import {
  copyFileSync,
  existsSync,
  mkdirSync,
  readFileSync,
  readdirSync,
  statSync,
  writeFileSync,
} from "node:fs"
import { dirname, isAbsolute, relative, resolve as resolvePath } from "node:path"
import { TextDecoder } from "node:util"
import type { ReverseMapFile, ReverseMapManifest, ReverseMapStoredTemplate, ReverseMapToken } from "./render"

export type ReverseOptions = {
  mapPath?: string
  include?: string | string[]
}

export type ReverseWarning = {
  outputPath: string
  token: string
  result: string
  message: string
}

export type ReverseResult = {
  filesWritten: number
  warnings: ReverseWarning[]
}

function isInsidePath(parent: string, child: string): boolean {
  const rel = relative(parent, child)
  return rel === "" || (!rel.startsWith("..") && !isAbsolute(rel))
}

function resolveInside(root: string, path: string): string {
  const resolved = resolvePath(root, path)
  if (!isInsidePath(root, resolved)) {
    throw new Error(`Refusing to write outside target directory: ${path}`)
  }
  return resolved
}

function isUtf8Text(buffer: Buffer): boolean {
  if (buffer.indexOf(0) !== -1) return false
  try {
    new TextDecoder("utf-8", { fatal: true }).decode(buffer)
    return true
  } catch {
    return false
  }
}

function readManifest(mapPath: string): ReverseMapManifest {
  const manifest = JSON.parse(readFileSync(mapPath, "utf-8")) as ReverseMapManifest
  if (manifest.version !== 1 || !Array.isArray(manifest.files)) {
    throw new Error(`Unsupported reverse map: ${mapPath}`)
  }
  return manifest
}

function normalizePath(path: string): string {
  return path.split("\\").join("/")
}

function escapeRegExp(text: string): string {
  return text.replace(/[|\\{}()[\]^$+?.]/g, "\\$&")
}

function globToRegExp(glob: string): RegExp {
  let source = "^"
  const pattern = normalizePath(glob)

  for (let i = 0; i < pattern.length; i++) {
    const char = pattern[i]!
    const next = pattern[i + 1]
    if (char === "*" && next === "*") {
      if (pattern[i + 2] === "/") {
        source += "(?:.*/)?"
        i += 2
      } else {
        source += ".*"
        i += 1
      }
    } else if (char === "*") {
      source += "[^/]*"
    } else if (char === "?") {
      source += "[^/]"
    } else {
      source += escapeRegExp(char)
    }
  }

  return new RegExp(`${source}$`)
}

function getIncludeMatchers(include: ReverseOptions["include"]): RegExp[] {
  if (!include) return []
  return (Array.isArray(include) ? include : [include]).map(globToRegExp)
}

function matchesAny(path: string, matchers: RegExp[]): boolean {
  const normalized = normalizePath(path)
  return matchers.some(matcher => matcher.test(normalized))
}

function replaceAtRange(content: string, token: ReverseMapToken): string | null {
  if (!token.range) return null
  const { start, end } = token.range
  if (start < 0 || end < start || end > content.length) return null
  if (content.slice(start, end) !== token.result) return null
  return `${content.slice(0, start)}${token.token}${content.slice(end)}`
}

function replaceFirst(content: string, token: ReverseMapToken): string | null {
  const index = content.indexOf(token.result)
  if (index === -1) return null
  return `${content.slice(0, index)}${token.token}${content.slice(index + token.result.length)}`
}

function applyActiveBranch(token: ReverseMapToken, branchContent: string): string {
  if (!token.activeRange) return token.token
  return [
    token.token.slice(0, token.activeRange.start),
    branchContent,
    token.token.slice(token.activeRange.end),
  ].join("")
}

function findPrefixEnd(content: string, before: string): number {
  if (before === "") return 0
  let candidate = before
  while (candidate.length >= 8) {
    const index = content.indexOf(candidate)
    if (index !== -1) return index + candidate.length
    candidate = candidate.slice(-Math.max(1, Math.floor(candidate.length / 2)))
  }
  return -1
}

function findSuffixStart(content: string, after: string, from: number): number {
  if (after === "") return content.length
  let candidate = after
  while (candidate.length >= 8) {
    const index = content.indexOf(candidate, from)
    if (index !== -1) return index
    candidate = candidate.slice(0, Math.floor(candidate.length / 2))
  }
  return -1
}

function replaceConditional(content: string, token: ReverseMapToken): string | null {
  const exactIndex = content.indexOf(token.result)
  if (exactIndex !== -1) {
    return [
      content.slice(0, exactIndex),
      token.token,
      content.slice(exactIndex + token.result.length),
    ].join("")
  }

  if (token.before === undefined || token.after === undefined) return null

  const branchStart = findPrefixEnd(content, token.before)
  if (branchStart === -1) return null

  const afterIndex = findSuffixStart(content, token.after, branchStart)
  if (afterIndex === -1) return null

  return [
    content.slice(0, branchStart),
    applyActiveBranch(token, content.slice(branchStart, afterIndex)),
    content.slice(afterIndex),
  ].join("")
}

function reverseContent(
  content: string,
  file: ReverseMapFile,
  warnings: ReverseWarning[],
): string {
  const contentTokens = file.tokens
    .filter(token => token.kind === "content")
    .sort((a, b) => (b.range?.start ?? -1) - (a.range?.start ?? -1))

  let reversed = content
  for (const token of contentTokens) {
    const rangeResult = replaceAtRange(reversed, token)
    if (rangeResult !== null) {
      reversed = rangeResult
      continue
    }

    const fallbackResult = replaceFirst(reversed, token)
    if (fallbackResult !== null) {
      reversed = fallbackResult
      continue
    }

    warnings.push({
      outputPath: file.outputPath,
      token: token.token,
      result: token.result,
      message: "Rendered value was not found; token was not restored",
    })
  }

  const conditionalTokens = file.tokens
    .filter(token => token.kind === "conditional")
    .sort((a, b) => (b.range?.start ?? -1) - (a.range?.start ?? -1))

  for (const token of conditionalTokens) {
    const result = replaceConditional(reversed, token)
    if (result !== null) {
      reversed = result
      continue
    }

    warnings.push({
      outputPath: file.outputPath,
      token: token.token,
      result: token.result,
      message: "Rendered conditional block was not found; block was not restored",
    })
  }

  return reversed
}

function writeSkippedTemplate(
  templateRoot: string,
  skipped: ReverseMapStoredTemplate,
): number {
  const templatePath = resolveInside(templateRoot, skipped.templatePath)
  if (skipped.kind === "directory") {
    mkdirSync(templatePath, { recursive: true })
    return 0
  }

  mkdirSync(dirname(templatePath), { recursive: true })
  const content = skipped.encoding === "base64"
    ? Buffer.from(skipped.content ?? "", "base64")
    : skipped.content ?? ""
  writeFileSync(templatePath, content)
  return 1
}

function replaceFlatTokens(content: string, manifest: ReverseMapManifest): string {
  const entries = Object.entries(manifest.tokens)
    .filter(([, tokens]) => tokens.length > 0)
    .sort(([a], [b]) => b.length - a.length)

  let result = content
  for (const [rendered, tokens] of entries) {
    if (rendered === "") continue
    result = result.split(rendered).join(tokens[0]!)
  }
  return result
}

function dirnamePath(path: string): string {
  const normalized = normalizePath(path)
  const index = normalized.lastIndexOf("/")
  return index === -1 ? "" : normalized.slice(0, index)
}

function basenamePath(path: string): string {
  const normalized = normalizePath(path)
  const index = normalized.lastIndexOf("/")
  return index === -1 ? normalized : normalized.slice(index + 1)
}

function joinPath(...parts: string[]): string {
  return parts
    .filter(part => part !== "")
    .join("/")
}

function buildDirectoryMap(manifest: ReverseMapManifest): Map<string, string> {
  const mappings = new Map<string, string>([["", ""]])

  function addMapping(outputDir: string, templateDir: string) {
    const outputParts = normalizePath(outputDir).split("/").filter(Boolean)
    const templateParts = normalizePath(templateDir).split("/").filter(Boolean)
    for (let i = 1; i <= outputParts.length; i++) {
      if (i <= templateParts.length) {
        mappings.set(outputParts.slice(0, i).join("/"), templateParts.slice(0, i).join("/"))
      }
    }
    mappings.set(normalizePath(outputDir), normalizePath(templateDir))
  }

  for (const file of manifest.files) {
    const output = normalizePath(file.outputPath)
    const template = normalizePath(file.templatePath)
    addMapping(dirnamePath(output), dirnamePath(template))
    if (file.tokens.some(token => token.kind === "path")) addMapping(output, template)
  }

  for (const skipped of manifest.skipped ?? []) {
    if (skipped.kind === "directory") continue
    addMapping(dirnamePath(skipped.templatePath), dirnamePath(skipped.templatePath))
  }

  return mappings
}

function inferTemplatePath(outputPath: string, directoryMap: Map<string, string>): string {
  const normalized = normalizePath(outputPath)
  const outputDir = dirnamePath(normalized)
  let bestOutputDir = ""
  let bestTemplateDir = ""

  for (const [mappedOutputDir, mappedTemplateDir] of directoryMap) {
    if (
      mappedOutputDir.length >= bestOutputDir.length
      && (outputDir === mappedOutputDir || outputDir.startsWith(`${mappedOutputDir}/`))
    ) {
      bestOutputDir = mappedOutputDir
      bestTemplateDir = mappedTemplateDir
    }
  }

  const suffix = bestOutputDir === ""
    ? outputDir
    : outputDir.slice(bestOutputDir.length).replace(/^\//, "")
  return joinPath(bestTemplateDir, suffix, basenamePath(normalized))
}

function walkFiles(root: string, excludedRoots: string[] = []): string[] {
  const files: string[] = []
  const pending = [root]

  while (pending.length > 0) {
    const current = pending.pop()!
    for (const entry of readdirSync(current).sort()) {
      const path = resolvePath(current, entry)
      if (excludedRoots.some(excluded => isInsidePath(excluded, path))) continue
      const stat = statSync(path)
      if (stat.isDirectory()) {
        pending.push(path)
      } else if (stat.isFile()) {
        files.push(normalizePath(relative(root, path)))
      }
    }
  }

  return files
}

function copyIncludedRenderedFiles(
  renderedRoot: string,
  templateRoot: string,
  includedOutputPaths: string[],
  directoryMap: Map<string, string>,
  manifest: ReverseMapManifest,
): number {
  let filesWritten = 0

  for (const outputPath of includedOutputPaths) {
    const renderedPath = resolveInside(renderedRoot, outputPath)
    const templatePath = resolveInside(templateRoot, inferTemplatePath(outputPath, directoryMap))
    mkdirSync(dirname(templatePath), { recursive: true })
    const content = readFileSync(renderedPath)
    if (isUtf8Text(content)) {
      writeFileSync(templatePath, replaceFlatTokens(content.toString("utf-8"), manifest))
    } else {
      copyFileSync(renderedPath, templatePath)
    }
    filesWritten += 1
  }

  return filesWritten
}

function getIncludedRenderedFiles(
  renderedRoot: string,
  templateRoot: string,
  mapPath: string,
  manifest: ReverseMapManifest,
  include: ReverseOptions["include"],
): string[] {
  const matchers = getIncludeMatchers(include)
  if (matchers.length === 0) return []

  const mappedOutputPaths = new Set(manifest.files.map(file => normalizePath(file.outputPath)))
  const mapRelativePath = normalizePath(relative(renderedRoot, mapPath))
  return walkFiles(renderedRoot, [templateRoot]).filter(outputPath => {
    return outputPath !== mapRelativePath
      && !mappedOutputPaths.has(outputPath)
      && matchesAny(outputPath, matchers)
  })
}

export function reverseDir(
  renderedDir: string,
  templateDir: string,
  options: ReverseOptions = {},
): ReverseResult {
  const renderedRoot = resolvePath(renderedDir)
  const templateRoot = resolvePath(templateDir)
  const mapPath = options.mapPath
    ? resolvePath(renderedRoot, options.mapPath)
    : resolvePath(renderedRoot, ".tdir-map.json")
  const manifest = readManifest(mapPath)
  const directoryMap = buildDirectoryMap(manifest)
  const includedOutputPaths = getIncludedRenderedFiles(
    renderedRoot,
    templateRoot,
    mapPath,
    manifest,
    options.include,
  )
  const warnings: ReverseWarning[] = []
  let filesWritten = 0

  for (const file of manifest.files) {
    const renderedPath = resolveInside(renderedRoot, file.outputPath)
    const templatePath = resolveInside(templateRoot, file.templatePath)

    if (!existsSync(renderedPath)) {
      warnings.push({
        outputPath: file.outputPath,
        token: "",
        result: "",
        message: "Rendered path does not exist; skipped",
      })
      continue
    }

    const stat = statSync(renderedPath)
    if (stat.isDirectory()) {
      mkdirSync(templatePath, { recursive: true })
      continue
    }
    if (!stat.isFile()) continue

    mkdirSync(dirname(templatePath), { recursive: true })
    const content = readFileSync(renderedPath)
    if (!isUtf8Text(content)) {
      copyFileSync(renderedPath, templatePath)
      filesWritten += 1
      continue
    }

    writeFileSync(
      templatePath,
      reverseContent(content.toString("utf-8"), file, warnings),
    )
    filesWritten += 1
  }

  for (const skipped of manifest.skipped ?? []) {
    filesWritten += writeSkippedTemplate(templateRoot, skipped)
  }

  filesWritten += copyIncludedRenderedFiles(
    renderedRoot,
    templateRoot,
    includedOutputPaths,
    directoryMap,
    manifest,
  )

  return { filesWritten, warnings }
}