package validation

import (
	"fmt"
	"regexp"
	"strings"
)

func ValidateConventionalCommit(commit string) error {
	// Regex to match the commit format
	// type(scope)!: description
	// or
	// type!: description
	// or
	// type: description
	re := regexp.MustCompile(`^(?P<type>[a-z]+)(?P<scope>\([a-z]+\))?(?P<breaking>!)?: (?P<description>[a-z].+)$`)
	match := re.FindStringSubmatch(commit)

	if len(match) == 0 {
		return fmt.Errorf("Invalid PR title")
	}

	typeIndex := re.SubexpIndex("type")
	scopeIndex := re.SubexpIndex("scope")
	breakingIndex := re.SubexpIndex("breaking")
	descriptionIndex := re.SubexpIndex("description")

	commitType := match[typeIndex]
	scope := match[scopeIndex]
	breaking := match[breakingIndex]
	description := match[descriptionIndex]

	// Type MUST be lowercase
	if commitType != strings.ToLower(commitType) {
		return fmt.Errorf("type must be lowercase")
	}

	// Description MUST start with lowercase
	if description != strings.ToLower(description) {
		return fmt.Errorf("description must start with lowercase")
	}

	// Scope MUST be lowercase
	if scope != "" && scope != strings.ToLower(scope) {
		return fmt.Errorf("scope must be lowercase")
	}

	// Check for breaking change indicator
	hasBreakingChangeFooter := strings.Contains(commit, "BREAKING CHANGE:")
	if breaking == "!" && hasBreakingChangeFooter {
		return fmt.Errorf("breaking change indicator and footer are mutually exclusive")
	}

	lines := strings.Split(commit, "\n")
	if len(lines) > 1 {
		body := strings.Join(lines[1:], "\n")
		// Check if body is separated from description by a blank line
		if !strings.HasPrefix(body, "\n") {
			return fmt.Errorf("body must be separated from description by a blank line")
		}
	}

	// Check for footers
	footerRegex := regexp.MustCompile(`(?m)^(?P<token>[A-Za-z-]+|BREAKING CHANGE): (?P<value>.*)$`)
	footerMatches := footerRegex.FindAllStringSubmatch(commit, -1)

	for _, footerMatch := range footerMatches {
		tokenIndex := footerRegex.SubexpIndex("token")
		token := footerMatch[tokenIndex]

		// BREAKING-CHANGE MUST be synonymous with BREAKING CHANGE
		if token == "BREAKING-CHANGE" {
			continue
		}

		// Token MUST use - in place of whitespace characters, except for BREAKING CHANGE
		if token != "BREAKING CHANGE" && strings.Contains(token, " ") {
			return fmt.Errorf("footer token must use - in place of whitespace characters")
		}
	}

	return nil
}