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

import "os"
import "io"
import "fmt"
import "log"
import "image"
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")
)

// 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 { return Theme { }, err }
		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(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.ParseMultipleComma (
			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.ParseMultipleComma(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
}

// 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
}

// 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 data in <icon-name>.icon files
type Icon struct {
	DisplayName           string
	EmbeddedTextRectangle image.Rectangle
	AttachPoints          []image.Point
}