package handlers

import (
	"context"
	"errors"
	"fmt"
	"net/http"
	"strings"

	"github.com/go-chi/chi"
	"sneak.berlin/go/webhooker/internal/archive"
	"sneak.berlin/go/webhooker/internal/database"
	"sneak.berlin/go/webhooker/internal/delivery"
)

// HandleTargetCreate handles adding a new target to a webhook.
func (h *Handlers) HandleTargetCreate() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		userID, ok := h.getUserID(r)
		if !ok {
			http.Redirect(
				w, r, "/pages/login", http.StatusSeeOther,
			)

			return
		}

		sourceID := chi.URLParam(r, "sourceID")

		h.archives.RenameLock().Lock()
		defer h.archives.RenameLock().Unlock()

		var webhook database.Webhook

		err := h.db.DB().Where(
			"id = ? AND user_id = ?", sourceID, userID,
		).First(&webhook).Error
		if err != nil {
			h.renderError(w, r, http.StatusNotFound)

			return
		}

		// The body size cap is enforced by the MaxBodySize
		// middleware, which runs before CSRF parses the form.
		err = r.ParseForm()
		if err != nil {
			h.renderError(w, r, http.StatusBadRequest)

			return
		}

		h.processTargetCreate(w, r, webhook)
	}
}

// processTargetCreate validates and creates a new target. A refused
// submission shows the webhook page again, with the add target form
// open on the chosen type, the values entered, and the reason.
func (h *Handlers) processTargetCreate(
	w http.ResponseWriter,
	r *http.Request,
	webhook database.Webhook,
) {
	in := targetFormInputFrom(r)

	target, errMsg := h.newTarget(r.Context(), webhook.ID, in)
	if errMsg != "" {
		h.renderSourceDetail(w, r, webhook, in, errMsg)

		return
	}

	err := h.db.DB().Create(target).Error
	if err != nil {
		h.serverError(w, r, "failed to create target", err)

		return
	}

	http.Redirect(
		w, r, withNotice("/hook/"+webhook.ID, targetAdded),
		http.StatusSeeOther,
	)
}

// newTarget validates a new target for a webhook and returns the row
// to create, or, when it refuses the target, the message the form
// shows. Every form that creates a target goes through here, so they
// all accept and refuse the same things.
func (h *Handlers) newTarget(
	ctx context.Context,
	webhookID string,
	in targetFormInput,
) (*database.Target, string) {
	target := &database.Target{
		WebhookID:   webhookID,
		Type:        in.Type,
		Active:      true,
		MaxAttempts: 1,
	}

	errMsg := h.setTargetFromForm(ctx, target, in)
	if errMsg != "" {
		return nil, errMsg
	}

	return target, ""
}

// setTargetFromForm validates a target form against the target's type
// and sets the target's name, settings and number of delivery attempts
// from it. It returns the message the form shows for anything it
// refuses, an unknown type among them; the caller then discards the
// target, which may be partly set.
// The add target form and the target edit form both go through here,
// so the two cannot come to disagree about what a target may be.
func (h *Handlers) setTargetFromForm(
	ctx context.Context,
	target *database.Target,
	in targetFormInput,
) string {
	if in.Name == "" {
		return "Name is required"
	}

	errMsg := h.setTargetSettings(ctx, target, in)
	if errMsg != "" {
		return errMsg
	}

	// An empty max_attempts keeps the target's count: the default of
	// 1 for a new target, and the stored count for an edited one,
	// since the forms for target types that do not retry have no such
	// field. A value that is filled in but invalid is refused rather
	// than becoming that count, so a typo cannot destroy the count a
	// target is delivering with.
	maxAttempts, err := parseMaxAttempts(in.MaxAttempts, target.MaxAttempts)
	if err != nil {
		return "Invalid delivery attempts: " + attemptsErrorMessage(err)
	}

	target.Name = in.Name
	target.MaxAttempts = maxAttempts

	return ""
}

// targetFormInput carries the raw values of a target form. Both the
// create and the edit path fill one and hand it to setTargetFromForm,
// so neither can come to validate a target differently from the
// other. Both forms are filled from one: the edit form with the
// stored values, and a refused form with the values submitted.
type targetFormInput struct {
	// Name is the target's name.
	Name string
	// Type is the type chosen on the add target form. The edit form
	// has none: a target's stored type decides.
	Type database.TargetType
	// URL is the destination for an HTTP target and the webhook URL
	// for a Slack target.
	URL string
	// Headers is an HTTP target's headers, one "Name: value" per
	// line.
	Headers string
	// Timeout is an HTTP target's per-request timeout in seconds.
	Timeout string
	// ForwardQuery is an HTTP target's checkbox that passes each
	// event's query string on to it.
	ForwardQuery bool
	// MaxAttempts is an HTTP or Slack target's max_attempts.
	MaxAttempts string
	// Expiry is a database (archive) target's row expiry.
	Expiry string
	// Rotation is a database (archive) target's rotation.
	Rotation string
}

// targetFormInputFrom reads a target form from a request body. The
// body size cap is enforced by the MaxBodySize middleware, which runs
// before CSRF parses the form.
//
// Every field is read with PostFormValue, not FormValue. FormValue
// falls back to the query string, which would let
// `POST /hook/{id}/targets?url=https://hooks.slack.com/...`
// configure a target from a value the request line carries — and the
// request line, unlike the body, is what logs, proxies, Referer
// headers and error trackers record. The headers field is under the
// same rule and for the same reason: its values are authorization
// tokens.
func targetFormInputFrom(r *http.Request) targetFormInput {
	return targetFormInput{
		Name:         r.PostFormValue("name"),
		Type:         database.TargetType(r.PostFormValue("type")),
		URL:          r.PostFormValue("url"),
		Headers:      r.PostFormValue("headers"),
		Timeout:      r.PostFormValue("timeout"),
		ForwardQuery: r.PostFormValue("forward_query") != "",
		MaxAttempts:  r.PostFormValue("max_attempts"),
		Expiry:       r.PostFormValue("expiry"),
		Rotation:     r.PostFormValue("rotation"),
	}
}

// setTargetSettings sets a target's settings from the submitted form
// values, or returns the message the form shows for a value it
// refuses. Which fields of in apply depends on the target type; a
// type without a URL ignores any URL submitted, and the settings a
// type does not use are left empty.
func (h *Handlers) setTargetSettings(
	ctx context.Context,
	target *database.Target,
	in targetFormInput,
) string {
	switch target.Type {
	case database.TargetTypeHTTP:
		return h.setHTTPTargetSettings(ctx, target, in)
	case database.TargetTypeSlack:
		return h.setSlackTargetSettings(ctx, target, in.URL)
	case database.TargetTypeDatabase:
		return setDatabaseTargetSettings(target, in.Expiry, in.Rotation)
	case database.TargetTypeLog:
		return ""
	default:
		return "Invalid target type"
	}
}

// setHTTPTargetSettings sets an HTTP target's SSRF-validated
// destination plus the optional headers, timeout and query string
// setting the delivery path honours.
func (h *Handlers) setHTTPTargetSettings(
	ctx context.Context,
	target *database.Target,
	in targetFormInput,
) string {
	errMsg := h.validateTargetURL(
		ctx, in.URL, "URL is required for HTTP targets",
	)
	if errMsg != "" {
		return errMsg
	}

	headers, err := delivery.ParseTargetHeaders(in.Headers)
	if err != nil {
		return fmt.Sprintf("Invalid headers: %v", err)
	}

	timeout, err := delivery.ParseTargetTimeout(in.Timeout)
	if err != nil {
		return fmt.Sprintf("Invalid timeout: %v", err)
	}

	target.URL = in.URL
	target.Headers = headers
	target.TimeoutSeconds = timeout
	target.ForwardQuery = in.ForwardQuery

	return ""
}

// setSlackTargetSettings sets a Slack target's one setting, its
// SSRF-validated webhook URL.
func (h *Handlers) setSlackTargetSettings(
	ctx context.Context,
	target *database.Target,
	targetURL string,
) string {
	errMsg := h.validateTargetURL(
		ctx, targetURL,
		"Webhook URL is required for Slack targets",
	)
	if errMsg != "" {
		return errMsg
	}

	target.URL = targetURL

	return ""
}

// validateTargetURL refuses an empty or SSRF-blocked destination,
// returning the message the form shows, or "" when the destination
// is accepted. missingMsg is the message for no URL at all.
//
// It is the single point at which a user-supplied destination enters
// the SSRF guard, on create and on edit alike. An edit path that
// reached storage without passing through here would reopen the hole
// the guard closes.
func (h *Handlers) validateTargetURL(
	ctx context.Context,
	targetURL, missingMsg string,
) string {
	if targetURL == "" {
		return missingMsg
	}

	err := h.ssrf.ValidateTargetURL(ctx, targetURL)
	if err != nil {
		// The submitted URL can be a credential (a Slack
		// incoming webhook URL is a bearer token), so the log
		// records only its scheme and host.
		h.log.Warn(
			"target URL blocked by SSRF protection",
			"url", delivery.MaskURL(targetURL),
			"error", err,
		)

		msg := "Invalid target URL: " + err.Error()

		// Only a private or reserved address's refusal says how
		// to allow it. Other refusals never do: link-local, the
		// unspecified addresses and the unconditional metadata
		// addresses cannot be opened, and the default
		// blocklist's public addresses, which listing does open,
		// hand out credentials.
		if errors.Is(err, delivery.ErrBlockedPrivateOrReservedIP) {
			msg += ". Private and reserved addresses are refused " +
				"by default; the server's ALLOWED_EGRESS_CIDRS " +
				"setting allows named networks (see \"Allowing " +
				"egress to your own network\" in the README)."
		}

		return msg
	}

	return ""
}

// setDatabaseTargetSettings sets a database (archive) target's
// expiry and rotation. Both are optional: an empty or never expiry
// keeps the archive forever, and an empty rotation is stored as none,
// one file. A bad value is refused here, at the form, instead of
// being stored.
func setDatabaseTargetSettings(
	target *database.Target,
	expiry, rotation string,
) string {
	archiveExpiry, err := archive.ParseExpiry(strings.TrimSpace(expiry))
	if err != nil {
		return fmt.Sprintf("Invalid archive expiry: %v", err)
	}

	err = archive.ValidateRotation(rotation)
	if err != nil {
		return fmt.Sprintf("Invalid archive rotation: %v", err)
	}

	if rotation == "" {
		rotation = archiveRotationNone
	}

	target.ArchiveExpiry = archiveExpiry
	target.ArchiveRotation = rotation

	return ""
}