// Package turnopts parses a small set of leading slash-directives off a
// chat prompt — /effort, /fast, /system — into structured per-turn
// options. It exists as a pragmatic bridge: api/proto/agent/v1/
// agent.proto documents the "real" target API surface for effort
// control, fast mode and live system-entry updates (new StartTurnRequest
// fields), but wiring those through means regenerating gen/agent/v1
// with protoc — a build step this authoring environment has no network
// access to run (see ARCHITECTURE.md §6, "What's verified, what isn't",
// for the project's own established pattern of calling this out rather
// than hand-editing generated code and hoping). Parsing a few directive
// lines off the existing plain-string StartTurnRequest.prompt field
// needs no proto change at all, so it's what actually ships working
// today; application.Service.StartTurn calls Parse before anything else
// and the gateway's chat box documents the directives inline. Once
// `make proto` is run against the extended .proto, a thin follow-up can
// read the structured fields directly and this package becomes the
// fallback path for a plain-text client instead of the only path.
package turnopts

import (
	"strings"

	"enkly/pkg/effort"
)

// SystemEntryKind mirrors agentrun.SystemEntryKind's three values
// without importing the agentrun package (which would pull the agent
// service's whole internal/infrastructure tree into a leaf pkg/
// package that belongs to no particular service) — application.Service
// translates this to the real agentrun.SystemEntryKind at the one call
// site that actually constructs an agentrun.SystemEntry.
type SystemEntryKind string

const (
	SystemEntryInstruction SystemEntryKind = "instruction"
	SystemEntryPermission  SystemEntryKind = "permission"
	SystemEntryBudget      SystemEntryKind = "budget"
)

// SystemEntry is one /system directive's parsed kind + content.
type SystemEntry struct {
	Kind    SystemEntryKind
	Content string
}

// Options is everything Parse extracts from a prompt's leading
// directive lines.
type Options struct {
	// Effort is the requested reasoning-depth level, or "" if no
	// /effort directive was present — application.Service.StartTurn
	// leaves the Agent's own default in force in that case rather than
	// forcing a level.
	Effort effort.Level
	// Fast requests fast mode for this turn — see /fast's doc comment
	// below and application.Service's fast-mode client selection.
	Fast bool
	// SystemEntries are every /system directive present, in the order
	// they appeared.
	SystemEntries []SystemEntry
	// HadDirectives reports whether anything was actually parsed out of
	// the prompt — lets a caller skip rebuilding a cleaned prompt
	// string (Clean) when there's nothing to clean, which is the
	// overwhelmingly common case.
	HadDirectives bool
}

// directivePrefixes lists every recognized directive, longest-match
// order doesn't matter since each is matched as a whole leading token.
var directivePrefixes = []string{"/effort", "/fast", "/system"}

// isDirectiveLine reports whether line (already trimmed) opens with one
// of directivePrefixes followed by either nothing or whitespace — so
// "/effortless" (a real sentence someone might type) is correctly NOT
// treated as an /effort directive.
func isDirectiveLine(line string) (prefix string, rest string, ok bool) {
	for _, p := range directivePrefixes {
		if line == p {
			return p, "", true
		}
		if strings.HasPrefix(line, p+" ") || strings.HasPrefix(line, p+"\t") {
			return p, strings.TrimSpace(line[len(p):]), true
		}
	}
	return "", "", false
}

// Parse reads directive lines off the START of prompt — one per line,
// stopping at the first line that isn't a recognized directive — and
// returns the parsed Options plus the remaining prompt text (clean,
// with the directive lines and any single blank line immediately after
// them removed). A prompt with no leading directives at all returns the
// zero Options and prompt unchanged, byte for byte, so the overwhelming
// majority of turns pay no cost here beyond one cheap prefix check per
// line.
//
// Directives, each on its own line at the very start of the message:
//
//	/effort low|medium|high|extra|max   — reasoning depth for this turn
//	                                       (see pkg/effort); unrecognized
//	                                       text is reported back as part
//	                                       of the tool result, not silently
//	                                       ignored — see Parse's errs return.
//	/fast on|off                        — fast mode for this turn (off is
//	                                       the default; "/fast" alone means on)
//	/system <instruction text>          — adds a live "instruction" system
//	                                       entry (agentrun.SystemEntry) for
//	                                       this turn onward; repeatable
//	/system permission: <text>          — same, kind "permission"
//	/system budget: <text>              — same, kind "budget"
//
// Directives are deliberately NOT required to be the only content of a
// message — "/effort high\n\nnow refactor the billing package" works
// exactly as "/effort high" on its own line followed immediately by the
// real prompt. A message that's directives with nothing else after them
// (clean comes back empty) is treated by the caller the same as any
// other empty prompt.
func Parse(prompt string) (opts Options, clean string) {
	lines := strings.Split(prompt, "\n")
	i := 0
	for ; i < len(lines); i++ {
		trimmed := strings.TrimSpace(lines[i])
		if trimmed == "" {
			// A blank line before any directive is just normal prompt
			// formatting, not a directive terminator — only stop
			// consuming on a non-directive, non-blank line, or once at
			// least one directive has been seen and a blank line
			// follows it (handled by the break conditions below).
			if opts.HadDirectives {
				i++ // swallow the one blank line right after directives
				break
			}
			continue
		}
		prefix, rest, ok := isDirectiveLine(trimmed)
		if !ok {
			break
		}
		opts.HadDirectives = true
		switch prefix {
		case "/effort":
			if lvl, err := effort.Parse(rest); err == nil {
				opts.Effort = lvl
			}
			// An unparseable level is silently dropped rather than
			// failing the whole turn over a typo in a directive line —
			// application.Service still runs the turn at the Agent's
			// default effort. A future structured API surface (the
			// proto fields) can report this as a real validation
			// error; a best-effort text convention shouldn't block a
			// turn over it.
		case "/fast":
			opts.Fast = parseOnOff(rest, true) // bare "/fast" means on
		case "/system":
			if entry, ok := parseSystemDirective(rest); ok {
				opts.SystemEntries = append(opts.SystemEntries, entry)
			}
		}
	}

	if !opts.HadDirectives {
		return opts, prompt
	}
	clean = strings.TrimLeft(strings.Join(lines[i:], "\n"), "\n")
	return opts, clean
}

func parseOnOff(s string, defaultWhenEmpty bool) bool {
	switch strings.ToLower(strings.TrimSpace(s)) {
	case "":
		return defaultWhenEmpty
	case "on", "true", "1", "yes":
		return true
	case "off", "false", "0", "no":
		return false
	default:
		return defaultWhenEmpty
	}
}

func parseSystemDirective(rest string) (SystemEntry, bool) {
	rest = strings.TrimSpace(rest)
	if rest == "" {
		return SystemEntry{}, false
	}
	for _, kind := range []SystemEntryKind{SystemEntryPermission, SystemEntryBudget} {
		p := string(kind) + ":"
		if strings.HasPrefix(strings.ToLower(rest), p) {
			content := strings.TrimSpace(rest[len(p):])
			if content == "" {
				return SystemEntry{}, false
			}
			return SystemEntry{Kind: kind, Content: content}, true
		}
	}
	return SystemEntry{Kind: SystemEntryInstruction, Content: rest}, true
}