package clawdforge

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"strings"
	"sync"
	"sync/atomic"
)

// ---------- v0.2: multi-turn Session API ------------------------------------
//
// The Session surface is purely additive — v0.1 callers (Client.Run,
// Client.UploadFile, etc.) keep their byte-identical behavior. The session
// methods wrap the server's /sessions/* endpoints introduced in v0.2.

// SessionOptions configures Client.NewSession. Both fields are optional; the
// zero value yields agent="claude" with no metadata.
type SessionOptions struct {
	// Agent is the ACPX agent to drive (default "claude" server-side when
	// blank). Mirrors the server's CreateSessionRequest.agent field.
	Agent string
	// Meta is an arbitrary JSON-serializable map persisted on the server's
	// session ledger. Useful for app-side correlation.
	Meta map[string]any
}

// TurnOption is the optional argument for Session.Turn. Multiple options
// passed are merged left-to-right (last non-zero field wins per field).
type TurnOption struct {
	// Files is a slice of file_token values previously returned by
	// Client.UploadFile / Client.UploadReader. Resolved server-side.
	Files []string
	// TimeoutMs is the per-turn timeout in milliseconds. Zero means use
	// the server's default. Note the server field is `timeout_secs`; the
	// SDK exposes ms here for symmetry with TurnResult.DurationMs and
	// converts on the wire (rounded up).
	TimeoutMs int
}

// TurnEvent is one structured event emitted during a turn — typed text,
// thinking, or a tool-call record. Fields not present on a given event type
// are zero-valued. Mirrors the server's event shape from acpx_runner.
type TurnEvent struct {
	Type    string         `json:"type"`
	Content string         `json:"content,omitempty"`
	Name    string         `json:"name,omitempty"`
	Args    map[string]any `json:"args,omitempty"`
	Result  any            `json:"result,omitempty"`
}

// TurnResult is the parsed response from POST /sessions/{id}/turn on success.
//
// Use Text() to concatenate just the "text" events into a single string,
// dropping thinking/tool_call frames.
type TurnResult struct {
	Ok         bool        `json:"ok"`
	SessionID  string      `json:"session_id"`
	TurnIndex  int         `json:"turn_index"`
	Events     []TurnEvent `json:"events"`
	StopReason string      `json:"stop_reason"`
	DurationMs int         `json:"duration_ms"`
}

// Text concatenates the Content of every event whose Type == "text",
// in order. Non-text events (thinking, tool_call) are skipped. Use this
// when you want the model's user-facing reply only.
func (r *TurnResult) Text() string {
	if r == nil || len(r.Events) == 0 {
		return ""
	}
	var b strings.Builder
	for _, ev := range r.Events {
		if ev.Type == "text" {
			b.WriteString(ev.Content)
		}
	}
	return b.String()
}

// SessionState is the parsed response from GET /sessions/{id}. Mirrors the
// server's session-state shape; LastTurnAt and ClosedAt are pointers because
// they're nullable until the first turn / first close.
type SessionState struct {
	SessionID  string `json:"session_id"`
	Agent      string `json:"agent"`
	AppName    string `json:"app_name,omitempty"`
	CreatedAt  int64  `json:"created_at"`
	LastTurnAt *int64 `json:"last_turn_at"`
	TurnCount  int    `json:"turn_count"`
	ClosedAt   *int64 `json:"closed_at"`
}

// Session is a handle to a multi-turn session on the server. Construct via
// Client.NewSession. Methods are safe for concurrent use; Turn calls on the
// same session are serialized via an internal mutex so the server sees them
// in order.
//
// Always Close the session when you're done — Close is idempotent (a second
// call short-circuits without a network round-trip via an atomic flag).
//
//	s, err := client.NewSession(ctx, nil)
//	if err != nil { ... }
//	defer s.Close(ctx)
type Session struct {
	client    *Client
	sessionID string
	agent     string
	createdAt int64

	// closed short-circuits the second Close call without hitting the
	// network. The server is itself idempotent, but this saves the round
	// trip and makes Close safe to call from any number of defers.
	closed atomic.Bool

	// turnMu serializes concurrent Turn calls on the same session so the
	// server observes them in caller-determined order. Per-session, NOT
	// global — different sessions on the same Client never block each
	// other.
	turnMu sync.Mutex
}

// ID returns the server-assigned session id.
func (s *Session) ID() string { return s.sessionID }

// Agent returns the agent name the session was created against
// (default "claude").
func (s *Session) Agent() string { return s.agent }

// CreatedAt returns the unix timestamp the server recorded at create time.
func (s *Session) CreatedAt() int64 { return s.createdAt }

// ---------- Client session methods ------------------------------------------

// createSessionResponse is the wire shape of POST /sessions on success.
type createSessionResponse struct {
	OK        bool   `json:"ok"`
	SessionID string `json:"session_id"`
	Agent     string `json:"agent"`
	CreatedAt int64  `json:"created_at"`
	Cwd       string `json:"cwd,omitempty"`
}

// NewSession issues POST /sessions and returns a *Session handle for
// follow-up Turn / Close / state calls.
//
// opts may be nil for the all-default case (agent="claude", no meta).
//
// Errors mirror the rest of the SDK: 401/403 → ErrAuth, transport failures
// → *TransportError, other non-2xx → *APIError.
func (c *Client) NewSession(ctx context.Context, opts *SessionOptions) (*Session, error) {
	body := struct {
		Agent string         `json:"agent,omitempty"`
		Meta  map[string]any `json:"meta,omitempty"`
	}{}
	if opts != nil {
		body.Agent = opts.Agent
		body.Meta = opts.Meta
	}
	buf, err := json.Marshal(body)
	if err != nil {
		return nil, fmt.Errorf("clawdforge: marshal SessionOptions: %w", err)
	}
	req, err := c.newRequest(ctx, http.MethodPost, "/sessions", bytes.NewReader(buf), "application/json")
	if err != nil {
		return nil, err
	}
	var out createSessionResponse
	if err := c.do(req, &out); err != nil {
		return nil, err
	}
	if out.SessionID == "" {
		return nil, errors.New("clawdforge: NewSession: server returned empty session_id")
	}
	return &Session{
		client:    c,
		sessionID: out.SessionID,
		agent:     out.Agent,
		createdAt: out.CreatedAt,
	}, nil
}

// GetSession issues GET /sessions/{id} and returns the server's view of the
// session — turn count, timestamps, closed state, etc. A 404 on a session
// that exists under a different token (cross-token access) surfaces as
// *APIError with StatusCode==404, matching the server's
// no-existence-leak design.
func (c *Client) GetSession(ctx context.Context, sessionID string) (*SessionState, error) {
	if sessionID == "" {
		return nil, errors.New("clawdforge: GetSession: sessionID is required")
	}
	req, err := c.newRequest(ctx, http.MethodGet, "/sessions/"+url.PathEscape(sessionID), nil, "")
	if err != nil {
		return nil, err
	}
	var out SessionState
	if err := c.do(req, &out); err != nil {
		return nil, err
	}
	return &out, nil
}

// listSessionsResponse is the wire shape of GET /sessions.
type listSessionsResponse struct {
	OK       bool           `json:"ok"`
	Sessions []SessionState `json:"sessions"`
	Count    int            `json:"count"`
}

// ListSessions issues GET /sessions and returns every session visible to the
// calling token (per-app isolation is enforced server-side). The result
// includes closed-but-not-yet-hard-deleted sessions by default.
func (c *Client) ListSessions(ctx context.Context) ([]SessionState, error) {
	req, err := c.newRequest(ctx, http.MethodGet, "/sessions", nil, "")
	if err != nil {
		return nil, err
	}
	var out listSessionsResponse
	if err := c.do(req, &out); err != nil {
		return nil, err
	}
	return out.Sessions, nil
}

// ---------- Session methods -------------------------------------------------

// turnRequestBody is the wire shape of POST /sessions/{id}/turn.
type turnRequestBody struct {
	Prompt      string   `json:"prompt"`
	Files       []string `json:"files,omitempty"`
	TimeoutSecs int      `json:"timeout_secs,omitempty"`
}

// Turn sends a prompt to the session and returns the structured result —
// the full event batch, stop reason, and timing. Multiple TurnOption values
// are merged; later values override earlier ones per-field when non-zero.
//
// Concurrent Turn calls on the same Session are serialized by an internal
// mutex so the server observes them in caller-determined order. Different
// sessions on the same Client never block each other.
func (s *Session) Turn(ctx context.Context, prompt string, opts ...TurnOption) (*TurnResult, error) {
	if s == nil {
		return nil, errors.New("clawdforge: Turn called on nil *Session")
	}
	if prompt == "" {
		return nil, errors.New("clawdforge: Turn: prompt is required")
	}
	if s.closed.Load() {
		return nil, errors.New("clawdforge: Turn called on closed session")
	}

	// Merge options left-to-right; non-zero fields override.
	body := turnRequestBody{Prompt: prompt}
	for _, o := range opts {
		if len(o.Files) > 0 {
			body.Files = o.Files
		}
		if o.TimeoutMs > 0 {
			// Server takes seconds; round UP so a sub-second SDK timeout
			// doesn't degrade to 0 (= "use default") on the wire.
			secs := o.TimeoutMs / 1000
			if o.TimeoutMs%1000 != 0 {
				secs++
			}
			body.TimeoutSecs = secs
		}
	}

	buf, err := json.Marshal(body)
	if err != nil {
		return nil, fmt.Errorf("clawdforge: marshal Turn body: %w", err)
	}

	// Serialize concurrent Turns on the same session. Held for the entire
	// HTTP round-trip so the server sees ordered prompt arrivals — the
	// real ordering constraint lives at the model/agent layer, but the
	// SDK can at least guarantee the request ordering it dispatches.
	s.turnMu.Lock()
	defer s.turnMu.Unlock()

	req, err := s.client.newRequest(
		ctx,
		http.MethodPost,
		"/sessions/"+url.PathEscape(s.sessionID)+"/turn",
		bytes.NewReader(buf),
		"application/json",
	)
	if err != nil {
		return nil, err
	}
	var out TurnResult
	if err := s.client.do(req, &out); err != nil {
		return nil, err
	}
	return &out, nil
}

// closeResponse is the wire shape of DELETE /sessions/{id}.
type closeResponse struct {
	OK            bool `json:"ok"`
	AlreadyClosed bool `json:"already_closed,omitempty"`
}

// Close issues DELETE /sessions/{id} to soft-close the session server-side.
//
// Close is idempotent — the second and subsequent calls short-circuit via
// an atomic flag without a network round-trip. The server's close endpoint
// is itself idempotent (returns {ok:true, already_closed:true} on a second
// hit), but the local short-circuit saves the request round-trip in the
// common defer-Close pattern.
//
// Safe to call from defer / cleanup paths regardless of prior state.
func (s *Session) Close(ctx context.Context) error {
	if s == nil {
		return nil
	}
	// CompareAndSwap so only one caller wins the network call when many
	// defers race. Subsequent callers see the flag already set and return
	// nil without contacting the server.
	if !s.closed.CompareAndSwap(false, true) {
		return nil
	}
	req, err := s.client.newRequest(
		ctx,
		http.MethodDelete,
		"/sessions/"+url.PathEscape(s.sessionID),
		nil,
		"",
	)
	if err != nil {
		// Roll the flag back so the caller can retry — Close failing on
		// network setup shouldn't strand the session as "locally closed
		// but actually open server-side" with no way to retry.
		s.closed.Store(false)
		return err
	}
	var out closeResponse
	if err := s.client.do(req, &out); err != nil {
		s.closed.Store(false)
		return err
	}
	return nil
}