package middleware

import (
	"encoding/json"
	"net/http"
	"os"
	"strconv"
	"strings"
	"time"

	"nearle/services"
	"nearle/utils"

	"github.com/gofiber/fiber/v2"
)

// Authorisation for the console.
//
// The `/web` surface has never had any. The console keeps its login record in
// per-tab `sessionStorage` and sends no `Authorization` header, so every
// endpoint under `/v1/web` reads `tenantid` off the query string and believes
// it. Changing one number in a URL reads another merchant's orders, stock,
// staff and takings.
//
// This is the same hole `posauth.go` was written to close on the POS surface,
// and it is closed the same way, in the same order:
//
//  1. the caller holds a token this server signed, and
//  2. the tenant they are naming is the tenant inside that token.
//
// The second is the one that matters. A valid session is not a licence to name
// any tenant — it is a licence to name *your* tenant.
//
// ── Why this could not wait for the assistant ───────────────────────────────
//
// Nearle Buddy answers questions over this same data. Behind REST, reading
// another merchant's books takes knowing the endpoints, knowing the fields and
// iterating. Behind an assistant it is one sentence — "summarise the top ten
// tenants by revenue" — and the model assembles the cross-tenant answer itself,
// accurately and helpfully, because the data was in scope. The permission rules
// the assistant needs have nothing to stand on until this exists.
//
// ── What this does NOT yet do ───────────────────────────────────────────────
//
// It verifies what a request NAMES. It does not yet make handlers derive their
// scope from the session instead of from the wire, and it does not validate
// `partnerid`, `customerid` or `appuserid`, which are the other scoping ids
// some list endpoints accept. Those are the next step, and until they land a
// handler that scopes on one of them is still trusting the caller.

// WebLocalsKey names where the verified claims are parked for handlers.
const WebLocalsKey = "webclaims"

// webAuthRequired reports whether a request without a valid token is refused.
//
// Defaults to OFF, for the same reason POS enforcement does: the console is in
// use by real merchants right now, and its sign-in does not yet hand back a
// token. Switching enforcement on before the console sends one would lock every
// user out of a working product.
//
// So the order is: this middleware ships, sign-in starts issuing tokens, the
// console starts sending them, and `WEB_AUTH_REQUIRED=true` closes the door.
// While it is off a token is still VERIFIED when one is sent, and a request
// carrying a token for the wrong tenant is still refused — the flag only
// decides what happens to a request carrying none.
//
// This is a temporary state and should be short. An unauthenticated `/web`
// surface is the most serious thing in this codebase.
func webAuthRequired() bool {
	return strings.EqualFold(strings.TrimSpace(os.Getenv("WEB_AUTH_REQUIRED")), "true")
}

// publicWebPaths are the endpoints that must work before anybody has a token.
//
// Sign-in, chiefly: guarding the login route with a session token means nobody
// can ever obtain one. Kept as suffixes rather than full paths so the group
// prefix can move without silently locking the door.
var publicWebPaths = []string{
	"/users/applogin",
	"/users/weblogin",
	"/tenant/weblogin",
	// First-password-set runs before a session exists, from a link in the
	// invitation mail.
	"/users/setpassword",
}

func isPublicWebPath(path string) bool {
	lower := strings.ToLower(path)
	for _, suffix := range publicWebPaths {
		if strings.HasSuffix(lower, suffix) {
			return true
		}
	}
	return false
}

// webLocationChecker is the only question this middleware asks of the database:
// does this tenant own this branch? Narrowed to one method so the guard can be
// tested without a database, and so it cannot quietly grow a second dependency.
type webLocationChecker interface {
	LocationAllowed(tenantID, locationID int) (bool, error)
}

// WebAuth verifies the console session and pins the request to its tenant.
func WebAuth(pos services.PosService) fiber.Handler { return webAuthWith(pos) }

func webAuthWith(locations webLocationChecker) fiber.Handler {
	return func(c *fiber.Ctx) error {
		if isPublicWebPath(c.Path()) {
			return c.Next()
		}

		token := webBearerToken(c)

		if token == "" {
			if webAuthRequired() {
				return webUnauthorized(c, "a session token is required; sign in again")
			}
			// A console that predates tokens. Allowed through unpinned, which is
			// exactly the state this middleware exists to end — see
			// webAuthRequired.
			return c.Next()
		}

		claims, err := utils.ParseWebToken(token, time.Now())
		if err != nil {
			// Always refused, flag or no flag. A token that does not verify is a
			// stronger signal than no token at all: nothing sends a broken one by
			// accident.
			return webUnauthorized(c, err.Error())
		}

		// Nearle's own staff work across every tenant and legitimately name any
		// of them. Checked once, here, rather than at each test below, so the
		// exemption is a single visible branch instead of three.
		if !claims.IsPlatformAccount() {
			if requested := requestedTenant(c); requested > 0 && requested != claims.Tenantid {
				return webForbidden(c, "this session cannot reach tenant "+strconv.Itoa(requested))
			}

			// A request can also scope by branch alone, naming no tenant at all,
			// so pinning the tenant is not enough on its own.
			if requested := requestedWebLocation(c); requested > 0 && requested != claims.Locationid {
				allowed, err := locations.LocationAllowed(claims.Tenantid, requested)
				if err != nil {
					return c.Status(http.StatusServiceUnavailable).JSON(fiber.Map{
						"code": http.StatusServiceUnavailable, "status": false,
						"message": "could not verify branch access",
					})
				}
				if !allowed {
					return webForbidden(c, "this session cannot reach branch "+strconv.Itoa(requested))
				}
			}
		}

		c.Locals(WebLocalsKey, claims)
		return c.Next()
	}
}

// webBearerToken reads the session out of the request.
//
// `Authorization: Bearer …` only. The POS reader next door also accepts
// `X-Pos-Token`, because shop routers between a till and this server strip
// Authorization headers on plain HTTP and a terminal that cannot authenticate
// is a shop that cannot trade. The console has no such problem — it is a
// browser on HTTPS — so it gets the one form, and a second accepted header is
// a second thing to get wrong.
func webBearerToken(c *fiber.Ctx) string {
	header := strings.TrimSpace(c.Get("Authorization"))
	if header == "" {
		return ""
	}
	if after, found := strings.CutPrefix(header, "Bearer "); found {
		return strings.TrimSpace(after)
	}
	if !strings.Contains(header, " ") {
		return header
	}
	return ""
}

// requestedTenant reads the tenant a request is naming, from wherever it put it.
//
// Query first, because that is where every `/web` list endpoint carries it, then
// the body, because the writes do not: `createdeliveries`, `publishproduct` and
// the rest post JSON. Checking only the query would leave every call that
// CHANGES another tenant's data unguarded, which is the wrong half to skip.
func requestedTenant(c *fiber.Ctx) int {
	for _, key := range []string{"tenantid", "tenant_id"} {
		if raw := strings.TrimSpace(c.Query(key)); raw != "" {
			if id, err := strconv.Atoi(raw); err == nil && id > 0 {
				return id
			}
		}
	}
	return bodyScopeID(c, "tenantid", "tenant_id")
}

// requestedWebLocation reads the branch a request is naming.
//
// Separate from the POS reader's `requestedLocation` because the two surfaces
// spell it differently: POS routes use `store_id`, the console uses
// `locationid`. Both spellings are read here anyway — a shared endpoint is
// cheaper to allow for than to discover.
func requestedWebLocation(c *fiber.Ctx) int {
	for _, key := range []string{"locationid", "location_id", "store_id"} {
		if raw := strings.TrimSpace(c.Query(key)); raw != "" {
			if id, err := strconv.Atoi(raw); err == nil && id > 0 {
				return id
			}
		}
	}
	return bodyScopeID(c, "locationid", "location_id", "store_id")
}

// bodyScopeID pulls a scoping id out of a JSON request body.
//
// Decoded loosely rather than into a request type, on purpose: this runs before
// the handler and must not refuse anything the handler would have accepted. A
// body that will not parse here is left for the handler to reject with its own
// message, and a request shape that changes later must not silently stop being
// authorised.
//
// `c.Body()` returns buffered bytes, so reading here does not consume the
// stream the handler goes on to parse.
//
// An ARRAY body — `createdeliveries` posts one — is walked too. A batch naming
// another tenant in its elements is precisely the call worth guarding, and a
// probe that only understood objects would wave it through.
func bodyScopeID(c *fiber.Ctx, keys ...string) int {
	body := c.Body()
	if len(body) == 0 || len(body) > 8<<20 {
		return 0
	}

	var raw json.RawMessage = body
	trimmed := strings.TrimLeft(string(body), " \t\r\n")
	if strings.HasPrefix(trimmed, "[") {
		var elements []json.RawMessage
		if err := json.Unmarshal(body, &elements); err != nil {
			return 0
		}
		for _, element := range elements {
			if id := scopeIDFromObject(element, keys); id > 0 {
				return id
			}
		}
		return 0
	}
	return scopeIDFromObject(raw, keys)
}

func scopeIDFromObject(raw json.RawMessage, keys []string) int {
	var fields map[string]json.RawMessage
	if err := json.Unmarshal(raw, &fields); err != nil {
		return 0
	}
	for _, key := range keys {
		if id := asScopeID(fields[key]); id > 0 {
			return id
		}
	}
	return 0
}

// asScopeID reads an id that may have been sent as a number or as a string.
//
// Both spellings are on the wire today — the console sends numbers, some app
// callers send strings — and a probe that understood only one would return 0
// for the other, which reads as "named no tenant" and waves the request past
// the check.
func asScopeID(raw json.RawMessage) int {
	if len(raw) == 0 {
		return 0
	}
	var number int
	if err := json.Unmarshal(raw, &number); err == nil {
		return number
	}
	var text string
	if err := json.Unmarshal(raw, &text); err == nil {
		if id, err := strconv.Atoi(strings.TrimSpace(text)); err == nil {
			return id
		}
	}
	return 0
}

func webUnauthorized(c *fiber.Ctx, message string) error {
	return c.Status(http.StatusUnauthorized).JSON(fiber.Map{
		"code": http.StatusUnauthorized, "status": false, "message": message,
	})
}

func webForbidden(c *fiber.Ctx, message string) error {
	return c.Status(http.StatusForbidden).JSON(fiber.Map{
		"code": http.StatusForbidden, "status": false, "message": message,
	})
}

// WebClaimsFrom returns the verified session on a request, if it carried one.
//
// The second return distinguishes "no token" from "a token claiming tenant 0",
// which is a platform account and a real answer. A handler that treated the two
// alike would give an unauthenticated caller the one session that reads
// everything.
func WebClaimsFrom(c *fiber.Ctx) (utils.WebClaims, bool) {
	claims, ok := c.Locals(WebLocalsKey).(utils.WebClaims)
	return claims, ok
}