package tools

import (
	"context"
	"encoding/json"
	"fmt"
	"strings"

	"github.com/krow/krow-backend/go-api/internal/domain"
	"github.com/krow/krow-backend/go-api/internal/repo"
)

// Moving a candidate through the funnel: the platform's second write.
//
// It exists to replace a capability rather than to add one. The browser panel
// could already mark an interview ready, through a matcher that recognised the
// phrasing and called the app's own mutation — instant, free, and reachable
// only by the handful of sentences somebody wrote a pattern for. Routing past
// that machinery is only honest if nothing is lost, and this is the thing that
// would otherwise have been lost.
//
// The second write is also the first test of whether the confirmation
// mechanism GENERALISES. assign_worker could have been special-cased into the
// gate a dozen ways without anyone noticing. This tool shares every piece of it
// — the binding, the renderer contract, the single-use token, the replay — and
// adds none of its own.

/* ── Vocabulary ─────────────────────────────────────────────────────────── */

// applicationStages is the funnel, in order.
//
// From the `application_status` enum, and in the enum's own order, because
// "forward" and "backward" are only meaningful against a fixed sequence. The
// two terminal outcomes sit outside it: hiring and rejecting are decisions, not
// positions in a queue, and treating them as "further along" would let a
// request to advance somebody one step quietly hire them.
var applicationStages = []string{"applied", "ai_screened", "shortlisted", "interview"}

// terminalStages are the outcomes a candidate can be moved to from anywhere.
var terminalStages = []string{"hired", "rejected"}

// settledStages are the outcomes that take somebody out of the running.
//
// `assigned` appears here and nowhere else in this file's vocabulary: it is not
// a stage this tool may *set* (see knownStage), but a candidate already placed
// on a shift is not waiting on a decision either. Leaving it out of this list is
// how a settled candidate gets chased twice.
var settledStages = []string{"hired", "rejected", "assigned"}

// quotedList renders a package-level vocabulary as a SQL literal list. Never
// reachable from caller input — every caller passes one of the vars above.
func quotedList(vs []string) string {
	out := make([]string, len(vs))
	for i, v := range vs {
		out[i] = "'" + v + "'"
	}
	return strings.Join(out, ", ")
}

// listableStage reports whether a stage can be asked for by name. Wider than
// knownStage: every status in the enum can be read, but `assigned` cannot be set.
func listableStage(s string) bool {
	return knownStage(s) || s == "assigned"
}

// stageLabels are how a person reads a stage. The enum values are for the
// database; a confirmation dialog saying `ai_screened` is a dialog written for
// the schema rather than for the person approving it.
var stageLabels = map[string]string{
	"applied":     "Applied",
	"ai_screened": "Screened",
	"shortlisted": "Shortlisted",
	"interview":   "Interview",
	"hired":       "Hired",
	"rejected":    "Rejected",
	"assigned":    "Assigned",
}

func stageLabel(s string) string {
	if l, ok := stageLabels[s]; ok {
		return l
	}
	return s
}

// knownStage reports whether a stage is one this tool may set.
//
// `assigned` is deliberately absent: an application becomes assigned because
// somebody was put on a shift, which is assign_worker's business. Letting this
// tool set it would create a second path to the same state that writes no
// assignment row — a candidate marked assigned to nothing.
func knownStage(s string) bool {
	for _, v := range applicationStages {
		if v == s {
			return true
		}
	}
	for _, v := range terminalStages {
		if v == s {
			return true
		}
	}
	return false
}

/* ── The tool ───────────────────────────────────────────────────────────── */

type moveApplicationInput struct {
	ApplicationID string `json:"application_id"`
	Stage         string `json:"stage"`
	Note          string `json:"note"`
}

// MoveApplication advances or rejects a candidate.
func MoveApplication(db repo.Querier) Tool {
	return Tool{
		Name: "move_application",
		Description: "Move a candidate to a different stage of the hiring funnel — screened, " +
			"shortlisted, interview, hired or rejected. This changes a real record and the " +
			"candidate's status in the product. Requires an application id from " +
			"candidates_quality or hires_recent; never invent one. A person must approve " +
			"before this takes effect.",
		InputSchema: map[string]any{
			"type": "object",
			"properties": map[string]any{
				"application_id": map[string]any{
					"type":        "string",
					"description": "The application's id, exactly as a lookup returned it.",
				},
				"stage": map[string]any{
					"type": "string",
					"enum": []string{"ai_screened", "shortlisted", "interview", "hired", "rejected"},
					"description": "Where to move them. Use 'interview' to mark someone ready to " +
						"interview. 'hired' and 'rejected' are final outcomes.",
				},
				"note": map[string]any{
					"type": "string",
					"description": "Optional one-line reason, shown to the person approving. " +
						"Say why this candidate and not the alternatives.",
				},
			},
			"required":             []string{"application_id", "stage"},
			"additionalProperties": false,
		},
		Effect:         EffectWrite,
		MaxResultBytes: DefaultMaxResultBytes,

		Confirm: func(ctx context.Context, tc Context, inputs json.RawMessage) (*Confirmation, *Result) {
			plan, denied := planMove(ctx, db, tc, inputs)
			if denied != nil {
				return nil, denied
			}

			details := []Detail{
				{Label: "Candidate", Value: plan.name},
				{Label: "Role", Value: plan.roleTitle},
				{Label: "Moving", Value: fmt.Sprintf("%s → %s",
					stageLabel(plan.currentStage), stageLabel(plan.stage))},
			}
			if plan.score > 0 {
				details = append(details, Detail{
					Label: "Match score", Value: fmt.Sprintf("%d", plan.score)})
			}
			if plan.note != "" {
				details = append(details, Detail{Label: "Reason", Value: plan.note})
			}

			var warnings []string
			// A terminal stage is the one a person most needs to be stopped on:
			// it is the hardest to walk back, and the model reaching it early is
			// the most expensive mistake available here.
			switch plan.stage {
			case "hired":
				warnings = append(warnings, fmt.Sprintf(
					"Hiring is a final outcome. %s will count as hired for this role.", plan.name))
			case "rejected":
				warnings = append(warnings, fmt.Sprintf(
					"Rejecting is a final outcome. %s will be out of the running for this role.", plan.name))
			}
			// Skipping stages is legitimate — a strong candidate can go straight
			// to interview — but it is worth pointing out, because a model
			// misreading which stage somebody is at produces exactly this shape.
			if plan.skipped > 1 {
				warnings = append(warnings, fmt.Sprintf(
					"This skips %d stage(s): %s is currently at %s.",
					plan.skipped-1, plan.name, stageLabel(plan.currentStage)))
			}
			if plan.currentStage == plan.stage {
				warnings = append(warnings, fmt.Sprintf(
					"%s is already at %s. Approving this changes nothing.",
					plan.name, stageLabel(plan.stage)))
			}

			summary := fmt.Sprintf("%s moves from %s to %s for %s.",
				plan.name, stageLabel(plan.currentStage), stageLabel(plan.stage), plan.roleTitle)
			if plan.stage == "interview" {
				summary = fmt.Sprintf(
					"%s will be marked ready to interview for %s, and will appear in the "+
						"interview queue.", plan.name, plan.roleTitle)
			}

			return &Confirmation{
				Title:    fmt.Sprintf("Move %s to %s", plan.name, stageLabel(plan.stage)),
				Summary:  summary,
				Details:  details,
				Warnings: warnings,
			}, nil
		},

		Handler: func(ctx context.Context, tc Context, inputs json.RawMessage) Result {
			plan, denied := planMove(ctx, db, tc, inputs)
			if denied != nil {
				return *denied
			}

			// Re-read and re-checked, like assign_worker: the approval was given
			// against a picture some minutes old, and somebody else may have
			// moved this candidate in between. Moving them again from a stage
			// the approver never saw is not what they agreed to.
			if plan.currentStage == plan.stage {
				return OK(map[string]any{
					"applicationId": plan.id,
					"candidate":     plan.name,
					"stage":         plan.stage,
					"changed":       false,
					"note": fmt.Sprintf("%s was already at %s; nothing was changed.",
						plan.name, stageLabel(plan.stage)),
				})
			}

			// screened_at is deliberately not written. Migration 000003 dropped
			// job_applications_screened_consistent because nothing in the product
			// ever sets that column; writing it here would make this tool its only
			// writer, so the column would come to mean "an agent touched this row"
			// rather than what its name says. status is the screening record.
			var updated string
			err := db.QueryRow(ctx, `
				UPDATE job_applications
				   SET status       = $3::application_status,
				       updated_date = now()
				 WHERE id = $1::uuid AND org_id = $2::uuid
				RETURNING status::text`,
				plan.id, tc.OrgID(), plan.stage,
			).Scan(&updated)
			if err != nil {
				return Failf(CodeFailed, "the candidate could not be moved")
			}

			return OK(map[string]any{
				"applicationId": plan.id,
				"candidate":     plan.name,
				"role":          plan.roleTitle,
				"from":          plan.currentStage,
				"stage":         updated,
				"changed":       true,
				"confirmed":     true,
			})
		},
	}
}

/* ── Resolution ─────────────────────────────────────────────────────────── */

type movePlan struct {
	id           string
	name         string
	email        string
	roleTitle    string
	currentStage string
	stage        string
	note         string
	score        int

	// skipped is how many stages forward this moves. 1 is the next one along;
	// more than that jumps the queue, which is allowed and worth saying.
	skipped int
}

// planMove authorizes, validates and resolves a move_application call.
//
// Shared by the renderer and the handler so the thing described and the thing
// done are resolved by identical code — the same reason assign_worker has
// planAssignment. Two resolutions would drift, and the drift lands exactly
// between what a person approved and what happened.
func planMove(ctx context.Context, db repo.Querier, tc Context, inputs json.RawMessage) (*movePlan, *Result) {
	// Update, not List. `job-applications` lists to everyone — a talent caller
	// may read their own — and updates for operators only. Asking the read
	// question here would let a candidate advance themselves.
	if _, denied := authorizeOp(tc, "job-applications", domain.OpUpdate, ""); denied != nil {
		return nil, denied
	}

	var in moveApplicationInput
	if err := json.Unmarshal(inputs, &in); err != nil {
		bad := Failf(CodeInvalidInput, "the arguments were not valid JSON")
		return nil, &bad
	}
	id := strings.TrimSpace(in.ApplicationID)
	stage := strings.TrimSpace(strings.ToLower(in.Stage))
	if id == "" {
		bad := Failf(CodeInvalidInput, "an application id is required")
		return nil, &bad
	}
	if !knownStage(stage) {
		bad := Failf(CodeInvalidInput,
			"%q is not a stage; use ai_screened, shortlisted, interview, hired or rejected", in.Stage)
		return nil, &bad
	}
	if stage == "applied" {
		// Moving somebody back to the start is not a funnel action, it is an
		// undo — and an undo that erases the record of having been screened.
		bad := Failf(CodeInvalidInput, "a candidate cannot be moved back to applied")
		return nil, &bad
	}

	plan := &movePlan{id: id, stage: stage, note: strings.TrimSpace(in.Note)}

	// Behind the caller's own read predicate. Referencing an application this
	// caller could not have read would confirm it exists.
	q, denied := authorizeAs(tc, "job-applications", "a")
	if denied != nil {
		return nil, denied
	}
	q.eq("id::text", id)

	if err := db.QueryRow(ctx, `
		SELECT a.id::text, a.applicant_name, a.email::text, a.status::text, a.ai_score,
		       coalesce(nullif(p.title, ''), 'an unnamed role')
		  FROM job_applications a
		  JOIN job_postings p ON p.id = a.job_posting_id
		 WHERE `+q.clause(), q.args...,
	).Scan(&plan.id, &plan.name, &plan.email, &plan.currentStage, &plan.score, &plan.roleTitle); err != nil {
		denied := Denied()
		return nil, &denied
	}
	if strings.TrimSpace(plan.name) == "" {
		plan.name = plan.email
	}

	plan.skipped = stagesBetween(plan.currentStage, plan.stage)
	return plan, nil
}

// stagesBetween counts how far forward a move goes.
//
// Zero for a terminal outcome or a move that is not forward along the funnel —
// there is no meaningful "distance" to rejecting somebody, and reporting one
// would produce a warning about skipping stages on a decision that skips
// nothing.
func stagesBetween(from, to string) int {
	index := func(s string) int {
		for i, v := range applicationStages {
			if v == s {
				return i
			}
		}
		return -1
	}
	f, t := index(from), index(to)
	if f < 0 || t < 0 || t <= f {
		return 0
	}
	return t - f
}

/* ── Lookup ─────────────────────────────────────────────────────────────── */

type candidatesInput struct {
	Stage string `json:"stage"`
	Limit int    `json:"limit"`
}

// CandidatesAwaiting lists candidates at a stage, with the ids to move them.
//
// §4: a tool whose schema demands an id the model was never given is a design
// bug, and the fix is a lookup rather than a friendlier error message. Every
// analytics tool in this package returns aggregates on purpose — an id in a
// count is noise — so move_application would be unusable without this.
//
// Ordered by match score. A person asking "who is waiting" almost always means
// "who should I look at first", and returning them in insertion order makes the
// model do ranking it has no basis for.
func CandidatesAwaiting(db repo.Querier) Tool {
	return Tool{
		Name: "candidates_awaiting",
		Description: "List candidates currently at a given stage of the funnel — strongest " +
			"match first — with the application id needed to move them. Use this before " +
			"moving anyone: it is the only way to learn an application's id, and an id must " +
			"never be guessed.",
		InputSchema: map[string]any{
			"type": "object",
			"properties": map[string]any{
				"stage": map[string]any{
					"type": "string",
					"enum": []string{"applied", "ai_screened", "shortlisted", "interview",
						"hired", "rejected", "assigned"},
					"description": "Which stage to list. Omit for everyone still in the running " +
						"(that is, not hired, rejected or already assigned to a shift).",
				},
				"limit": map[string]any{
					"type": "integer", "minimum": 1, "maximum": 50,
					"description": "How many to list. Defaults to 15.",
				},
			},
			"additionalProperties": false,
		},
		Effect:         EffectRead,
		MaxResultBytes: DefaultMaxResultBytes,
		Handler: func(ctx context.Context, tc Context, inputs json.RawMessage) Result {
			q, denied := authorizeAs(tc, "job-applications", "a")
			if denied != nil {
				return *denied
			}

			var in candidatesInput
			if len(inputs) > 0 {
				if err := json.Unmarshal(inputs, &in); err != nil {
					return Failf(CodeInvalidInput, "the arguments were not valid JSON")
				}
			}
			stage := strings.TrimSpace(strings.ToLower(in.Stage))
			if stage != "" && !listableStage(stage) {
				return Failf(CodeInvalidInput, "%q is not a stage", in.Stage)
			}

			if stage != "" {
				q.eq("status::text", stage)
			} else {
				// Still in the running. Built from this tool's own vocabulary
				// rather than a hand-written list, so a settled outcome added
				// there cannot be left behind here.
				q.raw("a.status NOT IN (" + quotedList(settledStages) + ")")
			}

			limit := in.Limit
			if limit <= 0 {
				limit = 15
			}
			if limit > 50 {
				limit = 50
			}

			args := append(append([]any{}, q.args...), limit)
			rows, err := db.Query(ctx, `
				SELECT a.id::text, a.applicant_name, a.email::text, a.status::text, a.ai_score,
				       coalesce(nullif(p.title, ''), 'an unnamed role'),
				       (a.status <> 'applied')
				  FROM job_applications a
				  JOIN job_postings p ON p.id = a.job_posting_id
				 WHERE `+q.clause()+`
				 ORDER BY a.ai_score DESC, a.created_date ASC
				 LIMIT $`+fmt.Sprint(len(args)), args...)
			if err != nil {
				return Failf(CodeFailed, "the candidates could not be read")
			}
			defer rows.Close()

			candidates := []map[string]any{}
			for rows.Next() {
				var (
					id, name, email, status, role string
					score                         int
					screened                      bool
				)
				if err := rows.Scan(&id, &name, &email, &status, &score, &role, &screened); err != nil {
					return Failf(CodeFailed, "the candidates could not be read")
				}
				if strings.TrimSpace(name) == "" {
					name = email
				}
				row := map[string]any{
					"applicationId": id,
					"name":          name,
					"role":          role,
					"stage":         status,
					"stageLabel":    stageLabel(status),
					"screened":      screened,
				}
				// Absent rather than 0: a candidate nobody scored has no score,
				// and reporting 0 invites the model to rank them as the worst.
				if score > 0 {
					row["matchScore"] = score
				}
				candidates = append(candidates, row)
			}
			if err := rows.Err(); err != nil {
				return Failf(CodeFailed, "the candidates could not be read")
			}

			data := map[string]any{
				"candidates": candidates,
				"count":      len(candidates),
				"stage":      stage,
			}
			if stage == "" {
				data["stage"] = "still in the running"
			}
			if len(candidates) == 0 {
				data["note"] = "Nobody is at that stage. This is a real answer, not a failure to look."
			}
			return OK(data)
		},
	}
}