package scraper

import (
	"sort"
	"strings"

	"github.com/go-enry/go-license-detector/v4/licensedb/filer"
)

// readmeCandidates are the filenames looked for, in priority order, when
// retrieving a repository's README.
var readmeCandidates = []string{"README.md", "README.rst", "README.txt", "README"}

// readmeFor returns the content of the repository's README on the given ref
// (default branch), picking from root (the pre-fetched root file listing) the
// first candidate found (case-insensitively). An empty string is returned when
// no README can be found; the repo is still kept in results either way.
func (s *ForgejoScraper) readmeFor(owner, name, ref string, root []filer.File) string {
	// Collect root file names, lowercased for case-insensitive matching, while
	// keeping the real name for the GetFile call.
	type rootFile struct {
		real string
		low  string
	}
	files := make([]rootFile, 0, len(root))
	for _, e := range root {
		if e.IsDir {
			continue
		}
		files = append(files, rootFile{real: e.Name, low: strings.ToLower(e.Name)})
	}

	// Candidate priority wins; ties broken by alphabetical real name for
	// deterministic picks when a repo has e.g. both README and README.md.
	sort.SliceStable(files, func(i, j int) bool {
		pi, pj := readmePriority(files[i].low), readmePriority(files[j].low)
		if pi != pj {
			return pi < pj // lower = higher priority
		}
		return files[i].real < files[j].real
	})

	var chosen string
	for i := range files {
		if readmePriority(files[i].low) >= 0 {
			chosen = files[i].real
			break
		}
	}
	if chosen == "" {
		return ""
	}

	data, _, err := s.Client.GetFile(owner, name, ref, chosen)
	if err != nil {
		return ""
	}
	return string(data)
}

// readmePriority returns the index of a lowercased filename in
// readmeCandidates, or -1 if it is not a readme candidate.
func readmePriority(low string) int {
	for i, c := range readmeCandidates {
		if low == strings.ToLower(c) {
			return i
		}
	}
	return -1
}