import { extname, normalize, relative, resolve } from 'pathe'
import { encodePath } from 'ufo'
import { resolveFiles, useNuxt } from '@nuxt/kit'
import { genImport, genDynamicImport, genArrayFromRaw, genSafeVariableName } from 'knitwork'
import escapeRE from 'escape-string-regexp'
import { filename } from 'pathe/utils'
import { hash } from 'ohash'
import type { NuxtPage } from 'nuxt/schema'

import { uniqueBy } from '../core/utils'

enum SegmentParserState {
  initial,
  static,
  dynamic,
  optional,
  catchall,
}

enum SegmentTokenType {
  static,
  dynamic,
  optional,
  catchall,
}

interface SegmentToken {
  type: SegmentTokenType
  value: string
}

export async function resolvePagesRoutes (): Promise<NuxtPage[]> {
  const nuxt = useNuxt()

  const pagesDirs = nuxt.options._layers.map(
    layer => resolve(layer.config.srcDir, layer.config.dir?.pages || 'pages')
  )

  const allRoutes = (await Promise.all(
    pagesDirs.map(async (dir) => {
      const files = await resolveFiles(dir, `**/*{${nuxt.options.extensions.join(',')}}`)
      // Sort to make sure parent are listed first
      files.sort()
      return generateRoutesFromFiles(files, dir)
    })
  )).flat()

  return uniqueBy(allRoutes, 'path')
}

export function generateRoutesFromFiles (files: string[], pagesDir: string): NuxtPage[] {
  const routes: NuxtPage[] = []

  for (const file of files) {
    const segments = relative(pagesDir, file)
      .replace(new RegExp(`${escapeRE(extname(file))}$`), '')
      .split('/')

    const route: NuxtPage = {
      name: '',
      path: '',
      file,
      children: []
    }

    // Array where routes should be added, useful when adding child routes
    let parent = routes

    for (let i = 0; i < segments.length; i++) {
      const segment = segments[i]

      const tokens = parseSegment(segment)
      const segmentName = tokens.map(({ value }) => value).join('')

      // ex: parent/[slug].vue -> parent-slug
      route.name += (route.name && '/') + segmentName

      // ex: parent.vue + parent/child.vue
      const child = parent.find(parentRoute => parentRoute.name === route.name && !parentRoute.path.endsWith('(.*)*'))

      if (child && child.children) {
        parent = child.children
        route.path = ''
      } else if (segmentName === 'index' && !route.path) {
        route.path += '/'
      } else if (segmentName !== 'index') {
        route.path += getRoutePath(tokens)
      }
    }

    parent.push(route)
  }

  return prepareRoutes(routes)
}

function getRoutePath (tokens: SegmentToken[]): string {
  return tokens.reduce((path, token) => {
    return (
      path +
      (token.type === SegmentTokenType.optional
        ? `:${token.value}?`
        : token.type === SegmentTokenType.dynamic
          ? `:${token.value}()`
          : token.type === SegmentTokenType.catchall
            ? `:${token.value}(.*)*`
            : encodePath(token.value))
    )
  }, '/')
}

const PARAM_CHAR_RE = /[\w\d_.]/

function parseSegment (segment: string) {
  let state: SegmentParserState = SegmentParserState.initial
  let i = 0

  let buffer = ''
  const tokens: SegmentToken[] = []

  function consumeBuffer () {
    if (!buffer) {
      return
    }
    if (state === SegmentParserState.initial) {
      throw new Error('wrong state')
    }

    tokens.push({
      type:
        state === SegmentParserState.static
          ? SegmentTokenType.static
          : state === SegmentParserState.dynamic
            ? SegmentTokenType.dynamic
            : state === SegmentParserState.optional
              ? SegmentTokenType.optional
              : SegmentTokenType.catchall,
      value: buffer
    })

    buffer = ''
  }

  while (i < segment.length) {
    const c = segment[i]

    switch (state) {
      case SegmentParserState.initial:
        buffer = ''
        if (c === '[') {
          state = SegmentParserState.dynamic
        } else {
          i--
          state = SegmentParserState.static
        }
        break

      case SegmentParserState.static:
        if (c === '[') {
          consumeBuffer()
          state = SegmentParserState.dynamic
        } else {
          buffer += c
        }
        break

      case SegmentParserState.catchall:
      case SegmentParserState.dynamic:
      case SegmentParserState.optional:
        if (buffer === '...') {
          buffer = ''
          state = SegmentParserState.catchall
        }
        if (c === '[' && state === SegmentParserState.dynamic) {
          state = SegmentParserState.optional
        }
        if (c === ']' && (state !== SegmentParserState.optional || buffer[buffer.length - 1] === ']')) {
          if (!buffer) {
            throw new Error('Empty param')
          } else {
            consumeBuffer()
          }
          state = SegmentParserState.initial
        } else if (PARAM_CHAR_RE.test(c)) {
          buffer += c
        } else {

          // console.debug(`[pages]Ignored character "${c}" while building param "${buffer}" from "segment"`)
        }
        break
    }
    i++
  }

  if (state === SegmentParserState.dynamic) {
    throw new Error(`Unfinished param "${buffer}"`)
  }

  consumeBuffer()

  return tokens
}

function findRouteByName (name: string, routes: NuxtPage[]): NuxtPage | undefined {
  for (const route of routes) {
    if (route.name === name) {
      return route
    }
  }
  return findRouteByName(name, routes)
}

function prepareRoutes (routes: NuxtPage[], parent?: NuxtPage, names = new Set<string>()) {
  for (const route of routes) {
    // Remove -index
    if (route.name) {
      route.name = route.name
        .replace(/\/index$/, '')
        .replace(/\//g, '-')

      if (names.has(route.name)) {
        const existingRoute = findRouteByName(route.name, routes)
        const extra = existingRoute?.name ? `is the same as \`${existingRoute.file}\`` : 'is a duplicate'
        console.warn(`[nuxt] Route name generated for \`${route.file}\` ${extra}. You may wish to set a custom name using \`definePageMeta\` within the page file.`)
      }
    }

    // Remove leading / if children route
    if (parent && route.path.startsWith('/')) {
      route.path = route.path.slice(1)
    }

    if (route.children?.length) {
      route.children = prepareRoutes(route.children, route, names)
    }

    if (route.children?.find(childRoute => childRoute.path === '')) {
      delete route.name
    }

    if (route.name) {
      names.add(route.name)
    }
  }

  return routes
}

export function normalizeRoutes (routes: NuxtPage[], metaImports: Set<string> = new Set()): { imports: Set<string>, routes: string } {
  return {
    imports: metaImports,
    routes: genArrayFromRaw(routes.map((page) => {
      const route = Object.fromEntries(
        Object.entries(page)
          .filter(([key, value]) => key !== 'file' && (Array.isArray(value) ? value.length : value))
          .map(([key, value]) => [key, JSON.stringify(value)])
      ) as Record<Exclude<keyof NuxtPage, 'file'>, string> & { component?: string }

      if (page.children?.length) {
        route.children = normalizeRoutes(page.children, metaImports).routes
      }

      // Without a file, we can't use `definePageMeta` to extract route-level meta from the file
      if (!page.file) {
        for (const key of ['name', 'path', 'meta', 'alias', 'redirect'] as const) {
          if (page[key]) { route[key] = JSON.stringify(page[key]) }
        }
        return route
      }

      const file = normalize(page.file)
      const metaImportName = genSafeVariableName(filename(file) + hash(file)) + 'Meta'
      metaImports.add(genImport(`${file}?macro=true`, [{ name: 'default', as: metaImportName }]))

      let aliasCode = `${metaImportName}?.alias || []`
      const alias = Array.isArray(page.alias) ? page.alias : [page.alias].filter(Boolean)
      if (alias.length) {
        aliasCode = `${JSON.stringify(alias)}.concat(${aliasCode})`
      }

      route.name = `${metaImportName}?.name ?? ${page.name ? JSON.stringify(page.name) : 'undefined'}`
      route.path = `${metaImportName}?.path ?? ${JSON.stringify(page.path)}`
      route.meta = page.meta && Object.values(page.meta).filter(value => value !== undefined).length ? `{...(${metaImportName} || {}), ...${JSON.stringify(page.meta)}}` : `${metaImportName} || {}`
      route.alias = aliasCode
      route.redirect = page.redirect ? JSON.stringify(page.redirect) : `${metaImportName}?.redirect || undefined`
      route.component = genDynamicImport(file, { interopDefault: true })

      return route
    }))
  }
}