/**
 * React Stage 2 — Generates hooks + context providers from Stage 1 output.
 *
 * Generated providers subscribe to the runtime kernel for state.
 * The kernel owns data, status, and error. React just renders.
 */

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 globalContexts = 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 = [
        "'use client'",
        '',
        '// AUTO-GENERATED by mizan — do not edit',
        '',
        "import { createContext, useContext, useState, useEffect, useCallback, useRef, useSyncExternalStore, type ReactNode } from 'react'",
        "import { registerContext, mizanFetch, mizanCall, type ContextState } from '@mizan/runtime'",
        '',
    ]

    // Import from Stage 1
    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'`)
        lines.push('')
    }

    // ── Helper hook: subscribe to kernel state ──────────────────────────

    lines.push('// Subscribe to kernel state via useSyncExternalStore')
    lines.push('function useContextState<T>(')
    lines.push('    name: string,')
    lines.push('    params: Record<string, any>,')
    lines.push('    fetchFn: () => Promise<T>,')
    lines.push('    initialData?: T,')
    lines.push('): ContextState<T> {')
    lines.push('    const ref = useRef<ReturnType<typeof registerContext> | null>(null)')
    lines.push('')
    lines.push('    if (!ref.current) {')
    lines.push('        ref.current = registerContext(name, params, fetchFn, initialData)')
    lines.push('    }')
    lines.push('')
    lines.push('    const handle = ref.current')
    lines.push('')
    lines.push('    // Fetch on mount if no data')
    lines.push('    useEffect(() => {')
    lines.push("        if (handle.getState().status === 'idle') handle.refetch()")
    lines.push('        return () => handle.unregister()')
    lines.push('    }, [handle])')
    lines.push('')
    lines.push('    return useSyncExternalStore(')
    lines.push('        handle.subscribe,')
    lines.push('        handle.getState,')
    lines.push('        handle.getState,')
    lines.push('    )')
    lines.push('}')
    lines.push('')

    // ── Mutation hook helper ────────────────────────────────────────────

    lines.push('// Mutation hook with loading/error state')
    lines.push('function useMutation<TArgs, TResult>(')
    lines.push('    callFn: (args: TArgs) => Promise<TResult>,')
    lines.push('): { mutate: (args: TArgs) => Promise<TResult>; isPending: boolean; error: Error | null } {')
    lines.push('    const [isPending, setIsPending] = useState(false)')
    lines.push('    const [error, setError] = useState<Error | null>(null)')
    lines.push('')
    lines.push('    const mutate = useCallback(async (args: TArgs) => {')
    lines.push('        setIsPending(true)')
    lines.push('        setError(null)')
    lines.push('        try {')
    lines.push('            const result = await callFn(args)')
    lines.push('            return result')
    lines.push('        } catch (e) {')
    lines.push('            setError(e as Error)')
    lines.push('            throw e')
    lines.push('        } finally {')
    lines.push('            setIsPending(false)')
    lines.push('        }')
    lines.push('    }, [callFn])')
    lines.push('')
    lines.push('    return { mutate, isPending, error }')
    lines.push('}')
    lines.push('')

    // ── Context hooks ───────────────────────────────────────────────────

    for (const [ctxName, ctxMeta] of Object.entries(contextGroups)) {
        const p = pascalCase(ctxName)
        const ctxFunctions = functions.filter(fn => fn.isContext === ctxName)
        const paramEntries = Object.entries(ctxMeta.params || {})

        lines.push(`// ── ${p} Context ──`)
        lines.push('')

        // Hook that returns the full kernel state
        if (paramEntries.length > 0) {
            lines.push(`export function use${p}Context(params: ${p}ContextParams): ContextState<${p}ContextData> {`)
            lines.push(`    const ssrData = typeof window !== 'undefined' ? (window as any).__MIZAN_SSR_DATA__ : null`)
            lines.push(`    return useContextState('${ctxName}', params, () => fetch${p}Context(params), ssrData)`)
        } else {
            lines.push(`export function use${p}Context(): ContextState<${p}ContextData> {`)
            lines.push(`    const ssrData = typeof window !== 'undefined' ? (window as any).__MIZAN_SSR_DATA__ : null`)
            lines.push(`    return useContextState('${ctxName}', {}, () => fetch${p}Context({} as any), ssrData)`)
        }
        lines.push('}')
        lines.push('')

        // Convenience hooks for individual data fields
        for (const fn of ctxFunctions) {
            const hookPascal = pascalCase(fn.camelName)
            if (paramEntries.length > 0) {
                lines.push(`export function use${hookPascal}(params: ${p}ContextParams): ${fn.outputType} | null {`)
                lines.push(`    const state = use${p}Context(params)`)
            } else {
                lines.push(`export function use${hookPascal}(): ${fn.outputType} | null {`)
                lines.push(`    const state = use${p}Context()`)
            }
            lines.push(`    return state.data?.${fn.name} ?? null`)
            lines.push('}')
            lines.push('')
        }
    }

    // ── Mutation hooks (with loading/error) ──────────────────────────────

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

    // ── Plain function hooks ────────────────────────────────────────────

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

    // ── Re-export runtime types ─────────────────────────────────────────

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

    return lines.join('\n')
}