package api

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net/http"

	mdagent "gitea.stevedudenhoeffer.com/steve/majordomo/agent"
	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
	"github.com/gin-gonic/gin"

	"gitea.stevedudenhoeffer.com/steve/pansy/internal/agent"
	"gitea.stevedudenhoeffer.com/steve/pansy/internal/domain"
)

// The garden assistant's chat surface (#56).
//
// Streaming, because a turn that clears a bed and replants it makes a dozen tool
// calls over tens of seconds. Without streaming that is a long silence followed
// by everything at once, which reads as a hang — and the whole design rests on
// watching the canvas change as it happens.

// chatRequest is the body of POST /agent/chat.
type chatRequest struct {
	GardenID int64  `json:"gardenId" binding:"required"`
	Message  string `json:"message" binding:"required"`
}

// chatEvent is one server-sent event. Exactly one field is set.
type chatEvent struct {
	// Step reports a completed model round trip: which tools it called.
	Step *stepEvent `json:"step,omitempty"`
	// Done carries the finished turn.
	Done *agent.Turn `json:"done,omitempty"`
	// Error is a turn that failed, in words meant for a person.
	Error string `json:"error,omitempty"`
}

type stepEvent struct {
	Index int      `json:"index"`
	Tools []string `json:"tools"`
}

func (h *handlers) agentChat(c *gin.Context) {
	var req chatRequest
	if err := c.ShouldBindJSON(&req); err != nil {
		writeAPIError(c, http.StatusBadRequest, "INVALID_INPUT", "a gardenId and a message are required")
		return
	}
	actor := mustActor(c)

	history, err := h.svc.AgentHistory(c.Request.Context(), actor.ID, req.GardenID)
	if err != nil {
		writeServiceError(c, err)
		return
	}

	// Headers before the first write, and a flush straight away: a proxy that
	// buffers the response would reintroduce exactly the silence streaming is
	// here to remove.
	c.Header("Content-Type", "text/event-stream")
	c.Header("Cache-Control", "no-cache")
	c.Header("X-Accel-Buffering", "no")
	c.Writer.Flush()

	send := func(ev chatEvent) {
		b, err := json.Marshal(ev)
		if err != nil {
			slog.Error("api: encode chat event", "error", err)
			return
		}
		_, _ = fmt.Fprintf(c.Writer, "data: %s\n\n", b)
		c.Writer.Flush()
	}

	turn, err := h.agent.Run(c.Request.Context(), actor.ID, req.GardenID, req.Message,
		replayHistory(history),
		func(s mdagent.Step) {
			send(chatEvent{Step: &stepEvent{Index: s.Index, Tools: toolNames(s)}})
		})
	if err != nil {
		// The stream is already open, so an error is an event rather than a
		// status code — the client has committed to reading a stream by now.
		send(chatEvent{Error: chatErrorMessage(err)})
		return
	}

	// Record before announcing: if persistence fails, the user should see that
	// their turn wasn't saved rather than a clean "done" followed by a thread
	// that has forgotten it.
	if _, err := h.svc.RecordAgentExchange(c.Request.Context(), actor.ID, req.GardenID,
		req.Message, turn.Reply, turn.ChangeSetID); err != nil {
		slog.Error("api: record agent exchange", "error", err, "garden", req.GardenID)
	}
	send(chatEvent{Done: turn})
}

// getAgentHistory returns the actor's thread for a garden.
func (h *handlers) getAgentHistory(c *gin.Context) {
	gardenID, ok := parseIDParam(c, "id")
	if !ok {
		return
	}
	msgs, err := h.svc.AgentHistory(c.Request.Context(), mustActor(c).ID, gardenID)
	if err != nil {
		writeServiceError(c, err)
		return
	}
	c.JSON(http.StatusOK, gin.H{"messages": msgs})
}

// deleteAgentHistory is the "start over" escape hatch.
func (h *handlers) deleteAgentHistory(c *gin.Context) {
	gardenID, ok := parseIDParam(c, "id")
	if !ok {
		return
	}
	if err := h.svc.ClearAgentHistory(c.Request.Context(), mustActor(c).ID, gardenID); err != nil {
		writeServiceError(c, err)
		return
	}
	c.Status(http.StatusNoContent)
}

// replayHistory turns stored text into model messages.
//
// Only the text is replayed — no stored tool calls. Continuity needs what was
// said and what came back; replaying a tool call would be replaying a decision
// made against a garden that has since moved on.
func replayHistory(msgs []domain.AgentMessage) []llm.Message {
	out := make([]llm.Message, 0, len(msgs))
	for _, m := range msgs {
		if m.Role == domain.AgentRoleUser {
			out = append(out, llm.UserText(m.Body))
		} else {
			out = append(out, llm.AssistantText(m.Body))
		}
	}
	return out
}

func toolNames(s mdagent.Step) []string {
	names := make([]string, 0, len(s.Results))
	for _, r := range s.Results {
		names = append(names, r.Name)
	}
	return names
}

// chatErrorMessage turns a failure into something worth reading. Permission
// errors in particular get named: "the agent broke" and "you can only view this
// garden" want very different reactions.
func chatErrorMessage(err error) string {
	switch {
	case errors.Is(err, domain.ErrForbidden):
		return "You can only view this garden, so I can't change anything in it."
	case errors.Is(err, domain.ErrNotFound):
		return "I can't find that garden."
	case errors.Is(err, domain.ErrInvalidInput):
		return "I didn't get a message to work from."
	case errors.Is(err, io.EOF), errors.Is(err, context.Canceled):
		return "The connection dropped partway through. Anything I'd already changed is on the canvas, and in History."
	case errors.Is(err, context.DeadlineExceeded):
		return "That took too long and I stopped. Anything I'd already changed is on the canvas, and in History."
	default:
		slog.Error("api: agent run failed", "error", err)
		return "Something went wrong talking to the model. Anything I'd already changed is on the canvas, and in History."
	}
}