package browser

import (
	"fmt"
	"time"

	"gioui.org/widget"
	"pad/internal/ui"
)

// Entry represents a single file or directory in the browser.
type Entry struct {
	Path    string    // Relative path from configured directory
	Name    string    // Display name (basename)
	Size    int64     // File size in bytes (0 for directories)
	ModTime time.Time // Last modification time
	IsDir   bool      // True if this is a directory
	IsFirst bool      // True if this is the first entry for its letter section
}

// Page represents a chunk of directory entries loaded from disk.
type Page struct {
	Index   int       // Page number (0-based)
	Entries []Entry   // Entries in this page
	Loaded  bool      // True if page data is in memory
	Dirty   bool      // True if page needs refresh (external change detected)
}

// BrowserState holds all mutable browser state owned by the logic goroutine.
type BrowserState struct {
	// Navigation
	CurrentPath  string // Currently browsed directory (relative to root)
	ScrollIndex  int    // Index of first visible entry (not pixel offset)
	VisibleCount int    // Number of entries currently visible

	// Lazy loading
	Pages        map[int]*Page // Loaded pages by page index
	TotalEntries int           // Total entry count (from cached index)
	Loading      bool          // True if a page load is in flight

	// Sorted index (position maps for each sort mode)
	SortIndex *DirectoryIndex // Cached index with position maps
	SortMode  SortMode        // Current sort mode

	// Search
	Query         string          // Current search query
	SearchResults []int           // Indices of matching entries (empty = no filter)
	SearchEditor  widget.Editor   // Gio editor for search input

	// Alphabetical index
	ActiveLetter  string         // Currently pressed letter (for highlighting)
	LetterOffsets map[string]int // First entry index for each letter

	// Interaction
	SelectedIndex int       // Currently selected entry (-1 = none)
	TapTimestamp  time.Time // For double-tap detection
}

const (
	PageSize     = 100  // Entries per page (tunable; ~5KB per page in memory)
	PrefetchDist = 2    // Pages to prefetch beyond visible region
)

// NewEntry creates a new Entry from the given parameters.
func NewEntry(path, name string, size int64, modTime time.Time, isDir bool) Entry {
	return Entry{
		Path:    path,
		Name:    name,
		Size:    size,
		ModTime: modTime,
		IsDir:   isDir,
	}
}

// NewPage creates a new Page with the given index and entries.
func NewPage(index int, entries []Entry) *Page {
	return &Page{
		Index:   index,
		Entries: entries,
		Loaded:  true,
	}
}

// NewBrowserState creates a new BrowserState with default values.
func NewBrowserState() *BrowserState {
	return &BrowserState{
		Pages:         make(map[int]*Page),
		LetterOffsets: make(map[string]int),
		SelectedIndex: -1,
		SortMode:      SortModeNameAsc, // Default sort mode
	}
}

// ToListItem converts an Entry to a ui.ListItem for rendering.
func (e *Entry) ToListItem() ui.ListItem {
	subtext := formatSize(e.Size)
	if e.IsDir {
		subtext = "Directory"
	}
	return ui.ListItem{
		Text:    e.Name,
		Subtext: subtext,
	}
}

// formatSize returns a human-readable file size string.
func formatSize(bytes int64) string {
	switch {
	case bytes < 1024:
		return fmt.Sprintf("%d B", bytes)
	case bytes < 1024*1024:
		return fmt.Sprintf("%.1f KB", float64(bytes)/1024)
	case bytes < 1024*1024*1024:
		return fmt.Sprintf("%.1f MB", float64(bytes)/(1024*1024))
	default:
		return fmt.Sprintf("%.1f GB", float64(bytes)/(1024*1024*1024))
	}
}

// EvictPages removes pages that are far from the current scroll position.
func (s *BrowserState) EvictPages() {
	minPage := s.ScrollIndex/PageSize - PrefetchDist
	maxPage := (s.ScrollIndex + s.VisibleCount)/PageSize + PrefetchDist
	for idx, page := range s.Pages {
		if idx < minPage || idx > maxPage {
			page.Entries = nil  // Release memory
			page.Loaded = false
		}
	}
}

// Reset clears all browser state for navigation.
func (s *BrowserState) Reset() {
	s.Pages = make(map[int]*Page)
	s.ScrollIndex = 0
	s.SelectedIndex = -1
	s.SearchResults = nil
	s.Query = ""
}