package server

import (
	"encoding/json"
	"net/http"
	"strconv"
	"strings"

	"git.misaka.ren/m1saka/record-asr/internal/audio"
	"git.misaka.ren/m1saka/record-asr/internal/store"
)

// writeJSON marshals v as JSON with the given status.
func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

// handleHealthz reports liveness and model readiness (public).
func (s *Server) handleHealthz(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, map[string]any{
		"status":          "ok",
		"models":          s.manager != nil && s.manager.Ready(),
		"version":         s.modelVersion(),
		"max_upload_bytes": s.cfg.MaxUploadBytes,
		"chunk_size":      s.cfg.ChunkSize,
	})
}

// handleRoot returns a tiny service descriptor (public).
func (s *Server) handleRoot(w http.ResponseWriter, r *http.Request) {
	if r.URL.Path != "/" {
		http.NotFound(w, r)
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{
		"name":    "record-asr",
		"engine":  "SenseVoiceSmall (int8) + silero VAD",
		"version": s.modelVersion(),
		"endpoints": []string{
			"POST   /api/tasks            (multipart: file) -> enqueue",
			"GET    /api/tasks            -> list",
			"GET    /api/tasks/{id}       -> detail",
			"DELETE /api/tasks/{id}       -> delete",
			"POST   /api/tasks/{id}/retry -> re-run failed task",
			"POST   /api/tasks/{id}/skip  -> abandon failed task",
			"GET    /api/tasks/{id}/transcript -> transcript",
		},
	})
}

// handleCreateTask accepts a multipart upload and enqueues a transcription task.
func (s *Server) handleCreateTask(w http.ResponseWriter, r *http.Request) {
	r.Body = http.MaxBytesReader(w, r.Body, s.cfg.MaxUploadBytes)
	if err := r.ParseMultipartForm(s.cfg.MaxUploadBytes); err != nil {
		renderError(w, http.StatusRequestEntityTooLarge,
			"upload rejected: "+err.Error())
		return
	}
	file, hdr, err := r.FormFile("file")
	if err != nil {
		renderError(w, http.StatusBadRequest, "missing 'file' multipart field")
		return
	}
	defer file.Close()

	name := hdr.Filename
	if name == "" {
		name = "upload.wav"
	}
	if !audio.IsSupported(name) {
		renderError(w, http.StatusUnsupportedMediaType,
			"unsupported extension; supported: "+audio.SupportedExtensions())
		return
	}

	t, err := s.store.Create(name, file, s.cfg.MaxUploadBytes, s.cfg.MaxRetries)
	if err != nil {
		renderError(w, http.StatusInternalServerError, "store: "+err.Error())
		return
	}
	w.Header().Set("Location", "/api/tasks/"+t.ID)
	writeJSON(w, http.StatusAccepted, t)
}

// --- resumable chunked uploads ---
//
// Files too large to fit a single request through a size-capping proxy (e.g.
// Cloudflare's 100MB body limit) are uploaded as many small slices instead.
// handleCreateUpload starts a session, handleUploadChunk appends one slice,
// handleCompleteUpload finalizes it into a task, and handleAbortUpload drops
// it. Each slice is <= ASR_CHUNK_SIZE_MB, safely under the proxy cap.

// handleCreateUpload starts a resumable chunked upload session. The request
// body is a small JSON {filename, size}; the response carries the upload id,
// the chunk size, and the total chunk count the client should send.
func (s *Server) handleCreateUpload(w http.ResponseWriter, r *http.Request) {
	var req struct {
		Filename string `json:"filename"`
		Size     int64  `json:"size"`
	}
	dec := json.NewDecoder(http.MaxBytesReader(w, r.Body, 1<<20))
	if err := dec.Decode(&req); err != nil {
		renderError(w, http.StatusBadRequest, "invalid JSON: "+err.Error())
		return
	}
	if req.Filename == "" {
		renderError(w, http.StatusBadRequest, "missing 'filename'")
		return
	}
	if req.Size <= 0 {
		renderError(w, http.StatusBadRequest, "missing or invalid 'size'")
		return
	}
	if !audio.IsSupported(req.Filename) {
		renderError(w, http.StatusUnsupportedMediaType,
			"unsupported extension; supported: "+audio.SupportedExtensions())
		return
	}
	sess, err := s.store.CreateUpload(req.Filename, req.Size, s.cfg.ChunkSize, s.cfg.MaxUploadBytes)
	if err != nil {
		renderError(w, http.StatusBadRequest, "init upload: "+err.Error())
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{
		"upload_id":    sess.UploadID,
		"chunk_size":   sess.ChunkSize,
		"total_chunks": sess.TotalChunks,
	})
}

// handleUploadChunk appends one chunk (#index, the 0-based query param) of a
// chunked upload session. The request body is the raw chunk bytes
// (application/octet-stream); each slice is capped at ASR_CHUNK_SIZE_MB.
func (s *Server) handleUploadChunk(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	idx, err := strconv.Atoi(r.URL.Query().Get("index"))
	if err != nil || idx < 0 {
		renderError(w, http.StatusBadRequest, "missing or invalid 'index' query param")
		return
	}
	r.Body = http.MaxBytesReader(w, r.Body, s.cfg.ChunkSize)
	if err := s.store.AppendChunk(id, idx, r.Body, s.cfg.ChunkSize); err != nil {
		if err == store.ErrUploadNotFound {
			renderError(w, http.StatusNotFound, "upload session not found or expired")
			return
		}
		renderError(w, http.StatusBadRequest, "chunk: "+err.Error())
		return
	}
	received, total, ok := s.store.UploadStatus(id)
	if !ok {
		renderError(w, http.StatusNotFound, "upload session not found")
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{
		"index":    idx,
		"received": received,
		"total":    total,
	})
}

// handleCompleteUpload finalizes a chunked upload and enqueues the task. The
// response mirrors POST /api/tasks (202 + the task) so the client treats the
// finalized upload exactly like a single-shot upload from this point on.
func (s *Server) handleCompleteUpload(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	t, err := s.store.CompleteUpload(id, s.cfg.MaxRetries)
	if err != nil {
		if err == store.ErrUploadNotFound {
			renderError(w, http.StatusNotFound, "upload session not found or expired")
			return
		}
		renderError(w, http.StatusBadRequest, "complete: "+err.Error())
		return
	}
	w.Header().Set("Location", "/api/tasks/"+t.ID)
	writeJSON(w, http.StatusAccepted, t)
}

// handleAbortUpload cancels a chunked upload session and removes its part
// file. Idempotent: a missing session still returns 204.
func (s *Server) handleAbortUpload(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	_ = s.store.AbortUpload(id)
	w.WriteHeader(http.StatusNoContent)
}

// handleListTasks returns all tasks newest-first.
func (s *Server) handleListTasks(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, map[string]any{"tasks": s.store.List()})
}

// handleGetTask returns one task.
func (s *Server) handleGetTask(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	t := s.store.Get(id)
	if t == nil {
		renderError(w, http.StatusNotFound, "task not found")
		return
	}
	writeJSON(w, http.StatusOK, t)
}

// handleDeleteTask removes a task and its audio.
func (s *Server) handleDeleteTask(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	if err := s.store.Delete(id); err != nil {
		if err == store.ErrNotFound {
			renderError(w, http.StatusNotFound, "task not found")
			return
		}
		renderError(w, http.StatusInternalServerError, "delete: "+err.Error())
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// handleRetryTask requeues a failed/skipped task for another attempt.
func (s *Server) handleRetryTask(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	if err := s.store.Retry(id); err != nil {
		if err == store.ErrNotFound {
			renderError(w, http.StatusNotFound, "task not found")
			return
		}
		renderError(w, http.StatusInternalServerError, "retry: "+err.Error())
		return
	}
	t := s.store.Get(id)
	writeJSON(w, http.StatusAccepted, t)
}

// handleSkipTask abandons a task so the queue moves on (the "continue" action).
func (s *Server) handleSkipTask(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	if err := s.store.Skip(id); err != nil {
		if err == store.ErrNotFound {
			renderError(w, http.StatusNotFound, "task not found")
			return
		}
		renderError(w, http.StatusInternalServerError, "skip: "+err.Error())
		return
	}
	t := s.store.Get(id)
	writeJSON(w, http.StatusAccepted, t)
}

// handleTranscript returns just the transcript of a completed task.
func (s *Server) handleTranscript(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	t := s.store.Get(id)
	if t == nil {
		renderError(w, http.StatusNotFound, "task not found")
		return
	}
	if t.Status != store.StatusCompleted || t.Result == nil {
		renderError(w, http.StatusConflict, "transcript not ready (status: "+t.Status+")")
		return
	}
	writeJSON(w, http.StatusOK, t.Result)
}

// --- auth ---

// authMiddleware wraps a handler with the password check. Auth is enforced
// for paths under /api/ and /v1/ (the OpenAI-compatible endpoint); /healthz
// and / stay public. When ASR_PASSWORD is unset, auth is disabled (a warning
// was logged at startup).
func (s *Server) authMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if (!strings.HasPrefix(r.URL.Path, "/api/") && !strings.HasPrefix(r.URL.Path, "/v1/")) || !s.cfg.AuthEnabled() {
			next.ServeHTTP(w, r)
			return
		}
		if !constantTimeEqual(extractToken(r), s.cfg.Password) {
			w.Header().Set("WWW-Authenticate", `Bearer realm="record-asr"`)
			renderError(w, http.StatusUnauthorized, "unauthorized")
			return
		}
		next.ServeHTTP(w, r)
	})
}

// extractToken pulls the shared secret from, in order: X-Api-Key header,
// Authorization: Bearer <token>, or ?token= query parameter.
func extractToken(r *http.Request) string {
	if v := strings.TrimSpace(r.Header.Get("X-Api-Key")); v != "" {
		return v
	}
	if v := r.Header.Get("Authorization"); v != "" {
		if strings.HasPrefix(strings.ToLower(v), "bearer ") {
			return strings.TrimSpace(v[7:])
		}
		return strings.TrimSpace(strings.TrimPrefix(v, "Bearer "))
	}
	return strings.TrimSpace(r.URL.Query().Get("token"))
}

// constantTimeEqual compares two strings in constant time.
func constantTimeEqual(a, b string) bool {
	if len(a) != len(b) {
		return false
	}
	var v byte
	for i := 0; i < len(a); i++ {
		v |= a[i] ^ b[i]
	}
	return v == 0
}