package main

import (
	"bufio"
	"os"
	"path/filepath"
	"sort"
	"strings"
)

// KeyFile is a freedesktop key file (a desktop entry, a mimeapps list): groups of key=value.
// Readers disagree on a group or a key written twice (GLib keeps the last, xdg-mime the first),
// so both are recorded rather than merged silently.
type KeyFile struct {
	Groups     map[string]map[string]string
	Order      []string
	DupGroups  []string
	DupKeys    []string // "group: key"
	Unparsable []int    // line numbers
}

// ParseKeyFile reads a key file; `#` lines are comments. A localised key (Name[de]) is kept under
// its own name.
func ParseKeyFile(text string) KeyFile {
	k := KeyFile{Groups: map[string]map[string]string{}}
	group := ""
	sc := bufio.NewScanner(strings.NewReader(text))
	sc.Buffer(make([]byte, 64<<10), 1<<20)
	n := 0
	for sc.Scan() {
		n++
		l := strings.TrimSpace(sc.Text())
		if l == "" || strings.HasPrefix(l, "#") {
			continue
		}
		if strings.HasPrefix(l, "[") && strings.HasSuffix(l, "]") {
			group = l[1 : len(l)-1]
			if _, seen := k.Groups[group]; seen {
				k.DupGroups = append(k.DupGroups, group)
			} else {
				k.Groups[group] = map[string]string{}
				k.Order = append(k.Order, group)
			}
			continue
		}
		key, value, ok := strings.Cut(l, "=")
		if !ok || group == "" {
			k.Unparsable = append(k.Unparsable, n)
			continue
		}
		key, value = strings.TrimSpace(key), strings.TrimSpace(value)
		if _, seen := k.Groups[group][key]; seen {
			k.DupKeys = append(k.DupKeys, group+": "+key)
			// The first value is kept, as xdg-mime reads it; the duplicate is reported.
			continue
		}
		k.Groups[group][key] = value
	}
	return k
}

// List splits a key's value at `;`, dropping empty items.
func List(v string) []string {
	var out []string
	for _, s := range strings.Split(v, ";") {
		if s = strings.TrimSpace(s); s != "" {
			out = append(out, s)
		}
	}
	return out
}

// Entry is one desktop entry, as the tools need it.
type Entry struct {
	ID        string   `json:"id"`
	File      string   `json:"file"`
	Name      string   `json:"name,omitempty"`
	Type      string   `json:"type,omitempty"`
	Exec      string   `json:"exec,omitempty"`
	TryExec   string   `json:"try_exec,omitempty"`
	Program   string   `json:"program,omitempty"`
	Found     bool     `json:"program_found"`
	MimeTypes []string `json:"mime_types,omitempty"`
	Hidden    bool     `json:"hidden,omitempty"`
	NoDisplay bool     `json:"no_display,omitempty"`
	OnlyShow  []string `json:"only_show_in,omitempty"`
	NotShow   []string `json:"not_show_in,omitempty"`
	// GnomeEnabled is X-GNOME-Autostart-enabled as written ("" when absent).
	GnomeEnabled string `json:"x_gnome_autostart_enabled,omitempty"`
	Broken       string `json:"broken,omitempty"`
}

// readEntry reads one desktop file; a dangling link or an unreadable file is an entry that says so.
func (m *Machine) readEntry(path string) Entry {
	e := Entry{ID: filepath.Base(path), File: m.tilde(path)}
	text, ok := m.read(path)
	if !ok {
		if _, err := os.Lstat(m.p(path)); err == nil {
			e.Broken = "a link to nothing, or unreadable"
		} else {
			e.Broken = "absent"
		}
		return e
	}
	g := ParseKeyFile(text).Groups["Desktop Entry"]
	if g == nil {
		e.Broken = "no [Desktop Entry] group"
		return e
	}
	e.Name, e.Type, e.Exec, e.TryExec = g["Name"], g["Type"], g["Exec"], g["TryExec"]
	e.MimeTypes = List(g["MimeType"])
	e.Hidden = g["Hidden"] == "true"
	e.NoDisplay = g["NoDisplay"] == "true"
	e.OnlyShow, e.NotShow = List(g["OnlyShowIn"]), List(g["NotShowIn"])
	e.GnomeEnabled = g["X-GNOME-Autostart-enabled"]
	e.Program = Program(e.Exec)
	if e.TryExec != "" {
		_, tryFound := m.executable(e.TryExec)
		_, execFound := m.executable(e.Program)
		e.Found = tryFound && execFound
	} else {
		_, e.Found = m.executable(e.Program)
	}
	return e
}

// Program is the program an Exec line runs: its first word, unquoted, past `env` and its
// assignments, and into the command of `sh -c` (and bash's, zsh's), where a launcher hides it.
func Program(exec string) string {
	words := splitExec(exec)
	for len(words) > 0 {
		w := words[0]
		switch {
		case filepath.Base(w) == "env":
			words = words[1:]
			for len(words) > 0 && (strings.Contains(words[0], "=") || strings.HasPrefix(words[0], "-")) {
				words = words[1:]
			}
			continue
		case isShell(w) && len(words) >= 3 && words[1] == "-c":
			words = splitExec(words[2])
			continue
		}
		return w
	}
	return ""
}

func isShell(w string) bool {
	switch filepath.Base(w) {
	case "sh", "bash", "zsh", "dash":
		return true
	}
	return false
}

// splitExec splits an Exec value into words: double quotes as the desktop-entry specification
// says (with backslash escapes), single quotes as a shell would, field codes left as words.
func splitExec(s string) []string {
	var words []string
	var cur strings.Builder
	in, quote, started := false, byte(0), false
	for i := 0; i < len(s); i++ {
		c := s[i]
		switch {
		case in && c == quote:
			in = false
		case in && quote == '"' && c == '\\' && i+1 < len(s):
			i++
			cur.WriteByte(s[i])
		case in:
			cur.WriteByte(c)
		case c == '"' || c == '\'':
			in, quote, started = true, c, true
		case c == ' ' || c == '\t':
			if started {
				words = append(words, cur.String())
				cur.Reset()
				started = false
			}
		default:
			cur.WriteByte(c)
			started = true
		}
	}
	if started {
		words = append(words, cur.String())
	}
	return words
}

// appDirs are where desktop files are found, most preferred first.
func (m *Machine) appDirs() []string {
	dirs := []string{filepath.Join(m.dataHome(), "applications")}
	for _, d := range m.dataDirs() {
		dirs = append(dirs, filepath.Join(d, "applications"))
	}
	return dirs
}

// findApp finds the desktop file an id names, as an application would: the first directory that
// has it. A link to nothing, or an entry marked Hidden, is not an installed application.
func (m *Machine) findApp(id string) (Entry, bool) {
	for _, d := range m.appDirs() {
		path := filepath.Join(d, id)
		if _, err := os.Lstat(m.p(path)); err != nil {
			continue
		}
		e := m.readEntry(path)
		if e.Broken != "" || e.Hidden {
			return e, false
		}
		return e, true
	}
	return Entry{ID: id}, false
}

// apps are every desktop file in the application directories, the first of each id.
func (m *Machine) apps() []Entry {
	seen := map[string]bool{}
	var out []Entry
	for _, d := range m.appDirs() {
		entries, _ := os.ReadDir(m.p(d))
		for _, de := range entries {
			if !strings.HasSuffix(de.Name(), ".desktop") || seen[de.Name()] {
				continue
			}
			seen[de.Name()] = true
			out = append(out, m.readEntry(filepath.Join(d, de.Name())))
		}
	}
	sort.Slice(out, func(i, j int) bool { return out[i].ID < out[j].ID })
	return out
}