package acquire

import (
	"context"
	"errors"
	"path"
	"strings"
	"sync"

	"github.com/jackc/pgx/v5/pgtype"

	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
	"git.fabledsword.com/bvandeusen/minstrel/internal/downloader"
	"git.fabledsword.com/bvandeusen/minstrel/internal/indexer"
	"git.fabledsword.com/bvandeusen/minstrel/internal/release"
)

// Taking a release (M502 #5521), ported from Fabled Librarian's grab.go and
// rivals.go. One live grab per want: a second is tie-broken against the
// download already running (FL #4470).

// Tag goes on every torrent Minstrel adds, so the operator can tell them
// from their own in the client.
const Tag = "minstrel"

// MissingClient is Taken.Missing when no download client is set up.
const MissingClient = "download_client"

// nearlyDone is how far along a running download stays whatever would
// replace it.
const nearlyDone = 0.9

// Downloader is the grab half of a Service.
type Downloader struct {
	Client downloader.Driver
	// Code is the client's acquisition_services row.
	Code string
	// Landing is the client's downloads folder as Minstrel sees it; each
	// grab lands in a folder of its own under it.
	Landing string
	// Fetch gets a result's .torrent from the source that offered it.
	Fetch Fetcher
}

// Origin says who took a release.
type Origin struct {
	By   string // OriginSchedule or OriginOperator
	User pgtype.UUID
}

// Contest is how a grab fared against the download already running.
type Contest struct {
	// Kept: the running one stays and this grab was not made. Replaced:
	// this grab took its place.
	Kept, Replaced bool
	Reason         string
	Rival          dbq.Grab
}

// Taken is what came of a grab.
type Taken struct {
	Chosen *Candidate
	// Added is the only field that means a download started.
	Added    bool
	SavePath string
	Grab     dbq.Grab
	// Gone: the search no longer offers the release.
	Gone bool
	// Refused: not taken; the reason is on Chosen.
	Refused bool
	// Unconfigured: Missing names what is not set up ("" for search).
	Unconfigured bool
	Missing      string
	Contest      *Contest
	Error        string
}

// Take searches again and grabs the candidate named by key: a person's
// grab. Searching again keeps the indexer's download link (which can carry
// its key) on the server, and finds a release gone since it was shown.
// force takes what the verdict would not.
func (s *Service) Take(ctx context.Context, want Want, key string, force bool, origin Origin) Taken {
	if s.Grabber == nil {
		return Taken{Unconfigured: true, Missing: MissingClient}
	}
	found := s.For(ctx, want)
	switch {
	case found.Unconfigured:
		return Taken{Unconfigured: true}
	case found.Error != "":
		return Taken{Error: found.Error}
	}
	chosen := pick(found.Candidates, key)
	if chosen == nil {
		return Taken{Gone: true}
	}
	return s.Grab(ctx, want, chosen, found.Candidates, force, origin)
}

// Grab hands a judged candidate to the download client. The schedule calls
// it with the candidate it has just judged; Take calls it after searching
// again.
func (s *Service) Grab(ctx context.Context, want Want, chosen *Candidate, all []Candidate, force bool, origin Origin) Taken {
	out := Taken{Chosen: chosen}
	if s.Grabber == nil || s.Grabber.Client == nil {
		out.Unconfigured, out.Missing = true, MissingClient
		return out
	}
	if chosen.Verdict == Blocked || (chosen.Verdict != Grab && !force) {
		out.Refused = true
		return out
	}

	unlock := lockWant(want.ID)
	defer unlock()
	contest := s.contest(ctx, want, chosen, all, origin)
	if contest != nil && contest.Kept {
		out.Contest = contest
		return out
	}

	add := downloader.Add{Magnet: chosen.Source.Magnet, Tags: []string{Tag}}
	hash := chosen.InfoHash
	if add.Magnet == "" {
		if s.Grabber.Fetch == nil {
			out.Error = "This release is a .torrent link, and nothing is set up to fetch it."
			return out
		}
		body, err := s.Grabber.Fetch.Download(ctx, chosen.Source)
		if magnet, ok := indexer.AsMagnet(err); ok {
			add.Magnet, err = magnet, nil
		}
		if err != nil {
			out.Error = indexer.FirstLine(err.Error())
			return out
		}
		if add.Magnet == "" {
			add.Torrent = body
			if meta, err := release.ParseTorrent(body); err == nil {
				if hash == "" {
					hash = meta.InfoHash
				}
				if refused := s.judgeFiles(ctx, want, chosen, hash, meta.Files, force); refused {
					out.Refused = true
					return out
				}
			}
		}
	}
	if hash == "" && add.Magnet != "" {
		hash = indexer.MagnetHash(add.Magnet)
	}
	add.SavePath = landingFor(s.Grabber.Landing, hash, chosen.Name)

	if err := s.Grabber.Client.AddTorrent(ctx, add); err != nil && !errors.Is(err, downloader.ErrDuplicate) {
		if errors.Is(err, downloader.ErrUnconfigured) {
			out.Unconfigured, out.Missing = true, MissingClient
		} else {
			out.Error = indexer.FirstLine(err.Error())
		}
		return out
	}
	out.Added, out.SavePath = true, add.SavePath
	if s.Memory == nil {
		return out
	}

	var replaced pgtype.UUID
	why := ""
	if contest != nil && contest.Replaced {
		out.Contest = contest
		replaced, why = contest.Rival.ID, "Replaced by "+chosen.Name+": "+contest.Reason+"."
	}
	g, err := s.Memory.Grabbed(ctx, dbq.InsertGrabParams{
		WantID: want.ID, InfoHash: hash, Name: chosen.Name, Key: Key(*chosen), Indexer: chosen.Indexer,
		Source: chosen.Source.Source, Client: s.Grabber.Code, SavePath: add.SavePath,
		Quality: string(chosen.Tier), Origin: origin.By, Forced: force, GrabbedBy: origin.User,
	}, replaced, why)
	if err != nil {
		out.Error = "The download started, but could not be recorded: " + indexer.FirstLine(err.Error())
		return out
	}
	out.Grab = g
	// Removed only after the new download was added and recorded, so a
	// failure never leaves the want with nothing running.
	if replaced.Valid && contest.Rival.InfoHash != "" {
		if err := s.Grabber.Client.Delete(ctx, true, contest.Rival.InfoHash); err != nil {
			contest.Reason += ". The download it replaced could not be removed from the client: " + indexer.FirstLine(err.Error())
		}
	}
	return out
}

// judgeFiles judges a chosen release again on its .torrent's file list, and
// sets it aside when the files say it is not the album, so no later search
// offers it again. force still takes it.
func (s *Service) judgeFiles(ctx context.Context, want Want, chosen *Candidate, hash string, files []release.File, force bool) bool {
	chosen.Files = files
	if chosen.FilesCount == 0 {
		chosen.FilesCount = len(files)
	}
	veto, reason, _ := release.JudgeFiles(want.Want, files)
	if veto == "" || force {
		return false
	}
	set(chosen, Rejected, Hard, veto, reason)
	if s.Memory != nil && hash != "" {
		_ = s.Memory.Block(ctx, dbq.BlockReleaseParams{
			InfoHash: hash, Name: chosen.Name, Reason: BlockFiles, Detail: reason, WantID: want.ID,
		})
	}
	return true
}

var wantLocks sync.Map // want id → *sync.Mutex

// lockWant settles two grabs for one want one after the other. The
// one-live-grab index is the backstop for anything outside this process.
func lockWant(id pgtype.UUID) func() {
	if !id.Valid {
		return func() {}
	}
	m, _ := wantLocks.LoadOrStore(id.Bytes, &sync.Mutex{})
	mu := m.(*sync.Mutex)
	mu.Lock()
	return mu.Unlock
}

// contest settles a grab against the download running for its want: a
// person's grab beats the schedule's; between two of a kind the better
// candidate wins; a tie, a download nearly done, or one that cannot be
// removed stays. Nil when nothing is running.
func (s *Service) contest(ctx context.Context, want Want, chosen *Candidate, all []Candidate, origin Origin) *Contest {
	if s.Memory == nil || !want.ID.Valid {
		return nil
	}
	running, ok, err := s.Memory.LiveGrab(ctx, want.ID)
	if err != nil || !ok {
		return nil
	}
	c := &Contest{Rival: running}
	if running.InfoHash != "" && running.InfoHash == chosen.InfoHash {
		c.Kept, c.Reason = true, "That release is already downloading for this album."
		return c
	}
	switch {
	case origin.By == OriginOperator && running.Origin == OriginSchedule:
		c.Reason = "you chose it over the one the schedule started"
	case origin.By == OriginSchedule && running.Origin == OriginOperator:
		c.Kept, c.Reason = true, "A download you started for this album is already running."
		return c
	default:
		var theirs *Candidate
		for i := range all {
			if (running.InfoHash != "" && all[i].InfoHash == running.InfoHash) || Key(all[i]) == running.Key {
				theirs = &all[i]
				break
			}
		}
		if theirs == nil || !better(*chosen, *theirs) {
			c.Kept, c.Reason = true, "A download for this album is already running, and this release is no better."
			return c
		}
		c.Reason = "it ranks above the one that was running"
	}
	if running.InfoHash == "" {
		c.Kept, c.Reason = true, "A download for this album is already running, and it cannot be identified to replace it."
		return c
	}
	if ts, err := s.Grabber.Client.Torrents(ctx, running.InfoHash); err == nil && len(ts) > 0 && ts[0].Progress >= nearlyDone {
		c.Kept, c.Reason = true, "A download for this album is already running and nearly done."
		return c
	}
	c.Replaced = true
	return c
}

// landingFor is the folder a download lands in: one per torrent, named by
// its infohash, so two grabs never unpack into the same place.
func landingFor(root, hash, name string) string {
	dir := hash
	if dir == "" {
		dir = slug(name)
	}
	if dir == "" {
		dir = "unnamed"
	}
	return path.Join(root, dir)
}

// slug keeps a folder name to characters every filesystem in the chain
// takes.
func slug(s string) string {
	var b strings.Builder
	for _, r := range strings.ToLower(strings.TrimSpace(s)) {
		if b.Len() >= 80 {
			break
		}
		switch {
		case r >= 'a' && r <= 'z', r >= '0' && r <= '9':
			b.WriteRune(r)
		case r == '-', r == '_', r == ' ', r == '.':
			b.WriteRune('-')
		}
	}
	return strings.Trim(b.String(), "-")
}