package ipc

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net"
	"sync"
	"time"
)

// Client — the module side of the boundary. Wraps a unix-socket connection
// and satisfies CoreAPI, so a module imports ipc, holds a CoreAPI, and is
// agnostic to whether it's been wired in-process (tests / daemon-embedded)
// or over this socket (full topology). The swappability is the seam auth
// will insert into without touching module code.
//
// One Client ⇒ one conn ⇒ one concurrent request at a time. A module that
// wants parallel requests opens one Client per goroutine; the store is the
// bottleneck anyway (single writer), so pipelining buys nothing here and a
// per-Client lock keeps frame interleaving impossible by construction.
type Client struct {
	conn net.Conn
	path string // kept so a dropped conn can be re-dialed (core restart)
	mu   sync.Mutex
}

// errConnLost marks a dropped connection — the write failed, or the read hit
// EOF because the peer went away (a core restart closes the accepted conn, and
// the failure can surface on either phase depending on socket-buffer timing).
// call() redials and retries once on this. Retry is safe for the case that
// actually happens — core restarted, so the request was never processed. The
// only unsafe window is a write method whose request the server committed and
// then died before replying; a retry would re-apply it. That's rare, and the
// store is append-only (a duplicate is a superseding row, not corruption), so
// self-healing across restarts is the right trade. ponytail: retry-once, not a
// full idempotency-key protocol — add request IDs if double-apply ever bites.
var errConnLost = errors.New("ipc: connection lost")

// Dial connects to a core socket at path and returns a Client. The module
// owns its Client lifecycle; Close on shutdown.
func Dial(path string) (*Client, error) {
	c, err := net.Dial("unix", path)
	if err != nil {
		return nil, fmt.Errorf("ipc: dial %s: %w", path, err)
	}
	return &Client{conn: c, path: path}, nil
}

func (c *Client) Close() error {
	if c.conn == nil {
		return nil
	}
	return c.conn.Close()
}

// call — the single request/response engine. Serialized by c.mu so a frame
// and its reply always pair up; no interleaving to disambiguate. A wire
// RpcError is rehydrated into the matching package sentinel (errors.Is works
// the same as the in-process path — the boundary is transparent to callers).
func (c *Client) call(ctx context.Context, m Method, params, result any) error {
	c.mu.Lock()
	defer c.mu.Unlock()

	// Honor ctx cancellation by closing the conn — a half-sent frame would
	// desync the stream; tearing down is the clean recovery. A fresh Dial
	// is the module's responsibility on the next call (modules are long-lived
	// processes; a dropped conn is recoverable, not fatal).
	select {
	case <-ctx.Done():
		c.drop()
		return ctx.Err()
	default:
	}

	var raw json.RawMessage
	if params != nil {
		b, err := json.Marshal(params)
		if err != nil {
			return fmt.Errorf("ipc: marshal params: %w", err)
		}
		raw = b
	}

	var resp Response
	err := c.roundtrip(m, raw, &resp)
	if errors.Is(err, errConnLost) {
		// Core likely restarted (new socket inode) and our cached conn is dead.
		// The write never landed, so redial (roundtrip re-dials on a nil conn)
		// and retry exactly once.
		err = c.roundtrip(m, raw, &resp)
	}
	if err != nil {
		return err
	}
	if resp.Error != nil {
		return hydrate(resp.Error)
	}
	if result == nil {
		return nil
	}
	// "null" body into a pointer is valid (sets the zero value); marshal a
	// RawMessage directly to avoid extra encode/decode churn.
	return json.Unmarshal(resp.Result, result)
}

// roundtrip sends one request and reads its reply on c.conn, lazily (re)dialing
// if the conn is nil (fresh Client or a prior drop). A write failure is wrapped
// in errConnLost (safe to retry); a read failure is returned bare (ambiguous).
// Either way a failed conn is dropped so the next call re-dials clean. Caller
// holds c.mu.
func (c *Client) roundtrip(m Method, raw json.RawMessage, resp *Response) error {
	if c.conn == nil {
		conn, err := net.Dial("unix", c.path)
		if err != nil {
			return fmt.Errorf("%w: dial %s: %v", errConnLost, c.path, err)
		}
		c.conn = conn
	}
	if err := writeFrame(c.conn, Request{Method: m, Params: raw}); err != nil {
		c.drop()
		return fmt.Errorf("%w: %v", errConnLost, err)
	}
	if err := readFrame(c.conn, resp); err != nil {
		c.drop()
		return fmt.Errorf("%w: %v", errConnLost, err)
	}
	return nil
}

// drop closes and forgets the current conn so the next call re-dials.
func (c *Client) drop() {
	if c.conn != nil {
		_ = c.conn.Close()
		c.conn = nil
	}
}

// hydrate rehydrates a wire RpcError into the matching package sentinel. The
// code↔sentinel table is the only place the wire "knows" about errors; keep it
// in sync with codeOf in wire.go.
func hydrate(e *RpcError) error {
	switch e.Code {
	case codeNoFact:
		return fmt.Errorf("%w: %s", ErrNoFact, e.Message)
	case codeConfidence:
		return fmt.Errorf("%w: %s", ErrConfidence, e.Message)
	case codeVoidsMissing:
		return fmt.Errorf("%w: %s", ErrVoidsMissing, e.Message)
	case codeNudgeNotFound:
		return fmt.Errorf("%w: %s", ErrNudgeNotFound, e.Message)
	case codeNudgeOutcome:
		return fmt.Errorf("%w: %s", ErrNudgeOutcome, e.Message)
	case codeReminderMissing:
		return fmt.Errorf("%w: %s", ErrReminderNotFound, e.Message)
	case codeReminderState:
		return fmt.Errorf("%w: %s", ErrReminderState, e.Message)
	case codeToolNotFound:
		return fmt.Errorf("%w: %s", ErrToolNotFound, e.Message)
	case codeUnknownMethod:
		return fmt.Errorf("%w: %s", ErrUnknownMethod, e.Message)
	case codeBadParams:
		return fmt.Errorf("%w: %s", ErrBadParams, e.Message)
	case codeForbidden:
		return fmt.Errorf("%w: %s", ErrForbidden, e.Message)
	default:
		return errors.New(e.Error())
	}
}

// CoreAPI implementation on *Client. Each method is a thin call() shim; the
// shape mirrors the CoreAPI interface 1:1 so the embedded-doc intent (module
// holds a CoreAPI, transport-agnostic) reads straight off the signatures.

func (c *Client) WriteFact(ctx context.Context, req WriteFactReq) (int64, error) {
	var r idResp
	if err := c.call(ctx, MethodWriteFact, req, &r); err != nil {
		return 0, err
	}
	return r.ID, nil
}

func (c *Client) LatestFact(ctx context.Context, key string) (Fact, error) {
	var f Fact
	if err := c.call(ctx, MethodLatestFact, keyReq{Key: key}, &f); err != nil {
		return Fact{}, err
	}
	return f, nil
}

func (c *Client) LatestFactBySource(ctx context.Context, key, source string) (Fact, error) {
	var f Fact
	if err := c.call(ctx, MethodLatestFactBySource, keySourceReq{Key: key, Source: source}, &f); err != nil {
		return Fact{}, err
	}
	return f, nil
}

func (c *Client) Since(ctx context.Context, key string, now time.Time) (time.Duration, error) {
	var r sinceResp
	if err := c.call(ctx, MethodSince, sinceReq{Key: key, Now: now}, &r); err != nil {
		return 0, err
	}
	return r.Dur, nil
}

func (c *Client) Presence(ctx context.Context) (Presence, error) {
	var p Presence
	if err := c.call(ctx, MethodPresence, nil, &p); err != nil {
		return Presence{}, err
	}
	return p, nil
}

func (c *Client) CreateReminder(ctx context.Context, fire time.Time, payload string) (int64, error) {
	var r idResp
	if err := c.call(ctx, MethodCreateReminder, createReminderReq{Fire: fire, Payload: payload}, &r); err != nil {
		return 0, err
	}
	return r.ID, nil
}

func (c *Client) MarkReminder(ctx context.Context, id int64, status string) error {
	return c.call(ctx, MethodMarkReminder, markReminderReq{ID: id, Status: status}, nil)
}

func (c *Client) RecordNudge(ctx context.Context, rule, channel, message string, ts time.Time) (int64, error) {
	var r idResp
	if err := c.call(ctx, MethodRecordNudge, recordNudgeReq{Rule: rule, Channel: channel, Message: message, Ts: ts}, &r); err != nil {
		return 0, err
	}
	return r.ID, nil
}

func (c *Client) ResolveNudge(ctx context.Context, id int64, outcome string, ts time.Time) error {
	return c.call(ctx, MethodResolveNudge, resolveNudgeReq{ID: id, Outcome: outcome, Ts: ts}, nil)
}

func (c *Client) RecentOutcomes(ctx context.Context, rule string, n int) ([]string, error) {
	var out []string
	if err := c.call(ctx, MethodRecentOutcomes, outcomesReq{Rule: rule, N: n}, &out); err != nil {
		return nil, err
	}
	return out, nil
}

func (c *Client) RecentFacts(ctx context.Context, n int) ([]Fact, error) {
	var out []Fact
	if err := c.call(ctx, MethodRecentFacts, nReq{N: n}, &out); err != nil {
		return nil, err
	}
	return out, nil
}

func (c *Client) RecentNudges(ctx context.Context, n int) ([]Nudge, error) {
	var out []Nudge
	if err := c.call(ctx, MethodRecentNudges, nReq{N: n}, &out); err != nil {
		return nil, err
	}
	return out, nil
}

func (c *Client) WriteNote(ctx context.Context, ts time.Time, text string, embedding []float32, source string) (int64, error) {
	var r idResp
	if err := c.call(ctx, MethodWriteNote, writeNoteReq{Ts: ts, Text: text, Embedding: embedding, Source: source}, &r); err != nil {
		return 0, err
	}
	return r.ID, nil
}

func (c *Client) QueryNotes(ctx context.Context, embedding []float32, k int) ([]Note, error) {
	var out []Note
	if err := c.call(ctx, MethodQueryNotes, queryNotesReq{Embedding: embedding, K: k}, &out); err != nil {
		return nil, err
	}
	return out, nil
}

func (c *Client) RecentNotes(ctx context.Context, n int) ([]Note, error) {
	var out []Note
	if err := c.call(ctx, MethodRecentNotes, nReq{N: n}, &out); err != nil {
		return nil, err
	}
	return out, nil
}

func (c *Client) ProposeTool(ctx context.Context, name, utterance string, ts time.Time) (bool, error) {
	var r proposeToolResp
	if err := c.call(ctx, MethodProposeTool, proposeToolReq{Name: name, Utterance: utterance, Ts: ts}, &r); err != nil {
		return false, err
	}
	return r.Proposed, nil
}

func (c *Client) EnableTool(ctx context.Context, name string, cmd []string, destructive bool, ts time.Time) error {
	return c.call(ctx, MethodEnableTool, enableToolReq{Name: name, Cmd: cmd, Destructive: destructive, Ts: ts}, nil)
}

func (c *Client) DisableTool(ctx context.Context, name string) error {
	return c.call(ctx, MethodDisableTool, disableToolReq{Name: name}, nil)
}

func (c *Client) AssertStepUp(ctx context.Context) error {
	return c.call(ctx, MethodAssertStepUp, nil, nil)
}

func (c *Client) LookupTool(ctx context.Context, name string) (Tool, error) {
	var t Tool
	if err := c.call(ctx, MethodLookupTool, lookupToolReq{Name: name}, &t); err != nil {
		return Tool{}, err
	}
	return t, nil
}

func (c *Client) ListTools(ctx context.Context, status string) ([]Tool, error) {
	var r listToolsResp
	if err := c.call(ctx, MethodListTools, listToolsReq{Status: status}, &r); err != nil {
		return nil, err
	}
	return r.Tools, nil
}

// Compile-time check: *Client satisfies CoreAPI.
var _ CoreAPI = (*Client)(nil)