package platform

import (
	"fmt"
	"os"
	"strings"
)

func blockMarkers(marker string) (string, string) {
	return fmt.Sprintf("# >>> %s >>>", marker), fmt.Sprintf("# <<< %s <<<", marker)
}

// EnsureBlock writes a marker-delimited block into path. If the file does
// not exist it is created. If a block with the same marker already exists
// it is replaced in place. Surrounding content is preserved.
func EnsureBlock(path, marker, content string) error {
	start, end := blockMarkers(marker)
	existing, err := os.ReadFile(path)
	if err != nil && !os.IsNotExist(err) {
		return err
	}
	block := start + "\n" + strings.TrimRight(content, "\n") + "\n" + end + "\n"

	text := string(existing)
	si := strings.Index(text, start)
	ei := strings.Index(text, end)
	if si >= 0 && ei > si {
		endPos := ei + len(end)
		if endPos < len(text) && text[endPos] == '\n' {
			endPos++
		}
		text = text[:si] + block + text[endPos:]
	} else {
		if text != "" && !strings.HasSuffix(text, "\n") {
			text += "\n"
		}
		text += block
	}
	return os.WriteFile(path, []byte(text), 0o644)
}

// HasBlock reports whether path contains a block with the given marker.
// A missing file yields (false, nil).
func HasBlock(path, marker string) (bool, error) {
	start, _ := blockMarkers(marker)
	data, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			return false, nil
		}
		return false, err
	}
	return strings.Contains(string(data), start), nil
}

// RemoveBlock deletes a marker-delimited block if present.
func RemoveBlock(path, marker string) error {
	start, end := blockMarkers(marker)
	data, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			return nil
		}
		return err
	}
	text := string(data)
	si := strings.Index(text, start)
	ei := strings.Index(text, end)
	if si < 0 || ei <= si {
		return nil
	}
	endPos := ei + len(end)
	if endPos < len(text) && text[endPos] == '\n' {
		endPos++
	}
	text = text[:si] + text[endPos:]
	return os.WriteFile(path, []byte(text), 0o644)
}