package server

import (
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"strconv"
	"strings"

	"steward/internal/api"
	"steward/internal/auth"
	"steward/internal/engine"
	"steward/internal/store"
)

// httpError is an error with an HTTP status.
type httpError struct {
	status int
	code   string
	msg    string
}

func (e *httpError) Error() string { return e.msg }

func badRequest(format string, args ...any) error {
	return &httpError{http.StatusBadRequest, "bad_request", fmt.Sprintf(format, args...)}
}

func notFound(format string, args ...any) error {
	return &httpError{http.StatusNotFound, "not_found", fmt.Sprintf(format, args...)}
}

func forbidden(format string, args ...any) error {
	return &httpError{http.StatusForbidden, "forbidden", fmt.Sprintf(format, args...)}
}

func conflict(format string, args ...any) error {
	return &httpError{http.StatusConflict, "conflict", fmt.Sprintf(format, args...)}
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.Header().Set("Cache-Control", "no-store")
	w.WriteHeader(status)
	enc := json.NewEncoder(w)
	enc.SetEscapeHTML(false)
	enc.Encode(v)
}

func writeError(w http.ResponseWriter, status int, code, msg string) {
	writeJSON(w, status, api.ErrorBody{Error: api.ErrorInfo{Code: code, Message: msg}})
}

func engineStatus(kind string) int {
	switch kind {
	case engine.KindBadRequest:
		return http.StatusBadRequest
	case engine.KindNotFound:
		return http.StatusNotFound
	case engine.KindConflict:
		return http.StatusConflict
	case engine.KindValidation:
		return http.StatusUnprocessableEntity
	}
	return http.StatusInternalServerError
}

// writeErr writes an error response. result, if given, is the preview of
// a refused change.
func (s *Server) writeErr(w http.ResponseWriter, r *http.Request, err error, result any) {
	var he *httpError
	if errors.As(err, &he) {
		writeError(w, he.status, he.code, he.msg)
		return
	}
	if ee, ok := engine.AsError(err); ok {
		body := api.ErrorBody{Error: api.ErrorInfo{Code: ee.Kind, Message: ee.Message, Problems: ee.Problems}}
		if result != nil {
			body.Error.Result, _ = json.Marshal(result)
		}
		writeJSON(w, engineStatus(ee.Kind), body)
		return
	}
	if errors.Is(err, store.ErrNotFound) {
		writeError(w, http.StatusNotFound, "not_found", "not found")
		return
	}
	if errors.Is(err, store.ErrConflict) {
		writeError(w, http.StatusConflict, "conflict", "already exists")
		return
	}
	s.log.Error("request failed", "method", r.Method, "path", r.URL.Path, "err", err)
	writeError(w, http.StatusInternalServerError, "internal", "internal server error: "+err.Error())
}

// handler is an authenticated API handler.
type handler func(w http.ResponseWriter, r *http.Request, p *auth.Principal) error

// decodeJSON reads a JSON body into v, refusing unknown fields.
func decodeJSON(r *http.Request, v any) error {
	ct := r.Header.Get("Content-Type")
	if ct != "" && !strings.HasPrefix(ct, "application/json") {
		return badRequest("expected a JSON body (Content-Type: application/json)")
	}
	dec := json.NewDecoder(r.Body)
	dec.DisallowUnknownFields()
	if err := dec.Decode(v); err != nil {
		if errors.Is(err, io.EOF) {
			return badRequest("the request body is empty")
		}
		var mbe *http.MaxBytesError
		if errors.As(err, &mbe) {
			return &httpError{http.StatusRequestEntityTooLarge, "too_large", "the request body is too large"}
		}
		return badRequest("invalid JSON: %v", err)
	}
	return nil
}

// decodeOptional is decodeJSON, but an empty body leaves v alone.
func decodeOptional(r *http.Request, v any) error {
	b, err := io.ReadAll(r.Body)
	if err != nil {
		return err
	}
	if strings.TrimSpace(string(b)) == "" {
		return nil
	}
	dec := json.NewDecoder(strings.NewReader(string(b)))
	dec.DisallowUnknownFields()
	if err := dec.Decode(v); err != nil {
		return badRequest("invalid JSON: %v", err)
	}
	return nil
}

func pathID(r *http.Request, name string) (int64, error) {
	v := r.PathValue(name)
	id, err := strconv.ParseInt(v, 10, 64)
	if err != nil || id <= 0 {
		return 0, badRequest("invalid %s %q", name, v)
	}
	return id, nil
}

func queryBool(r *http.Request, name string) bool {
	switch strings.ToLower(r.URL.Query().Get(name)) {
	case "1", "true", "yes", "on":
		return true
	}
	return false
}

func queryInt(r *http.Request, name string, def int) int {
	if v := r.URL.Query().Get(name); v != "" {
		if n, err := strconv.Atoi(v); err == nil {
			return n
		}
	}
	return def
}

func require(p *auth.Principal, resource string, write bool) error {
	if p.Can(resource, write) {
		return nil
	}
	access := "read"
	if write {
		access = "write"
	}
	return forbidden("permission denied: this needs %s:%s", resource, access)
}

func requireAdmin(p *auth.Principal) error {
	if !p.IsAdmin() {
		return forbidden("this needs an administrator (and not a restricted token)")
	}
	return nil
}

// via names where a request came from, for the history.
func via(r *http.Request, p *auth.Principal) string {
	switch {
	case strings.Contains(r.UserAgent(), "steward-cli"):
		return "cli"
	case p.Method == "session":
		return "web"
	}
	return "api"
}