package main

import (
	"encoding/base64"
	"fmt"
	"regexp"
	"strings"
	"unicode/utf8"
)

// Selections are the X selections xclip reaches.
var Selections = []string{"clipboard", "primary", "secondary"}

// MostCopy bounds what a caller may put on the clipboard.
const MostCopy = 1 << 20

var targetName = regexp.MustCompile(`^[A-Za-z0-9_][A-Za-z0-9_.+/;=-]{0,127}$`)

func checkTarget(t string) error {
	if t != "" && !targetName.MatchString(t) {
		return fmt.Errorf("%q is not a type a selection can be offered as", t)
	}
	return nil
}

// xclip runs xclip in the session, naming an unreachable display as such.
func xclip(s Session, c Cmd) (Result, error) {
	c.Name, c.Env = "xclip", s.Env()
	r := run(c)
	said := r.Stderr + r.Stdout
	switch {
	case r.Error != "":
		return r, failure(c, r)
	case strings.Contains(said, "Can't open display"):
		return r, fmt.Errorf("the X session at %s (found by %s) refused the connection: the display is gone, or the cookie in %s is not the server's", s.Display, s.FoundBy, orNone(s.XAuthority))
	case r.Status != 0:
		return r, failure(c, r)
	}
	return r, nil
}

func orNone(s string) string {
	if s == "" {
		return "(no authority file)"
	}
	return s
}

// CopyAnswer is what xclip_copy answers.
type CopyAnswer struct {
	Selection string  `json:"selection"`
	Type      string  `json:"type"`
	Bytes     int     `json:"bytes"`
	Session   Session `json:"session"`
	Note      string  `json:"note"`
}

// Copy puts text on a selection. xclip forks a process that holds the selection until another
// program takes it, so the command runs detached.
func Copy(text, selection, typ string) (CopyAnswer, error) {
	if len(text) > MostCopy {
		return CopyAnswer{}, fmt.Errorf("text is %d bytes; at most %d are copied", len(text), MostCopy)
	}
	if err := checkTarget(typ); err != nil {
		return CopyAnswer{}, err
	}
	s, err := findSession()
	if err != nil {
		return CopyAnswer{}, err
	}
	args := []string{"-selection", selection, "-in"}
	if typ != "" {
		args = append(args, "-t", typ)
	}
	if _, err := xclip(s, Cmd{Args: args, Stdin: text, Detached: true}); err != nil {
		return CopyAnswer{}, err
	}
	if typ == "" {
		typ = "UTF8_STRING"
	}
	return CopyAnswer{Selection: selection, Type: typ, Bytes: len(text), Session: s,
		Note: "xclip holds the selection until another program takes it; a clipboard manager may copy it into its history"}, nil
}

// PasteAnswer is what xclip_paste answers.
type PasteAnswer struct {
	Selection string `json:"selection"`
	Type      string `json:"type"`
	Empty     bool   `json:"empty"`
	Text      string `json:"text,omitempty"`
	Base64    string `json:"base64,omitempty"`
	Bytes     int    `json:"bytes"`
	Truncated bool   `json:"truncated,omitempty"`
}

// Paste reads a selection.
func Paste(selection, typ string) (PasteAnswer, error) {
	if err := checkTarget(typ); err != nil {
		return PasteAnswer{}, err
	}
	s, err := findSession()
	if err != nil {
		return PasteAnswer{}, err
	}
	args := []string{"-selection", selection, "-out"}
	if typ != "" {
		args = append(args, "-t", typ)
	} else {
		typ = "UTF8_STRING"
	}
	out := PasteAnswer{Selection: selection, Type: typ}
	r, err := xclip(s, Cmd{Args: args})
	if err != nil {
		// "Error: target … not available": the selection is empty, or not offered as that type.
		if strings.Contains(r.Stderr, "not available") {
			out.Empty = true
			return out, nil
		}
		return PasteAnswer{}, err
	}
	out.Bytes, out.Truncated = len(r.Stdout), r.Truncated
	if utf8.ValidString(r.Stdout) {
		out.Text = r.Stdout
	} else {
		out.Base64 = base64.StdEncoding.EncodeToString([]byte(r.Stdout))
	}
	out.Empty = out.Bytes == 0
	return out, nil
}

// Targets answers the types a selection is offered as.
func Targets(selection string) (map[string]any, error) {
	s, err := findSession()
	if err != nil {
		return nil, err
	}
	r, err := xclip(s, Cmd{Args: []string{"-selection", selection, "-out", "-t", "TARGETS"}})
	if err != nil {
		if strings.Contains(r.Stderr, "not available") {
			return map[string]any{"selection": selection, "targets": []string{}, "empty": true}, nil
		}
		return nil, err
	}
	return map[string]any{"selection": selection, "targets": lines(r.Stdout), "empty": strings.TrimSpace(r.Stdout) == ""}, nil
}

// SessionCheck answers the session and whether its X server answers.
func SessionCheck() (map[string]any, error) {
	s, err := findSession()
	if err != nil {
		return map[string]any{"found": false, "why": err.Error()}, nil
	}
	out := map[string]any{"found": true, "session": s}
	if _, err := Targets("clipboard"); err != nil {
		out["answers"], out["why"] = false, err.Error()
	} else {
		out["answers"] = true
	}
	return out, nil
}