package sessionread

import (
	"context"
	"fmt"
	"io"
	"log/slog"
	"strings"
	"time"

	"git.yeij.top/AskaEth/Cyrene_v2/internal/logger"
	"git.yeij.top/AskaEth/Cyrene_v2/pkg/plugins/sdk"
)

// ToolName is the registered tool name the model calls to read another session's
// context (design/22 §8.1 工具形态).
const ToolName = "session_read"

// Compile-time assertion that Tool implements sdk.Tool.
var _ sdk.Tool = (*Tool)(nil)

// Tool is the agent-facing shell of the cross-session read: it parses the tool
// arguments, delegates to Reader for the fail-closed authorization and the read,
// and hands the model the formatted material.
//
// It is safe for concurrent use and holds no per-call state.
type Tool struct {
	reader *Reader
}

// Option customizes the Tool (and the Reader behind it) built by New.
type Option func(*Reader)

// WithHistory injects the read-only history view the material is read from.
// *history.Store satisfies it. Without it every call fails with ErrNoHistory.
func WithHistory(h HistoryReader) Option {
	return func(r *Reader) { r.history = h }
}

// WithPersonas injects the role-name lookup used for the attribution labels.
// Without it the material shows raw role ids (no name is invented).
func WithPersonas(p PersonaNamer) Option {
	return func(r *Reader) { r.personas = p }
}

// WithLocation sets the timezone the timestamps are rendered in. A nil location
// keeps time.Local, matching the process-wide convention. The composition root
// passes the configured TZ so the material reads in the same clock as the loop's
// per-round "current time" injection.
func WithLocation(loc *time.Location) Option {
	return func(r *Reader) {
		if loc != nil {
			r.loc = loc
		}
	}
}

// WithLogger replaces the reader's logger (tagged source "runtime/sessionread").
func WithLogger(l *slog.Logger) Option {
	return func(r *Reader) { r.log = sourceLog(l) }
}

// New builds the tool over the injected dependencies. A tool built without a
// history reader still constructs (the composition root can log and refuse to
// register it); every call then fails with ErrNoHistory.
func New(opts ...Option) *Tool {
	r := &Reader{loc: time.Local, log: sourceLog(nil)}
	for _, opt := range opts {
		if opt != nil {
			opt(r)
		}
	}
	if r.personas == nil {
		r.personas = noPersonaNames{}
	}
	return &Tool{reader: r}
}

// Name returns the tool identifier.
func (t *Tool) Name() string { return ToolName }

// Description explains the tool to the model: it reads someone else's session as
// *external, read-only material* that is explicitly not the caller's own memory or
// voice (design/22 §8-3 的原意), reachable only for the Web sessions.
func (t *Tool) Description() string {
	return "Read another session's recent messages as external, read-only material. " +
		"The result is a transcript prefixed with a fixed attribution header naming the source role " +
		"and source session, so it is explicitly NOT your own memory and not your own words — never " +
		"quote or continue it as if you had said it. Only the Web main session (\"web\") and Web sub " +
		"sessions (\"web:<uuid>\") can be read, only from the owner's conversation; the target " +
		"session's read cursor is not advanced and nothing is written."
}

// Parameters returns the input JSON Schema (design/22 §8.1 参数表). No "maximum"
// bound is declared on limit on purpose: a limit above the cap is clamped in
// Execute (mirroring GET /sessions/{id}/messages) instead of being rejected as an
// invalid argument.
func (t *Tool) Parameters() (map[string]any, error) {
	return map[string]any{
		"type": "object",
		"properties": map[string]any{
			"sessionId": map[string]any{
				"type": "string",
				"description": "Target session id to read: the Web main session \"web\" or a Web sub " +
					"session \"web:<uuid>\". Any other session id is rejected.",
			},
			"limit": map[string]any{
				"type":        "integer",
				"description": "Max messages to return (optional, default 50, capped at 200).",
			},
			"before": map[string]any{
				"type": "integer",
				"description": "Millisecond cursor: return only messages older than it, to page further " +
					"back (optional; omit for the newest page).",
			},
		},
		"required": []any{"sessionId"},
	}, nil
}

// Execute reads the requested session and returns the formatted material.
//
// The return value is a plain string, not a struct: the loop renders a string tool
// result verbatim (loop.formatToolResult passes strings through, while any other
// value is JSON-encoded and would escape every newline), and the material is
// line-oriented text whose attribution header must survive intact.
func (t *Tool) Execute(ctx context.Context, args any) (any, error) {
	m, ok := args.(map[string]any)
	if !ok {
		return nil, fmt.Errorf("%s: args must be an object", ToolName)
	}
	sessionID := strings.TrimSpace(stringArg(m, "sessionId"))
	if sessionID == "" {
		return nil, fmt.Errorf("%s: sessionId is required", ToolName)
	}
	text, err := t.reader.Read(ctx, Request{
		SessionID: sessionID,
		Limit:     intArg(m, "limit"),
		Before:    int64(intArg(m, "before")),
	})
	if err != nil {
		return nil, fmt.Errorf("%s: %w", ToolName, err)
	}
	return text, nil
}

// stringArg reads a string argument, tolerating a missing or non-string value.
func stringArg(m map[string]any, key string) string {
	s, _ := m[key].(string)
	return s
}

// intArg reads an integer argument, tolerating a missing, non-numeric or
// fractional value (0 then means "not supplied", which every caller treats as its
// own default). A decoded-JSON number arrives as float64, hence the type switch.
func intArg(m map[string]any, key string) int {
	switch v := m[key].(type) {
	case int:
		return v
	case int32:
		return int(v)
	case int64:
		return int(v)
	case float32:
		return int(v)
	case float64:
		return int(v)
	default:
		return 0
	}
}

// sourceLog returns l tagged with source "runtime/sessionread", replacing a nil
// logger with a discard one so the reader can always log.
func sourceLog(l *slog.Logger) *slog.Logger {
	if l == nil {
		l = slog.New(slog.NewTextHandler(io.Discard, nil))
	}
	return logger.WithSource(l, "runtime/sessionread")
}