Frames are snapshots
		// of the latest state, so the newest is always the most valuable:
		// replace the unread one instead of dropping this one. A dropped
		// final frame would never be re-emitted (emission is event-driven),
		// leaving the consumer one state behind until the next event. Still
		// non-blocking: a drain from a buffer whose consumer is gone (e.g.
		// the post-done write drain) still just removes the unread frame.
		select {
		case <-l.frameChan:
		default:
			return // consumer gone; nothing to replace into
		}
		select {
		case l.frameChan <- f:
		default:
		}
	}
}

// EnableDebugCmdPoll starts a background poller (debug-only) that watches
// <dir>/cmd for a one-shot debug command (see applyDebugCmd) and forwards
// it to the owner for
// application. Used to jump the editor to specific scroll offsets for
// performance/clamping validation. The poller does the (blocking) file read
// off the owner and sends the command via debugCmdC; the owner applies it.
func (l *Logic) EnableDebugCmdPoll(dir string) {
	l.debugCmdC = make(chan string, 1)
	l.exitWg.Add(1)
	go func() {
		defer l.exitWg.Done()
		t := time.NewTicker(120 * time.Millisecond)
		defer t.Stop()
		cmdPath := filepath.Join(dir, "cmd")
		for {
			select {
			case <-l.done:
				return
			case <-t.C:
				b, err := os.ReadFile(cmdPath)
				if err != nil {
					continue
				}
				cmd := strings.TrimSpace(string(b))
				if cmd == "" {
					continue
				}
				// Consume the command so it is applied exactly once.
				_ = os.WriteFile(cmdPath, nil, 0o644)
				select {
				case l.debugCmdC <- cmd:
				case <-l.done:
					return
				}
			}
		}
	}()
}

// applyDebugCmd applies a one-shot debug scroll command from the cmd-file
// poller. Commands: "open <path>" (any page), and, on the editor page,
// "top", "bottom", "frac <0..1>", "dp <int>". Must be called on the logic
// goroutine.
func (l *Logic) applyDebugCmd(cmd string) {
	s := l.state
	fields := strings.Fields(cmd)
	if len(fields) == 0 {
		return
	}
	// "open <path>" works from any page: it opens the file and switches to
	// the editor. The pre-release frame profile (scripts/profile_emulator.sh)
	// uses it to open a known scrollable file deterministically instead of
	// pixel-tapping the browser list.
	if fields[0] == "open" {
		if len(fields) < 2 {
			log.Printf("DebugCmd: open needs a path")
			return
		}
		OpenFile(fields[1])
		l.emitFrame() // OpenFile only mutates state (the tap path emits via its handler)
		return
	}
	if s.page != EditorPage {
		log.Printf("DebugCmd: %q ignored (not on editor page)", cmd)
		return
	}
	var target ui.Dp
	switch fields[0] {
	case "top":
		target = 0
	case "bottom":
		target = s.MaxScroll
	case "frac":
		if len(fields) < 2 {
			return
		}
		f, err := strconv.ParseFloat(fields[1], 64)
		if err != nil || f < 0 || f > 1 {
			log.Printf("DebugCmd: bad frac %q", fields[1])
			return
		}
		target = ui.Dp(float64(f) * float64(s.MaxScroll))
	case "dp":
		if len(fields) < 2 {
			return
		}
		n, err := strconv.Atoi(fields[1])
		if err != nil {
			log.Printf("DebugCmd: bad dp %q", fields[1])
			return
		}
		target = ui.Dp(n)
	default:
		log.Printf("DebugCmd: unknown %q", cmd)
		return
	}
	if target < 0 {
		target = 0
	}
	if target > s.MaxScroll {
		target = s.MaxScroll
	}
	s.ScrollOffset = target
	log.Printf("DebugCmd: %q -> scroll=%d maxScroll=%d", cmd, int(s.ScrollOffset), int(s.MaxScroll))
	l.emitFrame()
}

// fullContentBytes reconstructs the full file content from the chunked
// buffer (or the deprecated full Buffer). Returns ok=false on error.
// Must be called on the logic goroutine.
func (l *Logic) fullContentBytes() ([]byte, bool) {
	if l.state.Editor.ChunkedBuffer != nil {
		fullContent, err := l.state.Editor.ChunkedBuffer.FullContent()
		if err != nil {
			log.Printf("Error reconstructing full content: %v", err)
			return nil, false
		}
		return []byte(fullContent), true
	}
	return []byte(l.state.Editor.Buffer), true
}

// markDirty triggers the auto-save debounce timer.
// Must be called on the logic goroutine.
//
// The timer callback runs on a timer goroutine and only sends a token on
// autosaveChan; the owner (Run loop) does all state reads and the worker
// dispatch. This keeps the timer goroutine out of state (architecture.md §1).
func (l *Logic) markDirty() {
	if l.state.Editor.Filename == "" {
		return
	}
	l.state.Editor.fileVersion[l.state.Editor.Filename]++

	// 1s debounce
	if l.saveTimer != nil {
		l.saveTimer.Stop()
	}
	l.saveTimer = time.AfterFunc(1*time.Second, func() {
		l.autosaveChan <- struct{}{}
	})
}

// handleWorkerResult processes results from the worker pool.
func (l *Logic) handleWorkerResult(res pool.Result) {
	if res.IsBrowserResult() {
		l.browserManager.HandleResult(res)
	} else if res.TaskType == pool.TypeReadFile {
		if res.Success {
			if content, ok := res.Data.([]byte); ok {
				if l.state.Editor.ChunkedBuffer != nil {
					// Full-load the in-range file: set the whole content (split into
					// resident chunks). No lazy load, so no stale-disk re-read.
					l.state.Editor.ChunkedBuffer.SetFileSize(int64(len(content)))
					l.state.Editor.ChunkedBuffer.SetContent(content)
					// Also update the Buffer field for backward compatibility and for tests checking it.
					l.state.Editor.Buffer = string(content)
				} else {
					// Fallback: populate the deprecated Buffer field
					l.state.Editor.Buffer = string(content)
				}
				// Relaunch restoration (spec §7): the content is in memory, so
				// land the snapshot's cursor/selection (clamped to the file)
				// and re-scan the restored find query. Path-guarded: a read
				// result for a file the user has since replaced must not apply
				// the snapshot to the replacement's buffer.
				if res.FilePath == l.state.Editor.Filename && l.restoreFile == res.FilePath {
					l.applyRestorePositions(len(content))
					l.restoreContentLanded = true
					// The snapshot has landed: resume session saving. restoreFile
					// and the armed scroll stay until the scroll itself lands in
					// the emitFrame hook (which needs this content for a real
					// MaxScroll), so a different open in between still aborts via
					// openFile's restoreFile guard.
					// Re-scan the restored query only when the bar was open:
					// with the bar closed, the result would be dropped (the apply
					// gate requires Visible) and Scanning would stay stuck true;
					// findShow re-scans on the next open instead.
					if f := &l.state.Editor.Find; f.Visible && f.Query != "" && !f.Scanning {
						l.state.Editor.findDispatchScan()
					}
					// No armed scroll: the snapshot has fully landed with the
					// content; lift the save suppression now (the emitFrame
					// hook does this when a scroll does land).
					if !l.restoreScrollArmed {
						l.session = SessionState{}
					}
				}
			}
		} else if res.FilePath == l.restoreFile {
			// The restored file's content could not be read: drop the
			// restore (the editor keeps the empty file view it has).
			l.abortRestore()
		}
	} else if res.TaskType == pool.TypeReadChunk {
		// In-range files load fully via SetContent, so this is only a fallback.
		if cb := l.state.Editor.ChunkedBuffer; cb != nil {
			delete(cb.loadingChunks, res.ChunkIdx) // Use explicit ChunkIdx field

			if res.Success {
				if chunk, ok := res.Data.([]byte); ok {
					for len(cb.chunks) <= res.ChunkIdx {
						cb.chunks = append(cb.chunks, nil)
					}
					cb.chunks[res.ChunkIdx] = chunk
				}
			} else {
				log.Printf("Logic: ReadChunkTask failed for %s chunk %d: %v", res.FilePath, res.ChunkIdx, res.Error)
			}
		}
	} else if res.TaskType == pool.TypeStatFile {
		if res.Success {
			if stat, ok := res.Data.(*pool.FileStat); ok {
				// Relaunch restoration (spec §7): the file exists, so land
				// the snapshot's find state now (the cursor/selection land
				// with the content, the query re-scans against the new file).
				if res.FilePath == l.restoreFile && l.restoreFile != "" {
					f := &l.state.Editor.Find
					f.Query = l.session.FindQuery
					f.Visible = l.session.FindVisible
					f.RestoreMatch = l.session.FindCurByte
					f.Restoring = l.session.FindVisible
				}
				// Size guard: refuse to edit files above the limit. The browser can
				// still list them; the editor shows a "too large to edit" notice.
				if stat.Size > MaxEditableFileSize {
					if l.restoreFile != "" {
						l.abortRestore() // no content load follows; nothing lands
					}
					l.state.Editor.TooLarge = true
					l.state.Editor.TooLargeSize = stat.Size
					log.Printf("Logic: %s is %d bytes, exceeds the %d-byte edit limit", stat.Path, stat.Size, MaxEditableFileSize)
					l.emitFrame()
					return
				}
				if l.state.Editor.ChunkedBuffer != nil {
					l.state.Editor.ChunkedBuffer.SetFileSize(stat.Size)
					// Full-load: read the whole file and dispatch a line index build.
					l.workerPool.Dispatch(pool.NewReadFileTask(stat.Path, l.mockFS))
					l.workerPool.Dispatch(pool.NewBuildLineIndexTask(stat.Path, l.mockFS))
				}
			}
		} else if res.FilePath == l.restoreFile && l.restoreFile != "" {
			// The restored file is gone (deleted/moved since the last
			// session): fall back to the browser instead of showing an
			// empty editor.
			l.abandonRestore()
		}
	} else if res.TaskType == pool.TypeBuildLineIndex {
		if res.Success {
			if idx, ok := res.Data.(*types.LineIndex); ok {
				if cb := l.state.Editor.ChunkedBuffer; cb != nil {
					cb.LineIndex = idx
					// The wrap index is created with the line index: same line
					// set, same lifecycle. Counts start at the all-ones
					// estimate and are corrected by shaped frames.
					cb.WrapIndex = NewWrapIndex(idx.LineCount())
				}
			}
		}
	} else if res.TaskType == pool.TypeWriteFile {
		f := res.FilePath
		wrote, tracked := l.writeInFlight[f]
		delete(l.writeInFlight, f)
		pending := l.savePending[f]
		delete(l.savePending, f)
		if res.Success {
			if tracked {
				// Record the version whose content was actually written (the
				// snapshot version), not the version now: edits made while the
				// write was in flight sit ahead of it and trigger the re-issue
				// below.
				l.state.Editor.lastWriteVersion[f] = wrote
			}
			l.state.Editor.SetWriteFailed(f, false)
			// Latest-state-wins re-issue: a save was deferred while this write
			// was in flight, or an edit arrived during it — write the newer
			// content now (only the active file is reconstructable).
			if f == l.state.Editor.Filename && (pending || l.state.Editor.fileVersion[f] > l.state.Editor.lastWriteVersion[f]) {
				l.requestSave(f)
			}
		} else {
			log.Printf("Auto-save failed for %s: %v", f, res.Error)
			l.state.Editor.SetWriteFailed(f, true)

			// Trigger retry logic: exponential backoff
			attempts := l.state.Editor.IncrementRetryAttempts(f)
			// Simple backoff: 1s, 2s, 4s, 8s... max 30s
			delay := time.Duration(1<<(attempts-1)) * time.Second
			if delay > 30*time.Second {
				delay = 30 * time.Second
			}
			l.retryScheduled[f] = time.Now().Add(delay)
			filename := f
			log.Printf("Scheduling retry for %s in %v (attempt %d)", filename, delay, attempts)
			time.AfterFunc(delay, func() {
				log.Printf("Firing retry for %s", filename)
				select {
				case l.retryChan <- filename:
				default:
					// A token for the same file is already queued; it will
					// re-snapshot the latest content when it fires. Dropping
					// keeps the timer goroutine from ever blocking.
					log.Printf("Retry token for %s dropped: one already queued", filename)
				}
			})
		}
	} else if res.TaskType == pool.TypeSearch {
		if res.Success {
			l.state.Editor.applySearchResult(res)
		}
	}
	l.emitFrame()
}

// State returns the current state.
func (l *Logic) State() *State {
	return l.state
}

// PruneMaps removes old entries to keep memory usage bounded.
// Keeps entries for the last 1000 files.
func (l *Logic) PruneMaps() {
	if len(l.state.Editor.fileVersion) <= 1000 {
		return
	}

	// Simply clear the maps for now. A true LRU would require
	// tracking access times.
	l.state.Editor.fileVersion = make(map[string]int)
	l.state.Editor.lastWriteVersion = make(map[string]int)
	l.state.Editor.writeFailed = make(map[string]bool)
	l.state.Editor.retryAttempts = make(map[string]int)
}

// Done signals the logic goroutine to stop.
func (l *Logic) Done() {
	close(l.done)
}

// WaitForExit blocks until the logic goroutine has fully stopped. After
// this returns, the caller (e.g. Shutdown) may touch state single-threaded.
func (l *Logic) WaitForExit() {
	l.exitWg.Wait()
}

// FlushAll triggers synchronous writes for all dirty files.
//
// Must be called either from the logic goroutine (e.g. via GoToBrowser) or
// after the logic goroutine has fully stopped (Shutdown). It touches state
// directly, so it must never run concurrently with Run (single-owner
// invariant, architecture.md §1).
func (l *Logic) FlushAll() {
	for filename := range l.state.Editor.fileVersion {
		if l.state.Editor.IsDirty() && l.state.Editor.Filename == filename {
			if _, inflight := l.writeInFlight[filename]; inflight {
				// A worker is already writing this file and we cannot block the
				// owner (we are it): defer. The write's result handler re-issues
				// a fresh write while the file is still dirty, so the disk ends
				// up with the latest content.
				l.savePending[filename] = true
				continue
			}
			content, ok := l.fullContentBytes()
			if !ok {
				continue
			}
			// In a real app, this would be a blocking call to the FS
			l.mockFS.WriteFileAtomic(filename, content)
			l.state.Editor.lastWriteVersion[filename] = l.state.Editor.fileVersion[filename]
		}
	}
}

// requestSave is the single entry point for "persist the active file now"
// (autosave tick, retry token, deferred re-issue). It implements the
// per-file write protocol:
//
//   - at most one write per file is in flight at any time. The worker pool is
//     shared and the on-disk staging file is per-file, so two concurrent
//     writes for the same file would interleave on the staging file and could
//     rename a byte-mixture into place;
//   - each write carries the file version at the moment its content was
//     snapshotted (writeInFlight[f]); on success exactly that version is
//     recorded as written, so any edit that arrived while the write was in
//     flight leaves the file dirty and the result handler re-issues a fresh
//     write with the newer content;
//   - a save requested while a write is in flight is deferred (savePending)
//     and re-issued by the result handler, so "last rename wins" always
//     coincides with "newest snapshot wins".
//
// Must be called on the owner goroutine.
func (l *Logic) requestSave(filename string) {
	if filename == "" || filename != l.state.Editor.Filename {
		// Only the active file's content lives in memory (its ChunkedBuffer);
		// a save for any previously opened file cannot be reconstructed.
		return
	}
	if _, inflight := l.writeInFlight[filename]; inflight {
		l.savePending[filename] = true
		return
	}
	content, ok := l.fullContentBytes()
	if !ok {
		return
	}
	l.writeInFlight[filename] = l.state.Editor.fileVersion[filename]
	l.workerPool.DispatchNonBlocking(pool.NewWriteFileTask(filename, content, l.mockFS))
}

const (
	// writeDrainTimeout bounds the post-done wait for in-flight writes so a
	// pathologically failing write can never hang shutdown.
	writeDrainTimeout = 5 * time.Second
	// writeDrainTick is the idle poll interval of the drain loop.
	writeDrainTick = 20 * time.Millisecond
)

// drainWrites waits for in-flight file writes (and armed retries) to settle
// after the done signal, so that Shutdown's post-exit synchronous FlushAll
// and workerPool.Stop cannot race a straggling worker write. The write
// protocol may re-issue follow-up writes while draining; the deadline bounds
// the wait. Must be called on the owner goroutine.
func (l *Logic) drainWrites() {
	if len(l.writeInFlight) == 0 && len(l.retryScheduled) == 0 {
		return
	}
	log.Printf("Logic: draining %d in-flight write(s) before exit", len(l.writeInFlight))
	deadline := time.Now().Add(writeDrainTimeout)
	for {
		if len(l.writeInFlight) == 0 && len(l.retryScheduled) == 0 {
			return
		}
		if time.Now().After(deadline) {
			log.Printf("Logic: write drain timed out with %d in flight; exiting (per-write unique temp files keep every rename a complete snapshot)", len(l.writeInFlight))
			return
		}
		select {
		case res := <-l.workerPool.ResultChan():
			l.handleWorkerResult(res)
		case filename := <-l.retryChan:
			delete(l.retryScheduled, filename)
			l.requestSave(filename)
		case <-l.autosaveChan:
			l.saveTimer = nil
			l.requestSave(l.state.Editor.Filename)
		case <-time.After(writeDrainTick):
			// No events: re-check settle and deadline.
		}
	}
}

// Shutdown gracefully shuts down the logic goroutine and worker pool.
// The logic goroutine is stopped FIRST so that FlushAll can touch state
// single-threaded; the worker pool is stopped last so in-flight results
// still have a reader until then.
func (l *Logic) Shutdown() {
	l.Done()
	l.WaitForExit()
	l.FlushAll()
	// Final relaunch snapshot (spec §7): after exit the caller owns the
	// state single-threaded, like FlushAll above, so one unconditional
	// save makes the file exact for the next launch.
	if l.sessionSaver != nil {
		l.sessionSaver(l.SnapshotSession())
	}
	l.workerPool.Stop()
}