package agent

import (
	"encoding/json"
	"os"
	"path/filepath"
	"time"

	"ollie/paths"
)

// usageEntry is one line in the append-only usage JSONL log.
type usageEntry struct {
	Timestamp      string  `json:"ts"`
	SessionID      string  `json:"session"`
	Backend        string  `json:"backend"`
	Model          string  `json:"model"`
	InputTokens    int     `json:"input"`
	OutputTokens   int     `json:"output"`
	CachedTokens   int     `json:"cached"`
	CreationTokens int     `json:"creation"`
	CostUSD        float64 `json:"cost_usd"`
}

// usageLogPath returns the path for the usage log file.
// Respects OLLIE_USAGE_LOG env var; defaults to ~/.local/share/ollie/usage.jsonl.
func usageLogPath() string {
	if p := os.Getenv("OLLIE_USAGE_LOG"); p != "" {
		return p
	}
	return filepath.Join(paths.DataDir(), "usage.jsonl")
}

// appendUsageLog writes a single usage entry to the append-only JSONL log.
func appendUsageLog(sessionID, backendName, model string, sess *Session) {
	path := usageLogPath()
	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
		return
	}
	f, err := os.OpenFile(path, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
	if err != nil {
		return
	}
	defer f.Close()

	entry := usageEntry{
		Timestamp:      time.Now().UTC().Format(time.RFC3339),
		SessionID:      sessionID,
		Backend:        backendName,
		Model:          model,
		InputTokens:    sess.turnInputTokens,
		OutputTokens:   sess.turnOutputTokens,
		CachedTokens:   sess.turnCachedTokens,
		CreationTokens: sess.turnCreationTokens,
		CostUSD:        sess.LastTurnCostUSD,
	}
	data, _ := json.Marshal(entry)
	data = append(data, '\n')
	f.Write(data) //nolint:errcheck
}