package web

import (
	"context"
	"errors"
	"fmt"
	"io"
	"math"
	"net/http"
	"path/filepath"
	"regexp"
	"strings"
	"time"
	"unicode"
	"unicode/utf8"

	"github.com/a-h/templ"

	"git.d-ma.be/mathias/tapir/internal/adapters/chat"
	"git.d-ma.be/mathias/tapir/internal/adapters/store"
	"git.d-ma.be/mathias/tapir/internal/config"
	"git.d-ma.be/mathias/tapir/internal/domain"
	"git.d-ma.be/mathias/tapir/internal/errkind"
	"git.d-ma.be/mathias/tapir/internal/uploads"
)

// Uploader accepts an uploaded recording for transcription (ADR-033).
// *uploads.Intake satisfies it. It is the whole of what the handlers know about
// validation, spooling and queueing.
type Uploader interface {
	Accept(ctx context.Context, userID, title string, lang domain.Language, src io.Reader) (id string, err error)
}

const (
	// uploadOverhead is headroom above the file-size cap for the multipart framing
	// and the title field; the cap itself is enforced on the file part by Intake.
	uploadOverhead = 1 << 20
	maxTitleRunes  = 200
	// maxLanguageBytes bounds the language field: the longest value is four bytes.
	maxLanguageBytes = 16
	// uploadPollEvery is how often an unfinished upload re-asks for its status.
	uploadPollEvery = "2s"
	// serviceSilentAfter is how long a job may go without any signal (heartbeat or
	// progress) before the page calls the service lost. The heartbeat is every 10 s, so
	// 45 s is four missed beats (ADR-035).
	serviceSilentAfter = 45 * time.Second
	// countedQuietAfter is how long a COUNTED phase (the deciding one) may go without
	// advancing before the page says it is quiet. Each decision has a two-minute timeout,
	// so five minutes is more than two in a row. A phase with no count is never quiet.
	countedQuietAfter = 5 * time.Minute
)

// uploadsView is what the /uploads page renders.
type uploadsView struct {
	Limits uploads.Limits
	Rows   []domain.UploadedTranscript
	Error  string // a synchronous rejection message, empty when none
}

// handleUploadsPage renders the upload form and the caller's own uploads.
func (a *App) handleUploadsPage(w http.ResponseWriter, r *http.Request) {
	userID, ok := a.currentUserID(w, r)
	if !ok {
		return
	}
	a.renderUploadsPage(w, r, userID, http.StatusOK, "")
}

func (a *App) renderUploadsPage(w http.ResponseWriter, r *http.Request, userID string, status int, msg string) {
	rows, err := a.Store.ListUploads(r.Context(), userID)
	if err != nil {
		a.serverError(w, r, "list uploads", err)
		return
	}
	a.renderStatus(w, r, status, UploadsPage(uploadsView{Limits: a.UploadLimits, Rows: rows, Error: msg}))
}

// handleUploadPost streams the multipart body: the optional title field, then the
// file part, which goes straight to Intake without being buffered in memory. A
// rejection is synchronous — a status code and a message on the upload page, no
// row, no timeout (ADR-033).
func (a *App) handleUploadPost(w http.ResponseWriter, r *http.Request) {
	userID, ok := a.currentUserID(w, r)
	if !ok {
		return
	}
	r.Body = http.MaxBytesReader(w, r.Body, a.UploadLimits.MaxBytes+uploadOverhead)
	mr, err := r.MultipartReader()
	if err != nil {
		a.renderUploadsPage(w, r, userID, http.StatusBadRequest, "Choose an audio file to upload.")
		return
	}
	title := ""
	lang := domain.LangSwedish
	for {
		part, err := mr.NextPart()
		if errors.Is(err, io.EOF) {
			break
		}
		if err != nil {
			var tooBig *http.MaxBytesError
			if a.abandoned(w, r) {
				return
			}
			if !errors.As(err, &tooBig) {
				// A malformed multipart body (a header with a control byte, a truncated
				// part) is the sender's to fix: a 400, not a server error, and the error
				// text is never logged: it quotes the headers, which carry the file name.
				a.logger().Info("upload rejected", "reason", "malformed")
				a.renderUploadsPage(w, r, userID, http.StatusBadRequest, "That upload could not be read. Please try again.")
				return
			}
			a.uploadFailure(w, r, userID, err)
			return
		}
		switch part.FormName() {
		case "title":
			b, err := io.ReadAll(io.LimitReader(part, maxTitleRunes*utf8.UTFMax))
			if err != nil {
				if a.abandoned(w, r) {
					return
				}
				a.renderUploadsPage(w, r, userID, http.StatusBadRequest, "That upload could not be read. Please try again.")
				return
			}
			title = cleanTitle(string(b))
		case "language":
			// A closed set read before the file: anything else is refused before the file
			// is spooled, so a crafted value never reaches an engine (tapir#61).
			b, err := io.ReadAll(io.LimitReader(part, maxLanguageBytes+1))
			if err != nil {
				if a.abandoned(w, r) {
					return
				}
				a.renderUploadsPage(w, r, userID, http.StatusBadRequest, "That upload could not be read. Please try again.")
				return
			}
			l, ok := domain.ParseLanguage(string(b))
			if !ok || len(b) > maxLanguageBytes {
				a.logger().Info("upload rejected", "reason", "language")
				a.renderUploadsPage(w, r, userID, http.StatusBadRequest, "Choose a language from the list.")
				return
			}
			lang = l
		case "file":
			if title == "" {
				title = titleFromFilename(part.FileName())
			}
			id, err := a.Uploads.Accept(r.Context(), userID, title, lang, part)
			if err != nil {
				a.uploadFailure(w, r, userID, err)
				return
			}
			http.Redirect(w, r, "/uploads/"+id, http.StatusSeeOther)
			return
		}
	}
	a.renderUploadsPage(w, r, userID, http.StatusBadRequest, "Choose an audio file to upload.")
}

// abandoned reports, logs at INFO and answers 499, because the client has already gone: its request
// context is cancelled, so there is nobody to answer and rendering a page would run its
// database read on a dead context and log a false ERROR. A hang-up mid-upload is routine.
func (a *App) abandoned(w http.ResponseWriter, r *http.Request) bool {
	if r.Context().Err() == nil {
		return false
	}
	a.logger().Info("upload abandoned", "reason", "client_gone")
	// 499 (the "client closed request" convention): a client that half-closed after sending
	// can still read, and an unwritten status would reach it as a false, empty 200.
	w.WriteHeader(499)
	return true
}

// uploadFailure maps an Accept (or multipart) error to a response: a validation
// rejection is the user's to fix (422, or 413 for size) and carries its own
// message; anything else is ours.
func (a *App) uploadFailure(w http.ResponseWriter, r *http.Request, userID string, err error) {
	if a.abandoned(w, r) {
		return
	}
	var rej *uploads.RejectError
	var tooBig *http.MaxBytesError
	switch {
	case errors.As(err, &rej):
		// Logged by reason only: the filename and title are private content.
		a.logger().Info("upload rejected", "reason", string(rej.Reason))
		status := http.StatusUnprocessableEntity
		switch rej.Reason {
		case uploads.ReasonTooLarge:
			status = http.StatusRequestEntityTooLarge
		case uploads.ReasonBusy:
			status = http.StatusTooManyRequests
		}
		a.renderUploadsPage(w, r, userID, status, rej.Message)
	case errors.As(err, &tooBig):
		a.logger().Info("upload rejected", "reason", string(uploads.ReasonTooLarge))
		a.renderUploadsPage(w, r, userID, http.StatusRequestEntityTooLarge,
			"This file is larger than the upload limit.")
	case errors.Is(err, uploads.ErrClientRead):
		// An error reading the CLIENT's body: theirs to retry, not a server fault. Only that
		// marker counts: io.ErrUnexpectedEOF alone is also what a database drop looks like.
		a.logger().Info("upload rejected", "reason", "truncated")
		a.renderUploadsPage(w, r, userID, http.StatusBadRequest, "The upload was cut off before it finished. Please try again.")
	default:
		// Not err: it can carry the file's name, a spool path or a database value.
		a.logger().Error("upload failed", "kind", errkind.Of(err))
		http.Error(w, "internal error", http.StatusInternalServerError)
	}
}

// handleUploadDetail renders one upload's page (GET /uploads/{id}). The row is
// read through the user-scoped store, so another user's id is a 404 — existence is
// not disclosed, and the title never appears in the response.
func (a *App) handleUploadDetail(w http.ResponseWriter, r *http.Request) {
	u, ok := a.loadOwnedUpload(w, r)
	if !ok {
		return
	}
	a.render(w, r, UploadPage(*u, a.Chat != nil, a.now()))
}

// handleUploadStatus renders the status fragment HTMX polls. Unfinished states
// keep polling; terminal states render without hx-trigger so the page stops
// asking (ADR-025: never a stuck spinner).
func (a *App) handleUploadStatus(w http.ResponseWriter, r *http.Request) {
	u, ok := a.loadOwnedUpload(w, r)
	if !ok {
		return
	}
	a.render(w, r, uploadStatus(*u, a.Chat != nil, a.now()))
}

// handleUploadDelete removes one of the caller's finished recordings and returns to the
// list. Another user's id is a 404 like every other upload route; a recording still being
// transcribed is refused (409) rather than deleted under the worker (#37).
func (a *App) handleUploadDelete(w http.ResponseWriter, r *http.Request) {
	userID, ok := a.currentUserID(w, r)
	if !ok {
		return
	}
	id := r.PathValue("id")
	if !uuidShape.MatchString(id) {
		http.NotFound(w, r)
		return
	}
	switch err := a.Store.DeleteUpload(r.Context(), userID, id); {
	case err == nil:
		http.Redirect(w, r, "/uploads", http.StatusSeeOther)
	case errors.Is(err, store.ErrUploadNotFound):
		http.NotFound(w, r)
	case errors.Is(err, store.ErrUploadInProgress):
		a.renderUploadsPage(w, r, userID, http.StatusConflict,
			"This recording is still being transcribed. You can delete it once it has finished.")
	default:
		a.serverError(w, r, "delete upload", err)
	}
}

func (a *App) loadOwnedUpload(w http.ResponseWriter, r *http.Request) (*domain.UploadedTranscript, bool) {
	userID, ok := a.currentUserID(w, r)
	if !ok {
		return nil, false
	}
	id := r.PathValue("id")
	if !uuidShape.MatchString(id) {
		// Not an id at all: the same 404 as an unknown or foreign one, never a database
		// error that surfaces as a 500 (and no oracle about which ids exist).
		http.NotFound(w, r)
		return nil, false
	}
	u, err := a.Store.GetUpload(r.Context(), userID, id)
	if errors.Is(err, store.ErrUploadNotFound) {
		http.NotFound(w, r)
		return nil, false
	}
	if err != nil {
		a.serverError(w, r, "get upload", err)
		return nil, false
	}
	return u, true
}

// titleFromFilename is the default title: the file's name without its extension.
func titleFromFilename(name string) string {
	base := filepath.Base(name)
	t := cleanTitle(strings.TrimSuffix(base, filepath.Ext(base)))
	if t == "" || t == "." {
		return "Untitled recording"
	}
	return t
}

// cloudProvider names the cloud service that produced a transcript, or false when it was
// served locally (or by an unknown endpoint). "Local" is config.IsLocalModel: the same
// definition the start-up validation uses, not a second string match here (#52).
//
// The endpoint is one alias, except for the two-engine path (ADR-034), which writes
// "<base> + <alt>, reconciled by <model>" (ensemble.go). That shape is taken apart exactly
// and each alias is judged whole, so a composite of local models is local, and anything
// else (a cloud alias, one with no provider prefix, one with a space or a connector word in
// it) is not. A string that is not that shape is one alias.
func cloudProvider(endpoint string) (string, bool) {
	endpoint = strings.TrimSpace(endpoint)
	if endpoint == "" {
		return "", false
	}
	aliases := []string{endpoint}
	if engines, reconciler, ok := strings.Cut(endpoint, ", reconciled by "); ok {
		aliases = append(strings.Split(engines, " + "), reconciler)
	}
	for _, a := range aliases {
		if a = strings.TrimSpace(a); !config.IsLocalModel(a) {
			provider, _, _ := strings.Cut(a, "/")
			if provider = strings.TrimSpace(provider); provider == "" {
				provider = a
			}
			return provider, true
		}
	}
	return "", false
}

// languageLabel is how the page names the language a recording was transcribed as.
func languageLabel(l domain.Language) string {
	if l == domain.LangAuto {
		return "Other (detected by the engine)"
	}
	return "Swedish"
}

// hasNote reports whether any phase carries a note. A note is the only warning for a
// recording that is shorter than its file claimed, so a record that has one is shown open.
func hasNote(steps []domain.ProgressStep) bool {
	for _, s := range steps {
		if s.Note != "" {
			return true
		}
	}
	return false
}

// uuidShape is the form of an upload id. Anything else cannot be one, so it is a 404.
var uuidShape = regexp.MustCompile(`^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$`)

// isBidiControl reports the invisible characters that change text direction. Emoji joiners
// (ZWJ, ZWNJ) and variation selectors are not among them and are kept.
func isBidiControl(r rune) bool {
	return r >= 0x202A && r <= 0x202E || r >= 0x2066 && r <= 0x2069 || r == 0x200E || r == 0x200F || r == 0x061C
}

// cleanTitle makes a title safe to store and show: invalid UTF-8 dropped, control
// characters (NUL, newlines, escapes) turned into spaces, runs of space collapsed, trimmed
// and clipped. A title is cosmetic; bad bytes in it must never fail an upload, and Postgres
// refuses NUL in text.
func cleanTitle(s string) string {
	s = strings.ToValidUTF8(s, "")
	s = strings.Map(func(r rune) rune {
		switch {
		case isBidiControl(r):
			return -1 // dropped: U+202E would reverse the rest of the title on its owner's page
		case unicode.IsControl(r):
			return ' '
		}
		return r
	}, s)
	return clipRunes(strings.Join(strings.Fields(s), " "), maxTitleRunes)
}

func clipRunes(s string, n int) string {
	if utf8.RuneCountInString(s) <= n {
		return s
	}
	return string([]rune(s)[:n])
}

// uploadFailureMessage turns a typed failure kind into words for the user. It is
// keyed on OUR kinds, never on a provider's error string (ADR-033).
func uploadFailureMessage(k domain.UploadErrorKind) string {
	switch k {
	case domain.UploadErrInterrupted:
		return "The server restarted before this recording was transcribed. Please upload it again."
	case domain.UploadErrBusy:
		return "Too many recordings were waiting to be transcribed when this one was uploaded. Please upload it again in a few minutes."
	case domain.UploadErrTooLong:
		return "This recording is longer than the limit once its audio is read (the file's header said otherwise). Please upload a shorter recording."
	case domain.UploadErrTranscriptionFailed:
		return "Transcription failed on every available service. Please upload it again later."
	default:
		return "This upload failed. Please upload it again."
	}
}

// handleUploadChat renders the chat page for a FINISHED upload (GET). The row is
// read through the user-scoped store, so another user's id is a 404 before any
// model is involved. An unfinished upload has no transcript to ask about yet, so
// it goes back to its status page.
func (a *App) handleUploadChat(w http.ResponseWriter, r *http.Request) {
	u, ok := a.loadOwnedUpload(w, r)
	if !ok {
		return
	}
	if u.Status != domain.UploadDone {
		http.Redirect(w, r, "/uploads/"+u.ID, http.StatusSeeOther)
		return
	}
	model, _ := a.resolveUploadModel("")
	a.render(w, r, UploadChatPage(*u, a.uploadChatView(*u, model, nil, false, "")))
}

// handleUploadChatMessage answers one question against the owner's uploaded
// transcript (POST), reusing the ADR-027 Chatter. Nothing is persisted: the prior
// turns ride in the form. The transcript goes to the model with the UPLOAD budget,
// not the caption default. A model failure is inline, not a 500.
func (a *App) handleUploadChatMessage(w http.ResponseWriter, r *http.Request) {
	u, ok := a.loadOwnedUpload(w, r)
	if !ok {
		return
	}
	if u.Status != domain.UploadDone {
		http.Redirect(w, r, "/uploads/"+u.ID, http.StatusSeeOther)
		return
	}
	if err := r.ParseForm(); err != nil {
		http.Error(w, "bad form", http.StatusBadRequest)
		return
	}
	model, ok := a.resolveUploadModel(r.FormValue("model"))
	if !ok {
		a.logger().Error("upload chat: no local model is configured; nothing was sent", "upload", u.ID)
		view := a.uploadChatView(*u, "", nil, false, "No local model is available for chat about a recording.")
		a.render(w, r, UploadChatPage(*u, view))
		return
	}
	history := parseHistory(r.Form["hq"], r.Form["ha"])
	question := strings.TrimSpace(r.FormValue("question"))

	view := a.uploadChatView(*u, model, history, false, "")
	if question != "" {
		reply, err := a.Chat.Answer(r.Context(), chat.Request{
			Model:      model,
			Transcript: u.Content,
			History:    history,
			Question:   question,
			MaxChars:   a.UploadChatMaxChars,
		})
		if err != nil {
			a.logger().Error("upload chat answer", "upload", u.ID, "model", model, "kind", errkind.Of(err))
			view.Error = "That model couldn't answer just now. Try again, or switch models."
		} else {
			view.History = appendTurn(history, chat.Turn{Question: question, Answer: reply.Answer})
			view.Truncated = reply.Truncated
		}
	}
	if isHTMX(r) {
		a.render(w, r, chatPanel(view))
		return
	}
	a.render(w, r, UploadChatPage(*u, view))
}

func (a *App) uploadChatView(u domain.UploadedTranscript, model string, history []chat.Turn, truncated bool, errMsg string) chatView {
	return chatView{
		VideoID:   u.ID,
		Title:     u.Title,
		Available: true,
		Models:    a.UploadChatModels,
		Selected:  model,
		History:   history,
		Truncated: truncated,
		Error:     errMsg,
		PostURL:   templ.SafeURL("/uploads/" + u.ID + "/chat"),
		Subject:   "recording",
	}
}

// maxSpotsShown is how many spots to check the page lists. The stored list holds every
// judged spot and the counts are exact; a page of two hundred "check this" items is not a
// page anyone reads, so the rest are counted, not listed.
const maxSpotsShown = 50

// minuteMark renders where in the recording a spot is, as the nearest minute.
func minuteMark(seconds float64) string {
	return fmt.Sprintf("~%d min", int(math.Round(seconds/60)))
}

// shownSpots is the part of the stored list the page renders: the spots a reader should
// check, changed or uncertain, in order, capped. A spot the model confidently kept is
// stored (ADR-035) but is not one to check, so it is not listed.
func shownSpots(r *domain.Reconciliation) []domain.ContestedSpot {
	var out []domain.ContestedSpot
	for _, c := range r.Contested {
		if c.Used == "alt" || c.Unsure {
			out = append(out, c)
			if len(out) == maxSpotsShown {
				break
			}
		}
	}
	return out
}

// moreSpots is how many spots to check are not listed, from the exact counts.
func moreSpots(r *domain.Reconciliation) int {
	return max(0, r.Changed+r.Unsure-len(shownSpots(r)))
}

// jobHealth is what the page can honestly say about a job it is still polling.
type jobHealth string

const (
	// healthRunning: the service is reporting and work is moving, or there is nothing yet
	// to say otherwise.
	healthRunning jobHealth = "running"
	// healthQuiet: the service is alive but a counted phase has not advanced for a while.
	healthQuiet jobHealth = "quiet"
	// healthLost: nothing has been heard from the service for too long. It may have
	// restarted or crashed; the start-up sweep fails the row once it is back.
	healthLost jobHealth = "lost"
)

// uploadHealth tells running from quiet from lost for an upload being transcribed (the
// page calls it for no other state: a queued or finished job has no heartbeat to judge). The
// two timestamps mean different things (ADR-035): alive_at is the heartbeat, which says
// the service is still reporting; progress_at moves only when work really moved. A
// single blocking engine call has no sub-progress, so only a counted phase can be quiet.
// silent is how long since the signal that decided it.
func uploadHealth(u domain.UploadedTranscript, now time.Time) (health jobHealth, silent time.Duration) {
	last := u.AliveAt
	if u.ProgressAt.After(last) {
		last = u.ProgressAt
	}
	if last.IsZero() {
		return healthRunning, 0
	}
	if d := now.Sub(last); d > serviceSilentAfter {
		return healthLost, d
	}
	for _, s := range u.Progress {
		if s.State == domain.StepRunning && s.Total > 0 && !u.ProgressAt.IsZero() {
			if d := now.Sub(u.ProgressAt); d > countedQuietAfter {
				return healthQuiet, d
			}
		}
	}
	return healthRunning, 0
}

// stepDuration renders how long a phase took or has run: "<1s", "42s", "3m 12s", "1h 02m".
func stepDuration(d time.Duration) string {
	switch {
	case d < time.Second:
		return "<1s"
	case d < time.Minute:
		return fmt.Sprintf("%ds", int(d.Seconds()))
	case d < time.Hour:
		return fmt.Sprintf("%dm %02ds", int(d.Minutes()), int(d.Seconds())%60)
	default:
		return fmt.Sprintf("%dh %02dm", int(d.Hours()), int(d.Minutes())%60)
	}
}

// stepTime is the time shown beside a phase: how long it has run, or how long it took.
func stepTime(s domain.ProgressStep, now time.Time) string {
	switch s.State {
	case domain.StepRunning:
		return stepDuration(now.Sub(s.StartedAt))
	case domain.StepDone, domain.StepFailed:
		return stepDuration(s.FinishedAt.Sub(s.StartedAt))
	}
	return ""
}

// stepMark is the glyph at the head of a phase line.
func stepMark(s domain.ProgressStep) string {
	switch s.State {
	case domain.StepDone:
		return "✓"
	case domain.StepFailed:
		return "✗"
	case domain.StepSkipped:
		return "–"
	}
	return "·"
}

// minutesAgo is a whole number of minutes for the health notes: "6 min", or "under a
// minute" when it is less.
func minutesAgo(d time.Duration) string {
	if m := int(d.Minutes()); m >= 1 {
		return fmt.Sprintf("%d min", m)
	}
	return "under a minute"
}

// resolveUploadModel picks the model for chat over an uploaded recording from the
// offered LOCAL set only: the posted one when it is in the set, else the configured
// default when it is, else the first. ok is false when no model is offered, in which
// case nothing may be sent anywhere (the whole private transcript is the payload).
func (a *App) resolveUploadModel(posted string) (model string, ok bool) {
	offered := func(m string) bool {
		for _, o := range a.UploadChatModels {
			if o == m {
				return true
			}
		}
		return false
	}
	switch {
	case posted != "" && offered(posted):
		return posted, true
	case a.UploadChatModel != "" && offered(a.UploadChatModel):
		return a.UploadChatModel, true
	case len(a.UploadChatModels) > 0:
		return a.UploadChatModels[0], true
	}
	return "", false
}