package mcpsrv

import (
	"context"
	"errors"
	"fmt"
	"net/url"
	"strings"
	"time"

	"github.com/modelcontextprotocol/go-sdk/mcp"

	"sourcecraft.dev/bigbes/sr-ht-dolt/beads"
)

// The beads-aware tools of docs/DESIGN.mcp.md §9.2: a hosted database that
// carries the beads (bd) issue schema, read as issues rather than as tables.
//
// They add three rules to the ones browse.go states for the whole surface:
//
//   - Nothing here reads the schema. Every answer below is a projection of
//     beads.Build / beads.BuildMilestones / beads.BuildMemories — the
//     fingerprint, the lane bucketing, the ready rule, the filters, the
//     dependency walk, the humanised history, the milestone rollup and the
//     memory revision walk are the ones the web board renders, and they are
//     shared on purpose (docs/DESIGN.mcp.md §2: no second reading of any schema).
//     A question this package could answer only by re-reading the tables is a
//     question it does not answer.
//   - The list/detail split is structural, not a habit. listIssuesOutput carries
//     issueCardJSON, which has no field a description, a design note, an
//     acceptance criterion or a comment could arrive in; the bodies are
//     get_issue's, one issue at a time. A board of 78 issues carrying every long
//     text is the agent's context window spent on text it did not ask for, which
//     is exactly what this surface exists to save.
//   - A database that is not a tracker is refused *per call*. MCP's tool list is
//     static per server, so all of them are advertised for every database on the
//     instance; one whose tables do not carry the fingerprint gets a sentence
//     naming the generic tools as the way to read it anyway. That refusal is an
//     ordinary answer about a database the caller can see — never the masked
//     not-found of a database it may not.
//
// What the projection reads and what it therefore cannot say: it reads up to
// beads.Max (2000) rows per table in one pass. list_issues reports that clip
// (table_truncated, table_total), because a board computed over a clipped table
// is a count a caller cannot otherwise check. get_issue, list_milestones and
// list_memories get no such signal from the projection and so make no claim
// about one: an id that is not in the first beads.Max rows of a large tracker
// reads as absent there, and list_issues is where a caller learns that the
// tracker is that large. list_memories has a clip of an entirely different kind
// and does report it — the revision walk's, which is about the history rather
// than about a table (see memoryJSON.Revision).

// The caps of docs/DESIGN.mcp.md §9.3 for the issue listing. They are applied
// *after* filtering — the limit clips a result set, not a table read — and, like
// every cap on this surface, the applied one is reported rather than assumed.
const (
	defaultIssueLimit = 200
	maxIssueLimit     = 500
)

// The three status categories the projection buckets a status into
// (beads.statusCategory). They are this surface's filter vocabulary because they
// are the only status grouping shared by every tracker: the status *names* are
// per-database (a tracker may define its own in custom_statuses), so filtering on
// one would be filtering on a string this service cannot enumerate.
const (
	categoryOpen       = "open"
	categoryInProgress = "in_progress"
	categoryClosed     = "closed"
)

// --- the shapes a caller decodes -------------------------------------------

// issueCardJSON is one issue as a *listing* carries it: identity, metadata, and
// the two counts and two flags a triage decision is made on.
//
// It carries no long text and it has no field one could arrive in — no
// description, no design, no acceptance criteria, no notes, no comment. That is
// the list/detail split of docs/DESIGN.mcp.md §9.2 made structural rather than
// remembered: a board is identity and metadata, and the bodies are get_issue's,
// one issue at a time. Adding such a field here would silently spend the context
// window of every agent that lists a tracker, so this type is the place the rule
// is enforced and the test asserts it over the serialised payload.
//
// Title is the exception that proves it: it is the issue's name, not its text.
type issueCardJSON struct {
	ID    string `json:"id"`
	Title string `json:"title"`

	// Type is the issue_type as stored ("task", "bug", "epic", "milestone", …),
	// and Priority is the raw priority ("0".."3", or "" when unset) rather than a
	// rendered label: an agent sorts on the number.
	Type     string   `json:"type"`
	Priority string   `json:"priority"`
	Assignee string   `json:"assignee"`
	Labels   []string `json:"labels"`

	// BlockedBy is how many dependencies this issue has, and Blocks how many
	// point at it. They are counts and not lists: the edges themselves are
	// get_issue's, with the titles and statuses that make them readable.
	BlockedBy int `json:"blocked_by"`
	Blocks    int `json:"blocks"`

	// Ready is bd's ready set: open, unblocked, and not a template or an
	// ephemeral scaffold. It is the projection's rule, the same one the board
	// paints and `bd ready` prints.
	Ready bool `json:"ready"`

	// Lane is where the board places this issue — "Rolling", "Lined Up",
	// "Stalled" or "Past Stand" — which carries one thing Category does not: an
	// open issue with an open blocker is Stalled rather than Lined Up.
	Lane string `json:"lane"`

	// Category is the status category the lane was derived from: open,
	// in_progress or closed. It is what the status filter matches.
	Category string `json:"category"`
}

// issueFilter is the board's own filter model (beads.Filter) as tool arguments.
// Every field is an exact match except q, and an unset field is no constraint.
type issueFilter struct {
	Status   string `json:"status,omitempty" jsonschema:"the status category: \"open\", \"in_progress\" or \"closed\". Individual status names are per-tracker and are not filterable; each issue's own status is on get_issue."`
	Type     string `json:"type,omitempty" jsonschema:"an exact issue type, e.g. \"task\", \"bug\", \"epic\", \"milestone\""`
	Priority string `json:"priority,omitempty" jsonschema:"an exact priority as stored: \"0\" (highest) through \"3\""`
	Assignee string `json:"assignee,omitempty" jsonschema:"an exact assignee"`
	Label    string `json:"label,omitempty" jsonschema:"a label the issue must carry, e.g. \"milestone:m3\""`
	Query    string `json:"q,omitempty" jsonschema:"a case-insensitive substring of the issue's id or title; it does not search bodies"`
	Ready    bool   `json:"ready,omitempty" jsonschema:"true narrows to the ready set — open, unblocked, not a template. false is no constraint: there is no way to ask for the issues that are *not* ready."`
}

type listIssuesInput struct {
	databaseRef
	Ref    string      `json:"ref,omitempty" jsonschema:"a branch name or a commit hash to read the tracker at; omit it for the database's default branch"`
	Filter issueFilter `json:"filter,omitempty" jsonschema:"narrows the listing; every field is optional and an omitted one is no constraint"`
	Limit  *int        `json:"limit,omitempty" jsonschema:"how many issues to return, at most 500; defaults to 200. It is applied after filtering."`
}

type listIssuesOutput struct {
	// Ref is the ref actually read, which is the default branch when the call
	// named none.
	Ref string `json:"ref"`

	// Issues are in the board's own parade order: Rolling, then Lined Up, then
	// Stalled, then Past Stand, and within each by priority, then age, then id.
	Issues []issueCardJSON `json:"issues"`

	// Total is how many issues matched the filter, before Limit clipped them —
	// the honest denominator of the list above.
	Total int `json:"total"`

	// Limit is the limit that was applied, which is not always the one asked
	// for: a request above the cap is answered at the cap.
	Limit int `json:"limit"`

	// Truncated reports that matches were left behind by Limit. Narrow the
	// filter or raise the limit; this tool does not page, because a filtered
	// board is meant to be small.
	Truncated bool `json:"truncated"`

	// TableTruncated reports the *other* clip, and it is a separate flag because
	// it is a different fact: the projection reads at most 2000 rows of a table
	// in one pass (docs/DESIGN.mcp.md §9.3), so on a tracker larger than that the
	// board above — and every count on it — was computed over the first 2000
	// issues rather than over all of them. Nothing here pages past it; read_rows
	// does, if the whole table is really wanted.
	TableTruncated bool `json:"table_truncated"`

	// TableTotal is the number of rows in the issues table at this ref, which is
	// what makes TableTruncated checkable rather than a bare warning.
	TableTotal int `json:"table_total"`
}

type getIssueInput struct {
	databaseRef
	ID  string `json:"id" jsonschema:"the issue id, as list_issues reports it (e.g. \"bd-42\")"`
	Ref string `json:"ref,omitempty" jsonschema:"a branch name or a commit hash to read the tracker at; omit it for the database's default branch"`
}

// issueJSON is the whole issue: every field the projection models, bodies
// included. This is the detail half of the split issueCardJSON is the list half
// of — one issue at a time, because that is what makes the long texts
// affordable.
type issueJSON struct {
	ID        string `json:"id"`
	Title     string `json:"title"`
	Status    string `json:"status"`
	IssueType string `json:"issue_type"`
	Priority  string `json:"priority"`

	// Lane is the board lane this issue's status category maps to. It is the
	// detail pane's lane and is derived from the status alone, so an open issue
	// with an open blocker reads "Lined Up" here while list_issues places it in
	// "Stalled" — the blocked signal is in DependsOn, which this answer carries
	// in full.
	Lane string `json:"lane"`

	Assignee  string `json:"assignee"`
	CreatedBy string `json:"created_by"`
	Owner     string `json:"owner"`

	EstimatedMinutes string `json:"estimated_minutes"`
	ExternalRef      string `json:"external_ref"`
	SpecID           string `json:"spec_id"`

	// The four long texts bd carries for an issue. They are why get_issue exists
	// and why no listing on this surface has them.
	Description        string `json:"description"`
	Design             string `json:"design"`
	AcceptanceCriteria string `json:"acceptance_criteria"`
	Notes              string `json:"notes"`

	// The timestamps as stored ("YYYY-MM-DD HH:MM:SS"), unparsed: this surface
	// reads a bare store without a SQL engine, so what it has is the stored
	// string, and re-typing it as a time would be a claim about a timezone
	// nobody recorded.
	CreatedAt   string `json:"created_at"`
	StartedAt   string `json:"started_at"`
	UpdatedAt   string `json:"updated_at"`
	ClosedAt    string `json:"closed_at"`
	CloseReason string `json:"close_reason"`

	Labels []string `json:"labels"`
}

// edgeJSON is one direct dependency edge, with the other end resolved to
// something readable.
type edgeJSON struct {
	IssueID string `json:"issue_id"`
	Title   string `json:"title"`

	// Type is the dependency type — "blocks", "parent-child", "related", … —
	// and it matters: only an open "blocks" edge blocks, while parent-child is
	// hierarchy.
	Type   string `json:"type"`
	Status string `json:"status"`
	Closed bool   `json:"closed"`
}

// treeNodeJSON is one node of a flattened transitive dependency tree. Depth is
// the indentation level: 0 is a direct edge of the issue asked about.
type treeNodeJSON struct {
	ID     string `json:"id"`
	Title  string `json:"title"`
	Type   string `json:"type"`
	Status string `json:"status"`
	Closed bool   `json:"closed"`
	Depth  int    `json:"depth"`
}

// subtaskJSON is one child of an epic — the far end of a parent-child edge
// pointing at it.
type subtaskJSON struct {
	ID       string `json:"id"`
	Title    string `json:"title"`
	Status   string `json:"status"`
	Category string `json:"category"`
	Priority string `json:"priority"`
	Assignee string `json:"assignee"`
	Blocked  bool   `json:"blocked"`
}

type commentJSON struct {
	Author    string `json:"author"`
	Text      string `json:"text"`
	CreatedAt string `json:"created_at"`
}

// activityJSON is one entry of the merged history: a comment, an audit event, or
// a dependency link (which beads records on the edge row rather than as an
// event). Summary is the humanised one-liner the projection builds
// ("changed status to in_progress"); Text carries a comment's body or an event's
// free-text note.
type activityJSON struct {
	Kind      string `json:"kind"`
	Event     string `json:"event"`
	Actor     string `json:"actor"`
	Summary   string `json:"summary"`
	Text      string `json:"text"`
	CreatedAt string `json:"created_at"`
}

type getIssueOutput struct {
	Ref   string    `json:"ref"`
	Issue issueJSON `json:"issue"`

	// IsEpic reports that this issue is a parent of subtasks, which is what makes
	// the two rollup counts below meaningful.
	IsEpic bool `json:"is_epic"`

	// DependsOn is what this issue waits on; DependedOnBy is what waits on it.
	// Both are the direct edges only.
	DependsOn    []edgeJSON `json:"depends_on"`
	DependedOnBy []edgeJSON `json:"depended_on_by"`

	// The transitive closures of those two directions, flattened pre-order with
	// a depth. They are bounded by the projection (6 levels, 200 nodes) so a
	// dense or cyclic graph cannot run away, and they are empty when they would
	// only repeat the direct edges above.
	DependsTree   []treeNodeJSON `json:"depends_tree"`
	DependentTree []treeNodeJSON `json:"dependent_tree"`

	// The epic rollup: the children, how many are closed, and how many there
	// are. Empty and zero for an issue that is not an epic.
	Subtasks     []subtaskJSON `json:"subtasks"`
	SubtaskDone  int           `json:"subtask_done"`
	SubtaskTotal int           `json:"subtask_total"`

	Comments []commentJSON `json:"comments"`

	// History is the comments and the audit trail merged and sorted oldest
	// first, which is the one place the *story* of an issue is readable.
	History []activityJSON `json:"history"`
}

type listMilestonesInput struct {
	databaseRef
	Ref string `json:"ref,omitempty" jsonschema:"a branch name or a commit hash to read the tracker at; omit it for the database's default branch"`
}

// milestoneMemberJSON is one issue under a milestone.
//
// It is a smaller shape than issueCardJSON on purpose rather than by omission:
// the milestone rollup does not compute the dependency counts or the ready flag,
// and reporting them as 0 and false here would be four lies an agent has no way
// to detect. Call list_issues with filter.label to get the full cards for a
// milestone's members.
type milestoneMemberJSON struct {
	ID       string `json:"id"`
	Title    string `json:"title"`
	Type     string `json:"type"`
	Priority string `json:"priority"`
	Assignee string `json:"assignee"`
	Category string `json:"category"`
}

// milestoneEpicJSON is an epic inside a milestone with the members nested under
// it. A child nests only when it carries the same milestone label as its epic —
// membership is purely label-based.
type milestoneEpicJSON struct {
	Issue    milestoneMemberJSON   `json:"issue"`
	Done     int                   `json:"done"`
	Total    int                   `json:"total"`
	Children []milestoneMemberJSON `json:"children"`
}

// milestoneJSON is one "milestone:<name>" label's rollup and its members.
type milestoneJSON struct {
	Name  string `json:"name"`
	Label string `json:"label"`

	// The arithmetic of the rollup: Total is every issue carrying the label, and
	// the three below partition it by status category.
	Total      int `json:"total"`
	Done       int `json:"done"`
	InProgress int `json:"in_progress"`
	Open       int `json:"open"`

	// The members, in the shallow hierarchy the projection arranges them in:
	// the milestone's own issue(s) first, then its epics with their children
	// nested, then everything else. Every member appears exactly once across the
	// three, and the three together are Total issues.
	Heads []milestoneMemberJSON `json:"heads"`
	Epics []milestoneEpicJSON   `json:"epics"`
	Loose []milestoneMemberJSON `json:"loose"`
}

type listMilestonesOutput struct {
	Ref        string          `json:"ref"`
	Milestones []milestoneJSON `json:"milestones"`

	// Unlabeled is how many issues carry no milestone label at all, and Total is
	// every issue read. A tracker that uses no milestone labels answers an empty
	// list with Unlabeled == Total, which is an answer and not an error.
	Unlabeled int `json:"unlabeled"`
	Total     int `json:"total"`
}

type listMemoriesInput struct {
	databaseRef
	Ref string `json:"ref,omitempty" jsonschema:"a branch name or a commit hash to read the tracker at; omit it for the database's default branch"`

	// Query is the memory view's ?q= and is handed to the projection as such,
	// rather than applied to the answer here: filtering afterwards would be a
	// second reading of the same rule, and it would also make the tool pay for
	// dating memories it is about to drop (the revision walk runs per key, after
	// the narrowing).
	Query string `json:"q,omitempty" jsonschema:"a case-insensitive substring of a memory's slug or of its text; omit it for every memory the tracker holds"`
}

// memoryRevisionJSON is when a memory's value last changed: the commit that
// wrote it, recovered from the history rather than read off the row — a config
// row is (key, value) and carries no timestamp at all
// (docs/DESIGN.views.md §2.1).
type memoryRevisionJSON struct {
	Commit string    `json:"commit"`
	Date   time.Time `json:"date"`
	Author string    `json:"author"`
}

// memoryJSON is one `bd remember` entry: the slug, the text, and what the walk
// could establish about when it was written.
//
// This is the one listing on this surface that carries prose, and it is not an
// exception to the list/detail split of §9.2 — it is the same rule applied. A
// memory *is* its text: there is no detail tool to send a caller to, and a
// listing of slugs alone would answer nothing. `q` is how a caller reads part of
// a large tracker's memories rather than all of them.
type memoryJSON struct {
	// Slug is the config key with bd's "kv.memory." prefix stripped, and Text is
	// the value with both newline spellings normalised — memories are typed into
	// shell strings as often as into files, so the same tracker holds real
	// newlines and literal "\n" escapes side by side.
	Slug string `json:"slug"`
	Text string `json:"text"`

	// Revision is the commit that last wrote this value, or **null** when the
	// revision walk could not reach it. Null is not "unknown for some reason": it
	// occurs only when walk_truncated is true, and it means this memory was not
	// written inside the last walk_max commits — i.e. it is older than that. (Not
	// the converse: a truncated walk can still have dated every memory it was
	// asked about.) Inventing a date the walk cannot support, or dropping the
	// field, would both turn that fact into something a caller cannot see.
	Revision *memoryRevisionJSON `json:"revision"`

	// AgeDays is how long ago that revision was, in whole days, measured against
	// the server's clock when the call was answered. It is null exactly when
	// Revision is.
	//
	// It is carried beside the date rather than left to the caller because it is
	// what Stale is computed from, and a flag whose input is invisible is a flag
	// that has to be trusted.
	AgeDays *int `json:"age_days"`

	// Stale is the projection's question — not a verdict — about a memory older
	// than stale_after_days: some memories are meant to be permanent, and only the
	// reader knows which.
	//
	// It can be true while Revision is null, and that is not a contradiction: when
	// the walk's own oldest commit is already past the threshold, the memory is at
	// least that old, and that much is known without a date.
	Stale bool `json:"stale"`
}

type listMemoriesOutput struct {
	Ref string `json:"ref"`

	// Memories are ordered by slug.
	Memories []memoryJSON `json:"memories"`

	// Total is how many memories the tracker holds before `q` narrowed them — the
	// honest denominator of the list above, and the way a caller tells "this
	// tracker has none" from "your search matched none".
	Total int `json:"total"`

	// WalkTruncated says the revision walk stopped at WalkMax commits with the
	// history still going, which is the only way a memory here carries no
	// revision. Read it with the null revisions above: it is the sentence "older
	// than the last walk_max commits" that the page renders in place of a date.
	WalkTruncated bool `json:"walk_truncated"`

	// WalkMax is how many commits back the walk looks, so the sentence above can
	// name its own number instead of asking a caller to trust a bound it cannot
	// see.
	WalkMax int `json:"walk_max"`

	// StaleAfterDays is the threshold every Stale flag was computed against. It is
	// one constant for the instance rather than a per-call knob, and it is
	// published for the same reason age_days is: a caller that disagrees with the
	// threshold can apply its own to the ages.
	StaleAfterDays int `json:"stale_after_days"`
}

// --- registration -----------------------------------------------------------

// registerBeadsTools installs the tools of docs/DESIGN.mcp.md §9.2.
//
// The descriptions tell an agent choosing between them what each one costs: the
// listing is cheap and carries no bodies, the detail is one issue and carries
// all of them. An agent that reads that stops asking for a board it will not
// read.
func (s *Server) registerBeadsTools() {
	mcp.AddTool(s.mcp, &mcp.Tool{
		Name:        "list_issues",
		Annotations: readOnlyTool,
		Description: "List the issues of a beads (bd) issue tracker hosted here, as cards: id, title, type, " +
			"priority, assignee, labels, how many dependencies the issue has and how many point at it, " +
			"whether it is ready to work, and which board lane it sits in.\n\n" +
			"**No bodies.** Descriptions, design notes, acceptance criteria and comments are not in this " +
			"answer at all — call get_issue for one issue when you need them. That split is what makes " +
			"listing a whole tracker affordable.\n\n" +
			"`filter` narrows the listing and every field is optional: `status` is the category " +
			"(`open`, `in_progress`, `closed`), `type`, `priority`, `assignee` and `label` are exact " +
			"matches, `q` is a case-insensitive substring of the id or title, and `ready: true` narrows " +
			"to what can be worked now — open, unblocked, not a template. That is bd's own ready set, " +
			"the answer to \"what should I pick up\".\n\n" +
			"`limit` defaults to 200, is capped at 500 and is applied after filtering; `total` is how " +
			"many issues matched before it, and `truncated` says matches were left behind. Separately, " +
			"`table_truncated` says the tracker has more than 2000 issues and only the first 2000 were " +
			"read, so the counts describe that prefix — `table_total` is the real number.\n\n" +
			"A database that is not a beads tracker says so and points at the generic tools; a database " +
			"you may not read is reported as not existing.",
	}, func(ctx context.Context, _ *mcp.CallToolRequest, in listIssuesInput) (*mcp.CallToolResult, listIssuesOutput, error) {
		out, err := s.listIssues(ctx, in)
		return nil, out, err
	})

	mcp.AddTool(s.mcp, &mcp.Tool{
		Name:        "get_issue",
		Annotations: readOnlyTool,
		Description: "Read one issue of a hosted beads tracker whole: every modelled field including the four " +
			"long texts (description, design, acceptance criteria, notes), both dependency directions " +
			"with the titles and statuses of the other ends, the transitive dependency trees, the " +
			"comments, and the merged history of comments and audit events oldest first.\n\n" +
			"`id` is the issue id list_issues reports, e.g. \"bd-42\". An id the tracker does not carry " +
			"is answered as such — about this database, which you are looking straight at.\n\n" +
			"When the issue is an epic, `is_epic` is true and `subtasks` carries its children with " +
			"`subtask_done`/`subtask_total` as the rollup. `depends_on` is what this issue waits on and " +
			"`depended_on_by` is what waits on it; only an open `blocks` edge actually blocks, while " +
			"`parent-child` is hierarchy. The two trees flatten those directions transitively with a " +
			"`depth`, and are empty when they would only repeat the direct edges.\n\n" +
			"This is the only tool on this surface that carries issue bodies. Use list_issues to find " +
			"the id, then this one for the issue you actually need.",
	}, func(ctx context.Context, _ *mcp.CallToolRequest, in getIssueInput) (*mcp.CallToolResult, getIssueOutput, error) {
		out, err := s.getIssue(ctx, in)
		return nil, out, err
	})

	mcp.AddTool(s.mcp, &mcp.Tool{
		Name:        "list_milestones",
		Annotations: readOnlyTool,
		Description: "Summarize a hosted beads tracker by milestone: for every \"milestone:<name>\" label, how " +
			"many issues carry it and how many of those are done, in progress and open, plus the " +
			"members themselves.\n\n" +
			"Members are arranged the way the tracker means them: `heads` are the milestone's own " +
			"issues (issue_type \"milestone\"), `epics` are its epics with their children nested and " +
			"their own done/total, and `loose` is everything else. Each member appears exactly once " +
			"across the three, and together they are `total`.\n\n" +
			"Membership is purely label-based: an issue in several milestones counts under each, and a " +
			"child nests under an epic only when it carries the same milestone label. `unlabeled` is " +
			"how many issues carry no milestone label at all.\n\n" +
			"A tracker that uses no milestone labels answers an empty list — that is an answer, not an " +
			"error. For the full cards of one milestone's members, call list_issues with " +
			"`filter.label` set to the label.",
	}, func(ctx context.Context, _ *mcp.CallToolRequest, in listMilestonesInput) (*mcp.CallToolResult, listMilestonesOutput, error) {
		out, err := s.listMilestones(ctx, in)
		return nil, out, err
	})

	mcp.AddTool(s.mcp, &mcp.Tool{
		Name:        "list_memories",
		Annotations: readOnlyTool,
		Description: "List the memories a hosted beads tracker holds — what `bd remember` writes — each with its " +
			"text and the revision its value was last written at.\n\n" +
			"Memories are the other half of what a tracker knows: durable notes an agent left for the next " +
			"one, stored as `kv.memory.<slug>` rows in the tracker's `config` table. Read them before " +
			"planning work on a tracker; they are where its conventions, its gotchas and its handoffs live.\n\n" +
			"A memory carries no timestamp — the row is (key, value) and nothing else — so `revision` is " +
			"recovered from the history: the commit whose `config` table first differs is the one that " +
			"wrote the value. That walk looks back at most `walk_max` commits. A memory not written inside " +
			"it has `revision: null` and `age_days: null`, and `walk_truncated` is true: null means \"older " +
			"than the last `walk_max` commits\", never \"date unavailable\".\n\n" +
			"`stale` is a question, not a verdict — it marks a memory older than `stale_after_days`, and " +
			"some memories are meant to be permanent. Both the age and the threshold are in the answer, so " +
			"judge for yourself rather than trusting the flag. A memory can be `stale` with a null " +
			"revision: the walk's oldest commit is already past the threshold.\n\n" +
			"`q` is a case-insensitive substring of a slug or of a memory's text; `total` is how many " +
			"memories the tracker holds before it narrowed them. A tracker whose `config` table holds no " +
			"memory — or that has no `config` table at all — answers an empty list, which is an answer and " +
			"not an error.\n\n" +
			"A database that is not a beads tracker says so and points at the generic tools; a database " +
			"you may not read is reported as not existing.",
	}, func(ctx context.Context, _ *mcp.CallToolRequest, in listMemoriesInput) (*mcp.CallToolResult, listMemoriesOutput, error) {
		out, err := s.listMemories(ctx, in)
		return nil, out, err
	})
}

// --- the handlers -----------------------------------------------------------

// listIssues answers list_issues: the board's cards, filtered, ordered and
// capped.
func (s *Server) listIssues(ctx context.Context, in listIssuesInput) (listIssuesOutput, error) {
	const tool = "list_issues"
	var out listIssuesOutput

	limit, err := pageLimit(in.Limit, defaultIssueLimit, maxIssueLimit, "issues")
	if err != nil {
		return out, err
	}
	// An unrecognised category is refused rather than matched against nothing: a
	// caller that typed "in-progress" would otherwise read an empty board as "no
	// work is under way", which is a false statement about the tracker.
	wantCategory, err := parseCategory(in.Filter.Status)
	if err != nil {
		return out, err
	}

	sess, ref, err := s.openTracker(ctx, tool, in.databaseRef, in.Ref)
	if err != nil {
		return out, err
	}
	defer sess.Close()

	data, err := beads.Build(ctx, sess, ref, boardQuery(in.Filter))
	if err != nil {
		// The ref resolved and the fingerprint matched a moment ago (openTracker),
		// so a failure here is a table this service could not read rather than a
		// question about a ref or a database.
		return out, internalError(err, tool)
	}

	out = listIssuesOutput{
		Ref:            ref,
		Issues:         []issueCardJSON{},
		Limit:          limit,
		TableTruncated: data.Truncated,
		TableTotal:     data.ShownOf,
	}
	for _, lane := range data.Lanes {
		category, ok := laneCategory(lane.Slug)
		if !ok {
			// The slugs are the projection's own. An unknown one means beads changed
			// its lanes and this mapping did not, and answering with a guessed
			// category would be this surface quietly disagreeing with the board.
			return listIssuesOutput{}, internalError(
				fmt.Errorf("the beads projection reported an unknown lane %q", lane.Slug), tool)
		}
		if wantCategory != "" && category != wantCategory {
			continue
		}
		for _, c := range lane.Issues {
			out.Total++
			if len(out.Issues) >= limit {
				continue
			}
			labels := c.Labels
			if labels == nil {
				labels = []string{}
			}
			out.Issues = append(out.Issues, issueCardJSON{
				ID:        c.ID,
				Title:     c.Title,
				Type:      c.Type,
				Priority:  c.Priority,
				Assignee:  c.Assignee,
				Labels:    labels,
				BlockedBy: c.BlockedBy,
				Blocks:    c.Blocks,
				Ready:     c.Ready,
				Lane:      lane.Name,
				Category:  category,
			})
		}
	}
	out.Truncated = out.Total > len(out.Issues)
	return out, nil
}

// getIssue answers get_issue: one issue whole, bodies included.
func (s *Server) getIssue(ctx context.Context, in getIssueInput) (getIssueOutput, error) {
	const tool = "get_issue"
	var out getIssueOutput

	id := strings.TrimSpace(in.ID)
	if id == "" {
		return out, errors.New("name the issue to read; list_issues reports the ids of a tracker")
	}

	sess, ref, err := s.openTracker(ctx, tool, in.databaseRef, in.Ref)
	if err != nil {
		return out, err
	}
	defer sess.Close()

	data, err := beads.Build(ctx, sess, ref, url.Values{"issue": {id}})
	if err != nil {
		return out, internalError(err, tool)
	}
	if data.Issue == nil {
		// An ordinary answer about a database the caller can see, in refMiss's
		// sense: naming the id back is not a leak, it is what the caller asked
		// with.
		return out, errors.New(noSuchIssue(in.databaseRef, ref, id))
	}

	out = getIssueOutput{
		Ref:           ref,
		Issue:         issueOf(data.Issue),
		IsEpic:        data.Mode == "epic",
		DependsOn:     edgesOf(data.DependsOn),
		DependedOnBy:  edgesOf(data.DependedOnBy),
		DependsTree:   treeOf(data.DependsTree),
		DependentTree: treeOf(data.DependentTree),
		Subtasks:      make([]subtaskJSON, 0, len(data.Subtasks)),
		SubtaskDone:   data.SubtaskDone,
		SubtaskTotal:  data.SubtaskTotal,
		Comments:      make([]commentJSON, 0, len(data.Comments)),
		History:       make([]activityJSON, 0, len(data.History)),
	}
	for _, st := range data.Subtasks {
		out.Subtasks = append(out.Subtasks, subtaskJSON{
			ID:       st.ID,
			Title:    st.Title,
			Status:   st.Status,
			Category: st.Category,
			Priority: st.Priority,
			Assignee: st.Assignee,
			Blocked:  st.Blocked,
		})
	}
	for _, c := range data.Comments {
		out.Comments = append(out.Comments, commentJSON{Author: c.Author, Text: c.Text, CreatedAt: c.CreatedAt})
	}
	for _, a := range data.History {
		out.History = append(out.History, activityJSON{
			Kind:      a.Kind,
			Event:     a.Event,
			Actor:     a.Actor,
			Summary:   a.Summary,
			Text:      a.Text,
			CreatedAt: a.CreatedAt,
		})
	}
	return out, nil
}

// listMilestones answers list_milestones: the milestone: labels rolled up.
func (s *Server) listMilestones(ctx context.Context, in listMilestonesInput) (listMilestonesOutput, error) {
	const tool = "list_milestones"
	var out listMilestonesOutput

	sess, ref, err := s.openTracker(ctx, tool, in.databaseRef, in.Ref)
	if err != nil {
		return out, err
	}
	defer sess.Close()

	view, err := beads.BuildMilestones(ctx, sess, ref)
	if err != nil {
		return out, internalError(err, tool)
	}

	out = listMilestonesOutput{
		Ref:        ref,
		Milestones: make([]milestoneJSON, 0, len(view.Milestones)),
		Unlabeled:  view.Unlabeled,
		Total:      view.Total,
	}
	for _, m := range view.Milestones {
		entry := milestoneJSON{
			Name:       m.Name,
			Label:      m.Label,
			Total:      m.Total,
			Done:       m.Done,
			InProgress: m.InProgress,
			Open:       m.Open,
			Heads:      membersOf(m.Heads),
			Epics:      make([]milestoneEpicJSON, 0, len(m.Epics)),
			Loose:      membersOf(m.Loose),
		}
		for _, e := range m.Epics {
			entry.Epics = append(entry.Epics, milestoneEpicJSON{
				Issue:    memberOf(e.Card),
				Done:     e.Done,
				Total:    e.Total,
				Children: membersOf(e.Children),
			})
		}
		out.Milestones = append(out.Milestones, entry)
	}
	return out, nil
}

// listMemories answers list_memories: the memories a tracker holds, each dated
// from the history by beads.BuildMemories.
//
// The clock is real (time.Now) and is passed into the projection rather than
// read inside it, exactly as the web view passes its own: staleness is the one
// thing about this answer that depends on when it was computed, and beads/
// reads no hidden clock.
//
// # Why the fingerprint here is still beads.Applies
//
// beads.AppliesMemories exists — the beads fingerprint plus a config table with
// key and value — and it is what decides whether the web board grows a Memory
// tab. It is *not* what this tool refuses on, and the difference matters.
// openTracker's refusal says "this database is not a beads issue tracker", and
// for a tracker whose config table simply is not there that sentence would be
// false: it is a tracker, it has no memories, and "no memories" is an answer the
// projection already gives (a missing config table degrades to an empty view,
// like every other optional table). A tab is a question about a page's layout; a
// tool call is a question about the data, and the data here is "none".
func (s *Server) listMemories(ctx context.Context, in listMemoriesInput) (listMemoriesOutput, error) {
	const tool = "list_memories"
	var out listMemoriesOutput

	sess, ref, err := s.openTracker(ctx, tool, in.databaseRef, in.Ref)
	if err != nil {
		return out, err
	}
	defer sess.Close()

	// BrowseSession's method set covers beads.MemorySession (Rows, plus Log and
	// TableHash, which the walk needs and only it needs), so the seam is handed
	// over as it is rather than adapted.
	now := time.Now()
	view, err := beads.BuildMemories(ctx, sess, ref, memoryQuery(in.Query), now)
	if err != nil {
		// The ref resolved and the fingerprint matched a moment ago, so what failed
		// here is a table or a history this service could not read. In particular a
		// history that cannot be walked is an error and not a page of memories with
		// every date quietly missing — that page is indistinguishable from a tracker
		// whose memories are all older than the walk.
		return out, internalError(err, tool)
	}

	out = listMemoriesOutput{
		Ref:            ref,
		Memories:       make([]memoryJSON, 0, len(view.Memories)),
		Total:          view.Total,
		WalkTruncated:  view.WalkTruncated,
		WalkMax:        view.WalkMax,
		StaleAfterDays: int(beads.MemoryStaleAfter / (24 * time.Hour)),
	}
	for _, m := range view.Memories {
		entry := memoryJSON{Slug: m.Slug, Text: m.Text, Stale: m.Stale}
		if m.Revision != nil {
			entry.Revision = &memoryRevisionJSON{
				Commit: m.Revision.Commit,
				Date:   m.Revision.Date,
				Author: m.Revision.Author,
			}
			// Whole days, measured against the same clock the projection judged
			// Stale with — two answers from one reading rather than two.
			days := int(now.Sub(m.Revision.Date) / (24 * time.Hour))
			entry.AgeDays = &days
		}
		out.Memories = append(out.Memories, entry)
	}
	return out, nil
}

// --- resolving a tracker ----------------------------------------------------

// openTracker is the whole preamble of a beads tool: resolve the database as the
// browse handlers do, open its store, settle the ref, and refuse a database that
// is not a tracker.
//
// The session is the caller's to close (defer sess.Close()), which is the browse
// discipline; returning it rather than a closure keeps that visible at the call
// site instead of hidden in a helper.
func (s *Server) openTracker(ctx context.Context, tool string, ref databaseRef, named string) (BrowseSession, string, error) {
	repo, err := s.resolveDatabase(ctx, tool, ref)
	if err != nil {
		return nil, "", err
	}
	sess, err := s.openStore(ctx, tool, repo)
	if err != nil {
		return nil, "", err
	}

	at, err := refFor(ctx, sess, tool, ref, named)
	if err != nil {
		sess.Close()
		return nil, "", err
	}

	tables, err := sess.Tables(ctx, at)
	if err != nil {
		sess.Close()
		return nil, "", refMiss(err, tool, noSuchRef(ref, at))
	}
	// The fingerprint is beads.Applies and is asked here, per call, because MCP's
	// tool list is static per server: these tools are advertised for every
	// database on the instance, so "is this one a tracker" is a question about the
	// argument rather than about the surface (docs/DESIGN.mcp.md §9).
	if !beads.Applies(tables) {
		sess.Close()
		return nil, "", errors.New(notATracker(ref, at))
	}
	return sess, at, nil
}

// boardQuery renders the tool's filter as the query the board projection parses,
// so that the filtering is beads.Filter's and not a second implementation of it
// reading the same rows.
//
// Status is absent from it deliberately: the projection has no status filter (a
// board shows every lane at once), so the category narrowing is applied to the
// lanes it answers with, in listIssues.
func boardQuery(f issueFilter) url.Values {
	q := url.Values{}
	set := func(key, value string) {
		if value = strings.TrimSpace(value); value != "" {
			q.Set(key, value)
		}
	}
	set("q", f.Query)
	set("type", f.Type)
	set("priority", f.Priority)
	set("assignee", f.Assignee)
	set("label", f.Label)
	if f.Ready {
		q.Set("ready", "1")
	}
	return q
}

// memoryQuery renders the tool's one filter as the query the memory projection
// parses, for boardQuery's reason: the substring rule is beads' and not a second
// implementation of it reading the same rows.
//
// The projection's other two parameters are deliberately not offered. ?key= is
// ?q= with an exactness this tool has no use for — a slug is a substring of
// itself — and ?sort= is a page's toggle: an answer with a stated order (slug)
// is one an agent can sort itself, and every ordering the projection can produce
// is derivable from the fields carried here.
func memoryQuery(q string) url.Values {
	values := url.Values{}
	if q = strings.TrimSpace(q); q != "" {
		values.Set("q", q)
	}
	return values
}

// parseCategory validates the status filter: empty is no constraint, one of the
// three categories is itself, and anything else is refused with the three named.
func parseCategory(want string) (string, error) {
	switch strings.ToLower(strings.TrimSpace(want)) {
	case "":
		return "", nil
	case categoryOpen:
		return categoryOpen, nil
	case categoryInProgress:
		return categoryInProgress, nil
	case categoryClosed:
		return categoryClosed, nil
	default:
		return "", fmt.Errorf("filter.status must be %q, %q or %q, not %q; "+
			"individual status names are per-tracker and are not filterable",
			categoryOpen, categoryInProgress, categoryClosed, want)
	}
}

// laneCategory maps a board lane to the status category it was bucketed from.
// Two lanes share "open": an open issue is Stalled when something open blocks it
// and Lined Up otherwise, which is a distinction about blockers rather than
// about status.
//
// An unknown slug is not defaulted — see listIssues, which turns it into a
// failure rather than a guess.
func laneCategory(slug string) (string, bool) {
	switch slug {
	case "rolling":
		return categoryInProgress, true
	case "past-stand":
		return categoryClosed, true
	case "lined-up", "stalled":
		return categoryOpen, true
	default:
		return "", false
	}
}

// --- the projections --------------------------------------------------------

func issueOf(i *beads.Issue) issueJSON {
	labels := i.Labels
	if labels == nil {
		labels = []string{}
	}
	return issueJSON{
		ID:                 i.ID,
		Title:              i.Title,
		Status:             i.Status,
		IssueType:          i.IssueType,
		Priority:           i.Priority,
		Lane:               i.Lane,
		Assignee:           i.Assignee,
		CreatedBy:          i.CreatedBy,
		Owner:              i.Owner,
		EstimatedMinutes:   i.EstimatedMinutes,
		ExternalRef:        i.ExternalRef,
		SpecID:             i.SpecID,
		Description:        i.Description,
		Design:             i.Design,
		AcceptanceCriteria: i.AcceptanceCriteria,
		Notes:              i.Notes,
		CreatedAt:          i.CreatedAt,
		StartedAt:          i.StartedAt,
		UpdatedAt:          i.UpdatedAt,
		ClosedAt:           i.ClosedAt,
		CloseReason:        i.CloseReason,
		Labels:             labels,
	}
}

func edgesOf(edges []beads.Edge) []edgeJSON {
	out := make([]edgeJSON, 0, len(edges))
	for _, e := range edges {
		out = append(out, edgeJSON{
			IssueID: e.IssueID,
			Title:   e.Title,
			Type:    e.Type,
			Status:  e.Status,
			Closed:  e.Closed,
		})
	}
	return out
}

func treeOf(nodes []beads.TreeNode) []treeNodeJSON {
	out := make([]treeNodeJSON, 0, len(nodes))
	for _, n := range nodes {
		out = append(out, treeNodeJSON{
			ID:     n.ID,
			Title:  n.Title,
			Type:   n.Type,
			Status: n.Status,
			Closed: n.Closed,
			Depth:  n.Depth,
		})
	}
	return out
}

func memberOf(c beads.Card) milestoneMemberJSON {
	return milestoneMemberJSON{
		ID:       c.ID,
		Title:    c.Title,
		Type:     c.Type,
		Priority: c.Priority,
		Assignee: c.Assignee,
		Category: c.Category,
	}
}

func membersOf(cards []beads.Card) []milestoneMemberJSON {
	out := make([]milestoneMemberJSON, 0, len(cards))
	for _, c := range cards {
		out = append(out, memberOf(c))
	}
	return out
}

// --- the sentences a caller reads -------------------------------------------

// notATracker is the refusal of docs/DESIGN.mcp.md §9: a database the caller may
// read, whose tables are not a beads tracker. It names the generic tools,
// because the database is perfectly readable — just not as issues — and it is
// pointedly not the masked not-found: the caller is looking straight at this
// database.
func notATracker(ref databaseRef, at string) string {
	return fmt.Sprintf("%s is not a beads issue tracker at %q: its tables carry no beads schema "+
		"(an \"issues\" table with id and status columns, and a \"dependencies\" table). "+
		"It is still a database you can read — list_tables names its tables and read_rows reads them.",
		ref, at)
}

// noSuchIssue is an ordinary answer about a tracker the caller can see.
func noSuchIssue(ref databaseRef, at, id string) string {
	return fmt.Sprintf("%s has no issue %q at %q; list_issues names the issues there", ref, id, at)
}