package model

import (
	"log/slog"
	"strings"
)

// Anthropic extended-thinking protocol bounds (design/04 §3.2).
const (
	// anthropicMinThinkingBudget is the smallest budget_tokens the Messages API
	// accepts for thinking.type=enabled; anything below it is rejected with a
	// 400, so a lower non-zero budget is raised and reported rather than sent.
	anthropicMinThinkingBudget = 1024
	// anthropicDefaultThinkingBudget is used when thinking is switched on without
	// an explicit budget.
	anthropicDefaultThinkingBudget = 4096
	// anthropicThinkingBodyReserve is the body room kept on top of the thinking
	// budget: max_tokens is shared by thinking and the visible answer, so the
	// budget must never be allowed to consume it all (design/04 §3.2 red line:
	// "预算与正文不得互相吃光").
	anthropicThinkingBodyReserve = 2048
)

// deepSeekAnthropicEndpoint reports whether an Anthropic-protocol request is
// really served by DeepSeek's /anthropic endpoint. The base URL is checked first
// because the endpoint — not the model name — decides whether budget_tokens is
// honoured, and a DeepSeek endpoint is commonly configured with a non-DeepSeek
// model name (the service silently maps unknown names onto deepseek-flash).
func deepSeekAnthropicEndpoint(model, baseURL string) bool {
	if strings.Contains(strings.ToLower(baseURL), "deepseek") {
		return true
	}
	return reasoningVendorFor(model, baseURL) == vendorDeepSeek
}

// anthropicThinkingFor resolves the extended-thinking directive together with the
// max_tokens it requires. It returns the (possibly raised) max_tokens and the
// wire block; a nil block means "do not send thinking" (no directive, or an
// explicit off). Because max_tokens is shared by thinking and the visible answer,
// the returned budget always leaves anthropicThinkingBodyReserve for the body,
// and a request whose budget would eat the answer raises max_tokens instead — the
// adjustment is logged so it is never a silent rewrite.
//
// This is the Anthropic endpoint's rule only. A DeepSeek /anthropic endpoint
// ignores budget_tokens, so it must not go through here (design/04 §3.2 fact 6).
func anthropicThinkingFor(th *Thinking, maxTokens int, log *slog.Logger) (int, *anthropicThinking) {
	if th == nil || (th.Enable != nil && !*th.Enable) {
		return maxTokens, nil
	}
	budget := th.BudgetTokens
	if budget == 0 {
		budget = anthropicDefaultThinkingBudget
	}
	if budget < anthropicMinThinkingBudget {
		log.Warn("thinking budget raised to the protocol minimum",
			"provider", "anthropic", "field", "thinking.budget_tokens",
			"budget_tokens", th.BudgetTokens, "sent", anthropicMinThinkingBudget)
		budget = anthropicMinThinkingBudget
	}
	if need := budget + anthropicThinkingBodyReserve; maxTokens < need {
		log.Warn("max_tokens raised to leave room for thinking plus the answer",
			"provider", "anthropic", "budget_tokens", budget,
			"max_tokens_requested", maxTokens, "max_tokens_sent", need,
			"body_reserve", anthropicThinkingBodyReserve)
		maxTokens = need
	}
	return maxTokens, &anthropicThinking{Type: anthropicThinkingTypeEnabled, BudgetTokens: budget}
}

// anthropicDeepSeekReasoning resolves the reasoning knobs for a DeepSeek
// /anthropic request. Two differences from the Anthropic endpoint drive it: that
// endpoint ignores budget_tokens, so max_tokens is left untouched (raising it
// would misreport the budget the provider actually applies), and strength is
// controlled by output_config.effort, which has no "none" value — there the "off"
// intent is carried by the thinking switch itself (design/04 §3.2 facts 2 and 6).
func anthropicDeepSeekReasoning(log *slog.Logger, model string, th *Thinking, effort string) (*anthropicThinking, *anthropicOutputConfig) {
	var block *anthropicThinking
	if th != nil {
		if th.BudgetTokens > 0 {
			log.Warn("thinking.budget_tokens ignored by the DeepSeek /anthropic endpoint: strength is output_config.effort, so max_tokens was not raised for the budget",
				"provider", "deepseek", "field", "thinking.budget_tokens",
				"budget_tokens", th.BudgetTokens, "model", model)
		}
		switch {
		case th.Enable != nil:
			block = &anthropicThinking{Type: thinkingSwitchValue(*th.Enable), BudgetTokens: th.BudgetTokens}
		case th.BudgetTokens > 0:
			block = &anthropicThinking{Type: thinkingTypeEnabled, BudgetTokens: th.BudgetTokens}
		}
	}
	effort = strings.TrimSpace(effort)
	if effort == "" {
		return block, nil
	}
	if effort == effortNone {
		if block == nil || block.Type == thinkingTypeEnabled {
			log.Warn(`reasoning_effort none mapped to thinking.type=disabled: the DeepSeek /anthropic endpoint has no output_config.effort "none"`,
				"provider", "deepseek", "field", "reasoning_effort", "value", effort, "model", model)
		}
		return &anthropicThinking{Type: thinkingTypeDisabled}, nil
	}
	if block != nil && block.Type == thinkingTypeDisabled {
		log.Warn("output_config.effort dropped: thinking is explicitly disabled",
			"provider", "deepseek", "field", "reasoning_effort", "value", effort, "model", model)
		return block, nil
	}
	tier, ok := normalizeDeepSeekEffort(effort)
	if !ok {
		log.Warn("reasoning_effort dropped: unrecognized value",
			"provider", "deepseek", "field", "reasoning_effort", "value", effort, "model", model)
		return block, nil
	}
	if tier != effort {
		log.Warn("reasoning_effort alias normalized to the tier DeepSeek applies",
			"provider", "deepseek", "field", "reasoning_effort",
			"value", effort, "sent", tier, "model", model)
	}
	return block, &anthropicOutputConfig{Effort: tier}
}

// anthropicThinkingOn reports the effective thinking state of a resolved DeepSeek
// /anthropic request: an omitted switch leaves the provider default in place, and
// DeepSeek's default is enabled.
func anthropicThinkingOn(th *anthropicThinking) bool {
	return th == nil || th.Type != thinkingTypeDisabled
}