/**
 * Einheitlicher Rücksprung-Kontext für PWA-Navigation (siehe NAV_RETURN_CONTEXT_SPEC.md).
 */
import {
  buildPlanningHubReturnState,
  PLANNING_HUB_PATH,
  planningHubPathFromReturnState,
} from './planningUnitRoutes'

export { PLANNING_HUB_PATH }

export const NAV_RETURN_STATE_KEY = 'appReturn'
export const EXERCISES_LIST_PATH = '/exercises'
export const TRAINING_MODULES_LIST_PATH = '/planning/training-modules'
export const PLAN_TEMPLATES_LIST_PATH = '/planning/plan-templates'
export const FRAMEWORK_PROGRAMS_LIST_PATH = '/planning/framework-programs'
export const SETTINGS_PATH = '/settings'
export const DASHBOARD_PATH = '/'

export function buildNavReturnContext(opts) {
  const path = String(opts?.path || '').trim()
  const label = String(opts?.label || '').trim()
  if (!path || !label) return null
  const ctx = { v: 1, path, label }
  if (opts?.kind) ctx.kind = opts.kind
  if (opts?.payload && typeof opts.payload === 'object') {
    ctx.payload = opts.payload
  }
  return ctx
}

export function buildExercisesListReturnContext() {
  return buildNavReturnContext({
    path: EXERCISES_LIST_PATH,
    label: 'Zurück zur Übungsliste',
    kind: 'exerciseList',
  })
}

export function buildTrainingModulesListReturnContext() {
  return buildNavReturnContext({
    path: TRAINING_MODULES_LIST_PATH,
    label: 'Zurück zur Modul-Bibliothek',
    kind: 'trainingModulesList',
  })
}

export function buildPlanTemplatesListReturnContext() {
  return buildNavReturnContext({
    path: PLAN_TEMPLATES_LIST_PATH,
    label: 'Zurück zu Vorlagen',
    kind: 'planTemplatesList',
  })
}

export function buildFrameworkProgramsListReturnContext() {
  return buildNavReturnContext({
    path: FRAMEWORK_PROGRAMS_LIST_PATH,
    label: 'Zurück zu Rahmenprogrammen',
    kind: 'frameworkProgramsList',
  })
}

export function buildSettingsReturnContext() {
  return buildNavReturnContext({
    path: SETTINGS_PATH,
    label: 'Zurück zu Einstellungen',
    kind: 'settings',
  })
}

export function buildDashboardReturnContext() {
  return buildNavReturnContext({
    path: DASHBOARD_PATH,
    label: 'Zurück zur Übersicht',
    kind: 'dashboard',
  })
}

export const MEDIA_LIBRARY_PATH = '/media'

export function buildMediaLibraryReturnContext() {
  return buildNavReturnContext({
    path: MEDIA_LIBRARY_PATH,
    label: 'Zurück zur Medienbibliothek',
    kind: 'mediaLibrary',
  })
}

export function buildTrainingRunReturnContext(unitId) {
  const id = String(unitId || '').trim()
  if (!id) return null
  return buildNavReturnContext({
    path: `/planning/run/${id}`,
    label: 'Zurück zum Trainingsablauf',
    kind: 'trainingRun',
    payload: { unitId: id },
  })
}

export function buildPlanningHubFallbackReturnContext() {
  return buildNavReturnContext({
    path: PLANNING_HUB_PATH,
    label: 'Zurück zur Planung',
    kind: 'planningHub',
  })
}

/** Router-Link state mit appReturn (optional zusätzlicher State). */
export function linkStateWithAppReturn(returnContext, extraState) {
  const state = { ...(extraState || {}) }
  if (returnContext) state[NAV_RETURN_STATE_KEY] = returnContext
  return Object.keys(state).length > 0 ? state : undefined
}

/**
 * Rücksprung zur aktuellen Route (z. B. Einheiten-Editor).
 */
export function buildCurrentLocationReturnContext(location, label) {
  const path = `${location?.pathname || ''}${location?.search || ''}`.trim()
  if (!path) return null
  return buildNavReturnContext({
    path,
    label: String(label || 'Zurück').trim(),
    kind: 'currentLocation',
  })
}

/** @param {ReturnType<typeof buildPlanningHubReturnState>|object} hubState */
export function buildPlanningHubReturnContext(hubState = {}) {
  const payload = buildPlanningHubReturnState(hubState)
  return buildNavReturnContext({
    path: planningHubPathFromReturnState(payload),
    label: 'Zurück zur Planung',
    kind: 'planningHub',
    payload,
  })
}

/** Legacy planningReturn → appReturn */
export function appReturnFromPlanningReturn(planningReturn) {
  if (!planningReturn || planningReturn.v !== 1) return null
  return buildPlanningHubReturnContext(planningReturn)
}

/**
 * @param {import('react-router-dom').Location|{ state?: object }|null|undefined} location
 */
export function readNavReturnFromLocation(location) {
  const state = location?.state
  if (!state || typeof state !== 'object') return null
  const raw = state[NAV_RETURN_STATE_KEY]
  if (raw?.v === 1 && raw.path && raw.label) return raw
  if (state.planningReturn) return appReturnFromPlanningReturn(state.planningReturn)
  return null
}

/**
 * @param {import('react-router-dom').Location|{ state?: object }|null|undefined} location
 * @param {{ path: string, label: string }|null|undefined} fallback
 */
export function resolveNavReturnTarget(location, fallback) {
  const ctx = readNavReturnFromLocation(location)
  if (ctx?.path && ctx?.label) {
    return { path: ctx.path, label: ctx.label, fromContext: true }
  }
  if (fallback?.path && fallback?.label) {
    return { path: fallback.path, label: fallback.label, fromContext: false }
  }
  return null
}

/**
 * @param {import('react-router-dom').NavigateFunction} navigate
 * @param {import('react-router-dom').Location|{ state?: object }|null|undefined} location
 * @param {{ path?: string, label?: string }|null|undefined} fallback
 */
export function goNavReturn(navigate, location, fallback) {
  const target = resolveNavReturnTarget(location, fallback)
  if (target?.fromContext && target.path) {
    navigate(target.path)
    return
  }
  if (typeof window !== 'undefined' && window.history.length > 1) {
    navigate(-1)
    return
  }
  if (fallback?.path) {
    navigate(fallback.path)
    return
  }
  navigate('/')
}

/**
 * @param {import('react-router-dom').NavigateFunction} navigate
 * @param {string} to
 * @param {ReturnType<typeof buildNavReturnContext>|null|undefined} returnContext
 * @param {object} [options]
 */
export function navigateWithAppReturn(navigate, to, returnContext, options = {}) {
  const state = { ...(options.state || {}) }
  if (returnContext) state[NAV_RETURN_STATE_KEY] = returnContext
  navigate(to, { ...options, state })
}

/**
 * Bestehenden appReturn (oder Legacy planningReturn) beim Weiterleiten erhalten.
 */
export function preserveAppReturnOnNavigate(navigate, location, to, options = {}) {
  const existing = readNavReturnFromLocation(location)
  const state = { ...(options.state || {}) }
  if (existing) state[NAV_RETURN_STATE_KEY] = existing
  navigate(to, { ...options, state })
}