import { existsSync, readFileSync, rmSync, statSync, writeFileSync } from 'node:fs'
import { join } from 'node:path'

export const LEGACY_SHIM_MARKER = '// tela-skills compatibility shim: the skill now lives in ../tela-studio/. Kept so previously copied commands keep working.'

const shims = {
    'preload.ts': `${LEGACY_SHIM_MARKER}\nimport '../tela-studio/preload.ts'\n`,
    'localhost-utils.ts': `${LEGACY_SHIM_MARKER}\nexport * from '../tela-studio/localhost-utils.ts'\n`,
}

/**
 * The skill used to install to ~/.claude/skills/tela/. Instead of deleting that directory, drop its
 * SKILL.md so Claude Code stops registering a second skill and turn the two documented entry points
 * into forwarders, leaving every other file (including anything the user added) in place.
 */
export function migrateLegacySkillDir(legacyDir: string) {
    if (!existsSync(legacyDir))
        return 'absent'

    const preload = join(legacyDir, 'preload.ts')
    const skillFile = join(legacyDir, 'SKILL.md')
    const hasSkillFile = existsSync(skillFile)
    const isShim = (file: keyof typeof shims) => {
        const path = join(legacyDir, file)
        return statSync(path, { throwIfNoEntry: false })?.isFile()
            && readFileSync(path, 'utf8') === shims[file]
    }
    const hasPreloadShim = isShim('preload.ts')
    if (!hasSkillFile && hasPreloadShim && isShim('localhost-utils.ts'))
        return 'already-migrated'

    // A partial migration may have removed SKILL.md already. Only our exact preload
    // shim can establish ownership in that case; never override a foreign SKILL.md.
    const isOurs = hasSkillFile
        ? existsSync(preload) && /^name: tela$/m.test(readFileSync(skillFile, 'utf8'))
        : hasPreloadShim
    if (!isOurs)
        return 'skipped'

    for (const [file, content] of Object.entries(shims))
        writeFileSync(join(legacyDir, file), content)
    rmSync(skillFile, { force: true })

    return 'migrated'
}