// Package term provides the tcell-backed Terminal for the Rogue port. It
// replaces curses and the 900-line escape-sequence decoder in mdport.c:
// tcell delivers decoded key events, which are translated here to the
// single-byte command codes the game understands.
package term

import (
	"context"
	"errors"
	"fmt"
	"os"
	"os/exec"

	"github.com/gdamore/tcell/v2"

	"git.eeqj.de/sneak/rgoue/game"
)

// Tcell renders game Windows on a tcell screen and turns key events into
// Rogue input bytes.
type Tcell struct {
	screen tcell.Screen
	last   *game.Window // last rendered window, for resize redraws
}

// ErrScreenTooSmall reports a terminal below the required 80x24.
var ErrScreenTooSmall = errors.New("screen too small")

// New initializes the terminal. The screen must be at least 80x24, as the
// C game required.
func New() (*Tcell, error) {
	s, err := tcell.NewScreen()
	if err != nil {
		return nil, err
	}

	initErr := s.Init()
	if initErr != nil {
		return nil, initErr
	}

	w, h := s.Size()
	if h < game.NumLines || w < game.NumCols {
		s.Fini()

		return nil, fmt.Errorf("sorry, %w: %dx%d required",
			ErrScreenTooSmall, game.NumCols, game.NumLines)
	}

	s.HideCursor()

	return &Tcell{screen: s}, nil
}

// Fini restores the terminal.
func (t *Tcell) Fini() {
	t.screen.Fini()
}

// Render blits a game window to the terminal (curses refresh).
func (t *Tcell) Render(w *game.Window) {
	t.last = w

	rows, cols := w.Size()
	for y := range rows {
		for x := range cols {
			ch, standout := w.CellAt(y, x)

			style := tcell.StyleDefault
			if standout {
				style = style.Reverse(true)
			}

			t.screen.SetContent(x, y, rune(ch), nil, style)
		}
	}

	t.screen.Show()
}

// ReadChar blocks for the next key, translated to the byte codes the C
// game reads: arrows become hjkl, control keys their C0 codes.
func (t *Tcell) ReadChar() byte {
	for {
		ev := t.screen.PollEvent()
		switch ev := ev.(type) {
		case *tcell.EventResize:
			if t.last != nil {
				t.Render(t.last)
			}
		case *tcell.EventKey:
			if b, ok := translateKey(ev); ok {
				return b
			}
		}
	}
}

// translateKey converts a key event to a game input byte; ok is false
// for keys the C game does not understand.
func translateKey(ev *tcell.EventKey) (byte, bool) {
	if b, ok := namedKey(ev.Key()); ok {
		return b, true
	}

	if ev.Key() >= tcell.KeyCtrlA && ev.Key() <= tcell.KeyCtrlZ {
		return byte(ev.Key()), true //nolint:gosec // G115: 1..26 fits
	}

	if r := ev.Rune(); r > 0 && r < 0x80 {
		return byte(r), true
	}

	return 0, false
}

// namedKey translates tcell's navigation and editing keys to the single
// bytes the C game reads (arrows become hjkl, etc.); ok is false for
// keys handled elsewhere.
func namedKey(k tcell.Key) (byte, bool) {
	if b, ok := motionKey(k); ok {
		return b, true
	}

	return editingKey(k)
}

// motionKey translates the arrow and paging keys to Rogue's movement
// letters (tcell.go ReadChar).
func motionKey(k tcell.Key) (byte, bool) {
	switch k {
	case tcell.KeyUp:
		return 'k', true
	case tcell.KeyDown:
		return 'j', true
	case tcell.KeyLeft:
		return 'h', true
	case tcell.KeyRight:
		return 'l', true
	case tcell.KeyHome:
		return 'y', true
	case tcell.KeyPgUp:
		return 'u', true
	case tcell.KeyEnd:
		return 'b', true
	case tcell.KeyPgDn:
		return 'n', true
	}

	return 0, false
}

// editingKey translates the editing and control keys to their C0 codes
// (tcell.go ReadChar).
func editingKey(k tcell.Key) (byte, bool) {
	switch k {
	case tcell.KeyEnter:
		return '\n', true
	case tcell.KeyEscape:
		return game.Escape, true
	case tcell.KeyBackspace, tcell.KeyBackspace2:
		return 8, true
	case tcell.KeyDelete:
		return 0x7f, true
	case tcell.KeyTab:
		return '\t', true
	case tcell.KeyCtrlC:
		return 3, true
	}

	return 0, false
}

// ShellEscape suspends the screen and runs the user's shell (main.c
// shell + md_shellescape).
func (t *Tcell) ShellEscape() {
	err := t.screen.Suspend()
	if err != nil {
		return
	}

	shell := os.Getenv("SHELL")
	if shell == "" {
		shell = "/bin/sh"
	}

	_, _ = fmt.Fprintln(os.Stdout,
		"[Entering shell; exit to return to the game]")

	// The shell session has no deadline by design; Background context.
	cmd := exec.CommandContext(context.Background(), //nolint:gosec // G204: the user's own $SHELL
		shell)
	cmd.Stdin = os.Stdin
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	_ = cmd.Run() // best effort: the shell is the user's business

	resumeErr := t.screen.Resume()
	if resumeErr != nil {
		panic(resumeErr) // terminal resume failure is unrecoverable
	}
}