package main

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"io/fs"
	"os"
	"path/filepath"
	"strings"

	"github.com/go-git/go-git/v5/plumbing/format/gitignore"
	gha "github.com/sethvargo/go-githubactions"
)

func main() {
	ghCtx, err := gha.Context()
	if err != nil {
		gha.Fatalf("gha.Context error: %v", err)
	}
	workdir := gha.GetInput("workdir")
	if len(workdir) == 0 {
		workdir = ghCtx.Workspace
	}

	inputPatterns := gha.GetInput("patterns")
	gha.Infof("input patterns: %s", inputPatterns)
	matchedFiles, hashResult, err := hashFiles(workdir, strings.Split(inputPatterns, "\n"))
	if err != nil {
		gha.Fatalf("hashFiles error: %v", err)
	}

	gha.SetOutput("hash", hashResult)
	gha.Infof("computed hash: %s", hashResult)

	matchedFilesJSON, _ := json.Marshal(matchedFiles)
	gha.SetOutput("matched-files", string(matchedFilesJSON))
	gha.Infof("matched files: %s", matchedFilesJSON)
}

func hashFiles(workdir string, patterns []string) ([]string, string, error) {
	var ps []gitignore.Pattern

	const cwdPrefix = "." + string(filepath.Separator)
	const excludeCwdPrefix = "!" + cwdPrefix

	for _, p := range patterns {
		cleanPattern := strings.TrimSpace(p)
		if len(cleanPattern) == 0 {
			continue
		}
		if strings.HasPrefix(cleanPattern, cwdPrefix) {
			cleanPattern = cleanPattern[len(cwdPrefix):]
		} else if strings.HasPrefix(cleanPattern, excludeCwdPrefix) {
			cleanPattern = "!" + cleanPattern[len(excludeCwdPrefix):]
		}
		ps = append(ps, gitignore.ParsePattern(cleanPattern, nil))
	}

	matcher := gitignore.NewMatcher(ps)

	var files []string
	if err := filepath.Walk(workdir, func(path string, fi fs.FileInfo, err error) error {
		if err != nil {
			return err
		}
		sansPrefix := strings.TrimPrefix(path, workdir+string(filepath.Separator))
		parts := strings.Split(sansPrefix, string(filepath.Separator))
		if fi.IsDir() || !matcher.Match(parts, fi.IsDir()) {
			return nil
		}
		files = append(files, path)
		return nil
	}); err != nil {
		return nil, "", fmt.Errorf("unable to filepath.Walk: %v", err)
	}

	if len(files) == 0 {
		return nil, "", nil
	}

	matchedFiles := make([]string, 0, len(files))
	resultHasher := sha256.New()

	for _, file := range files {
		f, err := os.Open(file)
		if err != nil {
			return nil, "", fmt.Errorf("unable to os.Open: %v", err)
		}

		hasher := sha256.New()

		if _, err := io.Copy(hasher, f); err != nil {
			return nil, "", fmt.Errorf("unable to io.Copy: %v", err)
		}

		if err := f.Close(); err != nil {
			return nil, "", fmt.Errorf("unable to Close file: %v", err)
		}

		if _, err := resultHasher.Write(hasher.Sum(nil)); err != nil {
			return nil, "", fmt.Errorf("unable to write resultHasher: %v", err)
		}

		matchedFiles = append(matchedFiles, strings.TrimPrefix(file, workdir+string(filepath.Separator)))
	}

	return matchedFiles, hex.EncodeToString(resultHasher.Sum(nil)), nil
}