package server

import (
	"io"
	"os"
	"os/exec"
	"regexp"

	"github.com/creack/pty"
)

// ansiRegex matches ANSI escape sequences for stripping terminal formatting.
var ansiRegex = regexp.MustCompile(`\x1b\[[0-9;]*[a-zA-Z]|\x1b\].*?\x07|\x1b\[[\?0-9;]*[a-zA-Z]`)

// stripAnsi removes ANSI escape codes from a string.
func stripAnsi(s string) string {
	return ansiRegex.ReplaceAllString(s, "")
}

// startPTY starts a command in a pseudo-terminal and returns the PTY master fd.
// The caller is responsible for closing the returned *os.File.
func startPTY(cmd *exec.Cmd) (*os.File, error) {
	ptmx, err := pty.StartWithSize(cmd, &pty.Winsize{Rows: 40, Cols: 120})
	if err != nil {
		return nil, err
	}
	return ptmx, nil
}

// readPTY reads from a PTY master and calls sendLine for each chunk of text.
// It splits on newlines so each SSE event is one line.
func readPTY(ptmx io.Reader, sendLine func(string)) {
	buf := make([]byte, 4096)
	var partial string
	for {
		n, err := ptmx.Read(buf)
		if n > 0 {
			text := partial + stripAnsi(string(buf[:n]))
			partial = ""

			// Split into lines, keep partial for next read
			for {
				idx := -1
				for i, b := range []byte(text) {
					if b == '\n' || b == '\r' {
						idx = i
						break
					}
				}
				if idx < 0 {
					partial = text
					break
				}
				line := text[:idx]
				// Skip empty lines from \r\n sequences
				if line != "" {
					sendLine(line)
				}
				// Skip past the newline character(s)
				text = text[idx+1:]
			}
		}
		if err != nil {
			// Send remaining partial text
			if partial != "" {
				sendLine(partial)
			}
			break
		}
	}
}