package llm

// RequestOption configures a single completion request.
type RequestOption func(*requestConfig)

type requestConfig struct {
	tools       *ToolBox
	temperature *float64
	maxTokens   *int
	topP        *float64
	stop        []string
	cacheConfig *cacheConfig
}

// cacheConfig holds prompt-caching settings. nil = disabled.
type cacheConfig struct {
	enabled bool
}

// WithTools attaches a toolbox to the request.
func WithTools(tb *ToolBox) RequestOption {
	return func(c *requestConfig) { c.tools = tb }
}

// WithTemperature sets the sampling temperature.
func WithTemperature(t float64) RequestOption {
	return func(c *requestConfig) { c.temperature = &t }
}

// WithMaxTokens sets the maximum number of tokens to generate.
func WithMaxTokens(n int) RequestOption {
	return func(c *requestConfig) { c.maxTokens = &n }
}

// WithTopP sets the nucleus sampling parameter.
func WithTopP(p float64) RequestOption {
	return func(c *requestConfig) { c.topP = &p }
}

// WithStop sets stop sequences.
func WithStop(sequences ...string) RequestOption {
	return func(c *requestConfig) { c.stop = sequences }
}

// WithPromptCaching enables automatic prompt-caching markers on providers
// that support it (currently Anthropic). On providers that don't support
// explicit cache markers (OpenAI, Google), this is a no-op.
//
// When enabled, the library places cache breakpoints at natural seams:
//   - the last tool definition (caches all tools)
//   - the last system message (caches tools + system)
//   - the last non-system message in the history (caches tools + system +
//     conversation so far)
//
// Breakpoints are placed only when the corresponding section is non-empty.
// Up to 3 markers are emitted per request, leaving one of Anthropic's 4
// marker slots for future use.
//
// Cache hits give a 90% discount on cached input tokens (5-minute ephemeral
// tier). Cache writes cost 25% more than normal input tokens, so this option
// is only worth enabling for prompts whose cacheable prefix exceeds the
// minimum (1024 tokens on Opus/Sonnet, 2048 tokens on Haiku) AND is re-sent
// at least twice within the 5-minute TTL.
func WithPromptCaching() RequestOption {
	return func(c *requestConfig) {
		c.cacheConfig = &cacheConfig{enabled: true}
	}
}