// Package iconTheme implements icon-theme-spec version 0.13.
package iconTheme

import "os"
import "io"
import "fmt"
import "log"
import "image"
import "strings"
import "path/filepath"
import "git.tebibyte.media/tomo/xdg/basedir"
import "git.tebibyte.media/tomo/xdg/key-value"

type iconThemeError string
func (err iconThemeError) Error () string { return string(err) }

const (
	// ErrThemeNotFound indicates that a theme could not be found.
	ErrThemeNotFound = iconThemeError("theme not found")
	// ErrGroupMissing indicates that a required group was not found in an
	// index.theme file.
	ErrGroupMissing = iconThemeError("group missing")
	// ErrIconThemeGroupMissing indicates that the [Icon Theme] group was
	// not found while parsing an index.theme file.
	ErrIconThemeGroupMissing = iconThemeError("icon theme group missing")
	// ErrDirectoryGroupMissing indicates that a directory group was not
	// found while parsing an index.Theme file.
	ErrDirectoryGroupMissing = iconThemeError("directory group missing")
	// ErrEntryMissing indicates that a required entry was not found in an
	// index.theme file.
	ErrEntryMissing = iconThemeError("entry missing")
	// ErrBadIconSizeType indicates that an invalid value for an icon size
	// type was given.
	ErrBadIconSizeType = iconThemeError("bad icon size type")
	// ErrCircularDependency indicates that an icon theme depends on one of
	// its dependents.
	ErrCircularDependency = iconThemeError("circular dependency")
	// ErrIconNotFound indicates that an icon could not be found.
	ErrIconNotFound = iconThemeError("icon not found")
)

// ThemeDirs returns the set of directories in which themes should be looked for
// in order of preference.
//
// It will return $HOME/.icons (for backwards compatibility), in
// $XDG_DATA_DIRS/icons and in /usr/share/pixmaps. Applications may further add
// their own icon directories to this list.
func ThemeDirs () ([]string, error) {
	home, err := os.UserHomeDir()
	if err != nil { return nil, err }
	dataDirs, err := basedir.DataDirs()
	if err != nil { return nil, err }
	
	dirs := make([]string, len(dataDirs) + 2)
	dirs[0]             = filepath.Join(home, ".icons")
	dirs[len(dirs) - 1] = "/usr/share/pixmaps"

	for index, dataDir := range dataDirs {
		dirs[index + 1] = filepath.Join(dataDir, "icons")
	}
	
	return dirs, nil
}

// FindTheme returns the theme of the given name located within the given search
// paths. If no search path is provided, the result of ThemeDirs is used. This
// function will also recursively find and read inherited themes. If an
// inherited theme is malformed and cannot be read, hicolor will be used
// instead. The directory structure and inheritence tree of a theme are only
// determined when this function is run, if a theme has been changed and needs
// to be reloaded this function should be called again.
func FindTheme (name string, path ...string) (Theme, error) {
	return findTheme(name, nil, false, path...)
}

// FindThemeWarn is like FindTheme, but emits warnings using the log package if
// it encounters a recoverable error (such as failing to parse/find an inherited
// theme).
func FindThemeWarn (name string, path ...string) (Theme, error) {
	return findTheme(name, nil, true, path...)
}

func findTheme (name string, trail []string, warn bool, path ...string) (Theme, error) {
	for _, step := range trail {
		if step == name {
			return Theme { }, ErrCircularDependency
		}
	}

	if len(path) == 0 {
		themeDirs, err := ThemeDirs()
		if err != nil { return Theme { }, nil }
		path = themeDirs
	}

	// find paths to all instances of this theme
	instances := []string { }
	for _, dir := range path {
		entries, err := os.ReadDir(dir)
		if err != nil { continue }
		
		for _, entry := range entries {
			if entry.Name() == name {
				instances = append (
					instances,
					filepath.Join(dir, entry.Name()))
				break
			}
		}
	}
	if len(instances) == 0 { return Theme { }, ErrThemeNotFound }

	// find an index.theme
	var lastParseErr error
	var theme        Theme
	var parents      []string
	for _, instance := range instances {
		indexPath := filepath.Join(instance, "index.theme")
		file, err := os.Open(indexPath)
		lastParseErr = err
		if err != nil { continue }
		defer file.Close()
		
		theme, parents, err = parseThemeIndex(file)
		lastParseErr = err
		if err != nil { continue }

		break
	}
	if lastParseErr != nil { return Theme { }, lastParseErr }

	// expand directories to cover all instances
	for index, directory := range theme.Directories {
		directory.Paths = make([]string, len(instances))
		for pathIndex, path := range directory.Paths {
			directory.Paths[pathIndex] = filepath.Join (
				instances[pathIndex],
				path, directory.Name)
		}
		theme.Directories[index] = directory
	}

	// this will not stomp memory its fine
	trail = append(trail, name)

	// parse parents
	for _, parent := range parents {
		parentTheme, err := findTheme(parent, trail, warn, path...)
		if err != nil {
			if warn {
				log.Printf (
					"xdg: could not parse inherited theme '%s': %v",
					parent, err)
			}
			continue
		}
		theme.Inherits = append(theme.Inherits, parentTheme)
	}

	// if no parents were successfuly parsed, inherit from hicolor
	if len(theme.Inherits) == 0 && name != "hicolor" {
		hicolor, err := findTheme("hicolor", trail, warn, path...)
		if err != nil { return Theme { }, err }
		theme.Inherits = []Theme { hicolor }
	}

	return theme, nil
}

func parseThemeIndex (reader io.Reader) (theme Theme, parents []string, err error) {
	file, err := keyValue.Parse(reader)
	if err != nil { return Theme { }, nil, err }

	iconThemeGroup, ok := file["Icon Theme"]
	if !ok { return Theme { }, nil, ErrIconThemeGroupMissing }

	// Name
	entry, ok := iconThemeGroup["Name"]
	if !ok { return Theme { }, nil, ErrEntryMissing }
	theme.Name, err = entry.Unescape()
	if err != nil { return Theme { }, nil, err }
	
	// Comment
	entry, ok = iconThemeGroup["Comment"]
	if !ok { return Theme { }, nil, ErrEntryMissing }
	theme.Comment, err = entry.Unescape()
	if err != nil { return Theme { }, nil, err }
	
	// Inherits (optional)
	if entry, ok := iconThemeGroup["Inherits"]; ok {
		parents, err = keyValue.ParseMultiple (
			keyValue.ParseString,
			entry.Value, ',')
		if !ok { return Theme { }, nil, err }
	}

	// Directories
	entry, ok = iconThemeGroup["Directories"]
	if !ok { return Theme { }, nil, ErrEntryMissing }
	theme.Directories, err = parseDirectories(entry, file)
	if err != nil { return Theme { }, nil, err }

	// ScaledDirectories (optional)
	if entry, ok := iconThemeGroup["ScaledDirectories"]; ok {
		theme.ScaledDirectories, err = parseDirectories(entry, file)
		if err != nil { return Theme { }, nil, err }	
	}

	// Hidden (optional)
	if entry, ok := iconThemeGroup["Hidden"]; ok {
		theme.Hidden, err = keyValue.ParseBoolean(entry.Value)
		if err != nil { return Theme { }, nil, err }	
	}

	// Example (optional)
	if entry, ok := iconThemeGroup["Example"]; ok {
		theme.Example, err = keyValue.ParseString(entry.Value)
		if err != nil { return Theme { }, nil, err }	
	}
	
	return theme, parents, nil
}

func parseDirectories (listEntry keyValue.Entry, file keyValue.File) ([]Directory, error) {
	names, err := keyValue.ParseMultiple(keyValue.ParseString, listEntry.Value, ',')
	if err != nil { return nil, err }
	directories := make([]Directory, len(names))
	for index, name := range names {
		directoryGroup, ok := file[name]
		if !ok { return nil, ErrDirectoryGroupMissing }

		directory := Directory {
			Name: name,
		}

		// Size
		entry, ok := directoryGroup["Size"]
		if !ok { return nil, ErrEntryMissing }
		directory.Size, err = keyValue.ParseInteger(entry.Value)
		if err != nil { return nil, err }

		// Scale (optional)
		if entry, ok := directoryGroup["Scale"]; ok {
			directory.Scale, err = keyValue.ParseInteger(entry.Value)
			if err != nil { return nil, err }
		} else {
			directory.Scale = 1
		}

		// Context (optional)
		if entry, ok := directoryGroup["Context"]; ok {
			directory.Context, err = keyValue.ParseString(entry.Value)
			if err != nil { return nil, err }
		}

		// Type (optional)
		if entry, ok := directoryGroup["Type"]; ok {
			stringTy, err := keyValue.ParseString(entry.Value)
			if err != nil { return nil, err }
			directory.Type, err = IconSizeTypeFromString(stringTy)
			if err != nil { return nil, err }
		} else {
			directory.Type = IconSizeTypeThreshold
		}
		
		// MaxSize (optional)
		if entry, ok := directoryGroup["MaxSize"]; ok {
			directory.MaxSize, err = keyValue.ParseInteger(entry.Value)
			if err != nil { return nil, err }
		} else {
			directory.MaxSize = directory.Size
		}
		
		// MinSize (optional)
		if entry, ok := directoryGroup["MinSize"]; ok {
			directory.MinSize, err = keyValue.ParseInteger(entry.Value)
			if err != nil { return nil, err }
		} else {
			directory.MinSize = directory.Size
		}
		
		// Threshold (optional)
		if entry, ok := directoryGroup["Threshold"]; ok {
			directory.Threshold, err = keyValue.ParseInteger(entry.Value)
			if err != nil { return nil, err }
		} else {
			directory.Threshold = 2
		}

		directories[index] = directory
	}
	return directories, nil
}

// Theme represents an icon theme.
type Theme struct {
	Name              keyValue.Entry
	Comment           keyValue.Entry
	Inherits          []Theme
	Directories       []Directory
	ScaledDirectories []Directory
	Hidden            bool
	Example           string
}

// FindIcon finds the best icon of the given name for the given size and scale.
// If a list of supported filetypes is not given, { PNG, SVG, XPM } is used
// instead.
func (theme Theme) FindIcon (name string, size, scale int, supported ...IconFileType) (Icon, error) {
	// this method is equivalent to FindIconHelper
	if len(supported) == 0 { supported = []IconFileType{ PNG, SVG, XPM } }

	// try to find icon in this theme first
	icon, err := theme.findIconHere(name, size, scale, supported...)
	if err == nil { return icon, nil }

	// if that didn't work, recurse through parent themes
	for _, parent := range theme.Inherits {
		icon, err := parent.FindIcon(name, size, scale, supported...)
		if err == nil { return icon, nil }
	}

	return Icon { }, ErrIconNotFound
}

func (theme Theme) findIconHere (name string, size, scale int, supported ...IconFileType) (Icon, error) {
	// this method is equivalent to LookupIcon

	// stage 1: attempt to find an exact match
	for _, directory := range theme.Directories {
		if directory.Fits(size, scale) {
			for _, path := range directory.Paths {
				for _, ty := range supported {
					icon, err := parseIcon(filepath.Join (
						path, ty.Extend(name)))
					if err == nil { return icon, err }
				}
			}
		}
	}

	// stage 2: find the best icon matching the name
	minimalDistance := int((^uint(0)) >> 1)
	closestFilename := ""
	for _, directory := range theme.Directories {
		sizeDistance := directory.SizeDistance(size, scale)
		if sizeDistance < minimalDistance {
			for _, path := range directory.Paths {
				for _, ty := range supported {
					iconFilename := filepath.Join (
						path, ty.Extend(name))
					if _, err := os.Stat(iconFilename); err == nil {
						closestFilename = iconFilename
						minimalDistance = sizeDistance
					}
				}
			}
		}
	}
	if closestFilename != "" {
		icon, err := parseIcon(closestFilename)
		if err == nil { return icon, err }
	}
	
	return Icon { }, ErrIconNotFound
}

// Directory represents a directory of an icon theme which directly contains
// icons.
type Directory struct {
	Name      string
	Paths     []string
	Size      int
	Scale     int
	Context   string
	Type      IconSizeType
	MaxSize   int
	MinSize   int
	Threshold int
}

// Fits returns whether icons in the directory fit the given size and scale.
func (directory Directory) Fits (size, scale int) bool {
	// this method is equivalent to DirectoryMatchesSize
	if directory.Scale != scale { return false }
	switch directory.Type {
	case IconSizeTypeFixed:
		return directory.Size == size
	case IconSizeTypeScalable:
		return directory.MinSize <= size && size <= directory.MaxSize
	case IconSizeTypeThreshold:
		return directory.Size - directory.Threshold <=
			size && size <=
			directory.Size + directory.Threshold
	}
	return false
}

// SizeDistance returns how close the size of this directory's icons is to the
// given size. A smaller number is closer.
func (directory Directory) SizeDistance (size, scale int) int {
	// this method is equivalent to DirectorySizeDistance
	// TODO: the pseudocode for DirectorySizeDistance in the spec seems
	// incredibly wrong, and the code here has been altered to correct for
	// that. figure out why the spec is the way it is.
	scaledSize := size * scale
	scaledDir  := directory.Size    * directory.Scale
	scaledMin  := directory.MinSize * directory.Scale
	scaledMax  := directory.MaxSize * directory.Scale
	threshMin  := (directory.Size - directory.Threshold) * directory.Scale
	threshMax  := (directory.Size + directory.Threshold) * directory.Scale

	switch directory.Type {
	case IconSizeTypeFixed:
		difference := scaledDir - scaledSize
		if difference > 0 {
			return difference
		} else {
			return -difference
		}
		
	case IconSizeTypeScalable:
		if scaledSize < scaledMin { return scaledMin  - scaledSize }
		if scaledSize > scaledMax { return scaledSize - scaledMax  }
	
	case IconSizeTypeThreshold:
		if scaledSize < threshMin { return threshMin  - scaledSize }
		if scaledSize > threshMax { return scaledSize - threshMin  }
	}
	return 0
}

// IconFileType specifies the file type of an icon.
type IconFileType uint; const (
	PNG IconFileType = iota
	SVG
	XPM
)

// String returns a string representation of the file type.
func (ty IconFileType) String () string {
	switch ty {
	case PNG: return ".png"
	case SVG: return ".svg"
	case XPM: return ".xpm"
	default:  return fmt.Sprintf("IconFileType(%d)", ty)
	}
}

// Extend applies the file extension to a file name.
func (ty IconFileType) Extend (name string) string {
	return name + ty.String()
}

// IconSizeType specifies how an icon can be scaled. Fixed icons cannot be
// scaled, scalable icons can be scaled to any size within a min and max range,
// and threshold icons can be scaled to any size within a certain distance of
// their normal size.
type IconSizeType int; const (
	IconSizeTypeFixed IconSizeType = iota
	IconSizeTypeScalable
	IconSizeTypeThreshold
)

// String returns a string representation of the type.
func (ty IconSizeType) String () string {
	switch ty {
	case IconSizeTypeFixed:     return "Fixed"
	case IconSizeTypeScalable:  return "Scalable"
	case IconSizeTypeThreshold: return "Threshold"
	default:                    return fmt.Sprintf("IconSizeType(%d)", ty)
	}
}

// IconSizeTypeFromString converts a astring into an IconSizeType, returning an
// error if it could not be converted.
func IconSizeTypeFromString (value string) (IconSizeType, error) {
	switch value {
	case "Fixed":     return IconSizeTypeFixed,     nil
	case "Scalable":  return IconSizeTypeScalable,  nil
	case "Threshold": return IconSizeTypeThreshold, nil
	default:          return 0, ErrBadIconSizeType
	}
}

// Icon represents an icon, and its associated data (if applicable).
type Icon struct {
	Path                  string
	FileType              IconFileType
	DisplayName           keyValue.Entry
	EmbeddedTextRectangle image.Rectangle
	AttachPoints          []image.Point
}

func parseIcon (path string) (Icon, error) {
	_, err := os.Stat(path)
	if err != nil { return Icon { }, err }

	ext := filepath.Ext(path)
	dataPath := strings.TrimSuffix(path, ext) + ".icon"

	if data, err := parseIconData(dataPath); err != nil {
		data.Path = path
		return data, nil
	} else {
		return Icon {
			Path: path,
		}, nil
	}
}

func parseIconData (path string) (Icon, error) {
	reader, err := os.Open(path)
	if err != nil { return Icon { }, err }
	file, err := keyValue.Parse(reader)
	if err != nil { return Icon { }, err }

	iconDataGroup, ok := file["Icon Data"]
	if !ok { return Icon { }, ErrGroupMissing }

	icon := Icon { }
	
	// DisplayName (optional)
	if entry, ok := iconDataGroup["DisplayName"]; ok {
		icon.DisplayName, err = entry.Unescape()
		if err != nil { return Icon { }, err }
	}
	
	// EmbeddedTextRectangle (optional)
	if entry, ok := iconDataGroup["EmbeddedTextRectangle"]; ok {
		embeddedTextRectangle, err := keyValue.ParseMultiple(keyValue.ParseInteger, entry.Value, ',')
		if len(embeddedTextRectangle) == 4 {
			icon.EmbeddedTextRectangle = image.Rect (
				embeddedTextRectangle[0],
				embeddedTextRectangle[1],
				embeddedTextRectangle[2],
				embeddedTextRectangle[3])
			if err != nil { return Icon { }, err }
		}
	}

	// TODO figure out what the actual fuck the spec is talking about with
	// regard to AttatchPoints. What even the fuck is that supposed to mean.
	// Ohhhh a list of points separated by |. Mf hoe what do you define as
	// a point.
	
	return icon, nil
}