import { resolve, join, dirname } from "node:path"
import { existsSync } from "node:fs"
import { readdir } from "node:fs/promises"
import { Glob } from "bun"

// --- Types ---

export interface RegimeConfig {
  templates: string | string[]
  vars?: Record<string, string>
}

export interface TemplateConfig {
  inherits?: string[]
  patterns?: Record<string, string>
}

export interface CollectedTemplate {
  files: Map<string, string[]> // relative path -> absolute paths (in chain order)
  patterns: Record<string, string>
  templateNames: string[] // ordered list of visited template names
}

// --- Constants ---

export const regimeDir = resolve(dirname(import.meta.dir))
export const templatesDir = join(regimeDir, "templates")

// --- Utilities ---

export function readFileSync(path: string): string {
  return require("fs").readFileSync(path, "utf-8")
}

export function readdirSyncRecursive(dir: string, prefix = ""): string[] {
  const fs = require("fs")
  const results: string[] = []
  for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
    const rel = prefix ? `${prefix}/${entry.name}` : entry.name
    if (entry.isDirectory()) {
      results.push(...readdirSyncRecursive(join(dir, entry.name), rel))
    } else {
      results.push(rel)
    }
  }
  return results
}

// --- Template resolution ---

export function resolveTemplateConfig(name: string): TemplateConfig {
  const configPath = join(templatesDir, name, ".regime-template.json")
  if (!existsSync(configPath)) return {}
  const raw = JSON.parse(readFileSync(configPath))
  return raw as TemplateConfig
}

export function resolveTemplateChain(names: string[]): CollectedTemplate {
  const visited = new Set<string>()
  const files = new Map<string, string[]>()
  const patterns: Record<string, string> = {}
  const templateNames: string[] = []

  function walk(name: string) {
    if (visited.has(name)) return
    visited.add(name)

    const dir = join(templatesDir, name)
    if (!existsSync(dir)) {
      console.error(`  warning: template "${name}" not found at ${dir}`)
      return
    }

    const config = resolveTemplateConfig(name)

    // Walk parents first so children override
    if (config.inherits) {
      for (const parent of config.inherits) {
        walk(parent)
      }
    }

    templateNames.push(name)

    // Collect patterns
    if (config.patterns) {
      Object.assign(patterns, config.patterns)
    }

    // Collect files (skip .regime-template.json)
    const entries = readdirSyncRecursive(dir)
    for (const entry of entries) {
      if (entry === ".regime-template.json") continue
      const existing = files.get(entry) ?? []
      existing.push(join(dir, entry))
      files.set(entry, existing)
    }
  }

  for (const name of names) {
    walk(name)
  }

  return { files, patterns, templateNames }
}

// --- Strategy matching ---

export function getStrategy(filePath: string, patterns: Record<string, string>): string {
  // Check exact match first
  if (patterns[filePath]) return patterns[filePath]

  // Check glob patterns
  for (const [pattern, strategy] of Object.entries(patterns)) {
    if (pattern.includes("*")) {
      const glob = new Glob(pattern)
      if (glob.match(filePath)) return strategy
    }
  }

  return "overwrite" // default
}

// --- Variable interpolation ---

export function interpolate(content: string, vars: Record<string, string>, context?: string): string {
  return content.replace(/<<(\w+)>>/g, (_, key) => {
    if (!(key in vars)) {
      console.error(`  warning: undeclared var "<<${key}>>"${context ? ` in ${context}` : ""}`)
    }
    return vars[key] ?? `<<${key}>>`
  })
}

export function deinterpolate(content: string, vars: Record<string, string>): string {
  let result = content
  for (const [key, value] of Object.entries(vars)) {
    result = result.replaceAll(value, `<<${key}>>`)
  }
  return result
}

// --- Deep merge (template values win; existing-only fields preserved) ---

export function deepMerge(base: any, overlay: any): any {
  if (typeof base !== "object" || base === null || Array.isArray(base)) return overlay
  if (typeof overlay !== "object" || overlay === null || Array.isArray(overlay)) return overlay

  const result = { ...base }
  for (const key of Object.keys(overlay)) {
    if (key in result) {
      result[key] = deepMerge(result[key], overlay[key])
    } else {
      result[key] = overlay[key]
    }
  }
  return result
}

// --- Merge all template JSON files into one combined object ---

export function mergeTemplateJsonFiles(paths: string[], vars: Record<string, string>, relPath: string): any {
  let merged: any = {}
  for (const p of paths) {
    const content = interpolate(readFileSync(p), vars, relPath)
    merged = deepMerge(merged, JSON.parse(content))
  }
  return merged
}

// --- Indentation detection ---

export function detectIndent(content: string): string {
  const match = content.match(/^(\s+)/m)
  return match?.[1] ?? "  "
}

// --- Diff reporting ---

export function diffJson(
  templateObj: any,
  existingObj: any,
  path: string[] = [],
): { field: string; expected: any; actual: any }[] {
  const diffs: { field: string; expected: any; actual: any }[] = []

  for (const key of Object.keys(templateObj)) {
    const fieldPath = [...path, key].join(".")
    const expected = templateObj[key]
    const actual = existingObj?.[key]

    if (actual === undefined) {
      diffs.push({ field: fieldPath, expected, actual: undefined })
    } else if (
      typeof expected === "object" &&
      expected !== null &&
      !Array.isArray(expected) &&
      typeof actual === "object" &&
      actual !== null &&
      !Array.isArray(actual)
    ) {
      diffs.push(...diffJson(expected, actual, [...path, key]))
    } else if (JSON.stringify(expected) !== JSON.stringify(actual)) {
      diffs.push({ field: fieldPath, expected, actual })
    }
  }

  return diffs
}

// --- Find all regime.config.json files in a repo ---

export async function findRegimeConfigs(repoDir: string): Promise<string[]> {
  const results: string[] = []

  async function walk(dir: string) {
    let entries
    try {
      entries = await readdir(dir, { withFileTypes: true })
    } catch {
      return
    }
    for (const entry of entries) {
      if (entry.name === "node_modules" || entry.name === ".git") continue
      const full = join(dir, entry.name)
      if (entry.isDirectory()) {
        await walk(full)
      } else if (entry.name === "regime.config.json") {
        results.push(full)
      }
    }
  }

  await walk(repoDir)
  return results
}