package main

import (
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strings"
)

// MeshList is the machine's default applications, the one mimeapps list this module writes.
const MeshList = "/etc/xdg/mimeapps.list"

// mimeLists are the mimeapps lists in the order an application consults them (the XDG MIME
// Applications specification): the account's configuration, the system's, then the deprecated
// lists in the application directories.
func (m *Machine) mimeLists() []string {
	var dirs []string
	dirs = append(dirs, m.configHome())
	dirs = append(dirs, m.configDirs()...)
	dirs = append(dirs, filepath.Join(m.dataHome(), "applications"))
	for _, d := range m.dataDirs() {
		dirs = append(dirs, filepath.Join(d, "applications"))
	}
	var out []string
	for _, d := range dirs {
		if m.Desktop != "" {
			out = append(out, filepath.Join(d, m.Desktop+"-mimeapps.list"))
		}
		out = append(out, filepath.Join(d, "mimeapps.list"))
	}
	return out
}

// deprecated is whether a list sits in an application directory, where the specification no
// longer looks first and the person no longer writes.
func (m *Machine) deprecated(list string) bool {
	return strings.HasSuffix(filepath.Dir(list), "/applications")
}

// MimeList is one mimeapps list that exists.
type MimeList struct {
	File   string  `json:"file"`
	Whose  string  `json:"whose"`
	Broken string  `json:"broken,omitempty"`
	Keys   KeyFile `json:"-"`
}

func (m *Machine) whose(list string) string {
	switch {
	case list == MeshList:
		return "the mesh's (module xdg)"
	case strings.HasPrefix(list, m.Home+"/") && !m.deprecated(list):
		return "the person's: programs and xdg_default write here; the mesh never does"
	case m.deprecated(list):
		return "deprecated location: read last, written by nothing current"
	}
	return "the system's, as found"
}

// lists are the mimeapps lists that exist, in order.
func (m *Machine) lists() []MimeList {
	var out []MimeList
	for _, f := range m.mimeLists() {
		if _, err := os.Lstat(m.p(f)); err != nil {
			continue
		}
		l := MimeList{File: m.tilde(f), Whose: m.whose(f)}
		if text, ok := m.read(f); ok {
			l.Keys = ParseKeyFile(text)
		} else {
			l.Broken = "a link to nothing, or unreadable"
		}
		out = append(out, l)
	}
	return out
}

// Decision is how a type's default was found.
type Decision struct {
	ID      string   `json:"id,omitempty"`
	File    string   `json:"decided_by,omitempty"`
	Skipped []string `json:"skipped,omitempty"` // "id (file): why"
}

// Decide finds a type's default as the specification says: the first list naming it in
// [Default Applications], the first application of its value that is installed; an application
// named but not installed is passed over, to the next one or the next list.
func (m *Machine) Decide(mime string) Decision {
	var d Decision
	for _, l := range m.lists() {
		v, ok := l.Keys.Groups["Default Applications"][mime]
		if !ok {
			continue
		}
		for _, id := range List(v) {
			if _, installed := m.findApp(id); installed {
				d.ID, d.File = id, l.File
				return d
			}
			d.Skipped = append(d.Skipped, fmt.Sprintf("%s (%s): not installed", id, l.File))
		}
	}
	return d
}

var (
	mimeType  = regexp.MustCompile(`^[a-z0-9][a-z0-9.+-]*/[A-Za-z0-9][A-Za-z0-9.+_-]*$`)
	urlScheme = regexp.MustCompile(`^[a-z][a-z0-9+.-]*$`)
	desktopID = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9 ._+-]*\.desktop$`)
)

// Normalise accepts a MIME type (text/html), a URL scheme (https, mailto:) or the scheme's own
// type (x-scheme-handler/https), and answers the type.
func Normalise(t string) (string, error) {
	t = strings.TrimSpace(t)
	if s := strings.TrimSuffix(strings.TrimSuffix(t, "://"), ":"); urlScheme.MatchString(s) {
		return "x-scheme-handler/" + s, nil
	}
	if mimeType.MatchString(t) {
		return t, nil
	}
	return "", fmt.Errorf("%q is neither a MIME type (text/html) nor a URL scheme (https, mailto)", t)
}

// Handler is who opens one type, and with what.
type Handler struct {
	Type     string   `json:"type"`
	XdgOpen  string   `json:"xdg_open"`
	Gio      string   `json:"gtk_programs,omitempty"`
	Disagree bool     `json:"readers_disagree,omitempty"`
	Decision Decision `json:"decision"`
	App      *Entry   `json:"application,omitempty"`
	Problem  string   `json:"problem,omitempty"`
}

// queryDefault asks xdg-mime, which is what xdg-open uses.
func (m *Machine) queryDefault(mime string) (string, error) {
	out, err := m.cmd("xdg-mime", "query", "default", mime)
	return strings.TrimSpace(out), err
}

var gioDefault = regexp.MustCompile(`(?m)^Default application for .*: (.+)$`)

// gioDefault asks GLib, which GTK and Electron programs use; "" when it has none or no gio.
func (m *Machine) gioDefault(mime string) string {
	out, err := m.cmd("gio", "mime", mime)
	if err != nil {
		return ""
	}
	if g := gioDefault.FindStringSubmatch(out); g != nil {
		return strings.TrimSpace(g[1])
	}
	return ""
}

// Handle answers who opens a type.
func (m *Machine) Handle(mime string) Handler {
	h := Handler{Type: mime, Decision: m.Decide(mime)}
	id, err := m.queryDefault(mime)
	if err != nil {
		h.Problem = err.Error()
	}
	h.XdgOpen = id
	h.Gio = m.gioDefault(mime)
	h.Disagree = h.Gio != "" && h.XdgOpen != "" && h.Gio != h.XdgOpen
	if id != "" {
		if e, ok := m.findApp(id); ok {
			h.App = &e
			if !e.Found {
				h.Problem = fmt.Sprintf("%s runs %s, which is not installed", id, e.Program)
			}
		} else {
			h.Problem = id + " is not installed"
		}
	} else if h.Problem == "" {
		h.Problem = "nothing opens it"
	}
	if h.Decision.ID == "" && id != "" {
		h.Decision.File = "no list names an installed application; " + id + " declares the type"
	}
	return h
}

// SetDefault makes an installed application the default for a type, through xdg-mime: it writes
// the person's own list, which the mesh never writes, and which comes before the mesh's.
func (m *Machine) SetDefault(mime, id string) (map[string]any, error) {
	if !desktopID.MatchString(id) {
		return nil, fmt.Errorf("%q is not a desktop file id (firefox.desktop)", id)
	}
	app, ok := m.findApp(id)
	if !ok {
		return nil, fmt.Errorf("%s is not installed: no application directory has it (xdg_open_handlers lists what is)", id)
	}
	before := m.Handle(mime)
	if _, err := m.cmd("xdg-mime", "default", id, mime); err != nil {
		return nil, err
	}
	after := m.Handle(mime)
	answer := map[string]any{
		"type": mime, "before": before.XdgOpen, "after": after.XdgOpen, "gtk_programs": after.Gio,
		"written_to": m.tilde(filepath.Join(m.configHome(), "mimeapps.list")),
		"note":       "the person's list: it outlasts every push and comes before the mesh's " + MeshList,
	}
	if after.XdgOpen != id {
		answer["problem"] = fmt.Sprintf("xdg-mime still answers %q: a list before the person's (%s) names it", after.XdgOpen, after.Decision.File)
	}
	if !app.Found {
		answer["warning"] = fmt.Sprintf("%s runs %s, which is not installed", id, app.Program)
	}
	return answer, nil
}

// InterestingTypes are the types xdg_open_handlers always answers for.
var InterestingTypes = []string{
	"x-scheme-handler/http", "x-scheme-handler/https", "x-scheme-handler/mailto", "text/html",
	"inode/directory", "text/plain", "text/markdown", "application/pdf", "image/png", "image/jpeg",
	"video/mp4", "audio/mpeg",
}

// DeadDefault is a default naming an application that is not installed.
type DeadDefault struct {
	File string `json:"file"`
	Type string `json:"type"`
	ID   string `json:"id"`
}

// deadDefaults are the defaults, in every list, that name an application not installed.
func (m *Machine) deadDefaults() []DeadDefault {
	var out []DeadDefault
	for _, l := range m.lists() {
		g := l.Keys.Groups["Default Applications"]
		for _, t := range sortedKeys(g) {
			for _, id := range List(g[t]) {
				if _, ok := m.findApp(id); !ok {
					out = append(out, DeadDefault{File: l.File, Type: t, ID: id})
				}
			}
		}
	}
	return out
}

// brokenHandlers are the desktop files that declare types and cannot run.
func (m *Machine) brokenHandlers() []Entry {
	var out []Entry
	for _, e := range m.apps() {
		if len(e.MimeTypes) == 0 || e.Hidden {
			continue
		}
		if e.Broken != "" || !e.Found {
			out = append(out, e)
		}
	}
	return out
}

// OpenHandlers is xdg_open_handlers.
func (m *Machine) OpenHandlers(extra []string) (map[string]any, error) {
	types := append([]string{}, InterestingTypes...)
	for _, t := range extra {
		n, err := Normalise(t)
		if err != nil {
			return nil, err
		}
		types = append(types, n)
	}
	var handlers []Handler
	seen := map[string]bool{}
	for _, t := range types {
		if !seen[t] {
			seen[t] = true
			handlers = append(handlers, m.Handle(t))
		}
	}
	var lists []map[string]string
	for _, l := range m.lists() {
		row := map[string]string{"file": l.File, "whose": l.Whose}
		if l.Broken != "" {
			row["broken"] = l.Broken
		}
		lists = append(lists, row)
	}
	return map[string]any{
		"handlers":            handlers,
		"lists_in_order":      lists,
		"dead_defaults":       m.deadDefaults(),
		"broken_handlers":     m.brokenHandlers(),
		"about_dead_defaults": "a default naming an application that is not installed is passed over: the next list, or an application declaring the type, answers instead",
	}, nil
}

func sortedKeys[V any](m map[string]V) []string {
	out := make([]string, 0, len(m))
	for k := range m {
		out = append(out, k)
	}
	sort.Strings(out)
	return out
}