package provider

import (
	"bytes"
	"context"
	"crypto/rand"
	"encoding/binary"
	"encoding/hex"
	"fmt"
	"net/http"
	"net/url"
	"strings"
	"sync/atomic"
	"time"

	"github.com/gorilla/websocket"
)

// Edge TTS constants. The protocol is the well-known "Read Aloud" protocol
// of Microsoft Edge, reverse-engineered by edge-tts. State of the
// implementation (2026): DRM token Sec-MS-GEC v2 (CS64 + obfuscated SHA-256
// variant, see edgedrm.go) + MUID cookie; otherwise the known WebSocket
// message format (speech.config + SSML, binary frames with a 2-byte header
// length, turn.end). If Microsoft changes it, the synthesis paths return
// clear errors hinting at a protocol change instead of failing silently.
const (
	// DefaultEndpointEdge is the production WebSocket endpoint (path without
	// query; token/ConnectionId/Sec-MS-GEC are added in requestURL).
	DefaultEndpointEdge = "wss://speech.platform.bing.com/consumer/speech/synthesize/readaloud/edge/v1"

	// EnvEdgeEndpoint overrides the endpoint (tests/corporate servers).
	EnvEdgeEndpoint = "TALK_EDGE_ENDPOINT"

	edgeTrustedClientToken = "6A5AA1D4EAFF4E9FB37E23D68491D6F4"
	edgeSecMSGECVersion    = "2-143.0.3650.75"
	edgeOrigin             = "chrome-extension://jdiccldimpdaibmpdkjnbmckianbfold"
	edgeUserAgent          = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/143.0.0.0 Safari/537.36 Edg/143.0.0.0"
	edgeOutputFormat       = "audio-24khz-48kbitrate-mono-mp3" // mp3!
)

// edgeIOTimeout bounds individual read/write operations and (if the caller
// provides no deadline) the whole synthesis.
const edgeIOTimeout = 20 * time.Second

// edgeClockSkew corrects local clock drift: on 403 the provider reads the
// Date header of the response and adjusts the tick calculation (one retry,
// like the edge-tts reference).
var edgeClockSkew atomic.Int64

// Edge is the free third tier of the chain: Microsoft's "Read Aloud"
// endpoint, no key needed. Synthesize opens a WebSocket connection, sends
// speech.config + the SSML request and collects the binary audio frames
// until turn.end. Return format: MP3 (24 kHz mono; the audio sink decodes
// the format).
type Edge struct {
	// Endpoint is the WebSocket URL (ws:// or wss://), empty = default.
	Endpoint string

	// Voices is the config mapping voice.edge.<lang> = id; empty = neutral
	// repo defaults (de-DE-KatjaNeural / en-US-AriaNeural).
	Voices map[string]string

	// Dialer is the WebSocket dialer; nil = websocket.DefaultDialer.
	Dialer *websocket.Dialer

	pinned string // --voice pin (VoicePinner)
}

// NewEdge builds the provider from the chain configuration: endpoint from
// TALK_EDGE_ENDPOINT > [providers.edge].endpoint > default.
func NewEdge(cfg ChainConfig) *Edge {
	return &Edge{
		Endpoint: endpointFrom(cfg, "edge", EnvEdgeEndpoint, DefaultEndpointEdge),
		Voices:   cfg.Voices["edge"],
	}
}

// Name implements Provider.
func (*Edge) Name() string { return "edge" }

// PinVoice implements VoicePinner (CLI flag --voice).
func (p *Edge) PinVoice(id string) { p.pinned = id }

// Available implements Provider: Edge only needs an endpoint, deliberately
// without a network call (reachability is determined by Synthesize, on
// whose error the chain falls back).
func (p *Edge) Available(ctx context.Context) bool { return p.Endpoint != "" }

// Synthesize implements Provider. Return format: MP3.
func (p *Edge) Synthesize(ctx context.Context, text, lang string) ([]byte, error) {
	if text == "" {
		return nil, fmt.Errorf("edge: empty text")
	}
	voice := resolveVoice("edge", lang, p.pinned, p.Voices)
	if voice == "" {
		return nil, fmt.Errorf("edge: no voice configured for language %q", lang)
	}
	if _, hasDeadline := ctx.Deadline(); !hasDeadline {
		var cancel context.CancelFunc
		ctx, cancel = context.WithTimeout(ctx, edgeIOTimeout)
		defer cancel()
	}

	conn, wsURL, err := p.dialWithSkewRetry(ctx)
	if err != nil {
		return nil, err
	}
	defer conn.Close()

	now := time.Now().UTC()
	messages := [][]byte{
		[]byte(edgeSpeechConfigMsg(now)),
		[]byte(edgeSynthesisHeaders(now, edgeRequestID()) + edgeSSML(voice, text)),
	}
	for _, msg := range messages {
		if err := conn.SetWriteDeadline(time.Now().Add(edgeIOTimeout)); err != nil {
			return nil, protocolErr(err)
		}
		if err := conn.WriteMessage(websocket.TextMessage, msg); err != nil {
			return nil, protocolErr(err)
		}
	}

	var audio bytes.Buffer
	for {
		if err := conn.SetReadDeadline(time.Now().Add(edgeIOTimeout)); err != nil {
			return nil, protocolErr(err)
		}
		msgType, msg, err := conn.ReadMessage()
		if err != nil {
			return nil, protocolErr(err)
		}
		switch msgType {
		case websocket.TextMessage:
			if strings.Contains(string(msg), "Path:turn.end") {
				if audio.Len() == 0 {
					return nil, fmt.Errorf("edge: server sent turn.end without audio frames; protocol changed? (%s)", redactURL(wsURL))
				}
				return audio.Bytes(), nil
			}
		case websocket.BinaryMessage:
			headerText, payload, ok := splitEdgeBinary(msg)
			if ok && strings.Contains(headerText, "Path:audio") {
				audio.Write(payload)
			}
		}
	}
}

// dialWithSkewRetry establishes the connection; on 403 (clock drift) the
// server timestamp is adopted and the dial is retried ONCE.
func (p *Edge) dialWithSkewRetry(ctx context.Context) (*websocket.Conn, string, error) {
	conn, wsURL, resp, err := p.dial(ctx)
	if err == nil {
		return conn, wsURL, nil
	}
	if resp != nil && resp.StatusCode == http.StatusForbidden {
		if serverDate := resp.Header.Get("Date"); serverDate != "" {
			if t, perr := http.ParseTime(serverDate); perr == nil {
				edgeClockSkew.Store(t.Unix() - time.Now().Unix())
				conn, wsURL, resp, err = p.dial(ctx)
				if err == nil {
					return conn, wsURL, nil
				}
			}
		}
	}
	if resp != nil {
		return nil, wsURL, fmt.Errorf("edge: WebSocket connection to %s failed (HTTP %d; network/timeout, or the Edge TTS protocol changed?): %w",
			redactURL(wsURL), resp.StatusCode, err)
	}
	return nil, wsURL, fmt.Errorf("edge: WebSocket connection to %s failed; network/timeout, or the Edge TTS protocol changed: %w",
		redactURL(wsURL), err)
}

// dial opens the connection according to the protocol: query with token,
// ConnectionId, Sec-MS-GEC (v2) and version; headers with Origin, Edge
// user agent and MUID cookie.
func (p *Edge) dial(ctx context.Context) (*websocket.Conn, string, *http.Response, error) {
	wsURL, err := p.requestURL(time.Now())
	if err != nil {
		return nil, "", nil, err
	}
	dialer := p.Dialer
	if dialer == nil {
		dialer = websocket.DefaultDialer
	}
	header := http.Header{}
	header.Set("Origin", edgeOrigin)
	header.Set("User-Agent", edgeUserAgent)
	header.Set("Pragma", "no-cache")
	header.Set("Cache-Control", "no-cache")
	header.Set("Accept-Language", "en-US,en;q=0.9")
	header.Set("Cookie", "muid="+edgeMUID())
	conn, resp, err := dialer.DialContext(ctx, wsURL, header)
	if err != nil {
		return nil, wsURL, resp, err
	}
	return conn, wsURL, nil, nil
}

// requestURL adds the protocol query parameters and validates the scheme
// (ws/wss).
func (p *Edge) requestURL(now time.Time) (string, error) {
	if p.Endpoint == "" {
		return "", fmt.Errorf("edge: no endpoint configured")
	}
	u, err := url.Parse(p.Endpoint)
	if err != nil {
		return "", fmt.Errorf("edge: endpoint %q unreadable: %w", p.Endpoint, err)
	}
	if u.Scheme != "ws" && u.Scheme != "wss" {
		return "", fmt.Errorf("edge: endpoint %q must be ws:// or wss:// (is %q)", p.Endpoint, u.Scheme)
	}
	q := u.Query()
	q.Set("TrustedClientToken", edgeTrustedClientToken)
	q.Set("ConnectionId", edgeRequestID())
	q.Set("Sec-MS-GEC", edgeSecMSGEC(now))
	q.Set("Sec-MS-GEC-Version", edgeSecMSGECVersion)
	u.RawQuery = q.Encode()
	return u.String(), nil
}

// edgeSecMSGEC produces the DRM token Sec-MS-GEC v2: Windows filetime ticks
// (100 ns, 5-minute grid, clock correction) + trusted client token →
// "<CS64>-<SHA256 variant>" (both upper-case hex, see edgedrm.go).
func edgeSecMSGEC(now time.Time) string {
	secs := now.Unix() + edgeClockSkew.Load() + drmWinEpoch
	secs -= secs % 300 // 5-minute grid
	ticks := uint64(secs) * 10_000_000
	strToHash := fmt.Appendf(nil, "%d%s", ticks, edgeTrustedClientToken)
	digest := drmSHA256Digest(strToHash)
	cs0, cs1 := drmCS64(strToHash, digest)

	var cs64Buf [8]byte
	cs64Buf[0] = byte(cs0)
	cs64Buf[1] = byte(cs0 >> 8)
	cs64Buf[2] = byte(cs0 >> 16)
	cs64Buf[3] = byte(cs0 >> 24)
	cs64Buf[4] = byte(cs1)
	cs64Buf[5] = byte(cs1 >> 8)
	cs64Buf[6] = byte(cs1 >> 16)
	cs64Buf[7] = byte(cs1 >> 24)

	var shaBuf [32]byte
	for i, w := range digest {
		shaBuf[i*4] = byte(w >> 24)
		shaBuf[i*4+1] = byte(w >> 16)
		shaBuf[i*4+2] = byte(w >> 8)
		shaBuf[i*4+3] = byte(w)
	}
	return strings.ToUpper(hex.EncodeToString(cs64Buf[:])) + "-" + strings.ToUpper(hex.EncodeToString(shaBuf[:]))
}

// protocolErr turns read/write/connection aborts into clear "protocol
// changed?" errors; Edge is an undocumented endpoint and changes should be
// diagnosable immediately.
func protocolErr(err error) error {
	return fmt.Errorf("edge: communication failed; network/timeout, or the Edge TTS protocol changed: %w", err)
}

// splitEdgeBinary splits a binary server message: the first 2 bytes
// (big-endian) give the length of the header block (CRLF lines such as
// "Path:audio"), followed by the audio payload.
func splitEdgeBinary(msg []byte) (header string, payload []byte, ok bool) {
	if len(msg) < 2 {
		return "", nil, false
	}
	headerLen := int(binary.BigEndian.Uint16(msg[0:2]))
	if 2+headerLen > len(msg) {
		return "", nil, false
	}
	return string(msg[2 : 2+headerLen]), msg[2+headerLen:], true
}

// edgeSpeechConfigMsg is the first client message: header block + JSON body
// with output format and metadata options (sentence boundaries on, word
// boundaries off; reference default).
func edgeSpeechConfigMsg(now time.Time) string {
	return fmt.Sprintf(
		"X-Timestamp:%s\r\nContent-Type:application/json; charset=utf-8\r\nPath:speech.config\r\n\r\n"+
			`{"context":{"synthesis":{"audio":{"metadataoptions":{"sentenceBoundaryEnabled":"true","wordBoundaryEnabled":"false"},"outputFormat":%q}}}}`,
		edgeTimestamp(now), edgeOutputFormat)
}

// edgeSynthesisHeaders is the header block of the SSML request. The
// trailing Z on the timestamp is reference behaviour ("Microsoft Edge
// bug"), deliberately carried along.
func edgeSynthesisHeaders(now time.Time, requestID string) string {
	return fmt.Sprintf(
		"X-RequestId:%s\r\nContent-Type:application/ssml+xml\r\nX-Timestamp:%sZ\r\nPath:ssml\r\n\r\n",
		requestID, edgeTimestamp(now))
}

// edgeSSML builds the speech request (xml:lang fixed to "en-US" like the
// reference; the text is stripped of control characters and XML-escaped).
func edgeSSML(voice, text string) string {
	return fmt.Sprintf(
		"<speak version='1.0' xmlns='http://www.w3.org/2001/10/synthesis' xml:lang='en-US'>"+
			"<voice name='%s'>"+
			"<prosody pitch='+0Hz' rate='+0%%' volume='+0%%'>%s</prosody>"+
			"</voice></speak>",
		voice, edgeEscape(text))
}

// edgeEscape removes unsupported control characters (reference:
// remove_incompatible_characters) and then escapes & < >.
func edgeEscape(s string) string {
	clean := make([]byte, 0, len(s))
	for i := 0; i < len(s); i++ {
		c := s[i]
		if c <= 8 || (c >= 11 && c <= 12) || (c >= 14 && c <= 31) {
			c = ' '
		}
		clean = append(clean, c)
	}
	esc := make([]byte, 0, len(clean))
	for _, c := range clean {
		switch c {
		case '&':
			esc = append(esc, "&amp;"...)
		case '<':
			esc = append(esc, "&lt;"...)
		case '>':
			esc = append(esc, "&gt;"...)
		default:
			esc = append(esc, c)
		}
	}
	return string(esc)
}

// edgeTimestamp formats the timestamp in the edge-tts format.
func edgeTimestamp(now time.Time) string {
	return now.Format("Mon Jan 02 2006 15:04:05 GMT+0000 (Coordinated Universal Time)")
}

// edgeRequestID produces a 32-character hex ID (UUID v4 without dashes).
func edgeRequestID() string {
	var b [16]byte
	if _, err := rand.Read(b[:]); err != nil {
		// Fallback: time based; the ID only has to be unique per request.
		now := time.Now().UnixNano()
		for i := 0; i < 16; i++ {
			b[i] = byte(now >> (uint(i%8) * 8))
		}
	}
	b[6] = (b[6] & 0x0f) | 0x40 // UUID version
	b[8] = (b[8] & 0x3f) | 0x80 // variant
	return hex.EncodeToString(b[:])
}

// edgeMUID produces the random MUID for the cookie (32 hex, upper case).
func edgeMUID() string {
	var b [16]byte
	if _, err := rand.Read(b[:]); err != nil {
		return edgeRequestID()
	}
	return strings.ToUpper(hex.EncodeToString(b[:]))
}

// redactURL masks the query parameters (they contain the DRM token and
// IDs) in error messages; the URL itself is enough for diagnosis.
func redactURL(raw string) string {
	u, err := url.Parse(raw)
	if err != nil {
		return raw
	}
	u.RawQuery = "…"
	return u.String()
}