package api

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

	"git.golem15.com/golem15/sm-seo-plugin/classes"
	"git.golem15.com/golem15/summercms/modules/cabana"
	"git.golem15.com/golem15/summercms/modules/lagoon"
	"git.golem15.com/golem15/summercms/modules/wire"
	"gorm.io/gorm"
)

// PermissionManage is the one SEO permission every management route
// requires (D-15).
const PermissionManage = "golem15.seo.manage"

// tokenCover is the scope a personal API token must cover.
const tokenCover = "golem15.seo.*"

// maxBody caps a management request body; an import has its own cap.
const maxBody = 1 << 20

// The answers of the management API.
const (
	errAuthenticationRequired = "Authentication required"
	errInsufficientPerms      = "Insufficient permissions"
	errNotFound               = "Not Found"
	errInternal               = "Internal Server Error"
	errInvalidBody            = "The request body is invalid."
)

// apiError is an error a management handler answers with its own status
// and body.
type apiError struct {
	Status int
	Body   any
}

func (e *apiError) Error() string { return http.StatusText(e.Status) }

// Fail answers status with {"error": message}.
func Fail(status int, message string) error {
	return &apiError{Status: status, Body: map[string]any{"error": message}}
}

// handler is a management endpoint: it returns the status and the body to
// answer, or an error the wrapper maps.
type handler func(ctx context.Context, svc *classes.Service, r *http.Request) (int, any, error)

// manage wraps a management endpoint (D-10, D-15, P-24): it resolves the
// backend administrator from a backend JWT, a personal API token or the
// in-process MCP dispatch marker (cabana.ResolveBackend, so an MCP call runs
// as the linked administrator), refuses 401 without one and 403 without
// golem15.seo.manage, and maps the service's typed refusals: a redirect
// loop is 422 {"error":"redirect_loop","path":[...]}, field problems 422
// {"error":"validation_failed","errors":{...}}, a missing row 404. Every
// answer carries X-Robots-Tag: noindex.
func manage(service func() *classes.Service, h handler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("X-Robots-Tag", "noindex")
		svc := service()
		if svc == nil {
			wire.WriteJSON(w, http.StatusServiceUnavailable, map[string]string{"error": "SEO is not available"})
			return
		}
		out, principal, err := cabana.ResolveBackend(svc.App(), r, tokenCover)
		if err != nil || principal == nil {
			if errors.Is(err, cabana.ErrTokenScope) {
				wire.WriteJSON(w, http.StatusForbidden, map[string]string{"error": errInsufficientPerms})
				return
			}
			wire.WriteJSON(w, http.StatusUnauthorized, map[string]string{"error": errAuthenticationRequired})
			return
		}
		if !cabana.Allows(principal, []string{PermissionManage}) {
			wire.WriteJSON(w, http.StatusForbidden, map[string]string{"error": errInsufficientPerms})
			return
		}
		status, body, err := h(out.Context(), svc, out)
		if err != nil {
			writeError(w, out.Context(), svc, err)
			return
		}
		if status == http.StatusNoContent {
			w.WriteHeader(status)
			return
		}
		wire.WriteJSON(w, status, body)
	}
}

// writeError maps a handler error to its answer.
func writeError(w http.ResponseWriter, ctx context.Context, svc *classes.Service, err error) {
	var api *apiError
	var loop *classes.LoopError
	var problems *classes.ProblemsError
	switch {
	case errors.As(err, &api):
		wire.WriteJSON(w, api.Status, api.Body)
	case errors.As(err, &loop):
		wire.WriteJSON(w, http.StatusUnprocessableEntity, LoopBody(ctx, svc, loop))
	case errors.As(err, &problems):
		wire.WriteJSON(w, http.StatusUnprocessableEntity, map[string]any{
			"error":  "validation_failed",
			"errors": ProblemMessages(ctx, svc, problems),
		})
	case errors.Is(err, classes.ErrBadURL):
		wire.WriteJSON(w, http.StatusUnprocessableEntity, map[string]any{"error": err.Error()})
	case errors.Is(err, classes.ErrNoRecord), errors.Is(err, gorm.ErrRecordNotFound):
		wire.WriteJSON(w, http.StatusNotFound, map[string]any{"error": errNotFound})
	default:
		log.Error("golem15.seo: management API", "error", err)
		wire.WriteJSON(w, http.StatusInternalServerError, map[string]any{"error": errInternal})
	}
}

// LoopBody is the answer of a refused redirect loop (D-19): the error
// code, the loop's path and the message in the request locale.
func LoopBody(ctx context.Context, svc *classes.Service, loop *classes.LoopError) map[string]any {
	return map[string]any{
		"error":   "redirect_loop",
		"path":    loop.Check.Path,
		"message": svc.LoopMessage(ctx, loop.Check),
	}
}

// ProblemMessages translates field problems in the request locale.
func ProblemMessages(ctx context.Context, svc *classes.Service, problems *classes.ProblemsError) map[string][]string {
	out := map[string][]string{}
	for field, list := range problems.Problems {
		for _, p := range list {
			out[field] = append(out[field], svc.PhraseCtx(ctx, p.Key, p.Params))
		}
	}
	return out
}

// decode reads a JSON body of at most limit bytes into v; an empty body
// leaves v as it is.
func decode(r *http.Request, limit int64, v any) error {
	if r.Body == nil {
		return nil
	}
	dec := json.NewDecoder(io.LimitReader(r.Body, limit+1))
	if err := dec.Decode(v); err != nil {
		if errors.Is(err, io.EOF) {
			return nil
		}
		return Fail(http.StatusUnprocessableEntity, errInvalidBody)
	}
	return nil
}

// pathID reads the {name} segment as a positive id.
func pathID(r *http.Request, name string) (uint, error) {
	n, err := strconv.ParseUint(strings.TrimSpace(r.PathValue(name)), 10, 64)
	if err != nil || n == 0 {
		return 0, Fail(http.StatusNotFound, errNotFound)
	}
	return uint(n), nil
}

// write runs fn in one transaction on the application's database, with
// the transaction on ctx (classes.WithTx) so every read of the service
// sees the write.
func write(ctx context.Context, svc *classes.Service, fn func(ctx context.Context, tx *gorm.DB) error) error {
	gdb, err := svc.GormDB()
	if err != nil {
		return err
	}
	return lagoon.Transaction(ctx, gdb, func(ctx context.Context, tx *gorm.DB) error {
		return fn(classes.WithTx(ctx, tx), tx)
	})
}

// read returns the database for a read handler.
func read(ctx context.Context, svc *classes.Service) (*gorm.DB, error) {
	return svc.DB(ctx)
}

// The page sizes of the list endpoints.
const (
	defaultPerPage = 50
	maxPerPage     = 200
)

// ListInput is the paging and search query every list tool shares.
type ListInput struct {
	Page    int    `json:"page,omitempty" query:"page" jsonschema:"the page number, from 1"`
	PerPage int    `json:"per_page,omitempty" query:"per_page" jsonschema:"rows per page, at most 200 (50 by default)"`
	Search  string `json:"search,omitempty" query:"search" jsonschema:"text the address or value contains"`
}

// listParams reads page, per_page and search.
func listParams(r *http.Request) ListInput {
	q := r.URL.Query()
	in := ListInput{Search: strings.TrimSpace(q.Get("search"))}
	in.Page, _ = strconv.Atoi(q.Get("page"))
	in.PerPage, _ = strconv.Atoi(q.Get("per_page"))
	if in.Page < 1 {
		in.Page = 1
	}
	if in.PerPage < 1 {
		in.PerPage = defaultPerPage
	}
	if in.PerPage > maxPerPage {
		in.PerPage = maxPerPage
	}
	return in
}

// paginate counts q and loads one page of it into dest.
func paginate(q *gorm.DB, in ListInput, dest any) (int64, error) {
	var total int64
	if err := q.Session(&gorm.Session{}).Count(&total).Error; err != nil {
		return 0, err
	}
	if err := q.Offset((in.Page - 1) * in.PerPage).Limit(in.PerPage).Find(dest).Error; err != nil {
		return 0, err
	}
	return total, nil
}

// listBody is a list answer: the rows and the paging.
func listBody(rows any, in ListInput, total int64) map[string]any {
	return map[string]any{"data": rows, "page": in.Page, "per_page": in.PerPage, "total": total}
}

// like is a case-insensitive LIKE pattern of text.
func like(text string) string {
	r := strings.NewReplacer(`\`, `\\`, `%`, `\%`, `_`, `\_`)
	return "%" + strings.ToLower(r.Replace(text)) + "%"
}