// Package suggestions implements the grammar-checkpoint endpoint and the
// accept/dismiss surface for LLM-proposed edits. Checkpoints run a single LLM
// pass over a document and persist the resulting pending suggestions; the
// frontend re-anchors each one by its `original` string at render time, so the
// stored positions are advisory only (spec Note #6).
package suggestions

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"net/http"
	"strings"

	"github.com/go-chi/chi/v5"

	"gitea.parodia.dev/drwily/petal/internal/db"
	"gitea.parodia.dev/drwily/petal/internal/llm"
)

// Handler holds the dependencies for the checkpoint + suggestion routes. The
// grammar checkpoint and the voice pass each get their own per-document rate
// limiter — they are independent passes with different cadences.
type Handler struct {
	DB         *db.DB
	Client     llm.LLMClient
	Limit      *llm.RateLimiter // grammar checkpoint floor
	VoiceLimit *llm.RateLimiter // voice-consistency floor
}

// New constructs a Handler with per-document checkpoint and voice rate limiters.
func New(database *db.DB, client llm.LLMClient) *Handler {
	return &Handler{
		DB:         database,
		Client:     client,
		Limit:      llm.NewRateLimiter(llm.CheckpointInterval),
		VoiceLimit: llm.NewRateLimiter(llm.VoiceInterval),
	}
}

// RegisterDocRoutes adds the document-scoped routes (check + voice + list) onto
// the existing /api/docs router so they share its base path.
func (h *Handler) RegisterDocRoutes(r chi.Router) {
	r.Post("/{id}/check", h.check)
	r.Post("/{id}/voice", h.voice)
	r.Post("/{id}/rewrite", h.rewrite)
	r.Get("/{id}/suggestions", h.listForDoc)
}

// Routes returns the router mounted at /api/suggestions for per-suggestion
// actions.
func (h *Handler) Routes() chi.Router {
	r := chi.NewRouter()
	r.Post("/{id}/accept", h.accept)
	r.Post("/{id}/dismiss", h.dismiss)
	r.Post("/{id}/chat", h.chat)
	return r
}

// check runs a grammar checkpoint over the document. Fast, typing-cadence pass.
func (h *Handler) check(w http.ResponseWriter, r *http.Request) {
	h.runPass(w, r, h.Limit, llm.RunCheckpoint, grammarScope)
}

// voice runs a Tier-1 voice-consistency pass over the whole document. Slow,
// explicit-action pass; replaces only the pending voice flags.
func (h *Handler) voice(w http.ResponseWriter, r *http.Request) {
	h.runPass(w, r, h.VoiceLimit, llm.RunVoice, voiceScope)
}

// pass is the signature shared by the grammar checkpoint and the voice pass:
// given the document text and the document's tone it returns the model's raw
// suggestions. The voice pass ignores tone (see llm.RunVoice).
type pass func(ctx context.Context, client llm.LLMClient, contentText, tone string) ([]llm.RawSuggestion, error)

// runPass is the shared body for both LLM passes. It loads the document text,
// enforces the pass's per-document rate limit, runs the model, swaps in the
// fresh batch scoped to this family, and returns the document's FULL pending set
// (both families) so the client always renders a unified picture.
func (h *Handler) runPass(w http.ResponseWriter, r *http.Request, limiter *llm.RateLimiter, run pass, scope pendingScope) {
	docID := chi.URLParam(r, "id")

	var contentText, tone string
	err := h.DB.QueryRow(
		`SELECT content_text, tone FROM documents WHERE id = ? AND user_id = ?`,
		docID, db.LocalUserID,
	).Scan(&contentText, &tone)
	if errors.Is(err, sql.ErrNoRows) {
		errorJSON(w, http.StatusNotFound, "document not found")
		return
	}
	if err != nil {
		serverError(w, err)
		return
	}

	// Nothing to analyze on an empty document — skip the LLM round-trip.
	if strings.TrimSpace(contentText) == "" {
		writeJSON(w, http.StatusOK, []db.Suggestion{})
		return
	}

	if ok, _ := limiter.Allow(docID); !ok {
		// Throttled: return the existing pending set unchanged rather than an
		// error, so the frontend keeps showing current suggestions.
		existing, err := h.fetchPending(docID)
		if err != nil {
			serverError(w, err)
			return
		}
		writeJSON(w, http.StatusOK, existing)
		return
	}

	raw, err := run(r.Context(), h.Client, contentText, tone)
	if err != nil {
		errorJSON(w, http.StatusBadGateway, "llm pass failed: "+err.Error())
		return
	}

	if err := h.replacePending(docID, contentText, raw, scope); err != nil {
		serverError(w, err)
		return
	}

	// Return the unified pending set (grammar + voice), not just this batch, so
	// a grammar check never drops the voice highlights from the client and the
	// throttle path above stays consistent with the success path.
	out, err := h.fetchPending(docID)
	if err != nil {
		serverError(w, err)
		return
	}
	writeJSON(w, http.StatusOK, out)
}

// pendingScope describes how one LLM pass touches the shared suggestions table:
// which family of pending rows it replaces, and the type to stamp on the rows it
// inserts. The grammar checkpoint and voice pass each own a disjoint family, so
// running one never disturbs the other's pending flags.
type pendingScope struct {
	deleteWhere string // extra WHERE clause scoping the DELETE to this family
	forceType   string // if set, every inserted row gets this type; else normalizeType
}

var (
	// grammarScope owns the grammar/phrasing/idiom/clarity flags (everything but voice).
	grammarScope = pendingScope{deleteWhere: "type != 'voice'", forceType: ""}
	// voiceScope owns the voice flags only.
	voiceScope = pendingScope{deleteWhere: "type = 'voice'", forceType: db.SuggestionTypeVoice}
)

// replacePending swaps a document's pending suggestions within one family for a
// fresh batch in a single transaction. Accepted/rejected suggestions and the
// other family's pending rows are left untouched.
func (h *Handler) replacePending(docID, contentText string, raw []llm.RawSuggestion, scope pendingScope) error {
	tx, err := h.DB.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()

	if _, err := tx.Exec(
		`DELETE FROM suggestions WHERE doc_id = ? AND status = ? AND `+scope.deleteWhere,
		docID, db.SuggestionStatusPending,
	); err != nil {
		return err
	}

	for _, s := range raw {
		typ := scope.forceType
		if typ == "" {
			typ = normalizeType(s.Type)
		}
		from, to := locate(contentText, s.Original)
		if _, err := tx.Exec(
			`INSERT INTO suggestions (doc_id, from_pos, to_pos, original, replacement, explanation, type)
			 VALUES (?, ?, ?, ?, ?, ?, ?)`,
			docID, from, to, s.Original, s.Replacement, s.Explanation, typ,
		); err != nil {
			return err
		}
	}

	return tx.Commit()
}

// listForDoc returns the document's current pending suggestions (used when the
// editor loads a document, before any new checkpoint fires).
func (h *Handler) listForDoc(w http.ResponseWriter, r *http.Request) {
	out, err := h.fetchPending(chi.URLParam(r, "id"))
	if err != nil {
		serverError(w, err)
		return
	}
	writeJSON(w, http.StatusOK, out)
}

func (h *Handler) fetchPending(docID string) ([]db.Suggestion, error) {
	rows, err := h.DB.Query(
		`SELECT id, doc_id, from_pos, to_pos, original, replacement, explanation, type, status, created_at
		   FROM suggestions
		  WHERE doc_id = ? AND status = ?
		  ORDER BY from_pos ASC, created_at ASC`,
		docID, db.SuggestionStatusPending,
	)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	out := []db.Suggestion{}
	for rows.Next() {
		var s db.Suggestion
		if err := rows.Scan(
			&s.ID, &s.DocID, &s.FromPos, &s.ToPos, &s.Original, &s.Replacement,
			&s.Explanation, &s.Type, &s.Status, &s.CreatedAt,
		); err != nil {
			return nil, err
		}
		out = append(out, s)
	}
	return out, rows.Err()
}

// accept marks a suggestion accepted (the client applies the replacement text).
func (h *Handler) accept(w http.ResponseWriter, r *http.Request) {
	h.setStatus(w, r, db.SuggestionStatusAccepted)
}

// dismiss marks a suggestion rejected.
func (h *Handler) dismiss(w http.ResponseWriter, r *http.Request) {
	h.setStatus(w, r, db.SuggestionStatusRejected)
}

func (h *Handler) setStatus(w http.ResponseWriter, r *http.Request, status string) {
	res, err := h.DB.Exec(
		`UPDATE suggestions SET status = ? WHERE id = ? AND status = ?`,
		status, chi.URLParam(r, "id"), db.SuggestionStatusPending,
	)
	if err != nil {
		serverError(w, err)
		return
	}
	if n, _ := res.RowsAffected(); n == 0 {
		errorJSON(w, http.StatusNotFound, "pending suggestion not found")
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// locate finds the plaintext offsets of original within contentText. Returns
// (-1, -1) when not found; the frontend anchors by string regardless, so a miss
// here is non-fatal.
func locate(contentText, original string) (int, int) {
	idx := strings.Index(contentText, original)
	if idx < 0 {
		return -1, -1
	}
	return idx, idx + len(original)
}

// normalizeType maps the model's type string onto a valid suggestion type,
// defaulting unknown values to grammar so a stray label never trips the CHECK.
func normalizeType(t string) string {
	switch strings.ToLower(strings.TrimSpace(t)) {
	case db.SuggestionTypeGrammar, db.SuggestionTypePhrasing, db.SuggestionTypeIdiom, db.SuggestionTypeClarity:
		return strings.ToLower(strings.TrimSpace(t))
	default:
		return db.SuggestionTypeGrammar
	}
}

// --- response helpers -------------------------------------------------------

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

func errorJSON(w http.ResponseWriter, status int, msg string) {
	writeJSON(w, status, map[string]string{"error": msg})
}

func serverError(w http.ResponseWriter, err error) {
	errorJSON(w, http.StatusInternalServerError, err.Error())
}