package mcp

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"strings"
	"time"

	"github.com/mathiasbq/hyperguild/ingestion/internal/brain"
	"github.com/mathiasbq/hyperguild/ingestion/internal/capture"
	"github.com/mathiasbq/hyperguild/ingestion/internal/claim"
	"github.com/mathiasbq/hyperguild/ingestion/internal/classification"
	"github.com/mathiasbq/hyperguild/ingestion/internal/notes"
)

// noteToolDescriptors are the model-facing halves of brain#4.
//
// brain_edit_root is deliberately absent: it dispatches but is not listed, the
// same de-surfacing ADR-0012 rule 4 applies to brain_index (#78). Hiding the
// verb matters here for a specific reason — brain content is ingested from the
// outside world and reaches a model's context, so a listed governance-file
// editor is a durable prompt-injection path: one poisoned page could rewrite
// the CLAUDE.md that a .dispatch-allow agent later obeys. A human who knows
// the tool exists can still call it; a model reading tools/list cannot
// discover it.
func noteToolDescriptors() []map[string]any {
	str := func(d string) map[string]any { return map[string]any{"type": "string", "description": d} }
	schema := func(required []string, props map[string]any) json.RawMessage {
		b, _ := json.Marshal(map[string]any{"type": "object", "required": required, "properties": props})
		return b
	}
	return []map[string]any{
		{
			"name": "brain_read",
			"description": "Return a note's raw markdown verbatim — no synthesis, no excerpting. " +
				"Use this to obtain the exact text before brain_edit; never build old_str from a " +
				"brain_query excerpt, which is truncated and normalised and will not match.",
			"inputSchema": schema([]string{"path"}, map[string]any{
				"path": str("brain-relative path under knowledge/ or wiki/, e.g. wiki/homelab/facts/x.md"),
			}),
		},
		{
			"name": "brain_edit",
			"description": "Replace exactly one occurrence of old_str with new_str in a note, leaving " +
				"every other byte identical. Fails loudly if old_str is absent or matches more than " +
				"once — extend old_str until it is unique. Does NOT stamp updated_at or supersedes " +
				"(brain_update does); it is a byte-level patch, not a metadata operation.",
			"inputSchema": schema([]string{"path", "old_str", "new_str"}, map[string]any{
				"path":    str("brain-relative path under knowledge/ or wiki/"),
				"old_str": str("exact text to replace; must occur exactly once"),
				"new_str": str("replacement text; empty string deletes old_str"),
			}),
		},
	}
}

// --- hyperguild#97: governance-rewrite observability -----------------------

// govNotifier raises an out-of-band alert. Declared here rather than importing
// internal/audit so the MCP package keeps depending on capture alone.
type govNotifier interface {
	Notify(ctx context.Context, msg string) error
}

// WithGovernanceObserver attaches the audit sink and notifier that observe a
// successful brain_edit_root. Both are optional; either may be nil.
func (s *Server) WithGovernanceObserver(sink capture.AuditSink, n govNotifier) {
	s.govAudit, s.govNotify = sink, n
}

type brainReadArgs struct {
	Path string `json:"path"`
}

func (s *Server) brainRead(_ context.Context, args json.RawMessage) (json.RawMessage, error) {
	var a brainReadArgs
	if err := json.Unmarshal(args, &a); err != nil {
		return nil, fmt.Errorf("parse args: %w", err)
	}
	content, err := notes.Read(s.brainDir, a.Path)
	if err != nil {
		return nil, err
	}
	return json.Marshal(map[string]any{"path": a.Path, "content": string(content)})
}

type brainEditArgs struct {
	Path   string `json:"path"`
	OldStr string `json:"old_str"`
	NewStr string `json:"new_str"`
}

// brainEdit is the model-facing editor: notes only.
//
// Deliberately NOT audited (#97). A note edit is already fully reconstructible
// from git history, which carries the same before/after bytes plus a diff.
// Governance files get the extra trail because they change what later agents
// obey — the asymmetry is about instruction-carrying content, not about how
// hard the change is to reconstruct. Auditing every note edit would also bury
// the rare governance record under routine traffic, which is how an alert
// stops being read.
func (s *Server) brainEdit(_ context.Context, args json.RawMessage) (json.RawMessage, error) {
	_, out, err := s.editWithScope(args, notes.ScopeNotes)
	return out, err
}

// brainEditRoot edits a governance file (CLAUDE.md). De-surfaced AND gated on
// the authenticated principal: only the static local-CLI token may call it, so
// a claude.ai-origin session — the one that may have just read an untrusted
// page — cannot rewrite the instructions later agents load.
func (s *Server) brainEditRoot(ctx context.Context, args json.RawMessage) (json.RawMessage, error) {
	info, ok := ctx.Value(principalKey).(principalInfo)
	if !ok || !info.viaStatic {
		return nil, fmt.Errorf("brain_edit_root requires the local static principal; " +
			"a governance file is not editable from a model-facing origin")
	}
	res, out, err := s.editWithScope(args, notes.ScopeRoot)
	if err != nil {
		// A refusal is not a rewrite. Recording or alerting on one would cry
		// wolf, and the gate already logs its own denials.
		return out, err
	}
	// A durable instruction rewrite should be loud, not silent.
	slog.Warn("brain_edit_root applied", "principal", info.principal, "result", string(out))
	s.observeGovernanceEdit(ctx, info.principal, res)
	return out, err
}

// observeGovernanceEdit records and alerts on a rewrite that already landed.
//
// Best-effort by construction: the bytes are written and brain-sync will commit
// them within the quarter hour, so failing the call here would report a
// non-rewrite to the caller while the rewrite sits on disk. A failure to
// observe is therefore logged at ERROR — the one case where the trail itself is
// what broke, and the only remaining signal.
func (s *Server) observeGovernanceEdit(ctx context.Context, principal string, res notes.Result) {
	// Path and hashes only. The notification leaves the cluster for a phone
	// via a third-party topic; a hash identifies the rewrite, the bytes would
	// leak whatever was written into an instruction file.
	msg := fmt.Sprintf("brain_edit_root applied\npath=%s\nprincipal=%s\nbefore=%s\nafter=%s",
		res.Path, principal, res.PrevContentHash, res.ContentHash)

	if s.govNotify != nil {
		if err := s.govNotify.Notify(ctx, msg); err != nil {
			slog.Error("brain_edit_root notify failed", "path", res.Path, "err", err)
		}
	}
	if s.govAudit == nil {
		return
	}
	// Internal, not Confidential: a governance file is not client data, and
	// Confidential would make DegradingSink REFUSE to record while loki is
	// down rather than buffer — losing exactly the record that matters most.
	outcome, err := s.govAudit.Reserve(ctx, classification.Internal)
	if err != nil {
		slog.Error("brain_edit_root audit reserve failed", "path", res.Path, "err", err)
		return
	}
	entry := capture.AuditEntry{
		Timestamp:               time.Now().UTC(),
		Principal:               principal,
		Actor:                   "brain_edit_root",
		Harness:                 "mcp",
		EffectiveClassification: classification.Internal.String(),
		Items:                   []string{res.Path},
		SecurityEvents: []string{fmt.Sprintf(
			"governance file rewritten: %s before=%s after=%s",
			res.Path, res.PrevContentHash, res.ContentHash)},
	}
	if err := s.govAudit.Record(ctx, entry, outcome); err != nil {
		slog.Error("brain_edit_root audit record failed", "path", res.Path, "err", err)
	}
}

func (s *Server) editWithScope(args json.RawMessage, scope notes.Scope) (notes.Result, json.RawMessage, error) {
	var a brainEditArgs
	if err := json.Unmarshal(args, &a); err != nil {
		return notes.Result{}, nil, fmt.Errorf("parse args: %w", err)
	}

	// hyperguild#123: brain_write/brain_update both validate the claim
	// envelope before writing (hyperguild#111: "same rules when a note
	// changes as when it's born"); brain_edit didn't — a byte-level string
	// replace has no frontmatter awareness at all, so it could rewrite an
	// existing half_life:/applies:/claim_provenance: line straight past the
	// validator entirely. Scoped to notes only (governance files have no
	// claim-envelope concept).
	if scope == notes.ScopeNotes {
		if verr := checkClaimEnvelope(s.brainDir, a.Path, a.OldStr, a.NewStr); verr != nil {
			return notes.Result{}, nil, fmt.Errorf("claim envelope: %w", verr)
		}
	}

	res, err := notes.Edit(s.brainDir, a.Path, a.OldStr, a.NewStr, scope)
	if err != nil {
		if errors.Is(err, notes.ErrDegenerate) && a.OldStr == "" {
			// hyperguild#115: "old_str is empty" alone doesn't say whether the
			// caller sent it empty or a hop between the caller and here lost
			// it. Naming the raw argument byte count makes that distinguishable
			// without a second investigation.
			return notes.Result{}, nil, fmt.Errorf("%w (raw arguments were %d bytes)", err, len(args))
		}
		return notes.Result{}, nil, err
	}

	// Reindex only when the edit could have changed what the index reads.
	// BuildWingIndex consumes title/created_at from the frontmatter block;
	// BM25 walks the filesystem live and embeddings are mtime-driven, so an
	// unconditional rebuild would buy nothing and dirty a second file —
	// _index.md being precisely the class brain-sync already needs a bespoke
	// conflict resolver for.
	if wing := wingOf(res.Path); wing != "" && touchesFrontmatter(a.OldStr, a.NewStr) {
		if ierr := brain.BuildWingIndex(s.brainDir, wing); ierr != nil {
			// Best-effort, matching every other index hook here: the write
			// already landed and will be committed, so failing the call would
			// make the caller retry an edit whose old_str no longer exists.
			res.ReindexError = ierr.Error()
		}
	}
	out, merr := json.Marshal(res)
	return res, out, merr
}

// wingOf returns the wing for a wiki path, or "" for knowledge/ and root.
func wingOf(rel string) string {
	parts := strings.Split(rel, "/")
	if len(parts) < 3 || parts[0] != "wiki" {
		return ""
	}
	return parts[1]
}

// touchesFrontmatter reports whether either side of the edit mentions a field
// the wing index reads.
func touchesFrontmatter(oldStr, newStr string) bool {
	for _, s := range []string{oldStr, newStr} {
		if strings.Contains(s, "title:") || strings.Contains(s, "created_at:") || strings.Contains(s, "---") {
			return true
		}
	}
	return false
}

// checkClaimEnvelope previews what old_str->new_str would produce — the
// exact strings.Replace(before, oldStr, newStr, 1) formula notes.Edit
// itself uses internally — and validates the resulting frontmatter's claim
// envelope before the real edit is allowed to run. Fail-closed: an invalid
// result blocks the edit entirely, the same posture writeHallNote/UpdateNote
// already apply on create/supersede.
//
// Gated on old_str appearing within the note's frontmatter BLOCK, not on
// old_str/new_str mentioning a claim-envelope field NAME — found in review:
// a field-name-substring gate misses a value-only edit like
// "asserted"->"guessed" on a claim_provenance line, which never mentions
// the field name at all. That is exactly the shape of edit a minimal,
// natural diff produces, so a field-name gate was closing the issue in
// name only. Checking block containment instead means any edit that
// couldn't possibly touch the frontmatter (its target text only exists in
// the body) is still skipped cheaply, while nothing inside the fence can
// slip through unvalidated regardless of which token it targets.
//
// This does not replicate notes.Edit's uniqueness/CRLF/conflict-marker
// checks — if old_str is absent or ambiguous, this preview may not match
// what Edit ultimately does, but Edit independently and correctly rejects
// those cases at write time regardless of what this function decides, so
// the only thing riding on this preview's accuracy is the envelope check
// itself, not write safety.
func checkClaimEnvelope(brainDir, path, oldStr, newStr string) error {
	if oldStr == "" {
		// hyperguild#115: strings.Replace treats "" as matching position 0,
		// which would make an empty old_str look like an edit that inserts
		// text before the fence — a degenerate-input case that belongs to
		// notes.Edit's own "old_str is empty" refusal, not to the envelope
		// check.
		return nil
	}
	before, err := notes.Read(brainDir, path)
	if err != nil {
		// Let notes.Edit itself produce the real error (missing file, etc.)
		// — this function's job is the envelope, not read failures.
		return nil
	}
	// No gate on where old_str falls relative to the frontmatter fence:
	// round 2 found that requiring old_str to be fully contained in the
	// extracted block was itself bypassable by an old_str disambiguated
	// across the closing "---" into the body. Simpler and bypass-proof:
	// always compute what the edit would produce and validate that
	// resulting state's envelope. A body-only edit leaves the frontmatter
	// (and thus the validation outcome) unchanged, so this is a no-op for
	// the common case and fail-closed for every case that touches the
	// envelope, regardless of how old_str is phrased.
	_, hadFence := frontmatterBlock(string(before))
	after := strings.Replace(string(before), oldStr, newStr, 1)
	_, hasFence := frontmatterBlock(after)
	if hadFence && !hasFence {
		// Round 3: an edit that drops the closing fence degrades `after`
		// to "unfenced" — frontmatterScalars then sees an empty map and
		// ValidateEnvelope({}) is nil by design (absent fields are valid),
		// so an invalid value would otherwise land with zero error while
		// also corrupting the note's structure. A previously-fenced note
		// must stay fenced, full stop.
		return fmt.Errorf("edit would remove the frontmatter fence")
	}
	return claim.ValidateEnvelope(frontmatterScalars(after))
}

// frontmatterBlock returns the raw text between doc's opening and closing
// `---` fences, or ok=false if doc has no (properly closed) fence.
func frontmatterBlock(doc string) (block string, ok bool) {
	if !strings.HasPrefix(doc, "---\n") {
		return "", false
	}
	rest := doc[len("---\n"):]
	end := strings.Index(rest, "\n---\n")
	if end < 0 {
		return "", false
	}
	return rest[:end], true
}

// frontmatterScalars extracts top-level "key: value" scalar pairs from
// doc's leading fence block, for the claim-envelope check only — not a
// general frontmatter parser. Indented lines (YAML block-list items,
// wrapped values) are skipped rather than misparsed as keys, same fix as
// hyperguild#126/#128 in the sibling packages this mirrors.
func frontmatterScalars(doc string) map[string]string {
	out := map[string]string{}
	block, ok := frontmatterBlock(doc)
	if !ok {
		return out
	}
	for _, line := range strings.Split(block, "\n") {
		if line != "" && (line[0] == ' ' || line[0] == '\t') {
			continue
		}
		key, val, ok := strings.Cut(line, ":")
		if !ok {
			continue
		}
		out[strings.TrimSpace(key)] = strings.TrimSpace(val)
	}
	return out
}