package main

import (
	"errors"
	"sync"
	"sync/atomic"
	"testing"
	"time"

	libpack_logger "github.com/lukaszraczylo/graphql-monitoring-proxy/logging"
	libpack_monitoring "github.com/lukaszraczylo/graphql-monitoring-proxy/monitoring"
	"github.com/stretchr/testify/assert"
)

func TestNewRequestCoalescer(t *testing.T) {
	tests := []struct {
		name    string
		enabled bool
	}{
		{
			name:    "enabled coalescer",
			enabled: true,
		},
		{
			name:    "disabled coalescer",
			enabled: false,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			logger := libpack_logger.New()
			monitoring := libpack_monitoring.NewMonitoring(&libpack_monitoring.InitConfig{})

			rc := NewRequestCoalescer(tt.enabled, logger, monitoring)

			assert.NotNil(t, rc)
			assert.Equal(t, tt.enabled, rc.enabled)
		})
	}
}

func TestRequestCoalescer_Do_SingleRequest(t *testing.T) {
	rc := NewRequestCoalescer(true, libpack_logger.New(), nil)

	executed := false
	response := &CoalescedResponse{
		Body:       []byte("test response"),
		StatusCode: 200,
	}

	fn := func() (*CoalescedResponse, error) {
		executed = true
		return response, nil
	}

	result, err := rc.Do("test-key", fn)

	assert.NoError(t, err)
	assert.True(t, executed)
	assert.Equal(t, response, result)

	stats := rc.GetStats()
	assert.Equal(t, int64(1), stats["total_requests"])
	assert.Equal(t, int64(1), stats["primary_requests"])
	assert.Equal(t, int64(0), stats["coalesced_requests"])
}

func TestRequestCoalescer_Do_ConcurrentRequests(t *testing.T) {
	rc := NewRequestCoalescer(true, libpack_logger.New(), nil)

	var executionCount atomic.Int32
	response := &CoalescedResponse{
		Body:       []byte("test response"),
		StatusCode: 200,
	}

	fn := func() (*CoalescedResponse, error) {
		executionCount.Add(1)
		time.Sleep(50 * time.Millisecond) // Simulate work
		return response, nil
	}

	// Launch concurrent requests with the same key
	concurrentRequests := 10
	var wg sync.WaitGroup
	wg.Add(concurrentRequests)

	results := make([]*CoalescedResponse, concurrentRequests)
	errs := make([]error, concurrentRequests)

	for i := 0; i < concurrentRequests; i++ {
		go func(index int) {
			defer wg.Done()
			results[index], errs[index] = rc.Do("same-key", fn)
		}(i)
	}

	wg.Wait()

	// Function should only execute once
	assert.Equal(t, int32(1), executionCount.Load())

	// All requests should get the same response
	for i := 0; i < concurrentRequests; i++ {
		assert.NoError(t, errs[i])
		assert.Equal(t, response, results[i])
	}

	stats := rc.GetStats()
	assert.Equal(t, int64(concurrentRequests), stats["total_requests"])
	assert.Equal(t, int64(1), stats["primary_requests"])
	assert.Equal(t, int64(concurrentRequests-1), stats["coalesced_requests"])

	// Check backend savings
	backendSavings := stats["backend_savings_pct"].(float64)
	assert.Greater(t, backendSavings, 0.0)
}

func TestRequestCoalescer_Do_DifferentKeys(t *testing.T) {
	rc := NewRequestCoalescer(true, libpack_logger.New(), nil)

	var executionCount atomic.Int32

	fn := func() (*CoalescedResponse, error) {
		executionCount.Add(1)
		return &CoalescedResponse{Body: []byte("response")}, nil
	}

	// Concurrent requests with different keys
	var wg sync.WaitGroup
	keys := []string{"key1", "key2", "key3"}

	for _, key := range keys {
		wg.Add(1)
		go func(k string) {
			defer wg.Done()
			rc.Do(k, fn)
		}(key)
	}

	wg.Wait()

	// Function should execute for each unique key
	assert.Equal(t, int32(len(keys)), executionCount.Load())

	stats := rc.GetStats()
	assert.Equal(t, int64(3), stats["primary_requests"])
	assert.Equal(t, int64(0), stats["coalesced_requests"])
}

func TestRequestCoalescer_Do_Error(t *testing.T) {
	rc := NewRequestCoalescer(true, libpack_logger.New(), nil)

	expectedErr := errors.New("test error")

	fn := func() (*CoalescedResponse, error) {
		return nil, expectedErr
	}

	result, err := rc.Do("error-key", fn)

	assert.NoError(t, err)
	assert.NotNil(t, result)
	assert.Error(t, result.Err)
	assert.Equal(t, expectedErr, result.Err)
}

func TestRequestCoalescer_Do_ConcurrentWithError(t *testing.T) {
	rc := NewRequestCoalescer(true, libpack_logger.New(), nil)

	expectedErr := errors.New("test error")
	var executionCount atomic.Int32

	fn := func() (*CoalescedResponse, error) {
		executionCount.Add(1)
		time.Sleep(50 * time.Millisecond)
		return nil, expectedErr
	}

	// Launch concurrent requests
	concurrentRequests := 5
	var wg sync.WaitGroup
	wg.Add(concurrentRequests)

	results := make([]*CoalescedResponse, concurrentRequests)

	for i := 0; i < concurrentRequests; i++ {
		go func(index int) {
			defer wg.Done()
			results[index], _ = rc.Do("error-key", fn)
		}(i)
	}

	wg.Wait()

	// Function should only execute once
	assert.Equal(t, int32(1), executionCount.Load())

	// All requests should get the same error in response
	for i := 0; i < concurrentRequests; i++ {
		assert.NotNil(t, results[i])
		assert.Error(t, results[i].Err)
		assert.Equal(t, expectedErr, results[i].Err)
	}
}

func TestRequestCoalescer_Do_Disabled(t *testing.T) {
	rc := NewRequestCoalescer(false, libpack_logger.New(), nil)

	var executionCount atomic.Int32

	fn := func() (*CoalescedResponse, error) {
		executionCount.Add(1)
		return &CoalescedResponse{Body: []byte("response")}, nil
	}

	// Launch concurrent requests with the same key
	concurrentRequests := 5
	var wg sync.WaitGroup
	wg.Add(concurrentRequests)

	for i := 0; i < concurrentRequests; i++ {
		go func() {
			defer wg.Done()
			rc.Do("same-key", fn)
		}()
	}

	wg.Wait()

	// When disabled, function should execute for each request
	assert.Equal(t, int32(concurrentRequests), executionCount.Load())

	stats := rc.GetStats()
	assert.Equal(t, false, stats["enabled"])
}

func TestRequestCoalescer_GetStats(t *testing.T) {
	rc := NewRequestCoalescer(true, libpack_logger.New(), nil)

	fn := func() (*CoalescedResponse, error) {
		time.Sleep(10 * time.Millisecond)
		return &CoalescedResponse{Body: []byte("response")}, nil
	}

	// Simulate some coalesced requests
	var wg sync.WaitGroup
	for i := 0; i < 10; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			rc.Do("key1", fn)
		}()
	}
	wg.Wait()

	// Add some non-coalesced requests
	rc.Do("key2", fn)
	rc.Do("key3", fn)

	stats := rc.GetStats()

	assert.Equal(t, true, stats["enabled"])
	assert.Equal(t, int64(12), stats["total_requests"])
	assert.Equal(t, int64(3), stats["primary_requests"])
	assert.Equal(t, int64(9), stats["coalesced_requests"])
	assert.Equal(t, int64(0), stats["inflight_count"])

	coalescingRate := stats["coalescing_rate_pct"].(float64)
	assert.Greater(t, coalescingRate, 0.0)
	assert.LessOrEqual(t, coalescingRate, 100.0)

	backendSavings := stats["backend_savings_pct"].(float64)
	assert.Greater(t, backendSavings, 0.0)
}

func TestRequestCoalescer_Reset(t *testing.T) {
	rc := NewRequestCoalescer(true, libpack_logger.New(), nil)

	fn := func() (*CoalescedResponse, error) {
		return &CoalescedResponse{Body: []byte("response")}, nil
	}

	// Generate some activity
	rc.Do("key1", fn)
	rc.Do("key2", fn)

	statsBefore := rc.GetStats()
	assert.Greater(t, statsBefore["total_requests"].(int64), int64(0))

	// Reset
	rc.Reset()

	statsAfter := rc.GetStats()
	assert.Equal(t, int64(0), statsAfter["total_requests"])
	assert.Equal(t, int64(0), statsAfter["primary_requests"])
	assert.Equal(t, int64(0), statsAfter["coalesced_requests"])
}

func TestRequestCoalescer_RaceCondition(t *testing.T) {
	rc := NewRequestCoalescer(true, libpack_logger.New(), nil)

	var executionCount atomic.Int32

	fn := func() (*CoalescedResponse, error) {
		executionCount.Add(1)
		time.Sleep(5 * time.Millisecond)
		return &CoalescedResponse{Body: []byte("response")}, nil
	}

	// Launch many concurrent requests in waves
	waves := 5
	requestsPerWave := 20

	for wave := 0; wave < waves; wave++ {
		var wg sync.WaitGroup
		wg.Add(requestsPerWave)

		for i := 0; i < requestsPerWave; i++ {
			go func() {
				defer wg.Done()
				rc.Do("race-key", fn)
			}()
		}

		wg.Wait()
		time.Sleep(10 * time.Millisecond) // Small delay between waves
	}

	// Execution count should be much less than total requests
	totalRequests := waves * requestsPerWave
	assert.Less(t, int(executionCount.Load()), totalRequests)

	stats := rc.GetStats()
	assert.Equal(t, int64(totalRequests), stats["total_requests"])
}

func TestRequestCoalescer_BackendSavingsCalculation(t *testing.T) {
	tests := []struct {
		name              string
		totalRequests     int64
		coalescedRequests int64
		expectedSavings   float64
	}{
		{
			name:              "50% savings",
			totalRequests:     100,
			coalescedRequests: 50,
			expectedSavings:   100.0, // 50 coalesced / 50 primary = 100%
		},
		{
			name:              "90% savings",
			totalRequests:     100,
			coalescedRequests: 90,
			expectedSavings:   900.0, // 90 coalesced / 10 primary = 900%
		},
		{
			name:              "no savings",
			totalRequests:     100,
			coalescedRequests: 0,
			expectedSavings:   0.0,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			rc := NewRequestCoalescer(true, libpack_logger.New(), nil)

			rc.totalRequests.Store(tt.totalRequests)
			rc.coalescedRequests.Store(tt.coalescedRequests)

			stats := rc.GetStats()
			savings := stats["backend_savings_pct"].(float64)

			assert.InDelta(t, tt.expectedSavings, savings, 0.1)
		})
	}
}

func TestRequestCoalescer_GlobalInstance(t *testing.T) {
	rc := InitializeRequestCoalescer(true, libpack_logger.New(), nil)
	assert.NotNil(t, rc)

	// Should return the same instance
	rc2 := GetRequestCoalescer()
	assert.Equal(t, rc, rc2)
}

func TestMin(t *testing.T) {
	tests := []struct {
		a        int
		b        int
		expected int
	}{
		{a: 5, b: 10, expected: 5},
		{a: 10, b: 5, expected: 5},
		{a: 5, b: 5, expected: 5},
		{a: 0, b: 10, expected: 0},
		{a: -5, b: 5, expected: -5},
	}

	for _, tt := range tests {
		result := min(tt.a, tt.b)
		assert.Equal(t, tt.expected, result)
	}
}

// TestRequestCoalescer_PanicSafety verifies that when the primary fn() panics,
// the coalescer still releases waiters and clears the inflight key instead of
// permanently deadlocking that key (waiters hang on wg.Wait and the entry
// leaks).
func TestRequestCoalescer_PanicSafety(t *testing.T) {
	rc := NewRequestCoalescer(true, nil, nil)

	// First call's fn() panics. Recover in a goroutine to emulate the
	// caller catching/handling the panic.
	panicDone := make(chan struct{})
	go func() {
		defer close(panicDone)
		defer func() { _ = recover() }()
		_, _ = rc.Do("key", func() (*CoalescedResponse, error) {
			panic("boom")
		})
	}()
	<-panicDone

	// A subsequent call for the same key must complete (not hang), proving the
	// key was released and the entry dropped.
	done := make(chan struct{})
	go func() {
		defer close(done)
		resp, err := rc.Do("key", func() (*CoalescedResponse, error) {
			return &CoalescedResponse{StatusCode: 200}, nil
		})
		assert.NoError(t, err)
		assert.Equal(t, 200, resp.StatusCode)
	}()
	select {
	case <-done:
	case <-time.After(3 * time.Second):
		t.Fatal("coalescer key still blocked after primary fn() panic")
	}
}

// TestRequestCoalescer_PanicSafety_WaitersGetError verifies that when the
// primary (in-flight owner) request panics, coalesced waiters receive a
// non-nil error instead of (nil, nil). A silent (nil, nil) response lets the
// consumer fall through to a blank HTTP 200 for every waiter instead of
// surfacing the failure. It also verifies the panic still propagates to the
// primary caller unchanged.
func TestRequestCoalescer_PanicSafety_WaitersGetError(t *testing.T) {
	rc := NewRequestCoalescer(true, nil, nil)

	const numWaiters = 5
	const panicKey = "panic-key"

	primaryStarted := make(chan struct{})
	var primaryStartedOnce sync.Once
	releasePrimary := make(chan struct{})

	// close(primaryStarted) must be idempotent: if a waiter is scheduled so
	// late that it misses the coalescing window below (e.g. after the
	// primary's panic-recovery defer has already deleted the inflight map
	// entry for panicKey), rc.Do treats it as a brand-new primary and
	// re-invokes fn. Without sync.Once, that second invocation would call
	// close on an already-closed channel and panic unrecovered in that
	// waiter's goroutine, killing the whole test binary. The deterministic
	// gate below is what actually prevents that scenario; this is a
	// belt-and-braces guard against it.
	fn := func() (*CoalescedResponse, error) {
		primaryStartedOnce.Do(func() { close(primaryStarted) })
		<-releasePrimary
		panic("boom")
	}

	// Launch the primary request first so subsequent calls coalesce onto it.
	primaryPanicked := make(chan any, 1)
	primaryDone := make(chan struct{})
	go func() {
		defer close(primaryDone)
		defer func() {
			primaryPanicked <- recover()
		}()
		_, _ = rc.Do(panicKey, fn)
	}()
	<-primaryStarted

	// Launch waiters that coalesce onto the in-flight (panicking) primary.
	var wg sync.WaitGroup
	wg.Add(numWaiters)
	responses := make([]*CoalescedResponse, numWaiters)
	errs := make([]error, numWaiters)
	for i := 0; i < numWaiters; i++ {
		go func(idx int) {
			defer wg.Done()
			responses[idx], errs[idx] = rc.Do(panicKey, fn)
		}(i)
	}

	// Deterministically wait until every waiter has coalesced onto the
	// primary's inflightRequest before releasing the panic, instead of a
	// fixed sleep. rc.Do increments the shared inflightRequest.waiters
	// counter synchronously, before it blocks on wg.Wait(), so observing
	// numWaiters+1 (the primary plus every coalesced waiter) proves each
	// waiter goroutine has already registered against this exact in-flight
	// entry - even if the entry is deleted from rc.inflight moments later,
	// the waiters already hold a reference to it. A fixed sleep cannot make
	// that guarantee: a waiter scheduled late enough would miss the window,
	// see no in-flight entry, and become a new primary that re-runs fn.
	deadline := time.Now().Add(3 * time.Second)
	for {
		existing, ok := rc.inflight.Load(panicKey)
		if ok && existing.(*inflightRequest).waiters.Load() >= int32(numWaiters+1) {
			break
		}
		if time.Now().After(deadline) {
			t.Fatal("waiters did not coalesce onto the primary within deadline")
		}
		time.Sleep(time.Millisecond)
	}
	close(releasePrimary)

	wg.Wait()
	<-primaryDone

	// The primary caller's own panic semantics are unchanged: the panic
	// propagates out of rc.Do rather than being swallowed.
	recovered := <-primaryPanicked
	assert.NotNil(t, recovered, "panic must propagate to the primary caller")
	assert.Equal(t, "boom", recovered)

	// Every coalesced waiter must observe a non-nil error, never the silent
	// (nil, nil) that would cause a blank HTTP 200 downstream.
	for i := 0; i < numWaiters; i++ {
		assert.NoError(t, errs[i], "rc.Do itself must not return an error")
		if assert.NotNil(t, responses[i], "waiter %d must receive a non-nil response", i) {
			assert.Error(t, responses[i].Err, "waiter %d must receive a non-nil error", i)
			assert.Contains(t, responses[i].Err.Error(), "boom")
		}
	}
}