// Copyright (c) 2026 Storm Dragon
// SPDX-License-Identifier: GPL-3.0-or-later

package tentacle

import (
	"fmt"
	"strings"
)

// AvailableUpdate describes a newer repository release for an installed tentacle.
type AvailableUpdate struct {
	ID               string
	Name             string
	InstalledVersion string
	AvailableVersion string
	RepositoryURL    string
	RepositoryID     string
	LocalID          string
}

// packageVersion accepts dotted numeric releases (including existing short
// versions such as 0.1), with optional SemVer prerelease and build identifiers.
type packageVersion struct {
	numbers    []string
	prerelease []string
}

func numeric_identifier(value string) bool {
	if value == "" {
		return false
	}
	for _, ch := range value {
		if ch < '0' || ch > '9' {
			return false
		}
	}
	return true
}

func version_identifiers(value string, prerelease bool) ([]string, error) {
	identifiers := strings.Split(value, ".")
	for _, identifier := range identifiers {
		if identifier == "" {
			return nil, fmt.Errorf("empty version identifier")
		}
		for _, ch := range identifier {
			if !(ch >= '0' && ch <= '9' || ch >= 'a' && ch <= 'z' || ch >= 'A' && ch <= 'Z' || ch == '-') {
				return nil, fmt.Errorf("invalid version identifier %q", identifier)
			}
		}
		if prerelease && numeric_identifier(identifier) && len(identifier) > 1 && identifier[0] == '0' {
			return nil, fmt.Errorf("prerelease number has a leading zero")
		}
	}
	return identifiers, nil
}

func parse_package_version(value string) (packageVersion, error) {
	var result packageVersion
	core := strings.TrimPrefix(strings.TrimSpace(value), "v")
	if before, build, found := strings.Cut(core, "+"); found {
		if _, err := version_identifiers(build, false); err != nil {
			return result, err
		}
		core = before
	}
	if before, prerelease, found := strings.Cut(core, "-"); found {
		var err error
		result.prerelease, err = version_identifiers(prerelease, true)
		if err != nil {
			return result, err
		}
		core = before
	}
	result.numbers = strings.Split(core, ".")
	for _, number := range result.numbers {
		if !numeric_identifier(number) {
			return result, fmt.Errorf("invalid numeric version %q", value)
		}
	}
	return result, nil
}

// Compare decimal strings without an integer-size limit.
func compare_version_number(first, second string) int {
	first, second = strings.TrimLeft(first, "0"), strings.TrimLeft(second, "0")
	if len(first) < len(second) {
		return -1
	}
	if len(first) > len(second) {
		return 1
	}
	return strings.Compare(first, second)
}

// IsNewerVersion compares release and prerelease precedence. Build metadata
// does not change precedence; missing numeric components are treated as zero.
func IsNewerVersion(available, installed string) (bool, error) {
	first, err := parse_package_version(available)
	if err != nil {
		return false, err
	}
	second, err := parse_package_version(installed)
	if err != nil {
		return false, err
	}
	for index := 0; index < len(first.numbers) || index < len(second.numbers); index++ {
		firstNumber, secondNumber := "0", "0"
		if index < len(first.numbers) {
			firstNumber = first.numbers[index]
		}
		if index < len(second.numbers) {
			secondNumber = second.numbers[index]
		}
		if compared := compare_version_number(firstNumber, secondNumber); compared != 0 {
			return compared > 0, nil
		}
	}
	if len(first.prerelease) == 0 || len(second.prerelease) == 0 {
		return len(first.prerelease) == 0 && len(second.prerelease) != 0, nil
	}
	for index := 0; index < len(first.prerelease) && index < len(second.prerelease); index++ {
		firstID, secondID := first.prerelease[index], second.prerelease[index]
		firstNumeric, secondNumeric := numeric_identifier(firstID), numeric_identifier(secondID)
		compared := strings.Compare(firstID, secondID)
		if firstNumeric && secondNumeric {
			compared = compare_version_number(firstID, secondID)
		}
		if firstNumeric != secondNumeric {
			return !firstNumeric, nil
		}
		if compared != 0 {
			return compared > 0, nil
		}
	}
	return len(first.prerelease) > len(second.prerelease), nil
}

// AvailableUpdates finds newer versions of installed repository tentacles.
func AvailableUpdates(snapshot Snapshot) []AvailableUpdate {
	var updates []AvailableUpdate
	for _, status := range snapshot.Entries {
		entry := status.Entry
		if entry.Repository == "" || entry.Version == "" {
			continue
		}
		for _, repository := range snapshot.Repositories {
			if repository.URL != entry.Repository || repository.ID != entry.RepositoryID {
				continue
			}
			for _, manifest := range repository.Tentacles {
				if manifest.ID != entry.LocalID {
					continue
				}
				newer, err := IsNewerVersion(manifest.Version, entry.Version)
				if err != nil || !newer {
					continue
				}
				updates = append(updates, AvailableUpdate{
					ID:               entry.ID,
					Name:             manifest.Name,
					InstalledVersion: entry.Version,
					AvailableVersion: manifest.Version,
					RepositoryURL:    repository.URL,
					RepositoryID:     repository.ID,
					LocalID:          manifest.ID,
				})
			}
		}
	}
	return updates
}