package copier

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"hash/fnv"
	"io"
	"math/rand/v2"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"sync"
	"time"

	"jukebox_maker/internal/config"
	"jukebox_maker/internal/db"
	"jukebox_maker/internal/disk"
	"jukebox_maker/internal/task"
)

type Options struct {
	DiskID            string
	MountPath         string
	MediaPath         string
	DestFolder        string // subfolder on disk, default "media"
	SourceRules       []config.SourceFolder
	AllowedExtensions []string
	ReserveFreeGB     float64
	OverwriteMode     config.OverwriteMode
	FileSelectMode    config.FileSelectMode
}

type Copier struct {
	tasks *task.Store

	mu      sync.Mutex
	cancels map[string]context.CancelFunc

	dbMu sync.RWMutex
	dbs  map[string]*db.DB
}

func New(tasks *task.Store) *Copier {
	return &Copier{
		tasks:   tasks,
		cancels: make(map[string]context.CancelFunc),
		dbs:     make(map[string]*db.DB),
	}
}

func (c *Copier) SetDB(diskID string, d *db.DB) {
	c.dbMu.Lock()
	if d == nil {
		delete(c.dbs, diskID)
	} else {
		c.dbs[diskID] = d
	}
	c.dbMu.Unlock()
}

func (c *Copier) getDB(diskID string) *db.DB {
	c.dbMu.RLock()
	defer c.dbMu.RUnlock()
	return c.dbs[diskID]
}

func (c *Copier) LastCopiedAt(diskID string) (time.Time, bool, error) {
	database := c.getDB(diskID)
	if database == nil {
		return time.Time{}, false, nil
	}
	return database.LastCopiedAt(diskID)
}

func (c *Copier) Start(ctx context.Context, opts Options) (string, error) {
	return c.startTask(ctx, "", opts)
}

func (c *Copier) Resume(ctx context.Context, taskID string, opts Options) error {
	_, err := c.startTask(ctx, taskID, opts)
	return err
}

func (c *Copier) startTask(ctx context.Context, existingTaskID string, opts Options) (string, error) {
	c.mu.Lock()
	defer c.mu.Unlock()

	if _, active := c.cancels[opts.DiskID]; active {
		return "", errors.New("copy already running")
	}

	database := c.getDB(opts.DiskID)
	if database == nil {
		return "", errors.New("no disk database available")
	}

	if opts.DestFolder == "" {
		opts.DestFolder = config.DefaultDestFolder
	}
	destFolder, err := config.NormalizeDestFolder(opts.DestFolder)
	if err != nil {
		destFolder = config.DefaultDestFolder
	}
	opts.DestFolder = destFolder

	_, free, err := disk.DiskUsage(opts.MountPath)
	if err != nil {
		return "", err
	}
	reserveBytes := int64(opts.ReserveFreeGB * 1e9)
	if free <= reserveBytes {
		return "", errors.New("free space is below reserve threshold")
	}

	var taskID string
	if existingTaskID == "" {
		t := c.tasks.Create("copy", opts.DiskID)
		payload, err := json.Marshal(opts)
		if err != nil {
			return "", err
		}
		if err := database.UpsertTask(*t, payload); err != nil {
			return "", err
		}
		taskID = t.ID
	} else {
		taskID = existingTaskID
		c.tasks.Update(taskID, func(t *task.Task) {
			t.Status = task.StatusQueued
			t.Phase = task.PhaseQueued
			t.Message = "Resuming after restart..."
			t.Error = ""
			t.SpeedBPS = 0
			t.ETASec = 0
		})
		if t, ok := c.tasks.Get(taskID); ok {
			if err := database.UpdateTask(*t); err != nil {
				return "", err
			}
		}
	}

	copyCtx, cancel := context.WithCancel(ctx)
	c.cancels[opts.DiskID] = cancel

	go c.run(copyCtx, taskID, opts, database)
	return taskID, nil
}

func (c *Copier) Cancel(diskID string) {
	c.mu.Lock()
	defer c.mu.Unlock()
	if cancel, ok := c.cancels[diskID]; ok {
		cancel()
	}
}

func (c *Copier) run(ctx context.Context, taskID string, opts Options, database *db.DB) {
	defer func() {
		c.mu.Lock()
		delete(c.cancels, opts.DiskID)
		c.mu.Unlock()
	}()

	setStatus := func(s task.Status, msg string, prog int) {
		c.tasks.Update(taskID, func(t *task.Task) {
			t.Status = s
			t.Message = msg
			t.Progress = prog
		})
		if t, ok := c.tasks.Get(taskID); ok {
			_ = database.UpdateTask(*t)
		}
	}
	fail := func(err error) {
		c.tasks.Update(taskID, func(t *task.Task) {
			t.Status = task.StatusFailed
			t.Error = err.Error()
		})
		if t, ok := c.tasks.Get(taskID); ok {
			_ = database.UpdateTask(*t)
		}
	}

	c.tasks.Update(taskID, func(t *task.Task) {
		t.Status = task.StatusRunning
		t.Phase = task.PhasePreparing
		t.Message = "Preparing..."
		t.Progress = 0
		t.Error = ""
	})
	if t, ok := c.tasks.Get(taskID); ok {
		_ = database.UpdateTask(*t)
	}

	destRoot := filepath.Join(opts.MountPath, opts.DestFolder)

	if opts.OverwriteMode == config.OverwriteDelete {
		c.tasks.Update(taskID, func(t *task.Task) {
			t.Status = task.StatusRunning
			t.Phase = task.PhaseReplacing
			t.Message = "Replacing destination media..."
			t.Progress = 0
		})
		if t, ok := c.tasks.Get(taskID); ok {
			_ = database.UpdateTask(*t)
		}
		if err := os.RemoveAll(destRoot); err != nil {
			fail(err)
			return
		}
	}

	var copiedPaths map[string]struct{}
	if opts.FileSelectMode == config.SelectNew {
		c.tasks.Update(taskID, func(t *task.Task) {
			t.Status = task.StatusRunning
			t.Phase = task.PhaseLoadingHistory
			t.Message = "Loading copy history..."
			t.Progress = 0
		})
		if t, ok := c.tasks.Get(taskID); ok {
			_ = database.UpdateTask(*t)
		}
		var err error
		copiedPaths, err = database.CopiedPaths(opts.DiskID)
		if err != nil {
			fail(err)
			return
		}
	}

	c.tasks.Update(taskID, func(t *task.Task) {
		t.Status = task.StatusRunning
		t.Phase = task.PhaseScanning
		t.Message = "Scanning sources..."
		t.Progress = 0
	})
	if t, ok := c.tasks.Get(taskID); ok {
		_ = database.UpdateTask(*t)
	}
	files, err := buildFileList(opts.MediaPath, opts.SourceRules, copiedPaths, opts.AllowedExtensions)
	if err != nil {
		fail(err)
		return
	}
	if len(files) == 0 {
		setStatus(task.StatusSuccess, "No files to copy.", 100)
		return
	}

	// случайный порядок — выбираем что копировать до начала копирования
	rand.Shuffle(len(files), func(i, j int) { files[i], files[j] = files[j], files[i] })

	_, free, err := disk.DiskUsage(opts.MountPath)
	if err != nil {
		fail(err)
		return
	}
	reserveBytes := int64(opts.ReserveFreeGB * 1e9)
	available := free - reserveBytes
	if available <= 0 {
		setStatus(task.StatusFailed, "Free space is below the reserved threshold.", 100)
		return
	}

	// суммарный объём для прогресса (всех файлов в списке)
	var totalBytes int64
	for _, f := range files {
		totalBytes += f.size
	}

	total := len(files)
	copied := 0
	var doneBytes int64
	startTime := time.Now()

	for i, f := range files {
		select {
		case <-ctx.Done():
			c.tasks.Update(taskID, func(t *task.Task) {
				t.Status = task.StatusCanceled
				t.Message = "Canceled"
				t.SpeedBPS = 0
				t.ETASec = 0
			})
			if t, ok := c.tasks.Get(taskID); ok {
				_ = database.UpdateTask(*t)
			}
			return
		default:
		}

		if f.size > available {
			continue
		}

		elapsed := time.Since(startTime).Seconds()
		var speedBPS, etaSec int64
		if elapsed > 0 && doneBytes > 0 {
			speedBPS = int64(float64(doneBytes) / elapsed)
			remaining := totalBytes - doneBytes
			if speedBPS > 0 {
				etaSec = remaining / speedBPS
			}
		}

		prog := int(float64(doneBytes) / float64(totalBytes) * 100)
		msg := fmt.Sprintf("Copying %s (%d/%d)", filepath.Base(f.srcAbs), i+1, total)

		c.tasks.Update(taskID, func(t *task.Task) {
			t.Status = task.StatusRunning
			t.Phase = task.PhaseCopying
			t.Message = msg
			t.Progress = prog
			t.SpeedBPS = speedBPS
			t.ETASec = int(etaSec)
		})
		if t, ok := c.tasks.Get(taskID); ok {
			_ = database.UpdateTask(*t)
		}

		dstAbs := filepath.Join(destRoot, f.relPath)
		if err := copyFile(ctx, f.srcAbs, dstAbs); err != nil {
			if errors.Is(err, context.Canceled) {
				c.tasks.Update(taskID, func(t *task.Task) {
					t.Status = task.StatusCanceled
					t.Message = "Canceled"
					t.SpeedBPS = 0
					t.ETASec = 0
				})
				if t, ok := c.tasks.Get(taskID); ok {
					_ = database.UpdateTask(*t)
				}
				return
			}
			continue
		}

		available -= f.size
		doneBytes += f.size
		copied++
		_ = database.RecordCopy(db.CopyRecord{
			DiskID:     opts.DiskID,
			SourcePath: f.relPath,
			FileSize:   f.size,
		})
	}

	setStatus(task.StatusSuccess, fmt.Sprintf("Done. Copied %d files.", copied), 100)
}

type fileEntry struct {
	srcAbs  string
	relPath string // relative to /media
	size    int64
}

func buildFileList(mediaPath string, rules []config.SourceFolder, skip map[string]struct{}, allowedExtensions []string) ([]fileEntry, error) {
	_ = mediaPath
	roots, selectedRoots, ruleMap := normalizeSourceRules(rules)
	aliases := sourceAliases(roots)
	allowedExts := makeAllowedExtensionSet(allowedExtensions)

	var result []fileEntry
	for _, src := range selectedRoots {
		root := owningRoot(src, roots)
		if root == "" {
			root = src
		}
		alias := aliases[root]
		if alias == "" {
			alias = filepath.Base(root)
			if alias == "." || alias == "" || alias == string(filepath.Separator) {
				alias = "source-" + shortHash(root)
			}
		}
		dir := src
		err := filepath.WalkDir(dir, func(path string, d os.DirEntry, err error) error {
			if err != nil || d.IsDir() {
				if err != nil {
					return nil
				}
				if path == dir {
					return nil
				}
				rel, relErr := filepath.Rel(root, path)
				if relErr != nil {
					return nil
				}
				rel = filepath.ToSlash(rel)
				if !isPathEnabled(path, ruleMap) && !hasEnabledDescendant(path, ruleMap) {
					return filepath.SkipDir
				}
				return nil
			}
			if !isPathEnabled(path, ruleMap) {
				return nil
			}
			if !isExtensionAllowed(path, allowedExts) {
				return nil
			}
			rel, _ := filepath.Rel(root, path)
			rel = filepath.ToSlash(rel)
			destRel := filepath.ToSlash(filepath.Join(alias, rel))
			if _, skipped := skip[rel]; skipped {
				return nil
			}
			if _, skipped := skip[destRel]; skipped {
				return nil
			}
			info, err := d.Info()
			if err != nil {
				return nil
			}
			result = append(result, fileEntry{srcAbs: path, relPath: destRel, size: info.Size()})
			return nil
		})
		if err != nil {
			return nil, err
		}
	}
	return result, nil
}

func makeAllowedExtensionSet(items []string) map[string]struct{} {
	normalized := config.NormalizeExtensions(items)
	if len(normalized) == 0 {
		normalized = config.DefaultAllowedExtensions()
	}
	result := make(map[string]struct{}, len(normalized))
	for _, item := range normalized {
		result[item] = struct{}{}
	}
	return result
}

func isExtensionAllowed(path string, allowed map[string]struct{}) bool {
	ext := strings.ToLower(filepath.Ext(path))
	if ext == "" {
		return false
	}
	_, ok := allowed[ext]
	return ok
}

func normalizeSourceRules(rules []config.SourceFolder) ([]string, []string, map[string]bool) {
	ruleMap := make(map[string]bool, len(rules))
	rootSet := make(map[string]struct{})
	for _, rule := range rules {
		src := filepath.Clean(strings.TrimSpace(rule.Path))
		if src == "" || src == "." {
			continue
		}
		ruleMap[src] = rule.Enabled
		if rule.Root {
			rootSet[src] = struct{}{}
		}
	}

	var roots []string
	for src := range rootSet {
		roots = append(roots, src)
	}
	sort.Strings(roots)

	var selectedRoots []string
	for src, enabled := range ruleMap {
		if !enabled || hasEnabledAncestor(src, ruleMap) {
			continue
		}
		selectedRoots = append(selectedRoots, src)
	}
	sort.Strings(selectedRoots)
	return roots, selectedRoots, ruleMap
}

func hasEnabledAncestor(path string, ruleMap map[string]bool) bool {
	for parent := parentSourcePath(path); parent != ""; parent = parentSourcePath(parent) {
		if ruleMap[parent] {
			return true
		}
	}
	return false
}

func hasEnabledDescendant(path string, ruleMap map[string]bool) bool {
	for other, enabled := range ruleMap {
		if enabled && isPathInside(path, other) && other != path {
			return true
		}
	}
	return false
}

func isPathEnabled(path string, ruleMap map[string]bool) bool {
	for current := path; current != ""; current = parentSourcePath(current) {
		if enabled, ok := ruleMap[current]; ok {
			return enabled
		}
	}
	return false
}

func parentSourcePath(path string) string {
	parent := filepath.Dir(path)
	if parent == "." || parent == path {
		return ""
	}
	return parent
}

func owningRoot(path string, roots []string) string {
	var best string
	for _, root := range roots {
		if isPathInside(root, path) {
			if len(root) > len(best) {
				best = root
			}
		}
	}
	return best
}

func sourceAliases(roots []string) map[string]string {
	counts := make(map[string]int, len(roots))
	for _, root := range roots {
		counts[strings.ToLower(filepath.Base(root))]++
	}

	aliases := make(map[string]string, len(roots))
	for _, root := range roots {
		base := filepath.Base(root)
		if base == "." || base == string(filepath.Separator) || base == "" {
			base = "source"
		}
		key := strings.ToLower(base)
		if counts[key] > 1 {
			base = fmt.Sprintf("%s-%s", base, shortHash(root))
		}
		aliases[root] = base
	}
	return aliases
}

func shortHash(value string) string {
	h := fnv.New32a()
	_, _ = h.Write([]byte(value))
	return fmt.Sprintf("%08x", h.Sum32())[:6]
}

func isPathInside(base, candidate string) bool {
	if candidate == base {
		return true
	}
	rel, err := filepath.Rel(base, candidate)
	if err != nil {
		return false
	}
	return rel != "." && rel != ".." && !strings.HasPrefix(rel, ".."+string(os.PathSeparator))
}

func copyFile(ctx context.Context, src, dst string) error {
	if err := os.MkdirAll(filepath.Dir(dst), 0o755); err != nil {
		return err
	}

	srcFile, err := os.Open(src)
	if err != nil {
		return err
	}
	defer srcFile.Close()

	srcInfo, err := srcFile.Stat()
	if err != nil {
		return err
	}

	offset := int64(0)
	if dstInfo, err := os.Stat(dst); err == nil {
		switch {
		case dstInfo.Size() < srcInfo.Size():
			offset = dstInfo.Size()
		case dstInfo.Size() == srcInfo.Size():
			return os.Chtimes(dst, srcInfo.ModTime(), srcInfo.ModTime())
		default:
			if err := os.Remove(dst); err != nil {
				return err
			}
		}
	} else if !errors.Is(err, os.ErrNotExist) {
		return err
	}

	if offset > 0 {
		if _, err := srcFile.Seek(offset, io.SeekStart); err != nil {
			return err
		}
	}

	dstFile, err := os.OpenFile(dst, os.O_CREATE|os.O_WRONLY, 0o644)
	if err != nil {
		return err
	}
	defer dstFile.Close()

	if offset > 0 {
		if _, err := dstFile.Seek(offset, io.SeekStart); err != nil {
			return err
		}
	} else if err := dstFile.Truncate(0); err != nil {
		return err
	}

	buf := make([]byte, 1024*1024)
	for {
		if err := ctx.Err(); err != nil {
			return err
		}

		nr, readErr := srcFile.Read(buf)
		if nr > 0 {
			nw, writeErr := dstFile.Write(buf[:nr])
			if writeErr != nil {
				return writeErr
			}
			if nw != nr {
				return io.ErrShortWrite
			}
		}

		if readErr != nil {
			if errors.Is(readErr, io.EOF) {
				break
			}
			return readErr
		}
	}

	if err := dstFile.Sync(); err != nil {
		return err
	}
	if err := os.Chtimes(dst, srcInfo.ModTime(), srcInfo.ModTime()); err != nil {
		return err
	}

	dstInfo, err := os.Stat(dst)
	if err != nil {
		return err
	}
	if dstInfo.Size() != srcInfo.Size() {
		return fmt.Errorf("copied size mismatch for %s", filepath.Base(src))
	}
	return nil
}