package fetch

import (
	"encoding/json"
	"fmt"
	"github.com/tweag/gomod2nix/types"
	"golang.org/x/mod/modfile"
	"golang.org/x/tools/go/vcs"
	"io/ioutil"
	"os/exec"
	"sort"
)

type packageJob struct {
	importPath    string
	goPackagePath string
	rev           string
}

type packageResult struct {
	pkg *types.Package
	err error
}

func worker(id int, replace map[string]string, jobs <-chan *packageJob, results chan<- *packageResult) {
	for j := range jobs {
		pkg, err := fetchPackage(j.importPath, j.goPackagePath, j.rev)
		results <- &packageResult{
			err: err,
			pkg: pkg,
		}
	}
}

func FetchPackages(goModPath string, goSumPath string, numWorkers int, keepGoing bool) ([]*types.Package, error) {

	// Read go.mod
	data, err := ioutil.ReadFile(goModPath)
	if err != nil {
		return nil, err
	}

	// Parse go.mod
	mod, err := modfile.Parse(goModPath, data, nil)
	if err != nil {
		return nil, err
	}

	// // Parse require
	// require := make(map[string]module.Version)
	// for _, req := range mod.Require {
	// 	require[req.Mod.Path] = req.Mod
	// }

	// Map repos -> replacement repo
	replace := make(map[string]string)
	for _, repl := range mod.Replace {
		replace[repl.Old.Path] = repl.New.Path
	}

	revs, err := parseGoSum(goSumPath)
	if err != nil {
		return nil, err
	}

	numJobs := len(revs)
	if numJobs < numWorkers {
		numWorkers = numJobs
	}

	jobs := make(chan *packageJob, numJobs)
	results := make(chan *packageResult, numJobs)
	for i := 0; i <= numWorkers; i++ {
		go worker(i, replace, jobs, results)
	}

	for goPackagePath, rev := range revs {
		// Check for replacement path (only original goPackagePath is recorded in go.sum)
		importPath := goPackagePath
		v, ok := replace[goPackagePath]
		if ok {
			importPath = v
		}
		jobs <- &packageJob{
			importPath:    importPath,
			goPackagePath: goPackagePath,
			rev:           rev,
		}
	}
	close(jobs)

	var pkgs []*types.Package
	for i := 1; i <= numJobs; i++ {
		result := <-results
		if result.err != nil {
			if keepGoing {
				fmt.Println(result.err)
				continue
			} else {
				return nil, result.err
			}
		}

		pkgs = append(pkgs, result.pkg)
	}

	sort.Slice(pkgs, func(i, j int) bool {
		return pkgs[i].GoPackagePath < pkgs[j].GoPackagePath
	})

	return pkgs, nil
}

func fetchPackage(importPath string, goPackagePath string, rev string) (*types.Package, error) {
	repoRoot, err := vcs.RepoRootForImportPath(importPath, false)
	if err != nil {
		return nil, err
	}

	if repoRoot.VCS.Name != "Git" {
		return nil, fmt.Errorf("Only git repositories are supported")
	}

	type prefetchOutput struct {
		URL    string `json:"url"`
		Rev    string `json:"rev"`
		Sha256 string `json:"sha256"`
		// path   string
		// date   string
		// fetchSubmodules bool
		// deepClone       bool
		// leaveDotGit     bool
	}
	stdout, err := exec.Command(
		"nix-prefetch-git",
		"--quiet",
		"--fetch-submodules",
		"--url", repoRoot.Repo,
		"--rev", rev).Output()
	if err != nil {
		return nil, err
	}

	var output *prefetchOutput

	err = json.Unmarshal(stdout, &output)
	if err != nil {
		return nil, err
	}

	return &types.Package{
		GoPackagePath: goPackagePath,
		URL:           repoRoot.Repo,
		// It may feel appealing to use output.Rev to get the full git hash
		// However, this has the major downside of not being able to be checked against an
		// older output file (as the revs) don't match
		//
		// This is used to skip fetching where the previous package path & rev are still the same
		Rev:  rev,
		Hash: fmt.Sprintf("sha256:%s", output.Sha256),
	}, nil

}