// Change history and undo (#49): zod-validated shapes for /gardens/:id/history
// and /change-sets/:id/revert, plus the hooks the editor's History tab uses.
//
// A revert is a real write that can partly succeed, so its mutation is unusual:
// a 409 is not a plain failure. It carries the change set that DID apply
// alongside the entities it deliberately left alone, and the caller is expected
// to report both.

import { useState } from 'react'
import { useInfiniteQuery, useMutation, useQueryClient } from '@tanstack/react-query'
import { z } from 'zod'
import { ApiError, api, errorMessage } from './api'
import { gardenFullKey } from './objects'

export const changeSourceSchema = z.enum(['ui', 'agent', 'api'])
export type ChangeSource = z.infer<typeof changeSourceSchema>

export const changeCountSchema = z.object({
  entityType: z.enum(['garden', 'object', 'planting']),
  op: z.enum(['create', 'update', 'delete']),
  // COUNT(*) can only ever be a non-negative integer; constraining it means bad
  // data fails loudly rather than quietly hiding an Undo button (totalChanges
  // gates it) or rendering "1.5 beds changed".
  n: z.number().int().nonnegative(),
})
export type ChangeCount = z.infer<typeof changeCountSchema>

export const changeSetSchema = z.object({
  id: z.number(),
  gardenId: z.number(),
  actorId: z.number(),
  actorName: z.string().default(''),
  source: changeSourceSchema,
  summary: z.string(),
  agentRunId: z.string().optional(),
  // Set when this change set reverts another.
  revertsId: z.number().optional(),
  // Set when another change set reverted this one.
  revertedById: z.number().optional(),
  counts: z.array(changeCountSchema).default([]),
  createdAt: z.string(),
})
export type ChangeSet = z.infer<typeof changeSetSchema>

export const revertConflictSchema = z.object({
  entityType: z.enum(['garden', 'object', 'planting']),
  entityId: z.number(),
  reason: z.enum(['changed', 'missing', 'exists', 'unsupported']),
  name: z.string().optional(),
})
export type RevertConflict = z.infer<typeof revertConflictSchema>

const historyPageSchema = z.object({
  changeSets: z.array(changeSetSchema),
  hasMore: z.boolean(),
})

const revertResultSchema = z.object({
  changeSet: changeSetSchema.nullable(),
  conflicts: z.array(revertConflictSchema).default([]),
})
export type RevertResult = z.infer<typeof revertResultSchema>

const PAGE_SIZE = 30

export function historyKey(gardenId: number) {
  return ['gardens', gardenId, 'history'] as const
}

/** A garden's change sets, newest first, paged on demand. */
export function useGardenHistory(gardenId: number, enabled = true) {
  return useInfiniteQuery({
    queryKey: historyKey(gardenId),
    enabled,
    initialPageParam: 0,
    queryFn: async ({ pageParam }) =>
      historyPageSchema.parse(
        await api.get(`/gardens/${gardenId}/history`, { params: { limit: PAGE_SIZE, offset: pageParam } }),
      ),
    // Offset paging, not cursor: history is append-only at the FRONT, so a new
    // entry arriving mid-scroll shifts the window by one. That's a duplicate row
    // at worst, and the alternative (a cursor on created_at) buys little for a
    // list you scroll a page or two of.
    getNextPageParam: (last, pages) => (last.hasMore ? pages.length * PAGE_SIZE : undefined),
  })
}

/** The conflicts carried by a 409 from a revert, or null if this isn't one. */
export function revertConflicts(err: unknown): RevertResult | null {
  if (!(err instanceof ApiError) || err.status !== 409) return null
  const parsed = revertResultSchema.safeParse(err.body)
  return parsed.success ? parsed.data : null
}

/**
 * Undo a change set. Invalidates the editor payload so the canvas redraws, and
 * the history list so the new entry (and the "reverted" mark on its target)
 * appear — on failure too, because a 409 means part of it applied.
 */
export function useRevertChangeSet(gardenId: number) {
  const qc = useQueryClient()
  const refresh = () => {
    void qc.invalidateQueries({ queryKey: gardenFullKey(gardenId) })
    void qc.invalidateQueries({ queryKey: historyKey(gardenId) })
  }
  return useMutation({
    mutationFn: async (changeSetId: number): Promise<RevertResult> =>
      revertResultSchema.parse(await api.post(`/change-sets/${changeSetId}/revert`, undefined)),
    onSuccess: refresh,
    onError: (err) => {
      if (revertConflicts(err)) refresh() // a partial revert still changed things
    },
  })
}

/** How many rows a change set touched, for "3 changes" in the list. Undefined
 *  counts total zero, which callers read as "no denominator to quote". */
export function totalChanges(cs: { counts?: ChangeCount[] }): number {
  return (cs.counts ?? []).reduce((sum, c) => sum + c.n, 0)
}

const ENTITY_NOUNS: Record<ChangeCount['entityType'], [string, string]> = {
  garden: ['garden setting', 'garden settings'],
  object: ['bed', 'beds'],
  planting: ['planting', 'plantings'],
}

const OP_VERBS: Record<ChangeCount['op'], string> = {
  create: 'added',
  update: 'changed',
  delete: 'removed',
}

/**
 * The change set's counts as a human phrase: "3 plantings added, 1 bed changed".
 * Returns '' when there's nothing to say, so callers can skip the line entirely
 * rather than render "0 changes".
 */
export function describeCounts(cs: ChangeSet): string {
  return cs.counts
    .filter((c) => c.n > 0)
    .map((c) => {
      const [one, many] = ENTITY_NOUNS[c.entityType]
      return `${c.n} ${c.n === 1 ? one : many} ${OP_VERBS[c.op]}`
    })
    .join(', ')
}

/** What a revert left alone, phrased for the person who asked for the undo. */
export function describeConflict(c: RevertConflict): string {
  const noun = c.name ? `“${c.name}”` : `that ${ENTITY_NOUNS[c.entityType][0]}`
  switch (c.reason) {
    case 'changed':
      return `${noun} was edited since, so it was left alone`
    case 'missing':
      return `${noun} no longer exists`
    case 'exists':
      return `${noun} exists again, so it wasn't restored over the top`
    case 'unsupported':
      return `${noun} can't be undone automatically`
  }
}

/**
 * The one undo implementation, shared by the history list and (per #49) the
 * agent turn's inline Undo in #57 — so an undo behaves identically wherever it
 * is offered, including how it explains a partial result.
 *
 * Outcomes are keyed by change set id, so a single instance serves a whole list.
 */
export function useUndo(gardenId: number) {
  const revert = useRevertChangeSet(gardenId)
  const [outcomes, setOutcomes] = useState<Record<number, UndoOutcome>>({})

  const undo = (cs: UndoTarget) => {
    setOutcomes((prev) => ({ ...prev, [cs.id]: { tone: 'pending', message: 'Undoing…' } }))
    revert.mutate(cs.id, {
      onSuccess: (result) => {
        setOutcomes((prev) => ({ ...prev, [cs.id]: describeUndo(cs, result) }))
      },
      onError: (err) => {
        const result = revertConflicts(err)
        setOutcomes((prev) => ({
          ...prev,
          [cs.id]: result
            ? describeUndo(cs, result)
            : { tone: 'error', message: errorMessage(err, "That couldn't be undone.") },
        }))
      },
    })
  }

  return {
    undo,
    // Per change set rather than a single global flag, so one row's pending
    // state can't disable the others.
    outcomeFor: (id: number): UndoOutcome | undefined => outcomes[id],
  }
}

/**
 * What undo needs to know about a change set.
 *
 * `counts` is optional because the chat panel offers Undo on a turn knowing only
 * its change set id — the agent's reply carries the id, not the tally. Fabricating
 * counts to satisfy a type would produce a confidently wrong "1 of 1 changes
 * undone"; leaving them out lets describeUndo say what it actually knows.
 */
export interface UndoTarget {
  id: number
  counts?: ChangeCount[]
}

export interface UndoOutcome {
  tone: 'pending' | 'ok' | 'partial' | 'error'
  message: string
}

/**
 * What actually happened, said in full. A revert can partly succeed, and "2 of 3
 * changes undone — “north bed” was edited since and was left alone" is the only
 * useful thing to report: a bare failure would be a lie about the two that did
 * apply, and a bare success would hide the one that didn't.
 */
export function describeUndo(target: UndoTarget, result: RevertResult): UndoOutcome {
  const skipped = result.conflicts.map(describeConflict).join('; ')
  // A NULL change set is the server's signal that nothing needed doing. An empty
  // `counts` is not the same thing and must not be read as one — that conflation
  // made a successful undo report "nothing left to undo", which is the worst
  // possible thing to tell someone about an action that just worked.
  const didSomething = result.changeSet != null
  const applied = result.changeSet ? totalChanges(result.changeSet) : 0
  if (result.conflicts.length === 0) {
    // Reachable by undoing a creation whose object is already gone.
    if (!didSomething) return { tone: 'ok', message: 'Nothing left to undo — this was already reversed.' }
    return { tone: 'ok', message: 'Undone.' }
  }
  if (!didSomething) {
    return { tone: 'error', message: `Nothing was undone — ${skipped}.` }
  }
  // Only claim a denominator when we have one. "2 of 3" from a caller that
  // never knew the total would be a number invented to fill a sentence.
  const total = totalChanges(target)
  const scale = total > 0 && applied > 0 ? `${applied} of ${total} changes undone` : 'Partly undone'
  return { tone: 'partial', message: `${scale} — ${skipped}.` }
}