package main

import (
	"bufio"
	"bytes"
	_ "embed"
	"encoding/json"
	"flag"
	"fmt"
	"html/template"
	"io"
	"log"
	"net/url"
	"os"
	"os/exec"
	"path/filepath"
	"reflect"
	"strings"
	"sync"
	"text/tabwriter"
	"time"
)

// For separating out commit line items.
const SEP = "6f6c1745-e902-474a-9e99-08d0084fb011"

//go:embed branch.html.tmpl
var bTmpl string

//go:embed home.html.tmpl
var rTmpl string

//go:embed commit.html.tmpl
var cTmpl string

//go:embed diff.html.tmpl
var dTmpl string

//go:embed object.html.tmpl
var oTmpl string

type repository struct {
	base     string
	Branches []branch
	Name     string
	temp     string
}

type branch struct {
	Commits []commit
	Name    string
	Project string
}

func (b branch) String() string {
	return b.Name
}

type hash struct {
	Hash  string
	Short string
}

func (h hash) String() string {
	return h.Hash
}

type object struct {
	Hash string
	Path string
}

type commit struct {
	Branch  string
	Body    string
	Abbr    string
	History []string
	Parents []string
	Graph   string
	Hash    string
	Author  author
	Date    time.Time
	Project string
	Tree    []object
	Subject string
}

type author struct {
	Email string
	Name  string
}

// https://stackoverflow.com/questions/28322997/how-to-get-a-list-of-values-into-a-flag-in-golang/
type manyflag []string

func (f *manyflag) Set(value string) error {
	// Make sure there are no duplicates.
	if !contains(*f, value) {
		*f = append(*f, value)
	}

	return nil
}

func (f *manyflag) String() string {
	return strings.Join(*f, ", ")
}

type options struct {
	Branches manyflag `json:"branches"`
	config   string
	Force    bool   `json:"force"`
	Project  string `json:"project"`
	Quiet    bool   `json:"quiet"`
	Repo     string `json:"repo"`
	URL      string `json:"url"`
}

// Helps store options into a JSON config file.
func (o *options) save(p string) error {
	bs, err := json.MarshalIndent(o, "", "  ")

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

	if err := os.WriteFile(filepath.Join(p, o.config), bs, 0644); err != nil {
		return fmt.Errorf("unable to save config file: %v", err)
	}

	return nil
}

func init() {
	// Override default usage output.
	flag.Usage = func() {
		// Print usage example ahead of lisiting default options.
		fmt.Fprintln(flag.CommandLine.Output(), "usage:", os.Args[0], "[<options>] <path>")
		flag.PrintDefaults()
	}

	// Swap default logger timestamps for a custom prefix.
	log.SetFlags(log.Lmsgprefix)
	log.SetPrefix("gtx: ")
}

func main() {
	opt := &options{
		config: ".jimmy.json",
	}

	flag.StringVar(&opt.Project, "p", "Jimbo", "Project title")
	flag.StringVar(&opt.Repo, "r", "", "Target repo")
	flag.Var(&opt.Branches, "b", "Target branches")
	flag.StringVar(&opt.URL, "u", "https://host.net/project.git", "Repo public URL")
	flag.BoolVar(&opt.Quiet, "q", false, "Be quiet")
	flag.BoolVar(&opt.Force, "f", false, "Force rebuild")
	flag.Parse()

	if opt.Quiet {
		log.SetOutput(io.Discard)
	}

	cwd, err := os.Getwd()

	if err != nil {
		log.Fatalf("unable to get current working directory: %v", err)
	}

	// Defaults to the current working directory if no argument present.
	outpath := flag.Arg(0)

	// Make sure `outpath` is an absolute path.
	if ok := filepath.IsAbs(outpath); !ok {
		outpath = filepath.Join(cwd, outpath)
	}

	// Create a separate options instance for reading config file values into.
	store := *opt

	// Need deep copy the underlying slice types.
	store.Branches = append(store.Branches, opt.Branches...)

	// Attempt to read saved settings.
	bs, err := os.ReadFile(filepath.Join(outpath, opt.config))

	if err != nil {
		log.Printf("unable to read config file: %v", err)
	}

	// If a config file exists and an option has not been set, override default to match.
	if err := json.Unmarshal(bs, &store); err != nil {
		log.Printf("unable to parse config file: %v", err)
	}

	// Collect flags provided.
	flagset := make(map[string]bool)

	// NOTE: These need to come before the output directory argument.
	flag.Visit(func(f *flag.Flag) {
		flagset[f.Name] = true
	})

	ref := reflect.ValueOf(store)
	tab := tabwriter.NewWriter(log.Writer(), 0, 0, 0, '.', 0)

	flag.VisitAll(func(f *flag.Flag) {
		// Attempt to source settings from config file, then override flag defaults.
		if !flagset[f.Name] {
			v := ref.FieldByNameFunc(func(n string) bool {
				return strings.HasPrefix(strings.ToLower(n), f.Name)
			})

			// Don't ask.
			if s, ok := v.Interface().(manyflag); ok {
				for _, b := range s {
					flag.Set(f.Name, b)
				}
			} else {
				// This has the welcome side effect of magically overriding `opt` fields.
				flag.Set(f.Name, v.String())
			}
		}

		fmt.Fprintf(tab, "gtx: -%s \t%s\t: %v\n", f.Name, f.Usage, f.Value)
	})

	tab.Flush()

	// The repo flag is required at this point.
	if ok := filepath.IsAbs(opt.Repo); ok {
		// Option considered repo-like if it contains a hidden `.git` dir.
		if _, err := os.Stat(filepath.Join(opt.Repo, ".git")); os.IsNotExist(err) {
			flag.Usage()
			os.Exit(1)
		}
	} else {
		// Allow for URL-looking non-local repos.
		if _, err := url.ParseRequestURI(opt.Repo); err != nil {
			flag.Usage()
			os.Exit(1)
		}
	}

	// Make sure `outpath` exists.
	if err := os.MkdirAll(outpath, 0750); err != nil {
		log.Fatalf("unable to create output directory: %v", err)
	}

	// Save current settings for future use.
	if err := opt.save(outpath); err != nil {
		log.Fatalf("unable to save options: %v", err)
	}

	ucd, err := os.UserCacheDir()

	if err != nil {
		log.Fatalf("unable to locate user cache folder: %s", err)
	}

	p, err := os.MkdirTemp(ucd, "gtx-*")

	if err != nil {
		log.Fatalf("unable to locate temporary host dir: %s", err)
	}

	log.Printf("user cache set: %s", p)

	repo := &repository{
		base: outpath,
		Name: opt.Project,
		temp: p,
	}

	// Create base directories.
	if err := repo.init(opt.Force); err != nil {
		log.Fatalf("unable to initialize output directory: %v", err)
	}

	// Clone target repo.
	if err := repo.save(opt.Repo); err != nil {
		log.Fatalf("unable to set up repo: %v", err)
	}

	branches, err := repo.branchfilter(opt.Branches)

	if err != nil {
		log.Fatalf("unable to filter branches: %v", err)
	}

	var wg sync.WaitGroup

	// Update each branch.
	for _, b := range branches {
		// NOTE: Is this needed still if the repo is downloaded each time the script is run?
		ref := fmt.Sprintf("refs/heads/%s:refs/origin/%s", b, b)

		cmd := exec.Command("git", "fetch", "--force", "origin", ref)
		cmd.Dir = repo.temp

		if _, err := cmd.Output(); err != nil {
			log.Printf("unable to fetch branch: %v", err)

			continue
		}

		log.Printf("processing branch: %s", b)
		wg.Add(1)

		go func() {
			defer wg.Done()

			dst := filepath.Join(outpath, "branch", b.Name, "index.html")

			if err := os.MkdirAll(filepath.Dir(dst), 0750); err != nil {
				if err != nil {
					log.Fatalf("unable to create branch directory: %v", err)
				}

				return
			}

			f, err := os.Create(dst)

			defer f.Close()

			if err != nil {
				// TODO: Remove from branches slice?
				log.Printf("unable to create branch page: %v", err)

				return
			}

			t := template.Must(template.New("branch").Parse(bTmpl))

			if err := t.Execute(f, b); err != nil {
				log.Printf("unable to apply template: %v", err)

				return
			}
		}()
	}

	for _, b := range branches {
		for i, c := range b.Commits {
			log.Printf("processing commit: %s: %d/%d", c.Abbr, i+1, len(b.Commits))

			base := filepath.Join(outpath, "commit", c.Hash)

			if err := os.MkdirAll(base, 0750); err != nil {
				if err != nil {
					log.Printf("unable to create commit directory: %v", err)
				}

				continue
			}

			for _, parent := range c.Parents {
				wg.Add(1)

				go func() {
					defer wg.Done()

					dst := filepath.Join(base, fmt.Sprintf("diff-to-%s.html", parent))
					f, err := os.Create(dst)

					defer f.Close()

					if err != nil {
						log.Printf("unable to create commit diff to parent page: %v", err)

						return
					}

					t := template.Must(template.New("diff").Parse(dTmpl))

					// NOTE: Use <em>, <ins>, and <del> instead of blue, green, red <font> elements
					cmd := exec.Command("git", "diff", "-p", fmt.Sprintf("%s..%s", parent, c.Hash))
					cmd.Dir = repo.temp

					out, err := cmd.Output()

					if err != nil {
						log.Printf("unable to diff against parent: %v", err)

						return
					}

					body := fmt.Sprintf("%s", out)
					data := struct {
						Body   string
						Commit commit
						// TODO: Make this a hash type?
						Parent string
					}{
						Body:   body,
						Commit: c,
						Parent: parent,
					}

					if err := t.Execute(f, data); err != nil {
						log.Printf("unable to apply template: %v", err)

						return
					}
				}()
			}

			for _, object := range c.Tree {
				dst := filepath.Join(outpath, "object", object.Hash[0:2], object.Hash)

				if err := os.MkdirAll(filepath.Dir(dst), 0750); err != nil {
					if err != nil {
						log.Printf("unable to create object directory: %v", err)
					}

					continue
				}

				wg.Add(1)

				go func(name string) {
					defer wg.Done()

					cmd := exec.Command("git", "show", "--no-notes", object.Hash)
					cmd.Dir = repo.temp

					out, err := cmd.Output()

					if err != nil {
						log.Printf("unable to show object: %v", err)

						return
					}

					f, err := os.Create(name)

					defer f.Close()

					if err != nil {
						log.Printf("unable to create object: %v", err)

						return
					}

					body := fmt.Sprintf("%s", out)
					data := struct {
						Body    string
						Hash    string
						Project string
					}{
						Body:    body,
						Hash:    object.Hash,
						Project: opt.Project,
					}

					t := template.Must(template.New("object").Parse(oTmpl))

					if err := t.Execute(f, data); err != nil {
						log.Printf("unable to apply template: %v", err)

						return
					}

					link := filepath.Join(base, fmt.Sprintf("%s.html", object.Path))

					if err := os.MkdirAll(filepath.Dir(link), 0750); err != nil {
						if err != nil {
							log.Printf("unable to create hard link path: %v", err)
						}

						return
					}

					if err := os.Link(name, link); err != nil {
						if os.IsExist(err) {
							return
						}

						log.Printf("unable to hard link object into commit folder: %v", err)
					}
				}(fmt.Sprintf("%s.html", dst))

				func(name string) {
					cmd := exec.Command("git", "cat-file", "blob", object.Hash)
					cmd.Dir = repo.temp

					out, err := cmd.Output()

					if err != nil {
						log.Printf("unable to save object: %v", err)

						return
					}

					f, err := os.Create(dst)

					defer f.Close()

					if err != nil {
						log.Printf("unable to create object: %v", err)

						return
					}

					if _, err := f.Write(out); err != nil {
						log.Printf("unable to write object blob: %v", err)

						return
					}
				}(dst)
			}

			wg.Add(1)

			go func() {
				defer wg.Done()

				dst := filepath.Join(base, "index.html")
				f, err := os.Create(dst)

				defer f.Close()

				if err != nil {
					log.Printf("unable to create commit page: %v", err)

					return
				}

				t := template.Must(template.New("commit").Parse(cTmpl))

				if err := t.Execute(f, c); err != nil {
					log.Printf("unable to apply template: %v", err)

					return
				}
			}()
		}
	}

	wg.Add(1)

	go func() {
		defer wg.Done()

		// This is the main index or project home.
		f, err := os.Create(filepath.Join(outpath, "index.html"))

		defer f.Close()

		if err != nil {
			log.Fatalf("unable to create home page: %v", err)
		}

		t := template.Must(template.New("home").Parse(rTmpl))
		data := struct {
			Branches []branch
			Link     string
			Project  string
		}{
			Branches: branches,
			Link:     opt.URL,
			Project:  opt.Project,
		}

		if err := t.Execute(f, data); err != nil {
			log.Fatalf("unable to apply template: %v", err)
		}
	}()

	wg.Wait()
}

// Creates base directories for holding objects, branches, and commits.
func (r *repository) init(f bool) error {
	dirs := []string{"branch", "commit", "object"}

	for _, dir := range dirs {
		d := filepath.Join(r.base, dir)

		// Clear existing dirs when -f true.
		if f && dir != "branch" {
			if err := os.RemoveAll(d); err != nil {
				return fmt.Errorf("unable to remove directory: %v", err)
			}
		}

		if err := os.MkdirAll(d, 0750); err != nil {
			return fmt.Errorf("unable to create directory: %v", err)
		}
	}

	return nil
}

// Saves a local clone of `target` repo.
func (r *repository) save(target string) error {
	if _, err := os.Stat(r.temp); err != nil {
		return err
	}

	return exec.Command("git", "clone", target, r.temp).Run()
}

// Goes through list of branches and returns those that match whitelist.
func (r *repository) branchfilter(whitelist manyflag) ([]branch, error) {
	cmd := exec.Command("git", "branch", "-a")
	cmd.Dir = r.temp

	out, err := cmd.Output()

	if err != nil {
		return nil, err
	}

	var m = make(map[string]bool)

	scanner := bufio.NewScanner(bytes.NewReader(out))

	for scanner.Scan() {
		t := strings.TrimSpace(scanner.Text())
		_, f := filepath.Split(t)

		m[f] = !strings.Contains(f, "HEAD")
	}

	if err := scanner.Err(); err != nil {
		return nil, err
	}

	// Filter to match options, but return all if no branch flags given.
	if len(whitelist) > 0 {
		for k := range m {
			m[k] = contains(whitelist, k)
		}
	}

	// Fill in resulting slice with desired branches.
	var results []branch

	for k, v := range m {
		if v {
			commits, err := r.commitparser(k)

			if err != nil {
				continue
			}

			results = append(results, branch{commits, k, r.Name})
		}
	}

	return results, nil
}

func (r *repository) commitparser(b string) ([]commit, error) {
	fst := strings.Join([]string{"%H", "%P", "%s", "%aN", "%aE", "%aD", "%h"}, SEP)
	ref := fmt.Sprintf("origin/%s", b)

	cmd := exec.Command("git", "log", "--graph", fmt.Sprintf("--format=%s", fst), ref)
	cmd.Dir = r.temp

	out, err := cmd.Output()

	if err != nil {
		return nil, err
	}

	results := []commit{}
	scanner := bufio.NewScanner(bytes.NewReader(out))

	for scanner.Scan() {
		data := strings.Split(scanner.Text(), SEP)

		k := strings.Split(data[0], " ")
		g, h := k[0], k[1]
		a := author{data[4], data[3]}

		date, err := time.Parse("Mon, 2 Jan 2006 15:04:05 -0700", data[5])

		if err != nil {
			log.Printf("unable to parse commit date: %s", err)

			continue
		}

		body, err := r.bodyparser(h)

		if err != nil {
			log.Printf("unable to parse commit body: %s", err)

			continue
		}

		tree, err := r.treeparser(h)

		if err != nil {
			log.Printf("unable to parse commit tree: %s", err)

			continue
		}

		var history []string
		var parents []string

		if data[1] != "" {
			parents = strings.Split(data[1], " ")
		}

		for _, p := range parents {
			diffstat, err := r.diffparser(h, p)

			if err != nil {
				log.Printf("unable to diff stat against parent: %s", err)

				continue
			}

			history = append(history, diffstat)
		}

		c := commit{
			Abbr:    data[6],
			Author:  a,
			Branch:  b,
			Body:    body,
			Date:    date,
			Hash:    h,
			History: history,
			Tree:    tree,
			Graph:   g,
			Parents: parents,
			Project: r.Name,
			Subject: data[2],
		}

		results = append(results, c)
	}

	if err := scanner.Err(); err != nil {
		return nil, err
	}

	return results, nil
}

func (r *repository) treeparser(h string) ([]object, error) {
	// git ls-tree --format='%(objectname) %(path)' <tree-ish>
	cmd := exec.Command("git", "ls-tree", "-r", "--format=%(objectname) %(path)", h)
	cmd.Dir = r.temp

	out, err := cmd.Output()

	if err != nil {
		return nil, err
	}

	var results []object
	feed := strings.Split(strings.TrimSuffix(fmt.Sprintf("%s", out), "\n"), "\n")

	for _, line := range feed {
		w := strings.Split(line, " ")

		results = append(results, object{
			Hash: w[0],
			Path: w[1],
		})
	}

	return results, nil
}

func (r *repository) diffparser(h, p string) (string, error) {
	// histo, file, changes, sum
	cmd := exec.Command("git", "diff", "--stat", fmt.Sprintf("%s..%s", p, h))
	cmd.Dir = r.temp

	out, err := cmd.Output()

	if err != nil {
		return "", err
	}

	var results []string
	feed := strings.Split(strings.TrimSuffix(fmt.Sprintf("%s", out), "\n"), "\n")

	for i, line := range feed {
		if i < len(feed) {
			// TODO: Parse filenames and stats.
		} else {
			// Last line needs no parsing.
		}

		results = append(results, strings.TrimSpace(line))
	}

	return strings.Join(results, "\n"), nil
}

func (r *repository) bodyparser(h string) (string, error) {
	// Because the commit message body is multiline and is tripping the scanner.
	cmd := exec.Command("git", "show", "--no-patch", "--format=%B", h)
	cmd.Dir = r.temp

	out, err := cmd.Output()

	if err != nil {
		return "", err
	}

	return strings.TrimSuffix(fmt.Sprintf("%s", out), "\n"), nil
}