package llm

import (
	"context"
	"errors"
	"sync"
)

// FakeClient 是测试用 LLMClient，可编程产出固定 stream 事件。
// 注意：本文件 NOT _test.go 后缀，因下游 integration test 需作为依赖导入。
type FakeClient struct {
	mu          sync.Mutex
	ProviderID  string
	Events      []StreamEvent // 流事件序列（按顺序 emit）
	StreamError error         // Stream() 立即返回的错误（如果非 nil）
	TokenCount  int           // CountTokens 返回值
	StreamCalls int
	// BlockCh, if non-nil, causes Stream goroutine to block after emitting all
	// Events until ctx is cancelled or BlockCh is closed. Useful for cancel tests.
	BlockCh chan struct{}
}

// NewFake 构造一个 FakeClient，默认 provider="fake"。
func NewFake() *FakeClient { return &FakeClient{ProviderID: "fake"} }

func (f *FakeClient) Provider() string { return f.ProviderID }

func (f *FakeClient) Stream(ctx context.Context, modelID string, req Request) (<-chan StreamEvent, error) {
	f.mu.Lock()
	f.StreamCalls++
	if f.StreamError != nil {
		err := f.StreamError
		f.mu.Unlock()
		return nil, err
	}
	events := append([]StreamEvent(nil), f.Events...)
	f.mu.Unlock()

	blockCh := f.BlockCh

	ch := make(chan StreamEvent, len(events)+1)
	go func() {
		defer close(ch)
		for _, e := range events {
			select {
			case <-ctx.Done():
				ch <- StreamEvent{Type: EventError, Err: errors.New("context canceled")}
				return
			case ch <- e:
			}
		}
		// If a block channel is set, pause here until ctx is cancelled or BlockCh
		// is closed. This lets cancel tests confirm mid-stream cancellation.
		if blockCh != nil {
			select {
			case <-ctx.Done():
			case <-blockCh:
			}
		}
	}()
	return ch, nil
}

func (f *FakeClient) CountTokens(ctx context.Context, modelID string, req Request) (int, error) {
	return f.TokenCount, nil
}

// FakeEmbedder is a deterministic Embedder for tests. Each input maps to a
// fixed-length vector derived from its bytes, so identical text always yields the
// same vector (lets tests assert idempotency / ranking without a real endpoint).
type FakeEmbedder struct {
	Dims   int   // output dimension; defaults to PlatformEmbeddingDims when 0
	Err    error // if non-nil, Embed returns it
	mu     sync.Mutex
	Calls  int
	Inputs []string // accumulated inputs across calls (for assertions)
}

// NewFakeEmbedder constructs a FakeEmbedder with the platform dimension.
func NewFakeEmbedder() *FakeEmbedder { return &FakeEmbedder{Dims: PlatformEmbeddingDims} }

var _ Embedder = (*FakeEmbedder)(nil)

func (e *FakeEmbedder) dims() int {
	if e.Dims > 0 {
		return e.Dims
	}
	return PlatformEmbeddingDims
}

// EmbedDims returns the configured dimension.
func (e *FakeEmbedder) EmbedDims(string) int { return e.dims() }

// Embed returns one deterministic vector per input. The vector is a normalized
// projection of a small hash of the input across the dimension, so distinct
// inputs are distinguishable and identical inputs are identical.
func (e *FakeEmbedder) Embed(_ context.Context, _ string, inputs []string) ([][]float32, error) {
	e.mu.Lock()
	e.Calls++
	e.Inputs = append(e.Inputs, inputs...)
	err := e.Err
	e.mu.Unlock()
	if err != nil {
		return nil, err
	}
	d := e.dims()
	out := make([][]float32, len(inputs))
	for i, s := range inputs {
		v := make([]float32, d)
		// Seed from a stable rolling hash of the bytes.
		var h uint32 = 2166136261
		for _, b := range []byte(s) {
			h ^= uint32(b)
			h *= 16777619
		}
		for j := 0; j < d; j++ {
			h ^= uint32(j) * 2654435761
			h *= 16777619
			// Map to [-1,1).
			v[j] = float32(int32(h)) / float32(1<<31)
		}
		out[i] = v
	}
	return out, nil
}