package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"time"

	"fn-registry/functions/infra"
)

// agentRunnerEndpoint returns the agent_runner_api base URL.
// Override with KANBAN_AGENT_RUNNER_API env var.
func agentRunnerEndpoint() string {
	if v := strings.TrimSpace(os.Getenv("KANBAN_AGENT_RUNNER_API")); v != "" {
		return v
	}
	return "http://127.0.0.1:8486"
}

// allowedStatusForBoard returns the canonical statuses a PATCH can set on a
// given board. Anything else returns 400 (taxonomy issue 0103).
func allowedStatusForBoard(board string) []string {
	switch board {
	case "issues":
		return []string{"pendiente", "en-curso", "en-revisión", "en-revision", "done", "deferred"}
	case "flows":
		return []string{"pending", "running", "done", "deferred"}
	default:
		return nil
	}
}

func isAllowedStatus(board, status string) bool {
	allowed := allowedStatusForBoard(board)
	for _, a := range allowed {
		if a == status {
			return true
		}
	}
	return false
}

// dirAndCacheForBoard returns the filesystem directory + cache for a board
// name. Unknown boards yield ("", nil).
func dirAndCacheForBoard(board string) (string, *cardsCache, func(string) string) {
	switch board {
	case "issues":
		return issuesDir(), issuesCache, mapIssueStatusToColumn
	case "flows":
		return flowsDir(), flowsCache, mapFlowStatusToColumn
	default:
		return "", nil, nil
	}
}

// findCardFile locates the .md file in dir whose leading numeric id matches
// the given card id. Returns "" if not found.
func findCardFile(dir, id string) (string, error) {
	id = strings.TrimSpace(id)
	if id == "" {
		return "", nil
	}
	entries, err := os.ReadDir(dir)
	if err != nil {
		return "", err
	}
	for _, e := range entries {
		if e.IsDir() {
			continue
		}
		name := e.Name()
		if !strings.HasSuffix(strings.ToLower(name), ".md") {
			continue
		}
		if isSkippedMarkdown(name) {
			continue
		}
		if deriveIDFromFilename(name) == id {
			return filepath.Join(dir, name), nil
		}
	}
	return "", nil
}

// GET /api/boards/{board}/cards
func handleListBoardCards() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		board := r.PathValue("board")
		dir, cache, _ := dirAndCacheForBoard(board)
		if dir == "" {
			notFound(w, "unknown board: "+board)
			return
		}
		if cached, ok := cache.get(); ok {
			infra.HTTPJSONResponse(w, http.StatusOK, cached)
			return
		}
		var (
			cards []IssueCard
			err   error
		)
		switch board {
		case "issues":
			cards, err = loadIssueCards(dir)
		case "flows":
			cards, err = loadFlowCards(dir)
		}
		if err != nil {
			serverError(w, err)
			return
		}
		cache.set(cards)
		infra.HTTPJSONResponse(w, http.StatusOK, cards)
	}
}

// PATCH /api/boards/{board}/cards/{id}  body: { status: "..." }
func handlePatchBoardCard() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		board := r.PathValue("board")
		id := r.PathValue("id")
		dir, cache, _ := dirAndCacheForBoard(board)
		if dir == "" {
			notFound(w, "unknown board: "+board)
			return
		}
		var body struct {
			Status string `json:"status"`
		}
		if err := infra.HTTPParseBody(r, &body, maxBodyBytes); err != nil {
			badRequest(w, err.Error())
			return
		}
		status := strings.TrimSpace(body.Status)
		if status == "" {
			badRequest(w, "status required")
			return
		}
		if !isAllowedStatus(board, status) {
			badRequest(w, fmt.Sprintf("invalid status for board %q: %q (allowed: %s)",
				board, status, strings.Join(allowedStatusForBoard(board), ", ")))
			return
		}
		file, err := findCardFile(dir, id)
		if err != nil {
			serverError(w, err)
			return
		}
		if file == "" {
			notFound(w, fmt.Sprintf("card %q not found on board %q", id, board))
			return
		}
		// Patch status; also bump updated to today (YYYY-MM-DD).
		if err := PatchFrontmatterField(file, "status", status); err != nil {
			serverError(w, err)
			return
		}
		_ = PatchFrontmatterField(file, "updated", time.Now().UTC().Format("2006-01-02"))
		cache.invalidate()
		if globalHub != nil {
			globalHub.Broadcast(ServerEvent{
				Board:     board,
				CardID:    id,
				Action:    "updated",
				EventType: "card_changed",
			})
		}
		infra.HTTPJSONResponse(w, http.StatusOK, map[string]any{
			"ok":     true,
			"id":     id,
			"board":  board,
			"status": status,
			"file":   file,
		})
	}
}

// POST /api/boards/{board}/cards/{id}/launch
// Proxies to agent_runner_api at /api/runs with payload including the issue id
// and the DoD items pulled from the .md frontmatter. If the runner is
// unreachable, returns 502 with a suggestion.
func handleLaunchBoardCard() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		board := r.PathValue("board")
		id := r.PathValue("id")
		dir, _, statusMapper := dirAndCacheForBoard(board)
		if dir == "" {
			notFound(w, "unknown board: "+board)
			return
		}
		file, err := findCardFile(dir, id)
		if err != nil {
			serverError(w, err)
			return
		}
		if file == "" {
			notFound(w, fmt.Sprintf("card %q not found on board %q", id, board))
			return
		}
		card, err := parseCardFile(file, statusMapper)
		if err != nil {
			serverError(w, err)
			return
		}
		// Drain incoming body (optional overrides from client). We do not
		// forward it as-is to avoid trust issues; we build a clean payload.
		_, _ = io.Copy(io.Discard, r.Body)

		payload := map[string]any{
			"board":       board,
			"issue_id":    card.ExternalID,
			"title":       card.Title,
			"priority":    card.Priority,
			"type":        card.Type,
			"flow_id":     card.FlowID,
			"dod_items":   card.DoDItems,
			"file_path":   card.FilePath,
			"launched_at": time.Now().UTC().Format(time.RFC3339),
		}
		buf, _ := json.Marshal(payload)

		url := strings.TrimRight(agentRunnerEndpoint(), "/") + "/api/runs"
		client := &http.Client{Timeout: 5 * time.Second}
		req, err := http.NewRequestWithContext(r.Context(), http.MethodPost, url, bytes.NewReader(buf))
		if err != nil {
			serverError(w, err)
			return
		}
		req.Header.Set("Content-Type", "application/json")
		resp, err := client.Do(req)
		if err != nil {
			infra.HTTPErrorResponse(w, infra.HTTPError{
				Status:  http.StatusBadGateway,
				Code:    "agent_runner_unreachable",
				Message: fmt.Sprintf("could not reach agent_runner_api at %s: %v (suggestion: start agent_runner_api service)", url, err),
			})
			return
		}
		defer resp.Body.Close()
		body, _ := io.ReadAll(resp.Body)
		// Forward status + body verbatim so the UI can show backend errors.
		w.Header().Set("Content-Type", "application/json")
		w.WriteHeader(resp.StatusCode)
		_, _ = w.Write(body)
	}
}

// GET /api/boards/{board}/stream  (text/event-stream)
//
// Long-lived SSE connection that emits one event per card change on the
// given board. Events:
//   - card_added    {"board","card_id","action":"created"}
//   - card_changed  {"board","card_id","action":"updated"}
//   - card_removed  {"board","card_id","action":"deleted"}
//   - keepalive     ts=<unix>
//
// Events for OTHER boards are filtered out (one subscription per board).
// A keepalive is emitted every 15s to prevent proxy timeouts.
func handleBoardStream() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		board := r.PathValue("board")
		dir, _, _ := dirAndCacheForBoard(board)
		if dir == "" {
			notFound(w, "unknown board: "+board)
			return
		}
		flusher, ok := w.(http.Flusher)
		if !ok {
			http.Error(w, "streaming unsupported", http.StatusInternalServerError)
			return
		}
		if globalHub == nil {
			http.Error(w, "hub not initialised", http.StatusInternalServerError)
			return
		}

		w.Header().Set("Content-Type", "text/event-stream")
		w.Header().Set("Cache-Control", "no-cache")
		w.Header().Set("Connection", "keep-alive")
		w.Header().Set("X-Accel-Buffering", "no")
		w.WriteHeader(http.StatusOK)
		flusher.Flush()

		ch := globalHub.Subscribe()
		defer globalHub.Unsubscribe(ch)

		// Honor Last-Event-ID is not supported yet (TODO: replay buffer).
		_ = r.Header.Get("Last-Event-ID")

		ticker := time.NewTicker(15 * time.Second)
		defer ticker.Stop()

		ctx := r.Context()
		for {
			select {
			case <-ctx.Done():
				return
			case <-ticker.C:
				if _, err := fmt.Fprintf(w, "event: keepalive\ndata: ts=%d\n\n", time.Now().Unix()); err != nil {
					return
				}
				flusher.Flush()
			case ev, ok := <-ch:
				if !ok {
					return
				}
				if ev.Board != board {
					continue
				}
				evType := ev.EventType
				if evType == "" {
					evType = "card_changed"
				}
				payload, err := json.Marshal(map[string]string{
					"board":   ev.Board,
					"card_id": ev.CardID,
					"action":  ev.Action,
				})
				if err != nil {
					continue
				}
				if _, err := fmt.Fprintf(w, "event: %s\ndata: %s\n\n", evType, payload); err != nil {
					return
				}
				flusher.Flush()
			}
		}
	}
}

// boardRoutes returns the additional routes for issues/flows boards. Called
// from apiRoutes() in handlers.go.
func boardRoutes() []infra.Route {
	return []infra.Route{
		{Method: "GET", Path: "/api/boards/{board}/cards", Handler: handleListBoardCards()},
		{Method: "GET", Path: "/api/boards/{board}/stream", Handler: handleBoardStream()},
		{Method: "PATCH", Path: "/api/boards/{board}/cards/{id}", Handler: handlePatchBoardCard()},
		{Method: "POST", Path: "/api/boards/{board}/cards/{id}/launch", Handler: handleLaunchBoardCard()},
	}
}