package processing

import (
	"strings"
)

// openAIChatUsesMaxCompletionTokens reports models that reject legacy max_tokens
// on Chat Completions (o-series + GPT-5 family including GPT-5.6).
// See https://developers.openai.com/api/reference/resources/chat
func openAIChatUsesMaxCompletionTokens(model string) bool {
	return openAIReasoningChatModel(model)
}

// openAIChatOmitsCustomTemperature reports models that reject non-default
// temperature (only the API default of 1 is accepted, if temperature is sent).
func openAIChatOmitsCustomTemperature(model string) bool {
	return openAIReasoningChatModel(model)
}

// openAIChatSupportsReasoningEffort reports Chat Completions models that accept
// top-level reasoning_effort (Responses API uses reasoning.effort instead).
func openAIChatSupportsReasoningEffort(model string) bool {
	return openAIReasoningChatModel(model)
}

// openAIReasoningChatModel matches OpenAI reasoning / GPT-5(+).5/5.6 chat models
// and common snapshot aliases (e.g. gpt-5.6-luna-2026-…).
func openAIReasoningChatModel(model string) bool {
	m := strings.ToLower(strings.TrimSpace(model))
	if m == "" {
		return false
	}
	// Strip provider prefixes used by OpenRouter-style gateways.
	if i := strings.LastIndex(m, "/"); i >= 0 {
		m = m[i+1:]
	}
	switch {
	case strings.HasPrefix(m, "o1"),
		strings.HasPrefix(m, "o3"),
		strings.HasPrefix(m, "o4"),
		strings.HasPrefix(m, "gpt-5"),
		strings.HasPrefix(m, "chatgpt-o"):
		return true
	default:
		return false
	}
}

// defaultReasoningEffort picks Chat Completions reasoning_effort when unset.
// Long formula-HTML enhance uses "low" so max_completion_tokens prefers visible
// HTML over deep hidden reasoning. Tiny probes use "none" for speed/cost.
func defaultReasoningEffort(model string, maxTokens int, explicit string) string {
	explicit = strings.ToLower(strings.TrimSpace(explicit))
	if explicit != "" {
		return explicit
	}
	if !openAIChatSupportsReasoningEffort(model) {
		return ""
	}
	if maxTokens <= 0 || maxTokens < 512 {
		return "none"
	}
	return "low"
}

// chatCompletionBody is the Chat Completions JSON body. Temperature is a pointer
// so reasoning models can omit it entirely (omitempty).
type chatCompletionBody struct {
	Model               string        `json:"model"`
	Messages            []chatMessage `json:"messages"`
	Temperature         *float64      `json:"temperature,omitempty"`
	MaxTokens           int           `json:"max_tokens,omitempty"`
	MaxCompletionTokens int           `json:"max_completion_tokens,omitempty"`
	ReasoningEffort     string        `json:"reasoning_effort,omitempty"`
}

// buildChatCompletionBody maps CompleteOptions onto the correct Chat Completions
// fields for classic vs GPT-5 / o-series models.
func buildChatCompletionBody(model string, messages []chatMessage, temperature float64, maxTokens int, reasoningEffort string) chatCompletionBody {
	body := chatCompletionBody{
		Model:    model,
		Messages: messages,
	}
	if openAIChatUsesMaxCompletionTokens(model) {
		if maxTokens > 0 {
			body.MaxCompletionTokens = maxTokens
		}
	} else if maxTokens > 0 {
		body.MaxTokens = maxTokens
	}
	if !openAIChatOmitsCustomTemperature(model) {
		t := temperature
		body.Temperature = &t
	}
	body.ReasoningEffort = defaultReasoningEffort(model, maxTokens, reasoningEffort)
	return body
}