// Package engine — stream_source_debrid.go implements a FileProvider that
// serves a /stream session straight from a debrid HTTPS direct URL (hueco #2 /
// 2a). No local file is involved: the browser's Range requests are translated
// into ranged GETs against the debrid link, so a cache-confirmed torrent plays
// instantly without ever hitting the swarm or touching disk.
//
// The web resolves the DirectURL server-side (resolveDebridDirectUrl) and only
// sends it when the hash is debrid-cached and the container is browser-native
// (mp4/m4v), so this provider stays a pure pass-through — same role as
// diskFileProvider/torrentFileProvider, just backed by HTTP Range instead of a
// file handle. http.ServeContent drives it exactly like a local file: it Seeks
// to discover size + the range start (no network), then Reads (lazy GET).
package engine

import (
	"context"
	"errors"
	"fmt"
	"io"
	"log"
	"net/http"
	"path"
	"strings"
	"sync"
	"time"
)

// debridHTTPClient is used for ranged debrid reads. Separate from the download
// httpClient so a slow streaming read can't starve a concurrent download's
// header-timeout budget, and vice versa. No overall timeout: a paused player
// can legitimately hold a body open for minutes; ResponseHeaderTimeout bounds
// the part that actually matters (a hung server before first byte).
var debridHTTPClient = &http.Client{
	Transport: &http.Transport{
		ResponseHeaderTimeout: 30 * time.Second,
		// debrid CDNs are remote; a generous idle-conn pool avoids a fresh TLS
		// handshake on every seek-driven reopen.
		MaxIdleConns:        4,
		IdleConnTimeout:     90 * time.Second,
		TLSHandshakeTimeout: 15 * time.Second,
	},
}

// NewDebridFileProvider builds a FileProvider backed by a debrid HTTPS URL.
// It performs a single HEAD up front to learn the exact file size (the torrent
// size the web knows can differ from the resolved file's size). If the HEAD
// fails or omits Content-Length, fallbackSize (from the StreamSession) is used.
// Returns an error only when neither a HEAD size nor a fallback is available —
// http.ServeContent needs a real size to range-serve, and serving size 0 would
// hand the browser an empty file.
// refresh, when non-nil, re-resolves a fresh debrid URL for the same content
// (hueco #2 / 2c) — called when the current link expires mid-stream. nil keeps
// 2a behaviour (an expired link is a hard error, no recovery).
func NewDebridFileProvider(ctx context.Context, directURL, fileName string, fallbackSize int64, refresh func(context.Context) (string, error)) (FileProvider, error) {
	if directURL == "" {
		return nil, errors.New("debrid provider: empty direct URL")
	}
	size := fallbackSize
	if headSize, ok := debridHeadSize(ctx, directURL); ok {
		size = headSize
	}
	if size <= 0 {
		return nil, fmt.Errorf("debrid provider: unknown file size (HEAD gave nothing, no fallback)")
	}
	// The name drives the served Content-Type (mimeTypeFromExt on FileName).
	// The web may pass a torrent title with no extension (its file-name
	// fallback), which would yield application/octet-stream and break <video>
	// on strict clients (Safari). The debrid URL reliably ends in the real
	// file name *with* its extension, so derive from it whenever the passed
	// name lacks one.
	name := fileName
	if name == "" || path.Ext(name) == "" {
		name = debridNameFromURL(directURL)
	}
	return &debridFileProvider{
		url:     directURL,
		name:    name,
		size:    size,
		refresh: refresh,
	}, nil
}

// debridFileProvider serves a file from a debrid HTTPS URL via ranged GETs. The
// URL is mutable: when it expires mid-stream, refreshURL swaps in a fresh one
// (shared across all readers this provider hands out) so the next range request
// uses the live link.
type debridFileProvider struct {
	mu            sync.Mutex
	url           string
	lastRefreshAt time.Time
	inflight      *refreshCall // non-nil while a refresh is running; coalesces concurrent callers
	refresh       func(context.Context) (string, error)

	name string
	size int64
}

// refreshCall is a single in-flight refresh whose result is shared by every
// reader that piles up behind it (singleflight). done is closed on completion.
type refreshCall struct {
	done chan struct{}
	url  string
	err  error
}

// currentURL returns the live debrid URL (mutated by refreshURL on expiry).
func (p *debridFileProvider) currentURL() string {
	p.mu.Lock()
	defer p.mu.Unlock()
	return p.url
}

// refreshURL re-resolves a fresh debrid link and stores it. A browser's <video>
// opens several concurrent range connections, so when a link expires N readers
// hit it at once — they must NOT each fire a (multi-second) re-resolution.
// Coalescing is two-layer: (1) a result refreshed in the last few seconds is
// reused without any call; (2) while a refresh is in flight, late callers wait
// on it and share its result (singleflight) rather than starting their own.
func (p *debridFileProvider) refreshURL(ctx context.Context) (string, error) {
	if p.refresh == nil {
		return "", errors.New("debrid provider: no URL refresher (refresh disabled)")
	}
	p.mu.Lock()
	if time.Since(p.lastRefreshAt) < 5*time.Second && p.url != "" {
		u := p.url
		p.mu.Unlock()
		return u, nil // refreshed very recently — reuse it
	}
	if call := p.inflight; call != nil {
		p.mu.Unlock()
		select {
		case <-call.done:
			return call.url, call.err // shared result from the in-flight refresh
		case <-ctx.Done():
			return "", ctx.Err()
		}
	}
	call := &refreshCall{done: make(chan struct{})}
	p.inflight = call
	p.mu.Unlock()

	u, err := p.refresh(ctx)

	p.mu.Lock()
	if err == nil {
		p.url = u
		p.lastRefreshAt = time.Now()
	}
	call.url, call.err = u, err
	p.inflight = nil
	close(call.done)
	p.mu.Unlock()

	if err != nil {
		return "", err
	}
	log.Printf("[stream] debrid URL refreshed (expired mid-stream)")
	return u, nil
}

func (p *debridFileProvider) NewFileReader(ctx context.Context) io.ReadSeekCloser {
	return &debridRangeReader{
		ctx:  ctx,
		prov: p,
		size: p.size,
	}
}

func (p *debridFileProvider) FileName() string { return p.name }
func (p *debridFileProvider) FileSize() int64  { return p.size }

// debridRangeReader is an io.ReadSeekCloser over an HTTP resource that supports
// Range. Seek is network-free: it only moves the logical position. Read opens
// (or reuses) a GET starting at the current position and streams the body; a
// Seek that moves away from the open body's cursor forces a reopen on the next
// Read. This matches how http.ServeContent works — Seek(0, SeekEnd) for size,
// Seek to the range start, then sequential Reads — so seeks the user makes in
// the player become a single reopened GET, never a full re-download.
type debridRangeReader struct {
	ctx  context.Context
	prov *debridFileProvider
	size int64

	pos    int64         // logical position (moved by Seek, advanced by Read)
	body   io.ReadCloser // current open response body, or nil
	bodyAt int64         // position the open body's next byte maps to
}

func (r *debridRangeReader) Read(p []byte) (int, error) {
	if r.size > 0 && r.pos >= r.size {
		return 0, io.EOF
	}
	// (Re)open when no body is held or a Seek moved us off the open body.
	if r.body == nil || r.pos != r.bodyAt {
		if err := r.reopen(); err != nil {
			return 0, err
		}
	}
	n, err := r.body.Read(p)
	r.pos += int64(n)
	r.bodyAt = r.pos
	if err == io.EOF {
		// Body drained. Drop it so the next Read reopens (covers a server that
		// closed the connection before the logical EOF). Surface EOF to the
		// caller only when we've actually reached end-of-file; otherwise hand
		// back the bytes read with no error and let the caller Read again.
		_ = r.body.Close()
		r.body = nil
		if r.size > 0 && r.pos < r.size {
			return n, nil
		}
	}
	return n, err
}

func (r *debridRangeReader) Seek(offset int64, whence int) (int64, error) {
	var abs int64
	switch whence {
	case io.SeekStart:
		abs = offset
	case io.SeekCurrent:
		abs = r.pos + offset
	case io.SeekEnd:
		abs = r.size + offset
	default:
		return 0, fmt.Errorf("debrid reader: invalid whence %d", whence)
	}
	if abs < 0 {
		return 0, errors.New("debrid reader: negative position")
	}
	r.pos = abs
	return abs, nil
}

func (r *debridRangeReader) Close() error {
	if r.body != nil {
		err := r.body.Close()
		r.body = nil
		return err
	}
	return nil
}

// reopen issues a fresh ranged GET from the current logical position. Closes
// any previously held body first. On an expired-link status (401/403/404/410)
// it re-resolves a fresh debrid URL via the provider and retries — bounded, so
// a permanently-dead link surfaces an error instead of looping (hueco #2 / 2c).
func (r *debridRangeReader) reopen() error {
	if r.body != nil {
		_ = r.body.Close()
		r.body = nil
	}
	// Attempts: 1 initial + 1 after a URL refresh. One fresh link is enough for
	// an expiry; if the refreshed link ALSO fails the content is genuinely gone,
	// so surface the error rather than burning more multi-second resolutions.
	const maxAttempts = 2
	for attempt := 0; attempt < maxAttempts; attempt++ {
		req, err := http.NewRequestWithContext(r.ctx, http.MethodGet, r.prov.currentURL(), nil)
		if err != nil {
			return fmt.Errorf("debrid reader: build request: %w", err)
		}
		// Always send a Range so a seek to 0 still gets a 206 (and so partial
		// reopens after a mid-file seek work). An open-ended range runs to EOF.
		req.Header.Set("Range", fmt.Sprintf("bytes=%d-", r.pos))
		resp, err := debridHTTPClient.Do(req)
		if err != nil {
			return fmt.Errorf("debrid reader: GET: %w", err)
		}
		switch resp.StatusCode {
		case http.StatusPartialContent:
			r.body = resp.Body
			r.bodyAt = r.pos
			return nil
		case http.StatusOK:
			// Server ignored Range and is sending the whole file from 0. Only
			// valid when we asked from 0; otherwise bytes wouldn't line up.
			if r.pos != 0 {
				resp.Body.Close()
				return fmt.Errorf("debrid reader: server ignored Range at offset %d (got 200)", r.pos)
			}
			r.body = resp.Body
			r.bodyAt = r.pos
			return nil
		case http.StatusRequestedRangeNotSatisfiable:
			resp.Body.Close()
			return io.EOF // seeked past end — treat as EOF, not a hard error
		case http.StatusUnauthorized, http.StatusForbidden, http.StatusNotFound, http.StatusGone:
			// Expired/dead debrid link — re-resolve and retry with the fresh URL.
			resp.Body.Close()
			if _, rerr := r.prov.refreshURL(r.ctx); rerr != nil {
				return fmt.Errorf("debrid reader: link expired (%d) and refresh failed: %w", resp.StatusCode, rerr)
			}
			continue
		default:
			resp.Body.Close()
			return fmt.Errorf("debrid reader: unexpected status %d %s", resp.StatusCode, resp.Status)
		}
	}
	return fmt.Errorf("debrid reader: link still failing after %d refresh attempts", maxAttempts)
}

// debridHeadSize issues a HEAD and returns the Content-Length when present.
// Best-effort: any failure returns (0, false) so the caller falls back to the
// size the web reported. A short timeout keeps a slow/HEAD-hostile CDN from
// stalling session setup — the fallback size is good enough to start.
func debridHeadSize(ctx context.Context, url string) (int64, bool) {
	hctx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()
	req, err := http.NewRequestWithContext(hctx, http.MethodHead, url, nil)
	if err != nil {
		return 0, false
	}
	resp, err := debridHTTPClient.Do(req)
	if err != nil {
		log.Printf("[stream] debrid HEAD failed (using fallback size): %v", err)
		return 0, false
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK || resp.ContentLength <= 0 {
		return 0, false
	}
	return resp.ContentLength, true
}

// debridNameFromURL extracts a filename from a URL path as a last resort when
// the server didn't send one. Strips query/fragment via path.Base on the path.
func debridNameFromURL(rawURL string) string {
	u := rawURL
	if i := strings.IndexAny(u, "?#"); i >= 0 {
		u = u[:i]
	}
	base := path.Base(u)
	if base == "" || base == "." || base == "/" {
		return "video.mp4"
	}
	return base
}