package mcpsrv

import (
	"context"
	"fmt"
	"strings"
	"time"

	"sourcecraft.dev/bigbes/sr-ht-spec/authn"
	"sourcecraft.dev/bigbes/sr-ht-spec/service"
)

// Commenter is everything spec_comment may reach, and the list is short on
// purpose: read the threads, read the revision they are anchored against, and
// append a reply.
//
// What it leaves out is the load-bearing part. *service.Service also has
// CommentOn and ResolveThread, and both are owner-only there; naming them here
// would be harmless today and a regression the first time somebody relaxed the
// service-side check. An unresolved thread suppresses policy auto-merge, so an
// agent that could open or resolve one would hold the gate that exists to hold
// its own output back. The handler is written against this interface rather
// than against Writer so that "the comment tool cannot resolve a thread" is a
// property of the types, not of the handler remembering not to.
type Commenter interface {
	Threads(ctx context.Context, p authn.Principal, proposalID int) ([]service.Thread, error)
	ReplyTo(ctx context.Context, p authn.Principal, threadID int, body string) (service.Comment, error)
	GetProposal(ctx context.Context, id int) (service.Proposal, error)
	ProposalDiff(ctx context.Context, p service.Proposal) ([]service.ProposalDoc, error)
}

type commentInput struct {
	Proposal int `json:"proposal" jsonschema:"the proposal whose review threads to read, or whose thread to reply to — the id spec_propose returned"`
	// Thread and Body together are the reply; omitting both lists.
	Thread int    `json:"thread,omitempty" jsonschema:"reply to this thread, given as the thread id from a listing. Omit both this and body to list the proposal's threads instead."`
	Body   string `json:"body,omitempty" jsonschema:"the reply text, required when thread is given"`
}

// commentAuthor is one message: a thread's root or a reply. Times are formatted
// strings rather than time.Time because the tool's schema is derived from this
// struct by reflection, and a time.Time would reach the agent as an object with
// no fields.
type commentAuthor struct {
	ID int `json:"id"`
	// Thread is the id of the thread this message belongs to. On a root it is
	// its own id, which is the value to send back as the thread argument.
	Thread int    `json:"thread"`
	Author string `json:"author"`
	// Agent reports whether an agent wrote this, so a reply of one's own is
	// distinguishable from the owner's critique without parsing the name.
	Agent   bool   `json:"agent"`
	Body    string `json:"body"`
	Created string `json:"created"`
}

type commentThread struct {
	commentAuthor
	// Document is the path of the document the thread is on, and DocID the
	// archive key its anchor was written against — the anchor survives a rename,
	// so the two can disagree.
	Document string `json:"document"`
	DocID    string `json:"doc_id,omitempty"`
	// Heading is the enclosing headings of the commented block, outermost
	// first. With Document it is how to find the block being talked about.
	Heading []string `json:"heading,omitempty"`
	// Side is which revision of the block was commented on: "new" for the
	// proposed text, "old" for a block the proposal deletes.
	Side string `json:"side,omitempty"`
	// State is how well the anchor still fits the CURRENT proposal branch:
	// "anchored" (the block is there verbatim), "edited" (the block is at that
	// position but its text has changed since the comment) or "outdated" (the
	// anchor lost its block). Acting on an outdated critique is the failure this
	// field exists to prevent.
	State string `json:"state"`
	// Block is the block's index in the document, or -1 when the anchor is
	// outdated and points at nothing.
	Block int `json:"block"`
	// Open reports whether the thread still awaits the owner. Only the owner can
	// close one; a reply never does.
	Open    bool            `json:"open"`
	Replies []commentAuthor `json:"replies,omitempty"`
}

type commentOutput struct {
	Proposal int `json:"proposal"`
	// Threads is set when listing, and empty when the proposal has no review
	// threads at all — which is a proposal nobody has commented on, not an
	// error.
	Threads []commentThread `json:"threads,omitempty"`
	// Reply is set when replying, and carries the stored reply as it was
	// attributed: an agent's reply comes back under its own agent identity.
	Reply *commentAuthor `json:"reply,omitempty"`
}

func commentHandler(ctx context.Context, c Commenter, in commentInput) (commentOutput, error) {
	if in.Proposal <= 0 {
		return commentOutput{}, fmt.Errorf("proposal must name a proposal id")
	}
	// The mode is chosen on whether body was sent at all, not on whether it has
	// anything in it: a whitespace body is a caller that meant to reply and
	// botched it, and quietly listing instead would look like the reply landed.
	body := strings.TrimSpace(in.Body)
	switch {
	case in.Thread > 0 && body == "":
		return commentOutput{}, fmt.Errorf("a reply to thread %d needs a body", in.Thread)
	case in.Thread <= 0 && in.Body != "":
		return commentOutput{}, fmt.Errorf("body needs the thread it answers; pass thread, " +
			"or omit body to list this proposal's threads")
	}

	// The principal is the one the resolver middleware put on this request.
	// service.Threads and service.ReplyTo apply the ACL — this layer forwards
	// the caller rather than deciding anything, so the read plane has one policy.
	principal := authn.PrincipalFromContext(ctx)

	// Threads runs before anything touches git, in both modes. It is one query,
	// it is where the ACL is enforced, and a proposal with no threads needs no
	// revision read at all.
	threads, err := c.Threads(ctx, principal, in.Proposal)
	if err != nil {
		return commentOutput{}, err
	}

	if in.Thread > 0 {
		return replyToThread(ctx, c, principal, threads, in.Proposal, in.Thread, body)
	}
	return listThreads(ctx, c, threads, in.Proposal)
}

// listThreads resolves every anchor against the proposal branch as it stands
// now and reports the fit.
//
// The anchoring is not optional decoration. A thread's stored anchor says where
// the comment was written, and the branch has moved since — often because this
// very agent revised it. An agent asking "what should I fix" that is not told
// the critique no longer describes any block will go and fix the wrong
// paragraph, so the state travels with every thread.
func listThreads(ctx context.Context, c Commenter, threads []service.Thread, proposalID int) (commentOutput, error) {
	out := commentOutput{Proposal: proposalID}
	if len(threads) == 0 {
		return out, nil
	}

	p, err := c.GetProposal(ctx, proposalID)
	if err != nil {
		return commentOutput{}, err
	}
	docs, err := c.ProposalDiff(ctx, p)
	if err != nil {
		return commentOutput{}, err
	}

	out.Threads = make([]commentThread, 0, len(threads))
	for _, t := range service.AnchorThreads(threads, docs) {
		out.Threads = append(out.Threads, threadEntry(t))
	}
	return out, nil
}

// replyToThread appends the reply, after checking the thread is one of this
// proposal's.
//
// A thread id is a global integer, so a mistyped one names a real thread on
// somebody else's proposal, and service.ReplyTo would accept it: the id is all
// it needs. Requiring the proposal and checking membership here turns that
// typo into an error instead of a reply that lands out of sight of the agent
// that wrote it. The threads were already read for the ACL check, so it costs
// nothing.
func replyToThread(ctx context.Context, c Commenter, p authn.Principal, threads []service.Thread, proposalID, threadID int, body string) (commentOutput, error) {
	found := false
	for _, t := range threads {
		if t.Root.ID == threadID {
			found = true
			break
		}
	}
	if !found {
		return commentOutput{}, fmt.Errorf("proposal %d has no review thread %d; "+
			"call spec_comment with only proposal to list its threads", proposalID, threadID)
	}

	reply, err := c.ReplyTo(ctx, p, threadID, body)
	if err != nil {
		return commentOutput{}, err
	}
	entry := authorEntry(reply)
	return commentOutput{Proposal: proposalID, Reply: &entry}, nil
}

func threadEntry(t service.Thread) commentThread {
	e := commentThread{
		commentAuthor: authorEntry(t.Root),
		Document:      t.DocPath,
		DocID:         t.Anchor.DocID,
		Heading:       t.Anchor.HeadingPath,
		Side:          string(t.Anchor.Side),
		State:         string(t.State),
		Block:         t.Block,
		Open:          t.Open(),
	}
	// A root's thread id is its own id: that is the value spec_comment takes
	// back as the thread argument.
	e.Thread = t.Root.ID
	for _, r := range t.Replies {
		e.Replies = append(e.Replies, authorEntry(r))
	}
	return e
}

func authorEntry(c service.Comment) commentAuthor {
	return commentAuthor{
		ID:      c.ID,
		Thread:  c.ParentID,
		Author:  c.Author,
		Agent:   c.Agent,
		Body:    c.Body,
		Created: c.Created.UTC().Format(time.RFC3339),
	}
}