package main

import (
	"context"
	"fmt"
	"os"
	"regexp"
	"strconv"
	"strings"

	"xterm/internal/desktop"
)

type xterm struct {
	d         desktop.Desk
	resources string
}

// PaletteNames are the colour resources xterm_colours reports, in the order the resources write them.
// Their values are the module's config values, read from the rendered resources (Rendered), never held here.
var PaletteNames = []string{
	"background", "foreground",
	"color0", "color8", "color1", "color9", "color2", "color10", "color3", "color11",
	"color4", "color12", "color5", "color13", "color6", "color14", "color7", "color15",
}

// ResourcesFile is where xorg writes the X resources, under the account's home: this module's resources are
// its contribution to the `normal` slot, filled with the module's config values.
const ResourcesFile = ".config/xorg/xresources"

// Rendered is the XTerm* resources of a rendered resources file, by name: `XTerm*faceSize: 12` is faceSize 12.
// The translations, which span lines, and every resource of another program are left out.
func Rendered(text string) map[string]string {
	out := map[string]string{}
	for _, l := range strings.Split(text, "\n") {
		k, v, ok := strings.Cut(l, ":")
		name, scoped := strings.CutPrefix(strings.TrimSpace(k), "XTerm*")
		if ok && scoped && !strings.Contains(name, ".") {
			out[name] = strings.TrimSpace(v)
		}
	}
	return out
}

// defaults are the resources the module's config values rendered, as xorg placed them: what the module sets, so
// what a terminal has unless the session's own resources say otherwise.
func (x xterm) defaults() (map[string]string, error) {
	text, err := os.ReadFile(x.resources)
	if err != nil {
		return nil, fmt.Errorf("the module's resources are not where xorg places them (%s): is xorg assigned to this machine, "+
			"and has its xresources file been written? %w", x.resources, err)
	}
	got := Rendered(string(text))
	if len(got) == 0 {
		return nil, fmt.Errorf("%s holds no XTerm* resource: the xterm module's resources are not in it", x.resources)
	}
	return got, nil
}

// openScript runs in the new terminal: into the directory, then the login shell, or a command
// through it so the account's environment and aliases are there.
const openScript = `cd -- "$1" || exit 1
if [ -n "$2" ]; then exec "${SHELL:-/bin/sh}" -lc "$2"; fi
exec "${SHELL:-/bin/sh}" -l`

// OpenArgs is the xterm command line open starts.
func OpenArgs(dir, command, title string, hold bool) []string {
	args := []string{"xterm"}
	if title != "" {
		args = append(args, "-title", title)
	}
	if hold {
		args = append(args, "-hold")
	}
	return append(args, "-e", "/bin/sh", "-c", openScript, "sh", dir, command)
}

func (x xterm) open(ctx context.Context, a desktop.Args) (any, error) {
	s, err := x.d.Find()
	if err != nil {
		return nil, err
	}
	dir := a.Opt("directory", desktop.Home())
	if strings.HasPrefix(dir, "~") {
		if dir, err = desktop.InHome(dir); err != nil {
			return nil, err
		}
	}
	if info, err := os.Stat(dir); err != nil || !info.IsDir() {
		return nil, fmt.Errorf("%s is not a directory here", dir)
	}
	hold, _, err := a.Bool("hold")
	if err != nil {
		return nil, err
	}
	argv := OpenArgs(dir, a.Opt("command", ""), a.Opt("title", ""), hold)
	launched, err := x.d.Launch(ctx, s, "xterm", argv...)
	if err != nil {
		return nil, err
	}
	return map[string]any{"session": s.Display, "directory": dir, "command": a.Opt("command", "(the login shell)"), "launched": launched}, nil
}

// Effective is a resource's value as an XTerm sees it in `xrdb -query`: its XTerm*-scoped value, else
// the global *-scoped one.
func Effective(query, name string) string {
	var global string
	for _, l := range strings.Split(query, "\n") {
		k, v, ok := strings.Cut(l, ":")
		if !ok {
			continue
		}
		switch strings.TrimSpace(k) {
		case "XTerm*" + name, "XTerm." + name, "XTerm*vt100." + name, "XTerm*VT100." + name:
			return strings.TrimSpace(v)
		case "*" + name:
			global = strings.TrimSpace(v)
		}
	}
	return global
}

var faceName = regexp.MustCompile(`^[A-Za-z0-9 ._-]{1,64}$`)

func (x xterm) font(ctx context.Context, a desktop.Args) (any, error) {
	s, err := x.d.Find()
	if err != nil {
		return nil, err
	}
	def, err := x.defaults()
	if err != nil {
		return nil, err
	}
	env := s.Env(x.d.Base)
	face := a.Opt("face", "")
	size, sized, err := a.Number("size")
	if err != nil {
		return nil, err
	}
	if face != "" || sized {
		var res []string
		if face != "" {
			if !faceName.MatchString(face) {
				return nil, fmt.Errorf("a face is a family name, as fc-list names it")
			}
			if fam := x.d.Run(ctx, env, nil, "fc-list", face, "family"); strings.TrimSpace(fam.Stdout) == "" {
				return nil, fmt.Errorf("no installed font is %q: the fonts module installs the mesh's faces", face)
			}
			res = append(res, "XTerm*faceName: "+face)
		}
		if sized {
			if size < 6 || size > 72 {
				return nil, fmt.Errorf("size is from 6 to 72 points")
			}
			res = append(res, "XTerm*faceSize: "+strconv.FormatFloat(size, 'f', -1, 64))
		}
		if r := x.d.Run(ctx, env, []byte(strings.Join(res, "\n")+"\n"), "xrdb", "-nocpp", "-merge", "-"); !r.OK() {
			return nil, r.Err()
		}
	}
	q := x.d.Run(ctx, env, nil, "xrdb", "-query")
	if !q.OK() {
		return nil, q.Err()
	}
	inForce := Effective(q.Stdout, "faceName")
	var points any = def["faceSize"]
	if n, err := strconv.ParseFloat(def["faceSize"], 64); err == nil {
		points = n
	}
	answer := map[string]any{
		"session": s.Display, "face": inForce, "size": Effective(q.Stdout, "faceSize"),
		"default": map[string]any{"face": def["faceName"], "size": points},
	}
	if inForce != "" {
		m := x.d.Run(ctx, env, nil, "fc-match", "-f", "%{family[0]}|%{style[0]}|%{file}", inForce)
		if parts := strings.SplitN(m.Stdout, "|", 3); m.OK() && len(parts) == 3 {
			answer["resolves_to"] = map[string]any{"family": parts[0], "style": parts[1], "file": parts[2],
				"exact": strings.EqualFold(parts[0], inForce)}
		}
	}
	if face != "" || sized {
		answer["lasts"] = "for terminals opened from now on, until the next login"
	}
	return answer, nil
}

var rgbSpec = regexp.MustCompile(`^rgb:([0-9a-fA-F]{1,4})/([0-9a-fA-F]{1,4})/([0-9a-fA-F]{1,4})$`)

// Hex writes an X colour (`rgb:9e/18/28`, `#rrggbb`) as #rrggbb; anything else (a colour name) as it is.
func Hex(v string) string {
	v = strings.TrimSpace(v)
	if m := rgbSpec.FindStringSubmatch(v); m != nil {
		out := "#"
		for _, c := range m[1:] {
			n, _ := strconv.ParseUint(c, 16, 32)
			max := uint64(1)<<(4*len(c)) - 1
			out += fmt.Sprintf("%02x", (n*255+max/2)/max)
		}
		return out
	}
	return strings.ToLower(v)
}

func (x xterm) colours(ctx context.Context, a desktop.Args) (any, error) {
	def, err := x.defaults()
	if err != nil {
		return nil, err
	}
	res, s, err := x.d.InSession(ctx, "xrdb", "-query")
	if err != nil {
		return nil, err
	}
	if !res.OK() {
		return nil, res.Err()
	}
	type colour struct {
		Name    string `json:"name"`
		Value   string `json:"value"`
		Default string `json:"default"`
		Differs bool   `json:"differs,omitempty"`
	}
	var out []colour
	for _, name := range PaletteNames {
		v, d := Hex(Effective(res.Stdout, name)), Hex(def[name])
		out = append(out, colour{name, v, d, v != d})
	}
	cursor := Hex(Effective(res.Stdout, "cursorColor"))
	return map[string]any{"session": s.Display, "colours": out, "cursor": cursor}, nil
}