#lang racket/base

;;; BOB Quantum Civilization Engine - Racket Bindings
;;; High-performance quantum simulation with FFI to C library
;;; Integrates with NATS message bus for distributed quantum computing

(require ffi/unsafe
         ffi/unsafe/define
         ffi/unsafe/alloc)

(provide
 (contract-out
  [rng-create (-> exact-nonnegative-integer? rng-handle?)]
  [rng-destroy (-> rng-handle? void?)]
  [rng-seed (-> rng-handle? exact-nonnegative-integer? void?)]
  [rng-uniform (-> rng-handle? (real-in 0 1))]
  [rng-normal (-> rng-handle? real?)]
  [rng-integer (-> rng-handle? integer? integer? integer?)]

  [lattice-create (-> exact-nonnegative-integer? exact-nonnegative-integer?
                      exact-nonnegative-integer? real? lattice-handle?)]
  [lattice-destroy (-> lattice-handle? void?)]
  [lattice-evolve (-> lattice-handle? exact-nonnegative-integer? real?)]
  [lattice-energy (-> lattice-handle? real?)]
  [lattice-entropy (-> lattice-handle? real?)]
  [lattice-correlation (-> lattice-handle? exact-nonnegative-integer? real?)]

  [state-create (-> exact-nonnegative-integer? symbol? state-handle?)]
  [state-destroy (-> state-handle? void?)]
  [state-measure (-> state-handle? exact-nonnegative-integer? (values integer? real?))]
  [state-apply-gate (-> state-handle? symbol? exact-nonnegative-integer? (listof real?) void?)]
  [state-normalize (-> state-handle? void?)]
  [state-expectation (-> state-handle? string? real?)]
  [state-amplitudes (-> state-handle? (listof (cons/c real? real?)))]

  [hamiltonian-create (-> exact-nonnegative-integer? symbol? hamiltonian-handle?)]
  [hamiltonian-destroy (-> hamiltonian-handle? void?)]
  [hamiltonian-add-term (-> hamiltonian-handle? (cons/c (cons/c real? real?) (listof integer?)) void?)]
  [hamiltonian-expectation (-> hamiltonian-handle? state-handle? (cons/c real? real?))]
  [hamiltonian-eigenvalues (-> hamiltonian-handle? exact-nonnegative-integer? (listof real?))]))

;;; =========================================================================
;;; Opaque Type Definitions
;;; =========================================================================

(define-cpointer-type _rng-handle)
(define-cpointer-type _lattice-handle)
(define-cpointer-type _state-handle)
(define-cpointer-type _hamiltonian-handle)
(define-cpointer-type _error-code)

;;; Error codes enumeration
(define ERROR_NONE 0)
(define ERROR_MEMORY_ALLOCATION_FAILED 1)
(define ERROR_INVALID_PARAMETER 2)
(define ERROR_INTERNAL_ERROR 3)
(define ERROR_NOT_IMPLEMENTED 4)
(define ERROR_FILE_IO_ERROR 5)
(define ERROR_UNKNOWN_ERROR 6)

;;; =========================================================================
;;; Opaque Type Constructors for Contracts
;;; =========================================================================

(define (rng-handle? x) (cpointer? x))
(define (lattice-handle? x) (cpointer? x))
(define (state-handle? x) (cpointer? x))
(define (hamiltonian-handle? x) (cpointer? x))

;;; =========================================================================
;;; Library Loading
;;; =========================================================================

(define libbob
  (ffi-lib (cond
             [(eq? (system-type 'os) 'windows)
              "libbob_quantum.dll"]
             [(eq? (system-type 'os) 'macosx)
              "libbob_quantum.dylib"]
             [else
              "libbob_quantum.so"])))

;;; =========================================================================
;;; FFI Function Declarations - RNG Subsystem
;;; =========================================================================

(define-ffi-definer define-bob libbob)

(define-bob bob_rng_create
  (_fun (_ptr o _rng-handle)
        -> _int))

(define-bob bob_rng_destroy
  (_fun _rng-handle
        -> _int))

(define-bob bob_rng_seed
  (_fun _rng-handle _uint64
        -> _int))

(define-bob bob_rng_uniform
  (_fun _rng-handle (_ptr o _double)
        -> _int))

(define-bob bob_rng_normal
  (_fun _rng-handle (_ptr o _double)
        -> _int))

(define-bob bob_rng_integer
  (_fun _rng-handle _int64 _int64 (_ptr o _int64)
        -> _int))

;;; =========================================================================
;;; FFI Function Declarations - Lattice Subsystem
;;; =========================================================================

(define-bob bob_lattice_create
  (_fun _int _int _int _double _uint64 (_ptr o _lattice-handle)
        -> _int))

(define-bob bob_lattice_destroy
  (_fun _lattice-handle
        -> _int))

(define-bob bob_lattice_evolve
  (_fun _lattice-handle _int (_ptr o _double)
        -> _int))

(define-bob bob_lattice_energy
  (_fun _lattice-handle (_ptr o _double)
        -> _int))

(define-bob bob_lattice_entropy
  (_fun _lattice-handle (_ptr o _double)
        -> _int))

(define-bob bob_lattice_correlation
  (_fun _lattice-handle _int (_ptr o _double)
        -> _int))

(define-bob bob_lattice_magnetization
  (_fun _lattice-handle _int _int _int (_ptr o _double)
        -> _int))

;;; =========================================================================
;;; FFI Function Declarations - State Subsystem
;;; =========================================================================

(define-bob bob_state_create
  (_fun _int _int (_ptr o _state-handle)
        -> _int))

(define-bob bob_state_destroy
  (_fun _state-handle
        -> _int))

(define-bob bob_state_measure
  (_fun _state-handle _int (_ptr o _int) (_ptr o _double)
        -> _int))

(define-bob bob_state_measure_multi
  (_fun _state-handle (_ptr i _int) _int (_ptr o _bytes) (_ptr o _double)
        -> _int))

(define-bob bob_state_apply_gate
  (_fun _state-handle _int _int (_ptr i _double) _int
        -> _int))

(define-bob bob_state_apply_controlled
  (_fun _state-handle _int _int _int (_ptr i _double) _int
        -> _int))

(define-bob bob_state_normalize
  (_fun _state-handle
        -> _int))

(define-bob bob_state_expectation
  (_fun _state-handle _string (_ptr o _double)
        -> _int))

(define-bob bob_state_amplitudes
  (_fun _state-handle (_ptr o _int) (_ptr o _pointer)
        -> _int))

(define-bob bob_state_clone
  (_fun _state-handle (_ptr o _state-handle)
        -> _int))

;;; =========================================================================
;;; FFI Function Declarations - Hamiltonian Subsystem
;;; =========================================================================

(define-bob bob_hamiltonian_create
  (_fun _int _int (_ptr o _hamiltonian-handle)
        -> _int))

(define-bob bob_hamiltonian_destroy
  (_fun _hamiltonian-handle
        -> _int))

(define-bob bob_hamiltonian_add_term
  (_fun _hamiltonian-handle _double _double (_ptr i _int) _int
        -> _int))

(define-bob bob_hamiltonian_expectation
  (_fun _hamiltonian-handle _state-handle (_ptr o _double) (_ptr o _double)
        -> _int))

(define-bob bob_hamiltonian_eigenvalues
  (_fun _hamiltonian-handle _int (_ptr o _pointer)
        -> _int))

(define-bob bob_hamiltonian_time_evolve
  (_fun _hamiltonian-handle _state-handle _double (_ptr o _state-handle)
        -> _int))

;;; =========================================================================
;;; RNG Wrapper Functions
;;; =========================================================================

(define (rng-create [seed 42])
  "Create quantum RNG with optional seed"
  (let ([h (malloc 'raw_pointer)])
    (let ([err (bob_rng_create h)])
      (if (= err ERROR_NONE)
          (begin
            (when (positive? seed)
              (bob_rng_seed (ptr-ref h _rng-handle 0) seed))
            (ptr-ref h _rng-handle 0))
          (error 'rng-create (format "FFI error code: ~a" err))))))

(define (rng-destroy rng)
  "Destroy RNG instance"
  (let ([err (bob_rng_destroy rng)])
    (unless (= err ERROR_NONE)
      (error 'rng-destroy (format "FFI error code: ~a" err)))))

(define (rng-seed rng seed)
  "Reseed RNG"
  (let ([err (bob_rng_seed rng seed)])
    (unless (= err ERROR_NONE)
      (error 'rng-seed (format "FFI error code: ~a" err)))))

(define (rng-uniform rng)
  "Generate uniform random in [0,1)"
  (let ([v (malloc 'raw_pointer)])
    (let ([err (bob_rng_uniform rng v)])
      (if (= err ERROR_NONE)
          (ptr-ref v _double 0)
          (error 'rng-uniform (format "FFI error code: ~a" err))))))

(define (rng-normal rng)
  "Generate normally distributed random"
  (let ([v (malloc 'raw_pointer)])
    (let ([err (bob_rng_normal rng v)])
      (if (= err ERROR_NONE)
          (ptr-ref v _double 0)
          (error 'rng-normal (format "FFI error code: ~a" err))))))

(define (rng-integer rng min max)
  "Generate random integer in [min, max]"
  (let ([v (malloc 'raw_pointer)])
    (let ([err (bob_rng_integer rng min max v)])
      (if (= err ERROR_NONE)
          (ptr-ref v _int64 0)
          (error 'rng-integer (format "FFI error code: ~a" err))))))

;;; =========================================================================
;;; Lattice Wrapper Functions
;;; =========================================================================

(define (lattice-create nx ny nz coupling)
  "Create quantum lattice"
  (let ([h (malloc 'raw_pointer)]
        [seed (random 4294967296)])
    (let ([err (bob_lattice_create nx ny nz coupling seed h)])
      (if (= err ERROR_NONE)
          (ptr-ref h _lattice-handle 0)
          (error 'lattice-create (format "FFI error code: ~a" err))))))

(define (lattice-destroy lat)
  "Destroy lattice instance"
  (let ([err (bob_lattice_destroy lat)])
    (unless (= err ERROR_NONE)
      (error 'lattice-destroy (format "FFI error code: ~a" err)))))

(define (lattice-evolve lat steps)
  "Evolve lattice by n Monte Carlo steps"
  (let ([e (malloc 'raw_pointer)])
    (let ([err (bob_lattice_evolve lat steps e)])
      (if (= err ERROR_NONE)
          (ptr-ref e _double 0)
          (error 'lattice-evolve (format "FFI error code: ~a" err))))))

(define (lattice-energy lat)
  "Get current system energy"
  (let ([e (malloc 'raw_pointer)])
    (let ([err (bob_lattice_energy lat e)])
      (if (= err ERROR_NONE)
          (ptr-ref e _double 0)
          (error 'lattice-energy (format "FFI error code: ~a" err))))))

(define (lattice-entropy lat)
  "Get von Neumann entropy"
  (let ([e (malloc 'raw_pointer)])
    (let ([err (bob_lattice_entropy lat e)])
      (if (= err ERROR_NONE)
          (ptr-ref e _double 0)
          (error 'lattice-entropy (format "FFI error code: ~a" err))))))

(define (lattice-correlation lat distance)
  "Get two-point correlation function"
  (let ([c (malloc 'raw_pointer)])
    (let ([err (bob_lattice_correlation lat distance c)])
      (if (= err ERROR_NONE)
          (ptr-ref c _double 0)
          (error 'lattice-correlation (format "FFI error code: ~a" err))))))

;;; =========================================================================
;;; State Vector Wrapper Functions
;;; =========================================================================

(define (state-create n-qubits initial-state)
  "Create quantum state vector with n qubits"
  (let ([h (malloc 'raw_pointer)]
        [state-code (case initial-state
                      [(zero) 0]
                      [(plus) 1]
                      [(random) 2]
                      [else 0])])
    (let ([err (bob_state_create n-qubits state-code h)])
      (if (= err ERROR_NONE)
          (ptr-ref h _state-handle 0)
          (error 'state-create (format "FFI error code: ~a" err))))))

(define (state-destroy state)
  "Destroy state instance"
  (let ([err (bob_state_destroy state)])
    (unless (= err ERROR_NONE)
      (error 'state-destroy (format "FFI error code: ~a" err)))))

(define (state-measure state qubit)
  "Measure single qubit in computational basis"
  (let ([outcome (malloc 'raw_pointer)]
        [prob (malloc 'raw_pointer)])
    (let ([err (bob_state_measure state qubit outcome prob)])
      (if (= err ERROR_NONE)
          (values (ptr-ref outcome _int 0)
                  (ptr-ref prob _double 0))
          (error 'state-measure (format "FFI error code: ~a" err))))))

(define (state-apply-gate state gate qubit params)
  "Apply single-qubit gate"
  (let ([gate-code (case gate
                     [(h) 0]
                     [(x) 1]
                     [(y) 2]
                     [(z) 3]
                     [(s) 4]
                     [(t) 5]
                     [(rx) 6]
                     [(ry) 7]
                     [(rz) 8]
                     [else 0])]
        [param-array (apply vector params)]
        [n-params (length params)])
    (let ([err (bob_state_apply_gate state gate-code qubit
                                      (pointer-to-cpointer param-array)
                                      n-params)])
      (unless (= err ERROR_NONE)
        (error 'state-apply-gate (format "FFI error code: ~a" err))))))

(define (state-normalize state)
  "Normalize state vector to unit norm"
  (let ([err (bob_state_normalize state)])
    (unless (= err ERROR_NONE)
      (error 'state-normalize (format "FFI error code: ~a" err)))))

(define (state-expectation state operator-str)
  "Compute expectation value of Pauli operator string"
  (let ([exp (malloc 'raw_pointer)])
    (let ([err (bob_state_expectation state operator-str exp)])
      (if (= err ERROR_NONE)
          (ptr-ref exp _double 0)
          (error 'state-expectation (format "FFI error code: ~a" err))))))

(define (state-amplitudes state)
  "Get full amplitude vector as list of (real . imag) pairs"
  (let ([n-ptr (malloc 'raw_pointer)]
        [amp-ptr (malloc 'raw_pointer)])
    (let ([err (bob_state_amplitudes state n-ptr amp-ptr)])
      (if (= err ERROR_NONE)
          (let ([n (ptr-ref n-ptr _int 0)]
                [amps (ptr-ref amp-ptr _pointer 0)])
            (for/list ([i (in-range n)])
              (let ([offset (* i 16)])
                (cons (ptr-ref amps _double offset)
                      (ptr-ref amps _double (+ offset 8))))))
          (error 'state-amplitudes (format "FFI error code: ~a" err))))))

;;; =========================================================================
;;; Hamiltonian Wrapper Functions
;;; =========================================================================

(define (hamiltonian-create n-qubits type)
  "Create Hamiltonian operator"
  (let ([h (malloc 'raw_pointer)]
        [type-code (case type
                     [(sparse) 0]
                     [(dense) 1]
                     [(mpo) 2]
                     [else 0])])
    (let ([err (bob_hamiltonian_create n-qubits type-code h)])
      (if (= err ERROR_NONE)
          (ptr-ref h _hamiltonian-handle 0)
          (error 'hamiltonian-create (format "FFI error code: ~a" err))))))

(define (hamiltonian-destroy ham)
  "Destroy Hamiltonian instance"
  (let ([err (bob_hamiltonian_destroy ham)])
    (unless (= err ERROR_NONE)
      (error 'hamiltonian-destroy (format "FFI error code: ~a" err)))))

(define (hamiltonian-add-term ham coeff qubits)
  "Add Pauli term to Hamiltonian"
  (let ([coeff-re (real-part coeff)]
        [coeff-im (imag-part coeff)]
        [qubit-array (apply vector qubits)]
        [n-qubits (length qubits)])
    (let ([err (bob_hamiltonian_add_term ham coeff-re coeff-im
                                          (pointer-to-cpointer qubit-array)
                                          n-qubits)])
      (unless (= err ERROR_NONE)
        (error 'hamiltonian-add-term (format "FFI error code: ~a" err))))))

(define (hamiltonian-expectation ham state)
  "Compute <ψ|H|ψ>"
  (let ([exp-re (malloc 'raw_pointer)]
        [exp-im (malloc 'raw_pointer)])
    (let ([err (bob_hamiltonian_expectation ham state exp-re exp-im)])
      (if (= err ERROR_NONE)
          (cons (ptr-ref exp-re _double 0)
                (ptr-ref exp-im _double 0))
          (error 'hamiltonian-expectation (format "FFI error code: ~a" err))))))

(define (hamiltonian-eigenvalues ham n-vals)
  "Compute lowest n eigenvalues"
  (let ([vals-ptr (malloc 'raw_pointer)])
    (let ([err (bob_hamiltonian_eigenvalues ham n-vals vals-ptr)])
      (if (= err ERROR_NONE)
          (let ([ptr (ptr-ref vals-ptr _pointer 0)])
            (for/list ([i (in-range n-vals)])
              (ptr-ref ptr _double (* i 8))))
          (error 'hamiltonian-eigenvalues (format "FFI error code: ~a" err))))))

;;; =========================================================================
;;; High-Level Example Functions
;;; =========================================================================

(define (example-simple-rng)
  "Example: Simple RNG usage"
  (let ([rng (rng-create 12345)])
    (try
      (begin
        (printf "Uniform: ~a\n" (rng-uniform rng))
        (printf "Normal: ~a\n" (rng-normal rng))
        (printf "Integer [0,100]: ~a\n" (rng-integer rng 0 100)))
      (finally
        (rng-destroy rng)))))

(define (example-quantum-state)
  "Example: Create and measure quantum state"
  (let ([state (state-create 2 'zero)])
    (try
      (begin
        (state-apply-gate state 'h 0 '())
        (let-values ([(outcome prob)
                      (state-measure state 0)])
          (printf "Measurement: ~a with prob ~a\n" outcome prob)))
      (finally
        (state-destroy state)))))

(define (example-lattice-evolution)
  "Example: Evolve quantum lattice"
  (let ([lat (lattice-create 4 4 4 1.0)])
    (try
      (begin
        (for ([i (in-range 10)])
          (lattice-evolve lat 1)
          (printf "Step ~a: E=~a S=~a\n"
                  i
                  (lattice-energy lat)
                  (lattice-entropy lat))))
      (finally
        (lattice-destroy lat)))))