"""Tests for Scheme-inspired forms: named let, letrec, dynamic-wind, eq?/eqv?/equal?."""

import pytest
from shared.sx import parse, evaluate, EvalError, Symbol, NIL
from shared.sx.types import Lambda


def ev(text, env=None):
    """Parse and evaluate a single expression."""
    return evaluate(parse(text), env)


# ---------------------------------------------------------------------------
# Named let
# ---------------------------------------------------------------------------

class TestNamedLet:
    def test_basic_loop(self):
        """Named let as a simple counter loop."""
        result = ev("""
            (let loop ((i 0) (acc 0))
              (if (> i 5)
                acc
                (loop (+ i 1) (+ acc i))))
        """)
        assert result == 15  # 0+1+2+3+4+5

    def test_factorial(self):
        result = ev("""
            (let fact ((n 10) (acc 1))
              (if (<= n 1)
                acc
                (fact (- n 1) (* acc n))))
        """)
        assert result == 3628800

    def test_tco_deep_recursion(self):
        """Named let should use TCO — no stack overflow on deep loops."""
        result = ev("""
            (let loop ((i 0))
              (if (>= i 10000)
                i
                (loop (+ i 1))))
        """)
        assert result == 10000

    def test_clojure_style_bindings(self):
        """Named let with Clojure-style flat bindings."""
        result = ev("""
            (let loop (i 0 acc (list))
              (if (>= i 3)
                acc
                (loop (+ i 1) (append acc i))))
        """)
        assert result == [0, 1, 2]

    def test_scheme_style_bindings(self):
        """Named let with Scheme-style paired bindings."""
        result = ev("""
            (let loop ((i 3) (result (list)))
              (if (= i 0)
                result
                (loop (- i 1) (cons i result))))
        """)
        assert result == [1, 2, 3]

    def test_accumulator_pattern(self):
        """Named let accumulating a result — pure functional, no set! needed."""
        result = ev("""
            (let loop ((i 0) (acc (list)))
              (if (>= i 3)
                acc
                (loop (+ i 1) (append acc (* i i)))))
        """)
        assert result == [0, 1, 4]

    def test_init_evaluated_in_outer_env(self):
        """Initial values are evaluated in the enclosing environment."""
        result = ev("""
            (let ((x 10))
              (let loop ((a x) (b (* x 2)))
                (+ a b)))
        """)
        assert result == 30  # 10 + 20

    def test_build_list_with_named_let(self):
        """Idiomatic Scheme pattern: build a list with named let."""
        result = ev("""
            (let collect ((items (list 1 2 3 4 5)) (acc (list)))
              (if (empty? items)
                acc
                (collect (rest items)
                         (if (even? (first items))
                           (append acc (first items))
                           acc))))
        """)
        assert result == [2, 4]

    def test_fibonacci(self):
        """Fibonacci via named let."""
        result = ev("""
            (let fib ((n 10) (a 0) (b 1))
              (if (= n 0) a
                (fib (- n 1) b (+ a b))))
        """)
        assert result == 55

    def test_string_building(self):
        """Named let for building strings."""
        result = ev("""
            (let build ((items (list "a" "b" "c")) (acc ""))
              (if (empty? items)
                acc
                (build (rest items)
                       (str acc (if (= acc "") "" ",") (first items)))))
        """)
        assert result == "a,b,c"


# ---------------------------------------------------------------------------
# letrec
# ---------------------------------------------------------------------------

class TestLetrec:
    def test_basic(self):
        """Simple letrec with a self-referencing lambda."""
        result = ev("""
            (letrec ((double (fn (x) (* x 2))))
              (double 21))
        """)
        assert result == 42

    def test_mutual_recursion(self):
        """Classic even?/odd? mutual recursion."""
        result = ev("""
            (letrec ((my-even? (fn (n)
                       (if (= n 0) true  (my-odd?  (- n 1)))))
                     (my-odd?  (fn (n)
                       (if (= n 0) false (my-even? (- n 1))))))
              (list (my-even? 10) (my-odd? 10)
                    (my-even? 7)  (my-odd? 7)))
        """)
        assert result == [True, False, False, True]

    def test_clojure_style(self):
        """letrec with flat bindings."""
        result = ev("""
            (letrec (f (fn (x) (if (= x 0) 1 (* x (f (- x 1))))))
              (f 5))
        """)
        assert result == 120

    def test_closures_see_each_other(self):
        """Lambdas in letrec see each other's final values."""
        result = ev("""
            (letrec ((a (fn () (b)))
                     (b (fn () 42)))
              (a))
        """)
        assert result == 42

    def test_non_forward_ref(self):
        """letrec with non-lambda values that don't reference each other."""
        result = ev("""
            (letrec ((x 10) (y 20))
              (+ x y))
        """)
        assert result == 30

    def test_three_way_mutual(self):
        """Three mutually recursive functions."""
        result = ev("""
            (letrec ((f (fn (n) (if (= n 0) 1 (g (- n 1)))))
                     (g (fn (n) (if (= n 0) 2 (h (- n 1)))))
                     (h (fn (n) (if (= n 0) 3 (f (- n 1))))))
              (list (f 0) (f 1) (f 2) (f 3)
                    (g 0) (g 1) (g 2)))
        """)
        # f(0)=1, f(1)=g(0)=2, f(2)=g(1)=h(0)=3, f(3)=g(2)=h(1)=f(0)=1
        # g(0)=2, g(1)=h(0)=3, g(2)=h(1)=f(0)=1
        assert result == [1, 2, 3, 1, 2, 3, 1]


# ---------------------------------------------------------------------------
# dynamic-wind
# ---------------------------------------------------------------------------

class TestDynamicWind:
    def _make_log_env(self):
        """Create env with a log! function that appends to a Python list."""
        log = []
        env = {"log!": lambda msg: log.append(msg) or NIL}
        return env, log

    def test_basic_flow(self):
        """Entry and exit thunks called around body."""
        env, log = self._make_log_env()
        result = ev("""
            (dynamic-wind
              (fn () (log! "enter"))
              (fn () (do (log! "body") 42))
              (fn () (log! "exit")))
        """, env)
        assert result == 42
        assert log == ["enter", "body", "exit"]

    def test_after_called_on_error(self):
        """Exit thunk is called even when body raises an error."""
        env, log = self._make_log_env()
        with pytest.raises(Exception):
            ev("""
                (dynamic-wind
                  (fn () (log! "enter"))
                  (fn () (do (log! "body") (error "boom")))
                  (fn () (log! "exit")))
            """, env)
        assert log == ["enter", "body", "exit"]

    def test_nested(self):
        """Nested dynamic-wind calls entry/exit in correct order."""
        env, log = self._make_log_env()
        ev("""
            (dynamic-wind
              (fn () (log! "outer-in"))
              (fn ()
                (dynamic-wind
                  (fn () (log! "inner-in"))
                  (fn () (log! "body"))
                  (fn () (log! "inner-out"))))
              (fn () (log! "outer-out")))
        """, env)
        assert log == [
            "outer-in", "inner-in", "body", "inner-out", "outer-out"
        ]

    def test_return_value(self):
        """Body return value is propagated."""
        result = ev("""
            (dynamic-wind
              (fn () nil)
              (fn () (+ 20 22))
              (fn () nil))
        """)
        assert result == 42

    def test_before_after_are_thunks(self):
        """Before and after must be zero-arg functions."""
        env, log = self._make_log_env()
        # Verify it works with native Python callables too
        env["enter"] = lambda: log.append("in") or NIL
        env["leave"] = lambda: log.append("out") or NIL
        result = ev("""
            (dynamic-wind enter (fn () 99) leave)
        """, env)
        assert result == 99
        assert log == ["in", "out"]


# ---------------------------------------------------------------------------
# Three-tier equality
# ---------------------------------------------------------------------------

class TestEquality:
    def test_eq_identity_same_object(self):
        """eq? is true for the same object."""
        env = {}
        ev("(define x (list 1 2 3))", env)
        assert ev("(eq? x x)", env) is True

    def test_eq_identity_different_objects(self):
        """eq? is false for different objects with same value."""
        assert ev("(eq? (list 1 2) (list 1 2))") is False

    def test_eq_numbers(self):
        """eq? on small ints — Python interns them, so identity holds."""
        assert ev("(eq? 42 42)") is True

    def test_eqv_numbers(self):
        """eqv? compares numbers by value."""
        assert ev("(eqv? 42 42)") is True
        assert ev("(eqv? 42 43)") is False

    def test_eqv_strings(self):
        """eqv? compares strings by value."""
        assert ev('(eqv? "hello" "hello")') is True
        assert ev('(eqv? "hello" "world")') is False

    def test_eqv_nil(self):
        """eqv? on nil values."""
        assert ev("(eqv? nil nil)") is True

    def test_eqv_booleans(self):
        assert ev("(eqv? true true)") is True
        assert ev("(eqv? true false)") is False

    def test_eqv_different_lists(self):
        """eqv? is false for different list objects."""
        assert ev("(eqv? (list 1 2) (list 1 2))") is False

    def test_equal_deep(self):
        """equal? does deep structural comparison."""
        assert ev("(equal? (list 1 2 3) (list 1 2 3))") is True
        assert ev("(equal? (list 1 2) (list 1 2 3))") is False

    def test_equal_nested(self):
        """equal? recursively compares nested structures."""
        assert ev("(equal? {:a (list 1 2)} {:a (list 1 2)})") is True

    def test_equal_is_same_as_equals(self):
        """equal? and = have the same semantics."""
        assert ev("(equal? 42 42)") is True
        assert ev("(= 42 42)") is True
        assert ev("(equal? (list 1) (list 1))") is True
        assert ev("(= (list 1) (list 1))") is True

    def test_eq_eqv_equal_hierarchy(self):
        """eq? ⊂ eqv? ⊂ equal? — each is progressively looser."""
        env = {}
        ev("(define x (list 1 2 3))", env)
        # Same object: all three true
        assert ev("(eq? x x)", env) is True
        assert ev("(eqv? x x)", env) is True
        assert ev("(equal? x x)", env) is True
        # Different objects, same value: eq? false, eqv? false, equal? true
        assert ev("(eq? (list 1 2) (list 1 2))", env) is False
        assert ev("(eqv? (list 1 2) (list 1 2))", env) is False
        assert ev("(equal? (list 1 2) (list 1 2))", env) is True