// SPDX-License-Identifier: GPL-3.0-or-later

package config

import (
	"bytes"
	_ "embed"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"unicode"
	"unicode/utf8"

	"krino/internal/sexp"
	"krino/internal/xdg"
)

//go:embed skel/krino.conf
var skelMain []byte

//go:embed skel/template.conf
var skelTemplate []byte

// Reserved are subcommand names; a directory with one of them could not be
// run by name.
var Reserved = map[string]bool{"init": true, "new": true, "check": true, "explain": true, "log": true, "undo": true}

// Init creates the directory holding mainFile with a commented krino.conf and
// template.conf, and a dirs/ directory. It never overwrites krino.conf, and
// keeps an existing template.conf. It returns the files it created.
func Init(mainFile string) ([]string, error) {
	dir := filepath.Dir(mainFile)
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return nil, err
	}
	if err := writeNew(mainFile, skelMain); errors.Is(err, fs.ErrExist) {
		return nil, fmt.Errorf("%s already exists; krino init leaves it alone", mainFile)
	} else if err != nil {
		return nil, err
	}
	created := []string{mainFile}
	if err := os.MkdirAll(filepath.Join(dir, "dirs"), 0o755); err != nil {
		return created, err
	}
	tmpl := filepath.Join(dir, "template.conf")
	switch err := writeNew(tmpl, skelTemplate); {
	case err == nil:
		created = append(created, tmpl)
	case !errors.Is(err, fs.ErrExist):
		return created, err
	}
	return created, nil
}

// NewDir creates dirs/<name>.conf from template.conf with the path filled
// in, and adds name to include in mainFile without changing anything else
// there. It returns the new file's path.
func NewDir(mainFile, name, path string) (string, error) {
	if !nameRE.MatchString(name) {
		return "", fmt.Errorf("bad directory name %q: use letters, digits, '.', '_' and '-'", name)
	}
	if Reserved[name] {
		return "", fmt.Errorf("%q is a krino command; choose another name", name)
	}
	abs, err := filepath.Abs(xdg.Expand(path))
	if err != nil {
		return "", err
	}
	// The path is written into the new file, and config files are UTF-8
	// text (the reader refuses anything else).
	if !utf8.ValidString(abs) {
		return "", fmt.Errorf("%q is not valid UTF-8; krino's config is UTF-8 text, so rename the directory first", abs)
	}
	// Nor control or bidirectional characters: a directory unpacked from a
	// download could name itself with escape codes (re-review cli F1).
	for _, r := range abs {
		if unicode.IsControl(r) || unicode.Is(unicode.Bidi_Control, r) || unicode.In(r, unicode.Zl, unicode.Zp) {
			return "", fmt.Errorf("%q holds control or bidirectional characters; rename the directory first", abs)
		}
	}
	if fi, err := os.Stat(abs); err != nil || !fi.IsDir() {
		return "", fmt.Errorf("%s is not a directory", abs)
	}
	src, err := os.ReadFile(mainFile)
	if errors.Is(err, fs.ErrNotExist) {
		return "", fmt.Errorf("%s not found; create it with: krino init", mainFile)
	} else if err != nil {
		return "", err
	}
	m, errs := ParseMain(mainFile, src)
	if len(errs) > 0 {
		return "", fmt.Errorf("fix %s first: %v", mainFile, errs[0])
	}
	if _, ok := m.IncludePos[name]; ok {
		return "", fmt.Errorf("%q is already included", name)
	}
	tmplPath := filepath.Join(filepath.Dir(mainFile), "template.conf")
	tmpl, err := os.ReadFile(tmplPath)
	if errors.Is(err, fs.ErrNotExist) {
		tmpl, err = skelTemplate, nil
	}
	if err != nil {
		return "", err
	}
	file := DirFile(mainFile, name)
	body := bytes.ReplaceAll(tmpl, []byte(`"@PATH@"`), []byte(sexp.Quote(xdg.Abbrev(abs))))
	newDir, derrs := ParseDir(name, file, body)
	if len(derrs) > 0 {
		return "", fmt.Errorf("template.conf is broken: %v", derrs[0])
	}
	if newDir.Path != abs {
		return "", fmt.Errorf("%s must contain (path \"@PATH@\")", tmplPath)
	}
	newMain := addInclude(src, m, name)
	if _, errs := ParseMain(mainFile, newMain); len(errs) > 0 {
		return "", fmt.Errorf("could not add %q to include: %v", name, errs[0])
	}
	if err := os.MkdirAll(filepath.Dir(file), 0o755); err != nil {
		return "", err
	}
	if err := writeNew(file, body); errors.Is(err, fs.ErrExist) {
		return "", fmt.Errorf("%s already exists", file)
	} else if err != nil {
		return "", err
	}
	if err := replaceFile(mainFile, newMain); err != nil {
		os.Remove(file)
		return "", err
	}
	return file, nil
}

// addInclude inserts name after the last element of the (include ...) form,
// or appends an include form when there is none.
func addInclude(src []byte, m *Main, name string) []byte {
	ins := " " + sexp.Quote(name)
	if m.IncludeNode == nil {
		out := bytes.Clone(src)
		if len(out) > 0 && out[len(out)-1] != '\n' {
			out = append(out, '\n')
		}
		return append(out, "(include"+ins+")\n"...)
	}
	kids := m.IncludeNode.Children
	at := kids[len(kids)-1].End.Offset
	out := make([]byte, 0, len(src)+len(ins))
	out = append(out, src[:at]...)
	out = append(out, ins...)
	return append(out, src[at:]...)
}

// writeNew creates path holding data, failing if it already exists.
func writeNew(path string, data []byte) error {
	f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o644)
	if err != nil {
		return err
	}
	if _, err := f.Write(data); err != nil {
		f.Close()
		os.Remove(path)
		return err
	}
	return f.Close()
}

// replaceFile atomically replaces the file at path, keeping its permissions.
// A symlink is followed and its target replaced, so dotfile links survive.
func replaceFile(path string, data []byte) error {
	real, err := filepath.EvalSymlinks(path)
	if err != nil {
		return err
	}
	fi, err := os.Stat(real)
	if err != nil {
		return err
	}
	tmp, err := os.CreateTemp(filepath.Dir(real), ".krino-*")
	if err != nil {
		return err
	}
	defer os.Remove(tmp.Name())
	if _, err := tmp.Write(data); err != nil {
		tmp.Close()
		return err
	}
	if err := tmp.Chmod(fi.Mode().Perm()); err != nil {
		tmp.Close()
		return err
	}
	if err := tmp.Sync(); err != nil {
		tmp.Close()
		return err
	}
	if err := tmp.Close(); err != nil {
		return err
	}
	return os.Rename(tmp.Name(), real)
}