package firmwareversion

import (
	"strconv"
	"strings"
)

type identifier struct {
	numeric bool
	number  uint64
	text    string
}

type semanticVersion struct {
	core [3]uint64
	pre  []identifier
}

// AtLeast compares SemVer-compatible versions. Vendor-specific opaque versions
// are accepted only when they exactly match the configured minimum, so an
// unorderable version can never silently bypass a minimum policy.
func AtLeast(current, minimum string) bool {
	current = strings.TrimSpace(current)
	minimum = strings.TrimSpace(minimum)
	if minimum == "" {
		return true
	}
	left, leftOK := parse(current)
	right, rightOK := parse(minimum)
	if !leftOK || !rightOK {
		return current == minimum
	}
	return compare(left, right) >= 0
}

func parse(value string) (semanticVersion, bool) {
	value = strings.TrimSpace(value)
	if strings.HasPrefix(value, "v") || strings.HasPrefix(value, "V") {
		value = value[1:]
	}
	if build := strings.IndexByte(value, '+'); build >= 0 {
		value = value[:build]
	}
	coreText, preText, _ := strings.Cut(value, "-")
	parts := strings.Split(coreText, ".")
	if len(parts) != 3 {
		return semanticVersion{}, false
	}
	var result semanticVersion
	for index, part := range parts {
		number, ok := numericIdentifier(part)
		if !ok {
			return semanticVersion{}, false
		}
		result.core[index] = number
	}
	if preText == "" {
		return result, true
	}
	for _, part := range strings.Split(preText, ".") {
		if part == "" || !validIdentifier(part) {
			return semanticVersion{}, false
		}
		if number, ok := numericIdentifier(part); ok {
			result.pre = append(result.pre, identifier{numeric: true, number: number, text: part})
		} else {
			result.pre = append(result.pre, identifier{text: part})
		}
	}
	return result, true
}

func compare(left, right semanticVersion) int {
	for index := range left.core {
		if left.core[index] < right.core[index] {
			return -1
		}
		if left.core[index] > right.core[index] {
			return 1
		}
	}
	if len(left.pre) == 0 && len(right.pre) == 0 {
		return 0
	}
	if len(left.pre) == 0 {
		return 1
	}
	if len(right.pre) == 0 {
		return -1
	}
	limit := min(len(left.pre), len(right.pre))
	for index := 0; index < limit; index++ {
		leftID, rightID := left.pre[index], right.pre[index]
		if leftID.numeric && rightID.numeric {
			if leftID.number < rightID.number {
				return -1
			}
			if leftID.number > rightID.number {
				return 1
			}
			continue
		}
		if leftID.numeric != rightID.numeric {
			if leftID.numeric {
				return -1
			}
			return 1
		}
		if leftID.text < rightID.text {
			return -1
		}
		if leftID.text > rightID.text {
			return 1
		}
	}
	if len(left.pre) < len(right.pre) {
		return -1
	}
	if len(left.pre) > len(right.pre) {
		return 1
	}
	return 0
}

func numericIdentifier(value string) (uint64, bool) {
	if value == "" || (len(value) > 1 && value[0] == '0') {
		return 0, false
	}
	for _, char := range value {
		if char < '0' || char > '9' {
			return 0, false
		}
	}
	number, err := strconv.ParseUint(value, 10, 64)
	return number, err == nil
}

func validIdentifier(value string) bool {
	for _, char := range value {
		if (char >= 'a' && char <= 'z') || (char >= 'A' && char <= 'Z') || (char >= '0' && char <= '9') || char == '-' {
			continue
		}
		return false
	}
	return true
}