package engineversion

import (
	"fmt"
	"strings"

	"golang.org/x/mod/semver"
)

// ParseSemver normalises version into the canonical "vMAJOR.MINOR.PATCH"
// form expected by `golang.org/x/mod/semver` and reports a wrapped
// ErrInvalidSemver when the resulting string is not a valid full semver.
//
// Whitespace is trimmed; a missing leading "v" is added before the
// validity check so callers may pass either "1.2.3" or "v1.2.3". The
// stripped base must carry exactly three dot-separated numeric
// components — `golang.org/x/mod/semver` accepts shortened forms such
// as "v1" or "v1.2", but the engine-version registry requires the full
// triple, so this function rejects anything narrower.
func ParseSemver(version string) (string, error) {
	candidate := strings.TrimSpace(version)
	if candidate == "" {
		return "", fmt.Errorf("%w: empty", ErrInvalidSemver)
	}
	if !strings.HasPrefix(candidate, "v") {
		candidate = "v" + candidate
	}
	if !semver.IsValid(candidate) {
		return "", fmt.Errorf("%w: %q", ErrInvalidSemver, version)
	}

	base := candidate
	if i := strings.IndexAny(base, "-+"); i >= 0 {
		base = base[:i]
	}
	if strings.Count(base, ".") != 2 {
		return "", fmt.Errorf(
			"%w: %q (need vMAJOR.MINOR.PATCH)",
			ErrInvalidSemver, version,
		)
	}
	return candidate, nil
}

// IsPatchUpgrade reports whether next is a same-major.minor upgrade of
// current. Both inputs are parsed through ParseSemver so callers may
// pass either bare or `v`-prefixed forms. A wrapped ErrInvalidSemver is
// returned when either argument fails to parse; the boolean result is
// undefined in that case.
func IsPatchUpgrade(current, next string) (bool, error) {
	curr, err := ParseSemver(current)
	if err != nil {
		return false, fmt.Errorf("current: %w", err)
	}
	nxt, err := ParseSemver(next)
	if err != nil {
		return false, fmt.Errorf("next: %w", err)
	}
	return semver.MajorMinor(curr) == semver.MajorMinor(nxt), nil
}