/**
 * React Stage 2 — Generates idiomatic React providers + hooks on top of the kernel.
 *
 * The kernel (@mizan/base) owns data, status, error. This adapter wraps each
 * registered context in a React Provider component so kernel subscription happens
 * once per provider mount, and consumer hooks read from React Context.
 *
 * Output shape:
 *   <MizanContext baseUrl="...">          root — calls configure(), auto-mounts global
 *     <UserContext user_id={...}>         per-named-context provider
 *       <App />
 *     </UserContext>
 *   </MizanContext>
 *
 *   useGlobalContext()                    full ContextState<GlobalContextData>
 *   useCurrentUser()                      convenience: data field
 *   useUserContext()                      full ContextState<UserContextData>
 *   useUserProfile()                      convenience: data field
 *   useEcho()                             mutation/plain — { mutate, isPending, error }
 *   useMizan()                            escape hatch — { call, fetch }
 */

function pascalCase(str) {
    return str.split(/[.\-_]/).map(p => p.charAt(0).toUpperCase() + p.slice(1)).join('')
}

export function generateReactAdapter(schema) {
    const functions = schema['x-mizan-functions'] || []
    const contextGroups = schema['x-mizan-contexts'] || {}
    const namedContexts = Object.entries(contextGroups).filter(([n]) => n !== 'global')
    const hasGlobal = !!contextGroups.global
    const globalFns = functions.filter(fn => fn.isContext === 'global')
    const mutations = functions.filter(fn => !fn.isContext && !fn.isForm && fn.affects)
    const plainFns = functions.filter(fn => !fn.isContext && !fn.isForm && !fn.affects)

    const lines = []

    // ── Header + imports ─────────────────────────────────────────────────

    lines.push(
        "'use client'",
        '',
        '// AUTO-GENERATED by mizan — do not edit',
        '',
        "import {",
        "    createContext,",
        "    useCallback,",
        "    useContext,",
        "    useEffect,",
        "    useRef,",
        "    useState,",
        "    useSyncExternalStore,",
        "    type ReactNode,",
        "} from 'react'",
        "import {",
        "    configure,",
        "    initSession,",
        "    mizanCall,",
        "    mizanFetch,",
        "    MizanError,",
        "    registerContext,",
        "    type ContextState,",
        "} from '@mizan/base'",
        '',
    )

    const stage1Imports = []
    for (const [ctxName] of Object.entries(contextGroups)) {
        const p = pascalCase(ctxName)
        stage1Imports.push(`fetch${p}Context`, `type ${p}ContextData`, `type ${p}ContextParams`)
    }
    for (const fn of [...mutations, ...plainFns]) {
        stage1Imports.push(`call${pascalCase(fn.camelName)}`)
    }
    if (stage1Imports.length > 0) {
        lines.push(`import { ${stage1Imports.join(', ')} } from './index'`, '')
    }

    // ── Internal helper: subscribe to kernel state from a Provider ──────

    lines.push(
        '// Internal — runs inside a Provider, registers with the kernel exactly once.',
        'function useContextSubscription<T>(',
        '    name: string,',
        '    params: Record<string, any>,',
        '    fetchFn: () => Promise<T>,',
        '    initialData?: T,',
        '): ContextState<T> {',
        '    const ref = useRef<ReturnType<typeof registerContext> | null>(null)',
        '    if (!ref.current) {',
        '        ref.current = registerContext(name, params, fetchFn, initialData)',
        '    }',
        '    const handle = ref.current',
        '',
        '    useEffect(() => {',
        "        if (handle.getState().status === 'idle') handle.refetch()",
        '        return () => handle.unregister()',
        '    }, [handle])',
        '',
        '    return useSyncExternalStore(handle.subscribe, handle.getState, handle.getState)',
        '}',
        '',
    )

    // ── Internal helper: mutation wrapper ───────────────────────────────

    lines.push(
        '// Internal — wraps an imperative call() with isPending / error state.',
        'interface MutationHook<TArgs, TResult> {',
        '    mutate: (args: TArgs) => Promise<TResult>',
        '    isPending: boolean',
        '    error: Error | null',
        '}',
        '',
        'function useMutation<TArgs, TResult>(',
        '    callFn: (args: TArgs) => Promise<TResult>,',
        '): MutationHook<TArgs, TResult> {',
        '    const [isPending, setIsPending] = useState(false)',
        '    const [error, setError] = useState<Error | null>(null)',
        '',
        '    const mutate = useCallback(async (args: TArgs) => {',
        '        setIsPending(true)',
        '        setError(null)',
        '        try {',
        '            return await callFn(args)',
        '        } catch (e) {',
        '            setError(e as Error)',
        '            throw e',
        '        } finally {',
        '            setIsPending(false)',
        '        }',
        '    }, [callFn])',
        '',
        '    return { mutate, isPending, error }',
        '}',
        '',
    )

    // ── Global context provider + hooks ─────────────────────────────────

    if (hasGlobal) {
        lines.push(
            '// ── Global Context ──',
            '',
            'const GlobalCtx = createContext<ContextState<GlobalContextData> | null>(null)',
            '',
            'export function GlobalContextProvider({ children }: { children: ReactNode }) {',
            "    const ssrData = typeof window !== 'undefined' ? (window as any).__MIZAN_SSR_DATA__ : undefined",
            "    const state = useContextSubscription('global', {}, () => fetchGlobalContext({} as any), ssrData)",
            '    return <GlobalCtx.Provider value={state}>{children}</GlobalCtx.Provider>',
            '}',
            '',
            'export function useGlobalContext(): ContextState<GlobalContextData> {',
            '    const ctx = useContext(GlobalCtx)',
            "    if (!ctx) throw new Error('useGlobalContext requires <MizanContext> or <GlobalContextProvider>')",
            '    return ctx',
            '}',
            '',
        )

        for (const fn of globalFns) {
            const p = pascalCase(fn.camelName)
            lines.push(
                `export function use${p}(): ${fn.outputType} | null {`,
                `    return useGlobalContext().data?.${fn.name} ?? null`,
                '}',
                '',
            )
        }
    }

    // ── Named context providers + hooks ─────────────────────────────────

    for (const [ctxName, ctxMeta] of namedContexts) {
        const p = pascalCase(ctxName)
        const ctxFunctions = functions.filter(fn => fn.isContext === ctxName)
        const paramKeys = Object.keys(ctxMeta.params || {})
        const hasParams = paramKeys.length > 0

        lines.push(
            `// ── ${p} Context ──`,
            '',
            `const ${p}Ctx = createContext<ContextState<${p}ContextData> | null>(null)`,
            '',
        )

        if (hasParams) {
            lines.push(
                `export function ${p}Context({ children, ...params }: ${p}ContextParams & { children: ReactNode }) {`,
                `    const state = useContextSubscription('${ctxName}', params, () => fetch${p}Context(params))`,
                `    return <${p}Ctx.Provider value={state}>{children}</${p}Ctx.Provider>`,
                '}',
            )
        } else {
            lines.push(
                `export function ${p}Context({ children }: { children: ReactNode }) {`,
                `    const state = useContextSubscription('${ctxName}', {}, () => fetch${p}Context({} as any))`,
                `    return <${p}Ctx.Provider value={state}>{children}</${p}Ctx.Provider>`,
                '}',
            )
        }
        lines.push('')

        lines.push(
            `export function use${p}Context(): ContextState<${p}ContextData> {`,
            `    const ctx = useContext(${p}Ctx)`,
            `    if (!ctx) throw new Error('use${p}Context requires <${p}Context>')`,
            '    return ctx',
            '}',
            '',
        )

        for (const fn of ctxFunctions) {
            const fnPascal = pascalCase(fn.camelName)
            lines.push(
                `export function use${fnPascal}(): ${fn.outputType} | null {`,
                `    return use${p}Context().data?.${fn.name} ?? null`,
                '}',
                '',
            )
        }
    }

    // ── Mutation + plain function hooks ─────────────────────────────────

    for (const fn of [...mutations, ...plainFns]) {
        const p = pascalCase(fn.camelName)
        if (fn.hasInput) {
            lines.push(
                `export function use${p}() {`,
                `    return useMutation<Parameters<typeof call${p}>[0], Awaited<ReturnType<typeof call${p}>>>(call${p})`,
                '}',
                '',
            )
        } else {
            lines.push(
                `export function use${p}() {`,
                `    return useMutation<void, Awaited<ReturnType<typeof call${p}>>>(() => call${p}() as any)`,
                '}',
                '',
            )
        }
    }

    // ── Root MizanContext provider ──────────────────────────────────────

    lines.push(
        '// ── MizanContext root provider ──',
        '',
        'export interface MizanContextProps {',
        '    /** Base URL for protocol endpoints. Defaults to "/api/mizan". */',
        '    baseUrl?: string',
        '    children: ReactNode',
        '}',
        '',
        '/**',
        " * Root provider — calls configure() once and mounts the global context (if defined).",
        ' * Must wrap any component using Mizan-generated hooks.',
        ' */',
        'export function MizanContext({ baseUrl, children }: MizanContextProps) {',
        '    const configured = useRef(false)',
        '    if (!configured.current) {',
        '        if (baseUrl) configure({ baseUrl })',
        '        configured.current = true',
        '    }',
    )
    if (hasGlobal) {
        lines.push('    return <GlobalContextProvider>{children}</GlobalContextProvider>')
    } else {
        lines.push('    return <>{children}</>')
    }
    lines.push('}', '')

    // ── Escape hatch: useMizan ──────────────────────────────────────────

    lines.push(
        '// ── Imperative escape hatch ──',
        '',
        '/**',
        ' * Returns the imperative kernel API. For test harnesses or rare cases where',
        ' * a typed generated hook does not fit. Most app code should use the typed hooks.',
        ' */',
        'export function useMizan() {',
        '    return { call: mizanCall, fetch: mizanFetch }',
        '}',
        '',
    )

    // ── Re-exports ──────────────────────────────────────────────────────

    lines.push(
        "export type { ContextState } from '@mizan/base'",
        "export { configure, initSession, MizanError } from '@mizan/base'",
        '',
    )

    return lines.join('\n')
}