package main

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"log/slog"
	"math/rand"
	"net/http"
	"time"
)

// httpllm.go is the shared OpenAI-compatible Chat Completions transport: one
// HTTP+retry implementation reused by every provider adapter. Grok and Gemini both
// expose this wire format, so the retry/backoff classification (429/5xx/network =
// retryable, other 4xx = terminal) lives once here, parameterised by base/key/
// headers, instead of being copied per provider.

// openAIClient performs OpenAI-compatible /chat/completions calls with retry.
type openAIClient struct {
	name    string // provider label for logs/errors ("xai", "gemini")
	base    string
	key     string
	http    *http.Client
	maxTry  int
	headers map[string]string // extra static headers (provider-specific), may be nil
	log     *slog.Logger
}

func newOpenAIClient(name, base, key string, headers map[string]string, logger *slog.Logger) *openAIClient {
	return &openAIClient{
		name:    name,
		base:    base,
		key:     key,
		http:    &http.Client{},
		maxTry:  3,
		headers: headers,
		log:     logger,
	}
}

// --- OpenAI-compatible wire types -------------------------------------------------

type openAIMessage struct {
	Role    string `json:"role"`
	Content string `json:"content"`
}

// openAITool is the wire shape of a model tool (e.g. web search). Only serialized
// when the request carries tools, so a plain completion's body is unchanged.
type openAITool struct {
	Type string `json:"type"`
}

type openAIRequest struct {
	Model       string          `json:"model"`
	Messages    []openAIMessage `json:"messages"`
	MaxTokens   int             `json:"max_tokens"`
	Temperature float64         `json:"temperature"`
	Stream      bool            `json:"stream"`
	// Optional; omitempty keeps the grok_direct body byte-identical to before.
	Tools           []openAITool `json:"tools,omitempty"`
	ReasoningEffort string       `json:"reasoning_effort,omitempty"`
	// SearchParameters drives xAI Live Search on chat/completions (the web route's
	// grok_web_search provider). nil for every non-web call, so it serializes away.
	SearchParameters any `json:"search_parameters,omitempty"`
}

type openAIUsage struct {
	PromptTokens        int `json:"prompt_tokens"`
	CompletionTokens    int `json:"completion_tokens"`
	PromptTokensDetails struct {
		CachedTokens int `json:"cached_tokens"`
	} `json:"prompt_tokens_details"`
}

type openAIResponse struct {
	ID      string `json:"id"`
	Choices []struct {
		Message struct {
			Content string `json:"content"`
		} `json:"message"`
		FinishReason string `json:"finish_reason"`
	} `json:"choices"`
	Usage openAIUsage `json:"usage"`
	// Citations is the source list xAI Live Search returns by default (absent on a
	// non-web call → nil).
	Citations []string `json:"citations"`
}

func (r *openAIResponse) Text() string {
	if len(r.Choices) == 0 {
		return ""
	}
	return r.Choices[0].Message.Content
}

// complete calls Chat Completions with retry on transient failures (429 / 5xx /
// network timeout, exponential backoff + jitter). Non-retryable 4xx fail
// immediately. On exhaustion the caller refunds the reserved request and notifies
// the user, so a transient failure is never silently swallowed (F6). reqHeaders are
// per-request headers (e.g. x-grok-conv-id) merged on top of the static ones; nil is
// fine.
func (c *openAIClient) complete(ctx context.Context, reqBody openAIRequest, reqHeaders map[string]string) (*openAIResponse, error) {
	payload, err := json.Marshal(reqBody)
	if err != nil {
		return nil, err
	}

	var lastErr error
	for attempt := 0; attempt < c.maxTry; attempt++ {
		if attempt > 0 {
			// 0.5s, 1s, 2s … capped at 8s, plus up to 250ms jitter.
			backoff := time.Duration(500<<uint(attempt-1)) * time.Millisecond
			if backoff > 8*time.Second {
				backoff = 8 * time.Second
			}
			backoff += time.Duration(rand.Intn(250)) * time.Millisecond
			select {
			case <-ctx.Done():
				return nil, ctx.Err()
			case <-time.After(backoff):
			}
		}

		resp, retryable, err := c.attempt(ctx, payload, reqHeaders)
		if err == nil {
			return resp, nil
		}
		lastErr = err
		if ctx.Err() != nil {
			return nil, ctx.Err()
		}
		if !retryable {
			return nil, err
		}
		if c.log != nil {
			c.log.Warn(c.name+" attempt failed, will retry", "attempt", attempt+1, "max", c.maxTry, "err", err)
		}
	}
	return nil, fmt.Errorf("%s: exhausted %d attempts: %w", c.name, c.maxTry, lastErr)
}

// attempt performs one HTTP call. It returns retryable=true for 429/5xx and
// network errors, false for other non-2xx (terminal 4xx). The per-attempt deadline
// bounds a single hung connection; the overall per-request deadline (set by the
// caller via ctx) bounds the whole retry loop so a cascade can't accrete minutes.
func (c *openAIClient) attempt(ctx context.Context, payload []byte, reqHeaders map[string]string) (*openAIResponse, bool, error) {
	attemptCtx, cancel := context.WithTimeout(ctx, 60*time.Second)
	defer cancel()

	req, err := http.NewRequestWithContext(attemptCtx, http.MethodPost, c.base+"/chat/completions", bytes.NewReader(payload))
	if err != nil {
		return nil, false, err
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Authorization", "Bearer "+c.key)
	for k, v := range c.headers {
		req.Header.Set(k, v)
	}
	for k, v := range reqHeaders {
		req.Header.Set(k, v)
	}

	resp, err := c.http.Do(req)
	if err != nil {
		// Network error / timeout — retryable (unless the parent ctx is done).
		return nil, ctx.Err() == nil, err
	}
	defer resp.Body.Close()
	data, _ := io.ReadAll(resp.Body)

	if resp.StatusCode == http.StatusTooManyRequests || resp.StatusCode >= 500 {
		return nil, true, fmt.Errorf("%s http %d: %s", c.name, resp.StatusCode, snippet(data))
	}
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return nil, false, fmt.Errorf("%s http %d: %s", c.name, resp.StatusCode, snippet(data))
	}

	var out openAIResponse
	if err := json.Unmarshal(data, &out); err != nil {
		return nil, false, fmt.Errorf("%s decode: %w", c.name, err)
	}
	// A 2xx is a billed call even when the model returns empty content (content
	// filter, finish_reason=length with no text, or no choices). Return it as a
	// success so the caller books the real cost via the ledger instead of refunding
	// the slot and losing the spend — which would let empty replies bypass BOTH the
	// per-user cap and the global ceiling. The caller just won't send an empty body.
	return &out, false, nil
}

func snippet(b []byte) string {
	const max = 300
	if len(b) > max {
		return string(b[:max]) + "…"
	}
	return string(b)
}