package admin

import (
	"encoding/json"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"sync"
	"time"
)

type ExtraFile struct {
	FilePath   string `json:"file_path"`
	OldContent []byte `json:"-"`
	NewContent []byte `json:"-"`
}

type ChangeDesc struct {
	Time        string      `json:"time"`
	Description string      `json:"description"`
	FilePath    string      `json:"file_path"`
	NewFilePath string      `json:"new_file_path,omitempty"`
	OldContent  []byte      `json:"old_content"`
	NewContent  []byte      `json:"new_content"`
	IsDelete    bool        `json:"is_delete"`
	IsCreate    bool        `json:"is_create"`
	ExtraFiles  []ExtraFile `json:"extra_files,omitempty"`
}

func (c ChangeDesc) ShortDesc() string {
	switch {
	case c.IsCreate:
		return fmt.Sprintf("Created %s", filepath.Base(c.FilePath))
	case c.IsDelete:
		return fmt.Sprintf("Deleted %s", filepath.Base(c.FilePath))
	case c.NewFilePath != "":
		return fmt.Sprintf("Renamed %s", filepath.Base(c.NewFilePath))
	default:
		return fmt.Sprintf("Edited %s", filepath.Base(c.FilePath))
	}
}

type UndoInfo struct {
	CanUndo     bool   `json:"can_undo"`
	CanRedo     bool   `json:"can_redo"`
	UndoDesc    string `json:"undo_desc"`
	RedoDesc    string `json:"redo_desc"`
	StackSize   int    `json:"stack_size"`
	RedoSize    int    `json:"redo_size"`
}

type UndoStack struct {
	mu       sync.Mutex
	dataDir  string
	history  []ChangeDesc
	redo     []ChangeDesc
	maxSize  int
	filePath string
}

func NewUndoStack(dataDir string) *UndoStack {
	us := &UndoStack{
		dataDir:  dataDir,
		maxSize:  100,
		filePath: filepath.Join(dataDir, ".admin_history.json"),
	}
	us.load()
	us.redo = nil
	return us
}

func (us *UndoStack) Push(desc ChangeDesc) {
	us.mu.Lock()
	defer us.mu.Unlock()
	desc.Time = time.Now().Format(time.RFC3339)
	us.history = append(us.history, desc)
	us.redo = nil
	if len(us.history) > us.maxSize {
		us.history = us.history[len(us.history)-us.maxSize:]
	}
	us.save()
	log.Printf("undo: push  %s", desc.ShortDesc())
}

func (us *UndoStack) Undo() *ChangeDesc {
	us.mu.Lock()
	defer us.mu.Unlock()
	if len(us.history) == 0 {
		return nil
	}
	last := us.history[len(us.history)-1]

	if err := us.applyUndo(last); err != nil {
		log.Printf("undo: failed %s: %v", last.ShortDesc(), err)
		return nil
	}

	us.history = us.history[:len(us.history)-1]
	us.redo = append(us.redo, last)
	us.save()
	log.Printf("undo: undid %s", last.ShortDesc())
	return &last
}

func (us *UndoStack) Redo() *ChangeDesc {
	us.mu.Lock()
	defer us.mu.Unlock()
	if len(us.redo) == 0 {
		return nil
	}
	last := us.redo[len(us.redo)-1]

	if err := us.applyRedo(last); err != nil {
		log.Printf("redo: failed %s: %v", last.ShortDesc(), err)
		return nil
	}

	us.redo = us.redo[:len(us.redo)-1]
	us.history = append(us.history, last)
	us.save()
	log.Printf("redo: redid %s", last.ShortDesc())
	return &last
}

func (us *UndoStack) applyUndo(c ChangeDesc) error {
	if c.NewFilePath != "" {
		os.Remove(c.NewFilePath)
	}
	if c.IsDelete {
		if c.OldContent == nil {
			return fmt.Errorf("no backup content to restore for %s", c.FilePath)
		}
		if err := os.WriteFile(c.FilePath, c.OldContent, 0644); err != nil {
			return fmt.Errorf("restore deleted %s: %w", c.FilePath, err)
		}
		for _, ef := range c.ExtraFiles {
			os.WriteFile(ef.FilePath, ef.OldContent, 0644)
		}
	} else if c.IsCreate {
		os.Remove(c.FilePath)
		for _, ef := range c.ExtraFiles {
			os.Remove(ef.FilePath)
		}
	} else {
		target := c.FilePath
		content := c.OldContent
		if c.NewFilePath != "" {
			target = c.FilePath
		}
		if err := os.WriteFile(target, content, 0644); err != nil {
			return fmt.Errorf("revert %s: %w", target, err)
		}
		for _, ef := range c.ExtraFiles {
			os.WriteFile(ef.FilePath, ef.OldContent, 0644)
		}
	}
	return nil
}

func (us *UndoStack) applyRedo(c ChangeDesc) error {
	if c.NewFilePath != "" {
		os.Remove(c.FilePath)
	}
	if c.IsCreate {
		target := c.FilePath
		if c.NewFilePath != "" {
			target = c.NewFilePath
		}
		if err := os.WriteFile(target, c.NewContent, 0644); err != nil {
			return fmt.Errorf("recreate %s: %w", target, err)
		}
		for _, ef := range c.ExtraFiles {
			os.WriteFile(ef.FilePath, ef.NewContent, 0644)
		}
	} else if c.IsDelete {
		os.Remove(c.FilePath)
		for _, ef := range c.ExtraFiles {
			os.WriteFile(ef.FilePath, ef.NewContent, 0644)
		}
	} else {
		target := c.FilePath
		content := c.NewContent
		if c.NewFilePath != "" {
			target = c.NewFilePath
		}
		if err := os.WriteFile(target, content, 0644); err != nil {
			return fmt.Errorf("reapply %s: %w", target, err)
		}
		for _, ef := range c.ExtraFiles {
			os.WriteFile(ef.FilePath, ef.NewContent, 0644)
		}
	}
	return nil
}

func (us *UndoStack) Info() UndoInfo {
	us.mu.Lock()
	defer us.mu.Unlock()
	info := UndoInfo{
		StackSize: len(us.history),
		RedoSize:  len(us.redo),
	}
	if len(us.history) > 0 {
		info.CanUndo = true
		info.UndoDesc = us.history[len(us.history)-1].ShortDesc()
	}
	if len(us.redo) > 0 {
		info.CanRedo = true
		info.RedoDesc = us.redo[len(us.redo)-1].ShortDesc()
	}
	return info
}

func (us *UndoStack) save() {
	type extraEntry struct {
		FilePath   string `json:"file_path"`
		OldContent string `json:"old_content"`
		NewContent string `json:"new_content"`
	}
	type entry struct {
		Time        string       `json:"time"`
		Description string       `json:"description"`
		FilePath    string       `json:"file_path"`
		NewFilePath string       `json:"new_file_path,omitempty"`
		OldContent  string       `json:"old_content"`
		NewContent  string       `json:"new_content"`
		IsDelete    bool         `json:"is_delete"`
		IsCreate    bool         `json:"is_create"`
		ExtraFiles  []extraEntry `json:"extra_files,omitempty"`
	}
	type saveData struct {
		History []entry `json:"history"`
		Redo    []entry `json:"redo"`
	}
	toEntries := func(changes []ChangeDesc) []entry {
		var entries []entry
		for _, c := range changes {
			var extra []extraEntry
			for _, ef := range c.ExtraFiles {
				extra = append(extra, extraEntry{
					FilePath:   ef.FilePath,
					OldContent: string(ef.OldContent),
					NewContent: string(ef.NewContent),
				})
			}
			entries = append(entries, entry{
				Time:        c.Time,
				Description: c.Description,
				FilePath:    c.FilePath,
				NewFilePath: c.NewFilePath,
				OldContent:  string(c.OldContent),
				NewContent:  string(c.NewContent),
				IsDelete:    c.IsDelete,
				IsCreate:    c.IsCreate,
				ExtraFiles:  extra,
			})
		}
		return entries
	}
	data := saveData{
		History: toEntries(us.history),
		Redo:    toEntries(us.redo),
	}
	b, err := json.Marshal(data)
	if err != nil {
		log.Printf("undo: failed to marshal history: %v", err)
		return
	}
	if err := os.WriteFile(us.filePath, b, 0644); err != nil {
		log.Printf("undo: failed to write history file: %v", err)
	}
}

func (us *UndoStack) load() {
	data, err := os.ReadFile(us.filePath)
	if err != nil {
		return
	}
	log.Printf("undo: loaded history from %s", us.filePath)
	type extraEntry struct {
		FilePath   string `json:"file_path"`
		OldContent string `json:"old_content"`
		NewContent string `json:"new_content"`
	}
	type entry struct {
		Time        string       `json:"time"`
		Description string       `json:"description"`
		FilePath    string       `json:"file_path"`
		NewFilePath string       `json:"new_file_path,omitempty"`
		OldContent  string       `json:"old_content"`
		NewContent  string       `json:"new_content"`
		IsDelete    bool         `json:"is_delete"`
		IsCreate    bool         `json:"is_create"`
		ExtraFiles  []extraEntry `json:"extra_files,omitempty"`
	}
	var saveData struct {
		History []entry `json:"history"`
		Redo    []entry `json:"redo"`
	}
	if err := json.Unmarshal(data, &saveData); err != nil {
		log.Printf("undo: failed to unmarshal history: %v", err)
		return
	}
	fromEntries := func(entries []entry) []ChangeDesc {
		var changes []ChangeDesc
		for _, e := range entries {
			var extra []ExtraFile
			for _, ef := range e.ExtraFiles {
				extra = append(extra, ExtraFile{
					FilePath:   ef.FilePath,
					OldContent: []byte(ef.OldContent),
					NewContent: []byte(ef.NewContent),
				})
			}
			changes = append(changes, ChangeDesc{
				Time:        e.Time,
				Description: e.Description,
				FilePath:    e.FilePath,
				NewFilePath: e.NewFilePath,
				OldContent:  []byte(e.OldContent),
				NewContent:  []byte(e.NewContent),
				IsDelete:    e.IsDelete,
				IsCreate:    e.IsCreate,
				ExtraFiles:  extra,
			})
		}
		return changes
	}
	us.history = fromEntries(saveData.History)
	log.Printf("undo: loaded %d history entries", len(us.history))
}