package pi

import (
	"bufio"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strings"
)

var defaultPiArgPattern = regexp.MustCompile(`^ARG[[:space:]]+PI_VERSION[[:space:]]*=(.*)$`)

// ReadPinnedVersion reads the repository's declared Pi runtime version. It deliberately reads
// only the default ARG, not the later ARG PI_VERSION declarations used by build stages.
func ReadPinnedVersion(projectDirectory string) (string, error) {
	path := filepath.Join(projectDirectory, "docker", "core.Dockerfile")
	file, err := os.Open(path)
	if err != nil {
		return "", fmt.Errorf("read Pi version pin: %w", err)
	}
	defer file.Close()

	var version string
	count := 0
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		match := defaultPiArgPattern.FindStringSubmatch(strings.TrimSuffix(scanner.Text(), "\r"))
		if len(match) != 2 {
			continue
		}
		count++
		version = strings.TrimSpace(match[1])
	}
	if err := scanner.Err(); err != nil {
		return "", fmt.Errorf("read Pi version pin: %w", err)
	}
	if count != 1 {
		return "", errors.New("docker/core.Dockerfile must contain exactly one default PI_VERSION")
	}
	if _, err := parseSemanticVersion(version); err != nil {
		return "", errors.New("docker/core.Dockerfile contains an invalid Pi version")
	}
	return version, nil
}