package api

import (
	"encoding/json"
	"fmt"
	"net/http"
	"strings"
	"time"

	"code.m3ta.dev/m3tam3re/talk/internal/queue"
)

// maxBodyBytes limits request bodies (announcements are short; protection
// against accidental huge payloads).
const maxBodyBytes = 64 << 10

// HandlerConfig bundles the dependencies of the HTTP surface. The handler
// knows neither config files nor env; the daemon injects everything, and
// process-boundary tests drive exactly this surface as a black box.
type HandlerConfig struct {
	// Queue is the daemon queue (Enqueue/Cancel/Current/Pending).
	Queue *queue.Queue

	// Mute is the persistent mute state (file mute in the config dir).
	Mute queue.MuteStore

	// Version is the daemon version for GET /status and serverInfo.
	Version string

	// KnownProviders are the valid provider names (validation of the
	// provider field in POST /speak; the daemon passes provider.Names()).
	KnownProviders []string

	// Provider resolves the active provider for GET /status (daemon side:
	// pin of the running item or first available chain tier). Optional.
	Provider func() string

	// AllowedOrigins is the CORS allow list for POST /speak (empty = no CORS
	// headers, the browser blocks; see cors.go).
	AllowedOrigins []string

	// Shutdown shuts the daemon down (POST /shutdown, `talk daemon stop`).
	// Must not block and must be callable more than once. Optional: nil
	// means the endpoint answers 501.
	Shutdown func()
}

// NewHandler returns the daemon's HTTP routes. Method binding via ServeMux
// patterns: wrong method 405, unknown path 404. The originGuard (cors.go)
// sits in front of the router: browser requests (Origin header) only reach
// POST /speak from listed origins; everything else is 403.
func NewHandler(cfg HandlerConfig) http.Handler {
	h := &handler{
		queue:          cfg.Queue,
		mute:           cfg.Mute,
		version:        cfg.Version,
		known:          make(map[string]bool, len(cfg.KnownProviders)),
		provider:       cfg.Provider,
		allowedOrigins: cfg.AllowedOrigins,
		shutdown:       cfg.Shutdown,
	}
	for _, name := range cfg.KnownProviders {
		h.known[name] = true
	}
	mux := http.NewServeMux()
	mux.HandleFunc("POST /speak", h.speak)
	mux.HandleFunc("OPTIONS /speak", h.speakPreflight) // CORS preflight
	mux.HandleFunc("GET /status", h.status)
	mux.HandleFunc("POST /cancel", h.cancel)
	mux.HandleFunc("POST /mute", h.muteEndpoint(true))
	mux.HandleFunc("POST /unmute", h.muteEndpoint(false))
	mux.HandleFunc("POST /shutdown", h.shutdownEndpoint)
	mux.HandleFunc("POST /mcp", h.serveMCP) // MCP Streamable HTTP
	mux.HandleFunc("GET /mcp", h.mcpGet)    // 405: no server-initiated streams
	return h.originGuard(mux)
}

// handler is the internal state of the HTTP surface.
type handler struct {
	queue          *queue.Queue
	mute           queue.MuteStore
	version        string
	known          map[string]bool
	provider       func() string
	allowedOrigins []string
	shutdown       func()
}

// speak handles POST /speak: validate, discard when muted (202, documented
// behaviour; deliberately not an error so callers need no special
// handling), otherwise enqueue and answer 202 {id}. The laws (rate-limit
// budget, quiet hours) may also discard on admission; the response then
// names the reason ({"discarded":"..."}). CORS headers only here and only
// for a listed origin (see cors.go).
func (h *handler) speak(w http.ResponseWriter, r *http.Request) {
	h.setSpeakCors(w, r)

	var req SpeakRequest
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, maxBodyBytes)).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid JSON body: "+err.Error())
		return
	}
	adm := h.admitSpeak(req)
	if adm.errMsg != "" {
		writeError(w, adm.status, adm.errMsg)
		return
	}
	writeJSON(w, adm.status, adm.resp)
}

// speakAdmission is the result of the shared admission path of POST /speak
// and the MCP tool speak: an HTTP status equivalent plus body. 202 with
// {id}/{muted}/{discarded} as the admission result, 400/503 with errMsg as
// an error (MCP translates both, see mcp.go).
type speakAdmission struct {
	status int
	resp   SpeakResponse
	errMsg string
}

// admitSpeak is the one admission path behind POST /speak and the MCP tool
// speak: validation, mute check, enqueue including the laws (rate-limit
// budget, quiet hours). Identical semantics for both doors, no contract
// drift.
func (h *handler) admitSpeak(req SpeakRequest) speakAdmission {
	if strings.TrimSpace(req.Text) == "" {
		return speakAdmission{status: http.StatusBadRequest, errMsg: "text is missing or empty"}
	}
	if req.Priority == "" {
		req.Priority = string(queue.PriorityNormal)
	}
	if !queue.Priority(req.Priority).Valid() {
		return speakAdmission{status: http.StatusBadRequest,
			errMsg: fmt.Sprintf("priority: invalid value %q (allowed: low, normal, high)", req.Priority)}
	}
	if req.Provider != "" && !h.known[req.Provider] {
		return speakAdmission{status: http.StatusBadRequest,
			errMsg: fmt.Sprintf("provider: unknown value %q", req.Provider)}
	}
	if req.Lang != "" && req.Lang != "de" && req.Lang != "en" {
		return speakAdmission{status: http.StatusBadRequest,
			errMsg: fmt.Sprintf("lang: invalid value %q (allowed: de, en)", req.Lang)}
	}

	if h.mute.Muted() {
		return speakAdmission{status: http.StatusAccepted, resp: SpeakResponse{Muted: true}}
	}

	adm, err := h.queue.Enqueue(queue.Item{
		Text:     req.Text,
		Lang:     req.Lang,
		Provider: req.Provider,
		Voice:    req.Voice,
		Priority: queue.Priority(req.Priority),
		Now:      req.Now,
	})
	if err != nil {
		return speakAdmission{status: http.StatusServiceUnavailable, errMsg: "enqueue: " + err.Error()}
	}
	if adm.Discarded != "" {
		// Law discard (rate-limit budget / quiet hours): documented
		// behaviour like mute, 202 with a reason instead of an error, so
		// callers need no special handling.
		return speakAdmission{status: http.StatusAccepted,
			resp: SpeakResponse{Discarded: adm.Discarded, Toast: adm.Toast}}
	}
	return speakAdmission{status: http.StatusAccepted, resp: SpeakResponse{ID: adm.ID, Truncated: adm.Truncated}}
}

// status handles GET /status: queue length (+ waiting IDs), current item,
// mute state, active provider, version, and the law state (rate limit with
// next slot, quiet-hours window).
func (h *handler) status(w http.ResponseWriter, r *http.Request) {
	pending := h.queue.Pending()
	ids := make([]string, len(pending))
	for i, it := range pending {
		ids[i] = it.ID
	}
	st := StatusResponse{
		Version:  h.version,
		Queue:    len(pending),
		QueueIDs: ids,
		Muted:    h.mute.Muted(),
		MCP:      true,
		Cors:     corsList(h.allowedOrigins),
	}
	if cur, ok := h.queue.Current(); ok {
		st.Current = &CurrentItem{
			ID:       cur.ID,
			Text:     cur.Text,
			Priority: string(cur.Priority),
			Now:      cur.Now,
		}
	}
	if h.provider != nil {
		st.Provider = h.provider()
	}
	law := h.queue.LawState()
	st.RateLimit, st.QuietHours = lawState(law)
	st.Limits = &LimitsState{MaxText: law.MaxText, MaxAge: law.MaxAge.String()}
	writeJSON(w, http.StatusOK, st)
}

// corsList copies the allow list as a JSON [] instead of null: the status
// should show "cors": [] when the door is closed.
func corsList(origins []string) []string {
	out := make([]string, len(origins))
	copy(out, origins)
	return out
}

// lawState converts the queue's law view into the JSON form of /status:
// timestamps only when they lie in the future (null = slot free / quiet
// hours inactive).
func lawState(l queue.LawState) (*RateLimitState, *QuietHoursState) {
	now := time.Now()
	rl := &RateLimitState{
		Interval:       l.RateLimit.String(),
		AllowHighBurst: l.AllowHighBurst,
	}
	if l.NextSlot.After(now) {
		slot := l.NextSlot.Format(time.RFC3339)
		rl.NextSlot = &slot
	}
	qh := &QuietHoursState{
		Window: l.Quiet.String(),
		Active: l.QuietActive,
		Mode:   l.QuietMode,
	}
	if !l.QuietUntil.IsZero() {
		until := l.QuietUntil.Format(time.RFC3339)
		qh.Until = &until
	}
	return rl, qh
}

// cancel handles POST /cancel: cancel the running announcement and clear
// the queue.
func (h *handler) cancel(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, CancelResponse{Cancelled: h.queue.Cancel()})
}

// muteEndpoint handles POST /mute and POST /unmute: persistent mute state
// (file in the config dir, survives daemon restarts).
func (h *handler) muteEndpoint(muted bool) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if err := h.mute.Set(muted); err != nil {
			writeError(w, http.StatusInternalServerError, err.Error())
			return
		}
		writeJSON(w, http.StatusOK, MuteResponse{Muted: muted})
	}
}

// shutdownEndpoint handles POST /shutdown (`talk daemon stop`): response
// first, then the shutdown trigger, so the caller gets its 200 before the
// server closes the connection.
func (h *handler) shutdownEndpoint(w http.ResponseWriter, r *http.Request) {
	if h.shutdown == nil {
		writeError(w, http.StatusNotImplemented, "this daemon has no shutdown trigger")
		return
	}
	writeJSON(w, http.StatusOK, ShutdownResponse{OK: true})
	h.shutdown()
}

// writeJSON writes a JSON response with a status code.
func writeJSON(w http.ResponseWriter, code int, body any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(code)
	_ = json.NewEncoder(w).Encode(body)
}

// writeError writes an error as {"error": "..."} with a status code.
func writeError(w http.ResponseWriter, code int, msg string) {
	writeJSON(w, code, map[string]string{"error": msg})
}