package main

import (
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"io/fs"
	"os"
	"os/signal"
	"path"
	"regexp"
	"strings"
	"syscall"

	yaml "gopkg.in/yaml.v3"
)

type Fields struct {
	Title   string
	Season  string
	Episode string
}

type MvNLn func(string, string) error

func main() {
	ctx, can := signal.NotifyContext(context.Background(), syscall.SIGINT)
	defer can()

	foo := Main
	if len(os.Args) == 2 && os.Args[1] == "r" {
		foo = Recursive
	}
	if err := foo(ctx); err != nil {
		panic(err)
	}
}

func Recursive(ctx context.Context) error {
	q := []string{"./"}
	for len(q) > 0 {
		d := q[0]
		q = q[1:]

		p := path.Join(d, ".show-ingestion.yaml")
		if _, err := os.Stat(p); err != nil {
		} else if err := func() error {
			var y struct {
				C Fields
				O string
				D bool
				P []string
			}
			b, _ := os.ReadFile(path.Join(d, ".show-ingestion.yaml"))
			if err := yaml.Unmarshal(b, &y); err != nil {
				return fmt.Errorf("%s: %w", p, err)
			}

			was, err := os.Getwd()
			if err != nil {
				return err
			}

			if err := os.Chdir(d); err != nil {
				return err
			}
			defer os.Chdir(was)

			if err := Run(ctx, y.O, "./", y.P, y.C, y.D); err != nil {
				return err
			}

			return os.Chdir(was)
		}(); err != nil {
			return fmt.Errorf("%s: %w", p, err)
		}

		entries, err := readDir(d)
		if err != nil {
			return err
		}
		for _, entry := range entries {
			if entry.IsDir() {
				q = append(q, path.Join(d, entry.Name()))
			}
		}
	}
	return nil
}

func Main(ctx context.Context) error {
	flags := flag.NewFlagSet(os.Args[0], flag.ContinueOnError)
	overridesS := flags.String("c", `{"title":"","season":"","episode":""}`, "overrides")
	ind := flags.String("i", "/dev/null", "in dir")
	outd := flags.String("o", "/dev/null", "out dir")
	dry := flags.Bool("d", true, "dry run")
	if err := flags.Parse(os.Args[1:]); err != nil {
		panic(err)
	}

	var overrides Fields
	json.Unmarshal([]byte(*overridesS), &overrides)

	return Run(ctx,
		*outd,
		*ind,
		flags.Args(),
		overrides,
		*dry,
	)
}

func Run(ctx context.Context, outd, ind string, patterns []string, overrides Fields, dry bool) error {
	mvNLn := RealMvNLn
	if dry {
		mvNLn = DryMvNLn()
	}
	return RunWith(ctx,
		outd,
		ind,
		append(patterns,
			`^\[[^\]]*\] (?P<title>.*) - (?P<episode>[0-9]+).*`,
			`^(?P<title>.*) S(?P<season>[0-9]+)E(?P<episode>[0-9]+).*`,
		),
		overrides,
		mvNLn,
	)
}

func RunWith(ctx context.Context, outd, ind string, patterns []string, overrides Fields, mvNLn MvNLn) error {
	entries, err := readDir(ind)
	if err != nil {
		return err
	}
	for _, entry := range entries {
		if !entry.Type().IsRegular() {
			continue
		}
		if err := one(ctx, outd, path.Join(ind, entry.Name()), patterns, overrides, mvNLn); err != nil {
			return err
		}
	}
	return nil
}

func one(ctx context.Context, outd, inf string, patterns []string, overrides Fields, mvNLn MvNLn) error {
	f := path.Base(inf)
	for _, pattern := range patterns {
		re := regexp.MustCompile(pattern)
		if !re.MatchString(f) {
			continue
		}

		found := overrides
		groupNames := re.SubexpNames()
		groups := re.FindStringSubmatch(f)
		for i := 1; i < len(groupNames); i++ {
			v := groups[i]
			switch groupNames[i] {
			case "title":
				found.Title = v
			case "season":
				found.Season = v
			case "episode":
				found.Episode = v
			default:
				return fmt.Errorf("unexpected capture group %q", groupNames[i])
			}
		}

		if found.Title == "" || found.Season == "" || found.Episode == "" {
			continue
		}
		found.Title = strings.Join(strings.Fields(found.Title), "_")

		return foundOne(ctx, outd, inf, found, mvNLn)
	}
	return nil
}

func foundOne(ctx context.Context, outd, inf string, fields Fields, mvNLn MvNLn) error {
	outf := path.Join(outd, fmt.Sprintf("%s_S%sE%s%s", fields.Title, fields.Season, fields.Episode, path.Ext(inf)))
	return mvNLn(outf, inf)
}

func RealMvNLn(outf, inf string) error {
	if stat, err := os.Stat(inf); err != nil || !stat.Mode().IsRegular() {
		return fmt.Errorf("cannot mv_n_ln(%s): (%v) mode=%v", inf, err, stat.Mode())
	}
	if _, err := os.Stat(outf); err == nil {
		return nil
	}
	if err := os.MkdirAll(path.Dir(outf), os.ModePerm); err != nil {
		return err
	}
	if err := os.Rename(inf, outf); err != nil {
		return err
	}
	return os.Symlink(outf, inf)
}

func DryMvNLn() func(string, string) error {
	outd := map[string]struct{}{}
	return func(outf, inf string) error {
		if _, err := os.Stat(outf); err == nil {
			return nil
		}

		if _, ok := outd[outf]; ok {
			return nil
		}
		outd[outf] = struct{}{}

		fmt.Fprintf(os.Stderr, "mv %q %q\n", inf, outf)
		return nil
	}
}

func readDir(d string) ([]fs.DirEntry, error) {
	entries, err := os.ReadDir(d)
	result := []fs.DirEntry{}
	for _, entry := range entries {
		if !strings.HasPrefix(entry.Name(), ".") {
			result = append(result, entry)
		}
	}
	return result, err
}