package main

import (
	"bytes"
	"io"
	"os"
	"sync"

	"github.com/charmbracelet/x/ansi"
)

// terminalCursorOutput decorates Bubble Tea's completed frame writes with a
// hardware cursor position. Bubble Tea otherwise parks the cursor at the
// bottom of every frame, which prevents a real insertion caret inside a custom
// editor.
type terminalCursorOutput struct {
	file *os.File

	mu      sync.Mutex
	visible bool
	column  int
	row     int
}

func newTerminalCursorOutput(file *os.File) *terminalCursorOutput {
	return &terminalCursorOutput{file: file}
}

func (o *terminalCursorOutput) SetCursor(visible bool, column, row int) {
	o.mu.Lock()
	defer o.mu.Unlock()
	o.visible, o.column, o.row = visible, column, row
}

func (o *terminalCursorOutput) FrameMarker() string {
	o.mu.Lock()
	defer o.mu.Unlock()
	if !o.visible {
		return ""
	}
	// This zero-width sequence makes frames at different insertion positions
	// distinct, preventing Bubble Tea from skipping a hardware-cursor-only
	// update. The output wrapper reasserts the same position after Bubble Tea
	// parks its cursor at the bottom of the frame.
	return ansi.CursorPosition(o.column, o.row)
}

func (o *terminalCursorOutput) Write(value []byte) (int, error) {
	o.mu.Lock()
	defer o.mu.Unlock()

	// Bubble Tea v1 can expose intermediate rows from an animated partial
	// repaint. This is especially visible when unchanged Markdown code blocks
	// below the changed rows contain dense ANSI styling. Terminals that support
	// synchronized output hold the completed frame until the reset sequence;
	// terminals that do not support it safely ignore both sequences.
	if !bytes.Equal(value, []byte(ansi.ShowCursor)) &&
		!bytes.Equal(value, []byte(ansi.HideCursor)) {
		if _, err := io.WriteString(o.file, ansi.SetSynchronizedOutputMode); err != nil {
			return 0, err
		}
		defer func() {
			_, _ = io.WriteString(o.file, ansi.ResetSynchronizedOutputMode)
		}()
	}

	written, err := o.file.Write(value)
	if err != nil || written != len(value) {
		return written, err
	}
	// Let Bubble Tea restore the cursor normally during startup/shutdown.
	if bytes.Equal(value, []byte(ansi.ShowCursor)) || bytes.Equal(value, []byte(ansi.HideCursor)) {
		if bytes.Equal(value, []byte(ansi.ShowCursor)) {
			_, _ = io.WriteString(o.file, ansi.SetCursorStyle(0))
		}
		return written, nil
	}
	if !o.visible {
		_, err = io.WriteString(o.file, ansi.HideCursor)
		return written, err
	}
	_, err = io.WriteString(
		o.file,
		ansi.SetCursorStyle(5)+
			ansi.CursorPosition(o.column, o.row)+
			ansi.ShowCursor,
	)
	return written, err
}

func (o *terminalCursorOutput) Read(value []byte) (int, error) {
	return o.file.Read(value)
}

func (o *terminalCursorOutput) Close() error {
	return nil
}

func (o *terminalCursorOutput) Fd() uintptr {
	return o.file.Fd()
}