// Package exchange provides tools for querying currency exchange rates
// via the ExchangeRate-API v6 (https://www.exchangerate-api.com).
//
// Tools exposed:
//   - exchange_rate_get        — current rate between two currencies
//   - exchange_rate_convert    — convert an amount from one currency to another
//   - exchange_rate_list       — list all supported currency codes
//   - exchange_rate_historical — exchange rate on a specific past date
package exchange

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"strings"
	"time"

	"github.com/enmanuel/agents/internal/config"
	"github.com/enmanuel/agents/tools"
)

const (
	baseURL        = "https://v6.exchangerate-api.com/v6"
	defaultTimeout = 10 * time.Second
	maxBodySize    = 64 * 1024 // 64 KB
)

// client holds shared HTTP client and resolved API key.
type client struct {
	http   *http.Client
	apiKey string
}

// newClient builds a shared client from config.
// Returns an error if no API key can be resolved.
func newClient(cfg config.ExchangeRateToolCfg) (*client, error) {
	apiKey := cfg.APIKey
	if apiKey == "" && cfg.APIKeyEnv != "" {
		apiKey = os.Getenv(cfg.APIKeyEnv)
	}
	if apiKey == "" {
		return nil, fmt.Errorf("exchange rate: no API key configured (set api_key or api_key_env in config)")
	}

	timeout := cfg.Timeout
	if timeout == 0 {
		timeout = defaultTimeout
	}

	return &client{
		http:   &http.Client{Timeout: timeout},
		apiKey: apiKey,
	}, nil
}

// get performs a GET request and returns the parsed JSON body.
func (c *client) get(ctx context.Context, path string) (map[string]any, error) {
	url := fmt.Sprintf("%s/%s/%s", baseURL, c.apiKey, path)
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return nil, fmt.Errorf("build request: %w", err)
	}
	req.Header.Set("User-Agent", "exchange-bot/1.0 (Matrix agent)")
	req.Header.Set("Accept", "application/json")

	resp, err := c.http.Do(req)
	if err != nil {
		return nil, fmt.Errorf("http request: %w", err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(io.LimitReader(resp.Body, maxBodySize))
	if err != nil {
		return nil, fmt.Errorf("read response: %w", err)
	}

	var result map[string]any
	if err := json.Unmarshal(body, &result); err != nil {
		return nil, fmt.Errorf("parse JSON: %w", err)
	}

	// ExchangeRate-API sets "result" field to "success" or "error"
	if res, ok := result["result"].(string); ok && res != "success" {
		errType, _ := result["error-type"].(string)
		return nil, fmt.Errorf("API error: %s", errType)
	}

	return result, nil
}

// normalizeCurrency uppercases and trims a currency code.
func normalizeCurrency(code string) string {
	return strings.ToUpper(strings.TrimSpace(code))
}

// getFloat safely extracts a float64 from a JSON-decoded map.
func getFloat(m map[string]any, key string) (float64, bool) {
	v, ok := m[key]
	if !ok {
		return 0, false
	}
	f, ok := v.(float64)
	return f, ok
}

// getString safely extracts a string from a JSON-decoded map.
func getString(m map[string]any, key string) string {
	v, ok := m[key]
	if !ok {
		return ""
	}
	s, _ := v.(string)
	return s
}

// ── Tool constructors ─────────────────────────────────────────────────────

// NewExchangeRateGet creates the exchange_rate_get tool.
// Returns the current exchange rate between two currencies.
func NewExchangeRateGet(cfg config.ExchangeRateToolCfg) (tools.Tool, error) {
	c, err := newClient(cfg)
	if err != nil {
		return tools.Tool{}, err
	}

	return tools.Tool{
		Def: tools.Def{
			Name: "exchange_rate_get",
			Description: "Get the current exchange rate between two currencies. " +
				"Returns the rate, last update time, and next update time. " +
				"Use ISO 4217 currency codes (e.g. USD, EUR, GBP, JPY, MXN, COP, ARS).",
			Parameters: []tools.Param{
				{
					Name:        "from",
					Type:        "string",
					Description: "Source currency code (ISO 4217), e.g. USD, EUR, GBP",
					Required:    true,
				},
				{
					Name:        "to",
					Type:        "string",
					Description: "Target currency code (ISO 4217), e.g. EUR, MXN, JPY",
					Required:    true,
				},
			},
		},
		Exec: func(ctx context.Context, args map[string]any) tools.Result {
			from := normalizeCurrency(tools.GetString(args, "from"))
			to := normalizeCurrency(tools.GetString(args, "to"))
			if from == "" || to == "" {
				return tools.Result{Err: fmt.Errorf("exchange_rate_get: 'from' and 'to' are required")}
			}

			data, err := c.get(ctx, fmt.Sprintf("pair/%s/%s", from, to))
			if err != nil {
				return tools.Result{Err: fmt.Errorf("exchange_rate_get: %w", err)}
			}

			rate, ok := getFloat(data, "conversion_rate")
			if !ok {
				return tools.Result{Err: fmt.Errorf("exchange_rate_get: unexpected API response")}
			}

			nextUpdate := getString(data, "time_next_update_utc")
			lastUpdate := getString(data, "time_last_update_utc")

			output := fmt.Sprintf(
				"💱 **%s → %s**\n\nTasa actual: **%.6f**\n\n"+
					"_Actualizado: %s_\n_Próxima actualización: %s_",
				from, to, rate, lastUpdate, nextUpdate,
			)
			return tools.Result{Output: output}
		},
	}, nil
}

// NewExchangeRateConvert creates the exchange_rate_convert tool.
// Converts an amount from one currency to another using the current rate.
func NewExchangeRateConvert(cfg config.ExchangeRateToolCfg) (tools.Tool, error) {
	c, err := newClient(cfg)
	if err != nil {
		return tools.Tool{}, err
	}

	return tools.Tool{
		Def: tools.Def{
			Name: "exchange_rate_convert",
			Description: "Convert a monetary amount from one currency to another using the current exchange rate. " +
				"Returns the converted amount and the rate used. " +
				"Use ISO 4217 currency codes (e.g. USD, EUR, GBP, JPY, MXN, COP, ARS).",
			Parameters: []tools.Param{
				{
					Name:        "from",
					Type:        "string",
					Description: "Source currency code (ISO 4217), e.g. USD",
					Required:    true,
				},
				{
					Name:        "to",
					Type:        "string",
					Description: "Target currency code (ISO 4217), e.g. EUR",
					Required:    true,
				},
				{
					Name:        "amount",
					Type:        "number",
					Description: "Amount to convert (e.g. 100, 1500.50)",
					Required:    true,
				},
			},
		},
		Exec: func(ctx context.Context, args map[string]any) tools.Result {
			from := normalizeCurrency(tools.GetString(args, "from"))
			to := normalizeCurrency(tools.GetString(args, "to"))
			amount, ok := args["amount"].(float64)
			if !ok {
				return tools.Result{Err: fmt.Errorf("exchange_rate_convert: 'amount' must be a number")}
			}
			if from == "" || to == "" {
				return tools.Result{Err: fmt.Errorf("exchange_rate_convert: 'from' and 'to' are required")}
			}
			if amount <= 0 {
				return tools.Result{Err: fmt.Errorf("exchange_rate_convert: 'amount' must be greater than 0")}
			}

			data, err := c.get(ctx, fmt.Sprintf("pair/%s/%s/%.2f", from, to, amount))
			if err != nil {
				return tools.Result{Err: fmt.Errorf("exchange_rate_convert: %w", err)}
			}

			rate, _ := getFloat(data, "conversion_rate")
			converted, ok := getFloat(data, "conversion_result")
			if !ok {
				return tools.Result{Err: fmt.Errorf("exchange_rate_convert: unexpected API response")}
			}

			output := fmt.Sprintf(
				"💰 **Conversión de divisas**\n\n"+
					"%.2f **%s** = **%.2f %s**\n\n"+
					"Tasa: 1 %s = %.6f %s",
				amount, from, converted, to,
				from, rate, to,
			)
			return tools.Result{Output: output}
		},
	}, nil
}

// NewExchangeRateList creates the exchange_rate_list tool.
// Returns all currency codes supported by the API.
func NewExchangeRateList(cfg config.ExchangeRateToolCfg) (tools.Tool, error) {
	c, err := newClient(cfg)
	if err != nil {
		return tools.Tool{}, err
	}

	return tools.Tool{
		Def: tools.Def{
			Name: "exchange_rate_list",
			Description: "List all currency codes supported by the exchange rate service. " +
				"Returns ISO 4217 codes with their full currency names. " +
				"Use this to discover valid currency codes before using other exchange rate tools.",
			Parameters: []tools.Param{
				{
					Name:        "filter",
					Type:        "string",
					Description: "Optional text filter to search currencies by code or name (case-insensitive, e.g. 'peso', 'EUR', 'dollar')",
					Required:    false,
				},
			},
		},
		Exec: func(ctx context.Context, args map[string]any) tools.Result {
			filter := strings.ToLower(strings.TrimSpace(tools.GetString(args, "filter")))

			data, err := c.get(ctx, "codes")
			if err != nil {
				return tools.Result{Err: fmt.Errorf("exchange_rate_list: %w", err)}
			}

			rawCodes, ok := data["supported_codes"].([]any)
			if !ok {
				return tools.Result{Err: fmt.Errorf("exchange_rate_list: unexpected API response")}
			}

			var sb strings.Builder
			sb.WriteString("🌐 **Monedas disponibles**\n\n")

			count := 0
			for _, entry := range rawCodes {
				pair, ok := entry.([]any)
				if !ok || len(pair) < 2 {
					continue
				}
				code, _ := pair[0].(string)
				name, _ := pair[1].(string)

				if filter != "" {
					codeLow := strings.ToLower(code)
					nameLow := strings.ToLower(name)
					if !strings.Contains(codeLow, filter) && !strings.Contains(nameLow, filter) {
						continue
					}
				}

				fmt.Fprintf(&sb, "• **%s** — %s\n", code, name)
				count++

				// Cap output at 100 entries to avoid flooding
				if count >= 100 {
					sb.WriteString("\n_... y más. Usa 'filter' para buscar una moneda específica._")
					break
				}
			}

			if count == 0 {
				sb.WriteString(fmt.Sprintf("No se encontraron monedas que coincidan con %q.", filter))
			} else if filter == "" {
				fmt.Fprintf(&sb, "\n_Total: %d monedas disponibles_", count)
			}

			return tools.Result{Output: sb.String()}
		},
	}, nil
}

// NewExchangeRateHistorical creates the exchange_rate_historical tool.
// Returns the exchange rate between two currencies on a specific past date.
func NewExchangeRateHistorical(cfg config.ExchangeRateToolCfg) (tools.Tool, error) {
	c, err := newClient(cfg)
	if err != nil {
		return tools.Tool{}, err
	}

	return tools.Tool{
		Def: tools.Def{
			Name: "exchange_rate_historical",
			Description: "Get the historical exchange rate between two currencies on a specific past date. " +
				"Returns the rate that was in effect on that date. " +
				"Use ISO 4217 currency codes and YYYY-MM-DD date format.",
			Parameters: []tools.Param{
				{
					Name:        "from",
					Type:        "string",
					Description: "Source currency code (ISO 4217), e.g. USD",
					Required:    true,
				},
				{
					Name:        "to",
					Type:        "string",
					Description: "Target currency code (ISO 4217), e.g. EUR",
					Required:    true,
				},
				{
					Name:        "date",
					Type:        "string",
					Description: "Date in YYYY-MM-DD format (e.g. 2024-01-15). Must be in the past.",
					Required:    true,
				},
			},
		},
		Exec: func(ctx context.Context, args map[string]any) tools.Result {
			from := normalizeCurrency(tools.GetString(args, "from"))
			to := normalizeCurrency(tools.GetString(args, "to"))
			dateStr := strings.TrimSpace(tools.GetString(args, "date"))

			if from == "" || to == "" {
				return tools.Result{Err: fmt.Errorf("exchange_rate_historical: 'from' and 'to' are required")}
			}
			if dateStr == "" {
				return tools.Result{Err: fmt.Errorf("exchange_rate_historical: 'date' is required (YYYY-MM-DD)")}
			}

			// Parse and validate date
			date, err := time.Parse("2006-01-02", dateStr)
			if err != nil {
				return tools.Result{Err: fmt.Errorf("exchange_rate_historical: invalid date format %q — use YYYY-MM-DD", dateStr)}
			}
			if !date.Before(time.Now()) {
				return tools.Result{Err: fmt.Errorf("exchange_rate_historical: date must be in the past")}
			}

			path := fmt.Sprintf("history/%s/%d/%d/%d",
				from, date.Year(), int(date.Month()), date.Day())

			data, err := c.get(ctx, path)
			if err != nil {
				return tools.Result{Err: fmt.Errorf("exchange_rate_historical: %w", err)}
			}

			// Navigate: data["conversion_rates"][to]
			ratesRaw, ok := data["conversion_rates"].(map[string]any)
			if !ok {
				return tools.Result{Err: fmt.Errorf("exchange_rate_historical: unexpected API response")}
			}

			rateVal, ok := ratesRaw[to]
			if !ok {
				return tools.Result{Err: fmt.Errorf("exchange_rate_historical: currency %s not found in historical data", to)}
			}
			rate, _ := rateVal.(float64)

			output := fmt.Sprintf(
				"📅 **Tasa histórica — %s**\n\n"+
					"**%s → %s**\n"+
					"Tasa: **%.6f**\n\n"+
					"_Datos del %s (cierre de mercado)_",
				dateStr, from, to, rate, dateStr,
			)
			return tools.Result{Output: output}
		},
	}, nil
}