package main

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

// meshMark is in the first lines of every file this module writes.
const meshMark = "(module xdg"

// UserDir is one line of user-dirs.dirs.
type UserDir struct {
	Name    string `json:"name"`
	Written string `json:"written"`
	Path    string `json:"path"`
	// Home is a folder pointed at the home itself: xdg-user-dirs' way of saying "not wanted".
	Home   bool   `json:"is_home"`
	Exists bool   `json:"exists"`
	Kind   string `json:"kind"` // directory, file, absent
	// Default is the folder xdg-user-dirs would have made, from its system defaults.
	Default string `json:"xdg_user_dirs_default,omitempty"`
}

var userDirLine = regexp.MustCompile(`^XDG_([A-Z0-9_]+)_DIR="(.*)"\s*$`)

// ParseUserDirs reads user-dirs.dirs as xdg-user-dirs writes it: XDG_xxx_DIR="$HOME/yyy" or "/yyy".
// The order of the file is kept.
func ParseUserDirs(text string) [][2]string {
	var out [][2]string
	sc := bufio.NewScanner(strings.NewReader(text))
	for sc.Scan() {
		if m := userDirLine.FindStringSubmatch(strings.TrimSpace(sc.Text())); m != nil {
			out = append(out, [2]string{m[1], strings.ReplaceAll(m[2], `\`, "")})
		}
	}
	return out
}

// resolve turns a written value into a path, as xdg-user-dir does.
func (m *Machine) resolve(written string) string {
	switch {
	case written == "$HOME" || written == "$HOME/":
		return m.Home
	case strings.HasPrefix(written, "$HOME/"):
		return filepath.Clean(filepath.Join(m.Home, strings.TrimPrefix(written, "$HOME/")))
	}
	return filepath.Clean(written)
}

func (m *Machine) kind(path string) string {
	info, err := os.Stat(m.p(path))
	switch {
	case err != nil:
		return "absent"
	case info.IsDir():
		return "directory"
	}
	return "file"
}

// UserDirsAnswer is xdg_user_dirs' answer.
type UserDirsAnswer struct {
	File    string    `json:"file"`
	Meshs   bool      `json:"written_by_the_mesh"`
	Dirs    []UserDir `json:"dirs"`
	Missing []string  `json:"defaults_without_a_line,omitempty"`
	Update  struct {
		Enabled   bool   `json:"enabled"`
		DecidedBy string `json:"decided_by"`
		Note      string `json:"note"`
	} `json:"xdg_user_dirs_update"`
	Locale string `json:"locale,omitempty"`
}

// userDirsDefaults reads the names xdg-user-dirs would create, from its system defaults.
func (m *Machine) userDirsDefaults() map[string]string {
	out := map[string]string{}
	text, _ := m.read("/etc/xdg/user-dirs.defaults")
	for _, l := range strings.Split(text, "\n") {
		l = strings.TrimSpace(l)
		if l == "" || strings.HasPrefix(l, "#") {
			continue
		}
		if k, v, ok := strings.Cut(l, "="); ok {
			out[k] = v
		}
	}
	return out
}

// updateEnabled is xdg-user-dirs-update's own reading of `enabled`: the account's user-dirs.conf
// over the system's, the last line saying it winning.
func (m *Machine) updateEnabled() (bool, string) {
	enabled, by := true, "xdg-user-dirs' built-in default"
	for _, f := range []string{"/etc/xdg/user-dirs.conf", filepath.Join(m.configHome(), "user-dirs.conf")} {
		text, ok := m.read(f)
		if !ok {
			continue
		}
		for _, l := range strings.Split(text, "\n") {
			k, v, ok := strings.Cut(strings.TrimSpace(l), "=")
			if ok && strings.TrimSpace(k) == "enabled" {
				enabled, by = strings.EqualFold(strings.TrimSpace(v), "true"), m.tilde(f)
			}
		}
	}
	return enabled, by
}

// UserDirs is xdg_user_dirs.
func (m *Machine) UserDirs() UserDirsAnswer {
	var a UserDirsAnswer
	file := filepath.Join(m.configHome(), "user-dirs.dirs")
	a.File = m.tilde(file)
	text, _ := m.read(file)
	a.Meshs = strings.Contains(firstLines(text, 3), meshMark)
	defaults := m.userDirsDefaults()
	seen := map[string]bool{}
	for _, kv := range ParseUserDirs(text) {
		path := m.resolve(kv[1])
		d := UserDir{Name: kv[0], Written: kv[1], Path: m.tilde(path), Home: path == m.Home, Kind: m.kind(path)}
		d.Exists = d.Kind == "directory"
		if def, ok := defaults[kv[0]]; ok {
			d.Default = "~/" + def
		}
		seen[kv[0]] = true
		a.Dirs = append(a.Dirs, d)
	}
	for _, k := range sortedKeys(defaults) {
		if !seen[k] {
			a.Missing = append(a.Missing, k)
		}
	}
	a.Update.Enabled, a.Update.DecidedBy = m.updateEnabled()
	if a.Update.Enabled {
		a.Update.Note = "enabled: at the next login it reassigns a folder it cannot find to the home, adds a line for each default above, and rewrites the file"
	} else {
		a.Update.Note = "disabled: it leaves the file as it is"
	}
	if l, ok := m.read(filepath.Join(m.configHome(), "user-dirs.locale")); ok {
		a.Locale = strings.TrimSpace(l)
	}
	return a
}

func firstLines(text string, n int) string {
	lines := strings.SplitN(text, "\n", n+1)
	if len(lines) > n {
		lines = lines[:n]
	}
	return strings.Join(lines, "\n")
}