package httpapi

import (
	"context"
	"encoding/json"
	"errors"
	"io"
	"log/slog"
	"net/http"
	"strconv"
	"strings"
	"time"

	"ballet-island/backend/internal/identity"
	"ballet-island/backend/internal/practice"
	"github.com/jackc/pgx/v5/pgxpool"
)

// IdentityVerifier is the only external identity dependency. Implementations
// return an app-scoped verified identity and must never trust client user IDs.
type IdentityVerifier interface {
	Exchange(context.Context, string) (string, error)
}

type app struct {
	store    *practice.Store
	verifier IdentityVerifier
}
type operation func(http.ResponseWriter, *http.Request, string) error

// NewAppHandler adds authenticated business routes while retaining independent health checks.
func NewAppHandler(pool *pgxpool.Pool, verifier IdentityVerifier, now func() time.Time) http.Handler {
	a := &app{store: practice.New(pool, now), verifier: verifier}
	mux := http.NewServeMux()
	mux.Handle("/", NewHandler(pool.Ping))
	mux.HandleFunc("POST /v1/session", a.login)
	mux.HandleFunc("GET /v1/projects", a.auth(a.projects))
	mux.HandleFunc("POST /v1/projects", a.auth(a.saveProject))
	mux.HandleFunc("PUT /v1/projects/order", a.auth(a.reorderProjects))
	mux.HandleFunc("PUT /v1/projects/{id}", a.auth(a.saveProject))
	mux.HandleFunc("DELETE /v1/projects/{id}", a.auth(a.removeProject))
	mux.HandleFunc("GET /v1/records", a.auth(a.records))
	mux.HandleFunc("GET /v1/records/{id}", a.auth(a.record))
	mux.HandleFunc("POST /v1/records", a.auth(a.saveRecord))
	mux.HandleFunc("PUT /v1/records/{id}", a.auth(a.saveRecord))
	mux.HandleFunc("DELETE /v1/records/{id}", a.auth(a.deleteRecord))
	mux.HandleFunc("GET /v1/review", a.auth(a.review))
	return mux
}

func respond(w http.ResponseWriter, status int, value any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.Header().Set("Cache-Control", "no-store")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(value)
}

func decode(w http.ResponseWriter, r *http.Request, value any) error {
	r.Body = http.MaxBytesReader(w, r.Body, 32*1024)
	d := json.NewDecoder(r.Body)
	d.DisallowUnknownFields()
	if err := d.Decode(value); err != nil {
		return practice.ErrInvalid
	}
	if err := d.Decode(new(any)); err != io.EOF {
		return practice.ErrInvalid
	}
	return nil
}

func failure(w http.ResponseWriter, err error) {
	status, code, message := 503, "service_unavailable", "服务暂时不可用，请稍后重试"
	switch {
	case errors.Is(err, practice.ErrUnauthorized), errors.Is(err, identity.ErrInvalidCode):
		status, code, message = 401, "unauthorized", practice.ErrUnauthorized.Error()
	case errors.Is(err, practice.ErrInvalid):
		status, code, message = 400, "invalid_input", practice.ErrInvalid.Error()
	case errors.Is(err, practice.ErrUnavailable):
		status, code, message = 404, "unavailable", practice.ErrUnavailable.Error()
	case errors.Is(err, practice.ErrArchived):
		status, code, message = 409, "archived_project", practice.ErrArchived.Error()
	case errors.Is(err, practice.ErrConflict):
		status, code, message = 409, "submission_conflict", practice.ErrConflict.Error()
	case errors.Is(err, practice.ErrDeleted):
		status, code, message = 410, "record_deleted", practice.ErrDeleted.Error()
	default:
		// Do not log raw database/network errors: they may contain notes, credentials or URLs.
		slog.Error("business request failed", "category", code)
	}
	respond(w, status, map[string]any{"error": map[string]string{"code": code, "message": message}})
}

func (a *app) auth(fn operation) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		ctx, cancel := context.WithTimeout(r.Context(), 8*time.Second)
		defer cancel()
		r = r.WithContext(ctx)
		header := r.Header.Get("Authorization")
		if !strings.HasPrefix(header, "Bearer ") {
			failure(w, practice.ErrUnauthorized)
			return
		}
		user, err := a.store.Authenticate(ctx, strings.TrimPrefix(header, "Bearer "))
		if err == nil {
			err = fn(w, r, user)
		}
		if err != nil {
			failure(w, err)
		}
	}
}

func (a *app) login(w http.ResponseWriter, r *http.Request) {
	ctx, cancel := context.WithTimeout(r.Context(), 8*time.Second)
	defer cancel()
	var input struct {
		Code string `json:"code"`
	}
	if err := decode(w, r, &input); err != nil || strings.TrimSpace(input.Code) == "" || len(input.Code) > 512 {
		failure(w, practice.ErrInvalid)
		return
	}
	identity, err := a.verifier.Exchange(ctx, input.Code)
	if err != nil {
		failure(w, err)
		return
	}
	session, err := a.store.Login(ctx, identity)
	if err != nil {
		failure(w, err)
		return
	}
	respond(w, 200, session)
}

func (a *app) projects(w http.ResponseWriter, r *http.Request, user string) error {
	projects, err := a.store.Projects(r.Context(), user, r.URL.Query().Get("includeArchived") == "true")
	if err == nil {
		respond(w, 200, map[string]any{"projects": projects, "today": a.store.Today()})
	}
	return err
}
func (a *app) reorderProjects(w http.ResponseWriter, r *http.Request, user string) error {
	var input struct {
		ProjectIDs []string `json:"projectIds"`
	}
	if err := decode(w, r, &input); err != nil {
		return err
	}
	if err := a.store.ReorderProjects(r.Context(), user, input.ProjectIDs); err != nil {
		return err
	}
	respond(w, 200, map[string]string{"action": "reordered"})
	return nil
}
func (a *app) saveProject(w http.ResponseWriter, r *http.Request, user string) error {
	var input struct {
		Name   string  `json:"name"`
		IconID *string `json:"iconId"`
	}
	if err := decode(w, r, &input); err != nil {
		return err
	}
	p, err := a.store.SaveProject(r.Context(), user, r.PathValue("id"), input.Name, input.IconID)
	if err == nil {
		respond(w, 200, p)
	}
	return err
}
func (a *app) removeProject(w http.ResponseWriter, r *http.Request, user string) error {
	mode, err := a.store.RemoveProject(r.Context(), user, r.PathValue("id"))
	if err == nil {
		respond(w, 200, map[string]string{"action": mode})
	}
	return err
}

func (a *app) records(w http.ResponseWriter, r *http.Request, user string) error {
	q := r.URL.Query()
	limit := 20
	if q.Has("limit") {
		var err error
		limit, err = strconv.Atoi(q.Get("limit"))
		if err != nil {
			return practice.ErrInvalid
		}
	}
	list, err := a.store.Records(r.Context(), user, q.Get("from"), q.Get("to"), q.Get("cursor"), limit)
	if err == nil {
		respond(w, 200, list)
	}
	return err
}
func (a *app) record(w http.ResponseWriter, r *http.Request, user string) error {
	record, err := a.store.Record(r.Context(), user, r.PathValue("id"))
	if err == nil {
		respond(w, 200, record)
	}
	return err
}
func (a *app) saveRecord(w http.ResponseWriter, r *http.Request, user string) error {
	var input practice.RecordInput
	if err := decode(w, r, &input); err != nil {
		return err
	}
	record, err := a.store.SaveRecord(r.Context(), user, r.PathValue("id"), input)
	if err == nil {
		respond(w, 200, record)
	}
	return err
}
func (a *app) deleteRecord(w http.ResponseWriter, r *http.Request, user string) error {
	err := a.store.DeleteRecord(r.Context(), user, r.PathValue("id"))
	if err == nil {
		respond(w, 200, map[string]string{"action": "deleted"})
	}
	return err
}
func (a *app) review(w http.ResponseWriter, r *http.Request, user string) error {
	review, err := a.store.Review(r.Context(), user, r.URL.Query().Get("period"), r.URL.Query().Get("date"))
	if err == nil {
		respond(w, 200, review)
	}
	return err
}