// Package httpapi exposes the internal full-sync control API through contract
// interfaces. Persistence and replay execution belong to the injected services.
package httpapi

import (
	"bytes"
	"crypto/subtle"
	"encoding/json"
	"errors"
	"io"
	"mime"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"unicode"
	"unicode/utf8"

	"git.5iot.com/iotlcm-public/iotlcm-worker-svr/internal/fullsync/contract"
	fullsyncruntime "git.5iot.com/iotlcm-public/iotlcm-worker-svr/internal/fullsync/runtime"

	"github.com/gogf/gf/v2/errors/gerror"
)

const maxReplayBodyBytes = 64 << 10

// Dependencies are the only application services used by the HTTP handlers.
type Dependencies struct {
	Runs     contract.RunReader
	List     contract.RunLister
	Failures contract.FailurePager
	Replays  contract.ReplayRequester
	Actions  contract.ActionReader
	Simple   *fullsyncruntime.SimpleReplay
}

// ErrorResponse is shared by authentication, routing, validation and service
// failures. Messages deliberately exclude underlying storage error details.
type ErrorResponse struct {
	Error APIError `json:"error"`
}

type APIError struct {
	Code    string `json:"code"`
	Message string `json:"message"`
}

// NewHandler exposes the control routes on the private Docker network. Admin
// performs the user JWT and permission checks before calling this listener.
func NewHandler(bearerToken string, deps Dependencies) (http.Handler, error) {
	if strings.ContainsFunc(bearerToken, func(r rune) bool { return unicode.IsSpace(r) || unicode.IsControl(r) }) {
		return nil, gerror.New("invalid full-sync HTTP token")
	}
	if deps.Runs == nil || deps.List == nil || deps.Failures == nil || deps.Replays == nil || deps.Actions == nil {
		return nil, gerror.New("full-sync HTTP requires run list, run, failure, replay and action services")
	}
	mux := http.NewServeMux()
	mux.HandleFunc(contract.ListRunsRoute, method(http.MethodGet, func(w http.ResponseWriter, r *http.Request) {
		query, err := url.ParseQuery(r.URL.RawQuery)
		if err != nil || len(query["limit"]) > 1 || len(query["syncKind"]) > 1 {
			writeError(w, contract.ErrInvalidArgument)
			return
		}
		filter := contract.RunListFilter{SyncKind: contract.SyncKind(query.Get("syncKind"))}
		if filter.SyncKind != "" && !filter.SyncKind.Valid() {
			writeError(w, contract.ErrInvalidArgument)
			return
		}
		if query.Get("limit") != "" {
			filter.Limit, err = strconv.Atoi(query.Get("limit"))
			if err != nil || filter.Limit < 1 || filter.Limit > 100 {
				writeError(w, contract.ErrInvalidArgument)
				return
			}
		}
		result, err := deps.List.ListRuns(r.Context(), filter)
		if err != nil {
			writeError(w, err)
			return
		}
		writeJSON(w, http.StatusOK, result)
	}))
	mux.HandleFunc(contract.GetRunRoute, method(http.MethodGet, func(w http.ResponseWriter, r *http.Request) {
		id := r.PathValue("runId")
		if err := contract.ValidateID(id); err != nil {
			writeError(w, err)
			return
		}
		view, err := deps.Runs.GetRun(r.Context(), id)
		if err != nil {
			writeError(w, err)
			return
		}
		writeJSON(w, http.StatusOK, view)
	}))
	mux.HandleFunc(contract.GetFailuresRoute, method(http.MethodGet, func(w http.ResponseWriter, r *http.Request) {
		id := r.PathValue("runId")
		if err := contract.ValidateID(id); err != nil {
			writeError(w, err)
			return
		}
		page, err := parsePage(r.URL.RawQuery)
		if err != nil {
			writeError(w, err)
			return
		}
		result, err := deps.Failures.ListFailures(r.Context(), id, page)
		if err != nil {
			writeError(w, err)
			return
		}
		if result.Items == nil {
			result.Items = []contract.Failure{}
		}
		writeJSON(w, http.StatusOK, result)
	}))
	mux.HandleFunc(contract.PostReplayRoute, method(http.MethodPost, func(w http.ResponseWriter, r *http.Request) {
		if deps.Simple != nil {
			id := r.PathValue("runId")
			if err := contract.ValidateID(id); err != nil {
				writeError(w, err)
				return
			}
			var request struct {
				RequestedBy string `json:"requestedBy"`
				MaxRounds   int    `json:"maxRounds"`
			}
			decoder := json.NewDecoder(http.MaxBytesReader(w, r.Body, maxReplayBodyBytes))
			decoder.DisallowUnknownFields()
			if err := decoder.Decode(&request); err != nil {
				writeError(w, contract.ErrInvalidArgument)
				return
			}
			if err := decoder.Decode(new(any)); err != io.EOF {
				writeError(w, contract.ErrInvalidArgument)
				return
			}
			accepted, err := deps.Simple.Request(r.Context(), id, request.RequestedBy, request.MaxRounds)
			if errors.Is(err, fullsyncruntime.ErrNoFailures) {
				writeAPIError(w, http.StatusUnprocessableEntity, "no_failures", "Run has no failures to replay")
				return
			}
			if err != nil {
				writeError(w, err)
				return
			}
			writeJSON(w, http.StatusAccepted, accepted)
			return
		}
		request, err := parseReplay(w, r)
		if err != nil {
			var tooLarge *http.MaxBytesError
			if errors.As(err, &tooLarge) {
				writeAPIError(w, http.StatusRequestEntityTooLarge, "body_too_large", "Replay request body is too large")
			} else {
				writeError(w, err)
			}
			return
		}
		accepted, err := deps.Replays.RequestReplay(r.Context(), request)
		if err != nil {
			writeError(w, err)
			return
		}
		// Construct a local status URL from the returned identity, never an
		// externally supplied redirect. Invalid service output is a server error.
		accepted.StatusURL, err = contract.ActionStatusURL(accepted.ActionID)
		if err != nil || contract.ValidateID(accepted.TargetRunID) != nil || !accepted.Status.Valid() {
			writeAPIError(w, http.StatusInternalServerError, "internal_error", "Internal server error")
			return
		}
		w.Header().Set("Location", accepted.StatusURL)
		writeJSON(w, http.StatusAccepted, accepted)
	}))
	mux.HandleFunc("/internal/v1/full-sync-replays/{replayRunId}", method(http.MethodGet, func(w http.ResponseWriter, r *http.Request) {
		if deps.Simple == nil {
			writeError(w, contract.ErrNotFound)
			return
		}
		status, err := deps.Simple.Status(r.Context(), r.PathValue("replayRunId"))
		if err != nil {
			writeError(w, err)
			return
		}
		writeJSON(w, http.StatusOK, status)
	}))
	mux.HandleFunc(contract.GetActionRoute, method(http.MethodGet, func(w http.ResponseWriter, r *http.Request) {
		if deps.Simple != nil {
			writeError(w, contract.ErrNotFound)
			return
		}
		id := r.PathValue("actionId")
		if err := contract.ValidateID(id); err != nil {
			writeError(w, err)
			return
		}
		action, err := deps.Actions.GetReplayAction(r.Context(), id)
		if err != nil {
			writeError(w, err)
			return
		}
		writeJSON(w, http.StatusOK, action)
	}))
	mux.HandleFunc("/", func(w http.ResponseWriter, _ *http.Request) {
		writeError(w, contract.ErrNotFound)
	})
	if bearerToken == "" {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			w.Header().Set("Cache-Control", "no-store")
			mux.ServeHTTP(w, r)
		}), nil
	}
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Cache-Control", "no-store")
		values := r.Header.Values("Authorization")
		if len(values) == 1 {
			parts := strings.Fields(values[0])
			if len(parts) == 2 && strings.EqualFold(parts[0], "Bearer") && subtle.ConstantTimeCompare([]byte(parts[1]), []byte(bearerToken)) == 1 {
				mux.ServeHTTP(w, r)
				return
			}
		}
		w.Header().Set("WWW-Authenticate", `Bearer realm="full-sync"`)
		writeAPIError(w, http.StatusUnauthorized, "unauthorized", "Valid bearer authentication is required")
	}), nil
}

func method(expected string, next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != expected {
			w.Header().Set("Allow", expected)
			writeAPIError(w, http.StatusMethodNotAllowed, "method_not_allowed", "Method not allowed")
			return
		}
		next(w, r)
	}
}

func parsePage(rawQuery string) (contract.PageRequest, error) {
	query, err := url.ParseQuery(rawQuery)
	if err != nil || len(query["cursor"]) > 1 || len(query["limit"]) > 1 {
		return contract.PageRequest{}, gerror.Wrap(contract.ErrInvalidArgument, "invalid pagination query")
	}
	page := contract.PageRequest{Cursor: contract.Cursor(query.Get("cursor"))}
	if value := query.Get("limit"); value != "" {
		page.Limit, err = strconv.Atoi(value)
		if err != nil {
			return contract.PageRequest{}, gerror.Wrap(contract.ErrInvalidArgument, "limit must be an integer")
		}
	}
	return page.Normalized()
}

func parseReplay(w http.ResponseWriter, r *http.Request) (contract.ReplayRequest, error) {
	var request contract.ReplayRequest
	if value := r.Header.Get("Content-Type"); value != "" {
		mediaType, _, err := mime.ParseMediaType(value)
		if err != nil || mediaType != "application/json" {
			return request, gerror.Wrap(contract.ErrInvalidArgument, "replay body must be JSON")
		}
	}
	data, err := io.ReadAll(http.MaxBytesReader(w, r.Body, maxReplayBodyBytes))
	if err != nil {
		var tooLarge *http.MaxBytesError
		if errors.As(err, &tooLarge) {
			return request, err
		}
		return request, gerror.Wrap(contract.ErrInvalidArgument, "cannot read replay body")
	}
	if !utf8.Valid(data) {
		return request, gerror.Wrap(contract.ErrInvalidArgument, "replay body must be UTF-8")
	}
	decoder := json.NewDecoder(bytes.NewReader(data))
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(&request); err != nil {
		return request, gerror.Wrap(contract.ErrInvalidArgument, "invalid replay JSON")
	}
	if err := decoder.Decode(new(any)); err != io.EOF {
		return request, gerror.Wrap(contract.ErrInvalidArgument, "replay body must contain exactly one JSON object")
	}
	if len(r.Header.Values(contract.IdempotencyHeader)) != 1 {
		return request, gerror.Wrap(contract.ErrInvalidArgument, "exactly one Idempotency-Key is required")
	}
	request.SourceRunID = r.PathValue("runId")
	request.IdempotencyKey = r.Header.Get(contract.IdempotencyHeader)
	return request, request.Validate()
}

func writeError(w http.ResponseWriter, err error) {
	switch {
	case errors.Is(err, contract.ErrInvalidArgument):
		writeAPIError(w, http.StatusBadRequest, "invalid_argument", "Invalid request")
	case errors.Is(err, contract.ErrNotFound):
		writeAPIError(w, http.StatusNotFound, "not_found", "Resource not found")
	case errors.Is(err, contract.ErrFailureDetailsUnavailable):
		writeAPIError(w, http.StatusGone, "failure_details_unavailable", "Live failure details are no longer available")
	case errors.Is(err, contract.ErrConflict), errors.Is(err, contract.ErrLeaseLost):
		writeAPIError(w, http.StatusConflict, "conflict", "Request conflicts with the current resource")
	case errors.Is(err, contract.ErrBusy):
		writeAPIError(w, http.StatusServiceUnavailable, "busy", "Resource is busy; retry later")
	default:
		writeAPIError(w, http.StatusInternalServerError, "internal_error", "Internal server error")
	}
}

func writeAPIError(w http.ResponseWriter, status int, code, message string) {
	writeJSON(w, status, ErrorResponse{Error: APIError{Code: code, Message: message}})
}

func writeJSON(w http.ResponseWriter, status int, value any) {
	// Marshal before writing headers so an invalid service payload cannot
	// produce a successful status with truncated JSON.
	data, err := json.Marshal(value)
	if err != nil {
		status = http.StatusInternalServerError
		data = []byte(`{"error":{"code":"internal_error","message":"Internal server error"}}`)
	}
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	_, _ = w.Write(append(data, '\n'))
}